Achromat Vs Semi-APO Vs APO - What's The Difference?

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Re: Achromat Vs Semi-APO Vs APO - What's The Difference?


Post by jbelden »


Thanks for the links, good reference material to read up with not just one beverage but a couple. My only experience in optics at the amateur level is I only made a dozen parabolic mirrors for Dobs and Newts, largest was an 18".

BTW, I see your in HI, I used to do projects for HECO so I made several flights to HI from ATL back in 2006 - 2012.

AP1600 GTO AE, AP1600 GTO, Paramount MX+, TOA130, 20" Obsession with ZOC mirror, Meade 14" ACF F8, STL6303E, ST8XME, STXL6303E, FLI Kepler KL400

Co-owner of RCOS 16" (Snowflake, AZ) :observatory:
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Re: Achromat Vs Semi-APO Vs APO - What's The Difference?


Post by j.gardavsky »

A triplet, or doublet plus singlet, allows to make a well corrected light gathering lens system with a higher speed, than the ED doublets.

The doublet plus singlet became a widespread design for the fast (F/4) objectives in the premium binoculars.
With the increasing aperture, it is the 4 wide spaced lenses design, 2 of them ED, like in the Leica 82mm APO Televid.

Otherwise, even an achromatic doublet can offer an "apochromatic performance" in the eye relief space behind the eyepiece, when the eyepiece is overcorrected to flip the focus deviations on the short wavelengths, and in the way like the yellow curve in the graphic I have posted before.
But even then, outside the range of the three crossings, the deviations will be much larger if compared with a true APO.

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Re: Achromat Vs Semi-APO Vs APO - What's The Difference?


Post by John Donne »

Although coming very late to the table, three fine courses already consumed and the wine bottles empty, I have found this thread a pleasure to consume.
I have nothing to add but my thanks to the chef, Mr JT, who set the table for this conversation.
Clear skies to all !
SCOPES :ES127 f7.5, SW100 f9 Evostar, ES80 F6, LXD75 8" f10 SCT, 2120 10" f10 SCT, ES152 f6.5.
MOUNTS: SW AZ/EQ5, MEADE LXD75, CELESTRON CG4, Farpoint Parallelogram.
BINOCULARS: CL 10X30, Pentax 8X43 DCF SP, Oberwerk 25X100.
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