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Istar vs chinese lenses

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#1 Wouter1981

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Posted 11 July 2020 - 01:51 AM

I am thinking for my next project to build a binoscope. The easiest way is to start with 2 mass produced f5 refractors (startravel 120 ,...) . An other possibility is to buy 2 Istar objectives and start from there. I really like the fact that they have already a collimatable cell.

Has anybody been able to compare the istar objectives with the Synta lenses and have an opinion if they are worth the extra cost? I am only talking about their achromatic lenses.

Istar is the only brand of such lenses I know, but are there others, preferably in Europe?



#2 Arjan

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Posted 11 July 2020 - 02:41 AM

Wouter, did you consider SurplusShed? Maybe their Wollensack objectives are good enough...

#3 Wouter1981

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Posted 11 July 2020 - 09:11 AM

Wouter, did you consider SurplusShed? Maybe their Wollensack objectives are good enough...

Well, now I have smile.gif  I will have to check the site once in a while. I have seen some 127mm f5.5 but havent got a clue if those are any good. Still a lot cheaper than the Istars, but I have no problem spending a good amount of money for some good lenses.


Edited by Wouter1981, 11 July 2020 - 09:12 AM.


#4 Alrakis

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Posted 11 July 2020 - 10:25 AM

Another option is contacting MASILMW.

 

He usually has lenses for sale. I believe they are typically lenses from refractors that have other issues (like dented tubes) and the lenses themselves are in great condition, at least according to those who have built refractors from them. 

 

Chris 


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#5 sunrag

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Posted 11 July 2020 - 11:22 AM

I am not a lens expert by any means.
I have obtained small and large Achromats from AliExpress (China), MASILMW, Surplus Shed, and also ScopeHed (Bill of Telescope Wearhouse). All of them have been excellent with no difference in quality compared to an original Celestron or Meade telescope. The challenge would be to find a suitable cell and a tube.
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#6 PETER DREW

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Posted 11 July 2020 - 02:15 PM

I have built several binoscopes using Skywatcher 150mm F8 and F5 telescopes, they have excellent optics for the sort of magnifications best suited to a binoscope. I also have a 150mm F10 Istar objective which I use in a solar telescope. I would rate the Istar as being slightly better on resolution and CA.

#7 Bill Lee

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Posted 11 July 2020 - 05:01 PM

You can get achromats direct from China at AliExpress.com. If you can be patient, it’s cheaper. 



#8 GlenM

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Posted 12 July 2020 - 07:17 AM

I have built several binoscopes using Skywatcher 150mm F8 and F5 telescopes, they have excellent optics for the sort of magnifications best suited to a binoscope. I also have a 150mm F10 Istar objective which I use in a solar telescope. I would rate the Istar as being slightly better on resolution and CA.

Got to agree with Peter on this. iStar do produce good lenses. I have built quite a few refractors using iStar Achromat lenses and never had a problem.

 

Stay safe,

Glen.



#9 bcarter1234

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Posted 13 July 2020 - 08:59 AM

I can't provide a comparison but I can say the Istar 127.5mm F/5.5 objectives work very well in a binocular telescope. The smiles on the faces of others who have looked through it would seem to indicate I'm not alone in holding that opinion. ;-) If money is not a primary concern I don't think you will be disappointed.

 

I'd love to compare them to a similar size and speed instrument with ED or triplet objectives. 

 

What configuration are you planning for the scope?

 

Take care,

Brent



#10 Wouter1981

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Posted 13 July 2020 - 09:07 AM

Thanks for all the answers everybody. Seems that Istar is a good source no matter what I'm planning.

 

 

I can't provide a comparison but I can say the Istar 127.5mm F/5.5 objectives work very well in a binocular telescope. The smiles on the faces of others who have looked through it would seem to indicate I'm not alone in holding that opinion. ;-) If money is not a primary concern I don't think you will be disappointed.

 

I'd love to compare them to a similar size and speed instrument with ED or triplet objectives. 

 

What configuration are you planning for the scope?

 

Take care,

Brent

I don't really have a configuration yet, but I'm certainly going for low power widefields with  fast achromats. I'm not sure about the size even! It will be at least 100mm but I'm rather afraid to go for the 150mm. They are much bigger than the 1.5x increase would indicate and the weight and price of everything quickly go up.
Another point that is a certainty is a EMS system with hellicoids to alter the IPD. It's such an elegant system. Expensive but it has a upright image, short optical path with only 2 optical surfaces.

But how everything will be connected, which focusers, cradle,... it's still yet to be determined. I have some other projects running and I'll use these to increase my machining skills first.

 


Edited by Wouter1981, 13 July 2020 - 09:42 AM.


#11 bcarter1234

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Posted 13 July 2020 - 01:12 PM

Wouter1981,

 

I would not be afraid of building using 150mm objectives if you can go with a Dob style alt/az set up. An 90 degree asymmetrical configuration can reduce the optical surfaces from 2 to 1 but you forego the upright image which is a deal breaker for some.

 

I also have an 80mm asymmetrical binocular telescope. The wide views it can provide are wonderful but come at the cost of some light grasp which from a light polluted suburban neighborhood can be a high price indeed. I've talked myself out of a 100mm ED binoscope several times now. I'd enjoy the potential for higher magnification but miss some of the dimmer objects the extra aperture brings into view.   

 

Have you considered the off the shelf Williams Optics 103 binocular telescope? It will cost a bit more than DIY but the time and labor savings could be significant.

 

Please keep us updated on your project. 

 

Take care,

 

Brent 



#12 Wouter1981

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Posted 14 July 2020 - 01:59 AM

Bcarter1234,

 

No I haven't considered a of the shelf sollution because that would defeat the entire goal of my the project. I have bought a mill about a year ago and decided to build some telescope equipment to learn it. I'm almost finished with parts for my Bresser 152mm f8, learned a lot with it and honestly, I don't think I'll use that telescope a lot! But I don't care because that was not the point of the project.

 

For the binoscope, the goal is different. I want it to become much used, but the binoscope will only be a part of the project. My first part is a mount on a height adjustable pier, able to carry that binoscope. Once that is finished I'll start the binoscope.



#13 Benach

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Posted 14 July 2020 - 03:53 AM

Wouter, if you can come to Halley observatory near 's-Hertogenbosch on Wednesday evening on an even week number, I can help you face to face.

#14 bcarter1234

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Posted 14 July 2020 - 07:12 PM

Wouter1981,

 

Just in case it helps with your decision I want to share last night's experience with the Istar 127mm f/5.5 objective equipped binocular telescope. I was cruising around at 38x with a pair of 18mm eyepieces having a fine time. I decided to take a look at the Double Double. I could not see a clean split so put in a pair of 6mm eyepieces for 116x. Nice clean split on both pairs. M57 is just down the street so off I went.

 

I was considering calling it a night and noticed a bright object just east of south fairly high in the sky. I haven't been out for a while so I'm thinking Antares. I swung around, saw a disc and thought I must have bumped something to get out of focus. Then I realized it was Jupiter. Very pleasing at 116X as was Saturn nearby. Everything looked promisingly stable so on to 170x with a pair of Barlowed 9mm eyepieces. I thought no chance but then again nothing to lose but a little sleep so the 9mm EPs were replaced with 6mm using #8 filters.

 

Now it's operating at 256x, both planets looked very good (not perfect, but I'm yet to see perfect) and Jupiter's moons looked like discs as opposed to the point of a star. No whirls for me yet but nice banding and an occasional hint of some detail. I could see banding (ring shadow?) on Saturn, a tiny bit of planet disc below the ring and Cassini division was sharp. 

 

Just for fun I went back over to the Double Double which featured clean, tight stars widely split. M57 was a suitable finish to a surprisingly fine evening.

 

Considering the lenses were operating at about two and a half times what they are designed to support I was very impressed. Combined with the ability to get 2.2 degrees at 29x it is a fairly versatile instrument.       

 

Take care,

Brent



#15 Oberon

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Posted 15 July 2020 - 04:38 AM

I don’t see the 127 f/5.5 on Istar’s website anymore...




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