Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· 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

Equipment Discussions >> Refractors

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | (show all)
Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: Istar refractors Pros and Cons? new [Re: stevew]
      #5828635 - 04/28/13 03:37 PM

To awed to type? Perhaps he is sourcing a crane to lift it on to the mount?!?

Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Istar refractors Pros and Cons? new [Re: stevew]
      #5831201 - 04/29/13 10:03 PM

Hi Steve.

I've had a handful of sessions (albeit moonlit) with the Istar, and last night finished a star test using a green filter under less than perfect seeing (5/10 to 6/10). I've also had it out with a TV-102 and then with an Antares 105/1500 the following session. I'm very familiar with both of these scopes (have owned and used them regularly for years). Based on the Polaris star test and head to head use with scopes that, for me, are a known quantity, the best I can determine is that the (1) scope is definitely better than merely diffraction limited and (2) if I had to cop to a P-V wavefront error estimate, it would be around 1/5 to 1/6, with slight overcorrection.

Regards,

Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
stevew
Now I've done it


Reged: 03/03/06

Loc: British Columbia Canada
Re: Istar refractors Pros and Cons? new [Re: jrbarnett]
      #5831401 - 04/30/13 12:13 AM

What is the F-ratio of the Istar?

Steve


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Istar refractors Pros and Cons? new [Re: stevew]
      #5831406 - 04/30/13 12:18 AM

4" f/12 in a home-built OTA.

- Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
Paul C-I
super member


Reged: 03/23/08

Loc: United Kingdom
Re: Istar refractors Pros and Cons? new [Re: jrbarnett]
      #5831613 - 04/30/13 05:58 AM

Jim,
That's sounds very positive to me. I'm eagerly awaiting the completion and delivery of my Istar 8" F12 R35 lens. I have a temporary rail with focuser one end to mount it on for focal length measuring and testing before deciding on home built tube or a TCR structure.

Paul


Post Extras: Print Post   Remind Me!   Notify Moderator  
mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: Istar refractors Pros and Cons? new [Re: jrbarnett]
      #5831983 - 04/30/13 10:57 AM

Jim if this scope turns out anything like my 10" f/11 R30 you may not want to give it back. I've had a slight issue with my star tests since collimating my scope with a laser and collimating eyepiece. At 5:00 oclock I was getting slightly more difraction "spikes" which I attributed to less than optimal seeing. Believing that atmosheric dispersion made the redish blue on top not as pronounced as the greenish white on the bottom of my airy disc and difraction rings. Well last night I switched out the 2" diagonals with the 6" scope. The GSO diagonal cleared the problem right up. The Celestron diagonal now will stay in the 6" f/8 Jaegers from now on. Now I'm right where I want to be with the Istar. A perfect bull's eye difraction test. Also I checked again with the Ronchi screen tester when the temps were of no consequence. The Jaegers had nice thick black bars absolutely straight as could be, whether I displayed 2-3 bars or a dozen. The Istar tested similarly with no indications of over or undercorrection. I always knew that the Jaegers was top notch as I've used it for over 32 years. Now to see the new Istar test out near identical was a pleasant surprise. Mike

Edited by mikey cee (04/30/13 10:59 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Istar refractors Pros and Cons? new [Re: Paul C-I]
      #5832044 - 04/30/13 11:28 AM

Certainly it speaks well for small aperture slow optics from Istar's source(s). The quality of the Istar is in line with or perhaps a bit better than that of the typical 4" f/9.8 Synta doublet, for context.

Of course, as aperture increases, the difficulty of fabricating an optic to a given quality level also increases. Similarly, as focal ratio drops, the difficult of fabricating an optic to a given quality level also increases.

I'll be very interested in hearing your results with an 8" optic. I'm interested in a 6-incher, so your experience with an 8-incher will likely be more instructive to me than my recent fun with a 4-incher.

The DKD's tested on astro-foren.de were larger examples, and none of them tested to even the diffraction limit. Hence my interest in reports that go beyond mere anecdotal reactions ("Wow! Just wow! ) from new users. An 8" f/12 is a big investment not only in pounds but also in effort to transport, mount and house. I expect that you will give it a thorough thrashing and share details of your observations (target, magnification, what was seen, etc.). That would have great value I think to many folks here on CN on the fence over large Istars.

Best of luck with the grand olde refractor. I am very interested in following your story.

Regards,

Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Istar refractors Pros and Cons? new [Re: mikey cee]
      #5832048 - 04/30/13 11:29 AM

Mike:

What was your Ronchi test setup and parameters (i.e., what tools did you use)? Just curious. I picked up a ronchi test eyepiece device and haven't used it yet.

And, as stated in my comments the Istar 4" f/12 wasn't quite as well figured as either of the other 4-inchers I compared it to (though it was close), so there's not much reason for me to want to keep it.

Other than Jim's tube assembly, that is. That was clearly a labor of love: royal blue with gold trim, proper 1-speed R&P A-P focuser with custom gold anodized oversized focusing knobs, and impressive dimensions. (Re: the oversized focsuer knobs - talk about brilliant. They supply additional focus granularity without the cost, complexity, fragility and bulk of a 2-speed system. Jim caught my attention with that detail. I've been doing the same with SCT focuser posts for years. It just never occurred to me to try it with a refractor. ).

Thanks,

Jim

Edited by jrbarnett (04/30/13 11:38 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Istar refractors Pros and Cons? new [Re: jrbarnett]
      #5832404 - 04/30/13 01:55 PM

Quote:


Of course, as aperture increases, the difficulty of fabricating an optic to a given quality level also increases. Similarly, as focal ratio drops, the difficult of fabricating an optic to a given quality level also increases.



Indeed it does. As I most recently posted in my test thread, I'm highly suspecting something off at the edge of mine now.

The interesting thing about it is that it doesn't impact the low power views in an obvious way (they are really very nice), and unless you are using something as a reference (or are specifically testing for it...), you might not know that there's a problem at high powers. I've said before that I've got pleasant planetary views with it when considering just the view itself. It's when you compare it back to back against another that the differences are seen.

This is one reason why I don't think a observing report alone from anyone is as telling a reference as the tests done by Mr. Rohr, or in a side by side test.

Clear skies,


Post Extras: Print Post   Remind Me!   Notify Moderator  
mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: Istar refractors Pros and Cons? new [Re: Gord]
      #5832567 - 04/30/13 03:13 PM

Gord no matter how many Istars Rohr tests with positive results you're never going to accept the fact that the one you buy won't be a fluke. So you'll have yours tested anyway. So you might as well do it now and get on with life. You'll always be a doubter regardless of how many test are done, that's just your nature. A blind man can see what's going on here here. Also what's to lose other than some shipping? I'm more than sure if you aren't pleased Ales will either replace it or give you back your money! Mike

Edited by mikey cee (04/30/13 06:06 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Istar refractors Pros and Cons? new [Re: mikey cee]
      #5833131 - 04/30/13 08:12 PM

"Gord no matter how many Istars Rohr tests with positive results you're never going to accept the fact that the one you buy won't be a fluke."

"Gord, no matter how many little gray men bodies we find at UFO crash sites you're never going to accept the fact that extra-terrestrial cow mutilators with links to Freemasons and the WTO exist and are watching you"

That's the problem, you see. Just as no one has ever seen any little gray spaceman bodies (because none exist), neither Rohr nor anyone else not affiliated with Istar's lens maker has published a single positive independent interferometer test. I think one or two "sizzlers" from Rohr would satisfy me and, though I shouldn't speak for him, I suspect for Gord too.

Rohr has, however, tested a few DKD large achromat objectives that look suspiciously similar right down to similar test report formats to the Istar objectives. Those sucked, frankly. The other thing one or two positive Istar reports on Astro-Foren would do is help sever suspicions to the effect that DKD makes the optics for the large Istar achromats.

It's also really disingenuous to preach that folks won't accept one or two positive, objective, rigorous independent tests of large Istar optics when not even one such test report exists. On the other hand, one or two really bad Istar large achromat test report of that kind would be pretty informative too. The truth would be served by even one such report, good or bad. The hysteria and theatrics, to me, sound like fear.

I may have to beg Gord to let me send his optic off to Germany for testing and back, though I'd prefer that one of the bigger ones be tested since it is at larger apertures that Istar is differentiated from competitors (i.e., there are plenty of decent quality affordable 6" and smaller Chinese achromats available; bigger than that not so many).

Regards,

Jim

Edited by jrbarnett (04/30/13 08:17 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
EverlastingSky
professor emeritus
*****

Reged: 09/12/06

Loc: Vancouver Canada
Re: Istar refractors Pros and Cons? new [Re: jrbarnett]
      #5833194 - 04/30/13 08:51 PM

Good work Jim, keep at it, very good stuff, I support you in your efforts to gain some real test data on these interesting optics

Post Extras: Print Post   Remind Me!   Notify Moderator  
mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: Istar refractors Pros and Cons? new [Re: jrbarnett]
      #5833254 - 04/30/13 09:32 PM

Jim why aren't you willing to buy an Istar product like I did? Why do the two you always insist on waiting for someone else to have their lens tested?? HHMMM?? I know for a fact that Ales Krivanek will either replace your lens or refund your money. Don't give me that "I don't have time to play games" stuff. Lord knows you spend enough time on CN. Mike

Post Extras: Print Post   Remind Me!   Notify Moderator  
A. Viegas
Pooh-Bah
*****

Reged: 03/05/12

Loc: New York City/ CT
Re: Istar refractors Pros and Cons? new [Re: mikey cee]
      #5833366 - 04/30/13 10:39 PM

For what its worth, my 2c here (personal views, not scientifically tested just my opinion, so fuggetabout any data backup or certified optical testing!)...

I just acquired a 150mm R30 F8 Istar. I bought it used from another amateur recently around the time of NEAF. I was in the market for a $2-3k slightly used refractor and I did some research for about a month or so, looked through a number of scopes, meeting a couple of local owners who were in the market to sell their quality refractors. I considered the following alternatives, (ES 127ED, TAK 106FSQ, WO 132 triplet and a Celestron C6R):

1. Out of all of these scopes, I found the build quality of the Istar to be excellent and definitely seemed the most robust. Frankly, the C6R was the worst, feeling like a cheap chinese toy... The other APOs had nice finishing, but frankly the Istar is a tank. Yes, it weighs like 30# and it looks like a freak'n bazooka!

2. I have a CPC1100, and I do mostly video astronomy. I was buying the Refractor for planetary views and for quick views of the obvious stuff, like brighter DSOs, doubles and the moon. I got to test each of the aforementioned scopes on Jupiter, M42 and M65.

On Jupiter & the moon all the scopes were very good. I was not too bothered by the slight chromatic aberration in the C6R, nor did I think the TAK or the WO 132 were that much better. When we went to the Moon... well I thought, lets look for the craterlets. With my CPC1100 and the Mallincam these are easy to see... Visually, however I thought it would be a challenge at higher magnification. So here the Istar blew the competition away, using my Delos 3.5mm, it was only in the Istar that I could definately make them out. No way as detailed as in the CPC1100 with the Mallincam, but visually I have to say it seemed crisper. Yes... Aperture...

3. M42, the TAK has the best view of the trapezium stars, but the nebulosity was pretty much the same in all the scopes, not much to distinguish any of the telescopes in this regard.

4. M65. I chose this object because I had just seen the recent SN in my Mallincam that same week, and I had not yet had a chance to look at the galaxy visually. Galaxy? you say? What galaxy... from the relatively heavy light pollution greater NYC area I have to say all the refractors sort of sucked. But here again, aperture... the Istar showed the galaxy, the others... well maybe with averted vision... and then it was a struggle.

5. Color. Looking at my notes, I really did not make much comment, except to say that the TAK had the cleanest look on Sirius, the Istar was not great, there was some more CA than in the ES, and I did not test either the WO nor the C6R on sirius.

6. Price. I got an awesome deal on the Istar. The Tak I thought was way over rated and over priced for what it was, again I was using it visually and the smaller aperture was a major let-down. The WO was also about 2x more expensive, but the build quality was excellent as well, and i thought the focuser was probably the smoothest of the bunch.

I started my refractor buying project in February. I got my Istar 2 weeks ago. Hopefully I will have some more to say about it over the next few weeks if I get some clear weekends to use it.

I am hopeful that my Istar will compliment my SCTs and give me reason to try and get back a little into visual astronomy... Maybe in 20 years if I ever get more than 1 or 2 nights a month to play around with my astro toys, then maybe I become more discriminating and upgrade to the AP175 Ferrari...

Al


P.S. This weekend looks like clear skies, so I will try and get out and play around with the Istar, if anyone is interested i may post a few pics here of what i can capture as I intend to try out my Mallincams on the Istar.


Post Extras: Print Post   Remind Me!   Notify Moderator  
ken svp120
Carpal Tunnel


Reged: 12/19/04

Loc: Ohio
Re: Istar refractors Pros and Cons? new [Re: jrbarnett]
      #5833848 - 05/01/13 08:48 AM

Jim - no need to go through the expense of shipping over to Europe - there are at least 3 independent optics test labs here in the US that would be more than happy to run some tests and send you the results. If you want their info, let me know. Also, PM sent.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jim Curry
Pooh-Bah
*****

Reged: 10/29/07

Loc: STL
Re: Istar refractors Pros and Cons? new [Re: jrbarnett]
      #5833851 - 05/01/13 08:51 AM Attachment (29 downloads)

Thanks, Jim. That was my first OTA. I find the AP Traveler focuser to be a nice counterweight to the lens assemblies on this 4" and my other 6" f/12. Here's a couple of photos of the knobs and focuser. I'm now starting up on two 4" f/15 Jaegers builds, one for myself, another for another CNer. I'll start a thread soon on the ATM forum.

Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jim Curry
Pooh-Bah
*****

Reged: 10/29/07

Loc: STL
Re: Istar refractors Pros and Cons? new [Re: Jim Curry]
      #5833860 - 05/01/13 08:57 AM Attachment (26 downloads)

Another.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Istar refractors Pros and Cons? new [Re: mikey cee]
      #5833994 - 05/01/13 10:12 AM

Quote:

Gord no matter how many Istars Rohr tests with positive results you're never going to accept the fact that the one you buy won't be a fluke. So you'll have yours tested anyway. So you might as well do it now and get on with life. You'll always be a doubter regardless of how many test are done, that's just your nature. A blind man can see what's going on here here. Also what's to lose other than some shipping? I'm more than sure if you aren't pleased Ales will either replace it or give you back your money! Mike



Mike,

Let's stick to the topic at hand and not discuss my personal "nature" (of which you know _NOTHING_ about). But your post does once again re-iterate some of the points that Jim has brought up about the religious fanboy fanaticism. Since there is no real hard data to base anything on, the only response to questions about process, unusual or less than perfect results are personal attacks.

I would love to see some real hard data on them to get an idea of how things really are. I'm continuing to learn all the time and one thing I've now realized from this is how much I don't know. And how much I thought I knew in the past (but didn't really). This goes for my earlier evaluations of the first of the IStar lenses I've used (and am currently using).

Contrary to some comments I've read in the past, IStar is not in the league of Astro-Physics, TEC, Takahashi, APM, etc. I'll be clear that IStar has never said such a thing, but there seems to be more than a few that have interpreted the marketing and user comments to get the impression that they are. They are just like any of the other middle tier producers with quality ranging from very good to very poor. I expect most are in the average-good range, but from my own experience, I'm wondering if most people won't be able to tell the difference between just average and good based on just looking at the scope alone (as in on it's own).

Initially looking at the achro I had on it's own, I was pretty impressed and thought it must be pretty good based on previous experience with other achromat's. But it wasn't until I started comparing it directly head to head, side by side with other scopes that the differences were made apparent. And this is where the picture of the IStar becomes more clear.

And it's interesting that I can think of 4 examples (off hand...) where the IStar's compare only similarly to average quality common scopes out there:

-My 6" F10 is far below a good C8 on planetary and appears to have some sort of edge defect
-Sean found his 6" F15 to be less sharp than a Jaeger's 6" F15
-Tom found his 5" F8 R30 to be less sharp than his Surplus Shed 5" on Jupiter
-Jim's recent test here of Jim's 4" F12 where he feels it's similar or slightly better than a Synta 4" achro

There was another test I saw that the owner found the 6" F15 he had to maybe have around 1/5 wave of SA. To me, all this is presenting a picture of average to some good (although it seems the average of everything is rising overall these days). I'm certainly not seeing spectacular and would love to see some examples of "sizzlers" as Jim says. The law of averages says there have to be some really good ones out there, but it's certainly not appearing that this is common.

BTW Mike, have you ever compared the 10" IStar to the 8" Brandt side by side?

Clear skies,


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Istar refractors Pros and Cons? new [Re: ken svp120]
      #5834058 - 05/01/13 10:42 AM

The advantage of Rohr at this point is that he also has a large and growing publicly available database of test reports all compiled using the same methods. In addition to understanding the "numbers" for a particular optic, the ability to compare those numbers to similarly gathered numbers for competitive optics is hugely beneficial.

If we could have such a thing here in North America...

- Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Istar refractors Pros and Cons? new [Re: mikey cee]
      #5834072 - 05/01/13 10:51 AM

"Jim why aren't you willing to buy an Istar product like I did? Why do the two you always insist on waiting for someone else to have their lens tested??"

Asked, and answered. A large refractor represents a substantial investment in mounting and transporting. I don't want a big, inconvenient piece of junk on my hands, frankly. Also, because I am a scrupulously honest seller, I would never try and foist a scope with lousy optics on another amateur, but instead would be compelled to fully disclose the low quality of the glass to prospective buyers. That's more time commitment, hassle and risk than I want to undertake. Since folks who have already purchased one have assumed the risk and accepted the hassles, and profess to be "happy" with the quality, they're in no worse shape than they're already in if their optic is tested. Whether it tests poorly or well, they can still be happy and the rest of us who care about fact rather than opinion can also benefit. Sooner or later, one of these larger Istars will be tested, and the chips will fall where they may.

Regards,

Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | (show all)


Extra information
22 registered and 44 anonymous users are browsing this forum.

Moderator:  Scott in NC, FirstSight, panhard, star drop 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 11931

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics