Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Cats & Casses

Pages: 1 | 2 | 3 | 4 | (show all)
Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Maks VS SCTs new [Re: Bob Abraham]
      #5597530 - 12/31/12 08:37 AM

Quote:

The focal length does matter though in the sense that in many cases it's easier to fabricate high quality slower optics than it is to fabricate high-quality fast optics




That's what I'm getting at. In theory, many designs could work well, if price were no object. In practice, price is always an object. There are many things many of us can not afford. When two scopes are made to equal tolerances, and so cost about the same to manufacture, the one with slower optics will be more forgiving at the eyepiece. This is not exactly true, because different manufacturers build to different quality at the same cost. The classic example is Tom Johnson's master block method, which lowered the price of Schmidt correctors by orders of magnitude. So, the fact that most Schmidt-Casses are made as fast as is practical, yet remain medium-focus (f/10), and most Maks are made long focus (f/15), means the practical issues of manufacturing and cost are likely to overwhelm generalized theory in this discussion. If you can not lift or afford a giant refractor, Newt, or, for that matter, Schiefspiegler, buy a Cat. Theory may guide your purchase, but in reality, the decision will be messy.

Once upon a time, we corrected our optics by making them long focus. Today, the trend is to pay a fortune for clarity in wider fields of view. $500 coma correctors, multi-thousand-dollar EdgeHD correctors, Nagler eyepieces instead of orthoscopics... All this is an expression of wanting wider views with clearer edges (and faster shooting of astrophotographs). It's all wonderful, but it's expensive. Cruise over to the Classics forum, and you'll find nostalgic Romantics who are often also sensitive to price, and gladly trade narrower fields of view for dollar-for-dollar beauty at the eyepiece. Correcting an f/10 system is likely to cost more than correcting an f/15 system. That's all I'm saying, and I see it as tossing a rather heavy monkey wrench into generalized comments about the relative superiority of Mak- versus Schmidt-Cats.


Post Extras: Print Post   Remind Me!   Notify Moderator  
RAKing
Postmaster
*****

Reged: 12/28/07

Loc: West of the D.C. Nebula
Re: Maks VS SCTs new [Re: Joe Cepleur]
      #5597595 - 12/31/12 09:36 AM

Quote:

I'm in the dangerous realm of knowing almost enough to follow all these cool discussions of wavefronts and such, but have certainly not played with enough examples of all these scopes to offer any but one maybe useful question. Most SCTs are f/10. Most Maks are longer, maybe f/15. Would not the typical Mak's additional focal length by itself make for a narrower field, but also inherently greater clarity at the eyepiece? Longer focal lengths are more tolerant of optical imperfections, making this an apples-to-oranges comparison (or, at least "Red Delicious" to "Granny Smith").

This thread mentions the importance of assuring that every component of an SCT is properly centered and rotated. Orion61, if anything salvages the salt-encrusted C8 you are fixing for me, it will be the careful adjustment of its optical train.




Joe,

For the record, my 8 inch STF-Mirage is an f/10 Mak and I am comparing it directly to my former C8 SCTs (regular and Edge). I have also owned a couple of smaller f/12 Maks, but can't make any comparisons due to aperture difference.

Cheers,

Ron


Post Extras: Print Post   Remind Me!   Notify Moderator  
Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Maks VS SCTs new [Re: Darren Drake]
      #5597638 - 12/31/12 10:03 AM

Quote:

If we assume identical apertures which scope design tends to be the better planetary performer the Mak Casses or SCTs? The Maks tend to be considerably more expensive especially in the larger apertures




Case in point. A meniscus lens has two spherical surfaces, and so would be cheaper than a Schmidt corrector to manufacture, except that the master block process reversed the economics. 

Quote:

my 8 inch STF-Mirage is an f/10 Mak and I am comparing it directly to my former C8 SCTs (regular and Edge)




That is the perfect technical comparison! Would you be comfortable commenting on the relative prices of these scopes? Not what you paid if you found a great deal, but typical street prices. Then again, it may be that Russian manufacturers have a significant advantage in pricing. What might a similar scope cost if Takahashi or Astro-Physics built it? It's a big world, with many factors distorting the purely technical discussion. 

Enough soap boxing from me! Point made, or, with apologies, over-made. Honestly, with the distortions of cost in mind, the technical discussions are far more interesting! Certainly there are connoisseurs who pay what they must for that last edge of performance, and lucky buyers paying little for great scopes. So, before I have to discipline myself for hijacking the thread, which'll it be, which is better for planetary work: Schmitt or Mak?!


Post Extras: Print Post   Remind Me!   Notify Moderator  
RAKing
Postmaster
*****

Reged: 12/28/07

Loc: West of the D.C. Nebula
Re: Maks VS SCTs new [Re: Joe Cepleur]
      #5597711 - 12/31/12 10:44 AM

Quote:

Quote:

my 8 inch STF-Mirage is an f/10 Mak and I am comparing it directly to my former C8 SCTs (regular and Edge)




That is the perfect technical comparison! Would you be comfortable commenting on the relative prices of these scopes? Not what you paid if you found a great deal, but typical street prices. Then again, it may be that Russian manufacturers have a significant advantage in pricing. What might a similar scope cost if Takahashi or Astro-Physics built it? It's a big world, with many factors distorting the purely technical discussion. 

Enough soap boxing from me! Point made, or, with apologies, over-made. Honestly, with the distortions of cost in mind, the technical discussions are far more interesting! Certainly there are connoisseurs who pay what they must for that last edge of performance, and lucky buyers paying little for great scopes. So, before I have to discipline myself for hijacking the thread, which'll it be, which is better for planetary work: Schmitt or Mak?!




This is a fair question. My STF-Mirage is similar to the TEC and A-P Maks, with super smooth optics and machined parts fitting perfectly together. They don't make a lot of these, the optics have been tested and certified to be better than 1/8 wave, and the "street price" to get one into the US is about $4000.00. Compare that to the cost of a mass-produced SCT: C8 ($1000) or C8-HD Edge ($1300) and you can see why more folks opt for the mass-produced SCT, even with average optics.

Are the views $3000 better? Maybe not, but I like the views through my scope and I also enjoy the fit, finish, and no-hassles of quality merchandise.

Cheers,

Ron


Post Extras: Print Post   Remind Me!   Notify Moderator  
Napersky
Carpal Tunnel
*****

Reged: 01/27/10

Loc: Chicagoland
Re: Maks VS SCTs new [Re: Darren Drake]
      #5598569 - 12/31/12 06:52 PM

Quote:

Hey Mark,
In the null test image the dark and lighter areas represent imperfections on the order in this case of somewhere on the order of a little more than a millionth of an inch from perfect which since the shadings are very subtle suggest this is a very good scope optically. I have done the same test on numerous other scopes and have seen all forms of aberrations quite obviously as the test is very sensitive. I have recently thought of the idea of starting an image gallery of various scopes showing the null test images along with pics of the scopes. Would anyone be interested in this??




A millionth of an inch = 25.39 nanometers or 1/10th of a wavelength. How do we know this or arrive at this metric?

Mark


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Maks VS SCTs new [Re: Darren Drake]
      #5598604 - 12/31/12 07:15 PM

Quote:

I have recently thought of the idea of starting an image gallery of various scopes showing the null test images along with pics of the scopes. Would anyone be interested in this??




Darren,

I think that would be very interesting to see.

Clear skies,


Post Extras: Print Post   Remind Me!   Notify Moderator  
Darren Drake
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
Re: Maks VS SCTs new [Re: Gord]
      #5599956 - 01/01/13 05:01 PM

Mark,
I really don't know exactly how highly sensitive the null image is accurate to. I do know what serious or damaging aberrations in a null test look like and see them often in other scopes but no such issues are seen in this image. I could only guess that this scope is in the 1/6 to 1/8 wave accuracy based on the null test and star test of the C8. Without qualitative measurements based on real data that's all I can really say. Also the images this scope has produced have been extremely impressive and no one would criticize the views as they are just that good under the right conditions.

I have seen many of the null test images on Rohr's site and even though I believe his images have twice the sensitivity as mine since (I think) the light source goes through the scope twice in his tests this scope still tests quite favorably to what most of the SCTs he has tested on his site do. If I am wrong about how Rohr tests his scopes someone please correct me. I plan to take more null test images in the future of more scopes and post here along with descriptions of how the scopes perform under the stars. I may consider starting an image gallery of the many scopes I have access to along with their null tests.

Edited by Darren Drake (01/01/13 06:26 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
aa6ww
professor emeritus
*****

Reged: 10/23/11

Loc: Sacramento, Calif.
Re: Maks VS SCTs new [Re: Denimsky]
      #5600270 - 01/01/13 08:21 PM

Quote:

This is first time that I heard a Questar 3.5" outperforms a 130mm APO refractor. It is even more surprised it is Tak TOA 130 which is among finest refractors.

Theoretically it is completely impossible for 3.5" Mak to outperform 5" APO refractor: aperture and central obstruction unless something is way off with the 130mm.

Was your scope fully cooled? How about collimation? was it spot on?

Few reviews that I read say a quality 4" APO refractor outperform a Questar 3.5" which does make sense to me.




It was a 7" questar, not the 3.5" model. I was there also and I did'nt see the comparison because I was enjoying some excellent views of venus with a 6" AP Superplanetary.

..Ralph in Sac


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Maks VS SCTs new [Re: Eddgie]
      #5600484 - 01/01/13 10:40 PM

Quote:


Linear resolution is a function of focal ratio and focal ratio alone.




It is true that linear resolution is a function of focal ratio but the angular resolution of a line, which is what is important in a telescope, is a function of the aperture and not the focal ratio.

Regarding focal ratio versus optical quality... Mak-Casses have fast primary mirrors, maybe F/3 or so, with a magnifying secondary and a corrector. A Newtonian or even a refractor at F/10 or F/15 has relatively shallow curves but this is not the case with compound scopes.. In my way of thinking, one has to think of a compound scope as having fast, generally spherical optics.

A MAK-Newtonian is like a standard Newtonian, if it's F/7,. the primary is F/7, no trick secondary mirrors to slow down the focal ratio by a factor of 4 or 5... this is probably another reason, besides the small secondary, that makes the MAK-Newt a good performer at high magnifications.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Asbytec
Guy in a furry hat
*****

Reged: 08/08/07

Loc: La Union, PI
Re: Maks VS SCTs new [Re: Jon Isaacs]
      #5600558 - 01/01/13 11:54 PM

Quote:

...Mak-Casses have fast primary mirrors, maybe F/3 or so, with a magnifying secondary and a corrector...In my way of thinking, one has to think of a compound scope as having fast, generally spherical optics.

A MAK-Newtonian is like a standard Newtonian...no trick secondary mirrors to slow down the focal ratio by a factor of 4 or 5... this is probably another reason, besides the small secondary, that makes the MAK-Newt a good performer at high magnifications.




Absolutely. Also the way in which each design handles SA is important, too, and the degree of succeeds achieved in production. (My post above.) Potentially, my understanding is the SCT has more potential but a more difficult aspheric term.

A Mak Newt makes very good use of it's relaxed spherical meniscus radii (less HSA) and a comfortably slow primary (and minimal CO.) Even a MCT would benefit from weaker curves, which is why they tend to have a bit longer focal ratios.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Napersky
Carpal Tunnel
*****

Reged: 01/27/10

Loc: Chicagoland
Re: Maks VS SCTs new [Re: Asbytec]
      #5600809 - 01/02/13 07:48 AM

Zambuto Mirror referencing Rohr

http://www.zambutomirrors.com/zambutoopticalcd.html


Post Extras: Print Post   Remind Me!   Notify Moderator  
skyjim
Carpal Tunnel
*****

Reged: 01/13/07

Loc: Carmel, NY
Re: Maks VS SCTs new [Re: Darren Drake]
      #5601175 - 01/02/13 12:33 PM

My take after having owned many Intes Micro and some of the better china import MCT's is that standard C8's will produce a brighter image and some of the best samples of C8's I have owned will come close but a good 7" MCT will win. This changed once I got my hand's on a C8HD, the HD scope was more portable, cool down faster, had pinpoint stars out to the edge of feild and even the focusing system was as good but had a buttery smooth feel which the MCT's never did and no focus shift or flop noted thus far. I did RTFM when I got the edge scope and un locked the mirror locks before ever turning the focus knob, I think that's were many run into isssue's with the scope's focuser. As far as planet's and lunar the C8HD does as well as the IM M703 I owned, same amount of fine detail but a brighter image plus the scope does very well on double's and DSO, spank's the 703 on dso's. As many may rememeber I have alway's had a warm spot when it came to MCT's but here in NY the C8HD has so much more going for it plus if you need service or part's you can get it were the russian mct's are almost imposible. As far as new prices the C8HD is half the cost of a new 7" Russian MCT and about the same as the China made Synta 7" MCT's but the MCT's need around 2 hours plus to cool down were the 8HD is less than an hour.
Happy New Year to all the gang here on CN.
Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Maks VS SCTs new [Re: Darren Drake]
      #5601242 - 01/02/13 01:14 PM

Quote:

Here is a series of very revealing comparisons from Rohr's site. I think the best SCT here is maybe the C8 Nextstar from 2005 and the best Mak is the 8 inch Intes Alter. Rohr has many other examples on his website but this is a revealing series nontheless.

http://translate.googleusercontent.com/translate_c?depth=1&ie=UTF8&ru...



Ugh! That is the most frightening thing I've ever seen Darren! This makes me reconsider the C11 EdgeHD I had my eye on... Surely a Tec Mak, Intes Micro or Mewlon would be a better bet for a smoother mirror. Those commercial mirrors are just ghastly.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Darren Drake
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
Re: Maks VS SCTs new [Re: johnnyha]
      #5601252 - 01/02/13 01:20 PM

Quote:

Quote:

Here is a series of very revealing comparisons from Rohr's site. I think the best SCT here is maybe the C8 Nextstar from 2005 and the best Mak is the 8 inch Intes Alter. Rohr has many other examples on his website but this is a revealing series nontheless

http://translate.googleusercontent.com/translate_c?depth=1&ie=UTF8&ru...



Ugh! That is the most frightening thing I've ever seen Darren! This makes me reconsider the C11 EdgeHD I had my eye on... Surely a Tec Mak, Intes Micro or Mewlon would be a better bet for a smoother mirror. Those commercial mirrors are just ghastly.




Actually I don't believe the mirrors are the cause of some of the roughness. I believe the corrector plates are the cause of most of he errors but that's only a suspicion since the correctors are much more difficult to fabricate than a spherical mirror.

Edited by Darren Drake (01/03/13 02:17 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Maks VS SCTs new [Re: Darren Drake]
      #5601347 - 01/02/13 02:26 PM

Ah! Thanks Darren.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Napersky
Carpal Tunnel
*****

Reged: 01/27/10

Loc: Chicagoland
Re: Maks VS SCTs new [Re: johnnyha]
      #5601407 - 01/02/13 03:07 PM

Quote:

Quote:

Here is a series of very revealing comparisons from Rohr's site. I think the best SCT here is maybe the C8 Nextstar from 2005 and the best Mak is the 8 inch Intes Alter. Rohr has many other examples on his website but this is a revealing series nontheless.

http://translate.googleusercontent.com/translate_c?depth=1&ie=UTF8&ru...



Ugh! That is the most frightening thing I've ever seen Darren! This makes me reconsider the C11 EdgeHD I had my eye on... Surely a Tec Mak, Intes Micro or Mewlon would be a better bet for a smoother mirror. Those commercial mirrors are just ghastly.





I wouldn't worry about the C11 Edge HD. Darren's good example here is his C8, my C8 1990s vintage is also an excellent performer. An Edge HD C11 should be much much better than those classic C8s.

Mark


Post Extras: Print Post   Remind Me!   Notify Moderator  
bcuddihee
Carpal Tunnel
*****

Reged: 11/04/06

Loc: Cincinnati Ohio
Re: Maks VS SCTs new [Re: Napersky]
      #5602880 - 01/03/13 12:12 PM

What is that strange radial spider pattern on the 2004 c11? I have seen this on one other c11 and wonder if it was just on the 2004 models.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Darren Drake
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
Re: Maks VS SCTs new [Re: bcuddihee]
      #5602953 - 01/03/13 12:52 PM

Brendan
I believe those radial patterns are caused by to much polishing pressure on the primary and the ribbed structures on the back of the primary imprinted into the figure as a result. I'm quite surprised celestron would let such a thing happen.

Edited by Darren Drake (01/03/13 02:19 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
bcuddihee
Carpal Tunnel
*****

Reged: 11/04/06

Loc: Cincinnati Ohio
Re: Maks VS SCTs new [Re: Darren Drake]
      #5603008 - 01/03/13 01:30 PM

Thanks Darren, a friend of mine has on of these c11's and I too am quite surprised that these were sold with this condition. It is evident even on a casual inspection of a due focused star. Bc

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff B
Carpal Tunnel
*****

Reged: 12/30/06

Re: Maks VS SCTs new [Re: bcuddihee]
      #5603017 - 01/03/13 01:34 PM

Quote:

What is that strange radial spider pattern on the 2004 c11? I have seen this on one other c11...




And whose C11 might that be ?

Yeah I figured it out last week when I was looking at pictures of a disassembled C14 and noticed the ribs on the back of the mirror. Also, as the mirror cools, those ribs will probably show themselves as well. I notice in my C11 they're much less visible but still there and fairly easy to see even after the scope has stabilized thermally . I catch a very faint hint of them in the C14 as well but I never would have gone looking if I had not seen the photo of the back of the C14 mirror.

Jeff


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | (show all)


Extra information
19 registered and 27 anonymous users are browsing this forum.

Moderator:  Cotts, Starman27, kkokkolis 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 5150

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics