lost on lenses!

[Omar Tayfour]

hi,this is prob my third thread on lenses? i know im hopeless but aim new to this and cant afford to make mistakes.
so iam in the market for a portait lens,first was comparing the 50mm f.14 nikkor vs sigma 50mm 1.4, then it became a general 50mm f1.4 vs 85 mm f1.8 (same price range) and problem is as i read more i get lost more,one site said that the portait range is 85-135mm which blew my head,the whole time i know a rule (never shoot portait with under 50 or 70 mm) and even that isnt a rule but any shorter ull start gettin the pic a bit flat right? so help?
not interested in online articles,want the opinion of the people here who use the lenses

[Rentham]

Originally Posted by Omar Tayfour

the whole time i know a rule (never shoot portait with under 50 or 70 mm) and even that isnt a rule but any shorter ull start gettin the pic a bit flat right?

Get this garbage out of your head and stop over analyzing things. Pick and lens and shoot the shit out of it. You'll eventually end up with both lenses so you can't go wrong. For what it is worth I shoot portraits with my 85 more than my 50.

[Omar Tayfour]

apperantly i did over analyze it,and will end up with both lenses. oh well,thanks for the tip,u dounded grumpy though,chill

[sk66]

I don't use primes.
That said the "rule" (which I break regularly) is you want an effective focal length around 80mm. On a crop body that would be the 50mm. This is because the effective working distance causes "pleasing" perspective (flattening of noses etc) and effective DOF control.

[Rentham]

Steve, are you saying that a 50mm on a crop sensor would give the same (or roughly equivalent) amount of compression as an 85mm on a full frame?

[Doug Sundseth]

A 50mm lens on a 1.5x crop factor will give the same appearance as a 75mm on a FF sensor. A 50mm on a 1.6 crop factor sensor will give the same appearance as an 80mm on a FF sensor. Note that this refers only to perspective distortion, not depth of field, but perspective distortion is what most people are referring to when they talk about how a longer lens is more pleasing for portraits. This also assumes that you use the same framing with all of the lenses.

[sk66]

Originally Posted by Rentham

Steve, are you saying that a 50mm on a crop sensor would give the same (or roughly equivalent) amount of compression as an 85mm on a full frame?

Yes, due to the resulting working distance as explained by Doug.