Focal length Results

jjbuzard · 11-01-2018, 12:32 PM

I have gone blank, I think it was that if using a film camera on a Digital camera you multiplied the lens length by 1.r to get the resulting Length. Example 105mm lens X 1.5 equaled 157.5mm.
Do I remember correctly

?

**BigMackCam** · 11-01-2018, 12:36 PM - **2 Likes**

The focal length of a lens never changes, regardless of the camera you use it with. Depending on the size of the sensor or film, it will capture a different field of view.

If you're using a 50mm lens on camera with an APS-C sensor - which has a 1.5x crop factor compared to 35mm film or so-called "full frame" - then the sensor will capture a field of view equivalent to a 75mm lens on full frame (50mm x 1.5 = 75mm). If you used that same 50mm on a micro four thirds camera - which has a 2x crop factor compared to full frame - then the sensor would capture a field of view equivalent to 50mm x 2 = 100mm on full frame.

Does that make sense?

jjbuzard · 11-02-2018, 08:00 AM

Yes, that makes sense I thought that was the ratio, but it has been a while since I used it I wasn't sure, I am using my trusty Pentax K10 D, 28 mm takumar + 42 mm

Adam · 11-02-2018, 01:03 PM

IMO, the best approach is to never multiply. Take a look at this instead, and see what field of view the focal length corresponds to on your type of camera:
The Crop Factor Unmasked - Articles and Tips | PentaxForums.com

Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)

PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

Wheatfield · 11-03-2018, 07:50 AM - **4 Likes**

Originally posted by jjbuzard

Yes, that makes sense I thought that was the ratio, but it has been a while since I used it I wasn't sure, I am using my trusty Pentax K10 D, 28 mm takumar + 42 mm

The whole multiplication factor thing is, to my mind, an invention with no practical use for people who shoot one format, and of little practical use for people who shoot multiple formats. The sole purpose of it these days seems to be for people to drill into the heads of other people how deficient their small sensor cameras are because they can’t get the razor thin depth of field that can be had with larger ones.
If you only shoot one format, there isn’t much need to know what a lens will do on another one.
At one time I shot 3 formats, 35mm, 6x7 and 4x5. I don’t recall ever doing the mental gymnastics that people inflict on themselves these days to figure out what one focal length would do on the formats I wasn’t using at the moment.

reh321 · 11-03-2018, 09:40 AM

Originally posted by jjbuzard

Yes, that makes sense I thought that was the ratio, but it has been a while since I used it I wasn't sure, I am using my trusty Pentax K10 D, 28 mm takumar + 42 mm

The important thing is that you know how a 28mm lens - and how a 42mm lens - work on that camera. I've largely stopped thinking about focal lengths since most all lenses I use are zooms .... so I just find a setting that does what I want to do.

jjbuzard · 11-04-2018, 09:07 AM

The reason for my question was I am trying to achieve Stereo pictures, and am using the Cha-Cha method, place your weight on one foot, snap a picture, shift your to the other foot, snap a picture, I have tried 50mm and 55mm and am not satisfied, I have shot on a rail on a tripod taking two pictures, not really happy. Somewhere I read to use a 48mm lens, I don't have a 48, so was wanting to try the 28mm on my K10, with that is only 42mm. But that is better. Any suggestion?

**twilhelm** · 11-04-2018, 09:19 AM

Try with a 35mm lens. I believe you’ll then get a “traditional” stereo image.

jjbuzard · 11-04-2018, 10:01 AM

Originally posted by twilhelm

Try with a 35mm lens. I believe you’ll then get a “traditional” stereo image.

Are you saying a Digital 35 o=r film 35?

**BigMackCam** · 11-04-2018, 10:06 AM

Originally posted by jjbuzard

Are you saying a Digital 35 o=r film 35?

I'm being picky here, but entirely for your benefit... Digital can mean several different sizes of sensor, so you're best off referring to the sensor or medium size rather than "digital" or "film". In your case, you're referring to APS-C

**twilhelm** · 11-04-2018, 10:09 AM - **1 Like**

Originally posted by jjbuzard

Are you saying a Digital 35 o=r film 35?

A 35mm lens has the same focal length whether film, apps-c, medium format or large format. The difference is the lens needs to make a larger circle to cover the larger formats. If you take a 35mm lens made for film and shoot it on the K-1, then shoot it on the K3, the image is 1.5x larger on the K-1. But if you crop the middle, you’ll have the same image the K3 captures. Technically there’s no difference with a 35mm lens regardless of format, just the image circle size.

**BigMackCam** · 11-04-2018, 03:08 PM

Originally posted by twilhelm

Technically there’s no difference with a 35mm lens regardless of format, just the image circle size.

Again, being picky, but the image circle from the lens stays exactly the same. What changes, based on the size of the sensor or film media, is the portion of that image circle that is captured...

**twilhelm** · 11-04-2018, 03:30 PM - **1 Like**

Originally posted by BigMackCam

Again, being picky, but the image circle from the lens stays exactly the same. What changes, based on the size of the sensor or film media, is the portion of that image circle that is captured...

I’d have to disagree with you here (respectfully of course). Take the DA20-40, yes the image at the wide end is 20mm regardless of the camera it is attached to, yet on the K-1 the image circle isn’t large enough to cover the entire sensor, leaving the corners dark.

I agree, the actual angle in degrees will not change, regardless of format. I think too much thought is put into what one lens does on one camera as compared to another. Since I’ve always shot at least two formats, I stopped worrying about lens conversions long ago.

I try to tell people to get to know the lens you have with the camera you’re using. If you need wider, then buy a wider lens. It actually makes it easier buying lenses because lens manufacturers have always stuck with one format when labeling lenses. Could you imagine what it would be like if aps-c lenses were labeled with the “crop” factor?

**clackers** · 11-04-2018, 03:37 PM - **1 Like**

Originally posted by twilhelm

I’d have to disagree with you here (respectfully of course). Take the DA20-40, yes the image at the wide end is 20mm regardless of the camera it is attached to, yet on the K-1 the image circle isn’t large enough to cover the entire sensor, leaving the corners dark.

We're all in agreement … Mike's saying the image circle hasn't changed, the sensor under it has gotten bigger leaving the corners dark, same as you.

**twilhelm** · 11-04-2018, 03:48 PM

Originally posted by clackers

We're all in agreement … Mike's saying the image circle hasn't changed, the sensor under it has gotten bigger leaving the corners dark, same as you.

I figured that’s what he was saying, but I wanted to clarify a bit for the OP.

A big part of the reason I switched to Pentax was I was shooting film alongside digital. I wanted to be able to have one set of lenses for both. After banging my head on the wall a few times figuring out the crop factor, I realized it didn’t really matter. Just frame the shot you see in the viewfinder and change lenses when necessary.

11-01-2018, 12:32 PM	#1
jjbuzard Junior Member Join Date: Nov 2008 Location: Illinois Photos: Gallery \| Albums Posts: 40	Focal length Results I have gone blank, I think it was that if using a film camera on a Digital camera you multiplied the lens length by 1.r to get the resulting Length. Example 105mm lens X 1.5 equaled 157.5mm. Do I remember correctly?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
The wrong focal length IBIS	blackest	Pentax DSLR Discussion	11	08-23-2017 01:52 PM
focal length and space compression	IgorZ	Pentax SLR Lens Discussion	8	05-25-2017 07:44 AM
Calculated focal length at MFD - Focus Breathing	audiobomber	Film SLRs and Compact Film Cameras	19	03-28-2017 09:23 AM
Determining Focal Length of a Photo	GlennG	General Photography	7	01-19-2017 05:39 AM
Focal length's for shake reduction.	sculptormic	Pentax K-1 & K-1 II	5	11-28-2016 10:29 AM

11-01-2018, 12:36 PM - 2 Likes	#2
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,669	The focal length of a lens never changes, regardless of the camera you use it with. Depending on the size of the sensor or film, it will capture a different field of view. If you're using a 50mm lens on camera with an APS-C sensor - which has a 1.5x crop factor compared to 35mm film or so-called "full frame" - then the sensor will capture a field of view equivalent to a 75mm lens on full frame (50mm x 1.5 = 75mm). If you used that same 50mm on a micro four thirds camera - which has a 2x crop factor compared to full frame - then the sensor would capture a field of view equivalent to 50mm x 2 = 100mm on full frame. Does that make sense?

11-02-2018, 08:00 AM	#3
jjbuzard Junior Member Join Date: Nov 2008 Location: Illinois Photos: Gallery \| Albums Posts: 40 Original Poster	Yes, that makes sense I thought that was the ratio, but it has been a while since I used it I wasn't sure, I am using my trusty Pentax K10 D, 28 mm takumar + 42 mm

11-02-2018, 01:03 PM	#4
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,594	IMO, the best approach is to never multiply. Take a look at this instead, and see what field of view the focal length corresponds to on your type of camera: The Crop Factor Unmasked - Articles and Tips \| PentaxForums.com Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

11-03-2018, 07:50 AM - 4 Likes	#5
Wheatfield Moderator Join Date: Apr 2008 Location: The wheatfields of Canada Posts: 15,981	Originally posted by jjbuzard Yes, that makes sense I thought that was the ratio, but it has been a while since I used it I wasn't sure, I am using my trusty Pentax K10 D, 28 mm takumar + 42 mm The whole multiplication factor thing is, to my mind, an invention with no practical use for people who shoot one format, and of little practical use for people who shoot multiple formats. The sole purpose of it these days seems to be for people to drill into the heads of other people how deficient their small sensor cameras are because they can’t get the razor thin depth of field that can be had with larger ones. If you only shoot one format, there isn’t much need to know what a lens will do on another one. At one time I shot 3 formats, 35mm, 6x7 and 4x5. I don’t recall ever doing the mental gymnastics that people inflict on themselves these days to figure out what one focal length would do on the formats I wasn’t using at the moment.

11-03-2018, 09:40 AM	#6
reh321 Pentaxian Join Date: Nov 2014 Location: South Bend, IN, USA Photos: Gallery \| Albums Posts: 23,177	Originally posted by jjbuzard Yes, that makes sense I thought that was the ratio, but it has been a while since I used it I wasn't sure, I am using my trusty Pentax K10 D, 28 mm takumar + 42 mm The important thing is that you know how a 28mm lens - and how a 42mm lens - work on that camera. I've largely stopped thinking about focal lengths since most all lenses I use are zooms .... so I just find a setting that does what I want to do.

11-04-2018, 09:07 AM	#7
jjbuzard Junior Member Join Date: Nov 2008 Location: Illinois Photos: Gallery \| Albums Posts: 40 Original Poster	The reason for my question was I am trying to achieve Stereo pictures, and am using the Cha-Cha method, place your weight on one foot, snap a picture, shift your to the other foot, snap a picture, I have tried 50mm and 55mm and am not satisfied, I have shot on a rail on a tripod taking two pictures, not really happy. Somewhere I read to use a 48mm lens, I don't have a 48, so was wanting to try the 28mm on my K10, with that is only 42mm. But that is better. Any suggestion?

11-04-2018, 09:19 AM	#8
twilhelm Loyal Site Supporter Join Date: Feb 2009 Location: Florida Photos: Gallery \| Albums Posts: 2,369	Try with a 35mm lens. I believe you’ll then get a “traditional” stereo image.

11-04-2018, 10:01 AM	#9
jjbuzard Junior Member Join Date: Nov 2008 Location: Illinois Photos: Gallery \| Albums Posts: 40 Original Poster	Originally posted by twilhelm Try with a 35mm lens. I believe you’ll then get a “traditional” stereo image. Are you saying a Digital 35 o=r film 35?

11-04-2018, 10:06 AM	#10
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,669	Originally posted by jjbuzard Are you saying a Digital 35 o=r film 35? I'm being picky here, but entirely for your benefit... Digital can mean several different sizes of sensor, so you're best off referring to the sensor or medium size rather than "digital" or "film". In your case, you're referring to APS-C

11-04-2018, 10:09 AM - 1 Like	#11
twilhelm Loyal Site Supporter Join Date: Feb 2009 Location: Florida Photos: Gallery \| Albums Posts: 2,369	Originally posted by jjbuzard Are you saying a Digital 35 o=r film 35? A 35mm lens has the same focal length whether film, apps-c, medium format or large format. The difference is the lens needs to make a larger circle to cover the larger formats. If you take a 35mm lens made for film and shoot it on the K-1, then shoot it on the K3, the image is 1.5x larger on the K-1. But if you crop the middle, you’ll have the same image the K3 captures. Technically there’s no difference with a 35mm lens regardless of format, just the image circle size.

Thread Tools	Search this Thread
	Search this Thread: Advanced Search

11-04-2018, 03:08 PM	#12
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,669	Originally posted by twilhelm Technically there’s no difference with a 35mm lens regardless of format, just the image circle size. Again, being picky, but the image circle from the lens stays exactly the same. What changes, based on the size of the sensor or film media, is the portion of that image circle that is captured...

11-04-2018, 03:30 PM - 1 Like	#13
twilhelm Loyal Site Supporter Join Date: Feb 2009 Location: Florida Photos: Gallery \| Albums Posts: 2,369	Originally posted by BigMackCam Again, being picky, but the image circle from the lens stays exactly the same. What changes, based on the size of the sensor or film media, is the portion of that image circle that is captured... I’d have to disagree with you here (respectfully of course). Take the DA20-40, yes the image at the wide end is 20mm regardless of the camera it is attached to, yet on the K-1 the image circle isn’t large enough to cover the entire sensor, leaving the corners dark. I agree, the actual angle in degrees will not change, regardless of format. I think too much thought is put into what one lens does on one camera as compared to another. Since I’ve always shot at least two formats, I stopped worrying about lens conversions long ago. I try to tell people to get to know the lens you have with the camera you’re using. If you need wider, then buy a wider lens. It actually makes it easier buying lenses because lens manufacturers have always stuck with one format when labeling lenses. Could you imagine what it would be like if aps-c lenses were labeled with the “crop” factor?

11-04-2018, 03:37 PM - 1 Like	#14
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	Originally posted by twilhelm I’d have to disagree with you here (respectfully of course). Take the DA20-40, yes the image at the wide end is 20mm regardless of the camera it is attached to, yet on the K-1 the image circle isn’t large enough to cover the entire sensor, leaving the corners dark. We're all in agreement … Mike's saying the image circle hasn't changed, the sensor under it has gotten bigger leaving the corners dark, same as you.

11-04-2018, 03:48 PM	#15
twilhelm Loyal Site Supporter Join Date: Feb 2009 Location: Florida Photos: Gallery \| Albums Posts: 2,369	Originally posted by clackers We're all in agreement … Mike's saying the image circle hasn't changed, the sensor under it has gotten bigger leaving the corners dark, same as you. I figured that’s what he was saying, but I wanted to clarify a bit for the OP. A big part of the reason I switched to Pentax was I was shooting film alongside digital. I wanted to be able to have one set of lenses for both. After banging my head on the wall a few times figuring out the crop factor, I realized it didn’t really matter. Just frame the shot you see in the viewfinder and change lenses when necessary.