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Craig Tuffin
28-Jan-2013, 06:30
I have stumbled across a convertible TT&H Cooke lens No. 13070 Series V 8.5x6.5, 11.2 Inches Eq focus f8 - f64, convertible to 17 Inches f16 - f64.

I know nothing about convertible lenses in general and after a forum search, haven't improved that by much. Can anyone tell me something about this lens? it's in good condition apart from a ding on the rear rim (no effect on the glass). Someone said A.Adams like the Cooke convertibles...is this one of them?

Any help is appreciated.

Louis Pacilla
28-Jan-2013, 08:19
Hi Craig

I was not aware that the series V was convertible as I thought it was a much higher series number was the convertible Cooke. The newer version is the Series XVA and original was the Series XV. Not sure if any of the Triplet Cooke's Like the series V is convertible but not sure about that.

Anyhow Here is a page from a Cooke Catalog.

Roger Hesketh
28-Jan-2013, 11:03
Some T.T.&H Triplets had extension lens which could be screwed on to the rear element extending the focal length

This is what the Vade Mecum says.

These were the longer focus rear glasses and were available for Series 11, 1V and V but
not for Series 111. These gave 50% increase in focus ie. 6in became 9in. It was noted that they were not
always suitable if the prime lens was a "long" one as the extension lens needed extra extension on the
camera and this might not be available. They were available in Series 11 by 1900. These do not seem to be
common today, often being 'lost' as equipment changes hands. Exposure needs to be increased by a factor of
2x, so f11 behaves as f16. One seen for Series 11 was No E24,254 to indicate the use, with equivalent focus
16.3in. In general, two sizes were noted (no data for Series 11):
Size 1V for 5, 6, 8, 9.5, 11, 13in lenses, and Size V for 7.5, 9, 11, 13, 16, 18in normal lenses.

Roger Hesketh
28-Jan-2013, 13:04
Hi Craig
I realised I did not really answer you question. Firstly your lens is not really a convertible lens as one generally tends to think of a convertible lens. It is a very high quality and sharp triplet lens for which was made a supplementary lens which increased it's focal length. You may or not still have have that supplementary lens. Don't worry if you have not as they crop up on Ebay quite regularly and do not make much as they are useless to anyone who has not got a lens like yours. The lens was made by Taylor Taylor and Hobson of Leicester England during the early part of the 20th Century.
T,T & H also made a Convertible lens. That was the lens that AA used.

A Convertible lens consists of two groups of elements which screw into either side of a barrel mount or shutter. It can either be used as a complete lens or the two groups can be used separately. When used separately the resulting focal length is generally twice the focal length of the complete lens though their are considerable variations. Their are lenses which are double convertible when the components of the lens are of equal focal length and their are triple convertible lenses where the components are unequal. So for example a combined focal length may be 12" made up of components of 21" and 25" for a triple .Or a double convertible might be of 5" focal length made up of two components of 9" focal length.
Generally these lenses will have two or three aperture scales. Often their performance is better when used combined but in any event most of the components are Anastigmats and are well corrected for most lens aberrations in their own right. Many of the components are made up of 3 or more elements some even as many as five.
Many well known lenses especially symmetrical lenses are convertible even if not marked as such. Protars, Dagors, ordinary Schneider Angulons, Gundlach Turner Reich Anastigmats , Schneider Symmars and Schneider Companons. Other less well known ones are the Dallmeyer Stigmatic, Ross Combinable and the Watson Holostigmat. Some are well known like the Wollensak Verito but are not generally known to be convertible
The WollensaK Extreme Wide Angle is also a convertible lens descended from the convertible Royal Anastigmat and is a very similarly designed lens to the Cooke Convertible that Louis mentioned to you and which you are no doubt disappointed that you do not have. Don't be disappointed you have a very fine lens and one that would more than likely outperform the convertible one.

Mark Sawyer
28-Jan-2013, 13:48
I suppose any lens with two or more groups that can be disassembled could be considered a "convertible", in that there's at least one positive group, and another group, positive or negative, that changes the focal length.

"Factory" convertibles are those that are meant to be used that way, and either don't show increased aberrations when converted, or are meant to have certain aberrations, like the Verito. The Cooke Series V was a triplet process lens with two positive elements and a negative element in the middle. You could use either the front or rear element alone as a "converted" lens, but it would certainly show the chromatic, spherical, and other aberrations inherent in all single element lenses.

Roger Hesketh
28-Jan-2013, 14:32
Hi Mark

The lens is converted by screwing on an extra extension element.

http://www.ebay.com/itm/TAYLOR-HOBSON-COOKE-EXTENSION-LENS-13-1-INCHES-LEATHER-CASE-/261152441854?nma=true&si=c0IoGZRWF16A1kKVa1aDZRqgopE%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

Here is one that sold recently on Ebay

Roger

kgm
28-Jan-2013, 16:36
I have stumbled across a convertible TT&H Cooke lens No. 13070 Series V 8.5x6.5, 11.2 Inches Eq focus f8 - f64, convertible to 17 Inches f16 - f64.

I know nothing about convertible lenses in general and after a forum search, haven't improved that by much. Can anyone tell me something about this lens? it's in good condition apart from a ding on the rear rim (no effect on the glass). Someone said A.Adams like the Cooke convertibles...is this one of them?

Any help is appreciated.

To answer your question about whether Ansel Adams used this lens, I've only seen him reference the Cooke Series XV triple convertible, which had 12 1/4", 19", and 25 1/2" configurations. The current Cooke Series XVa is an update of the original design with the same focal lengths.

Mark Sawyer
28-Jan-2013, 18:22
Hi Mark

The lens is converted by screwing on an extra extension element.

http://www.ebay.com/itm/TAYLOR-HOBSON-COOKE-EXTENSION-LENS-13-1-INCHES-LEATHER-CASE-/261152441854?nma=true&si=c0IoGZRWF16A1kKVa1aDZRqgopE%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

Here is one that sold recently on Ebay

Roger


Yes, I understand that, but that would be an "auxiliary" or "extension" lens. And if the focal length of that 13.1 inch Cooke Extension Lens is a positive focal length, it could also be used on its own with results probably similar to an early landscape lens, Plasticca, Imagon, Kodak Portrait Lens, etc. But the OP was talking about a Cooke Series V, a triplet process lens that converted from 11.2 to 17 inches. If the extension lens is a positive, it would make the converted focal length shorter, not longer. But I think I remember something about the Cooke Triplets being convertible to a longer focal length by removing the rear element, which is a positive. That might be what he's thinking about, though I've never seen one marked as a convertible. I don't know what the performance would be without the rear element...

My point was that, as far as defining what a "convertible lens" is, (and there seemed to be a little confusion about it), any lens with two or more groups could be considered a "convertible" if one were simply looking for an image. Some would be soft wide open, and some would be fairly sharp.

In photography's early years, Petzvals and Rapid Rectilinears were considered convertible to landscape lenses, sharp enough for "normal" work closed down. Today, they are sometimes used wide open as soft lenses. Plasmats, Dagors, Dialyts, and a few other designs are considered convertible with good performance for conventional sharp images, especially if the aperture is closed down a bit. The Cooke XV Convertible was a unique design as far as I know, with eight elements in four groups of two. Ansel Adams used a single cell of a Cooke XV to make Moonrise, Hernandez.

Jim Galli
28-Jan-2013, 22:31
No, it's not the one Ansel loved. And typically the Series V is considered a reproduction lens, rather like a G-Claron or Red Dot Artar. Not the same at all as the lovely Series XV that all the legends swirl around.

Craig Tuffin
28-Jan-2013, 23:01
Thank you all very much for the info.

It all makes complete sense to me now Roger. You're right in assuming that I don't have the extension lens for it. I have to many lenses at this FL (without the extension) so I need to decide what to do next.

Mark, I tried it without the rear element and in other combinations but it doesn't produce an image.

Craig Tuffin
28-Jan-2013, 23:14
Thank you too Jim. I think I knew it was too good to be true :)

Roger Hesketh
29-Jan-2013, 07:03
Mark to be honest I am not sure how the extension lens was used whether it replaced the rear lens in which case with it being a triplet lens I would expect it would throw everything out of kilter. Or as a supplementary lens which would I suppose would have meant that it would have had to have been negative. The Verito is the only other lens I know of that you can swap single lens elements in that case the front element which is only their to reduce the power of the rear group anyway so changing it or removing it does not affect the optical performance greatly.

I agree about what you say about convertibles in general which is why I pointed out to Craig that his lens is not one that we would generally think of as a convertible lens even though I strongly suspect it has two aperture scales. Whereas many of the lenses we have been discussing do not as they were never sold as being convertible or rarely they were once sold as convertibles but were later on in the production run not sold as such.

One such lens being the Wollensak Series IIIa Wide Angle which has a very similar optical formula to the Lee designed Cooke Series XV Convertible lens That of two air spaced doublets either side of a central stop.

See this link fellow forum member Desertrat explains much more eloquently than ever I possibly could.

http://www.largeformatphotography.info/forum/showthread.php?89861-A-Royal-Anastigmat-By-Another-
Name




88196




88197

I don't believe Ernst Gundlach is necessarily afforded the respect he deserves as a lens designer. People speak of his Turner Reich as just having an extra element to get round Zeiss's Protar patent. I don't believe so. I think he put it in their for a reason. Especially considering as we can see here he was perfectly capable of designing and building his own unque Anastigmat and one which was much easier to build. In many ways a very similar design the air space acting as an element. Quite an acheivement to design two unique anastigmat lenses which were still in production 60 years later.


Thanks for the info on RR and Petzvals Mark I do believe you have inspired me to have a play to see what sort of images can be made from bits of them Thanks

Jim Galli
29-Jan-2013, 07:59
Mark to be honest I am not sure how the extension lens was used whether it replaced the rear lens in which case with it being a triplet lens I would expect it would throw everything out of kilter. Or as a supplementary lens which would I suppose would have meant that it would have had to have been negative. The Verito is the only other lens I know of that you can swap single lens elements in that case the front element which is only their to reduce the power of the rear group anyway so changing it or removing it does not affect the optical performance greatly.

I agree about what you say about convertibles in general which is why I pointed out to Craig that his lens is not one that we would generally think of as a convertible lens even though I strongly suspect it has two aperture scales. Whereas many of the lenses we have been discussing do not as they were never sold as being convertible or rarely they were once sold as convertibles but were later on in the production run not sold as such.

One such lens being the Wollensak Series IIIa Wide Angle which has a very similar optical formula to the Lee designed Cooke Series XV Convertible lens That of two air spaced doublets either side of a central stop.

See this link fellow forum member Desertrat explains much more eloquently than ever I possibly could.

http://www.largeformatphotography.info/forum/showthread.php?89861-A-Royal-Anastigmat-By-Another-
Name




88196




88197

I don't believe Ernst Gundlach is necessarily afforded the respect he deserves as a lens designer. People speak of his Turner Reich as just having an extra element to get round Zeiss's Protar patent. I don't believe so. I think he put it in their for a reason. Especially considering as we can see here he was perfectly capable of designing and building his own unque Anastigmat and one which was much easier to build. In many ways a very similar design the air space acting as an element. Quite an acheivement to design two unique anastigmat lenses which were still in production 60 years later.


Thanks for the info on RR and Petzvals Mark I do believe you have inspired me to have a play to see what sort of images can be made from bits of them Thanks

Was Gundlach the designer at Wollensak in that time frame? Never heard his name mixed up with Wollensak lenses before.

Roger Hesketh
29-Jan-2013, 08:26
Wollensak were principally shutter makers. They bought the Rochester Optical Company in 1905 for it's line up of Royal Anastigmats.

The Rochester Optical Company was founded by Ernst Gundlach and was renamed when he left the coumpany in his day It was named something along the lines of the Ernst Gundlach Son and Co.

Gundlach designed the Royal Anastigmat which is what early Wollensak series 1 Convertibles are. The later ones when the Zeiss patent expired are Protar VIIa 'copys' .

Gundlach is also credited as patent holder of the Wollensak wide angle which is a stretched varient of the Royal Anastigmat. Stretched with wider glasses similar to the way the Watson Wde Angle Holostigmat is a stetched version of Watson's Series 1 Holostigmat.

Jim, Gundlach never worked for Wollensaks they bought his old company He worked pretty much everywhere else though. When he first came to the US he worked for B&L founding their microscope department.

Other lenses in the Wollensak line up were Rochester Optical products for instance The Vitax was previously available as the the Royal Portrait lens

Mark Sawyer
29-Jan-2013, 13:57
Mark to be honest I am not sure how the extension lens was used whether it replaced the rear lens in which case with it being a triplet lens I would expect it would throw everything out of kilter. Or as a supplementary lens which would I suppose would have meant that it would have had to have been negative. The Verito is the only other lens I know of that you can swap single lens elements in that case the front element which is only their to reduce the power of the rear group anyway so changing it or removing it does not affect the optical performance greatly.


I'm not too sure about it either, Roger. My suspicion is that it's a positive single achromati that shortens the focal length when screwed on the front, but it could also be a negative that lengthens it, and that would make more sense with the word "extension". I don't think it would replace an element, though I could be wrong...

There were a few other lenses that had removeable or interchangeable elements. The Portrait Plastigmat had a front element and could be used with or without, similar to the Verito. The 18" Verito's were available with a second front single-meniscus element that could be swapped out to make it a 22", and the 16" Vitax was available with a second front achromatic doublet cell that could be switched with its regular front cell to make it a 20" f/5 Petzval. And of course there were all sorts of casket sets around, so there was a fair amount of lens-element-swapping going on...

Hermes07
29-Jan-2013, 16:19
From the 1912 Cooke Brochure

"The Series III., IV. and V. Extension lenses are designed to
replace the back glass of the normal Cooke lenses, and the Series II.
and 11 A. are designed to replace the front glass. The exchange can be
effected quite easily, being simply a matter of unscrewing the normal
lens and screwing in the Extension."

Happy to email or upload it for anyone interested.

Mark Sawyer
29-Jan-2013, 17:29
Oh, well if I'd known we were actually going to look things up so we knew what we were talking about... :rolleyes:

882508825188252

Amedeus
29-Jan-2013, 17:52
I can confirm this for the Series II. I have a 8.2" Cooke Series II and the 12.8" extension lens for Series II. Just unscrew the front and screw in the (positive) extension lens for the new combination.


From the 1912 Cooke Brochure

"The Series III., IV. and V. Extension lenses are designed to
replace the back glass of the normal Cooke lenses, and the Series II.
and 11 A. are designed to replace the front glass. The exchange can be
effected quite easily, being simply a matter of unscrewing the normal
lens and screwing in the Extension."

Happy to email or upload it for anyone interested.

Roger Hesketh
29-Jan-2013, 19:25
Oh, well if I'd known we were actually going to look things up so we knew what we were talking about...

+1

A two stop decrease in effective aperture to gain a 50% increase in focal length seems rather a lot.