Okay, I'm ordering glass from Surplus Shed. Designing a single-element lens, to be used on 8x10 with no aperture. Need some help deciding what, though. Magnifying glasses are double convex, but Surplus shed has positive (and negative) meniscus lenses, achromatic, etc, etc. What's a good choice? And is there any way to predict coverage? Anything else I should be considering, too?

Thanks for any help.
Scott