Diy 6" apo

[Terry B]

These lens cells were brought to my attention. Might be of interest.
-about 1/2 way down the page.
http://www.owlastronomy.com/specials.htm

[traveller]

They are also for sale on ebay (http://www.ebay.com/itm/REFRACTOR-LENS-ASSEMBLY-6-INCH-ED-OBJECTIVE-OPTICS-F-2-F-4-USED-GREAT-COND-/300685543680?pt=US_Telescopes&hash=item4602414900)
Sounds almost too good to be true. What I want to know is: who was the previous owner (ex-military I suspect, had a rough life, judging by the dings on the larger cell barrel).
I'd be more interested if they have a test report backing their ED and f ratio claim.
Bo

[dannat]

these I'm sure were for sale at surplus shed as well -they aren't APO, a few on CN tried to get them working (i think they were from an aerial camera)
a few tried & most failed, the focus distance tolerances were very small

[Wavytone]

If those focal ratios are correct - and quite likely are judging by the curvature visible on the photos - these things are CONDENSER lenses from projectors.

They certainly are not suitable for imaging, nor as finders, and nowhere near good enough optically for use in telescopes. Secondly, it appears they were part of a more complex optical assembly so on their own as-is, they are highly unlikely to be corrected to give a sharp or flat image without the rest of the optical train.

There's an fair bit of mis-information on surplus websites including that one, most of it intended to con the unwary into buying something that is basically useless.

[rjbruce]

By the old saying, if something appears too good to be true, it generally is. If someone is selling a 6.1" APO (assumed by the ED element) for only US$199 then I would be very wary.

[clive milne]

ED doth not an apo make.

2c

[rjbruce]

So very true Clive