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New Russian Tal 125R Apolar APO refractor

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#26 Alan French

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Posted 10 March 2010 - 10:04 PM

Here's the spot diagram for the above design.

Clear skies, Alan

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#27 Alan French

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Posted 10 March 2010 - 11:14 PM

Ah, finally looked at the web page

It does look like an extension of Duplov's work, with obvious improvements. The Duplov design I posted has a tube length considerably longer than the effective focal length. This new design appears much better in this respect.

Clear skies, Alan

#28 scope dog

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Posted 10 March 2010 - 11:18 PM

It was Wolfgang Bush who develope the oiled triplet. B270 and KzFN2, But this was considered a semi, but I believe the KzFN2 is a abnormal flint. web page My first scope AP 127 f/12 KzFS-1. The KzFS-1 is a abnormal flint glass though and was used in the super-planetary series, I believe it was oiled. I'm not a AP buff, I only had a few of their scopes and never took a picture of that one. I will let Andrey know about your post.

#29 Alan French

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Posted 10 March 2010 - 11:51 PM

It was Wolfgang Bush who develope the oiled triplet. B270 and KzFN2, But this was considered a semi, but I believe the KzFN2 is a abnormal flint. web page My first scope AP 127 f/12 KzFS-1. The KzFS-1 is a abnormal flint glass though and was used in the super-planetary series, I believe it was oiled. I'm not a AP buff, I only had a few of their scopes and never took a picture of that one. I will let Andrey know about your post.


Thanks for the name and reference.

I have a similar lens using KzFSN-4 that I have been enjoying for more than 21 years.

Clear skies, Alan

#30 scope dog

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Posted 11 March 2010 - 01:27 PM

Hi Alen,

I had that KzFSN-4 in my blue tube 6" F/9 starfire. That, mine was a cemented triplet. I sent that in for a cleaning and I spoke to Roland about it. He may of made both imersion and cemented with that series.

#31 talteleoptics

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Posted 01 August 2011 - 09:39 PM

TAL 125-5APO has 6 elements.
First is a single biconvex lens, the second consists of a biconvex lens, biconcave lens and converging-meniscus lens, the third one consists of biconvex lens and biconcave lens. Two types of optical glass are used in the construction to provide superb corrections. available in usa from talteleoptics.com

#32 stanislas-jean

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Posted 02 August 2011 - 06:47 AM

Interresting information regarding this kind of "apo".
However if the chromatic aberration is one part of the global optical acuracy level, what about the P/V and RMS data expected (if there a specification with minimal characteristics guarantied?).
It remains the fact that a global P/V of 4 involves a trehl ratio of 80% only even with the CA level near 0.
Can we expect a P/V of 6 global minimum (that's become interresting with such) with a control bulletin?
Stanislas-Jean

#33 talteleoptics

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Posted 02 August 2011 - 09:57 AM

For practical test results on TAL 125-5APO visit this link from Germany. I hope this will provide real performance data for who is interested in design aspects. TAL 125-5 APO is a proprietary patented optical design trying to balance performance/ manufacturing and cost trade offs as any other manufacturer.

http://shop.hoo-germ...-Refraktor.html

#34 stanislas-jean

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Posted 02 August 2011 - 12:53 PM

Thanks for the link.
Just a last question about the design and the data given:
what can be the influence by assembly tolerances of the mutual distance between the lens group on the global acuracy? Are thermal expansions of the aluminium tube affecting the global acuracy?
Stanislas-Jean

#35 Old Will

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Posted 03 August 2011 - 09:54 PM

This is based on an old design, I remember seeing some time back....cool though

#36 RichA

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Posted 04 August 2011 - 11:25 AM

Why would anyone want one? 6 elements, 3 groups, we're talking about 6-12 optical surfaces. You might as well adapt a camera telephoto lens to function as a telescope.

#37 talteleoptics

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Posted 04 August 2011 - 02:43 PM

Rich, to simply answer you, TAL APO telescope was designed with Astro-Photography in mind unlike most telescopes. This optical design allows you to have flat field of view just like Photo lenses do as you picked on. Correcting for field curvature is essential (not to mention chromatic and special aberration) to get Hi quality images sharp across all field of view. That’s because camera CCD and CMOS sensors are flat and not curved, requiring in focus image across all sensor field at the same time. Those requirements make optical designs complex. Also a benefit to have sharp image in eyepiece across all field of view. Typical Refractor and most APOs have curved field of view that makes you re-focus on objects from edge of the field to the center. Not a big deal for human observing the sky real-time, but on image, you will have out of focus and in focus object at the same time. Not going to be an impressive image as result. All aftermarket field correctors are going to bring their own disadvantages with extra artifacts and light loss. TAL produced essentially an APO telephoto lens for your camera or CCD imager as you wondered, as well as great optically telescope for observation at reasonable price. Bottom line If you are into Astro Photography or want to try make pictures of stars or planets, this is excellent scope for you with second to none optical performance. If the goal is visual observation only, then may be price and specification is deciding factor.
Also I saw references to TAL125R in forum, so to clarify for users, TAL125R is not an APO scope, TAL125R is a larger version of TAL100RS refractor with Doublet air spaced objective lens. TAL125R uses same tube design as TAL125-5APO and on pictures may look the same but they are 2 different telescopes with different mounting brackets.

#38 stanislas-jean

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Posted 05 August 2011 - 12:38 AM

Can we say the design is a petzval plus a chromacor near the focus plan?
Stanislas-Jean

#39 talteleoptics

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Posted 09 August 2011 - 11:05 AM

I thought Petzval design had doublet objective lens and aperture stop in secondary group. Tal has single lens in objective, not 100% sure, but no aperture stops. I will try to find out from TAL what they call the optical design scheme.

#40 talteleoptics

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Posted 08 August 2012 - 08:39 AM

To all who are interested in looking at Prime Focus shots from TAL 125 5 APO, here is the link. All images are single shot without any stacking, images were converted from RAW format, and cropped. There is no CA or any purple fringing around bright edges. There are very few examples of TAL APO imagery out there. Hope this will give an idea on optics quality. http://www.talteleop...5APOIMAGES.html

#41 chboss

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Posted 09 August 2012 - 01:20 AM

Are these telescopes available from stock?
Have not seen any adertised lately....

How about colimation problems that were reported here?
http://www.astro-for...fraktor-125-940

How stable is the lens cell?

best regards
Chris

#42 talteleoptics

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Posted 09 August 2012 - 07:19 AM

What country are you looking to find telescopes in? Telescopes are available in US in stock (click “BACK” button on webpage with Moon Photos). If you are interested in details on collimation and performance, I would suggest looking into TAL Yahoo groups forum. There is a guy from Finland that has lots postings on using TAL Apo for photography. May be worth asking his opinion on that. I don’t think he had those issues described in your link. I also did not see that issue. Objective Cell on the scope all metal very solid, with adjustable focuser travel axis. BTW even triplet APOs can go out of collimation in shipping. It is not unheard of.
Roman

#43 John Huntley

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Posted 09 August 2012 - 03:41 PM

I was sent a TAL Apolar 125 to try last year. It came direct from the factory I think (the metal seals were still intact on the wooden trunk). Unfortunately one of the internal lens groups was smashed in transit and there was a 15mm scratch across the centre of the singlet objective lens. So it went back.

A second scope was sent, this time checked by the importers here (the seals were cut by the time it reached me). The second scope was in much better shape and performed very well on the control of chromatic aberration - there was virtually none that I could see in visual observing. I was not satisfied with the star test though as star airey disks were slightly egg shaped rather than circular. I suspect this could have been a collimation issue but I did not feel brave enough to tackle the collimation of a 6 element refractor that did not belong to me I'm afraid !.

I also found that I could not bring any 2" eyepieces to focus using the 2" diagonals that I owned (I tried a couple) because of lack of inward focuser travel.

I think the design has real promise but needs to be executed to a more consistent standard and made more robust for transit. The focuser design needs to have more inwards travel too as the views with a 2" wide field eyepiece could be potentially excellent.

#44 chboss

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Posted 10 August 2012 - 12:57 AM

Dear Roman

Thank you for your response, now I had a look at your website where you anounce that you have them in stock...
At least in Europe there seem no scopes in the market and none has shown up during recent star parties.

John's comments regarding his experience do not give me more confidence in this product... Good luck with your business.

regards
Chris

#45 talteleoptics

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Posted 10 August 2012 - 07:28 AM

Chris,
Glad that you found this discussion helpful. All scopes in stock here are verified and checked before delivery. There are no concerns on shipping issue or out of collimation problems. John's point on NON TAL 2" accessories use and focuser travel is a valid point and needs to be looked at individually with TAL APO design.
Regards
Roman






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