Prime lens DX/FX confusion

Ice Globe

Ice Globe

Ice Globe

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I'm thinking about getting a prime lens for greater sharpness and more control on depth of field sometime but a little confused with what focal length I will have as an end result.

I have the D5100, with a DX sensor. I'm looking for probably either 35mm or 50mm with compatible autofocus lens (AF-S).

Now I know the DX sensor gives 1.5x the actual focal length compared to 35mm film. Most if not all prime lens' I see with AF-S are FX. Would a 50mm FX lens give the same focal length as 50mm on my DX kit lens and therefore 75mm in comparison to film?

I'd most likely be using the prime for general shots, portraits, social events and the odd close-up; with the above questions in mind would 35mm or 50mm be recommended?
I'd also be interested to know how either prime lens would do for landscape photography in comparison to the 18-55mm kit lens with the main interest of achieving greatest sharpness.

Thanks :)
 
The focal length is always the focal length, so a 50mm lens is still a 50mm lens on either DX or FX. :)

But, the Field Of View is different. You're correct in that a Nikon DX sensor has a 1.5x crop factor, so what that means is the image that's captured with a 50mm lens on a DX camera is the same as a 75mm on a FX camera (or 35mm equivalent).

Think of it like just capturing the middle 2/3rds of an image, and you're about there. It's just like zooming in a bit, or cropping, which is where the term crop factor comes from.

For head and shoulder shots, a 50mm on a DX would be good, but for full length stuff a 35mm might be better.

For landscapes, you'd be stopping down quite a bit, say f8 or higher, for increased depth of field, and most kit lenses are pretty good around that aperture anyway. You won't necessarily see much of a difference IMHO.

The wide aperture short focal length primes come into there own for portraits or more creative photography needing shallow depth of field. But, the 35/50/85mm Nikon primes are cheap enough for you to buy and experiment with anyway.
 
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I quite like the 35mm DX lens myself, it's great in low light and nice and sharp.

The kit lens is also sharp as well, it just isn't as fast...

Try spending a day shooting with your kit lens zoomed to 35mm then set it to 50mm and see which focal length you prefer before picking up a prime. :)
 
Thanks for the explanations and advice.

Nikon appear to only offer:

35mm f/1.8G AF-S DX
50mm f/1.8G AF-S (FX)

which would autofocus on my camera and I can't justify the price of f/1.4G at all.

Can you clarify the below?

35mm f/1.8G AF-S DX - Would be same FOV as 35mm on my kit lens but would be 52.5 in relation to FX and Film.

50mm f/1.8G AF-S (FX) - Would be same FOV as 50mm on my kit lens or would it be 75mm on my kit lens?

Thanks again.
 
An AF-S lens will focus on just about all Nikon bodies, including yours.

I'm not 100% sure on the FOV but I'm guessing that all lenses on a DX will include the 1.5/6x crop factor, so 35 = 52.5 (in relation to FX) and 50 = 75 (....FX)
 
I've got the same camera + the 35mm AF-S prime and its focal length is roughly 52.5mm. It gives a cracking photo though and the cropped focal length on the 35 gets used vastly more than the 18-55mm AF-S VR lens I also own.
 
^ Snap, I find the D60 struggles in low light so the 35 works really well with it. :)
Ice Globe said:
Can you clarify the below?

35mm f/1.8G AF-S DX - Would be same FOV as 35mm on my kit lens but would be 52.5 in relation to FX and Film.

50mm f/1.8G AF-S (FX) - Would be same FOV as 50mm on my kit lens or would it be 75mm on my kit lens?

Thanks again.
Click to expand...
50mm f/1.8G AF-S (FX) - Would be same FOV as 50mm on your lens. :)
 
explicit4u said:
An AF-S lens will focus on just about all Nikon bodies, including yours.

I'm not 100% sure on the FOV but I'm guessing that all lenses on a DX will include the 1.5/6x crop factor, so 35 = 52.5 (in relation to FX) and 50 = 75 (....FX)
Click to expand...
You guess the opposite of the truth. I don't know of any DSLR lens, regardless of crop factor, where the focal length marked is not the true focal length. There's a very good reason for this as, certainly with Nikon, DX lenses can be used on FX cameras so to show anything other than the true focal length would be extremely confusing.
 
Snapshot said:
You guess the opposite of the truth. I don't know of any DSLR lens, regardless of crop factor, where the focal length marked is not the true focal length. There's a very good reason for this as, certainly with Nikon, DX lenses can be used on FX cameras so to show anything other than the true focal length would be extremely confusing.
Click to expand...

Straight from Nikon. 35mm DX lens equals 52.5mm on a Fx body

http://imaging.nikon.com/lineup/lens/singlefocal/normal/af-s_dx_35mmf_18g/index.htm
 
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