CANON EOS FAQ Version 2.4
Date: November 1993

All original material is Copyright © 1992, 1993, 1994, 1995 Alvin Chia-Hua Shih and Robert M. Atkins.

3. Flash:

Canon refers to flashes as "Speedlites". Their nomenclature typically specifies the guide number in meters at the long end of any zoom range, e.g the 430 EZ has an approximate guide number of 43m when zoomed out fully. The "E" indicates EOS compatibility and an additional "Z" indicates that the head can be "Zoomed" (see below).


  1. Other than the 430 EZ, what are my options?
  2. The 430EZ is currently Canon's top-of-the-line flash for the EOS line [the recently introduced 480EG may compete for "top of the line" status]. Third party flashes usually quite a bit cheaper, but typically lack certain features. (The Metz 40MZ-2 is an exception in both counts). Alvin Shih has compiled a table of data for the Canon and some 3rd party flashes. This table is given in Appendix A at the end of this FAQ.


  3. What's the difference between "meter" and "feet" versions of the 430EZ?
  4. The "meter" version is functionally identical to the "feet" version except that the distances displayed on the LCD panel for flash-coupling ranges in manual mode are given in metric units rather than imperial. In the USA, these units are probably grey market.


  5. Why doesn't the AF illuminator on my flash work with my 10S/A2?
  6. The 10S has 3 AF sensors and the A2 has 5. The centre cross-sensor detects both horizontal and vertical detail, and the outer vertical sensors detecting only horizontal detail. Canon AF sensors on earlier bodies were horizontal sensors which detected vertical detail. As such, the current flash units provide a pattern of vertical bars which are not useful to the outer AF sensors. In addition, the pattern is not wide enough to cover the outer AF sensors. So, on multi-AF sensor bodies, the AF illuminator on the flash is disabled in favour of the one built into the body.

    This is no great loss since the flash-integral AF illuminator is not much more powerful than the body-integral AF illuminator (if at all). The AF illuminator on the flash was mainly provided for the earlier EOS bodies which did not have built-in AF illuminators.


  7. Body-Integral Flash Questions:
    1. How does red-eye reduction work?
    2. From the "Canon EOS Speedlite System" brochure.

      The subject is illuminated by an incandescent lamp for 1.5 seconds before the flash fires. Unlike other systems that use flash bursts before the exposure, the EOS 100/Elan's red-eye reduction lamp is easy on the subject's eyes and less likely to cause blinking. By looking into the lamp, the subject's irises contract, reducing the red-eye effect. This should also be true for other EOS bodies with red-eye reduction capability.


    3. Can I get red-eye reduction with slow sync flash?
    4. Yes, for the Elan only (not the A2 or A2E) but only if you are using 1st curtain sync (Set via custom function.). Note that not all body-integral flashes support red-eye reduction (the 10s does not).

      ACS & RMA

    5. Can I use red-eye reduction with 2nd curtain sync?
    6. Although the manual doesn't explicitly forbid it, the answer is still "no" for the Elan. It is OK for the A2 and A2E.

      Normally, the red-eye reduction illuminator stays activated until just before the main flash. With 2nd curtain sync, the shutter is already open when the flash fires. Two possible reasons for not wanting the red-eye illuminator active while the shutter is open:

      1. The long duration of the red-eye reduction illuminator could result in some kind of "ghosting effect".

      2. The red-eye reduction illuminator is not designed to produce even illumination over the entire frame.

      Why Canon doesn't have the red-eye reduction illuminator deactivate before the first curtain opens in slow sync mode is subject to speculation. There are two conceivable reasons for Canon disabling it:

      1. Any significant amount of delay between the extinguishing of the red eye reduction lamp and the firing of the flash may allow the eyes to readjust to the darkness. This, of course, would give red eye anyway, and needlessly consume battery power at the same time.

      2. Too much of delay in taking the exposure would allow human subjects time to "squinch up" their faces in response to the red eye reduction lamp (making for rather unattractive people pictures).

      The easiest thing to do is stick with 1st curtain sync. If you must have 2nd curtain sync and find red eye unbearable, buy a hot shoe flash which supports 2nd curtain sync, like the 420/430EZ. By having the flash head farther off the lens axis, red eye is reduced without the need for any kind of red eye illumination.


    7. How do I get a smaller aperture with more DOF using my built-in flash?
    8. You have to use Manual mode. You set the aperture (for DOF), you set the shutter (to avoid camera shake) and TTL/OTF metering handles the rest. The usual suggested shutter speed is 1/60th.

      NOTE! Watch your guide number carefully. The built-in flashes have guide numbers in the 12-17m range (depending on flash zoom, and body type). The guide number formula is: range = GN/aperture. So f/8, ISO100, gives a shooting range of only 1.5m.

      Also note that with smaller apertures, more flash output is required. You will go through (expensive) lithium batteries more quickly. If you need more kick, try faster film or a shoe-mounted flash.


    9. When does the internal flash charge?
    10. It seems that, on models with built-in flash, the flash will charge up when you move the command dial from the "L" position to any other position. On some non-US models (which have automatic flash pop-up whenever the camera thinks it is needed) the flash may be kept charged whenever the camera is set to one of the "program" modes (landscape, sports etc), just in case it is needed. There have been claims that the internal flash will also charge up, even on some US models and even in the "creative" modes (Av,Tv,DOF,manual) if a button is pressed after the camera has stood unused for a long time (i.e. the flash has had time to discharge). While Canon have confirmed that the flash does charge when the command dial is moved from "L", their answers have suggested that the flash does not recharge when camera is left in a "creative" mode for long periods of time. A few reports from readers seem to support this - it doesn't seem to recharge.

      There would seem to be no good reason for the flash to charge at all, unless it is manually activated. The initial charging of the flash may be related to the "instant" pop-up flash capability of the European and Japanese EOS cameras, where you might want instant flash without having to wait for it to charge. It doesn't seem like a very good idea for US cameras though. It will certainly put an unnecessary drain on the battery and there appears to be no way to get around it.

      Whatever the true story is, it's probably not worth worrying about since there is nothing you can do about it anyway!


      Chuck Westfall of Canon has pointed out that the above is not entirely correct. He has added the following:

      "The EOS A2/A2E/5's built-in flash does not remain charged at all times in the Image Zone modes. It only charges up by itself when the camera's metering system detects low light or backlight, and then only in Green Zone, Portrait and Close-up. The built-in flash never charges by itself in Sports, Landscape, or any of the Creative Zone modes (Program, Shutter Priority, Aperture Priority, Manual or Depth)."

  8. On the A2, what does CF16 do?
  9. When CF16 is enabled, the automatic reduction of the flash is disabled. When the ambient brightness goes above EV10 (ISO 100), Canon decides that you're in a bright environment and that all you want is fill flash. So, between EV10 and EV13, there is a gradual reduction in flash output to achieve the "fill" effect. At EV13 and above, the flash reduction is at-1.5 stops. This feature is thrown in so that one does not have to "second guess" the camera and figure out where it is on the flash programme curve. Nice touch for those who like "hands on" photography! It is also useful in conditions with strong backlighting which may fool the flash exposure programme into thinking the subject is well-lit. Experiment and see what you like.

    [ The "Speedlite Reference Guide" is now out of print. ACS ]


  10. Can I get an off-camera flash cord for my 630/RT?
  11. The Canon off-camera shoe cord designed to support A-TTL does NOT work on the 630 nor RT (I have confirmed this with Canon Canada, despite rumours to the contrary). The flash works perfectly in the hot shoe, and the TTL modes have been reported to work correctly with the cord. However, any feature requiring the digital data bus will not work. This includes A-TTL and flash-exposure compensation, among others.

    The general consensus is that Canon increased to CPU clock speed to get faster AF, but in the process didn't upgrade the drivers on the shoe circuitry. This, combined with the capacitance of the cord results in the serial data degrading too severely for the body to communicate with the flash. Attempting to use the flash cord with A-TTL on a 630/RT will usually result in the minimum aperture, fastest X-sync speed, and 2nd curtain sync being set. The TTL modes still work, probably because they use trigger lines, and not the serial data line.

    It has been speculated upon that the drivers could be overloaded to the point of being damaged, so one should check flash functions when buying a used 630. However, Canon states that no damage should occur if one attempts to use the Off-Camera Shoe Cord with the 630/RT.

    The way to use off-camera flash with the 630 is to use TTL Manual mode. If you wish the 430EZ to be your main source of illumination and your subject is close, set Tv=125, Av=8. This will give good depth of field. To expose more for ambient light, use shutter priority with Tv=60. In general, use the guide number calculations leaving some margin for error, and let TTL flash metering do the rest.

    Finally, the shoe cord has RFI emission problems bodies other than the EOS1, 620, and 650.


    Peter Shizgal reports that he has had success with a custom-made cord from England. It is similar to the Canon off-camera cord in that it is coiled, and has a tripod socket for the flash shoe, but the difference is that it works with the 630! His comments from email and a previous post are included below:

    From: Peter Shizgal
    Subject: Re: CANON off camera flash cord. Operation with 630. Any info?
    X-Organization: Concordia University, Montreal, Quebec

    I have been using Leung's one-piece cord with the EOS 630 for quite some time now (about 1 year?), with very good results. The device is well-built, from Canon parts, and has withstood considerable knocking around in my camera bag. A strain relief is included and appears to work well. When connected to the EOS 630 by Leung's cord, the 430EZ flash behaves as if it were mounted directly on the hot shoe. The cord is expensive, but in my shooting, it has been worth the cost.

    The following is my original posting about the cord:

    Subject: Canon EOS off-camera shoe cord

    There have been several recent postings concerning the use of Canon's off-camera shoe cord with EOS-series cameras. Introduction of this cord lowers the cost of attaching a single Speedlite to an EOS camera and provides better functionality than the older multi-piece setup when only a single flash is used. The older setup can accommodate multiple flashes, but at the cost of sacrificing the preflash, A-TTL mode, flash head autozoom, infrared AF auxiliary light, and TTL mode distance readout. These functions share a data line that must be disconnected because of the possibility of contradictory preflash distance readings from multiple flashes.

    I have contacted a senior technical rep at Canon USA regarding the use of the one-piece off-camera shoe cord and have confirmed that it will NOT work with the EOS 630 and RT. The cord works fine with the EOS-1, 620, and 650. The cord will also work with the EOS 10, Elan, and Rebel, but exceeds the FCC noise regulations.

    I own an EOS 630 and a 430EZ Speedlite, so this wasn't good news for me. Fortunately, a fellow netter, Paul Sandy, recommended that I contact David S.H. Leung, a Canon (and Contax-Yashica) specialist in Ilford, England, regarding a custom-built cord. Using Canon parts, Leung manufactures a cord that allows the 430 EZ Speedlite to be connected off-camera to the EOS 630 while maintaining full functionality. (Leung's rep won't comment on whether on not the FCC noise spec is exceeded.) I have tested this one-piece cord, and as far as I can determine, it behaves as advertised. Simply put, the Speedlite appears to function as if it were mounted on-camera.

    I was pleased by the service provided by Leung's shop. I contacted them by FAX and received a prompt and informative reply. They somehow managed to ship the off-camera cord from England to Canada in less than a week.

    Now for the not-so-good news: The price is 68.00 sterling (about $120 US) including tax and shipping. I would imagine that a low volume of production and the use of Canon parts contribute to the high price, which is more than twice the cost of the Canon off-camera shoe cord (~ $50 US via mail order). However, the Canon off-camera shoe cord won't work with the EOS 630 and RT, so this comparison is moot for users of these cameras. The Canon setup that will work consists of the TTL Hot Shoe Adapter II, an off-camera shoe adapter, and a connecting cord. These items total about $95 US via mail order, not including shipping. Moreover, Leung's cord offers full functionality whereas the three-piece Canon setup does not. Finally, it is possible that Leung would agree to work with user-supplied components and would lower his price accordingly.

    The person who answered my inquiries concerning Leung's cord is Alan Burch. He can be reached care of

         David S.H. Leung
         33 Goodmayes Road
         Ilford, Essex IG3 9UN
         Tel. 81 590 3268
              81 599 6657
         FAX: 81 590 0293

    The shop is open every day except Thursday and Sunday. Exchange rates have changed since I posted this, and the price may have changed as well.

    Peter Shizgal CSBN, Concordia University Montreal, Quebec, Canada
    Internet: Shizgal@CSBN1.Concordia.CA


    Mike Coren managed to get some updated information:

    From: (Mike Coren)
    Subject: Re: EOS 630 w/off-camera 430EZ (repost)

    I called David Leung, the firm in Essex which Peter Shizgal recommended as a source for an off-camera shoe cord for the EOS-630 (see Canon EOS FAQ list version 1.65 Alpha, question 2.7, "Can I get an off-camera flash cord for my 630/RT?"). The cord is still available, and costs GBP 74.99. At the present exchange rate (Jan 1993), that's about US $115. They can ship overseas, and when doing so will subtract the 17.5% Value Added Tax (VAT) but will also charge for shipping (the two usually cancel each other out). They claim they've never had one go bad, but will provide a one year warrantee. They take VISA and Mastercard but not American Express. Their address is:

         David Leung
         33 Goodmayes Road
         Ilford, Essex  IG3 9UN
         Tel. 081-590-3268
              011-44-81-590-3268 from the US (dunno about Canada).

    When they first began selling the cables about five years ago, they made them themselves using Canon parts. Now they take Canon's off-camera shoe cord and use the same endpoints but rewire it with a different cable in between. That's all they would tell me without giving away any trade secrets! The person I spoke to said they did tell Canon about this modification and their success with it, but given that Canon is no longer making the 600-series I wouldn't hold my breath waiting for it from them.

    Q: Would it be better to replace the 630 with a 10s (or A2!) & use Canon's cord?

    That'll work, but it's a rather more expensive solution.

    Michael D. Coren (

  12. Why doesn't the A-TTL preflash out-of-range warning work on my camera?
  13. Canon has disabled the A-TTL preflash out-of-range warning on all bodies after the EOS 1, 630, and RT.

    Originally, Canon claimed this was done because it wasn't accurate beyond 25 ft. For objects of low reflectance, the flash would signal a false alarm. However, those who have used this feature have found it very useful.

    Canon now claims that the preflash exposure warning is disabled due to a patent held by another company.

  14. Is there an after flash underexposure warning?
  15. I am told that the patent which precludes the incorporation of preflash exposure warnings also precludes after flash exposure warnings. Thus, it is unlikely that this feature will be made available through Canon. However, some 3rd-party flashes do still offer after-flash exposure warnings.


  16. How do I change the fill-flash ratio?
  17. Except for the EOS A2/5, all bodies in the EOS line require the 430EZ in order to support variable fill flash ratio for shoe-mounted flashes. This includes the Elan which can vary the fill-flash ratio, but only for the built-in flash.

    For flashes without such controls, quite a lot of fiddling is required. In programme modes the exposure compensation control affects both flash exposure and ambient exposure so it is not possible to use exposure compensation to control the fill-flash ratio. To vary the fill flash ratio you can first use the manual exposure mode to set the correct exposure level for the ambient light. In this way you control the shutter speed (must be equal to or slower than the maximum sync speed) and aperture manually. You can then control the flash output by changing the film speed setting, thus "fooling" the flash into giving more output (if the film speed is lowered) or less output (if the film speed is rasied). Don't forget to reset the film speed after you sre through!

    This subject is covered in more detail in section 4A of the Speedlite Reference Guide (for availability see section 1.1.)


  18. A-TTL Questions:
    1. Why doesn't Canon use distance information for flash exposure calculations?
    2. Distance info is only useful so that the camera can apply the "guide number" formula: f-stop = GN/distance. This is only a rough approximation. Off-The-Film (OTF) metering measures the true exposure of the film, which is much more accurate than the guide number calculations.

      In A-TTL, Canon uses a preflash to actively judge the effective flash-to-subject distance rather than passively. This factors in light loss from bouncing off different kinds of surfaces (for example, flash modifiers), and light gains from bouncing off different kinds of surfaces (like ceilings and walls). You simply cannot make the remotest use the GN calculations for anything but direct flash.

      Personally, I avoid direct flash, and most light modifiers are bound to void the GN calculations, either because of light loss, or because they require the head to be up (like the Lumiquest pocket bouncer). So for most shots, the distance information would have to be thrown away.


    3. Is it OK to block the A-TTL sensor (with a softbox, say) with using plain TTL flash?
    4. It should be fine. TTL metering stands for "Through The Lens" metering. So, no metering takes place from the flash sensor. The sensor on the flash is only used for A-TTL metering. If you're still worried, just shoot some test exposures to make sure [I'm not sure if TTL exposure compensation works.]


    5. Is it OK to block the A-TTL sensor (with a softbox, say) when using A-TTL?
    6. The sensor on the flash is required for A-TTL metering. That's when the 430 EZ emits a preflash, checks the return signal with its own sensor, and then computes an aperture that will work. It's best to think of the A-TTL preflash/sensor combination as a kind of reflected light flash meter built into the flash itself (and it's supposedly quite accurate too).

      By blocking the sensor, the A-TTL program will definitely get confused. Similarly, if the A-TTL supporting flash is on a flash bracket it may give slightly different apertures if the sensor isn't pointed in the right direction.


    7. Why does blocking the A-TTL sensor give me smaller apertures?
    8. Some have tried fooling the A-TTL programme by blocking the sensor and found that it stops down more instead of less! This is because the IR preflash head is right beside it, and whatever you're using to block the sensor is probably in front of the IR emitter as well.

      So basically, you've put a reflector in front of the emitter/detector pair. If you carefully cover just the sensor, you will get the anticipated result; the flash will try to select the maximum aperture. The easiest way to avoid this is to tilt up the flash head so that the preflash exits from the main flash head.


    9. Why can't I use A-TTL with the off-camera TTL accessories?
    10. When you are using the TTL Hot Shoe Adaptor 2 with the Off-Camera Shoe Adaptor, you lose A-TTL. The A-TTL assumes the flash is in the camerashoe, or at least near it. It can be wildly inaccurate when far off camera, so it is disabled when using the off-camera TTL accessories. There is also the problem of multiple flashes returning conflicting information on the data bus. [Again, I don't know how flash exposure compensation is affected by this. Canon confirm it doesn't work unless you are using an EOS A2/5.]


    11. Can A-TTL cope with filters over the flash?
    12. If you're using a modifier that goes over the main flash head (filters, Sto-Fen Omnibounce, etc.), note that the preflash in direct mode comes from the IR sensor below the main flash head. This can confuse the A-TTL programme since the IR preflash will not be filtered, giving inaccurate results.

      By tilting the head up slightly, or using something to release the bouncelatch, the 420EZ/430EZ will assume you are bouncing the flash and will fire the preflash through the main head. This should yield more accurate results. If the head is being tilted up, perform tests to confirm evenness of flash coverage. The flash may require manual zooming to a wider angle to give better coverage.


    13. Can A-TTL be used with filters over the lens?
    14. The A-TTL sensor, being in the flash and not in the camera may yield bad apertures if filters are being used over the lens. In this case, you'll have to find some way to put a similar filter over the sensor.


    15. Is the A-TTL program affected by flash exposure compensation?
    16. In fiddling with my 430EZ, it seems as though it doesn't figure the exposure compensation into the selected aperture. If you say you want flash overexposure by 3 stops, it gives the same aperture as selecting flash underexposure by 3 stops.


      Note that in a TTL (or A-TTL) flash system auto flash exposure is changed by changing the flash duration at a fixed apertures. Thus you would not expect an aperture change. In a non TTL flash exposure system, flash exposure is changed by changing the aperture for a fixed degree of flash illumination. For more info see the Speedlite reference guide, p57 and 71.


    17. Why didn't Canon put the A-TTL sensor in the body?
    18. If we assume that A-TTL requires a separate sensor, then there are a few reasons that Canon may choose to avoid putting the sensor in the body itself:

      1) Cost: Including an extra sensor would incur an extra cost on every body manufactured. This could make Canon's bodies marginally less competitive. This is especially true if the majority of Canon owners do not wind up using A-TTL.

      2) Complexity: Cramming a 3rd sensor into the body would make the body more complicated in order to split the optical path yet again in order to feed the A-TTL sensor.

      3) Dim viewfinder: Bleeding off more light to another sensor would make the viewfinder dimmer than it already is.

      4) History: A-TTL was developed for the T-90 which did not have a multi-segment metering sensor. Thus, it was unable to distinguish foreground exposure from background exposure during the preflash.

      Personally, I'm inclined to believe #4, and that Canon has simply neglected to update its flash system. It is technically quite feasible to use the existing evaluative metering sensor to perform preflash exposure computations. [Rumour has it that Canon is currently throwing around ideas for a new generation of flash system. Cross your fingers, folks!]


  19. Is there a faster way to mount the flash?
  20. The locking pin on the 430EZ is spring loaded (to be compatible with bodies that didn't support locking pins). If you leave the locking pin down at the same level as the hot shoe contacts when the flash is not mounted, you can quickly and securely mount the flash by just slipping it into the shoe. The pin will rise like the contacts when being inserted into the shoe, and then pop down into the little hole when the flash is properly seated. This trick is especially useful for bodies without a built-in flash.


  21. How can I find out more about using flash with my EOS?
  22. Canon publishes the "Speedlite Reference Guide". Stephen Page posted the following summary:

    From: (Stephen Page)

    Many thanks to someone (sorry, I've lost the posting!) who passed on a tip about the Canon USA booklet, "Speedlite Reference Guide" (Chuck Westfall, 1991). This is an excellent little book and it contains some essential information which Canon have not bothered to tell the world in their instruction manuals.

    The booklet can be obtained from Canon USA, One Canon Plaza, Lake Success, NY 11042, USA; telephone +1-516-488 6700. They sent mine immediately and there was no charge.

    I've summarized some key points below which may help others. Do get the book, though; it's got lots more of the same. Also write to Canon and blast them for a pathetic user manual... I cannot see how anyone could work out how to use the flash correctly without this book. My summary is valid for EOS-1/430EZ; other models have slight differences. Early models of Speedlites work differently.

    [Anyone know if Canon have any other hidden reference guides from national offices in the US or elsewhere? ]

    1) Types of flash exposure.

    In "normal" flash exposure, the exposure is calculated for the foreground subject and the background is underexposed.

    In "fill-in" flash exposure, the shutter speed and aperture are set to expose the BACKGROUND correctly. The flash duration is adjusted to expose the subject correctly. The Speedlites operate in fill-in mode most of the time (see below).

    2) Flash exposure and the camera modes.

    In Program mode, the camera will use fill-in exposure provided that the light level is EV10 or above. If the ambient light is below EV10, the shutter speed will be locked at 1/60 sec and the flash will work in "normal" mode, i.e. the background will be underexposed.

    In Aperture-priority (Av) or Shutter-priority (Tv) modes, the camera will ALWAYS use fill-in exposure mode. The exposure will be set to match the background (ambient light level), so if the ambient light is low then a slow speed and/or large aperture will be selected.

    3) Tinkering with the light levels.

    When the ambient light is above EV10, the Speedlite's flash level is reduced on a linear scale to a maximum of the equivalent of 1.5 EV steps less than the standard exposure level (at EV13 and above). This is to preserve the natural lighting a bit, by not blasting it away with flash.

    4) Exposure compensation.

    The exposure compensation controls on the camera affect BOTH background and foreground exposure.

    To adjust the foreground independently of the background, use the control on the flash (430EZ) itself.

    5) A-TTL vs TTL.

    The Speedlites can be switched to use "TTL" rather than the default "A-TTL" mode. Some flashes, e.g. ring flash ML-3, only use TTL mode.

    TTL mode disables the preflash (near-infrared in normal flash head position, white in bounce position). This has the advantage that it doesn't make the subject think that the picture has been taken, and it doesn't set off any slave units. However, in TTL mode you get no pre-exposure distance measurement, so the camera can't scream if you are out of range. You can work it out by using the distance scale, or by looking at the indicator light AFTER the flash.

    I hope this helps some of you to work out the mysterious behaviour of your equipment!!

    Stephen Page, or uknet!aclondon!sdpage

  23. In A-TTL, how can you read the subject distance with the light reflected (what is the physics law)?
  24. From Chuck Westfall:

    In a direct flash situation, the near-infra-red preflash located below the main flash head is used with all current A-TTL Speedlites (300TL, 300EZ, 420EZ and 430EZ). Since the intensity of the preflash illumination is a known quantity, calculating subject distance becomes a simple matter of comparing the level of illumination returned to the external sensor of the A-TTL Speedlite with the original amount. The bounce flash situation is slightly different in that the preflash is emitted through the main flash head, but the principle remains essentially similar. The difference is that in a bounce flash situation, the external flash sensor factors in the light loss caused by the increased flash-to-subject distance as well as the amount of light absorbed by the bounce surface. The net result is equally accurate. Please keep in mind that the objective of the A-TTL preflash is to measure flash-to-subject distance, which is not necessarily the same as camera-to-subject distance.


  25. Can spot metering be used for the ambient exposure with the EOS 5/A2 (like partial metering with the 10s) ?
  26. From Chuck Westfall: With the EOS 5, you can select the ambient light metering pattern of your choice in all Creative Zone exposure modes except Program AE, which cancels your metering selection and replaces it with peripheral metering as with previous EOS models. This ability to select ambient light metering patterns is a definite improvement for the EOS 5 over earlier EOS cameras as well as the T90.


  27. Are there 5 vertical sections of the TTL sensor in the EOS 5/A2?
  28. From Chuck Westfall: The EOS 5 uses the same 3-segment sensor as the EOS 10s for its TTL flashmetering. The EOS 5 designers elected to use the 3-segment TTL flash sensor from the EOS 10 mainly because it cost less than developing a newer sensor, but also because they felt it was quite adequate for its purpose given the layout of the camera's 5 focusing points from left to right.


  29. How is ambient light metered in A-TTL and TTL flash photography with the EOS 1?
  30. From Chuck Westfall: During A-TTL or TTL flash photography with the EOS-1, ambient light is measured by the peripheral metering pattern regardless of the user-selected metering pattern, including center-weighted average metering selected by CF8. RMA

  31. How does the camera-flash communication differ when the flash is on and off the camera?
  32. From Chuck Westfall: A comparison of differences in communication between the flash and the camera when multiple flash off-camera accessories are used is covered on page 62 in the SRG in Section 2, fourth paragraph.


  33. Why don't you recommand the use of "C"-size NiCd batteries in Battery Pack TP ?
  34. From Chuck Westfall: Unlike NiCd Pack TP, Battery Magazine TP is not equipped with a fuse to prevent damage to Transistor Pack E which can be caused by defective "C"-size NiCd cells.


  35. What about the use of flash with the EF-M?
  36. From Chuck Westfall:

    As a cost-reduction measure, the EF-M camera body does not contain a TTL flashmetering sensor (or its associated circuitry). Therefore, it depends on the external exposure control system built into the Speedlite 200M for automatic flash photography. Because of its lack of TTL flashmetering, the EF-M is not recommended for use with the 200E, 300EZ or 430EZ EOS system Speedlites.

    When the EF-M is used in either Program AE, Aperture-priority AE or Shutter-priority AE with the 200M (with the 200M set for automatic operation), it automatically locks its shutter speed at 1/90 and sets the lens aperture according to film speed (f/5.6 for ISO 100, f/8 for ISO 200, f/11 for ISO 400, etc.). These settings are adequate for flash snapshots in low-light or indoor shooting conditions, but they cannot be recommended for fill-in flash photography in bright conditions if the correct exposure for the existing light exceeds the camera's shutter speed/aperture setting.

    When the EF-M is set for manual mode and the 200M is set for automatic, you can override the shutter speed setting in the range from 30 seconds to 1/90 and you can select any aperture you want. This gives you a limited capability for fill-in flash photography. In a typical outdoor situation, your best bet is to set the shutter speed to 1/90, and adjust the aperture until the viewfinder's metering scale indicates correct exposure for the existing light. However, please keep in mind that your effective flash-to-subject distance range is controlled by the combination of guide number, film speed and aperture setting. Here's a chart showing the usable range (in feet) for a variety of film speed/aperture combinations with the 200M:

    Film Speed (ISO)  f/2.8  f/4  f/5.6  f/8  f/11  f/16
    100               23.5  16.5  11.8   8.3   5.9   4.2  
    200               33.0  23.5  16.5   11.8  8.3   5.9
    400               47.0  33.0  23.5   16.5  11.8  8.3

    Realistically, on a sunny day your aperture setting is likely to be in the range between f/11 and f/16 at 1/90 second with ISO 100 film, thus producing an effective range of approximately 6 ft. with the Speedlite 200M. This range can increase only if the existing light level is reduced, such as by shooting in a shaded area or perhaps on a cloudy day.

  37. Why doesn't the flash work on my Elan when the film speed is set to ISO 5000?
  38. There is what might be described as a "bug" in the Elan. It seems that above about ISO 2500, TTL flash may not work properly. Things seem to be fine with all other EOS bodies (even The Rebels) all the way up to ISO 6400. The behavior of the Elan is not a malfunction in the sense that it cannot be "repaired" either under warranty or in any other way. Not all Elans show this behavior--it seems to be a problem in the design which must be related to some component tollerance. Before you complain too much however, note that many Nikon cameras (e.g. the 8008) have a recommended ISO maximum of ISO 1000 for TTL flash and all Elans meet or beat that!


  39. Can I use a non-Canon, non-dedicated flash with my EOS camera?
  40. [From Chuck Westfall]


    Before using any unfamiliar studio strobe or other non-dedicated flash unit with an EOS camera, we STRONGLY recommend that you determine its trigger circuit voltage. Excessive trigger circuit voltage can damage the shutter units and X-contacts of most modern 35mm SLR cameras. Please be aware of the following information:

    Trigger Circuit Voltage: The "trigger circuit" is the part of any electronic flash that detects the X-sync signal from the camera and then fires the flash. In order to do this, it supplies a certain amount of voltage through the sync cord or hot shoe to the camera's X-sync contact. The camera's X-sync contact, whether in the form of a PC socket or a dedicated hot shoe, is connected to the camera's shutter by a very thin connecting wire. When the first shutter curtain reaches the end of its travel, a small part of the shutter mechanism contacts the connecting wire, thus completing the circuit. At that moment, a change in resistance is detected by the flash's trigger circuit, causing the flash to fire.

    Canon dedicated Speedlites pass no more than 6 volts DC through their trigger circuits. This is the level for which all EOS cameras, including the EOS-1 as well as the A2/A2E, 10s, 630, RT, Elan, Rebel etc. are designed.


    Most independently-made strobes that are "dedicated for Canon," whether they are shoe-mount or handle-mount, have safe trigger circuit voltage levels, but there are no guarantees. Trigger circuit voltages up to around 20 or 30 volts DC are not immediately dangerous, but they may damage the camera's X-sync contact, connecting wire or shutter unit over a period of time and usage.

    However, many non-dedicated flash units, especially older studio strobe designs, use trigger circuits that may exceed 50 to 60 volts DC. This level is excessive for almost every currently made SLR, not just Canon. Certain independent flash equipment manufacturers (Lumedyne & Wein), in recognition of the problem, now sell a "sync filter" (connected between the power pack and the sync cord) that lowers the trigger circuit voltage to a safer level.

    High voltage conducted through the camera's connecting wire can also generate electro-magnetic interference or "noise" which can have various unwanted effects on camera operation. These can include metering errors, shutter speed errors, aperture size errors, shutter release failure, etc. The effect varies according to the camera model, because the interference can affect different parts of IC chips according to the circuit layout.

    It's easy to test any electronic flash for trigger circuit voltage level using a standard voltmeter. Digital voltmeters are relatively inexpensive and easy to find at stores like Radio Shack. The plus (+) lead is attached to the positive contact in the PC sync cord, while the minus (-) lead is attached to the ground contact of the PC contact on the sync cord. With hot shoe flash units, the plus lead should be placed on the + contact in the middle of the hot shoe, while the minus lead should be grounded on the hot shoe's ground terminal, usually located on the side above the lock nut. Usually the voltmeter or multimeter has several different settings for DC voltage depending on the range you're trying to measure. With an unknown strobe, it's best to start in the high range just in case.

    Here is a list of known trigger circuit voltage levels for independently manufactured flash units and studio strobes. (Most of this data provided courtesy of Charles Tucek, Midwest Region Pro Market Representative):

    Date   Brand Name      Model Number      Trigger Circuit          
    9/4/92  Calumet (Bowens) PS Series               30.0
    9/4/92  Calumet (Bowens) Traveller Series        15.0
    9/4/92  Comet            CX244                   11.0
    11/6/92 Dynalite         All Current Models      10.0
    9/4/92  Metz             60CT4                    5.0
    9/4/92  Speedotron       D604 Brown Line         64.8
    9/4/92  Speedotron       2403CX Black Line       66.3
    9/4/92  Vivitar          283*                     5.0
    *This is accurate only for 283s manufactured during or after 1987.


    1. There are several ways of firing a studio flash without using a sync cord at all. One way that works well is to use a 420EZ or 430EZ on 1/32 power manual flash, while the optical slave trigger of the flash is activated. By using the bounce feature of the 420 or 430, it's possible to direct the light away from the subject and into the optical slave trigger.
    2. If that's not convenient, various companies including Quantum Instruments and Lindahl sell radio slave triggers consisting of a transmitter that connects to the camera's PC contact (or PC socket adapter), and a receiver that attaches to the studio strobe's power pack. In addition to radio slaves, there are also some IR slave devices that work basically the same way, but require a direct line of sight between transmitter and receiver. (Don't forget to test the slave transmitter for trigger circuit voltage as described above.) Be aware that the use of radio or IR slaves usually causes a small delay in flash firing that can cause problems when attempting 1/250 sync. Studio photographers generally don't care about this, but sports photographers usually do. In this case we recommend conducting a series of test exposures at various shutter speeds to find the usable maximum sync speed for any given equipment combination.


    There are three things to look for if an EOS camera is not firing a studio strobe:

    1. Some of the independently manufactured PC socket adapters have metal shoes. This may cause a short circuit with the dedicated contacts in the camera's hot shoe, and can sometimes prevent the flash from firing. The remedy for this is to use the Canon PC Socket Adapter, which has a plastic shoe. Alternatively, covering the 4 small contacts in the camera's hot shoe with electrical tape should solve the problem.
    2. Due to the polarity of the X-sync contact used with the EOS A2E, A2, 10s, Elan and Rebel series cameras, electronic flash units with reverse polarity compared to the camera's X-sync contact will not fire. This can be a problem with some studio strobes. The polarity is caused by a diode attached to the camera's X-contact to protect the camera's built-in flash. When a strobe with reverse polarity is attached to the terminal, the strobe constantly sees a short circuit which prevents it from firing.

      (This is generally not a problem with the EOS-1, 620, 630, 650 or RT cameras because their X-sync contacts have no such diode. They don't need the diode because they don't have a built-in flash.)

      If you're sure that the PC socket adapter isn't the problem, and if you are using an EOS A2E, A2, 10s, Elan or Rebel series camera body, try reversing the polarity of the sync cord. On some studio strobes, the end of the sync cord that plugs into the power pack is a regular 2-bladed household-style plug. For this type, it's a simple matter of turning the plug around 180 degrees. Other sync cords may have headphone-jack type plugs; this type has to be rewired in order to work. Some photographers make a reverse-wired extension cord that plugs into their existing sync cord, while others just rewire a whole cord and make that one their "EOS" sync cord.

    3. Last but not least, if the first two solutions don't work, excessive trigger circuit voltage as discussed earlier in this bulletin may prevent the EOS camera from firing the studio strobe. In this case, it's best to use the solutions recommended in "Safe Ways to Fire Studio Strobes with EOS Cameras."

  41. Does the PC adaptor offered by CPS confer some kind of electrical isolation to protect the camera?
  42. [From Chuck Westfall via ACS]

    Well...sort of. If the trigger circuit voltage conducted through the sync cord is high enough, it melts the solder between the PC terminal and its connecting wire, thus breaking the circuit. But there's no guarantee that the camera will be protected from damage caused by high trigger circuit voltage. Therefore, it's the customer's responsibility to check that out before using the equipment.

    [Sounds to me like it would be most unwise to depend on any protection being afforded by the PC adapter! RMA].

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