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f stop at normal lenses used for dx format
Hello,.

I know that when you use a 35 mm lens on a dslr like the Nikon D80, that the focal length is 52.5 mm (1.5 * 35)..

What happens with the aperature? Does is stay the same, or is the aperature range bigger when using a dslr?.

Greets and thanks!Bart..

Comments (10)

Bart Roskam wrote:.

Hello,.

I know that when you use a 35 mm lens on a dslr like the Nikon D80,that the focal length is 52.5 mm (1.5 * 35)..

What happens with the aperature? Does is stay the same, or is theaperature range bigger when using a dslr?.

Greets and thanks!Bart.

For starters, the focal length of a 35mm lens does not become 52.5mm on a D80. It's still a 35 and the aperture also doesn't change. The only thing that happens is that your crop or field of view becomes the same as if you were using a 52.5mm lens on a 35mm camera. The magnification stays the same as does the focal length and aperture..

Think of it this way. The 35mm lens casts a image circle that would cover a 35mm sensor at the focal plane. Now with an APS crop sensor, you're not using that whole image circle, You're using a cropped part of it or 2/3rds of it, but that image circle stays the same. You don't magically get a different lens...

Comment #1

But realize that depth of field will behave differently. Say, for example you are shooting with an 85mm lens. If you want the exact framing from a full frame camera and crop camera with that lens, you have to be closer to the subject on the full frame camera. Therefore, your DOF changes..

You will get a shallower DOF with the full frame camera when you shoot with the same framing. The crop sensor will give you wider DOF for identical framing..

I hope that made sense..

I don't know anything about photography. I just like to press the shutter button and hear that sound...

Comment #2

DOF behaves exactly the same though. With the full frame, you moved closer. DOF always decreases as the subject distance decreases, all else being equal..

Had you stayed in the same place and cropped the full frame to the APS camera, DOF would be the same..

The only thing that changes is field of view and how many photosites you're putting on the subject when you crop by using a smaller sensor...

Comment #3

When you put a 35mm FF lens on an c sensor camera, the field of is reduced so that it equals a 52.5mm lens. IN ALL OTHER RESPECTS THE LENS BEHAVES THE SAME, AS IT STILL IS A 35MM LENS...

Comment #4

Guidenet wrote:.

DOF behaves exactly the same though. With the full frame, you movedcloser. DOF always decreases as the subject distance decreases, allelse being equal..

Had you stayed in the same place and cropped the full frame to theAPS camera, DOF would be the same..

Yes, that is true..

My point was that, in practice, if you are taking, say a portrait, you frame the subject in camera, not later with a crop..

Same in-camera framing results in shallower DOF on full-frame..

It's not the lens that behaves differently, it's just that in real-life applications, it is used differently to accommodate framing your subject in camera..

I don't know anything about photography. I just like to press the shutter button and hear that sound...

Comment #5

Lets say I take a two pictures..

One with a full frame camera with a 50mm lens f/2one with a dx-format camera with a 35mm lens f/2 (equals 52.5 mm on full frame).

Will the DOF be the same on the two (otherwise roughly identical) pictures?.

Thanks for your patience and responses!..

Comment #6

If the distance to your subject it's the same the 35 mm will have a deeper DOF. If the frame is filled the same way with full frame you have a shallower DOF (because you are closer to the subject and the real aperture is larger, 25 mm instead of 17.5 mm).So in both situations the cropped sensor will have deeper DOF.VictorBucuresti, Romaniahttp://s106.photobucket.com/albums/m268/victor_petcu/http://picasaweb.google.com/teodor.nitica/..

Comment #7

Bart Roskam wrote:.

Lets say I take a two pictures..

One with a full frame camera with a 50mm lens f/2one with a dx-format camera with a 35mm lens f/2 (equals 52.5 mm onfull frame).

Will the DOF be the same on the two (otherwise roughly identical)pictures?.

Thanks for your patience and responses!.

Bart, you can answer your questions by playing with this depth-of-field calculator:.

Http://www.dofmaster.com/dofjs.html.

Which is quite informative..

In the case you describe, the 35mm lens on DX format would give greater d-o-f than the 50mm lens on a full-frame camera (assuming that the field of view is about the same in each case, i.e. the same subject-to-camera distance)..

If your subject is 10 feet away, you get a d-o-f from 9.3 to 10.8 feet in the first case, and 9.1 to 11 feet in the second case. Bear in mind that these values are estimates based on what looks sharp to a normally good eye at a typical viewing distance, but they will do for most purposes..

This is generally the case. If you switch from a full-frame camera to a smaller sensor camera, you need a shorter focal length lens to get the same field of view, and this increases the depth of field, all other things being equal..

Best wishesMike..

Comment #8

Oh Boy I whish I could find it again...somewhere in the Pentax talks there is a link to a couple of photos that show the difference quite clearly...how the vanishing point is a deeper v for the smaller sensor (If I remember correctly)...the shot was taken of 2 similar objects one set closer to the camera then the other on a tile floor. The apparent V that the tiles make is longer and the distance between the two objects appears greater than in the shot using the same lens on a ff camera..

I have made a simple diagram showing why there is a size difference iin the image...http://www.flickr.com/photos//equivalence/dark.htm..

Comment #9

52.5 f3 on FFAs someone else said see:http://www.josephjamesphotography.com/equivalence/dark.htm.

Shoot...

Comment #10

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