Formula for sensor size and crop factor?

DesertShot · 01-02-2012, 06:46 PM

Hi,
is there an easy way to determine what lens will do what angle in mm going from a former full size SLR frame to a APS-c sensor with a 1.5 crop factor?

Sorry if this has been asked before...

bobmaxja · 01-02-2012, 06:52 PM

You can use this site
Depth of field comparison tool, Tamron USA

SpecialK · 01-02-2012, 06:55 PM

Focal length comparison tool, Tamron USA

Marc Sabatella · 01-02-2012, 07:35 PM

The question does not make sense as asked - angles are not measured in mm. It sounds like you are simply asking how the crop factor is applied, and the answer is, the word "factor" is taken literally. That is, you multiply. So a 50mm lens on APS-C format will have the same field of view of as a 75mm lens on 135 format. If you literally want to know the angle - measured in degrees, not in mm - there is indeed a formula for that, but I'd have to Google it...

**interested_observer** · 01-02-2012, 08:04 PM

There is a Photographer's Calculator here that provides a number of capabilities. The Pentax crop factor (focal length multiplier) is 1.53.

http://www.tawbaware.com/maxlyons/calc.htm

DesertShot · 01-02-2012, 10:14 PM

Originally posted by Marc Sabatella

The question does not make sense as asked - angles are not measured in mm. It sounds like you are simply asking how the crop factor is applied, and the answer is, the word "factor" is taken literally. That is, you multiply. So a 50mm lens on APS-C format will have the same field of view of as a 75mm lens on 135 format. If you literally want to know the angle - measured in degrees, not in mm - there is indeed a formula for that, but I'd have to Google it...

Correct,
what I tried to ask is for
Lens Equivalence / Diffraction Calculator
which the next poster has send a link to.
Thank you all very much.

RioRico · 01-02-2012, 10:25 PM

AOV= 2*ATAN(diag/(2*degs))*(180/PI)

where diag= frame diagonal in mm
and degs= focal length in degrees

35mm full-frame diagonal= 43.3mm
Nominal APS-C diagonal= 30.1mm
Actual K20D diagonal= 28.1mm

01-02-2012, 06:46 PM	#1
DesertShot New Member Join Date: Dec 2011 Posts: 8	Formula for sensor size and crop factor? Hi, is there an easy way to determine what lens will do what angle in mm going from a former full size SLR frame to a APS-c sensor with a 1.5 crop factor? Sorry if this has been asked before...

01-02-2012, 08:04 PM	#5
interested_observer Loyal Site Supporter Join Date: Jun 2009 Location: Tumbleweed, Arizona Photos: Gallery \| Albums Posts: 5,707	There is a Photographer's Calculator here that provides a number of capabilities. The Pentax crop factor (focal length multiplier) is 1.53. http://www.tawbaware.com/maxlyons/calc.htm

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01-02-2012, 06:52 PM	#2
bobmaxja Veteran Member Join Date: Mar 2010 Location: Laval, Quebec Canada Posts: 2,171	You can use this site Depth of field comparison tool, Tamron USA

01-02-2012, 06:55 PM	#3
SpecialK Pentaxian Join Date: Dec 2006 Location: So California Photos: Gallery Posts: 16,480	Focal length comparison tool, Tamron USA

01-02-2012, 07:35 PM	#4
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	The question does not make sense as asked - angles are not measured in mm. It sounds like you are simply asking how the crop factor is applied, and the answer is, the word "factor" is taken literally. That is, you multiply. So a 50mm lens on APS-C format will have the same field of view of as a 75mm lens on 135 format. If you literally want to know the angle - measured in degrees, not in mm - there is indeed a formula for that, but I'd have to Google it...

01-02-2012, 10:14 PM	#6
DesertShot New Member Join Date: Dec 2011 Posts: 8 Original Poster	Originally posted by Marc Sabatella The question does not make sense as asked - angles are not measured in mm. It sounds like you are simply asking how the crop factor is applied, and the answer is, the word "factor" is taken literally. That is, you multiply. So a 50mm lens on APS-C format will have the same field of view of as a 75mm lens on 135 format. If you literally want to know the angle - measured in degrees, not in mm - there is indeed a formula for that, but I'd have to Google it... Correct, what I tried to ask is for Lens Equivalence / Diffraction Calculator which the next poster has send a link to. Thank you all very much.

01-02-2012, 10:25 PM	#7
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	AOV= 2ATAN(diag/(2degs))*(180/PI) where diag= frame diagonal in mm and degs= focal length in degrees 35mm full-frame diagonal= 43.3mm Nominal APS-C diagonal= 30.1mm Actual K20D diagonal= 28.1mm

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