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Istar best achromat for big refractor build ?

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#1 Kunama

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Posted 08 September 2013 - 06:03 PM

I am planning to build a large refractor in the future. I previously had a 6"F10 Istar which was excellent so will most likely go that way again.
I wonder if there are any other brands of objectives that can match them for price/quality?

We don't have much choice here in Australia so hopefully some European or USA members can chime in here.

I am considering 8" F8 or larger.

Many thanks in advance.

#2 timps

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Posted 08 September 2013 - 09:01 PM

Why not a reflector for a big scope?

#3 Kunama

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Posted 08 September 2013 - 09:13 PM

I will be building a reflector later as well but am really more interested in the refractors.

#4 plyscope

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Posted 08 September 2013 - 09:19 PM

I've considered this myself and I think Istar is probably the best value option other than a reflector.

There is the APM 203/1800 with TMB designed lens that would be wonderful but at a much greater cost.

web page

My conclusion is to do the ATM thing with an 8" lens from Istar or else go for a high end ATM dob (Royce, Zambuto, Lockwood etc.) 10 or 12" for similar cost.

Before any of that I need to catch up on my current projects. :cool:

#5 jrbarnett

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Posted 08 September 2013 - 09:21 PM

Nah. I'd say a premium Dob is the best way to go for a big scope. And if we're talking only refractors, I'd say a top quality large apochromat (TEC, A-P, APM/LZOS, etc.) would be the best option. Years of proven quality. Low depreciation/solid and liquid investment. Decent availability, etc. But not cheap.

[note: post edited by FirstSight]

Regards,

Jim

#6 plyscope

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Posted 08 September 2013 - 09:35 PM

One thing that sways me towards refractors rather than reflectors is that there is no local facility for re-coating mirrors. The only option is shipping the mirror to the other side of Australia and back (>3000km each way). This adds to the future running costs. Refractors can be virtually maintenance free with due care.

I have a decent 8" f6 mirror that needs a re-coat but it will cost over $300 so it is on hold for now. I can buy a new GSO mirror for that or a new Royce mirror for under a $1000 delivered.

#7 Kunama

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Posted 09 September 2013 - 12:16 AM

I am hoping to get a look through the Oddie II refractor at some stage, I have already had a good look at the lens in it and it certainly looks the goods.
It is more of a scope building exercise and an achromat is more than sufficient, I have no need for TECs or other APOs, my TAK TSA is fine for those purposes. Reflectors really aren't my thing (although I intend to build one at some stage).



#8 mikey cee

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Posted 09 September 2013 - 12:39 AM

Matt as a person living the dream of using a larger Istar refractor my answer would be a definite yes. At 9" and larger there aren't many options. If you could only have been with me last night after midnight. These lenses are really more than just good. ;)

[note: Post Edited by FirstSight]

Mike

#9 Messyone

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Posted 09 September 2013 - 01:48 AM

Matt,
An 8" would be have been my choice if I had a mount to take it. As you know I'm doing a 6" f12.
Locally available is 203mm 3mm thick drawn aluminium pipe that would hold an 8" beautifully.
I would go for as long an FL as you could and would get an Istar R 35 f12 objective would be the one I would choose.
Why oh why when you ask which refractor objective to get the reply from some is...get a dob....
Matt

#10 Kunama

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Posted 09 September 2013 - 02:47 AM

Hey Matt, I thought posting in the refractor forum would have been sufficient but have amended the thread title.
I have the enormous Gaunt Mount c1865 that will easily carry anything I can build, I'll look into the 8" lens. Looks like Istar has no competition as I think the others only sell complete scopes.
I'm trying to finish the other refractors so I can start the big project.

#11 James Ling

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Posted 09 September 2013 - 06:10 AM

Hi Matt...

You should go for the Istar 8" F12 R30 lens....
If your mount can take it........

Regards

James Ling

#12 plyscope

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Posted 09 September 2013 - 06:12 AM

Hi Matt

You can buy the APM TMB lens in cell only however it is 2850 Euros.

web page

There is D & G but only in f12 or longer.

web page

Then there is Barride Optics from China. I would expect them to be less expensive than Istar and I have no direct experience.

web page

Other than those you are left with waiting for a secondhand lens to pop up on the classifieds or Astromart.

#13 opticsguy

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Posted 09 September 2013 - 10:11 AM

Have you considered custom made? I kind of remember an optician; Ross Optical? Not sure if that is the correct name.

#14 t.r.

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Posted 09 September 2013 - 10:43 AM

RF Royce will make large achromats...oil spaced too!

Royce

#15 tomharri

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Posted 09 September 2013 - 10:51 AM

That APM 203 f/9 really looks tempting. But after my results with the 127 f/8 R30, will never do a basic achromat again. The blue fringe at 250x on the planets is almost nothing. About the same as a Carton 100/1300.
The 'R' works.

#16 roscoe

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Posted 09 September 2013 - 01:03 PM

[post edited by FirstSight]

#17 dlapoint

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Posted 09 September 2013 - 05:01 PM

I'd love the 8" f8.8 myself but have not the mount. I'm now looking at the 5" f12 r30

#18 Kunama

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Posted 09 September 2013 - 07:25 PM

Thanks everyone for the suggestions, I will get to work on current 80F15 scopes, get them finished and then get onto the big one. Looks like the 8"F8.8 might be the one.
The APM looks tempting but I think the $$$ might be vetoed by the Finance Minister.

#19 RGM

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Posted 09 September 2013 - 07:58 PM

I'd love the 8" f8.8 myself but have not the mount. I'm now looking at the 5" f12 r30


Great scope, rides very well on my G11. Works well with all the eyepieces I have. Depth of focus on the f12 is great for double star work.

#20 RGM

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Posted 09 September 2013 - 08:02 PM

Post edited by FirstSight

#21 FirstSight

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Posted 09 September 2013 - 08:07 PM

This thread is now RE-OPEN for posting comments. Constructive, respectful critiquing of Istar achromats is welcome, provocatively disrespectful comments toward same or other members, not so much.

#22 dlapoint

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Posted 10 September 2013 - 06:16 PM

Bob, doubles and planetary viewing is what I want the scope for. Where did you buy yours?

#23 A. Viegas

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Posted 10 September 2013 - 06:48 PM

Just a generic question, but why not an 8" F16 for super planetary type work? is the mounting issues of such a long tube the main problem? FL would be like 3200, so not too much in terms of magnification... Just wondering why nobody builds longer FL than F12 generally?

Al

#24 David Pavlich

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Posted 10 September 2013 - 07:46 PM

Just a generic question, but why not an 8" F16 for super planetary type work? is the mounting issues of such a long tube the main problem? FL would be like 3200, so not too much in terms of magnification... Just wondering why nobody builds longer FL than F12 generally?

Al


Think about the mount you'd need for that 8" lever. And think about where you'd house it. All big stuff.

David

#25 beanerds

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Posted 10 September 2013 - 08:36 PM

Good choice the Isatr's are and Matt I look forward to what ever you decide on .
If I had a mount like your beautiful 'Gaunt' I would definatly look at the 7.1 inch f8 or f12 slim , R35 by Istar and if these are as good as I hear you will be right by one of these .
One of these would keep the weight down as well .

By the way here is a shot of Venus taken last Saturday night in my Istar 127mm f8 achro , this is raw , no work except a small zoom and crop with sizing for CN's .
Great objectives .

Brian.

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