Near infared Achromat used in visual scope?

After some more research, I arrived at the same conclusiion.
Thanks for the input!
Dave


Tim Killian wrote:
That's awfully large for a cemented lens -- I wouldn't bother with it.
Look around, if you really want to build your own refractor you can find
some decent, 100 mm visual spectrum achromats for $80-$100.

wrote:

Thanks for the responses.
The lens I'm refering to is described:

"This is a diffraction limited cemented doublet optimized for 1550nm.
It was designed to be achromatic from 1520nm to 1620nm. The clear
aperture is 105mm. 500mm Focal length. Anti-Reflection coating to 0.5%
of maximum reflectance."

Is that too far off for decent visual work?

Thanks again
Dave

Gary Burk wrote:

An "achromat" usually refers to a doublet lens that is well corrected


for

chromatic abberitions over a range of about 300nm, perhaps a bit


less. So

if an achromat is optimized in the near IR , let's say 800nm, it


would be

quite poor chromatically for use in the green-blue end of the visible



spectrum. However, it might well satisfy a visual user.
"david johanson" wrote in message
...

How would a "near infared" optimized achromat lens work as a


telescope

lens? Would the chromatic problems be "noticible" "nonexistant"


"horrible"

Thanks for any info
Dave