Overexposure problem

Discussion in 'Nikon' started by john_pike|4, Feb 6, 2013.

  1. Hi,
    I'm having a problem with overexposure on my studio shots. I've done a grey card test and the histogram is good, but all the pictures appear washed out and I have to use auto curves on every shot I take. I'm no techy so would be grateful if somebody could come up with a suggestion, which is probably something not set up properly in the camera?
    Thanks, John
     
  2. Can you help us help you by describing:

    1) Telling us what sort of lights you're using.

    2) Describing ow you're using the grey card

    3) Talking about how you have the exposure set up on the camera (is auto ISO on?).

    4) Perhaps posting a down-sized image showing what you're getting - but please keep the EXIF data intact.
     
  3. 5) Check your exposure comp - make sure it is set to "0".
     
  4. What you are describing can easily happen, for example, in shots where - A) your camera exposure meter is using an averaging reading, like Matrix Metering, AND B) the subject is fairly brightly lit, AND C) the background is very dark. This type situation creates a high contrast scene that can fool the camera's exposure system. A common example is a performer on a stage being lit by stage lights against an otherwise dark background. I dont know if this description matches your particular setup, I'm just guessing, based on what you describe.
    If this is whats going on in your setup, one possible solution is to dial in some negative exposure compensation (-) EV, so that the actual image exposure is less bright than what the camera system "thinks" it should be. In other words, try using the Exposure Compensation feature on the camera to dial in a range of negative values like (-) 1, (-) 1.5, (-) 2, (-) 2.5, (-) 3, etc. Then evaluate the compensated images to see if any are acceptable. Doing this should at least fix the problem of the subject being brightly "washed out" (due to over exposure).
     
  5. Err, how are the Histograms of the actual shots? I assume they're right-inclined, ie overexposed.
    If the settings (to shoot a grey card) produce a mole-hill centred on the LCD screen histogram are then set in the cameras Manual mode, ie f8 @ 1/200th with Auto ISO OFF and Exp Comp to 0...etc etc, a mid toned subject should be exposed OK.
    However, if you're shooting white wedding dresses or dark camouflaged overalls, the shots are going to come out wrong, either washed-out or very gloomy respectively.
     
  6. pge

    pge

    John, are you using constant lighting or strobes? I assume you are shooting in Manual with auto iso shut off, am I right?
    If Alan describes your problem accurately, just spot meter. Also, again assuming Alan is correct, when you look at your histogram is it apparent which bump is the subject and which values are the background? If so worry about where the subject is in the histogram, not the background. It is not necessarily a bad thing in studio photography for your background to slide off the histogram on either end.
    You appear to be getting exposure and white balance confused. Don't worry about your grey card for a moment.
    The other thing that can wash out a studio shot is excessive bounce back into the camera lens. Try to avoid this with the positioning of the lights or a flag.
     
  7. Hi,
    Thank you all for your responses.
    I'm using 2 Elinchrome 250's at 45% to the canvas print, which is situated in the same position as the grey card that I used. I shot the canvas on manual - ISO 100 at f8 - 1/125 sec with no exposure compensation.
    I would upload the shot if I could figure out how to do it.
    [​IMG]
    00bK2o-518277584.JPG
     
  8. So if f/8 is too light just try f/11. If you want to fine tune it a little more than that, start at f/8 and shoot a series of shots stoppign down 1/3 of a stop each time. See which one you like the best. That's all there is to it.
     
  9. Are you using Adobe RGB?
     
  10. Depending on which lens you're using, f8 or f11 might be straying away from the sharpest aperture. DoF is not an issue with flat copy work.
    So if it's an f2 lens, sharpest will be ~f5.6. So it's down to maybe 30% power on the flashes and f5.6 on the lens.
    There's some serious vignetting going on here, is that the right lens hood? Lens vignetting at f8 is not good! It's worse at the top corners, so something hinkey is going on.
    It's pretty low contrast overall, what lens is that? It doesn't look like a modern multi-coated lens. Also if the rest of the wall is white, you'll be getting a lot of reflected light, reducing contrast. Mask off with black, leaving a few inches of free white space.
     
  11. I'm betting it is the white wall that is throwing exposure off. In doing copy or closeup work, Only the subject wants to be visible in the viewfinder.
     
  12. That's what I thought, but this is the same set up with a black velvet background and it still appears overexposed. It happens with all my studio shots, whatever the background, and I really need to know why it happens and how I can correct it. Auto curves sometimes sorts it out, but I haven't got time to wade through 100's of shots and correct them.
     
  13. We're missing something, John. If you are consistently over-exposed when you use manual shutter speed, manual aperture, and a known, fixed ISO (with auto ISO turned off), you should be able simply stop down your lens a bit, or power down the flash units a bit to get the exposure where you want it. If you're really setting the exposure (not the white balance) by using a grey card and looking for a centered spike in the histogram, then it seems like you're hitting the grey card wrong, angle-wise, or you've got a grey card that's overly reflective/too hot for the way you're using it.
     
  14. It's a strange one. All my studio shots look as though they've been taken in a haze, at all exposures, but look OK as soon as I click auto curves. I can't figure it out, but thanks for your suggestions.
     
  15. To me the telling bit has got to be the really low contrast of the actual subject....ie the canvas.
    Yes, the shot against white is maybe 1/3 over, but it's really flat too....the histogram of the canvas part is no-where near either end of the scale.

    Interestingly, the shot on black's histogram is centered, but again the tonal range of the canvas is well short at both ends.
    John, can you tell us what camera and lens you're using? Is there something like a cloudy film building on an element somewhere or the beginnings of fungus?
     
  16. Yes Mike, all my studio shots seem to suffer from low contrast.
    I'm using a D200 with a 18-200 Nikkor Lens 3.5-5.6 if it's any help.
     
  17. pge

    pge

    ISO 100 at f8 - 1/125 sec with no exposure compensation​
    So try ISO 100 at f11.
    Also bump your shutter speed up to 1/250, it will not affect the strobe light that is entering your camera because it is much shorter than 1/250 of a second, but it will reduce any ambient light that somehow might be messing with your exposure.
     
  18. Not overexposed IMO - just flat (low contrast). Are you shooting JPEG or RAW? If JPEG, what are the picture control settings (you might actually be telling the camera to record low contrast images). If RAW, then how do you process?
    That's indeed horrible vignetting for f/8. I only used a 18-200 once and hence can't tell if the low contrast is at least partially due to the lens. Are you making sure there is no stray light hitting the lens? And that you aren't using some low quality filter? If it isn't the camera settings (or processing settings), then I would try another lens and see if the issue persists.
     
  19. John, how's your monitor look? I ask because the image that you posted looks pretty good to me. The contrast is fairly low, but if you're taking a photo of another image, lower contrast is to be expected. I wouldn't say that the shot of the canvas looks great, but it's about what I would expect to come directly out of the camera.
    My experience with auto-anything from any software is it is generally too contrasty. If your monitor's contrast is too low (perhaps if it is several years old, or just plain off), then a too-contrasty image might appear perfect on your monitor. Ditto for brightness levels.
    The easiest thing to do is to use a known printer - either one you own, a lab you use, or even a self-service kiosk that you've used before - and print out a copy without any changes, and a copy with the auto levels applied. If you use a lab, be sure to tell them not to correct your images before printing. Once you compare the printed images with what you see on screen, you'll have a much better idea of what the problem is.
    I realize that I may also be saying that because my monitor is TOO contrasty. This monitor I'm using is a little bright, but the contrast seems roughly the same as my actual calibrated monitor, so I'm guessing that I'm not too far off.
    Oh, also ... are you using a UV filter? Is it a good one? There are arguments galore about whether or not you should use a UV filter, and I'm not going to drudge up that old chestnut. One thing that everyone can agree on is that if your UV filter is a cheap one, it WILL degrade image quality, often by increasing flare and/or reducing contrast. If these are shot with a filter, try removing it. If that helps, then either keep the filter off, or buy a better one, based on where you fall in that argument.
     
  20. I think the exposure is good only a tiny bit too light if that. Since you use a gray card so you have same exposure either with white or black border it has no influence on exposure. The image is very low in contrast so it's either your lens or contrast setting on your camera.
     
  21. The shot on black is correctly exposed. The shot against white is maybe 1/3-1/2 stop over. There is also a slight colour shift between the two....that may be due to exposure differences.
    Maybe just raise the contrast settings in Picture Control? I don't have a D200, but guess it's in there somewhere. If all the images need the same it should be possible in-camera.
    00bKB6-518447684.jpg
     
  22. Many thanks guys for all your responses. I've changed the optimization from normal to vivid, hence more contrast, and the results are convincing. Much appreciated help!
    John
     
  23. John, the quality of lighting can have a big effect on the contrast of your copy. I don't see any sign of overexposure in the example you've posted, since none of the highlights hit pure white anywhere. The contrast is lacking however, and I'd suggest that this is down to the lighting and studio environment causing excessive reflection from the dark parts of the artwork.
    Contrary to what many people will tell you, you need hard light for copying, as hard as possible. From looking at the shadows cast at the edge of the canvas, it appears that you have some diffusing modifiers on the lights. If so, remove them. If not, you need to move the lights a lot further back to well behind the camera lens position, still keeping their 45 degree angles of course. The area behind the camera should be kept as dark as possible - and ideally painted matt black. White-painted studios make it extremely difficult in general to control the depth of shadows, and IMHO should be avoided. In any case, moving the lights further back will also improve the evenness of illumination.
    If you're still concerned about your exposure, try this: Just take an incident reading from a handheld meter at the surface of the artwork. Or lacking an incident meter you can substitute a double thickness of white copier paper for your grey card (which may not have a truly 18% reflectance). Open up 2.5 stops from the white paper reading and you'll be as close to an exact 18% exposure as you can get.
    Edit. I think I'm seeing a little hotspot "burn" just off-centre of the canvas. You're not using the on-camera flash to fire your Elinchroms are you? If so, that's a definite no-no for copying work.
     
  24. Rodeo, do you mean that 'flare' behind the first horses' backside?....too many oats maybe...:)

    Looking at the 2 histograms, it does suggest the 'Canvas on White' exposure is right biased.....not blown by any means, but requiring of correction in post, therefore wrong at the moment of exposure.
    I'll second the hatred for white painted studios. It's hard to get good contrast with the walls acting as huge diffuse lights, big studio flashes seem to emphasize this as the shooter doesn't really see the flash in action, just the soft modelling light.
    Vignetting. It seems this lens is notorious for this. However, it does have a sweet-spot around 50mm @ f5.6/8. However, I'm not sure why it appears worse at the top? Pretty sure it's the lens not the lighting!
     
  25. John, the picture control won't do anything to your RAW files. Picture control only affects jpgs. It looks like it's affecting your RAW files, because all cameras use a jpg file for the LCD preview. But once it's loaded onto the computer, it's back to an unedited RAW file.
    Unless you've got edits preselected in your RAW converter, the ONLY colour/contrast setting that will affect a RAW image is white balance, in as much as it will have the one you picked in the camera already applied when you upload the file.
     
  26. John -- the orthodox way to do a copy like that is with cross-polarization. This will solve all of your issues with glare off the canvas, which is what your problem looks like to me. All issues of exposure will work themselves out here.
    How to do it: (1) Take two sheets of Rosco polarizer gel and attached over the strobe, in front of the reflector. Orient these two sheets the same way, e.g., vertically with respect to polarization. (2) Use a circular reflector on your object lens. Using the modeling lights, dial in the circular polarizer until the reflections disappear. You will need a lose a stop or two obviously.
    I don't recommend that you fix this any other way. This has been frequently discussed at LuLa, where there are a number of people who do this work for a living.
     
  27. Joe has a good point. Depending on the surface of the print as well as the angle of the light you may have some specular reflection. If the light is hard you can easily see the hot spot but if it's soft you can have the entire light source reflected in the print but you don't notice it. It simply reduce the contrast of the image.
     
  28. Cross polarisers are not, not, NOT needed for 90% of copying jobs. They're only useful where the artwork isn't flat or has a deeply textured shiny surface. They won't fix low contrast due to diluted shadow detail, like here. In fact using polarisers will almost certainly lower the contrast even further. Polarisers aren't even necessary for artwork behind glass if you light it right. So why recommend overcomplicating things with x-polarisers unless it's absolutely essential? Polarisers can also introduce strange colour shifts of their own, and a professional copyist should strive for the best colour fidelity they can achieve.
    The real solution is to use hard, directional and controlled lighting to keep the camera and lens in the dark as much as possible and to prevent extraneous reflections from tripods, stands, studio walls etc. Anyone seriously doing copy work for a living should know that and have a purpose-made black-painted copy area.
     
  29. By the way, the "flare behind the horse's backside" was the dust flying when his back legs trailed through the brush fence - and I'm not using the on camera flash to fire the Elinchromes.
    I've finally got the result I was after and I can't thank you all enough! Your comments have been extremely productive and given me much food for thought.
    Thanks again,
    John
     
  30. You can see various sides debated here:
    http://www.luminous-landscape.com/forum/index.php?topic=73552.0
    RJ: saying 'not' three times in bold and all caps doesn't make an answer more authoritative. These are reasonable issues for debate. Canvas in fact is a good candidate for cross-polarization.
     
  31. I'm fully with Rodeo on this one.
    And yes I've used 'cross polars' on lights and lens etc, it has its place on reflective 3D stuff and 'potentially' on fine art. Deciding how much brush texture you want by varying the angle of the lens polarizer is just part of the technique. I guess this is an inkjet canvas print, ie a finely nobbled surface, with not much in the way of specular content.
    Canvas in fact is a good candidate for cross-polarization.​
    Traditionally canvas is a fairly coarse woven cotton or linen fabric loves by artists. You only ever need to X-polarize the final picture is if it has really, really textured brush marks with high gloss paint...or has a warped and wrinkly canvas with awful shiny, lumpy varnish where light position can never correct everything.
    You can make patent leather thigh boots look like fisherman's wellies if you're not careful with polarizers....:)
     

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