Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-07-2010, 06:52 PM   #1
New Member




Join Date: Jan 2010
Location: Vancouver, BC
Posts: 2
Manual Focal Length Input

Hi,

I am using a few Pentax-M lenses on my K-x. They obviously work wonderfully, but when the camera first turns on it says "Input Focal Length". Since there is a difference between the focal length indicated on the lens and the ACTUAL focal length due to the crop factor, I was wondering which one I should put in. For instance, for an old 50mm lens, would I input the lens focal length of 50mm or would I account for the crop factor and put the actual focal length of 75mm?

Anyone know?

01-07-2010, 06:56 PM   #2
Forum Member
Sasquatch's Avatar

Join Date: Aug 2008
Location: Indianapolis
Posts: 69
Enter the true focal length of the lens. If the lens is 50mm, enter that.

I just started fooling around with my K-m and my old lenses today as well. Use this very helpful blog if you get stuck anywhere:
Shooting manual lenses on Pentax DSLRs « robertsdonovan.com
01-07-2010, 07:02 PM   #3
New Member




Join Date: Jan 2010
Location: Vancouver, BC
Posts: 2
Original Poster
Thanks a lot!
01-07-2010, 07:55 PM   #4
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,314
QuoteOriginally posted by WhichWayIsUp? Quote
Hi,

I am using a few Pentax-M lenses on my K-x. They obviously work wonderfully, but when the camera first turns on it says "Input Focal Length". Since there is a difference between the focal length indicated on the lens and the ACTUAL focal length due to the crop factor, I was wondering which one I should put in. For instance, for an old 50mm lens, would I input the lens focal length of 50mm or would I account for the crop factor and put the actual focal length of 75mm?

Anyone know?
Not to disappoint you but there is no difference between the lens focal length and focal length due to the crop factor. That is a mith,

Focal length is a physical characteristic of a lens, irrespective of the size or format of the film or sensor.

what really needs to be discussed is field of view relitive to format, but since that is harder to understand (i.e. 55 degrees as opposed to 40 degrees) the industry has tried to make it simple by making an incorrect technical statement.

01-07-2010, 08:34 PM   #5
Forum Member
Sasquatch's Avatar

Join Date: Aug 2008
Location: Indianapolis
Posts: 69
QuoteOriginally posted by Lowell Goudge Quote
Not to disappoint you but there is no difference between the lens focal length and focal length due to the crop factor. That is a mith,

Focal length is a physical characteristic of a lens, irrespective of the size or format of the film or sensor.

what really needs to be discussed is field of view relitive to format, but since that is harder to understand (i.e. 55 degrees as opposed to 40 degrees) the industry has tried to make it simple by making an incorrect technical statement.
Yeah that's what I meant too.
03-17-2012, 10:47 AM   #6
Veteran Member




Join Date: Aug 2011
Location: Niagara
Photos: Gallery | Albums
Posts: 791
Just researching this "input focal length" as I just purchased a Voigtlander 58mm f1.4 from a fellow Pantaxian in Marketplace. The options for inputing don't allow 58, just 55 and 65. Is there a way to store the info for each manual focus lens (a la Nikon) ? What changes does my K5 make for differing focal lengths, is exposure affected, focusing?

Thanks for your input
03-17-2012, 10:48 AM   #7
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 40,984
Practically it shouldn't matter whether it thinks the lens is a 55 or a 58. I would go ahead and input 55 as it's the closest FL below yours.
03-17-2012, 11:06 AM - 1 Like   #8
Veteran Member
Anvh's Avatar

Join Date: Sep 2011
Posts: 4,616
QuoteOriginally posted by Franky2step Quote
Just researching this "input focal length" as I just purchased a Voigtlander 58mm f1.4 from a fellow Pantaxian in Marketplace. The options for inputing don't allow 58, just 55 and 65. Is there a way to store the info for each manual focus lens (a la Nikon) ? What changes does my K5 make for differing focal lengths, is exposure affected, focusing?
It needs the number for the shake reduction, for the rest it doesn't really use the information for anything else.

The manual lenses don't have a digital information contact so the camera doesn't know which lens is on the camera so therefore no way to store this information.
With autofocus lenses, those lenses have the digital info contact and over that contact also goes the focal length information so no need for you to tell the focal length.

If you're using a manual zoom lens it might be better to turn the shake reduction off unless you know you will use the lens mostly on one focal length.

12-14-2016, 10:17 AM   #9
New Member




Join Date: Dec 2016
Posts: 1
What about using a zoom...which focal lenth should be input?...minimum or maximum?
12-14-2016, 10:47 AM   #10
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,817
I try to guess where I'm using it most often, then keep in mind that the compensation might not be as awesome as I'm used to. I put in 135mm for a 70-200 and that works fine. A 28-200 is tougher - I might go with 50mm and try to be really steady at higher focal lengths.
12-14-2016, 02:24 PM   #11
Moderator
Site Supporter
MarkJerling's Avatar

Join Date: May 2012
Location: Wairarapa, New Zealand
Photos: Gallery | Albums
Posts: 5,218
QuoteOriginally posted by pcaple Quote
What about using a zoom...which focal lenth should be input?...minimum or maximum?
There's been numerous discussions about that. Most people seem to favor entering the mid-value. Some suggest entering the value that you'll most likely shoot at.
12-15-2016, 05:32 AM   #12
Senior Member




Join Date: Oct 2016
Location: Norfolk
Posts: 146
I use an adapter to attach my K20D to the eyepiece of my scope for digiscoping. My two eyepieces are 20x and 32x. These give relative focal lengths, apparently, of 1000mm and 1600mm. Since the maximum focal length I can input is 800mm, I always use that, and hope. The scope, of course, has no aperture control, so I use exposure compensation and get 'acceptable' results - my major problem is using it in a hide, with people walking around, shaking the floor and causing camera shake. With a hide clamp, things are no better, so I generally restrict myself to using it outdoors, tripod not fully extended to minimise camera movement. I turn SR off, of course.

Tony
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, camera, crop, factor, input, length, lens, pentax help, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Focal length input K(s)evin Pentax SLR Lens Discussion 6 10-27-2010 04:03 PM
What focal length input DutchAus Troubleshooting and Beginner Help 3 12-24-2009 09:15 AM
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
Input Focal Length lutzvo Photographic Technique 9 01-10-2009 02:51 PM



All times are GMT -7. The time now is 11:30 PM. | See also: NikonForums.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