7D + 400/5.6 in Tv mode uses 6.3!

Discussion in 'Canon EOS' started by tele_tele, Sep 16, 2010.

  1. Hi,
    with 7D (1.2.2) and a 400mm f/5.6 lens in Tv mode and AutoISO, camera shows and takes pictures at aperture 6.3.
    Sometimes it is jumping from 5.6 to 6.3 all the time, mainly settles at 6.3 and then takes pictures at 6.3.
    This is happening in AutoISO mode. ISO is greater than 200, so it is not too much light that is problem ( camera is closing down aperture)
    Any ideas? :-(
     
  2. Because as the light changes the lens stops down - that's what it's meant to do.
     
  3. If you want your lens to shoot at f/5.6 then perhaps you should be using Av and manually selecting f/5.6 yourself. If you want control over both shutter speed and aperture, then choose M.
    Maybe I just don't understand your question.
     
  4. So, either the camera is broken, or it's choosing what it thinks are the best settings.
    If the image exposure and focus are on the mark then it's not broken.
    If you think you can come up with better settings, then that's what M - manual mode is for.
    If you think that the Canon engineers and firmware programmers made a mistake in their calculations, then you should let them know.
     
  5. ISO is set on A (Auto ISO) and already high (above 400) as shown in viefinder.
    So for example, instead of metering 1/500, f/5.6 and ISO800 camera meters 1/500, f/6.3 and ISO800.

    So ISO is already high, but camera wants to close aperture to 6.3.
     
  6. Sometimes slight shift to the right or left puts aperture to f/5.6. Maybe meter gets confused - but then logically it would increase ISO rather than close down aperture.
     
  7. [[but then logically it would increase ISO rather than close down aperture.]]
    How can you be so certain of this? You're shooting in Tv. You're letting the algorithms built into the camera decide what aperture to choose.
     
  8. tele tele, you need to read your user manual. It is clear that you do not understand what TV means! In TV mode you select the speed and ISO (or use AUto ISO) and the camera choses what aperture to use. I would never use Auto ISO btw. Set the ISO to what makes sense!
     
  9. tele tele, you confused yourself
    logically it would increase ISO rather than close down aperture​
    You should have said: "logically it would decrease ISO rather than close down aperture"
    or "logically it would open up aperture rather than increase ISO"
    Also you said "instead of metering 1/500, f/5.6 and ISO800 camera meters 1/500, f/6.3 and ISO800" which should be "instead of metering 1/500, f/5.6 and ISO640 camera meters 1/500, f/6.3 and ISO800"
    If you think the way the camera chose the ISO is not good (bad, wrong, unwise, ... ) then don't use Auto ISO. And ISO 640 and 800 are not much different anyway(maybe a little stop down makes more difference), I believe that happened only for the convenience of the programmer who programs it.
    Your conclusion: No more Auto ISO, my conclusion: No more Auto
     
  10. Ron:
    This is how it is on Nikon (which I shoot for years and still do) - in shutter priority mode it always increases just the ISO and leaves aperture at lowest setting (if there is not enough light for base ISO).
    Only if there too much light for chosen shutter speed it stops the aperture.
    I presumed it is the same on Canon or at least documented somewhere if different and how it behaves.
    So in situation above Nikon would choose (1/500) f/5.6 ISO 640 (decreasing ISO), Canon choosed 1/500 f/6.3 ISO800 (kept higher ISO, but stopped down 1/3 aperture).
    Why would camera close the aperture if there is not enough light in the first place and
    iso is already high? Instead of ISO800 camera could take picture at
    ISO640, and picture would be of better quality.
    Seems like there is some inside logic that is not documented like ISO-focal length relationship, round ISO number preference or it is just a fault.
    Juergen: There is no mention of this in manual - how Tv mode works with AutoISO or AutoISO with focal length. See page 63 and 98-99.
     
  11. John:
    Yes, that was my typing mistake. Thx for correcting.

    I really suspect it was programmers choice - keeping round ISO number and prefer to close aperture instead. :-/
    From exposure side of things it really doesn't matter (maybe little more noise), but from DOF side (shooting wide open) it does.
    BTW Where can one online submit such "errors/request" to Canon?
     
  12. [[I presumed it is the same on Canon or at least documented somewhere if different and how it behaves.]]
    Why not test the reverse? Select Av and check the shutter speeds it picks compared to what you had selected in Tv. (Obviously it would only be a valid test if you did both Av and Tv test in the same light at the same time.)
     
  13. Ron:
    I think this test wouldn't prove much. Exposure wise 1/500,6.3, ISO800 or 1/500, 5.6, ISO640 is the same. It is camera's choice to close the aperture when light is bad and keep higher ISO, instead of trying to shoot wide open, that is what bothers me and I am also used with Nikon.
     
  14. I'll guess, that if you contact Canon, they'll tell you that the noise difference between ISO 640 and 800 is minimal therefore the camera choose 800 and that moving to F6.3 give better image quality than F5.6...... just a guess.
    Out of interest, I'd be curious to see a noise comparison test between ISO 640 and 800 on a 7D.
     
  15. tele - having used this lens with auto iso a lot, if you want to keep it wide open there's no point in using TV in the first point. Use AV. It's not an error.
     
  16. Check Custom Function 1-2 maybe you set it to 1 stop
     
  17. Brett: I know. Sometimes if background is even and light also I usually shoot in AutoISO off. But if background is very different (dark wood, light grass and bright sky all in same place) and constantly changing light, AV mode with ISO400 for example can be fooled by meter and choose too slow of a shutter speed to freeze action, thus I prefer shutter priority (and on Nikon also Manual mode, since in Nikon Manual mode+AutoISO you can do exposure compensation which you cannot on 7D). But hey, this is another long story... :)
    Marting: I guess you're right. Maybe I wouldn't achieve anything contacting them as they believe that this is right by design (similar to Nikon's preference for wide open aperture in tv). :-(
    BTW Noise difference isn't any. Picture wise 7D is great. It is the aperture changing that bothered me, good thing is that I changes it always just by 1/3 of stop.
     
  18. John:
    >Check Custom Function 1-2 maybe you set it to 1 stop
    Didn't help. BUT changing Custom Function 1-1 to 1/2 stop (exposure) did the trick! Thanks for helping!

    It seems as if all this 1/3 exposure up/down twidling causes this effect.
    Because it always just changed from 5.6 to 6.3 (1/3 stop) no more. Now that this is setup to 1/2 it doesn't have any problems.
    I tried it many times, and the "error" is repeatable. BTW I am a SW/HW tester. :)
     
  19. Thanks everyone for quick help, especially John.

    As this is now understood and cleared, where it is best to contact Canon so they check this option and possibly tweak it?

    They actually had a similar bug resolved in 1.2.1, which states:
    "When Auto ISO is used and Program Shift is applied, the ISO setting will be more stable and not change as frequently when the Main Dial is rotated. "

    This could well be some sort of AutoISO unstable behaviour as it is changing aperture way to quicky. For example I focus on some plant, just moving a centimeter to the right it changes aperture to 6.3 then again few cm away to 5.6 and then it repeats as I move lens a bit. Way too quickly.
     
  20. Wow, another bug.
    In Tv mode and Auto ISO, setting exposure compensation directly with back dial works (iso decreases), while pushing ISO button and setting exposure compensation with back dial doesn't work (it say so in finder, but metering stays the same).
    It seems AutoISO has lots of tweaking to do.
    Now seriously, what is the best way to contact Canon international on this issues (in my country there is no service)?
     
  21. Maybe it's just a round off display. The correct exposure is possibly F6.0 ISO 800. The camera cannot set F5.6 ISO640 because not enough exposure and it cannot display F6.0 in the finder or in EXIF.
    Now you set exposure step to 1/2 stop, the aperture is still F6.0 but it rather displays 5.6 better than 7.2
     
  22. All this is fine, but why wouldn't you be shooting in AV to select your aperture and selecting your ISO and letting S/S float within a tolerable range for subject? This way the camera will only be selecting one variable instead of two. Using either TV or AV and then selecting auto-ISO doesn't make sense to me. I use AV and then use +EV or -EV to adjust for the lighting within a scene. I watch the S/S in the viewfinder to make sure it fits my situation and use ISO changes and/or aperture changes to force it up and down.
     
  23. In the various auto ISO threads I see on PN it seems like people are not understanding the purpose of auto ISO. It's not there to help you determine proper ISO because it's somehow hard to do it on your own.
    It's there for when low light is an issue and the rapidity of your shooting and decision making does not allow you adequate time to constantly hand-adjust the ISO and test your shutter speed.
    It can be very useful in aperture and shutter priority modes. Used this way you're basically in P mode, except that you can give priority to shutter or aperture.
     
  24. In exact situation, I guess your Nikon DSLR with Auto ISO would display F5.6 ISO640 Speed 1/500 but since that exposure is not accurate for your situation(remember, I assume ISO 800 F6.0 speed 1/500 is correct). At least one of the three numbers 5.6, 640, or 1/500 are fake you just don't know which ones
    Canon just chose the number 5.6-6.3 to be incorrect
     
  25. Nicely said. AutoISO saves lives in light challenging conditions. :)
    Using Nikon I see Nikon gets AutoISO better in Tv, M modes and allows more configuration also for A mode and has it available with EC in manual mode (setting both DOF and stopping action while changing ISO) which 7D lacks.

    Actually it is the only feature I really miss on 7d and now that I at least know workaround to my original posted problem I can get similar AutoISO behavior on 7D and D300 in tv mode.
    Thanks all
     
  26. If you want f/5.6 then put the camera on manual and set it there. I think it most likely that the other perturbations that bother you are "features" not "bugs."
     
  27. Hi
    I have the "same" problem with my Canon MarkIV + Canon 400mm 5.6.
    Best regards
    Omar Brännström
     
  28. If someone is using ISO it's because of the need for split-second decision making without having to worry about achieving a proper exposure or worrying about changing ISO, or at least it should be. Going to manual mode is the opposite of this. Use AV, keep your Auto ISO if you want, or don't, and open up to 5.6. You will stay at 5.6. If the shutter starts to drop below your focal length and you aren't on a tripod, then you can go to auto ISO.
     
  29. Omar:
    Does it work better if you change Custom Function 1-1 from 1/3 to 1/2 stop?
    Full name of the Custom Function is C.Fn I Exposure - Exposure level increments in case the numbering is different on MarkIV.
    For me this constant changing from 5.6 to 6.3 (on the same subject and same low light) disappeared when I set this and now it keeps to the lowest aperture of 5.6.
     
  30. "AutoISO saves lives in light challenging conditions. :)"
    Well, then don't complain about the results. If you leave two variable open the camera's programs will often change two variables.
    Lots of us look in the viewfinder and change either aperture, ISO or S/S with the wheel on the top right, very quickly to suit the subject. You don't have to be in TV to control the shutter speed. Only a slight awareness of the interaction between S/S, aperture, ISO and EV allows you to work in other modes. If you prefer TV, that fine, but turn off the auto ISO if you want only the aperture to change. Go to AV with fixed ISO if you want only S/S to change. You can always see the resultant variable in the viewfinder.
     
  31. Not sure about Canon but I think you have a choice between ISO in 1 EV or 1/3 EV steps. If the steps are 1EV, then auto ISO can only move in 1EV increments, e.g. 100-200-400. You've locked the shutter at one particular speed. If the camera's meter says it wants 1/3 EV less light, it's going to stop the lens down 1/3 EV to f/5.6. Possibly this wouldn't have happened if ISO was set to EV 1/3 steps...but you're leaving it up to the camera to decide. As long as exposure is correct, who cares? If you do, you shouldn't use Tv for this.
     
  32. perhaps the camera chooses smaller apperture because engineers are aware that lens performs better when stopped down? since you let the camera control two variables (iso and apperture), you shouldn't expect it to use the same strategy as you would choose.
     
  33. Hi
    I use the 400mm 5.6 handheld with Canon MarkIV.
    I also use tv offen 1600-2000/s for action and in low light I might go down to 1/640s. I want maximum shutterspeed and low ISO, and not higher aperture.
    I use safety shift (ISO) cfn I-8:2.
    Regardeless of light i got the shuttertime I think I need, and ISO changes accordingly, but I do not want it to change the aperture.
    I wonder if other lenses behaves like this, with my former 500mm f/4 IS I used av so I did not have the same settings. I have ordered the new 500mm f/4 IS II and will test when I got it, but I probably have to wait a year for it.
    For instance
    Shooting sparrow hawk in air, in this case I used 1/2000s and ISO changes
    http://www.pbase.com/omar_brannstrom/image/128031633/original
    In this settings I had 1/2500s and suddenly I sparrowhawk was flying/hunting low with background in AV I might got 1/500s? and that would probably be soft compared to 1/2500s and higher ISO with safetyshift.
    http://www.pbase.com/omar_brannstrom/image/128102009/original
    It will be sharp but the problem is that ISO can get to high and it will be even higher if the camera will set higher aperture than 5.6, like 6.3 or something.
    If I set the camera on 1/3 step it sometimes changes the aperture to 6.3 and if I set the camera on 1/2 step it will sometime set the aperture at 6.7 instead.
    When I shoot handheld very early in the morning, I might go down to 1/640s so the ISO will not be to high.
    Here is a wild red deer running and at 1/640s handheld camera, aperture 5.6 and if it would be at 6.3 och 6.7 the iso would be even higher, there are already to much noise in the picture.
    http://www.pbase.com/omar_brannstrom/image/128322679/original
    Here is another one with Canon MarkIII instead at 1/640s
    http://www.pbase.com/omar_brannstrom/image/117633427/original
    Best regards from Sweden
    Omar Brännström
     
  34. Excuse me if I missed the point, but you KNOW you want a specific shutter speed and you KNOW you want a specific aperture. Just put it on Manual and let the ISO float. The 7D will do auto ISO in M mode.
    I chose Canon for a variety of reasons, but I do understand that Nikon is just ever so slightly smarter when it comes to automatic exposure settings. I suppose you just can't have the best of both worlds.
     
  35. Hi
    On my MarkIV I can not exposure compensate at all if I put it on manual. I offen use like + 1-2 for birds against clouds and sometimes when it is dark outside I use -2.0 exposure compensation like this wild red deer
    http://www.pbase.com/omar_brannstrom/image/128581441/original
    Is it possible to exposure compensate with 7D in manual and auto ISO?
    Best regards from Sweden
    Omar Brännström
     

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