1.6 'crop' factor and perspective ...?

[waynelittle]

I undestand what your saying skip, of course thats true and basic.

As i said the word perspective was not the right one.It was the distortion produced with lower focal lengths i was concerned with...

[skipd]

If the super-wide lenses were distortion-free (and few are better than close), the perspective thing would be identical to the telephoto scenario I wrote about before. That is, if you used a 22mm lens on a 1DS MkII (or other full-frame camera) and a 14mm lens on a 20D you should have exactly the same images.

 

However (and this is where my knowledge is really minimal), the distortions of super-wide lenses - pincushion and barrel, for example - tend to add to the differences you might see between the above examples.

 

The apparent spacial distortions you see in a lot of super-wide angle photos is, in my opinion, because people don't look at people's noses from a few centimeters and still take in a lot of extra scenery around them. That's why the camera's image with the really long nose looks so different from what we expect to see with our eyes.

[christopher_bibbs]

Wayne,

 

You may want to consider that the barrel and pincushion distortion, which I believe is what you are thinking of, happens mostly at the outer portions of the image. Exactly the part cropped out in a APS-C sized sensor dSLR.

 

You may also want to consider this: If a focal length always has its basic "distortion" properties regardless of crop and a 15mm lens has this "distortion". Then why isn't it apparent in digicams that regurlarily use a 5-15mm zoom?

[primoz]

Alistair yes I agree. I should write that but it was about perspective etc. Yes DOF is pretty much only thing you will notice even though when comparing full frame and 1:1.3 or 1:1.6 sensor, difference in dof is not that huge. But yes there is difference in dof.

[waynelittle]

yes I think I have 'Seen the Light'. I think I have a much better understanding of all the aspects that this question raised.

 

So really, I'm not going to be getting the tiny distortion a 'normal' 24mm lens might give me on my new 24-70 Sigma. But I should be getting the 38.4mm-122mm eqiuvilent (in 35mm format)

 

thanks for all the very detailed responses, sorry if it was going over old ground.

 

Regards wayne

[mark u]

Look here:

 

http://www.vanwalree.com/optics/distortion.html

 

(explains various kinds of distortion, and why (wide angle) retrofocus lenses tend to suffer more than other lenses inter alia)

 

and here:

 

http://www.vanwalree.com/optics/dof.html

 

(discussion of crop, perspective, background blur and DoF itself are all useful)

[kevin_krumwiede2]

"So if a portrait was taken with for example a 24mm lens from 1 m the subjects nose would look distorted. If however it was taken with a 50mm lens at 1 m it would look less distorted."

 

Wayne, just to make sure you understand... your above statement is wrong. However, if you moved closer with the 24mm so that the subject's head appeared the same size in both shots, then yes, the nose would appear distorted.

[waynelittle]

thanks, I have got that cleared up now.

[jay dougherty]

<a href="http://www.photocamel.com/index.php/topic,355.0.html">This</a> may be the best explanation of crop factor I've seen.