Tt&h cooke convertible lens questions

[Craig Tuffin]

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]

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]

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]

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]

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]

Hi Mark

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

http://www.ebay.com/itm/TAYLOR-HOBSO...p2047675.l2557

Here is one that sold recently on Ebay

Roger

[kgm]

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]

Hi Mark

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

http://www.ebay.com/itm/TAYLOR-HOBSO...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]

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]

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.