Wait a minute. What the—??? Shutter thread conundrum.

[chris_burck1]

I purchased a

lens recently

which has led

me in

direction I

didn't expect.

It's an Ilex. In

barrel, later

vintage (I

think--it

"feels" '60s or

'70s vintage,

side and

black). No

diaphragm. It

is marked

simply: "6⅜”

f:4.5 ILEX

PARAGON

MADE IN

U.S.A." No

other

markings of

any kind, not

even a serial

number. The

rear lens cell

has the

numbers

164.4

scratched into

the outside

perimeter

{presumably

the back

focus). A

cursory test

on the ground

glass shows

this thing to

be *really*

sharp even at

its fixed f:4.5.

 

Anyway, I

have a copy

of their Series

S Caltar in

Acme #3, and

took a small

gamble on

this Paragon,

thinking the

cells were

almost sure

to go right

into the

Acme. Boy

was I wrong.

Turns out that

the Acme

seems to

have a

different

thread pitch

on the front,

than the rear.

The Paragon

cells are

completely

interchangeable

on the barrel,

and the rear

cell screws

right into the

shutter (and

so would the

front, if the

rear of the

shutter had

enough

depth). But

neither

Paragon cell,

nor the rear

cell of the

Caltar, will

screw into the

front of the

shutter.

 

I don't recall

ever running

into a

situation like

this before

(though, by

the same

token, I don't

know that I've

ever tried

swapping

cells around,

either), or

even seeing a

reference to

it. Certainly, I

have

observed that

some shutters

have a

different

diameter at

the front than

at the rear.

But different

thread pitch?

Is this. . .

normal?

[dave_s]

<p>The <a href="http://www.skgrimes.com/library/used-obsolete-discontinued-shutters/ilex">S K Grimes site</a> says a #3 Ilex Acme shutter should have 48 tpi threads. <a href="http://www.sizes.com/tools/shutter_photo.htm">www.sizes.com</a> says 50 tpi, which is a less common pitch, so I wonder if it is accurate. (There are probably other sites on the web with Ilex shutter data, but those are the ones in my bookmarks.)</p>

<p>Neither site says the front and back thread pitch should be different, so perhaps some special mount was made for the shutters which were made to fit Caltar lenses. There are people here (and on the other photography forums) with considerable knowledge of arcane stuff like this, so message them directly if they don't see this thread.</p>

<p>Your lens sounds like it was designed for recording X-ray phosphors or oscilloscope screens, but you probably know that. The '164.4' will indeed be the precisely measured focal length. I understand those lenses can have limitations when they're repurposed for general photography. I can't speak from experience-- never used one.</p>

[thirteenthumbs]

<p>There is little information on Ilex lens. The one you have in barrel is most likely an industrial or medical copy of the lens. Many manufactures use different mountings for the different applications, consumer, medical, scientific, and industrial applications.<br>

The thread pitch can be determined with a fine graduation ruler or caliper and a calculator. Measure from the inner most thread peak to the outer most thread peak. Count the number of peaks in that distance. Divide the distance of the thread peaks by the number of peaks. This is the threads distance. Divide 1 by the threads per inch (tpi) of published thread pitch to get its thread distance. 1/48=0.02083, 1/49= .020408, 1/50=.02. Due to tolerances of threads a 48tpi might measure 49tpi or 50tpi but not 55tpi or 40tpi.</p>

[jodys]

<p>It sounds like your Acme shutter was specially made for a situation where they didn't want people to be able to mix up the front and rear cells. I have a couple upstairs, I might have a look at mine to see if that's common?</p>

<p>As for the 48-50tpi conundrum, they are completely interchangeable on a short length of threading such as a lens cell. There is no way you could even measure the difference without some specialized gear. If you hold the front and rear cells side-by-side, you should see a rather pronounced difference in the pitch of the threading, otherwise the cells would risk threading into the barrel/shutter and getting stuck.</p>