Canon EF-S 17-55mm VS Sigma 17-50mm VS Tamron 17-50mm?

jitteringjr wrote:

Sovern wrote:

jitteringjr wrote:

Sovern wrote:

jitteringjr wrote:

You need to do more homework on perspective. Here read this:

http://www.josephjamesphotography.com/equivalence/#perspective

"Perspective is a function only of the distance of the camera from the subject"

So you point to some random photographers website as a reference? How come when I mount my 85mm 1.8 on my 450 and a 5D the perspective does not change? Can you explain that to me? I get the same compression just sides of the frame are chopped off on the 450D if I'm shooting at the location so I have to back up which leaves me with less bokeh or less capable bokeh.

The only thing that changes is the field of view between the different size formats which makes you either move forward or move backward if you want to get the same scene as one format.

A 50mm is going to be a 50mm on a crop body or not, the only thing that changes is field of view hence why people say 50mm on 1.6X body (or 80mm FOV).

A 50mm lens on a crop body will not magically give you the perspective (which means features such as compression) as an 80mm lens it only changes the field of view of which you see. You will have less field of view on the crop body forcing you to back up to get the same shot as you would on a FF body.

Joeseph James aka posting now under Great Bustard is not random and is an authority on this. The same 'prime' lens on crop and full frame can't give equivalent images. If you stand in the same placeswitch the same lens, then perspective will not change because the camera didn't move. However the cropped image will be just a cropped version of the FF. So say you try to move the crop camera back with the same prime lens to frame the same image. Well then you moved the camera relative to the subject and ask have said three times now, you just changed the perspective of the subject. So your image is not equivalent. So to get equivalent images, you need to be standing in the same location relative to the subject and use a focal length 1.6 times longer on FF. I'm not going into aperture yet until this part is understood.

Actually the perspective is the same. You're just moving back to get the same FOV as the full frame user got. The full frame user will have more bokeh due to being closer to the subject so thats how aperture plays a role in all of this.

You don't gain more compression distortion from stepping backwards or else users would use a 50mm and step back to 100mm equiv, crop it and it would have the compression of 100mm and thus the perspective of it which is bogus.

I'll post some pictures later. You just aren't getting it verbally. And you don't get more bokeh. You get more blur. Bokeh is qualitative and not quantitative.

Actually you're right sorry for spreading false information. Thanks for pointing all of this out. I did more research into this and there are a lot of mixed views on this but it turns out that perspective is only relative to the distance from subject to camera.

So if you mount a 50mm lens on a 1.6X crop body than it does act like an 80mm lens and has the same compression as an 80mm lens as you are forced to step back more to get the same shot than you would using full frame which alters the distance compression.

I also learned that there are is no such thing as lens compression but distance compression and no such thing as wide angle distortion but again distance distortion from being too close.

So an 85mm lens will act like a 135mm lens on crop including the compression and out of focus wise there will be a slight difference coming from a 85 1.8 on a crop body to a 135mm 1.8 lens on full frame as the 85 1.8 will have a wider focal plane on the crop body so you can get away shooting at wider apertures on crop body while retaining a wider plane of focus.

The funny thing is that there are a lot of "professional" well knwon photographers spreading false information saying that the perspective does not change from one body to another. They are correct in a sense but to get the same framing as full frame on a 1.6x body as you would on a full frame body the perspective does change because you are forced to move further back.

This would be the same as shooting a shot with a 50mm lens followed by shooting it with a 200mm lens. If you cropped the 50mm lens to frame it the same way the 200mm lens shot was shot than both photos would be identical distance compression wise thus perspective wise too.

Whats really weird is that I could see this being an advantage to using cheap Rebel DSLR's in low lighting situations at wide apertures.

Because you have a wider focal plane with the crop bodys you can get away with shooting wide open (say 2.8) and getting tack sharp photos, using the sweet spot of the lens, and getting better low light shots vs using a full frame (comparing cheap Rebels to say a 5DClassic) where you would have to raise your f stop a decent amount to get the same focal plane as the crop body even when considering the changes in lens focal length to get the same distance perspective (basically shooting from the same distance with both formats and getting the same framing via using different lenses).

These are definitely some interesting findings though.