I'm attaching a .pdf showing 4 shots of a rattlesnake in an exhibit. Not great shots, but no matter. Each was taken at f/8, 1/160, manual with auto ISO, 8mm center weighted. The 4 shots appear nearly identical in subject and background. But ISO bumps up from 3600 to 4000, then 8000 , then 12800 (a range of two stops). It seems like the initial exposure should have been sufficient (ISO 3600). Naturally, I don't want to be jacking ISO higher than I need to. I'm thinking of either going to a 12mm CW or matrix with exposure compensation. Does anyone see in these photos what is causing ISO to rise? Am I just getting the same instability that often occurs with spot metering?
Register now to gain access to all of our features. Once registered and logged in, you will be able to create topics, post replies to existing threads, give reputation to your fellow members, get your own private messenger, post status updates, manage your profile and so much more. If you already have an account, login here - otherwise create an account for free today!
Need some help explaining variation in exposures
#1
Posted 15 June 2016 - 09:08 PM
#2
Posted 15 June 2016 - 10:57 PM
I suspect that you might be right. The heavily centerweighted metering is more like a semi-spot and must be used carefully.
Another factor is how the terrarium was lit. Under incandescent lighting, exactly where in the on-off cycle the exposure is locked can make a big difference. If you switch Auto-ISO off in such conditions, the meter will even things out. 1/160 can be high enough to get erratic exposure under some light sources anyway as the light cycles so you need at least 1/60 if not longer to get a full cycle.
#3
Posted 16 June 2016 - 07:55 AM
I agree with Merco on the light cycle, but I also see that from the lowest to the highest ISO, the center area in the image gets progressively darker so it is quite possible that a wider center-weighted area might have helped. You should also be able to limit the highest ISO if need be.