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Post by 1953djb1953 on Apr 24, 2013 21:44:44 GMT -5
Gord:
Actually a double pass autocollimation test with a 100-133 LPI screen is very accurate and revealing, easy to do too.
Also, try stopping the lens down to 5" and redo your star test, especially with the Chromacor II in place (hint: There will be Z-E-R-O CA on axis, even as you pan across focus)
Jeff
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Post by istarmullet on Apr 25, 2013 9:16:54 GMT -5
Does Gord buy telescopes to test them or to use them for their intended purpose? I, for one, will continue to use mine happy in the knowledge that it is a fine scope and that I did not waste my time trying to prove otherwise. What a waste of time.
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Post by Ales - iStar Optical on Apr 25, 2013 9:56:48 GMT -5
There does seem to exist a cadre of "refractor police" on CN. For years I've noticed they all seem to have a common link, they're APO owners. So apparently, once your nose gets elevated in that milieu, any upstart trying to separate themselves from the pack needs a good beat-down. Mr. Barnett has a 4" f/12 Istar achro he's playing with. Let's see what he says if he posts something. Jim That is a very interesting piece of information. But how can anyone be sure that this is actually true? We did not sell that many 100 F12, they are not popular.. our best selling sizes are 150 and 204mm. But I will see what happens, thank you for sharing this, Ales
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Post by Ales - iStar Optical on Apr 25, 2013 10:01:22 GMT -5
Ales: I understand your reasoning early on but at this point I think you're putting too much out there. As a suggestion, take down any and all of those test reports and don't provide them in the future. Publish what you guarantee you build the lenses to in specification (written) format but not the pretty pictures that the experts are just going to sharpshoot you with. Does Synta provide them, AP, TEC? Any other achro company? Just a polite suggestion. Kind regards, Jim Jim, a decision was made recently to supply each lens with only complete set of spot diagrams or no test of any kind. It does not mean that we will stop testing lenses. We will only keep all tests for our own records since each Serial Number is linked to the actual lens test report. So yes, you are absolutely correct, regards, Ales
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Post by mikey cee on Apr 25, 2013 13:14:13 GMT -5
Hi Ales. Well I use my scope and so far the lens is performing very well thankyou. There is no sign of coma or SA. The "tree" rings as I call them to my wife look the same intra thru extra. Only difference is the color hue. They look text book to me. I always check those extremely tight doubles not only in the center but at the edge of the field. I thought plossls were supposed to be inferior to orthos. But I see virtually no difference out at the edge. Maybe just a hint of lateral color but you realy have to convince yourself that you are seeing any. This lens test out just like my 8" Brandt lens that I used over a 30 period. Only difference is a different residual color but less of it if you can believe that. But it's true. It even amazed me. So even if I did have someone like Wolfgang Rohr test it and everything tested out like so so with a few deficiencies here and there....so what? I can see no room for improvement. That's what's wrong with certain individual lens users. Even tho' the image is very very good they think they have to have a lens that tests out at 98%+ on the reports. Again so what? That's like saying even if my car has an identical ET in the 1/4 mile as yours but you say that your car's better because you have 20HP more based on dynamometer test or whatever have you. I like the end result I don't give a damn how it got there. Mike
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Post by mikey cee on Apr 25, 2013 16:53:00 GMT -5
Oh by the way I forgot to mention this. The other day I made a ronchi tester. I had a piece of plastic grating film laying in my drawer for 30 years. It was from Edmunds. It was with another fine grating that you could see a spectrum with which of course is way to fine. This one is labeled 130 lines per inch. I made me a cheap but very useable tester. So I simply used a plastic 35mm film canister. First I cut the bottom out. Then I drilled a nice 1/4" hole in the cap top. There is a little moulding dimple right in the center of the cap to give you a precise center spot. Taking a 1/2"+ square of grating film I then glued it to the bottom side of the cap with some 100% silicone. Snapped the cap back on and voila! I now have a slightly tapered ronchi screen 1-1/4" "eyepiece". I have used it several nights now on Regulus. First I let the lens stabilize which was probably around an hour...it was a mild night. My ronchi lines can be adjusted to just several thick lines to as many as a dozen or more thinner ones. I prefer five lines maybe 6 but that's all I need. The lines were as straight as the bars on a prison cell door!! To say that I'm pleased is an understatement. I say Ales I feel that you are a man who can be trusted to deliver. I can't believe that I actually got my money's worth first time around with a complete stranger. Oh yeah I read handfull of opinions by some satisfied customers. But those were customers with 4", 5" and 6" lenses. I was going for a 10" and there was noone I could talk to about the quality. So I took a chance and it all worked out very well. Looking back I'm glad I did. Mike
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Post by jimcurry on Apr 26, 2013 6:38:53 GMT -5
Mikey:
We all sort of took a "chance" buying their lenses. Other than a hiccup or two their first year I haven't heard anything negative.
Oh, BTW, how do you know how straight the bars in a jail cell are? :>)
Jim
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gord
Full Member
Posts: 82
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Post by gord on Apr 26, 2013 9:21:08 GMT -5
Jeff,
Yes, I've tested it with the C-II in place and the color correction is incredible. Out of focus pattern is effectively white on both sides. On axis of course. I'll have to try stopped down as well, and Ed suggests with a CO as well.
I suppose by testing with various combinations of aperture stops and obstructions, you could effectively isolate each zone and test them individually. I really need to get those filters as I understand my standard wratten one's won't be sufficient.
Thanks, -Gord
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gord
Full Member
Posts: 82
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Post by gord on Apr 26, 2013 9:24:28 GMT -5
Mullet,
I enjoy using all my telescopes (they seem to be breeding lately!) and testing them is just part of that process. What's wrong with trying to understand exactly how good (or bad) something is and how it performs relative to that?
If you don't want to, it's ok. No one is forcing you to find out.
Clear skies, -Gord
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gord
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Posts: 82
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Post by gord on Apr 26, 2013 9:32:03 GMT -5
Mike,
Thanks for sharing your test setup experience. Sounds like an easy process. You will have to change your process a little as from what I have been reading on CN, you aren't getting sensitive enough results to tell you anything other than if there is a gross error.
You are testing in single pass mode, and as I understand it with all ronchi tests, you need to have as few of lines as possible. 5-6 would be too many. 2-3max will give the sensitivity needed from what I read, although in most cases they are talking DPAC. I'm not sure if even that is enough for single pass. If you go with more lines, it will look overly positive.
Might be worth asking in the ATM forum to be sure.
Clear skies, -Gord
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Post by mikey cee on Apr 26, 2013 12:09:21 GMT -5
Yes Gord I checked it with two lines, three and up to 10-12 lines they are all straight. Good Lord Gord is there anything else we must consider? If we do that we should've done this. If we do this we should've done that. I've more than passed the point where I'm more interested in how it performs than how it tests out!! Mike
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gord
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Posts: 82
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Post by gord on Apr 26, 2013 21:31:39 GMT -5
Mike,
It's my understanding that this is just scratching the surface in terms of evaluating things. It isn't even touching on measuring the color correction (LA) or the SA correction at those other colors, or getting a real close look at what the figure is really like. Gives an appreciation for why the optics produced using this manner of process are so expensive. They need to test each surface at all the different points in the process and keep working them until the hit a certain result. And the test needs to be done multiple times, at different orientations, etc. I believe Astro-Physics works them until they hit 1/10th wavefront error as measured on the interferometer and then calls them done.
The results though is they are consistently perfect. And you pay for it! I looked into a custom produced piece using this type of process and was warned that it will not be cheap. After seeing more of what the process is about, I would really call it expensive, at least not in the sense of them just charging a lot of money. There's real WORK involved!
Good to hear things looked out at 2 fringes!
Clear skies, -Gord
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Post by mikey cee on Apr 27, 2013 1:02:04 GMT -5
Gord the way this lens performed on Saturn a few minutes ago I'm speechless. Only color I could detect was the red and blue of that atmospheric dispersion. But I was amazed at how little it was that low in the sky. I could easily watch where the Cassini gap disappeared inside of the limb of the planet that was below the rings. Yet visually I could still detect that thin shadow like line all of the way across the face of the rings. Very delicate with very steady seeing helping out. The Crepe ring I could follow all the way. One of the best nights of seeing I've had around here since last fall. Dew shield was starting to get damp and I forgot to turn on my dew heater. Luckily the lens hadn't begun to fog. Mike
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Post by Watcher3 on Apr 27, 2013 11:19:49 GMT -5
I for one would take that report above any "test" report, ANY DAY. When some one of Mikey Cee's stature and experience in the hobby tells you specifics about what can and can't be seen, It's beyond me how some over at CN can dismiss it as "fanboy" optimism. I mean JEEZ people! I've seen Barnett give favorable reports about scopes he has purchased, and nobody asks him to send off his lens to Germany to prove it. Yet he won't take Mikey's word? Laughable is the only description that comes to mind.
Rant off. Joe
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Post by Ales - iStar Optical on Apr 30, 2013 4:42:26 GMT -5
Myself and Istarmullet seem to be the only one's trying to put a good face on Istar's products and lenses. But I have a question to ask you Istar enthusiasts. Could I ask at least a handfull to help us out by getting involved instead of not looking too hard, lurking or just sitting back and being entertained. I believe Istar is getting a lot of seeds of doubt cast their way. Plus most of these naysayers expect someone else to do their bidding for them by having your lenses tested. BS to this is what I have to say. Those guys can do it like we did and purchase these lenses themselves. You nor I sat back and waited for someone else to do it for us. They complain that they don't see or hear of enough positive reports about Istar lenses. They have even gone so far as to say you are too ashamed of the mistake you made to admit it. They don't care that only people who get a bad product bitch and moan but that satisfied customers don't always chime in with a positive note. Thanks for your input. Mike Mike, Mr. Barnett posted some very short but down to the point test results with his first Istar scope he recently looked thru. His initial reaction was positive and I very much appreciate his willingness and courage to post something positive about Istar optics on CN. One thing I can’t understand though. For some reason, when he was posting his fairly negative statements on this CN forum, he had dozens of people participating. Now he posted a positive thread (for Istar) and only one guy bothered to react to it, only asking some basic question about Focal ratio of Istar lens tested or something like that. So Mike and others, why don’t you ask more specific question to Mr. Barnett about his test results, how he obtained them, etc... I will do the same once I have more time, very hard to find now before my departure and yet another 2 Mo. long trip overseas.. Anyhow, thanks to all Istar optics owners for your continuous support. I would be long gone from the market if it was not for you. And a BIG thanks to Mr. Barnett for his recent post, regardless of what he said about Istar in the past. I don’t expect Mr. Barnett to become an Istar fan because of this, but many others won’t be scared to buy Istar lens or scope based on his own findings. I’m really glad that he finally looked thru one of the Istar scopes (actually this one was home made build with Istar lens) and was happy with what he saw. best regards, Ales
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