33 replies to this topic

[PawPaw]

Debated where to post this but ultimately chose the scholarly Classics forum.  

 

I am curious about what manufacturers designed an APO and Achromat in exactly the same objective size and FL, and offered them at the same time?  Or did anyone?

 

Clear skies

 

Don

[ccwemyss]

Pentax briefly offered the standard achromat and ED doublet apochromat versions of their 100 f/12 at the same time. For a while it was possible to buy the ED objective separately as an upgrade. I think they were clearing out the last of the standard objectives, and testing the waters to see if the market would pay for the apochromat before discontinuing the achromat. The f/12 ED design wasn't around for long, as they then switched over to the shorter EDHF designs. 

 

Chip W. 

[PawPaw]

Thanks Chip! 

 

Makes sense that the Apo and Achro would be a longer FL.  What years were these offered?

[ccwemyss]

Not sure of the exact years, but shortly after I worked in the scope shop, so mid to late 1980's.

Chip W. 

[Astrojensen]

Zeiss. 

 

 

Clear skies!

Thomas, Denmark

[Pickwick]

I think also Vixen had 80mm and 100mm Achro, ED and Fluorite doublets, not sure about their focal lengths.

Around the end of the '90s years.

[PawPaw]

Zeiss. 

 

 

Clear skies!

Thomas, Denmark

Thomas can you provide the model #'s?   Objective Diam and FL.

 

Thanks

 

Don

[Bomber Bob]

Mizar circa 1986...  GT-80S ACHRO & FA-80 Fluorite APO.  I got the first one, and watch ZEN for the second...

 

BORG... sorta / kinda.  I can easily swap my 76 ACHRO lens assembly with the 77ED version...

[Astrojensen]

Thomas can you provide the model #'s?   Objective Diam and FL.

 

Thanks

 

Don

For many years, from around 1908 to 1940-ish, they made achromatic E lenses and apochromatic B triplets in the following, standardized dimensions:

 

60/850mm

80/1200mm

110/1650mm

130/1950mm

150/2250mm

200/3000mm 

 

From 1926 onwards, they also made AS doublet semi-apos with the same specifications.  

 

The intention was that you could buy a telescope with an achromatic objective, and then later change to an apochromat, if so desired.

 

The AS lens replaced the A doublet apochromat, which had a different focal length and wasn't interchangeable with the E and B objectives. 

 

After WW2, it took until 1972, before Zeiss offered an achromat and a semi-apochromat with the same aperture, namely the C63/840mm achromat and the AS 63/840mm semi-apo. It wasn't until 1986, with the introduction of the APQ 100/1000, you could once again buy a true Zeiss apochromat. It shared the same OTA with the AS100/1000mm semi-apo.

 

 

Clear skies!

Thomas, Denmark

[dothead]

Lichtenknecker

[Weisswurst Josef]

Takahashi also did. Ok, nearly ..

TS 65 P Triplet Semi Apochromat (65/500)

FC 65 Fluorite Doublet Apochromat (65/500)

But the TS 65 Achromat had f 800 ...

So that fails. Nearly.

No Takahashi did not. Sorry.

[RichA]

Lichtenknecker

Lichtenknecker VAS -1.jpg

Lichtenknecker VAS -2.jpg

Anyone know anyone who has used / owned one of those Lichtenknecker quadruplets?  

Edited by RichA, 02 April 2025 - 01:32 AM.

[RichA]

Takahashi also did. Ok, nearly ..

TS 65 P Triplet Semi Apochromat (65/500)

FC 65 Fluorite Doublet Apochromat (65/500)

But the TS 65 Achromat had f 800 ...

So that fails. Nearly.

No Takahashi did not. Sorry.

Didn't Telescope Express offer 102mm f11 achro, ED and SD telescopes?

[deSitter]

Didn't Telescope Express offer 102mm f11 achro, ED and SD telescopes?

I don't understand why f/10 EDs are not more common. And at f/12 the ED equals the APO triplet in performance, for practical purposes.

 

-drl

[bobhen]

I don't understand why f/10 EDs are not more common. And at f/12 the ED equals the APO triplet in performance, for practical purposes.

 

-drl

Triplets are usually faster so, much better for imaging. Long FLs are okay at 4" but the tubes really get long as apertures increase. And there is no optical advantage to a F12 ED when Takahashi offers 100mm F8 and F7.4 ED doublets that are optically stunning.

 

Bob   

[PawPaw]

Nikon debuted their 6.5 cm f/12 achromat in November 1983 and in March 1984 they released the ED version which used the same proprietary glass as the 10cm ED.    The only difference visually to tell one from the other is by looking for a gold ring between the dewshield and the objective cell.  This ring denotes the APO version.  The Achromat has no ring.

 

    

 

 

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[k5apl]

I owned a BORG 100mm Achromatic refractor;  somewhere around f6 or so.  It was modular and very light weight.  There was an option to upgrade to an APO objective/cell of same configuration/size.

Maybe about 15 years ago.

Wes

[Terra Nova]

I think also Vixen had 80mm and 100mm Achro, ED and Fluorite doublets, not sure about their focal lengths.

Around the end of the '90s years.

The ED and Fluorite apochromats had shorter F.l. In the case of the 102s (they didn’t offer a 100) the achromat was 1000mm (F9.8), the fluorite was 900mm IIRC; the ED was 660mm (F6.5). I have one of the 102mm ED apos. It’s an excellent scope all around, both solar system and stellar system viewing.

[Bomber Bob]

The BORG approach makes common sense to me:  I got the 76 ACH OTA uber cheap, so "upgrading" to the 77ED isn't prohibitive.  But... it's not gonna replace my outstanding '84 FC-76, so why bother?  But for someone w/o Too Many Old Scopes... they could ease into an APO...

[RichA]

I don't understand why f/10 EDs are not more common. And at f/12 the ED equals the APO triplet in performance, for practical purposes.

 

-drl

Well, SD is even better and even at f12, there is some minor visible differences.  But f10 is the same as f11, running up against the fast imaging scopes, requiring a bigger mount, less easy to use. 

[RichA]

Debated where to post this but ultimately chose the scholarly Classics forum.  

 

I am curious about what manufacturers designed an APO and Achromat in exactly the same objective size and FL, and offered them at the same time?  Or did anyone?

 

Clear skies

 

Don

True or false:  The centre area of an good achromatic lens (decently long-focus, f10 or longer) filtered in green is superior to an apochromat in-terms of spot-size?

[luxo II]

Neither - it depends on the specifics of the design of the two objectives youre comparing - and the quality of the production of each.

[CHASLX200]

Been nice to see a older ED 4" Unitron at f/12.

[deSitter]

True or false:  The centre area of an good achromatic lens (decently long-focus, f10 or longer) filtered in green is superior to an apochromat in-terms of spot-size?

True! More glass is always worse other things equal.

 

And the APO will be figured to eliminate spherochromaticism, which will affect the spherical correction.

 

-drl

[rfic1]

GOTO made six in the 80mm f/15 configuration and three at f/12.5

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