I decided to go out to take a couple of brick wall photos today with my Nex 7 and a couple of lenses to take a look at the edges. I didn't get very far, because I noticed an oddity in exposure.
In Aperture Preferred mode, I took a shot with my 24mm Sony/Zeiss at f1.8, then an identical shot, changing only the aperture to f5.6. The exposures did not come out the same. The f1.8 shot was noticeably brighter than the f5.6 shot. (ISO stayed the same at 100)
I tried the same setup with my CV 35mm f1.2, at 1.2 and at 5.6. Same result.
So I came indoors, put the 24mm back on, turned up the ISO, and pointed the camera at the ceiling at f1.8 and f5.6. Same exact results yet again. It is obvious looking at the images and at the histogram. These two ceiling shots are below.
I'm using Lightroom 3, with no post processing at all.
What could be causing this Is the shutter not accurate?? Something screwy with the metering? Operator error?
I tried setting the Nex 7 it to both center weighted and spot and had the same results. The f1.8 is about 3/4 of a stop brighter than that at f5.6.
Out of curiosity, I tried the same test on my Nex 5N, set on center weighted. There was a difference there, too, between exposures, although much less. Maybe 1/4 of a stop, if that.
I've not done a real vignetting comparison between the 5N and 7.
However, it is not just this lens. I saw the same behavior on my CV 35 f1.2, and just ran another test on the Contax G 90. This time I compared f2.8 and f8. Same thing, yet again, with the camera set on center weighting.
partitura wrote:
I've not done a real vignetting comparison between the 5N and 7.
However, it is not just this lens. I saw the same behavior on my CV 35 f1.2, and just ran another test on the Contax G 90. This time I compared f2.8 and f8. Same thing, yet again, with the camera set on center weighting.
hmmm...
I asked about the vignetting because, if the NEX-7 vignettes any of these lenses more than the 5N, that could be a reason for the differences in exposure. Does the CV 35 vignette more on the 7 than the 5N?
I just did a little test on both cameras - shooting a featureless wall with the CV 35mm with aperture set at f1.2.
In Lightroom, it takes almost the same vignetting correction to fix both. So it appears to me that the 7 is not vignetting more than the 5N when using this lens.
Partitura, I did a 5N and 7 comparison, when I shot the same shot wide open and at f:5.6 with both cameras, and there is no difference in exposure. I used a ZM 35 f:2.0. So, at least, it means that the problem you encountered is not systematic.
I'm thinking now it might have been DRO. I thought I had it turned off, and when I went to the menu it said off (really, I promise!), but I turned it off again, and now everything seems ok. Who knows?? Anyway, no more problems as of today. Thanks for your help folks.
Is the shutter not accurate?? Something screwy with the metering? Operator error?