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Astro-Physics 10" Mak-Cass

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#26 Jared

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Posted 05 October 2017 - 12:59 PM

Has there been any recent information about when A-P will start shipping its new 10" Mak-Cass?  I have been on the notification list for one since June 2001.

 

Back on April 3, 2017, Roland Christen stated on the A-P Yahoo Group that he would be making a "limited number" of the new 10" Mak-Cass "this year."

 

Thank you.

 

Heywood

I don't have any information on the scope that hasn't already been presented in this thread, but I DO have a picture of one from last week's AIC conference...  It's mounted on a 1600, and that's Roland explaining some of its features to a conference attendee.

 

JSW2019165.jpg


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#27 Heywood

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Posted 05 October 2017 - 03:29 PM

Jared,

 

Thank you for the great pic!  bow.gif

 

Heywood

 

P.S.  Anyone care to guess Astro-Physics' price for the new 10" Mak-Cass?


Edited by Heywood, 05 October 2017 - 05:56 PM.

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#28 skyward_eyes

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Posted 05 October 2017 - 04:17 PM

I believe it was about $12k from what I understood but I don't believe that is official. I think they stated it would be a run of around 25 units or somewhere about there. 



#29 Jared

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Posted 05 October 2017 - 04:48 PM

George mentioned 24 units to me at the AIC show.  

 

Here is a pic of the spec sheet.  Sorry about the glare--right over the critical portion that shows the (presumably) outrageously high Strehl ratio!  Still, look at that interferogram.  And the 23% central obstruction.  Pretty impressive.

 

JSW2019166.jpg


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#30 Jared

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Posted 05 October 2017 - 04:50 PM

And here's one more view of it...

 

JSW2019160.jpg


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#31 Howard Gao

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Posted 05 October 2017 - 06:13 PM

Thanks for sharing the pictures. Anyone knows people on the list to which year will be able to get one of the 25 units?

#32 Edd Weninger

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Posted 05 October 2017 - 06:16 PM

Yes, very wide views when appropriate, along with high magnification of the same target.

 

Cheers,  

 

 

Go for the gusto.  A 16" APM Matthias Wirth f/10 Rumak.

 

Cheers,

Edd, do i see a traveler riding on your Rumak?

 


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#33 vahe

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Posted 06 October 2017 - 08:59 AM

I have never seen the original AP Mak, but based on the pictures that I have seen it pretty much follows the same design principles of all Mak Cassegrains in as far as the primary F ratio is concerned, which is roughly F/3 give and take, I have three TEC Maks and their F ratios are F/2.7 to F/3.3 with their average right on F/3. This makes all Mak Cassegrains noticeably longer than SCT’s which employ F/2 primaries.

.
That said, looking at the most recent pictures of the new AP Mak posted in this thread, the scope appears noticeably shorter than the typical Mak, much shorter, I would be curious to know what F ratio was used in this scope.

.

Vahe



#34 Jared

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Posted 06 October 2017 - 12:54 PM

Vahe, I'm not sure, but it may be possible to back into the focal ratio of the primary from the following:

 

Design--Gregory Maksutov 

Focal ratio--f/14.5

Aperture--254mm

Radius of Curvature--310mm

Back focal length--85.6mm

 

I'm not sure what the optical formula is, but I think it should be possible to back into the focal ratio of the primary from that.  Maybe you need the index of refraction for the meniscus as well, or the thickness of the meniscus, or some knowledge of what was done to aspherize the central spot.  I suspect those would have little impact on the Petzval surface, though.  Someone with more knowledge of optics than I could probably answer that fairly quickly.  My impression with most cat's was that the ratio of the powers of the two reflective surfaces was the primary determinant of field curvature for a given aperture and focal length.



#35 Paul G

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Posted 06 October 2017 - 01:42 PM

Vahe and Jared, I can't remember if Roland gave the focal ratio of the primary but he did post that it was chosen in part to make the image less susceptible to temperature changes.

Edit: Not the post that had the info above, but here is a post he made about the original 10 that touches on some factors he takes into account when choosing the focal ratio of the primary.

"The 10" Mak-Cass was a particular design (aspheric Gregory)
that is not easy to produce. It requires a complex aspheric on the primary
mirror. Aspherics are hard to make smooth and perfect, and in this case it took me
almost 1 year to make just a small number of these scopes. Each mirror took
about 1 week of painstaking hand work (all the optics were pre-polished by our
supplier, and all I did was to do the final smoothing on all the surfaces and
aspherizing on the mirrors).

After that expersince, I took a long break from making that sort of optic
again. By contrast, an all-sperical Simak or Rumak design, which was made by TEC
for a number of years, is simple and straight forward. The main disadvantage
is that for a fully coma corrected design, the Rumak requires somewhat larger
central obstruction for any given F-ratio. The aspheric Gregory has the
smallest possible obstruction for a coma-free design. Nevertheless, if I ever make
any more Maks, they will have all-spherical design, because the aspheric design
is not practical.

Interstingly, the 7" Meade is a form of aspheric Gregory. Unfortunately they
chose to make a huge secondary obstruction > 35%. I believe they achieved the
aspheric surface by deforming the primary during polishing. The main problem
that I see with that approach is that it is almost inevitable that some
astigmatism will result in the primary figure. It is more straight forward to make a
Mak with separate secondary and all surfaces spherical.

You can always do a very small amount of localized figuring to reduce or
eliminate the inevitable 5th order. Just about every optics that uses refractive
elements has some 5th order. All you need to do to bring it to a non-issue is
to reduce it below 1/10 wave P-V. This does not change the reality that an
all-spherical design is the most practical of all.

There are other reasons besides 5th order that causes most Maks to have an
unsymmetrical shadow breakout. The most common reason is due to thermal
instability, which adds a certain amount of 3rd order undercorrection to the figure.
If the thermal design is right, and the optics have been figured correctly,
then you will see pretty close to ideal inside/outside and in-focus images.

Secondly, the amount of 5th order is dependent on the focal ratio of the
primary. The longer the primary, the smaller will be the 5th order component (and
the longer will be the tube assembly). F2 primaries will have large amounts,
F3 and longer primaries will have small amounts. Of course, the longer the
primary focal ratio, the larger will be the obstruction ratio for any given focal
length. Some have suggested longish F-ratios to keep the secondary size down,
but this limits the scope to just planetary observing. Wide field deep sky and
imaging would be compromised. I don't know what the ideal F-ratio is for a
Mak-Cass, but F20 seems to me to be way too limiting. Even the 10" at F14.6 was
a bit long."

Edited by Paul G, 06 October 2017 - 01:55 PM.


#36 vahe

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Posted 06 October 2017 - 02:02 PM

When this Mak was first announced, just by reading between the lines somehow I got the impression that it was essentially a carbon copy of the older model, but now that I can see a close up image of the scope I sense that although it follows the same design principals it is not a carbon copy.

.
One indication is a change in system focal ratio, the older Mak was f/14.6, this one is f/14.5 although a tiny difference it tells me that the design was refined. Since it is a Gregory Mak it is aspherized, and as far as I know the primary is the component that is aspheric, not the center spot. Refiguring the secondary is usually a risky affair resulting in roughness, one of the major SCT makers, either Celestron or Meade does that and you can see the resulting mess in the final image.

.
As for doing a reverse engineering to arrive at the primary F ratio, that is way over my pay scale.

.

Vahe



#37 Jared

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Posted 06 October 2017 - 05:37 PM

As for doing a reverse engineering to arrive at the primary F ratio, that is way over my pay scale.

.

Vahe

 

 

Mine, too, unfortunately! :)

 

Interesting that Roland appears to have gone back to the Gregory despite his swearing it off earlier because of it's not being cost effective.  Of course, he's only doing a limited run of 24 or so.  Maybe it's still just as impractical, but he's bored with 130's.



#38 TG

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Posted 06 October 2017 - 06:27 PM

 

As for doing a reverse engineering to arrive at the primary F ratio, that is way over my pay scale.

.

Vahe

 

 

Mine, too, unfortunately! smile.gif

 

Interesting that Roland appears to have gone back to the Gregory despite his swearing it off earlier because of it's not being cost effective.  Of course, he's only doing a limited run of 24 or so.  Maybe it's still just as impractical, but he's bored with 130's.

 

You don't need to be an optical engineer - use the image of the optical layout and measure it in an editing program:

 

eBElEaUh.jpg

 

I get ~ f/2.66 for the primary, which means the secondary is 5.4x.

 

Tanveer.



#39 freestar8n

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Posted 06 October 2017 - 07:00 PM

What does he say about the amount of coma in this scope?  I can't read what the document says.

 

I don't like calling this design "Gregory" because the idea of aluminizing a spot on the corrector dates back to Maksutov himself - and Gregory just popularized the idea with two specific semi-spherical 6" designs later.  I prefer to call them all "spot" Maksutovs - which covers many options including ones where the spot is locally figured differently from the corrector - and the other curves can be spherical or asphere.

 

Does the 23% include the baffle on the secondary spot?  Does it have a baffle?  The one on the Meade is huge.

 

Is that an actual Astro-Physics document on the optical performance?  "Transversal Spherical Aberration" is very weird terminology - I only know Longitudinal and Transverse.

 

Frank



#40 Jared

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Posted 07 October 2017 - 12:28 AM

Yes, that was the laminated spec sheet that Astro-Physics had attached to the scope for reference.  I’ll check the original image tomorrow to see if the coma amounts are legible.

 

Tanveer, I’m not sure you can just measure the document.  That would assume I was holding it flat.  Good enough for one decimal, but not sure about two and almost certainly not three.


Edited by Jared, 07 October 2017 - 12:33 AM.


#41 TG

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Posted 07 October 2017 - 01:05 AM

Yes, that was the laminated spec sheet that Astro-Physics had attached to the scope for reference.  I’ll check the original image tomorrow to see if the coma amounts are legible.

 

Tanveer, I’m not sure you can just measure the document.  That would assume I was holding it flat.  Good enough for one decimal, but not sure about two and almost certainly not three.

I just offered three figure accuracy because I measured pixels to 3 figures but I think it's certainly in the range of f/2.5-f/3. I don't think there is much distortion in the picture because the lines I drew on top would show it if there was.

 

Tanveer.



#42 freestar8n

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Posted 07 October 2017 - 01:06 AM

Well the old and often quoted text from Roland above makes reference to a "coma-free" mak - and it seems like if he had made this to be coma-free he would have mentioned that up front.  

 

If those four simulated Airy patterns across the field are accurate then it does appear to be fairly coma free out to 1/4 degree.

 

If it really doesn't have a baffle then I'm not sure how well it would work on the moon.  And if it does have a baffle the obstruction may be larger.

 

Frank



#43 vahe

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Posted 07 October 2017 - 08:33 AM

 

If it really doesn't have a baffle then I'm not sure how well it would work on the moon.  And if it does have a baffle the obstruction may be larger.

 

Assuming that the new design follows the older model which I believe it does, with some minor changes, then the 23% co comes with some strings attached.

.
The 23% co. along with the main center baffle blocks the stray light from entering the eyepiece only for a very small area at the center, not the entire field, this assumes that for high power use a short eyepiece with small field lenses would be used and therefore no stray light will enter the field.

.
But for larger 2” eyepieces or any other widefield eyepiece with much larger field lens the 23% co is undersized for this specific design, for these larger eyepieces AP offers an additional add on co. disc that increases the actual obstruction size to something around 30% or thereabouts in order to block the stray light.

.
So, if you are viewing the Moon with a low power or a widefield and do not wish to include stray light in the view then you will be viewing the Moon with 30% co. which really defeats the scopes potential for refractor like high contrast view.

.

Vahe



#44 Jared

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Posted 07 October 2017 - 11:30 AM

 

Yes, that was the laminated spec sheet that Astro-Physics had attached to the scope for reference.  I’ll check the original image tomorrow to see if the coma amounts are legible.

 

Tanveer, I’m not sure you can just measure the document.  That would assume I was holding it flat.  Good enough for one decimal, but not sure about two and almost certainly not three.

I just offered three figure accuracy because I measured pixels to 3 figures but I think it's certainly in the range of f/2.5-f/3. I don't think there is much distortion in the picture because the lines I drew on top would show it if there was.

 

Tanveer.

 

Fair enough.



#45 Jared

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Posted 07 October 2017 - 11:37 AM

Here is a more legible shot of the coma measurements.

 

JSW2019166.jpg


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#46 Heywood

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Posted 07 October 2017 - 02:22 PM

I believe it was about $12k from what I understood but I don't believe that is official. I think they stated it would be a run of around 25 units or somewhere about there. 

 

Are you sure that you heard "about $12k"?  That seems low, at least to me.  Do you recall from whom you learned that information?

 

Thank you.

 

Heywood



#47 payner

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Posted 08 October 2017 - 12:17 PM

While the it is true the Meade 178-mm MCT has a large CO, it is a great performer on planets, double stars, etc. I have had a Russian 230-mm MCT, have Apos, and a Mewlon 250CRS, so have experience with great optical performance. For its aperture, the Meade is a truly great performer, by my evaluation.

 

Randy



#48 Don W

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Posted 08 October 2017 - 12:42 PM

I don't recall the exact year, but about 20 years ago, Roland brought his first 10" Mak to Astrofest in Kankakee, Illinois. The views through that scope we absolutely jaw dropping. I had viewed through his 8" and 10" refractors in previous years. The Mak was as good or better. The contrast and sharpness were phenomenal! The sky was like black velvet. It's permanently burned into my memory. I am extremely envious of anyone that can own one.



#49 Heywood

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Posted 13 October 2017 - 09:15 PM

On the Yahoo Astro-Physics User Group, the Christens announced, in answer to a query, that glass for the new 10" Mak-Cass has been ordered, hopefully to arrive before the end of the year.  So, it is certain that the new Mak-Cass will go into production.  But no price has been set, and no orders will be taken anytime soon.  I would guess that notifications are still at least six months away.



#50 Heywood

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Posted 29 January 2018 - 07:46 PM

Roland has just announced on the Yahoo Group that there WILL be a production run of the 10" Mak-Cass this year, and he will make 25 of them.


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