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#26 TG

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Posted 14 January 2020 - 01:21 AM

The design used a crown and a flint, plus an abnormal-dispersion or "short-flint" as a center element. Essentially the two flints synthesize a flint that is a good match to the crown element.

Clear skies, Alan

TMB in his famous A-P history article very clearly says two abnormal dispersion flints were used in the first StarFire series which gave a 5x better violet correction. I can testify to this, being the owner of a 7" version of this design. Roland has sadly never made this design public.

Tanveer

#27 Alan French

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Posted 14 January 2020 - 07:38 AM

TMB in his famous A-P history article very clearly says two abnormal dispersion flints were used in the first StarFire series which gave a 5x better violet correction. I can testify to this, being the owner of a 7" version of this design. Roland has sadly never made this design public.

Tanveer

Tanveer,

 

Thanks. Guess it's time I reread the TMB A-P history article.  

 

The TMB article says the design used two "abnormal dispersion flints," which only implies they lie off the Abbe line. I don't think it's appropriate to take that as meaning two "short flints" as in post #19.  

 

The "super-planetary" design used BaFN-10, which lies very close to the Abbe line, and KzFSN-4 (short flint), which lies off the Abbe line.

 

Clear skies, Alan


Edited by Alan French, 14 January 2020 - 10:01 AM.


#28 Brian A

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Posted 14 January 2020 - 10:02 AM

Thank you to all for all the great information! I have a much better understanding of what I am in store for and I cant wait. I also posted a question to the classic scope forum as someone here wisely suggested and JA posted the following. I think he nailed it.

 

post-16843-0-28343200-1578975826_thumb.jpg

post-16843-0-42723900-1578975896_thumb.jpg

 

Thanks Brian



#29 Wildetelescope

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Posted 14 January 2020 - 10:40 AM

Thank you to all for all the great information! I have a much better understanding of what I am in store for and I cant wait. I also posted a question to the classic scope forum as someone here wisely suggested and JA posted the following. I think he nailed it.

 

attachicon.gifpost-16843-0-28343200-1578975826_thumb.jpg

attachicon.gifpost-16843-0-42723900-1578975896_thumb.jpg

 

Thanks Brian

Great!  You have a real piece of history here!    Keep in mind that at that time in the consumer market, a triplet lens refractor was a rare unicorn!    Very unusual.  And the performance was very close to the MUCH more expensive Japanese Fluorite refractors.    Believe it or not, the AP was the bargain option, undercutting the rest of the premium refractor market:-)   Also, VISUAL observation was by far the dominate type of astronomy.   These early scopes at F8 and F9 were considered FAST by the standards of the day.  They represent the beginning of the imaging revolution that shapes the hobby today. 

 

JMD

 

Out of curiosity, does anyone know what the difference between the Standard triplet and the Starfire model in the ad was?  


Edited by Wildetelescope, 14 January 2020 - 10:41 AM.


#30 Jeff B

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Posted 14 January 2020 - 10:40 AM

Nice scope Brian and yes, it is indeed a "Standard Christen Triplet".  I had a very similar one about 10 years ago.  I cut back the tube to make it bino-friendly.  Very "mount friendly" too.

 

Optically, mine was very good, doing quit well in direct comparisons to my TMB 130 F9.25 LZOS triplet.  Only at powers greater than say 130X could I start to tease out differences in color correction and sharpness.  It was a very satisfying sample.  Roland told me years ago that, overall, these would be similar to a 5" F30-ish achromat.

 

Jeff

Attached Thumbnails

  • Sleek or scratch.jpg
  • AP130 F8 C.jpg
  • AP130 F8 D.jpg

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#31 Brian A

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Posted 14 January 2020 - 11:46 AM

Thanks for the photos Jeff. That nails it, even down to the green felt tabs.

 

I cant wait to have some fun and compare side by side with my old FS-102. Who knows, maybe ill mount both on my new CEM60!

 

Brian



#32 Brian A

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Posted 14 January 2020 - 12:55 PM

Found this very cool link if anyone is interested in old telescope catalogs.

https://web.archive....taire/classics/

Brian



#33 Wildetelescope

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Posted 14 January 2020 - 01:08 PM

Thanks for the photos Jeff. That nails it, even down to the green felt tabs.

 

I cant wait to have some fun and compare side by side with my old FS-102. Who knows, maybe ill mount both on my new CEM60!

 

Brian

My experience with my 5 inch is that the contrast is superb for visual work. On really still nights I have gotten amazing detail on Jupiter at ~200X.   I was able to resolve one of the moons against the planet. I only notice a faint indigo halo around Sirius at ~200X.   I have never noticed color on the moon or Jupiter, or any other planet.  I have not looked at Venus, but I would expect a little color there, based on my experience with Sirius, Vega, etc...   When imaging the moon or planets, I see no color either.    I will see some color on bright stars in DSO images, if I blow things up and go looking for it.  If you check out my gallery, you can see different imaging I have done with the 5 inch F8 Starfire.  Where these really shine though is for visual use.  Well executed modern triplets are certainly better color corrected, but these old AP's are still very good and I think you would be hard pressed to find a scope with a better lens figure.

 

Enjoy!

 

JMD



#34 TG

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Posted 14 January 2020 - 02:22 PM

@Wildetelescope, I have to say that I own the later iteration (pre-ED "StarFire") and it's easy to see color on the moon with it. It manifests as a faint purple tinge bleeding over from the sunlit part to the dark part of craters. It actually is the indication that you are in perfect focus, similar to BK7-F2 achromats! Defocusing a bit will remove the purple tinge but then you are not operating at the diffraction limit of the scope. I suspect some people do this to remove improve the image color-wise but lose out on definition.

 

I would probably never have paid attention to the color had I not owned an excellent Zambuto mirror as well.

 

Tanveer.



#35 TG

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Posted 14 January 2020 - 02:24 PM

Tanveer,

 

Thanks. Guess it's time I reread the TMB A-P history article.  

 

The TMB article says the design used two "abnormal dispersion flints," which only implies they lie off the Abbe line. I don't think it's appropriate to take that as meaning two "short flints" as in post #19.  

 

The "super-planetary" design used BaFN-10, which lies very close to the Abbe line, and KzFSN-4 (short flint), which lies off the Abbe line.

 

Clear skies, Alan

Alan, I thought that the available abnormal dispersion flints were just Schott's short-flints. But then I'm no optical expert...

 

It would be fun to get the pre-ED Starfire design and simulate in OSLO but Roland won't say.

 

Tanveer.



#36 Alan French

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Posted 14 January 2020 - 02:51 PM

Alan, I thought that the available abnormal dispersion flints were just Schott's short-flints. But then I'm no optical expert...

 

It would be fun to get the pre-ED Starfire design and simulate in OSLO but Roland won't say.

 

Tanveer.

Tanveer,

 

The ones I am most familiar with use Schott short flints.

 

https://shop.schott....lass/glass-KZFS

 

I am hardly an expert but am curious to know more about the use of two abnormal flints. Mike Simmons (NOT the Mike Simmons with Astronomy without Borders!) wrote about designs using a crown with two dense flint elements, such as BaLKN3 with SF18 and SF11, but I never saw any specific designs. With modern extra-low dispersion glasses available such designs are mostly a curiosity, but are interesting.

 

Clear skies, Alan



#37 Wildetelescope

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Posted 14 January 2020 - 03:34 PM

Tanveer,

 

The ones I am most familiar with use Schott short flints.

 

https://shop.schott....lass/glass-KZFS

 

I am hardly an expert but am curious to know more about the use of two abnormal flints. Mike Simmons (NOT the Mike Simmons with Astronomy without Borders!) wrote about designs using a crown with two dense flint elements, such as BaLKN3 with SF18 and SF11, but I never saw any specific designs. With modern extra-low dispersion glasses available such designs are mostly a curiosity, but are interesting.

 

Clear skies, Alan

https://www.telescop...po_examples.htm

 

Folks have been speculating on the Glass combinations in the early triplets forever.   The popular site above lists 2 examples of what they think approximates the composition of the early Christen Triplets at F8 and F10.  Don't know where they got their info or if it is just an educated guess, but I suspect they are pretty close. In any event it gives you a rough idea of what was possible with the short flints. Found it interesting and thought I would share given the discussion.

 

JMD
 



#38 lee14

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Posted 14 January 2020 - 04:26 PM

These are from an AP catalog circa 1990. Actual photo prints on Kodak paper were included.

 

Lee

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  • AP 1.jpg
  • AP 2.jpg

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#39 Brian A

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Posted 14 January 2020 - 06:42 PM

Nice scope Brian and yes, it is indeed a "Standard Christen Triplet".  I had a very similar one about 10 years ago.  I cut back the tube to make it bino-friendly.  Very "mount friendly" too.

 

Optically, mine was very good, doing quit well in direct comparisons to my TMB 130 F9.25 LZOS triplet.  Only at powers greater than say 130X could I start to tease out differences in color correction and sharpness.  It was a very satisfying sample.  Roland told me years ago that, overall, these would be similar to a 5" F30-ish achromat.

 

Jeff

Hi Jeff - What mounting rings are you using for the 130?

 

Brian



#40 Jeff B

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Posted 14 January 2020 - 08:24 PM

Hi Jeff - What mounting rings are you using for the 130?

 

Brian

Brian, I no longer have the scope but in the photo with the Losmandy GM8 I was using the old pair of stock AP rings (non-hinged).  In the photo with the Vixen SP mount, they were some Synta based rings with a little extra felt.  You tube O.D. is 6".

 

Here is my latest which is a 127mm Starfire recently serviced by Roland as the cement used between the elements aged, putting stress on the glass.  During service, under partial warranty, he went ahead and refigured it, then put in the latest spacing oil.  Said it will last at least several generations now.  I also cut the tube back on this one to make it bino-friendly.

 

Did you get the scope yet?

 

Jeff

 

Edit:  This scope was in terrible shape when I got it.  It had been left lying on a table in the old observatory for decades with both ends open.  Dust and crud on both exposed surfaces to the point where you could not really look through the lens and the tube was full of spider webs.  But I removed the lens from the cell and it cleaned up wonderfully, looking brand new.  I've included a photo of the lens block, and it was indeed a "block" of glass with the cement.  Note that it does not have Kapton tape on the edges, which is typically used in a lens of this vintage to stabilize the block and seal the edges since it is oil spaced .  Roland and I both believe the deceased previous owner, who was a chronic tinkerer, replaced the oil with cement at some point.  He did a good job but it was not durable and I could easily see the resulting turned edge in star and DPAC testing.  Roland said when he initially set up the lens in the interferometer it gave a Strehl of .88 in green light and when he separated the elements, let them relax for a while, then set it back up in the interferometer, it came in at .94 Strehl.  Roland felt he could do better and went ahead and refigured the lens.  It now has a Strehl of .98 in green.  It is a very sharp lens with, at best, scant "CA". 

 

Don't ever give up on these old lenses! 

 

Jeff

Attached Thumbnails

  • 5 inch F8 Pre ED Starfire 2.jpg
  • Lens Block.jpg

Edited by Jeff B, 14 January 2020 - 08:49 PM.

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#41 Chris Cook

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Posted 15 January 2020 - 03:55 PM

I haven't taken possession yet but here are the photos I do have.

 

Thanks

Hey Brian,
We're fairly close to one another, I'm in Harwich on the Cape.  Once you get the scope, we could do a shoot out with my 1992 A-P 130EDT.



#42 Brian A

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Posted 15 January 2020 - 06:29 PM

Thats a cool idea Chris. I have to wait for the new CEM60 to come in before I can play with this new toy!


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