Carl Zeiss Perimetar and its huge flat Ziggurat rear glass blocks

[Mustafa Umut Sarac]

205709205711

I found these technical drawings.

I want to ask what are the uses of rear , ziggurat like flat glass blocks ?

Can we make a lens out of these kinds of flat blocks ?

Thank you,

Mustafa Umut Sarac
Istanbul

[Ethan]

I’ve never seen that lens before, and have no clue what that giant block of glass does, but my understanding of optics is that the curvature of the elements is very important for making the lens work. As far as I know, flat glass elements don’t affect the image projection, which is why a filter can be placed in front of a lens without affecting it.

[Steve Goldstein]

I think the Gigapixel lens also used a thick glass plate. My guess is it's to do with color correction. Perhaps Nodda Duma will chime in here, he's a professional lens designer when he's not making dry plates.

[Jim Jones]

Mustapha -- All of the surfaces of the three elements in the rear group of the Perimetar type #3 lens are slightly curved. The front surface of the last element of the type #2 lens is slightly curved, but the rear surface is flat. Perhaps Nodda Duma will provide much more authorative than I can.

[Nodda Duma]

Those aren’t blocks. Those are optics!

I’d bet a beer it’s used primarily for correction of lateral color but also fine tuning field curvature / astigmatism.

As Jim indicates, replicating them would require the original lens drawings and/or prescription to select the proper glasstypes, thicknesses, radii of curvature, glass quality, etc etc (the image appears to provide estimates)

[reddesert]

The column of "R1 ... R9" values in the first picture gives the radii of curvature of the lens surfaces (note there are two entries for R8, so ten independent surfaces). Negative means concave, positive convex, for a ray traveling left to right. Only the last value is infinity, so only the last surface is truly flat. A couple of the other surfaces have a large radius, so are only slightly curved.

A plane parallel plate, like a filter, introduces a focus shift but little aberration for the on-axis (perpendicular) ray. However, the aberrations it causes get much stronger for faster beams and for larger off-axis angles. So that would have been factored into the lens design.

These issues are generally pretty irrelevant for putting a filter in front of the lens, but they could matter more for a filter used behind the lens (because, the beam behind the lenses is more strongly converging).