Achromatic doublets, coverage and resolution

[genotypewriter]

I suspect that, with a simple, inexpensive doublet of unknown charactaristics, you're going to run into other resolution limits long before you hit the diffraction limits. The diffraction limits will depend in the wavelength of light, the distance you're focusing at, etc. And rather than being a hard "limit", it will just be a judgement call of "is this an acceptable size for an airy disc, depending on the degree of enlargement (if any), or not?"

Hi Mark,

As I mentioned in post #3, I'm not going to enlarge the images. So, approximately 11.8 lines/mm (which I consider as the naked-eye's resolution for my purposes) is limited by diffraction with ~550nm light at f/125. Yes, there's always a bit of give or take due to one parameter (e.g. wavelength) and but another parameter might take or give (human vision) too. At the end of the day it's an approximate value but it's still a usable value when planning things. Same could be said about the validity of wind tunnel simulations in the real world but people still do them

As for the doublets I had in mind, by no means they're inexpensive. One of them I have in mind is around 140mm in diameter, coated, used for close-up work and costs over 2 grand... another reason for me to deliberate over this to this extent.

[Øyvind:D]

As for the doublets I had in mind, by no means they're inexpensive. One of them I have in mind is around 140mm in diameter, coated, used for close-up work and costs over 2 grand... another reason for me to deliberate over this to this extent.

SURPLUSSHED.COM: Achromat & menisc: 2 of each will not break your wallet! To get them mounted on each side of aperture might ;-) SK Grimes can help you! Or buy a casket lens set, mine fit perfectly to a 150mm f4.5 Tessar-shutter.
L5630 ACH ø22.4mm 1531 Y $7.00: 765mm f/32
L5931 PMN ø30.0mm 1357 Y $4.00: 678mm f/22
L8093 PMN ø42.0mm 2000 Y $4.00: 1000mm f/25
L8112 PMN ø30.0mm 1000 N $4.00: 500mm f/17

[genotypewriter]

SURPLUSSHED.COM: Achromat & menisc: 2 of each will not break your wallet! To get them mounted on each side of aperture might ;-) SK Grimes can help you! Or buy a casket lens set, mine fit perfectly to a 150mm f4.5 Tessar-shutter.
L5630 ACH ø22.4mm 1531 Y $7.00: 765mm f/32
L5931 PMN ø30.0mm 1357 Y $4.00: 678mm f/22
L8093 PMN ø42.0mm 2000 Y $4.00: 1000mm f/25
L8112 PMN ø30.0mm 1000 N $4.00: 500mm f/17

Thanks. I've already experimented with some positive meniscus lenses... 72mm diameter 1000mm focal length ones. I tried using a stop with a single lens only and it improved the sharpness off-axis a lot. When I combined the two with the backs reversed (with some gap in between but without any stops), I didn't find them producing any better/larger image circles than single element. With achromats I expect the same experiments to give better results. Hope I'm on the right track.

[Øyvind:D]

I tried using a stop with a single lens only and it improved the sharpness off-axis a lot. When I combined the two with the backs reversed (with some gap in between but without any stops), I didn't find them producing any better/larger image circles than single element.

I think you need to stop down to see difference. Try this site http://translate.google.no/translate...avant-1900.HTM

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