Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
02-20-2009, 05:33 PM   #1
Veteran Member
lurchlarson's Avatar

Join Date: Nov 2008
Location: Oregon, USA
Photos: Albums
Posts: 683
What do I input when using old manual focus lens?

When I'm using my old 50mm f/1.7 on my k200d and then thing comes up to input the focal length, should i put it 50mm or should i put in 75mm because of the 1.5x crop factor?

02-20-2009, 05:41 PM   #2
Veteran Member
rparmar's Avatar

Join Date: Jan 2008
Photos: Gallery
Posts: 8,783
It's a 50mm lens no matter what body it is on. So put in 50mm.
02-20-2009, 06:58 PM   #3
Veteran Member




Join Date: Dec 2007
Location: San Francisco, CA
Posts: 452
QuoteOriginally posted by rparmar Quote
It's a 50mm lens no matter what body it is on. So put in 50mm.
Absolution true. The 1.5 crop factor just says that a 50 mm lens on an APC sensor camera will give you same photo as a 75 mm lens on a 35 mm senor or film.
02-20-2009, 10:24 PM   #4
Veteran Member
Jewelltrail's Avatar

Join Date: May 2008
Location: Rhode Island
Photos: Albums
Posts: 4,180
I think this is one of the most asked questions for a good reason: it is the subject of great confusion. The crop DSLR world must be a daunting one for the new folks.

02-22-2009, 04:02 PM   #5
Veteran Member
lurchlarson's Avatar

Join Date: Nov 2008
Location: Oregon, USA
Photos: Albums
Posts: 683
Original Poster
Thank you.

I was just wondering because of the change in field of view with the crop factor.
02-22-2009, 11:33 PM   #6
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by lurchlarson Quote
I was just wondering because of the change in field of view with the crop factor.
It's only a "change" if you compare between a film SLR and a digital SLR. But you digital SLR doesn't even know that film SLR's existed. As far as it is concerned, what it sees is all there to see.
02-23-2009, 06:34 AM   #7
Pentaxian
Wheatfield's Avatar

Join Date: Apr 2008
Location: The wheatfields of Canada
Posts: 10,157
I was supposed to write a sticky about this.
02-23-2009, 07:56 AM   #8
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,212
QuoteOriginally posted by lurchlarson Quote
When I'm using my old 50mm f/1.7 on my k200d and then thing comes up to input the focal length, should i put it 50mm or should i put in 75mm because of the 1.5x crop factor?
The 75mm is the FOV comparison anyway that is often confused in brochures including Pentaxes to be the focal length that has changed.

02-23-2009, 01:59 PM   #9
Senior Member




Join Date: Nov 2008
Location: The Cow Belt
Photos: Gallery
Posts: 162
QuoteOriginally posted by Blue Quote
The 75mm is the FOV comparison anyway that is often confused in brochures including Pentaxes to be the focal length that has changed.
Do we take it then that in a lens of a given focal length, say 50mm, the size of the image remains the same for an APS-C sensor frame when compared with a 35mm film frame or a 35mm digital sensor frame ; only the amount of the image visible, or the field-of-view (FOV), is less in the APS-C sensor?
02-23-2009, 02:51 PM   #10
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by chhayanat Quote
Do we take it then that in a lens of a given focal length, say 50mm, the size of the image remains the same for an APS-C sensor frame when compared with a 35mm film frame or a 35mm digital sensor frame ; only the amount of the image visible, or the field-of-view (FOV), is less in the APS-C sensor?
Correct. The sensor can't magically make the lens project a different image; the lens doesn't know if its projecting onto APS-C or 35mm. But when the image is projected onto the smaller "screen" of APS-C, the edges of the images are lost. If you then take this smaller/cropped image from an APS-C and the larger image from 35mm and blow them up to the same size, then effect is very similar to what would happen had you shot with a 1.5X longer lens on 35mm, which is where the idea of using a "crop factor" to compare focal lengths comes from. It works very well as it accurately captures the change in FOV. It does not, however, account for the difference in DOF - the 1.5X longer focal length lens on 35mm would give less DOF than the shorter lens on APS-C, all else being equal. But "most" people are more concerned about FOV than DOF "most" of the time.
02-23-2009, 02:57 PM   #11
Pentaxian
Wheatfield's Avatar

Join Date: Apr 2008
Location: The wheatfields of Canada
Posts: 10,157
QuoteOriginally posted by chhayanat Quote
Do we take it then that in a lens of a given focal length, say 50mm, the size of the image remains the same for an APS-C sensor frame when compared with a 35mm film frame or a 35mm digital sensor frame ; only the amount of the image visible, or the field-of-view (FOV), is less in the APS-C sensor?
Yup.

more characters
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
50mm, input, k-mount, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can a manual-focus lens have back focus problems? PocketPixels Pentax DSLR Discussion 33 02-13-2011 05:37 AM
f stop input for manual lenses? axl Digital Processing, Software, and Printing 6 06-30-2010 05:09 AM
Front focus/ back focus on Manual lens. Possible? WangJianWei Troubleshooting and Beginner Help 6 04-20-2009 07:50 PM
SR Focal Length Input for a Manual Zoom Lens? frank Pentax SLR Lens Discussion 13 03-15-2009 03:04 PM
Input focal length for a manual lens jpzk Photographic Technique 11 01-14-2009 08:50 PM



All times are GMT -7. The time now is 06:38 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top