Lens question - focal length - crop vs full frame

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So if I have a 200mm designed for FX and mount it on a crop sensor (DX), I would get 320mm but if it was designed for DX then I only get 200mm or does it always * 1.6?
 
1.5x iirc.

DX lenses give the same crop factor but if used on an FX body would only partially cover the sensor.

It's really not that you are getting extra reach with the crop.
 
1.5x iirc.

DX lenses give the same crop factor but if used on an FX body would only partially cover the sensor.

It's really not that you are getting extra reach with the crop.

Correct, 1.5. 1.6 is Canon.

Okay, thanks. So my kit lens really gives me 27mm-157.5mm.
 
The focal length is still 200mm in a DX camera, focal length doesn't change, what changes is the field of view, do a search in the forums as this has been discussed many times.
 
This might help: Crop factor - Wikipedia, the free encyclopedia

Because it's DX you're not seeing the whole frame... so what you do see takes up the whole image, making it what would be the equivilent of 1.5x more magnification on full frame.

It can be a tricky thing to get a good understanding of...
 
The focal length is still 200mm in a DX camera, focal length doesn't change, what changes is the field of view, do a search in the forums as this has been discussed many times.

OK. Does the field of view change from a DX lens to a crop sensor body?
 
Crop = DX
Full Frame = FX

So a DX lens was made for a crop sensor body.

FX/DX lenses will appear the same on all bodies, however if you use a DX lens on a full frame body it will go into DX mode and reduce the image size to that of a DX sensor to accomodate for the lens. Using an FX lens on a DX body is usually beneficial because you don't have to worry about soft corners, etc because you can't see them anyway :)
 
The focal length printed on the lens, is always the focal length (not counting small inaccuracies).

Placing the lens onto a camera with a 'crop sized' sensor, does not change the focal length of the lens. "DX" or "EF-S" lenses etc., which are designed for digital bodies, are still exactly what is printed on them.

An 18-55mm does not become a 27-83mm.


The 'crop factor' is simple a comparison. It compares the field of view (FOV) of a camera & lens, to the FOV that you would expect with a certain focal length on a 35MM FILM SLR. The reason is because 35mm film SLR cameras were the 'standard' for a few decades before digital SLR cameras became the norm.

So unless you are quite familiar with using a 35mm FILM SLR, you should not be concerned with the crop factor. 18mm on your "1.5 crop factor" camera is what it is, a fairly wide FOV. That won't change and you aren't actually getting 28mm.

Of course, there are 'full frame' DSLR cameras, where the sensor is the same size as 35mm film, and thus they have no 'crop factor'.
 
Focal length is a focal length. It is the optical property of the lens. It has nothing to do with your sensor size. So a lens with focal length of 50mm is going to be 50mm (focal length) when it attached to DX or FX camera.

However, when you attach a 50mm lens to a DX camera body such as your D7000, the field of view is smaller when it is compared to a 35mm film (or full frame sensor).

If you never use a full frame sensor camera nor 35mm film camera, you do not really need to worry about the crop factor. All you need to pay attention is to find out if a particular focal length works for what you want to do.

If a person who shoot with 35mm film in the past and now switch to DX sensor digital camera, the crop factor may means more to him/her because the lens that attach to the camera is now give a different field of view when he/she look through the view finder. (or take a photo)
 
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