Some tips on Waterhouse Stops manufacture!

[Steven Tribe]

Up to now, I have always been able to find old waterhouse stops that could be modified to fit lenses which needed them.

But now I have a Euryscope VIIa, 8 which needed some and nothing was available.
All the brass/bronze plates I had were a little on the thick size so I looked around for alternatives.

Some years ago, I built a massive square trough for my wife's hobby - basketry. The willow has to be soaked for weeks to be flexible. This was built in building quality zinc - obviously with some metal additives to stop oxidation.

So I used the remaining material to attempt some waterhoiuse stop manufacture.

This quality zinc was easy to cut, drill and file - without getting bent at the edges.
It was much easier to work with compared with aluminium of the same thickness.
It appears to bond well to mat black enamel.

Now I was working without a dummy stop, so I have a few comments that might be useful for others:

Cut blanks with the right width.
Check these fit.
Do not worry about the vertical position of the hole - my experience is that this is best adjusted after the hole has been made.
Make a central vertical mark with a sharp hobby knife.
Drill out the various holes in the blanks - making about 1-2mm undersize. The hole will not be completely round with ordinary drill tools.
File the holes (chain saw file?) and make completely round using appropriate wet/dry wrapped round a finger or round object. A slight bevel towards the front of the lens can easily be added.
Make ink marks on the largest new stop that correspond to the "framing" ring diameter in the stop frame.
Remove gradually material at the two corners at the end of the largest stop until the two marks can be seen to just touch the top and bottom.
Repeat for the stop blanks. Do not use the first as a template for the others as the angle of cut of the edges and the precise width of the individual stops will have surprisingly large effects on an exact central position.

I also discovered that you should not rely on the engraved F value for calculating the exact iris diameter without stops. This Euryscope says F18 - but the basic iris diameter corresponds to F16 - there must have been a large waterhouse stop which corresponded to the F.18.

As the strength of this material obviously less than brass, I have made the stops so that there is quite a large area at the top to grab hold of.

[DarkroomDan]

Thank you for the informative post. I have one lens I need to make some stops for. Reading your post has inspired me to get to it.

Dan

[Leigh]

This Euryscope says F18 - but the basic iris diameter corresponds to F16

The f-number is the ratio of the focal length to the diameter of the entrance pupil, not to the physical aperture diameter.

The entrance pupil is the aperture viewed through the front lens elements.

- Leigh

[Leigh]

You can buy shim stock in small sizes and virtually any thickness quite inexpensively in brass, stainless steel, and other materials.

Auto supply stores carry the more common types and sizes. You can find a large selection at McNaster-Carr www.mcmaster.com

- Leigh

[Steven Tribe]

Agreed about the availability of other materials. My point is that pure zinc sheeting(not galvanised steel!) is a very easy material to work with to create Waterhouse stops.

Measuring the optical width through the front lens still gives an F.16 result!

[Leigh]

Hi Steven,

Yes, zinc is soft and quite easy to work.

For the same reason, it may be less than ideal for an accessory that's subject to a lot of handling. It also oxidizes and deteriorates easily in its pure form.

But if it works for your application, that's great.

- Leigh

[vitality]

The f-number is the ratio of the focal length to the diameter of the entrance pupil, not to the physical aperture diameter.

The entrance pupil is the aperture viewed through the front lens elements.

- Leigh

Is there much difference if are talking about normal or telephoto lenses?

[Steven Tribe]

High quality zinc sheeting produced for the building industry is a very different "kettle of fish" from the non-specific zinc we all remember as being brittle and with a powdery oxide coating. It is used as roofing and facade panels.

The first photo showed a section of the zinc that "tested" outside for 3 years.

[Paul Fitzgerald]

"The entrance pupil is the aperture viewed through the front lens elements."

"Measuring the optical width through the front lens still gives an F.16 result!"

That is NOT how Voightlander did it.

Put a transparent scale in front of that lens, as close to the glass as possible, and view through from the rear to adjust for the optical difference.