Focal length and full sensor vrs.crop sensor

Equivalence of what?

The only think that really is equivalent (to something different) in this scenario is the FOV (as mentioned in the original post).

I just stated what it was equivalent of. A 400mm lens is equivalent to a 600mm lens on a crop body.

The DOF, the perspective, the magnification...these things do not change because of the 'crop factor' of the camera.

Magnification is the only thing that remains constant.
 
That's my take on it also. A 50mm lens is supposed to see what the natural eye sees or as close to it aproxamately. Thats why a 50mm takes nice portraits. What the lens sees and is recorded is the same whether on a full frame body or a crop body. The crop bodies just cuts the edges off.
The perspective is the same.

Since the FOV of 50mm on APS-C is equivalent to ~85mm FF, you need more distance to the subject to get the same shot, therefore the perspective is not the same, and that's why people like the the 50mm for portraiture on APS-C, not because "it sees like the "the natural eye sees".
 
Depth of field does indeed change based on sensor size, as Village Idiot said. The smaller the sensor, the larger the DOF. Look at digital camcorders for instance, it's incredibly hard to do selective focusing with those tiny sensors. Try to do video on a 5D Mark II, you get incredible depth of field control.

Angle of view and depth of field change.

Perspective doesn't change, magnification doesn't change. What Samriel says about needing to move further away is indeed true, but if you shoot with a 50mm from 5 feet away with a full frame and a cropped sensor, it'll be the same perspective, same distortion, same everything except depth of field and angle of view.

People only use the "35mm equivelant" terminology out of laziness. It's a rough guideline to what focal length you'd need to use to get the same angle of view on full frame. It is indeed misleading, when stated improperly. Everyone lazes out by just saying, "My 50mm lens is a 75 on my 1.5 times crop factor body.".... simplifcations almost always lead to confusion.
 
My opinion, Is Forget about what is equivalent to what! Aps-c and 35mm are different format sizes; just like medium and large formats.

Secondly, I would be willing to bet that the vast majority of crop camera owners have never even shot 35mm SLRs to begin with, so what is the point in comparing lenses on a crop body to 35mm if you have no Idea what it looked like on a 35mm camera in the first place.

Buy the lenses you need, shoot, and be happy.
 
Alex ..your missing it completely.. A 50mm on crop body gives the same DOF as on a full frame body ..It's just the FOV is different.


A 28mm on a full frame body is a hell of a lot wider than on a crop body but the the DOF is the same. get it?

The lens sees the same and in the same aspect regardless of the body. The crop body just cuts the edges off.

But the image recorded is identical except the edges are cut off.

And yes there is a difference, An image taken with a 400 mm lens has a different DOF then one taken on a 600mm.

Put a subject in the foreground with either lens keeping the foreground subjects the same size and the background is dramatically different between the 400 and the 600.
hmm... lol the DoF is different I believe...


10MP FF vs 10MP Crop:
The FF captures more of the scene but if you were to "crop" the FF so it has the same scene as the crop does, you are cutting out those extra pixels and the effective megapixels is less, so in that "scene" that the crop has, it has more pixels than the cropped version of the FF, make sense? :p
 
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It's not the optical magnification that is important. It's the ratio between subject size on the sensor, and size of the sensor. This ratio will of course change with a change in sensor size.

DOF doesn't change with a change in sensor size alone, but the change of focal length, or lens to subject distance that is required to match the FOV on difference sensors indirectly forces a change in DOF.
It's pointless to compare two different sensors producing two different images (different FOV), and then suggest DOF is the same.

When comparing similar images with the same FOV, smaller formats (including sensors) will always produce lower image resolution and greater DOF compared to their larger format cousins. That's all you really need to know.

Sark
 

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