· Get a Cloudy Nights T-Shirt · Submit a Review / Article Click here if you are having trouble logging into the forums Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User You are not logged in. [Login] Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar Equipment Discussions >> Eyepieces Previous   Index   Next   Threaded   Pages: 1 Dreamon member Reged: 01/12/13 RKE       #5739709 - 03/17/13 09:49 PM Edit   Reply   Quote Quick Reply   Bright night, well I dropped my RKE, then gave it a shake or two. Something came loose and rattled abit. So, I disassembled it to find the rattle. The retaining ring needed some minor tightening is all. Looking at the lenses, the doublet surface facing the obj is "concave". Does this mean that the doublet might have a "negative" property? Does the concave surface, over plano for instance, add to the performance of the RKE? Post Extras:       izar187 Pooh-Bah Reged: 09/02/06 Loc: 43N Re: RKE [Re: Dreamon]       #5739768 - 03/17/13 10:11 PM Edit   Reply   Quote Quick Reply   It is not performance adding. It's just part of the chosen curves for the types of glass and their refractive idicii, intended to send the light where it needs to go, in a three element 45 degree field design. They've somewhat better eye relief, and handle somewhat faster focal ratio's somewhat better than kellners. Therefore a definitive improvement in a three element by most criteria. Post Extras:       Dreamon member Reged: 01/12/13 Re: RKE [Re: izar187]       #5739855 - 03/17/13 11:46 PM Edit   Reply   Quote Quick Reply   I understand. would you say the doublets concave surface (facing the obj) has a "negative" value? Post Extras:       izar187 Pooh-Bah Reged: 09/02/06 Loc: 43N Re: RKE [Re: Dreamon]       #5740042 - 03/18/13 03:14 AM Edit   Reply   Quote Quick Reply   I'd say it is just the right shape in the right place. Comparing the design of the RKE to other three element eyepieces makes it look like a derivation of one of Albert Konig's numerous designs. Trimmed down to a manageable sized field of view, for better astigmatism suppression, in more focal ratio's. Apologies if you have already seen the images in this link. But it's still pretty illustrative of the RKE's non kellner-esque pedigree, in spite of Edmunds ad copy. http://www.google.com/search?q=eyepiece+design&hl=en&client=safari&am... Post Extras:       Brian Albin Seeker Reged: 08/22/06 Loc: Western Oregon Re: RKE [Re: izar187]       #5741237 - 03/18/13 05:36 PM Edit   Reply   Quote Quick Reply   The doublet in an RKE is positive. The concave surface is on a negative lens if that lens is considered by itself, but once it is cemented to the biconvex, the doublet lens as a whole is positive. Yes, using a concave here instead of planar does improve it's performance. I believe the correction they were going after with this curve was the spherical aberration. But all the curves work together to reduce all the aberrations. Post Extras:       Dreamon member Reged: 01/12/13 Re: RKE [Re: Brian Albin]       #5746501 - 03/20/13 10:39 PM Edit   Reply   Quote Quick Reply   IZAR, now thats a link to some eyepieces!!!!!!!!! Brian, thank you, just the answer I was looking for. Thought the Barlow concept was at work here. Post Extras:       Dreamon member Reged: 01/12/13 Re: RKE [Re: Dreamon]       #5746508 - 03/20/13 10:42 PM Edit   Reply   Quote Quick Reply   This might be arbitrary, but this place is sure busy lately!!! Trying for a couple evenings to get back here. I would think everyone would be outside instead of slowing this place down. Ha Ha Post Extras:       Brian Albin Seeker Reged: 08/22/06 Loc: Western Oregon Re: RKE [Re: Dreamon]       #5748130 - 03/21/13 05:39 PM Edit   Reply   Quote Quick Reply   Yes! I was surprised that access was unavailable recently. I wonder if the site was under attack by one of those invader programs. I was once at a forum that was several times attacked by some sort of robotic visitor which specializes in visiting forums. I never did learn it's purpose, but it made it look like the forum had far more visitors than it actually had. Post Extras:       Pages: 1 Previous   Index   Next   Threaded   Extra information 7 registered and 14 anonymous users are browsing this forum. 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