FZ1

Agreed. I'm skint AND braindead, so I've got no chance ............ Jon

Oops, sorry John - just my reading of the discussion so far with no intent to cut it short. Let’s just call it a mid-discussion summary from just one point of view! Everyone Please crack-on with adding any additional value ! Cheers Jon

Thanks for all the info folks. The tech info is really what I was after, and I got that in spades, but discussion about different scopes is always interesting (Like I said in the OP, I'm not looking to buy, I'm just interested in the science, terminology and theory) In summary [1] for anyone browsing this thread in future: In terms of use, it seems that there's not a lot of difference in visual observing between a a good Achro doublet and an Apo triplet., so the definitions of each are less relevant or meaningful. However, for astro photography, long exposures with CCD or CMOS sensors are more sensitive than our eyes, so GENERALLY a triplet Apo will be better colour-corrected and therefor help give better photos. [1] - This is a generalisation of all input above. Everyone knows someone who paid 30-bob for doublet that takes better photos than the Hubble or knows of a £5,000 Quad that is rubbish .... but this is a summary! Cheers and Happy Christmas Jon

Thanks very much for the info Dave and John and thanks for the detailed explanation Vlaiv; very helpful I learn loads from reading all the posts in these forums and its rare that I end-up having to ask my own questions (and that's usually because I haven't spotted what I need in the search results) Thanks again gents, much appreciated. Jon

Quick question: I thought that an APO was a device that can bring all parts of the visible spectrum to focus at the same point. Received wisdom suggests that this can only be done with a triplet lens. However, I've seen adverts for Doublet APO refractors, so how can a doublet achieve Apochromatic results rather than the more usual Achromatic for a two lens system? And if its genuine APO performance, why does anyone bother buying a triplet? Any enlightenment will be much appreciated. Thanks! Jon P.S. I'm not buying, just interested.

Thanks for the tip - just watched it. Same for me with the landings of this and Elon Musk's one! Jon

Hi Joel, Just for info, there is a separate "Wanted" forum, so you might get more luck in there! Cheers, Jon

Darn it (Darn? Socks? .... I'll get me coat)

Thanks gents, much appreciated. Jon

Thanks Magnus, much appreciated. Good point about "which wavelength". Given that the wavelength of visible light is (about) 0.4 to 0.7 micrometres, presumably the figures for red and blue light may be significantly different, so I assume there's an agreed standard. Jon

After a bit more searching, I found an answer that works for me (and answers my own question), but in case anyone else is interested ............ This thread from 2015 has a simple explanation and also clarification about Lambda and RMS values. It also has a simple explanation of the Strehl ratio as a bonus! cheers, Jon

Another basic question! I see things like 1/8th wave or 1/10th wave in high end scope specs. I get the idea that the higher the denominator, the better the optic, but please can anyone explain what it means? (or provide a link that does). Thanks, Jon

FOUND Please close

Hi Martin, I'll have these if still available please , coz I still have the mount! Thanks, Jon

SOLD - COMPLETED