thickness of waterhouse stops

[rippo]

so i'm finally getting around to building my own lenses. all based on the 'Primitive Photography' book's designs, although i've realized after building an 8x10 camera that it's more fun and efficient to put these funky things on my Toyo instead. currently i'm working on a 300mm single-element landscape lens, just to get my chops back in shape.

so here's my question. this lens will have various stops that fit over the end, as a sort of lens cap with a hole in it. does the material the stop is made of need to be super thin? the book recommends construction paper, which isn't very durable. if my stops are thicker, will i get defraction problems? how thick is too thick? i was eying some DVD case plastic, which is 1-2 mm thick. it's a pain to cut though, so i'm looking for alternatives.

or to ask the question a different way: how thick are waterhouse stops on an old brass lens?

[Ole Tjugen]

The thickness varies. Some are as thin as 0.15mm, others as thick as 0.75mm.

If you want to use thicker materials, you can bevel the edge of the hole - as on most of the thicker stops I have.

Diffraction doesn't depend on the thickness, but light fall-off and reflections do. That's the reason(s) for the bevelling.

[Pete Watkins]

I'm sorry if I've misunderstood your question but all the lenses that I've come accross that use/need Waterhouse stops have a slot between the lens elements where the Waterhouse stop slots in. For front mounting it sems to be a "suck it and see" senario, sorry.
Pete.

[rippo]

Ole: ok thanks, that was i guess was my real question, i just didn't know it: "is diffraction effected by edge thickness?"

i understand the reflections issue. not so sure about the light falloff. i understand that a stop that was a meter thick would cause some pretty serious vignetting. but is the difference between say .5 mm and 3mm going to make much difference?

Pete: i was asking about waterhouse stops as an example, because they seem closest to what i'm trying to do. they're holes, not irises. they're made from old-school technology. i'm not actually putting my stops in a slot. i just want to know thick they are, so i can decide what the general ballpark is.

basically, as with many decisions, it comes down to: paper or plastic?

i might just see what the local art-supply house has in terms of extra-thick poster board. more durable than construction paper, easier to cut than the plastic i've been using.

thanks!

[Pete Watkins]

Rippo, I got my wife to cut some apature holes in home made Waterhouse stops made of thin black card, no problems!
Pete.

[rippo]

i was concerned about the durability of the card, since it will be on the end of the lens rather than as a drop-in stop. however i just bought some posterboard on my lunch break and will give it a shot. it's not like i'm going to throw these around much, and i can always replace it if it gets bashed up too much.

[Randy H]

I made a set for a lens I sold some time back, and I cut them from 1/32 thick aluminum sheet. They worked very well. The aluminum gave the rigidity they needed, and I was able to calculate where hole "center" would be for the aperture. I also left a rectangular tab on the top with a hole in it and strung them up on a key ring.

[Gene McCluney]

Ideally you could cut your waterhouse stops from brass sheet. Then you can get some chemical blackening from a stained-glass supplies place to turn the brass mat black. I see brass sheet available in hobby-sized quantities at hardware and hobby shops.

[rippo]

thanks gene, interesting idea!

i have the patience of a ferret, so i will try the posterboard stops first. when they get all ratty i'll try the brass sheet instead. although something that fancy might make the PVC tube and surplus lens feel bad.

that really is a cool idea, especially the blackening. i would never have thought of that. i'll go check it out...

(later)

well the lens is done. it's mounted in the barrel, and i've cut paper stops for it. i can't use it yet. i've sent my packard shutter and a lensboard to a friend for drilling, and then will use Ash's packard technique to mount it. will be a few weeks before i can use it, but i've held it up to a copal #1 lensboard and focused, and it looks pretty good on the gg.

[John MacManus]

Hi Rippo:
I'm more than an "LF Greenhorn" and even worse building lenses! On the ones I've assembled in plumbing pipe (also inspired by Green's Primitive Photo book), I have used plastic sheet for the Waterhouse stops. It is Lexan from a report cover purchased at Stables business supply, with holes cut with an Olpha "compass" cutter. I don't think paper will stand up to the use, and brass shim isn't worth the trouble. I found that the stop had to be tight to avoid light leaks and so needs to be sturdy.

Best wishes with your assemblage ... John