catman161 Posted March 3, 2012 Share Posted March 3, 2012 Hey guys when it comes to refractors could someone tell me the difference between: Apo and achro And Doublet and triplet Thanks Felix Link to comment Share on other sites More sharing options...
Guest Kheldar Posted March 3, 2012 Share Posted March 3, 2012 Not an expert, but my understanding is this. It's all about focusing the different wavelengths of light at the same point so you don't get chromatic aberration. Refractors struggle at doing this, reflectors don't. (Simple physics about the difference between refraction and reflection of wavelengths of light.) Doublet and triplet, well it's the number of pieces of glass in the objective lens. Three is better than two however a cheap triplet is worse than a good doublet. Achromatic to a scientist means two colours lie in focus, Apochromatic means three : not sure how best to explain it, but Apo is better than Achro. Triplet and Apo also mean £££££ Link to comment Share on other sites More sharing options...
catman161 Posted March 3, 2012 Author Share Posted March 3, 2012 Thanks Stephen Link to comment Share on other sites More sharing options...
Brantuk Posted March 3, 2012 Share Posted March 3, 2012 Stephen's about nailed it. Doublets tend to focus red and green together others red and yellow iirc, and triplets focus RGB in the same plane. Trouble is you have to bend the glass a lot to get it to do that due to the different wavelengths of the colour. That introduces coma, cromatic abberation and curved fields which have to be corrected. The CA and coma is corrected by figuring the glass. Field flateners deal with the curved field. Triplets are 4x-5x the cost of equivalent doublets. Link to comment Share on other sites More sharing options...
catman161 Posted March 3, 2012 Author Share Posted March 3, 2012 (edited) Crikey 4 to 5 times more expensive?! That's something I will just dream of then. In the meantime I will keep saving for the starwave ED80. I really like the look of them. Thanks for the info Kim. Also this is my 500th post-that happened quickly Edited March 3, 2012 by catman161 Link to comment Share on other sites More sharing options...
Doc Posted March 3, 2012 Share Posted March 3, 2012 Congratulations on your 500th post Felix. Link to comment Share on other sites More sharing options...
Brantuk Posted March 3, 2012 Share Posted March 3, 2012 Lol happy 500th post Felix Link to comment Share on other sites More sharing options...
Brantuk Posted March 3, 2012 Share Posted March 3, 2012 I forgot achromatic - these lenses correct for chromatic and spherical abberation only. Here's a link that explains it pretty well: http://en.wikipedia.org/wiki/Achromatic_lens Link to comment Share on other sites More sharing options...
catman161 Posted March 3, 2012 Author Share Posted March 3, 2012 Thanks for the congrats mick and Kim. Thanks also for the link Kim Link to comment Share on other sites More sharing options...
Guest Altair Posted August 31, 2012 Share Posted August 31, 2012 If it helps, achromats can provide very good levels of colour correction and show a flatter field. The longer the focal ratio, the better they perform. In fact an f11+ achromat is a good scope for general observing, while still being portable and practical. These longer FL optics are much easier to make at a good quality level and consist of crown and flint elements in doublet configuration with an air space between them. I am trying out an f11 4" achromat at the moment which offers good enough colour correction and star image to add to our product line. By request, it has been optimised for best correction in green wavelengths, rather than red, which is what most achromat manufacturers seem to do. Green is the wavelength the human eye is most sensitive to, so the image appears sharper than achromats of similar focal length which I've used before. I'll bring it up to Kelling Heath and put it on our stand for folks to check out. Its quite an impressive scope being quite long at F11 - it looks like a "proper telescope" as one customer in our shop put it. Retro, but a surprisingly effective visual observing tool, and it could still be a viable product in this new world of super fast APOs with exotic glass which is mainly driven by the need for portability and fast FL for imaging... Nick Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now