Anyone own Dallmeyer 3A waterhouse stops? Aperture size help needed

[Nasir]

I'm looking for aperture hole sizes so that I can have waterhouse stops made for my Dallmeyer 3A. Does anyone own a set they can measure, please?

I've made a dummy from card and measured the internal f4 aperture after drawing around it and it measures 3 7/10", so, calculating the aperture size by dividing the focal length (16") by the f-stop doesn't calculate to be accurate.

After contacting around 5 different owners who's work I found on Flickr using a 3A I haven't received a single reply so I'm trying on here.

If you own an original set of WHS please would you measure the aperture sizes and share this information.

Many thanks

[Ron (Netherlands)]

I have two big WHS stops laying around unused; what is the size of the WHS slit of a 3A?

[Steven Tribe]

The patent Petzval Dallmeyer 3A’s were made over many decades and there are variations - even in the original rear defusion version!
The focal lengths of the 3 adjustable patent Petzvals became a little longer ( well the 3B did and I believe the other series did as well!) and the dimensions of the lenses and the rear lens cells changed as well. I once had a number of incomplete 3B’s and found surprising differences in the rear cells - even though they were all made in the same decade.

In the same manner, the original sets of Waterhouse stops provided by Dallmeyer were subject to change during their production lifetime. There were changes in the number supplied, the size of the apertures and the labeling of the individual stops. The causes of changes made is due mostly to the historical evolution of F scales, but also because Dallmeyer did some rationalization of Waterhouse stop production across all his photographic lens production - there were not an infinite number of barrel diameters. I have seen a table of Dallmeyers various sized Waterhouse stops listing which lenses (Portrait, Rectilinear, etc) require which stop set - this may also have the range of apertures provided.

I regret that I do not remember where I saw this aperture set / suitability for different lens table! Perhaps someone else could provide the link - it would give you more opportunities to make a clone of an original set from somebody.

Your measurement of the aperture giving 3.7”instead of 4” gives you the key to making your own correct set of stops.

Making an stop F8 will require an aperture with a diameter of 1.85” (instead of 2”!).

Making stops from brass with normal hobby tools does involve a few safety issues and I prefer to use black stiff card where the only hazard is sharp blades!

[Steven Tribe]

I have two big WHS stops laying around unused; what is the size of the WHS slit of a 3A?

So do I.
Remember the thickness of brass stops varies - I don’t think there was a standard.
I have 2 identical lenses Francais Rectilinear series A no.5. Both have Waterhouse slots. One came with a set of stops. The width of the stops precludes use in the other lens! So I am making a card set this week.

[Nasir]

I have two big WHS stops laying around unused; what is the size of the WHS slit of a 3A?

95mm wide. Thanks.

[Nasir]

Thanks, Steve.

I've found this online calculator: http://calctool.org/CALC/phys/optics/f_NA

Does this look correct? I've used Focal Length = 16 inches, Aperture diameter = 92mm (as measured from my lens) and the f# on this calculator comes out as 4.4. Does this mean my lens max aperture is f4.4 instead of f4?

[Steven Tribe]

Take the focal length of the 3A has “around 16 inches”! But it could be a little less or greater than 16”

Dallmeyer used the optical quality glass they could get hold of. Even within a batch of glass there will be slight variations in the refractive index and differences will be even greater through decades as sand deposits are not homogenous. Even though the qualities of the glass varies a little, the optical design is robust enough to retain the properties of the “3A”. The most obvious change would be in the focal length.

Remember the aperture diameter used in the simple equation is the aperture “seen” from in front of lens and not the internal physical distance.

[Nasir]

Thanks, Steven.

While we're discussing the 3A, I have a question about the rotating soft focus control on the rear of my version. When the rear element is screwed all the way in, the index screw is in front of the 4 notches. Is this zero soft focus effect? How does the soft focus scale work? 1 notch = least effect?

[mhayashi]

The belows are the measurements of 3A’s WHS.

F4 88.89mm
F5.6 64.63mm
F8 46.00mm
F11 32.11mm
F16 22.72mm
F22 15.91mm

I measured the WHS holes by vernier calipers.
The second decimals vary so round to the first decimals.
I hope the measurements help you.

[Steven Tribe]

Thanks, Steven.

While we're discussing the 3A, I have a question about the rotating soft focus control on the rear of my version. When the rear element is screwed all the way in, the index screw is in front of the 4 notches. Is this zero soft focus effect? How does the soft focus scale work? 1 notch = least effect?

From memory - screwed in is the sharpest. There are 4 “positions” as you unscrew though 360 degrees. Of course you can use intermediate positions to achieve effects based on previous experience. And you can further increase softness by going beyond a single unscrewing rotation.
The later “turn the barrel” 3A design has no “compass” markings.

My estimate for the F8 was 4.69cm and our Tokyo colleague measured a real F8 stop diameter to 4.60 cm!