DIY macro lens for 10x8

How can i make a macro lens for a 10x8 wet plate camera?
I heard there is a place that sells cheap lenses but i forget the name, something 'shed' it is called.
I tried putting some old 35mm condenser enlarger lenses together and the effect was ok but only worked on one point eg the tip of a pen. I would like to photograph stuff on a table, eg 50cm x 50cm. Would i need a meniscus lens + 2 planoconvex lenses stuck into a tube?
Or something else?
Thanks,
Mark

Why make a crappy improvised lens when you can buy a good one? Why handicap yourself?

Process lenses aren't that expensive. Since you're shooting wet plate you may not need a shutter.

At what magnification do you want to work? How much extension does your camera have?

If you answer these questions many of us will be able to suggest process lenses that will work well in your situation or to tell you that your combination of desired magnification and extension is impossible.

If you can't find a macro lens already on surplus shed...

Do you know what focal length you need? Maybe equivalent to your film diagonal?

Find two meniscus lenses which are the same, and each being double your desired focal length. They should have a little bit of thickness to them...ie not too thin. Flints are a better choice but two crowns (ie BK-7) will work. Meniscus achromats would be awesome for this. You are going to place them in a barrel with the concave surfaces facing each other separated by a distance that gives you a good image (should be a couple inches or less). But first, make an aperture of about f/16 - f/22. Might be able to get faster but that depends on the glass type. Put that aperture in the barrel between the two lenses. Then adjust the spacings until you have good image. Keep the spacing from each lens to the aperture in the center roughly the same.

Film plane should be roughly same distance to the lens as the lens is to the subject for sharpest image and for 1:1 mag. I think the back focal length will be double your effective focal length (with a factor for lens refractive index) in this case but I don't have the equations in front of me. As you move closer to the subject for higher magnification you'll need to move the film plane farther away.

That should give you a workable anastigmat.

Hope this helps.
Jason

Oh and spray paint the inside of the barrel flat black