[LowVoltage]

The situation: I stumbled on Surplus Shed, a seller of used/overstock lens elements, lens blanks, and other flimflam. It seems they are a good source for a huge variety of different lens types - achromats, meniscus lenses, etc.

I'm hoping somebody can, at least, point me towards a resource for deciding what is the best type of simple, single element lens to get if I were to try building a Brownie-style box camera. And no, I'm not interested in simply using an old Brownie! (just to get that out of the way)

I'd like try taking some large format style images with printing paper, similar to a homemade pinhole camera, but I'd like to use a real glass lens. The problem is that I don't know what kind of lens to get. At SurplusShed.com they have a lens finder feature where you can dial in the type and focal length you desire, but I have no idea what type of lens is appropriate. I'd like to do something in the realm of 5x7 size images. The reason I cite Brownies as an inspiration is because they typically used simple meniscus lenses, but I have no idea what diameter or focal length to start with.

Does anybody know of some literature I can use for this project?

[RioRico]

I can't cite sources, just pass along some basics. The 'normal' focal length for any format is the diagonal of its frame. For a 5x7", that's 8.6" or ~220mm. A meniscus lens is totally uncorrected and will show aberrations. An achromat or anastigmat or other corrected lens will have less 'character' ie problems. You might check the Wikipedia entry on LENSES for more info.

To see how a meniscus performs on a dSLR, get a cheap bellows and a cheaper magnifying lens, one that focuses ~4in / 100mm maybe. To see what slight corrections can do, I'll put a Raynox DCR-250 (+8 dioptres) on a M42 bellows, then put a 49mm +2 dioptre lens on that, for a 100/3.5. Or I'll put an old Brownie or Polaroid lens (glued into a body cap) on the bellows.

[LowVoltage]

I can't cite sources, just pass along some basics. The 'normal' focal length for any format is the diagonal of its frame. For a 5x7", that's 8.6" or ~220mm. A meniscus lens is totally uncorrected and will show aberrations. An achromat or anastigmat or other corrected lens will have less 'character' ie problems. You might check the Wikipedia entry on LENSES for more info.

Thank you for this. I forgot about the simplicity of measuring a format's diagonal to find the so-called "normal" focal length, although I had already found a few sources quoting the 190-220mm range as being adequate.

The other issue is determining the appropriate distance of the lens from the image plane of the receiving material, i.e. film/paper/etc. and I can't seem to find any resource for this. I know having a ground glass or some other visual aid would help. This is meant to be a simple construction, so I won't be buying a ground glass. There are things to consider like circles of confusion and diameter of the lens, but I'm hoping there's a simple way to divine the distance of lens-to-paper because we're talking about a single element.

[rhodopsin]

... The other issue is determining the appropriate distance of the lens from the image plane of the receiving material, i.e. film/paper/etc. and I can't seem to find any resource for this. I know having a ground glass or some other visual aid would help. This is meant to be a simple construction, so I won't be buying a ground glass. There are things to consider like circles of confusion and diameter of the lens, but I'm hoping there's a simple way to divine the distance of lens-to-paper because we're talking about a single element.

distance from simple lens to focal point is same as focal length for infinity focus, frther to focus closer than infinity!