50mm prime. Is it really 50mm?

[Kierano]

Hello,

I'm thinking of investing in a 50mm prime for my portait work, but I'm wondering whether, in crop factor terms, it will be really be 50mm or rather 75mm?

Speaking of which, is 50mm (or 75mm) the optimum focal length for portraits? If anyone has any suggestions based on their experience, I would be grateful.

Is there anyone out there who has figured this out already?

Ta,
Kierano

[donoreo]

The 50 mm works out to be about 80 mm with the 1.6x crop factor. That is a suitable length for portraits. Some prefer more, some less.

[nikonian]

A fixed 50mm lens has an AOV of 46.79 degrees. Using it on a crop frame camera does not alter this, it only seems to due to the cropping. For portraits the ideal is 80m with its AOV of 30.26 degrees.

[chris-p]

Originally Posted by nikonian

A fixed 50mm lens has an AOV of 46.79 degrees. Using it on a crop frame camera does not alter this, it only seems to due to the cropping. For portraits the ideal is 80m with its AOV of 30.26 degrees.

Sorry, no. You've got that the wrong way round. The angle of view (AoV) DOES change, it's the focal length that doesn't. The whole reason it looks different is precisely because the AoV changes.

There is also no such thing as an "ideal" focal length for portraits, although the AoV of 85mm on 135 cameras is often considered "classic". You're fairly close to mimicing this with a 50mm lens on an APS-C camera.

In reality, it depends on what sort of portraits. A 50mm or 85mm lens will give you good separation from the background, especially on a cropped camera.

The question of "is it really 50mm" only has one answer. Yes. It is 50mm. It just looks different. Same as a 50mm lens on a medium format camera looks wider.

[ap4a]

Also, the perspective created by the focal length is generally more important than the FOV. If you need to you can move closer to or further from a subject, or crop an image. But you can't manipulate the perspective which is a feature of the focal length.

Focal lengths around 50-135mm are often considered ideal for portraits due to the pleasing perspective - ie. there isn't the distortion of wide angles that can result in bulging noses etc. Factors to consider for telephoto are that the longer the lens is, the further away from the subject you are, so available working space becomes a consideration.

See here for more: http://www.bobatkins.com/photography...it_lenses.html

[nikonian]

Originally Posted by chris-p

Sorry, no. You've got that the wrong way round. The angle of view (AoV) DOES change, it's the focal length that doesn't. The whole reason it looks different is precisely because the AoV changes.

There is also no such thing as an "ideal" focal length for portraits, although the AoV of 85mm on 135 cameras is often considered "classic". You're fairly close to mimicing this with a 50mm lens on an APS-C camera.

In reality, it depends on what sort of portraits. A 50mm or 85mm lens will give you good separation from the background, especially on a cropped camera.

The question of "is it really 50mm" only has one answer. Yes. It is 50mm. It just looks different. Same as a 50mm lens on a medium format camera looks wider.

Obviously you know nothing about lens. How can a fixed prime lens alter its AOV from body to body. (cropped to full format). Your last paragraph proves you wrong. IT JUST LOOKS WIDER.

[nikonian]

Originally Posted by ap4a

Also, the perspective created by the focal length is generally more important than the FOV. If you need to you can move closer to or further from a subject, or crop an image. But you can't manipulate the perspective which is a feature of the focal length.

Focal lengths around 50-135mm are often considered ideal for portraits due to the pleasing perspective - ie. there isn't the distortion of wide angles that can result in bulging noses etc. Factors to consider for telephoto are that the longer the lens is, the further away from the subject you are, so available working space becomes a consideration.

See here for more: http://www.bobatkins.com/photography...it_lenses.html

Please differentiate between AOV and FOV. FOV is when you bring the eyepiece into the equation. For example what you see.

[ap4a]

Originally Posted by nikonian

Please differentiate between AOV and FOV. FOV is when you bring the eyepiece into the equation. For example what you see.

If you want to get needlessly pedantic then please be my guest. However for simplicity's sake I'll continue to use FOV in the common usage, to mean the field of view as captured by the camera, not as observed through an eye piece.

[nikonian]

Originally Posted by ap4a

If you want to get needlessly pedantic then please be my guest. However for simplicity's sake I'll continue to use FOV in the common usage, to mean the field of view as captured by the camera, not as observed through an eye piece.

FOV can never be used for doing a trig calculation

[ap4a]

Originally Posted by nikonian

FOV can never be used for doing a trig calculation

The terminology in general use for describing crop factors or their effects is field of view crop factors which is determined by the angle of view and the sensor size (and depending on your POV perhaps the size of the imaging circle).

Also, FWIW, camera and lens manufacturers often use the terms AOV and FOV interchangeably when describing the features of a lens. Eg.

Focus breathing is particularly well controlled in this lens – to where the undesirable alteration of angle of view with actuation of the focus control is now virtually eliminated.

Focus breathing in these new lenses achieved even further improvement over their predecessors with the incorporation of new optical refinements – to where the undesirable alteration of field of view with actuation of the focus control is now virtually eliminated.

Those are both descriptions of the same Canon lens made by Canon on their web site.

Or from the Canon Full Frame CMOS white paper:

The original lenses will now have the field-of-view, or angle-of-view, of 1.6 times longer lenses

So, to keep matters simple, and to not have to bog description down with pedantry or excessive technicalities, I'll stick to using the generally accepted term of FOV when describing the effects of a crop factor.