K10D + lens focal length

jshurak · 10-17-2007, 10:09 AM

I've been reading up on DOF and Hyperfocal length. I came across a little chart that will tell you the the hyperfocal length given the focal length of the lens and the aperture you want to use.

I know that the digital sensor increases the focal length of a lens, so my question is this: IS it a standard increase for different lenses?

Peter Zack · 10-17-2007, 10:18 AM

Actually the focal length doesn't change. The FOV (field of view) does because the sensor is smaller some of the image projected back is not captured or cropped from what the lens can see on a full frame lens. On a DA series lens the image is cropped to match the sensor size. So the lens remains the same and to the best of my knowledge the DOF and HFD stay the same for the given focal range.

**Lowell Goudge** · 10-17-2007, 10:44 AM

Originally posted by Peter Zack

Actually the focal length doesn't change. The FOV (field of view) does because the sensor is smaller some of the image projected back is not captured or cropped from what the lens can see on a full frame lens. On a DA series lens the image is cropped to match the sensor size. So the lens remains the same and to the best of my knowledge the DOF and HFD stay the same for the given focal range.

While what you state is true when you consider the raw image at the sensor, and providing that that image is enlarged to the same extent in printing, there is a practical aspect to consider here. We will enlarge the image from the digital sensor MORE.

Depth of field and hyper focal distance are things that were on 35 mm film standardized based upon a specific level of enlargement where the image was viewed not as perfectly sharp, but as acceptably sharp.

If we blow up an image, by 50% more (eg. making a 4 x 6 inch print from the "cropped image" of a DSLR), the definition of "acceptable" changes.

10-17-2007, 10:09 AM	#1
jshurak Veteran Member Join Date: Jul 2007 Location: philadelphia Posts: 626	K10D + lens focal length I've been reading up on DOF and Hyperfocal length. I came across a little chart that will tell you the the hyperfocal length given the focal length of the lens and the aperture you want to use. I know that the digital sensor increases the focal length of a lens, so my question is this: IS it a standard increase for different lenses?

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10-17-2007, 10:18 AM	#2
Peter Zack Pentaxian Moderator Emeritus Join Date: May 2007 Location: Edmonton Alberta, Canada Photos: Gallery \| Albums Posts: 10,643	Actually the focal length doesn't change. The FOV (field of view) does because the sensor is smaller some of the image projected back is not captured or cropped from what the lens can see on a full frame lens. On a DA series lens the image is cropped to match the sensor size. So the lens remains the same and to the best of my knowledge the DOF and HFD stay the same for the given focal range.

10-17-2007, 10:44 AM	#3
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,886	Originally posted by Peter Zack Actually the focal length doesn't change. The FOV (field of view) does because the sensor is smaller some of the image projected back is not captured or cropped from what the lens can see on a full frame lens. On a DA series lens the image is cropped to match the sensor size. So the lens remains the same and to the best of my knowledge the DOF and HFD stay the same for the given focal range. While what you state is true when you consider the raw image at the sensor, and providing that that image is enlarged to the same extent in printing, there is a practical aspect to consider here. We will enlarge the image from the digital sensor MORE. Depth of field and hyper focal distance are things that were on 35 mm film standardized based upon a specific level of enlargement where the image was viewed not as perfectly sharp, but as acceptably sharp. If we blow up an image, by 50% more (eg. making a 4 x 6 inch print from the "cropped image" of a DSLR), the definition of "acceptable" changes.