What lens is better for the Nikon D5100? - 1

50mm 1.8g or 85mm 1.8g?

Different Uses!

A 50mm has a wider view of the world then a 85mm
Hence different uses! Using a 50mm where you rather use a 85mm is just as ackward as using a 85mm where you rather had the more width of a 50mm.

You can't just compare it like that, you have to think about usage. How do you use your lens, what is your subject, what do you try to reach with it.

And… A D5100 is a crop sensor camera. So effective, I say it EFFECTIVE a 50mm lens acts as a 75mm lens. And a 85mm lens acts as a 127mm lens.

So you just can't compare it this simple. First you have to define your usage then find out what lens fits such profile better.

And that is how you do it.

Neither lens is better. It all depends on your needs.

Historically, for 35mm film cameras (as well as professional full frame DSLRs) the 50mm lens is considered a "normal" lens, which means it provides pretty much the same view as what your eye sees.

The 85mm lens is historically a portrait lens.

But while either lens can be used for either purpose, portrait lenses are somewhat of a niche lens as they are optically designed to give the best results for portraiture.

While your camera has a crop factor to contend with, meaning it seems as the lenses have a longer focal length, this is really not quite a true statement as the characteristics of each lens are finite, regardless of which camera they are uses on.

In other words, the optical advantages of the 85mm lens for portraiture are there regardless of whether or not the lens is used on a full fame or cropped camera. And if the 50mm lens is used on a cropped camera (and some will say it results in a 75mm effective focal length), this does not necessarily mean the 50mm lens will result in the same result.

Thing is, the best way to think of it is that you will need to simply back up a bit when using a cropped camera. So if you buy an 85mm lens for portraiture, if used on a cropped camera, you will just have to backup a bit further.

But it is still not quite that simple. Backing up results in the focus point becoming greater, which results in a deeper DoF. This then means that selective focus is not as good on a cropped camera as it would be on a full frame DSLR at 85mm.

So you see, there's no correct answer to your question, as there are many considerations to be aware of when selecting your lens. You must be aware of these to obtain full benefit; otherwise you could end up with a $500 lens sitting in the closet. If you don't have enough experience to know why you need either lens, I would suggest not buying one until you do. Otherwise, you may be wasting a lot of money.

If you're asking a question like this, you aren't ready for either.

Both are portrait lenses, the 50mm is good when space is limited, and you need to work close. The 85mm needs more space but gives clearer separation between subject and background.

They're both top lenses, so your decision should be made based upon your budget and working conditions.