waterhouse stops for Euryscop(?)

**Andrew ren** · 17-Mar-2010, 17:43

Greetings all,

So, I got my first brass from my friend. I was told it is an Euryscop(?), not sure what that means.

Now, I want to make some stops myself. I might need a couple more stops, beside the wideopen. f11 and f45.

I was told its a 10" brass, my measuring turned out it is 12"(300mm) from the waterhouse slot to the GG. I made a card board cut. the inner diameter is about 45mm.

do the math, 300 x0.93 / 45mm = f 6.2.

so what will be size of the f11 and f45, I knew the 1.4 standard was not been used @ 1890's.

Cheers

Andrew

all right, can i just simply do this?

f11-- 279/11
f45-- 279/45

**eddie** · 17-Mar-2010, 19:38

the square root of two is the number you need for f stop. it has nothing to do with the year. twice as much (or less) of light is exactly that. you are on your way. 1.4141135

i am not sure what the ".93" is in your above equation......find the wide open hole in the lens (the smallest part of the lens) . this is about f6+ or so as you said. divide that number by 1.41 and you will have half as much light.....

**eddie** · 17-Mar-2010, 19:47

okay...i looked at all the photo....

i get f6.8. if wide open is 44 mm then one stop down will be 31.2mm at about f10 or so.....

great lens BTW

**Andrew ren** · 17-Mar-2010, 19:50

eddie,

thanks.

I grab that from somewhere I can't remeber, literally it says that the real focal is shorter than the labelled one, caused by some sort of distortion/diffusion. its about .93, that's the number.

I got numbers, hole size wise.

f11-- 300x.93/11 = 25mm
f45-- 200x.93/45 = 6mm