 Eliot F. Gomez |
Underexposure problem with new Tamron lens I just bought a new lens, the Tamron SP 24-135 f/3.5-5.6, and so far I like it, except that it is consistently producing images that are 1/3 or even as much as a whole stop underexposed. For example I was out giving it a whirl, it was about 4:00 and the sun was setting with it setting in the background and pretty cloud out otherwise. I was getting images that needed almost a stop compensation. I thought it might have been a tough lighting situation so I took it home and did some other tests with it and still about 1/3 stop underexposed. Please check out the images from the website and let me know what you think http://homepages.uc.edu/~gomezef/tamrontesting.htm Also if this is the case then would Tamron be nice enough to replace it since it is under warranty? Anyone with experience in this? Thank you.
|
|
|
|
||
|
Alan N. Marcus |
Hi Eliot, The test subject you are using appears to be the back of a truck painted white of slightly off white. While you might suspect the lens I know you were unwise to use the truck as a test target. You need to know that the light measuring ability of your camera is limited. In this case the expanse of the white truck was read and averaged. The exposure logic is look for a scene that is more complex than the mundane truck. The metering logic correctly attempted to render the truck as a shade of gray rather than white. You need to run more tests on a mixture of subjects under various conditions before you conclude the lens is somehow at fault. From what I see, the metering system is function quite normally. Since you will surely doubt my diagnosis, I challenge you to read your camera manual and also check out web sights that cover in detail how to measure exposure. Best regards, Alan Marcus
|
|
|
|
||
|
Pete H |
Hello Eliot, I have to agree with Alan on this one. Although you photographed the same subject, you really have no idea (what) the meter was looking at. Prosumer cameras have a nasty habit of giving inconsistant results in focus AND metering, unless the subject is extremely consistant in contrast range. For ANY (basic) tests with a camera when evaluating shooting results, you MUST use full manual AND a consistent target...AND consistent light in f value and color. That being said; is it possible the lens is at fault? Sure it is. One lens may truly be at f/22 while the other is at f/16 or f/19..I've seen it, but only once. I would evaluate the lens a little more before blaming the lens. I think Alan might agree; when testing (anything), standardization and control are everything. all the best, Pete
|
|
|
|
||
|
Eliot F. Gomez |
I suppose that has been the general agreement across the board. Still new to DSLR photography, I am still learning. I will give my lens another test. Thank you!
|
|
|
|
||
|
Christopher A. Walrath |
Eliot, you don't need to know digital photography so much as understand the light you are trying to record on your image sensor. Your camera is dumb. I am not insulting your choice of camera. This is merely a statement as to how your camera thinks you want your image to look. It assumes that you want your image to have the same brightness as a dull medium gray. An average exposure from an averaging light meter. If you meter a lump of coal and go with automatic and meter a field of snow and go with the automatic setting again, you will get the same color. Your camera doesn't know that the coal is black or that the snow is white. It just wants to give a middle exposure in hopes that it is close to what you want. A good way to see an example of this, and it really works well with digital because you can see it quickly, is this. Pick a single colored textured subject such as a cinder block wall with even lighting. Make a meter reading and mark down the exposure settings your camera chose. Make the exposure. This will be called Zone V. Now make five exposures in manual mode, intentionally decreasing exposure by one stop in each progressive exposure. One less stop will be Zone IV. Two stops Zone III. Three stops less Zone II. Four stops Zone I. Five stops, Zone 0. Now go the other way. Intentionally increase exposure by one stop progressively over five exposures. One stop is now Zone VI. Two stops is Zone VII. Three stops, Zone VIII. Four stops, Zone IX. Five stops Zone X. Now we compare. Zone V should be a basic gray, 18% gray to be precise. Don't know why it is 18% instead of 15% or 25%. This is just the standard chosen by scientific photographers as the midpoint of visual luminances possible in a photographic negative. Zone V is your middle gray. As you go through your exposures in sequence, Zone IV is a bit darker, as is Zone III. Zone II you should still have a little texture but the image is dark. Zone I there should be a luminance difference from Zone II but the texture is now gone and Zone 0 should be nearly total black. Going the other way from Zone V, Zones VI and VII are progressively brighter. Zone VIII is very bright and should still have some texture. Zone IX should lose the texture and Zone X is near white. By studying your subject you can see how far off your meter's averaging is from the actual luminance of the subject as perceived by the human eye. Armed with this information you can begin to test and anticipate this difference in your images and apply them everyday to make better photographs. Oh, and by the way. Though only on a basic level, you just learned the Zone System. Happy shooting and Merry Christmas.
|
|
|
|
||
|
Eliot F. Gomez |
Thank you Chris! That has been more than helpful, I will try this out. I now see that it is the photographer error, not the lens. I'm realizing that exposure is one of the biggest obstacles I must overcome. I have read "Understanding Exposure" which has been very helpful, but any other tips or suggestions (especially practical examples like the one Chris gave) will be very helpful. Thank you for all your help.
|
|
|
|
||
|
This old forum is now archived. Use improved Forum here
Report this Thread |
||