# The best choise of Nikkor 200m + ?

Started Apr 1, 2020 | Discussions thread
Running the numbers

Nikon3500guy wrote:

HiI do not have any photos immediately, but imagine a pheasant or dove (about this size) and larger animals (deer etc.) - at distances around 50-100m (maybe up to 150m for deer, etc.)?

(I would like 4-500mm, but they are extremely expensive and probably not an option?)

OK, the general rule for sizing focal length depends on the subject size, subject distance, and sensor size:

Subject width / subject distance = sensor width / focal length

Which gives us focal length = sensor width x subject distance / subject width

This is the law of similar triangles, which may be familiar from geometry. This formula is for 'filling the frame' with your subject. You can get away with a shorter focal length to allow room for good composition and cropping.

Your camera's sensor is 25.1 millimeters wide by 16.7 mm high.

The length of a pheasant is around 0.5 meters, while doves are about 0.3 meters wide, and full-grown red deer or elk are roughly 2 meters wide.

At 50 meters:

Pheasant: focal length = 25.1 mm x 50 m / 0.5 m = 2510 mm

Dove: focal length = 25.1 mm x 50 m / 0.3 m = 4183 mm

Deer: focal length = 25.1 mm x 50 m / 2 m = 627.5 mm

At 100 meters:

Pheasant: focal length = 25.1 mm x 100 m / 0.5 m = 5020 mm

Dove: focal length = 8367 mm

Deer: focal length = 1255 mm

At 150 meters:

Deer: focal length = 25.1 mm x 150 m / 2 m = 1882 mm

OK, with the possible exception of deer at 50 meters, the idea of photographing these animals and "filling the frame" with them is not financially practical. Certainly you can crop and get a decent enough shot of them, so for a half-frame shot, you'd need half the focal length, and for a quarter of the frame you'll need a quarter of the focal length, which is far more practical and still might get you decent enough image quality.

Cropping heavily is often necessarily in wildlife photography, and ¼ of your camera's frame is about 1500 pixels across which might be quite good if your optics are good and if you don't look too closely at your final image. 1000 pixels might be ok as well, especially for Instagram or other social media, and so you divide all of the focal lengths above by 6, but that is pushing the image quality.

One inexpensive option is a catadioptric lens, that is, a lens that incorporates a mirror like a telescope, and you can get a 500 mm lens for less than US\$300. However, image quality is rather poor, as its bokeh is ring shaped, they have a large, fixed f/stop, and you have to manually focus. See here for samples photos taken with this kind of lens, and judge for yourself:

https://www.flickr.com/groups/10494981@N00/pool/

Another option is getting a long lens, and then adding a high-quality teleconverter to it, which increases the focal length but at the expense of increasing the f/stop, which means you might have difficulties in poor light, especially if you don't have a good camera support.

Mark Scott Abeln's gear list:Mark Scott Abeln's gear list
Nikon D200 Nikon D7000 Nikon D750 Nikon AF-S DX Nikkor 35mm F1.8G Nikon AF Nikkor 50mm f/1.8D +3 more
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