PDA

View Full Version : Focus lens



Chris7521
23-Sep-2016, 13:41
I'm still pretty new to LF and have wondered what attributes a "focus lens" has? This pertains to a lot of those old lenses around EBay. Sorry if it's a dumb question but, I just don't find the info around. Thanks for any help!

Dan Fromm
23-Sep-2016, 13:58
I just did a search for "focus lens" on eBay. Ain't no LF "focus lenses" there. Please give some examples.

When you ask a question, please be as specific as possible. Make it easy for people to understand what you're asking about.

I did find "auto focus lens," "manual focus lens," "soft focus lens," even "fixed focus lens." The first two instances of "fixed focus lenses" were auto-focus Nikkors. Go figure.

Jac@stafford.net
23-Sep-2016, 14:03
Your question is the best start-point to large format photography. I am somewhat amazed how people make LF photographs with little or no understanding of the complexities. AND THAT IS PERFECTLY GOOD. oops, me shouting.

Your adventure begins with understanding what focal-length means and then your understanding will devolve when you pay attention to the metric-nerds.

No help, I know. I hope my response will arouse the best informed of this site.

Oren Grad
23-Sep-2016, 14:08
Dan, here's an example of the sort of listing that might be triggering the OP's question: "Aldis f8 10 Inch Focus Large Format Lens". Of course, in that case it's simply referring to the focal length.

djdister
23-Sep-2016, 14:08
Please read:

http://www.largeformatphotography.info/lenses-primer/

Photography With Large-Format Cameras, Eastman Kodak
The Camera, Ansel Adams

Dustin McAmera
23-Sep-2016, 15:07
Not really for LF, but I've come across sets of 'focusing lenses', i.e. auxiliary lenses just like a portrait attachment for a box camera, to give a fixed-focus camera more than one focus distance. I even have a set (Beck, if I remember right).

Bob Salomon
23-Sep-2016, 15:28
To me I thought that he is asking about a focusing loupe.

Mark Sawyer
23-Sep-2016, 16:34
As the OP mentions "focus lenses" as "old lenses", I'd ponder a guess he might be referring to old lenses with tangential or radial drive focusing. The feature might be nice on a simple rigid box camera, but doesn't matter on a camera that focuses with bellows extension.

Chris7521
23-Sep-2016, 19:10
Ok, sorry I asked such a stupid question and not explaining well enough. That is what newbies do. You where all there. I swear I have seen lets say a COOKE lens that just says "focus" but most say "EQ focus", some of which are clearly SF lenses with the softness adjustment, some no. What I want to know I guess for now is, what eq focus means. Can't seem to find the one I just saw that only said focus..
Ebay examples
Eq focus only 361725776182
Eq focus Process 291881025383

Chris7521
23-Sep-2016, 19:11
You have me all wrong. I am not that lost but, thanks...

Your question is the best start-point to large format photography. I am somewhat amazed how people make LF photographs with little or no understanding of the complexities. AND THAT IS PERFECTLY GOOD. oops, me shouting.

Your adventure begins with understanding what focal-length means and then your understanding will devolve when you pay attention to the metric-nerds.

No help, I know. I hope my response will arouse the best informed of this site.

djdister
23-Sep-2016, 20:21
Ok, sorry I asked such a stupid question and not explaining well enough. That is what newbies do. You where all there. I swear I have seen lets say a COOKE lens that just says "focus" but most say "EQ focus", some of which are clearly SF lenses with the softness adjustment, some no. What I want to know I guess for now is, what eq focus means. Can't seem to find the one I just saw that only said focus..
Ebay examples
Eq focus only 361725776182
Eq focus Process 291881025383

Okay, that is really just an old fashioned way of referring to focal length. If you look at pages 8 through 11 of the Goerz catalog, you will see how the terms focal length, equivalent focal length, equivalent focus, and focus are all terms used around describing focal length of a lens.

http://www.cameraeccentric.com/html/info/goerz_4.html

If you compare descriptions of lens focal length between Goerz, Taylor Hobson and Dallmeyer lenses in the catalogs at the Camera Eccentric website, you will see some variations in terminology used in how they described focal length.

Steven Tribe
24-Sep-2016, 00:40
Makers were a bit different.

The equivalent focal length (EFL) is the distance from the optical centre of the lens to the sharp image when focussing on infinity. Originally, lenses did not have an aperture system placed around this optical center (Up to around 1857) or if they did, they were hidden inside the the barrel.

Makers were also bad at engraving focal lengths, or even series number and size on the brass. Even published material from makers (which were often so basic that they can't be called catalogues!) often used the term "back focus" which gives the EFL as measured from the back of the lens. Whether this is measured from the very back of the brass or the the centre of the rear lens, I do not know. Back focus for Landscape meniscus lens is the correct EFL. Many makers (Including Dallmeyer) did not always mention focal length at all - they talked about practical use of the lens in studios. The distance required to take a bust or full figure when mounted on a camera.

Specification of focal length tightened up in the late 1880's and T,T & H went to the extreme of individually engraving the EFL to two decimal points on their early lenses. Yes, there are differences real differences between the "same" model - which makes sense of selected lenses as stereo pairs!

Chris7521
24-Sep-2016, 04:36
Okay, that is really just an old fashioned way of referring to focal length. If you look at pages 8 through 11 of the Goerz catalog, you will see how the terms focal length, equivalent focal length, equivalent focus, and focus are all terms used around describing focal length of a lens.

http://www.cameraeccentric.com/html/info/goerz_4.html

If you compare descriptions of lens focal length between Goerz, Taylor Hobson and Dallmeyer lenses in the catalogs at the Camera Eccentric website, you will see some variations in terminology used in how they described focal length.


Makers were a bit different.

The equivalent focal length (EFL) is the distance from the optical centre of the lens to the sharp image when focussing on infinity. Originally, lenses did not have an aperture system placed around this optical center (Up to around 1857) or if they did, they were hidden inside the the barrel.

Makers were also bad at engraving focal lengths, or even series number and size on the brass. Even published material from makers (which were often so basic that they can't be called catalogues!) often used the term "back focus" which gives the EFL as measured from the back of the lens. Whether this is measured from the very back of the brass or the the centre of the rear lens, I do not know. Back focus for Landscape meniscus lens is the correct EFL. Many makers (Including Dallmeyer) did not always mention focal length at all - they talked about practical use of the lens in studios. The distance required to take a bust or full figure when mounted on a camera.

Specification of focal length tightened up in the late 1880's and T,T & H went to the extreme of individually engraving the EFL to two decimal points on their early lenses. Yes, there are differences real differences between the "same" model - which makes sense of selected lenses as stereo pairs!

Thank you for the detailed explanations. I guess like many things, eventually most manufactures decide to standardize terms or what have you, to make it less confusing for all. Thanks again and I'll try to explain my questions better in the future.