RahulKhosla wrote:
What is the recommended ISO setting in a D850 - both for A and S modes - to enable fast shutter speeds especially for shots of flying birds.
Should I put a minimum / maximum limit and what should the ISO sensitivity setting be?
It sounds as if you are planning to use Auto ISO with A and S modes. That's sort of a "double" auto mode, using Auto ISO with either of those other auto exposure modes... and is something I'd NEVER do, personally.
A/Av is Aperture Priority Auto Exposure... you choose the aperture AND the ISO, the camera chooses an appropriate shutter speed.
S/Tv is Shutter Priority AE... you choose the shutter speed AND the ISO, the camera chooses an aperture.
P is Program AE... you choose the ISO, the camera chooses a combination of aperture and shutter it deems to be appropriate.
M with Auto ISO is just another form of AE... you choose the shutter speed and aperture, leaving it to the camera to select an appropriate ISO.
M without Auto ISO is fully manual mode... you choose ISO, shutter speed and aperture.
For fast moving subjects like birds in flight, wanting to freeze movement and needing to use some form of AE (due to variable lighting conditions) I'd use either S/Tv or M w/Auto ISO, so that I could control the shutter speed. Pointing a camera toward a bright sky while using any AE mode will often cause the bird to be significantly underexposed, so some + Exposure Compensation is likely to be needed. On a sunny day, I'd try +1 stop E.C. first, then adjust from there. On an overcast day, it might be a little less. Even more E.C. is likely to be needed if shooting the shaded underside of the bird (and not using fill flash).
If lighting isn't variable, I'd use M
without Auto ISO.... fully manual... and simply lock in my exposures. When it's possible to use that, it guarantees the most consistency. Any of the camera's AE modes gives up some of your control... but AE modes can be necessary if lighting conditions are at all variable.
Only you can say what ISO levels are acceptable to you. You should shoot a series of test shots with your D850 at different ISOs and decide for yourself.