View Full Version : Variations in the design of the rear cells of the Dallmeyer Soft lens Petzvals

Steven Tribe
24-Feb-2014, 02:42
A discussion about the design and actual appearance/dimensions of these lenses has filled up the "soft lens sales data" thread in the last few days. As a definitive list, description and images of the many types do not appear to have posted before, I thought it might be a good idea to start a separate thread where we can gradually build up documentation and perhaps equate with serial numbers? I don't know whether it is possible/advisable to move some data from that thread to this one?

One thing is quite certain, the old version of quadrant notches and rear turn did continue parallel with the introduction of the "smart" front barrel turn type.

Tim Meisburger
24-Feb-2014, 02:52
Thanks Steven. I sent a note to the moderators asking if they can move the off topic posts from the soft focus sales thread to this one.

24-Feb-2014, 08:01
Good idea, Steven & Tim~
I definitely hope the lens is real as I said, dear Tim.

Steven Tribe
25-Feb-2014, 04:00
I don't have enough images to cover the following text - which is an expanded version of what was posted in "Soft lens sales" thread.
These will follow, by contributions from others and myself.

The original design of patent Dallmeyer's A, B and D series works by unscrewing ultimate part of the rear cells, containing the last lens, The other lens is in a separate housing remains in a fixed position. Positions at 45 degrees, 90 degrees etc. are indicated by rough (round file?)Roman numerals ( I, II, III and IIII) which are alligned with a small indicator - which eventually gets a little bent. There is, however, no limit on the softness which can be acheived. The mount is the standard brass Sleeve with flange attachment and barrel. Note the thread between the 2 sections of the real cells is found in at least 2 different diameters. In addition, Dallmeyer sold these lenses without the soft lens facility - they are without the "Patent" engraving. As far as I know, these are the 2C, 3C, 1B, 1B long and 2B. It is only the 2B which is found in 2 versions. Although the later versions made up the bulk of the later production, Dallmeyer still produced the simpler rear adjustment system into the 20th century.

The more modern version is made up of a complex last lens mount which includes the flange thread. The somewhat shorter barrel (it doesn't "overlap the final lens") has the achromat at one end and the first of the rear lenses at the back. This single rear lens mount in the barrel has a thread which screws into the first mentioned last lens mount which is already attached to the flange/lens board. Screwed right in - it is in the Sharp position and it screws out to attain the soft effect wanted.
There are different versions of this, some where this last thread is anticlockwise. There must have been complaints because when attempting to increase softness by screwing the barrel assembly out, the whole lens might turn around on the flange. Some, at least, have a locking latch to ensure this doesn't happen!

The direction of the arrow "turn for soft" indicates, of course, whether it has a clockwise or anti-clockwise thread for removal!

Note that the reverse thread type says "Turn for Soft" whilst the normal thread type says "Unscrew for softness". I think this is not just a co-incidental difference!

Here are photos of the two types (posted earlier by Garrett and Pierre).

25-Feb-2014, 07:57
A black barrel Dallmeyer 3B:

Handwritten form

25-Feb-2014, 08:00
Tim's brass Dallmeyer 3B:

Steven Tribe
25-Feb-2014, 09:46
More from an earlier posting (Louis Pacilla).

Sometime around 90.000 I would guess Dallmeyer had a light bulb moment and changed the direction of the SF to the right so at worst you tighten the barrel to flange when you engage the SF .

Here's a 3A #69735 with the lock on the flange and turn to the left. You can see the flange lock above the f8 mark. The 4A #102355 and this turns to the right so they did away with lock on flange and no notches at all. just the center mark for start."

As Tim/Pierre's serial number is over 100,000 it has the right soft turn as Louis mentions.

The last photo is a close up of the appearance of the left-turn rear section. Note that the notches system has been continued at this stage.

Steven Tribe
27-Feb-2014, 12:56
This is what the inner cell of the back adjustment early type looks like with the turning soft adjustment lens removed. The outer thread screws into the barrel, just like the front achromat cell.

The simple indicator brass screw is highlighted. The thread is much narrower than the body proper and probably will have tendency to shear off!

The inner thread diameter, which is not the same on all Dallmeyers (the 3B at least), is also shown. I'll post the female thread diameters when I have them both.

27-Feb-2014, 16:10
Left is Crown glass.
Right is flint.

12-Nov-2014, 14:44
I was noticing that the aperture scales also changed in the later lenses. Some are "wide open" with the adjustment lever fully clockwise others completely "stopped down".

Has any one ever tried to remove the aperture assembly on one of these? I need to make a new adjustment lever....