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Post by Watcher3 on Jul 26, 2011 18:31:22 GMT -5
Ok, so I'm getting a 6" F/5 R65 lens in my scope. What is really the effect of a 65% reduction in CA. I've been figuring that it should have about the same amount of false color as a scope with a 65% longer focal length, or about the same as an F/8.25. Is this right, or am I figuring wrong?
Joe
Sorry. It's hard to keep up, but I guess it's R60 now, and if I am on the right track should be equal to an F/8.
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Post by Mike on Jul 28, 2011 22:55:42 GMT -5
Joe, I sent this question directly to Zdenek. I believe the reduction in CA will be greater than the comparison you're making to a F8.25. Also the smaller spot size comes in to play. I'll let you know what he says.
Mike
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Post by Mike on Jul 31, 2011 8:33:51 GMT -5
You are right Joe. The R65 lens should have about the same amount of false color as a scope with a 65% longer focal length, or about the same as an F/8.25.
Best regards, Zdenek Rehor, master optician, ISTAR Optical
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Post by Watcher3 on Jul 31, 2011 14:35:57 GMT -5
Thank you Mike, and Zdenek. That was my hope from the beginning. A 6" F/5 with the same color correction of an F/8, with the better optics compared to a run of the mill Synta, will be perfect for my intended use! Something that can be used for very wide fields and still stand pumping up the magnification for all DSO applications. If I'm going to be observing only planets, I still may choose my Carton 100/1300, or if time permits, my IM715, but the CA in a 6" F8 is not very objectionable to me, Especially in an F/5 scope! Nice to know I won't have to drag out two scopes if I want to look at a planet on the same night I'll be looking mainly at DSOs. I think this lens is going to be a real classic! I think the next lens that ISTAR makes with the R60 design should be the 150mm F/12. The Conrady CA spec on 6 inch refractors calls for F/18. An R60 F/12 would give the equivalent of an F/19.2. That should also be a real winner. A scope that kills a D&G F/15 in an F/12 package will be AWESOME!  |
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Post by rwiederrich on Sept 18, 2011 18:27:35 GMT -5
Hello.. I'm still confused as to HOW you are correcting the CA in a faster ratio objective without abnormal dispersion glasses?
What is the physics that makes an f/5 act like an f/8?
Rob(Owner of Art Devany's last objective)
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Post by Mike on Sept 18, 2011 20:34:06 GMT -5
Rob, I can't be specific about our designs any more than any other lens manufacturer would. Our designs are what sets us apart from the rest. I can tell you two things. The first is that an exotic high index material is used in one of the elements. This is basic optical physics and design 101. The second is that it works, quite well with no negative side effects except greater weight. Now the bad news. The exotic material we were using for the R60 has went up in cost by 300% since the first of the year putting that design in jeopardy. We are producing the R30 currently and have a new line of scopes coming out, the Asteria, in December that use it. As I have stated before and tested with my own eyes it makes an F12 behave like a F15.6 in color correction and spot size. If you want to see for your self, email me to place an order  Mike |
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Post by rwiederrich on Sept 18, 2011 20:59:26 GMT -5
Mike..thank you so much for taking the time to address my question. So without revealing any design specifications..it is safe to assume the abdormal dispersion material in your doublet design is in effect an ED objective...as we understand them?
The reason I ask is often times the definition of ED can take on various definitions depending on the manufacturer. I'm very impressed with what you are doing...and I have a friend who recently recieved his R30 anastigmatic objective and his review will be anticipated, and will contribute to any decision I may make on the subject.
Can I also ask what you mean by anastigmatic?
Thanks
Rob
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Post by Mike on Sept 19, 2011 14:47:46 GMT -5
Anastigmatic is most commonly a camera lens term which means near perfect correction of spherical aberration, coma and astigmatism. According to Zdenek our optician, his design meets this criteria. So far from what I've seen, I can't argue with that fact. I'm quite confident in Mikey Cee's lens, but I'm looking forward to his review. A common doublet is flint and crown, right? What if one of those materials could be altered in composition (melt) to get a higher index of refraction? Then the term "abnormal dispersion" would be correct. Lens designs are only limited by the glass available. If you have a really good designer and can get the right kind of material the possibilities are... The beauty is we are achieving these results without going to expensive materials like FPL51, FPL53, or the like. I look forward to selling you a new lens or scope after Mikey's review. |
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Post by rwiederrich on Sept 19, 2011 15:27:57 GMT -5
Mike...one last question if I may. since anastigmatic represents an objective free of coma, astigmatism and spherical aberrations..can one not assume that most long focus objectives of excellent design and manufacture meet this definition? Like a quality D&G f/15?
I look forward to further reviews on the R30 substraight you are suplimenting in your doublet designs.
Thanks again,
Rob
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Post by Mike on Sept 19, 2011 15:56:13 GMT -5
Rob, yes I would say that name (description) could be used on any lens meeting the criteria. Since Ales is the owner and "namer" of our lines of scopes, I'll let him tell you why he decided to use the name. Fortunately for Istar, the excellent design and manufacture of long focal length scopes that meet the criteria are few or two. |
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Post by rwiederrich on Sept 22, 2011 17:03:09 GMT -5
Mike...can someone get blanks of these R30 elements from suppliers..or are the melts strictly available through Istar?
Rob
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Post by Mike on Sept 22, 2011 20:53:53 GMT -5
I'm sorry Rob. The design and composition are patent pending. The R30 is only available finished from Istar.
Mike
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Post by rwiederrich on Sept 23, 2011 8:19:49 GMT -5
Thanks Mike..that is what I wanted to know.
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Post by Watcher3 on Oct 5, 2011 18:41:02 GMT -5
Just wondering guys. Now that the glass price increase has put the R60 out of my reach, and possibly out of existence, what kind of results would there be in a 6" F/5 doublet made with FPL-51(or it's FCD-whatever equivalent)? Could a 6" lens using this be made for less than the R60, and what kind of color correction could be had?
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Post by Mike on Oct 7, 2011 0:30:57 GMT -5
Couple things Joe. FPL51 and FPL53 is far more expensive than the glass used in the R60. More expensive by 2 1/2 times. You have to order in a huge quantity to get competitive prices. We don't have those kind of orders... yet. Believe me when I say we are all over this glass situation. We are in touch with every glass manufacturer on the planet. The prices charged by custom scope manufacturers such as Astro Physics and TEC are for good reason. TEC quit making 160 ED triplets for this very reason. Top quality glass for a "reasonable" price is hard to come by. Some people have questioned why we use Lanthanum. They have said it's an older technology. In longer focal length APO triplets Lanthanum achieves excellent color correction at a reasonable price. Our Forfax 140-12 APO triplet is less than $4000 for a complete scope. And, it tested as good as or better than two different short focal length APO refractors at twice the price. We need to build quality refractors at an affordable price or we're no different than the rest. The cost of the material for R60 put us out of that category. Mike PS. I love being able to use other manufacturers names without being chastised. Thanks Joe! |
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Mike