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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?

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    This doesn't answer the question, so I'll put this in a comment. If you really want to improve your wildlife shots using focal lengths longer than 200-300mm, you need to put your camera (actually, the lens) on a tripod with a gimbal mount or, at the very least, on a monopod. It will make a world of difference versus handheld at 300-600mm! It may allow you to use lower shutter speeds and still get crisper shots, if the main source of your blur is camera motion, rather than subject movement. – Michael C Jan 7 at 3:54
  • Thanks @MichaelC - I know what you mean, and sometimes I do use a monopod. Other times I rest the camera on my knee, if I'm sitting down or something – Mike Willis Jan 7 at 4:29
  • I'll preface this by saying I am not a wildlife photographer, but I can't think of many situations to use a shutter speed of 1/2000th or faster. A bird diving for fish or something, sure, but for most shots I think you could go much slower. – Robin Jan 7 at 18:00
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A full frame sensor gathers more light for the total area, but that's because there is more total area. The light gathered for the same sized portion of the recording medium is the same for any combination of f-stop and shutter speed — no matter the total size.

This means that if you are getting the exposure you want with f/8 and ¹⁄₅₀₀₀th at ISO 640 on one camera, you'll get (approximately, give or take minor differences between the setups) the same exposure on any other camera regardless of shutter speed.

However, you noticed something important:

One difference I noticed immediately is that the full frame image has significantly less noise even though the ISO is the same.

This is the advantage of the larger sensor. So, you can use higher ISO, which will let you use faster shutter speeds.

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    Thanks @mattdm, so what it comes down to then is that I can "safely" use a higher ISO without getting the same noise that I would get on my crop camera, in exchange for losing the crop-camera's added reach? Also side-benefit in my case is that the Z 6 has in-body stabilization which (I think) works in combination with the lens' stabilization, so maybe sharper images at same shutter speed as crop..? – Mike Willis Jan 7 at 1:58
  • @MikeWillis Re: IBIS - Only if the blur is caused by camera movement. Neither in-body nor lens-based IS will do anything for subject motion. You need a shorter exposure time ("faster shutter speed") for that. With the wider angle of view provided by the same lens on a FF camera, though, the same amount of (the smaller) subject movement will be less in terms of angular movement. That is, the same 1 inch movement of the subject will cover only 67% of the number of pixels such a movement would cover on a 1.5X crop body with the same number of pixels as the FF camera. – Michael C Jan 7 at 3:50
  • @MichaelC got it, thank you again! For birds etc that means I still need fast shutter speed, but maybe for hand-held with (mostly) stationary animals the IBIS will be helpful – Mike Willis Jan 7 at 4:32
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    @Mike Willis: yes, with the Z6 you can "safely" go much in ISO than some other Nikons. I think noise is a matter of personal taste, so perhaps try different ISO speeds and have a good look at the images at the enlargement you are likely to use, and decide for yourself what your maximum ISO is. The Z6 has fairly large pixels, so you've made a good choice for a camera that can shoot nice images at relatively high ISO. The Z6 manual does indeed imply VR and the in-body stabilisation will work together, although this is not clearly stated. Have fun! – user59085 Jan 7 at 15:28
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ISO is an equivalent to film era sensitivities and basically describes the accumulated values you get on a piece of sensor area. If you move your sensor closer to the camera (which is what happens when zooming out or using crop factors), you get a smaller part of the light cone and the readings decrease. To compensate for that, aperture values are specified as ratios f:x. So your gain in light for the larger lenses for the larger "film"-lens distance has already been factored into the aperture number. You stay at the same ISO level for the same exposure even though you have larger photo sites collecting more light. The larger photo sites, however, have then much less noise at the same ISO level.

That's the reason that the race in ISO levels for small sensors is mostly a race in noise reduction algorithms and snake oil: light gathering efficiency has not increased at nearly the same pace as what camera settings now offer and "noise reduction" effectively decreases resolution, partly drastically.

To get similar per-pixel noise as a full-frame sensor at ISO400, on a small sensor you'd probably need something like ISO10. Apart from the problem of getting enough light, the sensors saturate too fast since they don't have the area for charge wells sufficient to hold the charges corresponding to such amounts of light. Also increasing the charge wells would lead to smaller resulting voltages and make it harder to implement the higher ISO ratings people consider a good idea.

So basically stick with your ISO experience in relation to your aperture numbers: exposure will be just the same. But noise per ISO will take a nose dive.

  • Thanks, I often wonder why they even bother touting insanely high ISO ranges (like max 51,000 or so). Also, I always thought that for wildlife photography, the added reach of the crop camera was a huge advantage over full-frame, and I just dealt with the noise in post-processing. Now I'm not so sure about how big that advantage is. Seems like I'll often have a tough choice: less noise + less reach, or more noise + more reach.. – Mike Willis Jan 8 at 15:25
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You are probably aware that with the same lens attached to both the FF Z6 and the DX D500 the D500 will only record a smaller portion of the scene (crop factor)... so it should make complete sense that the exposure settings for the same area/portion would be the same (and they are).

If you instead use a shorter FL on the DX body it makes the apparent size of both the source and the aperture opening (entrance pupil) smaller, which changes the system etendue. I.e. assuming a uniform scene, with a wider/shorter FL lens you include more of the scene but you get less light/area... same exposure.

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