What is this?

[Stelex]

 

[pdeeh]

If it's got a fitment for a shoe, then it's an accessory 'finder.
On the other hand it looks like a linen proofer to me, and if so it'll be good for a negative or lf gg loupe

 

[Old-N-Feeble]

https://www.bhphotovideo.com/bnh/co...pi=1876,{creative},{keyword}&is=REG&A=details

 

[Mr Bill]

They call 'em linen testers, presumably to count threads per distance. But they sure are convenient and useful in photography. I don't use the base when looking at negatives 'cuz I'm worried about scratches.

 

[k.hendrik]

Thread counter, I use it with my Cambo 5x7 NOT on negs.
http://www.pcbsupplies.com/thread-counter-6-5x-20mm-by-carson-optical/

 

[Helinophoto]

I usually tape one of these to a makeshift ground-glass when adjusting my lenses.
Foldable, cost $3 in the local nick-nack store.

 

[Stelex]

Thanks guys, I wasn't sure what it was, it looked like some film magnifying glass. Got it in a film camera set that bought a little while ago, never figured out what it does

Cheers everyone.

 

[Luckless]

Also minor side note, they fold around more than shown in the original post. Or at least they're supposed to.

Handy little things. I have a similar one stashed in my backpack and have used it as a general magnifying glass for looking at all kinds of things. Had one for ages before losing it, and recently got a new one after I got into large format, with the plan of adding a dark cloth of some manner around it. Should probably finish that project at some point.

 

[AgX]

Also minor side note, they fold around more than shown in the original post.

Yes, the OP has put it up erroneously.
The rectangular frame is put on the subject ("linen") with the markings showing up, to serve as scale for the object ("threads").

Here it is called "threads counter".

I got to know such lens as a child, even before holding any camera, thuse there never was a chance to mix things up.

 

[Leigh B]

It's a linen tester, improperly configured.

You need to rotate the scale and the lens 180 degrees.

The scale sits on the linen with the markings up so they can be seen through the lens.

- Leigh

 

[Helinophoto]

I got into large format, with the plan of adding a dark cloth of some manner around it. Should probably finish that project at some point.

I can recommending folding it out like in the OP's photo (only 180 degrees, so that the folding stays in place and you can see the markings) and then simply clad the thing with black electrical-tape on all open sides
- apart from the bottom! .

Works a treat, only wished it had slightly more magnification sometimes.

 

[AgX]

I guess the cheapest loupe would be a defunct 50mm 1.8 lens out of the rummage box.