Theoretical question...

[quickben]

If I get a lens that has 31.25mm in it's range (on a 1.6x crop factor camera), is it the same as having a 50mm lens, in that it has the same perspective as the human eye i.e neither wide-angle nor telephoto ?

Or does the 31.25mm have the same perspective as it should have (wide-angle) only we get a smaller portion of the image magnified ?

What I mean is, are the perspective properties of a lens determined by the optics or the percieved focal length ?

In other words, would a 10D with a 31.25mm lens give exactly the same image as a 1Ds with a 50mm lens (aside from resolution and other camera-specific traits) ? Or would the 10D still produce an image with the symptoms of a WA lens ?

This is confusing the hell out of me !!!

Help ?

Gary.

[DocFrankenstein]

If you want the human eye perspective and you assume it's 50 mm. You should divide the 50 mm by 1.6 and get 31.25 mm. So for "natural" pespective on the rebel, you'll want a 35 mm prime approximately.

Or does the 31.25mm have the same perspective as it should have (wide-angle) only we get a smaller portion of the image magnified ?
LOL both :lol:

Look at it this way: If you have a pic on your computer taken with a wide angle lens, say 18 mm. Then you crop it in such a way that the crop is only 50% of the area of the original image. You crop from the center. The resulting crop is the equivalent of a pic taken with 18*(1/.5)=32mm

If you crop only 5% of the image by area, you're gonna get 18*(1/.05)=320mm. Had you mounted a 320 mm prime and took a pic with it, you'd see that same thing. Only the resolution would be different.

In other words, would a 10D with a 31.25mm lens give exactly the same image as a 1Ds with a 50mm lens (aside from resolution and other camera-specific traits) ?
I'm not sure if 1Ds has the full frame chip, but if it does then yes. The WIELD OF VIEW will be the same.

Or would the 10D still produce an image with the symptoms of a WA lens ?
Not sure what you mean by the symptoms. The FOV will be the same.

Clear? Hope this helps

[dn7elson]

What I mean is, are the perspective properties of a lens determined by the optics or the percieved focal length ?

Take a look at this http://www.sweeting.org/mark/lenses/

[Longwatcher]

Think of the crop factor as a Field of View (FoV) crop.

The lens and the way it bends light is the same as it always was, but the area of the lens that is imaged is smaller.

So within the FoV the 10D sensor has (which is 1.6x smaller then a FF 35mm camera) the way the picture will look will be the same, however a FF camera such as the 1Ds will have a wider FoV with the same lens because it can use the full extent of the lens, but if you cropped it to the same area seen by the 10D, there should be no difference (except as a result of a better (not bigger) sensor on the 1Ds).

Another attempt: a 35mm (or a 31.25) lens on a 10D will be very similiar to the results that a 50mm lens on a 1Ds (or other FF camera) would give, however they will not be exactly the same because of course the lenses are different, but it will be close enough for 99.9% of us. The field of view will be visually the same (although technically may be slightly different). The best part though is usually the center of the lens has better quality then the outside of a lens so potentially you may get better results from a 35mm lens on a 10D then a 50mm on a FF camera with similiar charateristics in terms of sensor and processing. (The 1Ds has a different sensor and processor so doesn't count for this). By better results I mean color aburations and stray light effects.

Finally a 50mm lens on a FF 35mm format camera is considered "normal" because it has the same field of view the human eye usually has.

Just my attempt to explain.

[petiot]

"What I mean is, are the perspective properties of a lens determined by the optics or the percieved focal length ? "

Dont forget that the perspective only depends on the distance subject / lens. So that a 500 mm lens on a 10D or a full frame will be the same. However, the 1.6 multiplier forces you to keep more distance between subject and camera, and therefore to compress the perspective (for a sujet that would fill the frame in a similar way using both type of camera)

look at this link or google : lens AND focal AND perspective

hope this is helpfull!! i have learned that few weeks ago! ;)

Dan

[petiot]

sorry i meant 50mm

and here is the link http://www.reasonableexpectations.com/Photo_Myths/Perspective/perspective.htm

sorry again

Dan

[DocFrankenstein]

Dont forget that the perspective only depends on the distance subject / lens. So that a 50 mm lens on a 10D or a full frame will be the same. However, the 1.6 multiplier forces you to keep more distance between subject and camera, and therefore to compress the perspective (for a sujet that would fill the frame in a similar way using both type of camera)

look at this link or google : lens AND focal AND perspective
BUT if you mount the 31.25 on the 1Ds and 50 mm on the rebel, everything's gonna be identical. (except the resolution of course)

[Jon]

Dont forget that the perspective only depends on the distance subject / lens. So that a 50 mm lens on a 10D or a full frame will be the same. However, the 1.6 multiplier forces you to keep more distance between subject and camera, and therefore to compress the perspective (for a sujet that would fill the frame in a similar way using both type of camera)

look at this link or google : lens AND focal AND perspective
BUT if you mount the 31.25 on the 1Ds and 50 mm on the rebel, everything's gonna be identical. (except the resolution of course)

Oops! Other way 'round. 50 on a DR is an 80 on the 1Ds.