PDA

View Full Version : Altering lens configuration



tonyowen
20-Nov-2016, 03:50
I've noticed several threads on LFPF referring to the removal of lens cells to 'create' a different focal length and/or to give some softness to a lens.

I have a Schneider xenar f4.7 135mm lens, whose front and rear sections are screwed into the appropriate side of a synchro- compur 0 shutter.

Is anyone aware of any other configuration that can meaningfully be 'created' by this "tessar type" lens???

regards

Tony

LabRat
20-Nov-2016, 05:37
There were threads here about increasing the spacing distance of the front element of Tessar type lenses, but in practice, it is difficult (or impossible) to change the front element seating with most lenses as the elements are mounted from the insides. and would push the rear element backwards (if these could be adjusted at all)...

You can try using aux lenses on top of these lenses, like + or - to change the FL, or find or make soft filters that can work very nicely with the lens... (I use a -4 Telek lens with my 135mm Xenar f4.7 (on a Crown Graphic) to convert it to (about a) 260mm/f10 lens that is sharp stopped way down, but has pleasing slight edge softness when wider open...)

It's worth trying out some different combinations with these...

Steve K

tonyowen
20-Nov-2016, 06:42
... (I use a -4 Telek lens with my 135mm Xenar f4.7 (on a Crown Graphic) to convert it to (about a) 260mm/f10 lens that is sharp stopped way down, but has pleasing slight edge softness when wider open...) Steve K
Steve, thank you very much.
I googled -4 Telek, but got nothing related to auxiliary lenses.
I'm assuming the minus 4 relates to optical strength or weakness.
Please clarify 'Telek'
regards and thanks again

Tony

LabRat
20-Nov-2016, 07:03
Telek is the Kodak name for a - conversion lens (- is in diopters)... (The opposite of positive close-up lenses)... These might not be made today, as they were popular back when cameras had double or triple extension bellows (as the lenses then required variable extension to use these) ... These were made with -1,-2,-3,-4, and sometimes -10... Old Kodak photo manuals and photoguides (from 50's to 60's) usually had a section on the use of these... You can find the lenses on that auction site or sometimes in an old camera store with the filters and C/U lenses...

Good Luck!!!

Steve K

Luis-F-S
20-Nov-2016, 09:55
Very capable lens designers spent a lot of their time and effort working with their slide rules, logarithms and ray tracing in the old days, and computers more recently to come up with the best lens design they were capable. I have no interest in bastardizing their work by my trying to "improve" on it by switching cells, spacing, etc. I'll use their lenses the way they designed and intended them to be used. Anyone else is free to do what they wish, after all, their your photos. L

Alan Gales
20-Nov-2016, 10:56
I've noticed several threads on LFPF referring to the removal of lens cells to 'create' a different focal length and/or to give some softness to a lens.

Tony, I don't know if you are aware of it but there are special lenses designed to change focal lengths by removing cells. They are called convertibles. Here is the fantastic Cooke triple convertible which you can remove or even change cells. It comes from your neighborhood. :)

http://www.cookeoptics.com/l/xva.html

mdarnton
20-Nov-2016, 11:11
The Tessar doesn't work well for this. The back component has a very short focal length relative to the whole, and narrow coverage. On convertibles, the individual components are longer than the whole and cover more. I just took a 300 mm Tessar-type lens apart, and the back is around 190mm or so, comes nowhere covering the original format, and quickly degrades moving from center.

Regarding Teleks, I have a watch on Ebay for them. Almost all of the ones that show up are Series VI and -1 or -2. I almost never see anything larger or stronger, so you may be looking a long time for a -4!

One lens that might be suited for what you want to do is a Eurynar. The short ones like 135/4.5 are easy to find and cheap, and the halves are usable individually. But also, older, short convertible Symmars don't cost much these days, either. Under $100--and a 135mm Fujinon would do as well for this and cost even less.

There are two problems with splitting convertible lenses, though. One is that the resulting lens will be a stop or two slower than the whole. The other is that most of these end up not being "soft focus" lenses, but rather just bad lenses that need to be stopped down to look any good. If you want to have a soft focus lens with a nice personality there are better ways to do it, including soft focus filters.

tonyowen
20-Nov-2016, 12:17
Very capable lens designers spent a lot of their time and effort working with their slide rules, logarithms and ray tracing in the old days, and computers more recently to come up with the best lens design they were capable. I have no interest in bastardizing their work by my trying to "improve" on it by switching cells, spacing, etc. I'll use their lenses the way they designed and intended them to be used. Anyone else is free to do what they wish, after all, their your photos. L

I think you're missing the point of my posting. I was curious as to what might be done, there was no inference of bettering a commercial lens design. Your comments infer that filters should not be used since they alter the effect of the image that would be captured by an unfiltered lens.
regards
Tony

tonyowen
20-Nov-2016, 12:33
Tony, I don't know if you are aware of it but there are special lenses designed to change focal lengths by removing cells. They are called convertibles. Here is the fantastic Cooke triple convertible which you can remove or even change cells. It comes from your neighborhood. :)http://www.cookeoptics.com/l/xva.html

Alan, thank you. Yes I was aware of convertibles - I did not know they were manufactured in Leicestershire. My posting was mainly a curiosity - my degree of large format interest limits my justification in buying lenses for the sake of a particular attribute. Hence the query about any functional variability of my xenar lens.
I've found that placing a general even na´ve posting on this forum generates a lot of information that I otherwise would not have acquired.

regards and thanks again
Tony

tonyowen
20-Nov-2016, 12:36
The Tessar doesn't work well for this. Regarding Teleks, I have a watch on Ebay for them. Almost all of the ones that show up are Series VI and -1 or -2. I almost never see anything larger or stronger, so you may be looking a long time for a -4!One lens that might be suited for what you want to do is a Eurynar. The short ones like 135/4.5 are easy to find and cheap, and the halves are usable individually. But also, older, short convertible Symmars don't cost much these days, either. Under $100--and a 135mm Fujinon would do as well for this and cost even less..

Mdarnton, thanks you very much for the extensive information in your response.

regards
Tony

Luis-F-S
20-Nov-2016, 17:33
I think you're missing the point of my posting. I was curious as to what might be done, there was no inference of bettering a commercial lens design. Your comments infer that filters should not be used since they alter the effect of the image that would be captured by an unfiltered lens.
regards
Tony
Tony, filters are fine, though they will have some effect which is why I typically only use wratten gel filters, and why there are cheap and expensive filters. I thought you were referring to the folks who try to improve lenses by changing the spacing, or make up new focal lengths by swapping cells.................Convertible lenses were typically designed as such, though as everything, there is some price to pay. L

tonyowen
21-Nov-2016, 02:06
I thought you were referring to the folks who try to improve lenses by changing the spacing, L

No problem, posting are easily not fully explained or misunderstood

regards
Tony

LabRat
21-Nov-2016, 02:50
Other mfgs also made Telek type lenses, such as Tiffen, Enteco, Milo, and other house brands... Usually they come in series 6, but I have some in series 7 & 8... They are out there, quietly sitting in the dark somewhere...

Steve K

tonyowen
21-Nov-2016, 09:51
Other mfgs also made Telek type lenses, Usually they come in series 6, but I have some in series 7 & 8... Steve K

Steve, unless I'm mistaken the series lenses are slip-in not screw in lenses. I've seen several items purporting to be aux telephoto lens [ AVIGON AUX. TELEPHOTO LENS – COLLECTORS? EXPERIMENTERS? ( 162280194135 )] - some of which would screw straight into the 'filter thread of my xenar lens.

What are the advantages of the series type lens - or am I still confused.

regards
Tony

LabRat
21-Nov-2016, 13:18
Steve, unless I'm mistaken the series lenses are slip-in not screw in lenses. I've seen several items purporting to be aux telephoto lens [ AVIGON AUX. TELEPHOTO LENS – COLLECTORS? EXPERIMENTERS? ( 162280194135 )] - some of which would screw straight into the 'filter thread of my xenar lens.

What are the advantages of the series type lens - or am I still confused.

regards
Tony

The series sizes are regular filter sizes that have un-threaded mounts, that are placed inside a ring that usually slips over the outside of the lens barrel, and the filter is held in place by a retaining ring that screws into the barrel ring... The ser 6 is about 1 5/8" / 41mm dia, and the ser 7 is about 2" / 50mm dia...

These type of lenses are like a camera filter single element negative lens, the opposite of a C/U lens, and should be fairly cheap... Not to be confused with the aux multi-element attachments (which could work too), but the teleks are good to leave in the bottom of your camera kit if another lens is not available, but not nearly as good as a prime lens...

The nice thing about series filters is that with the proper adapter (for that size group), they can fit on a number of lenses so less filters to carry around, esp with smaller lens barrels... But every lens needs an adapter for it...

Steve K

tonyowen
22-Nov-2016, 01:39
Steve,
as always thank you very much
Tony