Crop vs Full Frame Metering and Exposure

Discussion in 'Canon EOS' started by beth_wiggins, Dec 16, 2012.

  1. Hi there!

    I recently purchase my first full frame camera. My primary body has been a 50D and my new one is the 5D Mark II (the III is too rich for
    my blood). Anyways, I understand how the full frame lets in more light but how does this affect metering tools like an incident meter?

    I did some testing in my studio yesterday using the same exact settings that I use with my 50D (f8 @ 125, 100 ISO), and the exposure
    was a stop+ overexposed with my 5DMII.

    I have tried searching the net some similiar situations or solutions. I found a few forums talking about it but there was nothing really that
    informative.

    Suggestions? Thoughts? My incident meter seems spot on with my 50D but so off with the 5DMII. Should I just calibrate the meter to my
    5DMII? That is the way I am leaning since the 50D will be a backup/second camera and I will not use the incident meter with it that
    much.

    Thanks for looking!
    Beth
     
  2. How are you determining that it's off on the 5DII? Are you looking at JPG-based histograms? If so, how are you telling the 5D to make those JPGs (in terms of brightness, contrast, saturation, etc). The JPGs won't be the same because the two camera bodies (and their on-board software) handle them differently.

    Likewise, it's quite possible that the two lenses you're using are handling the stop-down instructions from the camera a little bit differently. What happens when you use the same lens on both cameras?

    On the overall concept: the metering/exposure considerations shouldn't be different at all, in the scheme of things, if you're using an incident meter. The light is the light, shutter speed is shutter speed, and (within reason) aperture is aperture.

    Lastly: did you have the ISO set the same on both bodies?
     
  3. Beth, the full frame camera won't let more light in, it is the lens the one in charge of allowing more or less light pass
    through it's aperture, but the sensor will receive exactly the same amount of light, no matter it's size.

    As Matt said, there should be something else going on in your testing, because both cameras should show a very similar
    response to the same lighting. it is possible, nevertheless, for meters to be off by up to a third of a stop, so a third of a
    stop off in one direction in your camera's meter, and the same amount in the other direction in the handheld meter would
    show almost a stop in difference.
     
  4. "I did some testing in my studio yesterday using the same exact settings that I use with my 50D (f8 @ 125, 100 ISO), and the exposure was a stop+ overexposed with my 5DMII."
    If you used the same lens on both the 50D and the 5D II then angle might be different allowing for more or less light to hit the sensor.
     
  5. Something else is wrong here. The exposure that works on full frame will be the same one that works on crop, on P&S, on MF, and on 8x10 LF.
    (To the extent that you might get caught up in the misleading idea that "more light" is getting into your camera with one system than the other, the intensity of the light is the same at every point - e.g. photo site - in either case - and that is the only relevant issue here.)
    If your cameras are correctly and similarly set up and adjusted and you shoot the same scene with both in the same lighting, as far as exposure goes, the same values should yield essentially the same exposure in raw mode. There are a few variables that might trick you a bit, such as the possibility that a particular lens might show more vignetting with the full frame camera.
    Since I've seen it happen, are you sure that you didn't have some exposure compensation setting dialed in on one of the cameras? You are shooting raw, right?
    Dan
     
  6. I shall try to answer all of these:

    I never mentioned JPG, I shoot raw, import to Aperture and compare. Even on the cameras LCD it is sooo obvious that
    the 5DMII overexposed the image in compasison to the 5D.

    As I mentioned previously, the settings are the same, so EXACTLY the same.

    Same lens tested on both bodies, same settings, same angle, same exact light setup.

    I do appreciate all of your input, this is quite mind boggling.

    Beth
     
  7. Could you post an image from each camera for us to help you with this?
     
  8. Same lens tested on both bodies, same settings, same angle, same exact light setup​
    ? Same lens on both bodies means different FOV. maybe that is the problem.
     
  9. Because most people need more than one format to maximize their "gear", I happen to have a 5Dmkii (bought new last march after I saw the features on the mark iii) AND a 'new' 50D. I simply shoot with each of them - having set up the internal parameters the same way on both.
    I have never noticed any difference in exposure with the same lenses when shooting in P or other modes - nor, I confess, have I worried about it either.
     
  10. Gosh I feel like such an idiot. I was getting the images ready to post and I realized that I had to 5DMII set to 400 ISO.
    That would be the issue!

    I was SOOO sure I have changes the ISO but I guess in my excitement somehow I didn't get it all the way to 100, plus I
    was trying to set all of my custom configurations.

    Well, thank you all for your input, sorry to waste your precious time!
     
  11. Look at the bright side ) at least you know its not a problem with the camera like you initially suspected. Though ISO 400 is 2 stops over 100. Did you run the test again?
     
  12. "Gosh I feel like such an idiot. I was getting the images ready to post and I realized that I had to 5DMII set to 400 ISO. That would be the issue!"
    No worries. We've all done stuff like that! ;-)

    Dan
     
  13. Yeah, I'd be guilty of forgetting the ISO too. It happens.
    That said, I've noticed in the past that camera models might differ by a significant fraction of a stop in their exposure -- same settings, same subject, slightly different exposure.
    Also, to be technical, a FF camera DOES let in more light than a crop, but the brightness of light on the sensor in any one spot remains the same for a given aperture. The only reason you're collecting more light is that you have a larger sensor. Think of it like a solar array: A big solar array with lots of panels collects more light/energy than a smaller one with relatively fewer panels, but the brightness of the light on any one panel is the same.
     
  14. Yes, I did try another test last night with ISO 100 and all is well! Silly me..grrr...

    Thank you for your input about FF Sarah. I know some people like to get SUPER technical about it.

    Beth
     
  15. Sarah, to be super technical, the lens "lets in" the same amount of light whether you put it on a full frame camera or a cropped sensor camera or a LF camera. The "amount of light" passing through the lens is controlled by the lens alone. The only difference is that "same amount of light" that was "let in" falls on a larger sensor/film (instead of something else besides the sensor) when the format is larger.
    I suppose that you might say (but please don't! ;-) that "more light is captured by the larger sensor," but this, unfortunately still ends up confusing some people. I think that it is best to sort of let the "more light" thing go and simply respond to this sort of question by pointing out that a) the same amount of light falls on any point of the sensor/film regardless, and b) there is no need to change the exposure if you shoot at the same ISO and f/4 with different formats on this account.
    We're saying roughly the same thing, in the end, but I'm going to be a bit pedantic (and right... ;-) about this issue, since I've seen the misconception about "more light in larger formats" lead people of in some very bizarre directions. (Some make an assumption that is equivalent to answering the question, "How much did it rain yesterday?" with "It rained X amount at my house, but my neighbor got twice as much rain since her lot is twice as large as mine" when both lots received the same 1" of rain.)
    Take care,
    Dan
     
  16. Beth this is normal sometimes we forget the
    basics and dig in to advance

    My last trip to Bangkok I was getting
    overexposed shots then I realized that my
    daughter fiddle with exposure
    compensation
     
  17. No argument from me, Dan! I just didn't want to go that far in explaining it. ;-) But really, if you compare native lenses with native lenses (i.e. EF on a FF and EF-S on a crop), the EF lens does let in more light than the EF-S, simply because of the bigger image circle.
     
  18. the EF lens does let in more light than the EF-S, simply because of the bigger image circle.​
    Sarah, as you're measuring the incident light what defines the amount of light is also the part of scene you're framing and if you frame exactly the same area there will be no difference due to the lens you're using, disregarding it is an EF or EF-S...but you'll need to change the distance from the camera to the subject to compensate for the 1.6x crop factor.

    If you put the 2 cameras at the same distance you can not exclude finding exposure differences, if the additional part covered by the EF lens has a big lighting difference to the average of the one framed by the EF-S lens...and this may mean either more or less light reaching the sensor, because the subject nature and not the image circles.
     
  19. For some reason, when I thought I was writing f-stop, I instead ended up babbling: "... ISO and f/4..."

    Not sure where that came from. ;-)

    Dan
     
  20. Antonio, that's the hazard of not getting super specific and pedantic in discussing this issue. Depending on how one argues what, almost any interpretation is possible. So to be very specific:
    FF camera with EF lens, vs. APS-C camera with EF-S lens. Both lenses at the same aperture. ISO and other settings identical between cameras. Different focal lengths that yield the same angle of view. Both cameras framing up the very same patch of white wall, with no luminance differences over the surface of the wall. Result: Both sensors are uniformly illuminated with the same luminance of light. Both rigs should ideally meter the same (arriving at the same shutter speed). However, the larger sensor collects more total light (more light energy), and the EF lens lets in more total light over a larger image circle.
    Same setup, except we are now comparing an APS-C camera vs. a FF camera, both now having EF lenses. Result: Both sensors are uniformly illuminated with the same luminance of light. Both rigs should ideally meter the same (arriving at the same shutter speed). However, the larger sensor collects more total light (more light energy). Both lenses let in approx. the same amount of light (assuming the same size of image circle), but much of the light let through to the APS-C camera hits the sides of the mirror box and is therefore wasted.
     
  21. Just for the record, "collecting more total light" is completely and utterly irrelevant to anything related to exposure settings
    or the question in this thread. To assume otherwise is to risk a great deal of confusion and some very wrong-headed
    conclusions.

    I know that most of you get this, but there are those who assume that this "more light" business is somehow relevant. It is not.

    Dan
     
  22. ^^^ Agreed
     

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