I enjoy amateur wildlife photography, and have always used crop camera bodies + long lenses, and usually shoot handheld. Obviously the main difficulty is that I need very fast shutter speeds to get sharp photos, especially of moving subjects. Equally obvious is that I have no control over the weather (aka lighting) or the wildlife. Lastly, as an amateur I just can't spend the kind of money needed for a prime lens, so for example right now my zoom is a Sigma 150-600 Sport, f5-f6.3.
All of this means when the light is bad and/or the wildlife is fast-moving, I often find myself increasing my ISO up into the thousands. I decided to get a full-frame camera as an alternative to switch to when the light isn't great. I thought that since the full-frame gathers more light, I wouldn't need as high an ISO to get the same shutter speed. This would mean less noise, and better shots in less light. But with a few tests so far, it seems like the full-frame requires similar settings. Maybe I'm missing something?
For example today I was taking pictures of a snowy owl. I started with my crop camera, and at 600mm / f8 / ISO 640 I was getting shutter speeds of about 1/5000. This was fine, it was sunny out but sometimes a cloud blocked the sun and the shutter speed dropped to about 1/2000, which is the minimum I like to go to for subjects that might move. I decided to switch to the full-frame and do some testing, and I found that in order to get the same shutter speed, I had to increase the ISO to exactly the same setting. Yes the lens and aperture setting were the same, but doesn't the full frame still get more light and therefore require less ISO? The full-frame body was shooting in full mode, not crop.
Here is the specific gear list, thanks so much for any advice!
- crop: Nikon D500
- full frame: Nikon Z 6
- lens: Sigma 150-600mm F5-6.3 DG OS HSM Sport
Edit: after posting this I took another look at two if the images for comparison. One difference I noticed immediately is that the full frame image has significantly less noise even though the ISO is the same. That's great, but I still need fast shutter speeds for moving subjects. Do full frames not require as fast a shutter speed to avoid motion blur / handheld-shake etc? In this case maybe I could safely lower the ISO and take shots at something like 1/1000?