Portrait Focal L. - APSC + FOV/Magnification adjustment

[LifeORiley]

Hi all,


Q) Finding 135mm on APSC


What is 135 on APSC (mag 1.5x 90mm = 135) ?

I'm confused. :er:

Some say just FOV changes on APSC and no 'real' magnification takes place. So is it better to use 135mm(202.5 equiv) and back-up from the subject... or.... use 90mm to get the a full frame "look" of 135.

Why do I ask? I watched a video that demonstrated the effect of FL on the shape of faces - 135 being the sweet spot.

Thanks...

 

[SpikeyJohnson]

Depending on your camera (canon or nikon), you will divide 135 by 1.5 (nikon) or 1.6 (canon). So for a Nikon you need a 90mm lens. For a Canon you need somewhere around 84.375mm.

 

[Desi]

The qualities of the image will be dependent on the lens. The size of the image will depend on the focal length and the crop factor of your sensor.

The blur quality (bokeh) and distortion inherent to the focal length and lens characteristics are the same for that lens on any camera you attach it to. What changes is the amount of the image that your sensor will see. A smaller sensor will see a smaller image. That makes it "as if" it were magnified (the crop factor), but a 90 does NOT become a 135 on a crop sensor.

Now, to get the same amount of your frame taken up by the same image on a crop and a full frame camera, you will need a longer focal length on a full frame lens...this will lead to a shallower depth of field, assuming the same aperture.

 

[LifeORiley]

I think I understand.

thanks guys.

 

[tirediron]

....Some say just FOV changes on APSC and no 'real' magnification takes place. So is it better to use 135mm(202.5 equiv) and back-up from the subject...

^^That^^ At least for all intents and purposes. There are some changes which occur if you want to get into theoretical discussions of optics and their underlying principles, however the real-world impact is that only the field of view changes, so, putting your 135mm lens on your crop-sensor camera will give you the looks and feel of a 135mm lens (because that's what it is), but it will give you the field of view (FOV) of a ~200mm lens.

 

[CameraClicker]

I think Desi and Tirediron have it.

I heard a lot of nonsense about crop factors and magnification when I got into dSLR's. Having both crop and full frame bodies, I can do my own tests. Nothing to do with portraits, but I put some thoughts with examples together on a page here: CameraClicker: Sensors

 

[enzodm]

Excellent resource from a forum member: http://www.thephotoforum.com/forum/...rence-between-full-frame-cropped-sensors.html

 

[LifeORiley]

read all....

Got it and thanks

 

[Ido]

Not sure if it was already mentioned or linked to (read through the comments very quickly without much thought).
The "effect of FL on the shape of faces" isn't about the focal length at all, actually - it's all about perspective. You could get the same distortion-free look to the face if you were using a 135mm lens or a 16mm lens - as long as you're shooting from the exact same spot and pointing in precisely the same direction, and just crop the 16mm shot. Obviously that isn't practical, as so much data will be thrown away in the crop that you won't see information in the face (it will be made up of just a handful pixels), but you can try it yourself and see what happens with your own eyes - even with a kit zoom lens.

So you've probably understood it by now - it's not what focal length you're using, but the distance between the lens and the subject. And to get the same lens-to-subject distance without cropping as those 35mm frame users do with a 135mm lens without cropping, you simply need to divide 135mm by your camera sensor's crop factor, which is approximately 1.6x for Canon, 1.7x for Sigma, and 1.5x for any other APS-C format (Nikon, Sony, Fujifilm, Pentax, Samsung).