Can someone explain lens cast by aperture to me

Started 3 months ago | Discussions thread
Tons o Glass 0 Class
Tons o Glass 0 Class Contributing Member • Posts: 753
Re: Can someone explain lens cast by aperture to me

fferreres wrote:

Tons o Glass 0 Class wrote:

Dropbox, Google Drive? Neither may be ideal but I believe they would work.

That was's the link to the two RAW files:

Thank you! The difference in the thumbnails was drastic. The camera was set to Auto for both of those exposures as opposed to being set to the same white balance. I can confirm that Auto WB behaves this way for me as I stop down a lens. I think the Auto WB algorithm may get pushed hot or pushed cold depending on Axial CA and/or PF or the lack thereof. When white balance is held truly constant, however, I think lenses typically do cool want to cool down a bit as we've noticed when you close them down. I've seen camera-based Auto WB push it one way, and have Capture One push it in the opposite direction though... I still have to digest Hank and Alan's discussion.

What about lenses with shiny aperture blades - they can sometimes cause a loss in contrast as the aperture closes down. Depending on the scene, the white balance an algorithm or our eyes would want to see could get pushed hot or cold if warm or cool colors are bounced around by the aperture blades, respectively.

I popped these into Capture One and let it decide the white balance. It wanted to warm up the f/8-ish shot, and wanted to cool down the f/1.8 shot, but there was still a sizeable gap between the two shots in that regard.

FWIW here's the two shots where I took C1's Auto WB on the f/8-ish shot to be "bible" and set both shots to that, then haphazardly and imperfectly pushed the f/8-ish shot such that the histograms roughly matched.

Exposure was brought down an additional (subractional?) 0.7EV from as shot. The stopped down shot undoubtedly had more contrast and the sunlight also seemed more intense here? I dunno. Maybe the camera didn't want to clip the shadows.

Hmm... which one's cooler now? This one may need to be a little warmer, actually, which is consistent with what we've observed already.

I see that -1.7 EV was dialed when you were shooting. Was it your intention to expose for the sunlight in doing that? My eyes are drawn to it first, that's for sure.

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