Orientation of the meniscus lens in a simple box camera

james orme · Jun 21, 2020

Great Thanks ! Will order now- they are really cheap. Going to try and build a large Brownie type box camera around for a 5" x 7" type of negative... trial and error of course.

james orme · Jun 21, 2020

Just bought: '40mm Dia. x 238mm FL, Positive Meniscus Lens, Grade 1'. Wish me luck, not sure how big the box will be... Thanks !

james orme · Jun 21, 2020

If anyone can let me know if this experiment will be an obvious failure before I try it out please let me know. I'm new here (and hope it's ok to post on this thread...)

Donald Qualls · Jun 21, 2020

Nice! This one should be just about right for a 6x9 "box camera" -- put an f/16 aperture and spring rotary shutter in front at the correct distance (10-15 mm is likely a good guess, but there's a formula around somewhere for the optimum location and size) and you'll have recreated the sophisticated optics of the Ansco Shur-Shot Jr. (and most of the other 6x9 box cameras ever made). A pair of these, concave toward each other, with the aperture halfway between (again, there's a spacing formula around for this "periskop" type lens), and you'll have what a Speedex Jr. used.

Donald Qualls · Jun 21, 2020

james orme said:
If anyone can let me know if this experiment will be an obvious failure before I try it out please let me know. I'm new here (and hope it's ok to post on this thread...)

That's a pretty long lens, but then again, it should cover 8x10. Stop to around f/16, and expect shutter times around 1/5 second with enlarging paper or ortho lith film. No obvious, immediate disasters that I can see. Set up hyperfocal, and you can have all the fun that's legal in your jurisdiction and involves photo chemicals.

james orme · Jun 22, 2020

Great, thanks- thought this project might just be a fool's errand. 8x10 is fine by me ! I'm not very technically minded but will probably try it out with a cardboard box to start off. But for the build I will probably break up a Brownie 2A casing and stick the lens area on the front of a wooden box so I don't have to worry about all the measurements and mechanics- and also be able to see the viewfinders. In theory at least...

Donald Qualls · Jun 22, 2020

If your ratio of film diagonal (about 300 mm for 8x10) to lens focal length is close to that of the original camera, the viewfinders might actually give a reasonable approximation of what will go on your film/paper.

james orme · Jun 22, 2020

Time will tell how big the negative (paper) will need to be- as the current images are 2.5" x 4.25" I will cut the negative (paper) to a 9:13 ratio. Doubt the lens will come some kind of holding...gonna be tricky. Will let you know how I get on. Thanks again.

Bud Hamblen · Jun 22, 2020

If the lens is behind the aperture stop the front surface is concave (Wollaston landscape lens). I've got an Ansco Buster Brown like that.

Nodda Duma · Jun 22, 2020

james orme said:
Just bought: '40mm Dia. x 238mm FL, Positive Meniscus Lens, Grade 1'. Wish me luck, not sure how big the box will be... Thanks !

link to the lens you bought and I’ll model it up in zemax and tell you what your aperture stop to lens distance should be.

edit: found the lens but they didn’t give any info to model with lol.

Anyways, place the stop in front of the lens about 1/5 to 1/7 the focal length of the lens. Stop the aperture down to f/22 - f/32. The distance corrects for coma and balances astigmatism...fine-tune distance to minimize and adjust the “swirl” at the edges within that distance. It’ll go from sagittal (ugly) to tangential (swirly). Outside that range coma blows up as does astigmatism..starting to affect image quality closer to the center. The meniscus shape corrects spherical aberration. Reducing the stop helps with color and sph ab.

james orme · Jun 22, 2020

Thanks Bud, Nodda.

I can manage 1/5 to 1/7 tip I think- it means I can't break up the Box Brownie 2A and use the front of it (fixed onto a wooden box) as the aperture holes are fixed in space in relation to the lens.. Also I think the smallest aperture, of the 3 options, is supposed to be f16 (could be wrong). Colour is not an issue as it image will be b/w (or blue and white). I will have to search your technical terms :0 ...

Donald Qualls · Jun 22, 2020

The f/16 aperture for the original lens (120mm?) is going to be much smaller for the longer focal length. If my guess is right on the original focal length, the same aperture stop will give approximately f/32 with your longer lens, which might be a little small (you can use the larger apertures, if needed). With the lens out of the Brownie front end, you can directly measure the aperture and calculate your f ratio.

james orme · Jun 22, 2020

As I am using photo paper and a very long exposure I imagine a small aperture wouldn't be a problem (and might help with overall focus). It sounds like I will have to move the aperture further away (outwards) from the lens which is a pain as I will have to build something, rather than using the brownie mechanics.

Donald Qualls · Jun 22, 2020

Yes, you'll need to about double the distance between lens and stop. You bought the 40mm diameter, 273mm fl lens, right? You may be able to make a lens mount and spcer from a PVC pipe coupler and a short piece of pipe to slip into it to hold the lens. A 40mm diameter lens should fit into a 1 1/4" pipe size coupler...

james orme · Jun 22, 2020

Yes, that's the one. Think I can save the casing/viewfinders/switch of the Brownie. So if I have a 238mm FL I divide that by (approx) 6 (?) to get the distance from the aperture to the lens = 39.7 mm. That means I can remove the aperture 'dipstick' from inside the camera and stick it on the front - slightly raised. Think in general the margin of error is pretty massive...
Thanks

Nodda Duma · Jun 22, 2020

Color correction does matter, as Panchromatic B&W film sees the full visible spectrum. Lack of color correction means different wavelengths do not focus at the same distance. Instead of color fringing as for color film, lack of color correction for B&W means transitions from light to dark areas are not sharp and distinct... it looks unpleasantly soft like a slight defocus. So you’ll need to stop it down as suggested to help that.

so using the original aperture is probably the way to go.

Tolerances will be tighter than you think, albeit “loose” on an optical design scale. You can help dial in the spacing by getting a threaded male/female set of suitable pipe. Mount the lens in one of them, and you can fine-tune the distance by screwing the lens/barrel in and out.

james orme said:
Thanks Bud, Nodda.

I can manage 1/5 to 1/7 tip I think- it means I can't break up the Box Brownie 2A and use the front of it (fixed onto a wooden box) as the aperture holes are fixed in space in relation to the lens.. Also I think the smallest aperture, of the 3 options, is supposed to be f16 (could be wrong). Colour is not an issue as it image will be b/w (or blue and white). I will have to search your technical terms :0 ...

james orme · Jun 22, 2020

Thanks, I knew I was out of my depth... so I stop down by using a smaller aperture I guess.

Donald Qualls · Jun 22, 2020

Yep, you should be within tolerance anywhere from about 33 to 48 or so mm between lens and stop. Ideally, you'd want the shutter and stop at the same plane, else the shutter opening forms a secondary stop -- in your case, too close to the lens. I was suggesting you mount the lens further back than the original. Most box cameras had the lens mounted to a literal board, and the thickness of the board determined the spacing between lens and stop (lens on the back, stop and shutter on the front).

Nodda Duma · Jun 22, 2020

james orme said:
Thanks, I knew I was out of my depth... so I stop down by using a smaller aperture I guess.

no worries.. I added a comment on fine-tuning spacing above. Note the *optimal* distance is somewhere in the range of 1/5 to 1/7... not all-inclusive. The actual distance depends on specifics of the lens, which are unknown. Just make sure you can accommodate accurate adjustment within that range, and adjust accordingly once you can view the image on a ground glass.

james orme · Jun 22, 2020

Great. If I understand correctly, the shutter and stop remain in situ and the only thing I need to do is draw the lens back into the camera- sounds like a perfect solution !

Donald Qualls · Jun 22, 2020

james orme said:
Great. If I understand correctly, the shutter and stop remain in situ and the only thing I need to do is draw the lens back into the camera- sounds like a perfect solution !

Exactly. And if you want adjustable focus, you can make nesting boxes that slide one into the other -- or you can use that to hold your photo paper in place.

james orme · Jun 22, 2020

Thanks Nodda- sounds like I need to have that adjustability factor...

james orme · Jun 22, 2020

Donald that's great ! The lens can stay in place then. All I've gotta do is build the damn thing...

james orme · Jun 22, 2020

Thanks everyone for your contributions - your time and expertise. I realise that I have missed some things here and there but will see how I get on with the project, either way it has been a pleasure. Will be in touch in a couple of weeks or so... wish me luck !

Nodda Duma · Jun 22, 2020

Nice... the most important thing is to do it!

james orme · Jul 3, 2020

Will update my progress tomorrow with some classic mistakes and a bit of bad DIY...

(I love this forum)

Orientation of the meniscus lens in a simple box camera

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