davidrb wrote:
I'm wondering what that application for an ISO this low. Does anyone here use this and under what circumstances do you use it? Google search gave little information. DPReview had a minor discussion but nobody I can find uses it. It's on cameras for a reason, what might that be?
Many modern digitals don't have ISO 50... but a few do. In all I'm aware of it's a software interpolated "pull" down from the native ISO (usually 100... 200 in a few cases), which might cause a slight loss of contrast or dynamic range (where "push" ISOs above the native tend to have increased image noise and some loss of resolution... both increasing with each higher step up in ISO).
Actually, I wish they were able to provide even lower ISO such as 25, 12 and even 6. There are times they would be useful... but probably not practical as yet.
An extra low ISO (i.e., decreased sensor sensitivity to light) can be useful when you want to use a slow shutter speed for blur effects. It also can be helpful when wanting to use an extra large aperture for shallow depth of field effects in brighter lit conditions.
With DSLRs mostly offering no slower than 100, and only some 50 ISO, today we instead use quality Neutral Density filters for the same reasons.
Back in the days of film really slow, low ISO also tended to be the most grain free.... "Slow" film had the finest silver halide structure. For that reason I used a lot of Kodak 25 and 32 B&W films... until Fuji came out with their Neopan Acros 100 which had equally fine grain, but with a richer pallet.
There also were a lot of ISO (actually ASA in those days) 25, 32 and 64 color films... both negative for prints and slide transparency in the 1950s.... The slow negative films gradually disappeared in the 1960s, but some of the slow slide films were still being offered into the 1970s and later. In fact, Fujichrome Velvia 50 (which I always liked better than most faster slide films) is still available in 35mm, 120, 4x5 and 8x10 formats.
This is not the case with digital. ISO's below the native give up some image quality, instead of improving it. So, depending upon what you're trying to do, it might be better to avoid any extra low ISOs.