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Equipment Discussions >> Refractors

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scope dog
Carpal Tunnel
*****

Reged: 07/26/04

Loc: USA
Re: New Russian Tal 125R Apolar APO refractor new [Re: drago]
      #3672974 - 03/10/10 06:18 PM

I spoke to Andrey he said "it's new APO (Apolar-abbreviation from apochromat of Russian amateur of astronomy) from NPZ. It's APO with normal glasses only. There is no one glass with ubnormal dispersion in the design."
He also said they are comming out with a 152mm. Andrey produced a 5 element 4" apo with no ubnormal elements.
I recall some other designer said it couldn't be done


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Alan French
Night Owl
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Reged: 01/28/05

Loc: Upstate NY
Re: New Russian Tal 125R Apolar APO refractor new [Re: scope dog]
      #3672983 - 03/10/10 06:24 PM

Quote:

I spoke to Andrey he said "it's new APO (Apolar-abbreviation from apochromat of Russian amateur of astronomy) from NPZ. It's APO with normal glasses only. There is no one glass with ubnormal dispersion in the design."
He also said they are comming out with a 152mm. Andrey produced a 5 element 4" apo with no ubnormal elements.
I recall some other designer said it couldn't be done




There is a paper showing a design using only normal glasses - I'll have to dig it up - but not at apertures and focal lengths that make sense for amateur astronomy. IIRC, the element spacing is large, which can lead to difficulties.

If they mean nothing like FPL53, 52, 51, or CaF2, it has been done before using short flints. These glasses lie well off the Abbe line and are considered to have abnormal characteristics.

Clear skies, Alan


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scope dog
Carpal Tunnel
*****

Reged: 07/26/04

Loc: USA
Re: New Russian Tal 125R Apolar APO refractor new [Re: Alan French]
      #3673087 - 03/10/10 07:27 PM

Alen,

There is a discussion Here , that will shed some light on the LAS design.


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Alan French
Night Owl
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Reged: 01/28/05

Loc: Upstate NY
Re: New Russian Tal 125R Apolar APO refractor new [Re: scope dog]
      #3673405 - 03/10/10 10:00 PM

Jim,

My guess is that it uses a short flint or other abnormal glass. This was used for the original "super planetary" design that Roland Christen published in Sky & Telescope, and an earlier design done independently in Germany. (I'll have to look up my reference on the latter.) Such a lens does not use any "ED" glass. As I mentioned earlier, short flints do have abnormal dispersion characteristics.

Clear skies, Alan


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Alan French
Night Owl
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Reged: 01/28/05

Loc: Upstate NY
Re: New Russian Tal 125R Apolar APO refractor new [Re: Alan French]
      #3673409 - 03/10/10 10:03 PM Attachment (229 downloads)

Here is one of the only designs I know of that actually only uses vanilla, normal crowns and flints.

Note it has several very undesirable characteristics.

Clear skies, Alan


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Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: New Russian Tal 125R Apolar APO refractor new [Re: Alan French]
      #3673419 - 03/10/10 10:04 PM Attachment (196 downloads)

Here's the spot diagram for the above design.

Clear skies, Alan


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Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: New Russian Tal 125R Apolar APO refractor new [Re: Alan French]
      #3673575 - 03/10/10 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

Edited by Alan French (03/10/10 11:41 PM)


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scope dog
Carpal Tunnel
*****

Reged: 07/26/04

Loc: USA
Re: New Russian Tal 125R Apolar APO refractor new [Re: Alan French]
      #3673583 - 03/10/10 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.

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Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: New Russian Tal 125R Apolar APO refractor new [Re: scope dog]
      #3673635 - 03/10/10 11:51 PM

Quote:

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


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scope dog
Carpal Tunnel
*****

Reged: 07/26/04

Loc: USA
Re: New Russian Tal 125R Apolar APO refractor [Re: Alan French]
      #3674702 - 03/11/10 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.


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talteleoptics
Vendor (Tal Optics)
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Reged: 08/17/10

Loc: USA
Re: New Russian Tal 125R Apolar APO refractor new [Re: scope dog]
      #4725688 - 08/01/11 10:39 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


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: New Russian Tal 125R Apolar APO refractor new [Re: talteleoptics]
      #4726113 - 08/02/11 07:47 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


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talteleoptics
Vendor (Tal Optics)
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Reged: 08/17/10

Loc: USA
Re: New Russian Tal 125R Apolar APO refractor new [Re: stanislas-jean]
      #4726367 - 08/02/11 10:57 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-germany.de/product_info.php/language/en/info/p484_TAL-125R-Apolar-APO-Refraktor.html


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: New Russian Tal 125R Apolar APO refractor new [Re: talteleoptics]
      #4726631 - 08/02/11 01:53 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


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Old Will
sage


Reged: 02/12/10

Loc: Utah
Re: New Russian Tal 125R Apolar APO refractor new [Re: stanislas-jean]
      #4729073 - 08/03/11 10:54 PM

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

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RichA
sage
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Reged: 06/03/10

Loc: Toronto, Canada
Re: New Russian Tal 125R Apolar APO refractor new [Re: drago]
      #4729857 - 08/04/11 12:25 PM

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.

Edited by RichA (08/04/11 12:26 PM)


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talteleoptics
Vendor (Tal Optics)
*****

Reged: 08/17/10

Loc: USA
Re: New Russian Tal 125R Apolar APO refractor new [Re: RichA]
      #4730169 - 08/04/11 03:43 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.


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: New Russian Tal 125R Apolar APO refractor new [Re: talteleoptics]
      #4731005 - 08/05/11 01:38 AM

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


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talteleoptics
Vendor (Tal Optics)
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Reged: 08/17/10

Loc: USA
Re: New Russian Tal 125R Apolar APO refractor new [Re: stanislas-jean]
      #4738680 - 08/09/11 12:05 PM

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.

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talteleoptics
Vendor (Tal Optics)
*****

Reged: 08/17/10

Loc: USA
Re: New Russian Tal 125-5 Apolar APO refractor new [Re: talteleoptics]
      #5357726 - 08/08/12 09:39 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.talteleoptics.com/TELESCOPES/TAL125APO/TAL1255APOIMAGES.html

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