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A few months ago I bought a Nikon D5500, now I want to buy a 50 mm lens, but I just discovered the meaning of DX on my camera. So on the lens reviews I read that if I buy a 50mm to my D5500 it would act like a 75 mm lens and the recommendations is to buy a 35mm. My question is:
If I buy the 50mm what would be the difference, do I have to be farther from the subject or what? If I want to have the 50mm effect do I have to buy the 35mm to simulate 52mm?
Thanks for the help.
The "meaning of DX" on your camera is no different with prime lenses, FX or DX, than it is with your current 18-55mm DX lens. The field of view (FoV) obtained with your 18-55mm lens is also affected in the exact same way by the size of the DX sensor in your camera as any prime lens will be.
A 35mm DX lens will provide the same field of view on your DX camera as a 35mm FX lens would, which is also the same FoV as what you get with your 18-55mm lens set to 35mm.
A 50mm DX lens will provide the same field of view on your DX camera as a 50mm FX lens would, which is also the same FoV as what you get with your 18-55mm lens set to 50mm.
If your decision is based upon field of view, then any 35mm prime lens you buy will give the same FoV on your D5500 as the FoV you get with your 18-55mm lens set to 35mm and any 50mm lens you buy will give the same FoV on your D5500 as the FoV you get with your 18-55mm lens set to 50mm (within the minor variation of the exact focal length of each lens - some 35mm lenses may actually be 33mm lenses while others may be 37mm lenses or anywhere in between and some 50mm lens may be anywhere from 45-55mm actual focal length).
If your decision is based upon which f/1.8 lens will give you shallower depth of field then the question is a bit more complex. But in general if you're shooting at different distances to get the same framing with both lenses the DoF will be virtually the same. Shooting at 10 feet with a 35mm lens at f/1.8 gives a DoF of 1.77 feet. Shooting at 14.3 feet with a 50mm lens at f/1.8 gives a DoF of 1.76 feet.¹
What will change by shooting further back with the 50mm lens to get the same framing as with the 35mm lens when both lenses are used on your D5500 is the perspective. Things behind your subject will look closer with the 50mm lens shot from about 14 feet away from your subject than they will with the 35mm lens shot from 10 feet away from your subject. To understand why, please see: Why is the background bigger and blurrier in one of these images?
1. In practice the difference in design tolerances and manufacturing tolerances between the two lenses will be greater than the theoretical difference of 0.01 feet (1/8 inch). Are both lenses exactly 35mm and 50mm respectively? Are both apertures exactly f/1.8? Is the difference in shooting distance you are using exactly 1.428571428571429 times further? Probably not.
Since your kit lens covers 18-55mm, you can get a very good idea of the difference by taking a set of photos at 35mm and another set at 50mm. The main things you'll be gaining by adding a prime to your kit will be sharpness (although probably not much - the kit lens isn't bad) and the wider aperture. On the assumption that you're trying to decide between a 35mm f/1.8 and a 50mm f/1.8, the wider aperture will be more notable on the 50mm, because the kit lens gets a narrower relative aperture at 50mm than at 35mm. (You can find the values it achieves by using A mode and opening as wide as possible). However, the framing is much more obvious than the differences in depth of field.
TL;DR try the two focal lengths with your kit lens and decide which is a higher priority for you.
A thing that you may consider on choosing between these two lenses is that the nikon 35 mm is a dx lens. So I consider investing in 50mm is better, in case that you want to upgrade your camera later.
Another opinion from me: If you want to buy secondhand, it is easier to get 50mm than 35mm, and later if you want to sell, I think, that it will be also easier to sell 50mm, since many people shoot with 50mm
