Why Set Manual Focal Length?

almo · 09-30-2014, 10:28 PM

First a tiny bit of background. I used canon DSLRs for ten years. The end.

I have no experience using manual lenses on a modern DSLR, well almost none, I had a K10D and kind of played around with one lens, but not much. I just have no idea what the reason for setting the focal length is, and what happens if you don't set it correctly, which I have forgotten to do when switching between my 50mm and 28mm lenses.

TIA!

Adam · 09-30-2014, 10:32 PM

Originally posted by almo

First a tiny bit of background. I used canon DSLRs for ten years. The end.

I have no experience using manual lenses on a modern DSLR, well almost none, I had a K10D and kind of played around with one lens, but not much. I just have no idea what the reason for setting the focal length is, and what happens if you don't set it correctly, which I have forgotten to do when switching between my 50mm and 28mm lenses.

TIA!

It's so that the in-camera shake reduction system knows how much camera shake to compensate for. Conveniently, the focal length is also stored in the exif data.

**pacerr** · 09-30-2014, 10:51 PM

You might note that it isn't necessary for modern auto focus lenses which automatically input that data -- it's only required when using lenses without data transfer contacts.

The great advantage is that SR is available even for older manual focus lenses.

Incorrectly reporting the FL will cause the SR system to over- or under-compensate for camera shake.

jimr-pdx · 09-30-2014, 11:19 PM

What they said. Very nice with primes, but with a manual zoom lens it gets harder. You can set it near the middle of the range or reset as you go, I have done it both ways. It's partly why I try to stick with auto zooms and manual primes

or zooms with a narrow range like the old Sigma 21-35.

almo · 10-01-2014, 03:18 AM

Originally posted by Adam

It's so that the in-camera shake reduction system knows how much camera shake to compensate for. Conveniently, the focal length is also stored in the exif data.

Oh, good reason!

---------- Post added 10-01-2014 at 03:25 AM ----------

Originally posted by jimr-pdx

What they said. Very nice with primes, but with a manual zoom lens it gets harder. You can set it near the middle of the range or reset as you go, I have done it both ways. It's partly why I try to stick with auto zooms and manual primes

or zooms with a narrow range like the old Sigma 21-35.

It was my plan to only use manual primes. I have two AF zooms that will be here today actually, but I figured already that when it comes to manual primes are probably going to be the best option. I started out using old Pentax film gear in the stone ages, and all we had were primes. I have had a few 70-210 zooms over the years at one point or another, but i never really got great results with manual zooms. Something about that loose push/pull zoom thing never really worked for me.

jadedrakerider · 10-01-2014, 04:08 AM - **1 Like**

Originally posted by almo

Something about that loose push/pull zoom thing never really worked for me.

Agreed. Autofocus zooms work just fine, but I never knew what I was missing until I came across an old Vivitar internal zoom manual focus lens. I don't think I would use any other kind by choice now.

almo · 10-01-2014, 05:39 AM

Originally posted by jadedrakerider

Agreed. Autofocus zooms work just fine, but I never knew what I was missing until I came across an old Vivitar internal zoom manual focus lens. I don't think I would use any other kind by choice now.

I don't think I have ever had an internal zoom manual lens before. Accept maybe for really short ones, but not telephoto. I might have to look into that.

jadedrakerider · 10-01-2014, 05:52 AM

Originally posted by almo

I don't think I have ever had an internal zoom manual lens before. Accept maybe for really short ones, but not telephoto. I might have to look into that.

Mine is the Vivitar 75-205mm f3.8 Macro

The aperture-lever shield needs to be filed down before it can be mounted onto a contemporary digital camera, but once you do you it's a pleasure to use.

reeftool · 10-01-2014, 05:59 AM

You still need the SR with an internal focus lens as it's the magnification that requires the stability, not the actual physical length of the lens. I have a 500mm mirror lens that is about the same length and weight as a 135/2.8 I own but it's nearly impossible to hold steady. With a manual zoom, best results will be with at length set as close to the focal length as possible. I have neglected to set the length on occasion and the results weren't good.

09-30-2014, 10:28 PM	#1
almo Senior Member Join Date: Jan 2008 Location: Flawda Posts: 101	Why Set Manual Focal Length? First a tiny bit of background. I used canon DSLRs for ten years. The end. I have no experience using manual lenses on a modern DSLR, well almost none, I had a K10D and kind of played around with one lens, but not much. I just have no idea what the reason for setting the focal length is, and what happens if you don't set it correctly, which I have forgotten to do when switching between my 50mm and 28mm lenses. TIA!

09-30-2014, 10:32 PM	#2
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,593	Originally posted by almo First a tiny bit of background. I used canon DSLRs for ten years. The end. I have no experience using manual lenses on a modern DSLR, well almost none, I had a K10D and kind of played around with one lens, but not much. I just have no idea what the reason for setting the focal length is, and what happens if you don't set it correctly, which I have forgotten to do when switching between my 50mm and 28mm lenses. TIA! It's so that the in-camera shake reduction system knows how much camera shake to compensate for. Conveniently, the focal length is also stored in the exif data. 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:

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Manual focus zoom lens Focal length setting	Bertminator	Pentax K-30 & K-50	11	10-12-2016 12:03 AM
hmmm... not clear how to "manually" set the focal length??	MJSfoto1956	Pentax K-3 & K-3 II	37	02-02-2014 07:02 AM
Focal length for manual zoom on K-5	prepelica	Pentax K-5 & K-5 II	13	10-31-2013 03:40 PM
Manual Focus Focal Length Setting	bunjes	Troubleshooting and Beginner Help	5	07-10-2013 02:21 AM
manual lens focal length	nodretep	Pentax DSLR Discussion	3	03-11-2009 04:16 AM

09-30-2014, 10:51 PM	#3
pacerr Loyal Site Supporter Join Date: Jan 2008 Location: Paris, TN Photos: Gallery \| Albums Posts: 3,349	You might note that it isn't necessary for modern auto focus lenses which automatically input that data -- it's only required when using lenses without data transfer contacts. The great advantage is that SR is available even for older manual focus lenses. Incorrectly reporting the FL will cause the SR system to over- or under-compensate for camera shake.

09-30-2014, 11:19 PM	#4
jimr-pdx Pentaxian Join Date: May 2010 Location: now 1 hour north of PDX Photos: Gallery \| Albums Posts: 3,897	What they said. Very nice with primes, but with a manual zoom lens it gets harder. You can set it near the middle of the range or reset as you go, I have done it both ways. It's partly why I try to stick with auto zooms and manual primes or zooms with a narrow range like the old Sigma 21-35.

10-01-2014, 03:18 AM	#5
almo Senior Member Join Date: Jan 2008 Location: Flawda Posts: 101 Original Poster	Originally posted by Adam It's so that the in-camera shake reduction system knows how much camera shake to compensate for. Conveniently, the focal length is also stored in the exif data. Oh, good reason! ---------- Post added 10-01-2014 at 03:25 AM ---------- Originally posted by jimr-pdx What they said. Very nice with primes, but with a manual zoom lens it gets harder. You can set it near the middle of the range or reset as you go, I have done it both ways. It's partly why I try to stick with auto zooms and manual primes or zooms with a narrow range like the old Sigma 21-35. It was my plan to only use manual primes. I have two AF zooms that will be here today actually, but I figured already that when it comes to manual primes are probably going to be the best option. I started out using old Pentax film gear in the stone ages, and all we had were primes. I have had a few 70-210 zooms over the years at one point or another, but i never really got great results with manual zooms. Something about that loose push/pull zoom thing never really worked for me.

10-01-2014, 04:08 AM - 1 Like	#6
jadedrakerider Senior Member Join Date: Oct 2008 Location: Mohave Valley, AZ Photos: Gallery Posts: 214	Originally posted by almo Something about that loose push/pull zoom thing never really worked for me. Agreed. Autofocus zooms work just fine, but I never knew what I was missing until I came across an old Vivitar internal zoom manual focus lens. I don't think I would use any other kind by choice now.

10-01-2014, 05:39 AM	#7
almo Senior Member Join Date: Jan 2008 Location: Flawda Posts: 101 Original Poster	Originally posted by jadedrakerider Agreed. Autofocus zooms work just fine, but I never knew what I was missing until I came across an old Vivitar internal zoom manual focus lens. I don't think I would use any other kind by choice now. I don't think I have ever had an internal zoom manual lens before. Accept maybe for really short ones, but not telephoto. I might have to look into that.

10-01-2014, 05:52 AM	#8
jadedrakerider Senior Member Join Date: Oct 2008 Location: Mohave Valley, AZ Photos: Gallery Posts: 214	Originally posted by almo I don't think I have ever had an internal zoom manual lens before. Accept maybe for really short ones, but not telephoto. I might have to look into that. Mine is the Vivitar 75-205mm f3.8 Macro The aperture-lever shield needs to be filed down before it can be mounted onto a contemporary digital camera, but once you do you it's a pleasure to use.

10-01-2014, 05:59 AM	#9
reeftool Pentaxian Join Date: Dec 2007 Location: Upstate New York Photos: Gallery \| Albums Posts: 9,553	You still need the SR with an internal focus lens as it's the magnification that requires the stability, not the actual physical length of the lens. I have a 500mm mirror lens that is about the same length and weight as a 135/2.8 I own but it's nearly impossible to hold steady. With a manual zoom, best results will be with at length set as close to the focal length as possible. I have neglected to set the length on occasion and the results weren't good.

Thread Tools	Search this Thread
	Search this Thread: Advanced Search