Dallmeyer Series 3B Lenses Differences?

**Steven Tribe** · 13-Dec-2015, 03:53

I know the 3B has been described as both 11.5" and 12". I think it is the earliest models which are the shortest. Dallmeyer did not give focal lengths (efl or back focus) in early catalogues/adverts. My "knowledge" is just what I have read. All 4 3Bs I have played with were all 12". Perhaps the earlier 2B's were also slightly shorter?

**Steven Tribe** · 13-Dec-2015, 04:57

Back to the OP's question!

A couple of years ago I discovered a complete set of lens cells for the "turn the barrel/iris" model of the Dallmeyer 3B. I made a new brass setting for this lens set, making a replacement WH slot instead of an iris. I have described this here - but what I didn't mention was the loaner (and eventually, purchaser) of this lens actually compared it with a standard 3B. He virtually accused me of witchcraft as the home assembled 3B was quite a lot faster than the ordinary 3B. I did try to explain it away with new balsam, but I realise now that it was just due to increased aperture possible due to the WHS system.

**PawelR** · 13-Dec-2015, 05:51

My lenses:
3b is 300mm 121XX serial number
2b is 220mm 271XX serial number
2b is 210mm without cellar..

**goamules** · 13-Dec-2015, 07:59

Here is what I believe accounts for slight variances in focal lengths of the same manufacturer's lenses. This probably applies up until the 1920s, when manufacturing became a lot more standarized, including the types of glass. There are actually two things going on here:

1. As is documented, lens makers had to test each new lot of glass that they got. They tested the glass' variation in refractive index, mainly. Each lens was then ground and optimized for several critical optical parameters, such as spherical aberration (sharpness), field curve, etc. They did NOT try to standardize the exact focal length to the fraction of an inch. Instead, they ensured each lens was as optically perfect as it could be, even if the focal length varied a few fractions of an inch. You will note some manufactures acknowledged this variation. Taylor, Taylor and Hobson for a period would engrave the exact focal length on the barrel like this one that is 10.65". If you bought another from them that month, it would be slightly different, and marked so. I'm sure this convinced TTH customers they were buying a precisely measured and build lens. Dallmeyer didn't worrry about it.

The one thing that was standardizes was their brass barrels. So you don't get fluctuating barrel lengths, another way they could have possibly standardized the focal length. So they let the focal length fluctuate, and ensured the barrels were physically the same, and the quality of each lens was the same. These lenses were all hand made, matched, and optimized, each element for each lens.

2. The other thing is that during different periods, the lens designs and manufacturing were slightly updated. Again, the companies knew large format lenses were put on focusing body cameras. It didn't matter if what they called an 8" lens was actually 8.39" or 8.2" etc.

**goamules** · 13-Dec-2015, 08:02

This brings up a very important consideration. These lenses were hand made, and hand fitted and optimized. They were not standardized in terms of swappable parts. Many times over the years I've heard people say "I have a XYZ petzval, missing the rear crown glass element....and need to find one..." I keep my mouth shut, but know that if they find a piece of glass that physically fits into the brass, they are NOT going to get the precision and quality that the original maker intended. Because each piece of glass was matched up, in each individual lens.

**Steven Tribe** · 13-Dec-2015, 10:32

I agree with almost all of the foregoing. But I always thought (and still do!) that the two decimal points on early T,T&H represent the efl of all the lenses made for a particular format. Although The Lens VM doesn't actually say it, it does give two decimal point figures for a few of the early lenses, but mostly just refers to format sizes.

What especialy makes me think that same two decimal point figure appears on all lenses is the casket RR/WAR/RV set I have. The same barrel has all three efls engraved. RV is 8.72, RR is 7.28 and WAR is 4.12. I don't think T,T&H would manage to coordinate the measuring of 3 different efls and engrave them. The serial number is 5235 - a set for 1/2 plate

**goamules** · 13-Dec-2015, 12:24

Here is how my hypothesis can be proven. If anyone has another 5x8 R.V. can tell us if it says exactly 10.65, like mine, or something different and specific to the lens, like I suppose. I sold another to Gandolfi, but can't remember what it was engraved with.

I just called a friend who has a casket set, and his WAR is engraved 5.44".
Yours WAR is 4.12 so those are fairly different lengths.

But here are two more casket sets, with these WARs listed:

WAR ser no. 3969 listed as 4.13" focal length
WAR ser no. 5802 listed as 4.11" focal length
http://www.earlyphotography.co.uk/site/entry_L24.html

I believe TTH engraved the exact FL of each lens. I rest my case!

**Steven Tribe** · 13-Dec-2015, 13:42

Well done - and the variation is far more than I thought possible. So selection of paired lenses for stereo use must have been tricky!

My 1/2 plate set is simpler than the first set shown in earlyphotography, but is probably the same as the second one, not illustrated. It is also closer in serial number and with the other RR and WAR efls.

For future reference, the figures for these two no. 3 caskets for 1/2 plate from T,T & H are:

no. 5802. RR. 7.41" WAR. 4.11" RV. 8.68" (ex. from earlyphotography)
no. 5235. RR. 7.28". WAR. 4.12". RV. 8.72" (my own)