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Equipment Discussions >> Cats & Casses

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Darren Drake
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Maks VS SCTs
      #5587747 - 12/24/12 09:05 PM

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 and also are slower and not easy to collimate. They also tend to have slightly smaller obstructions and perhaps smoother surfaces. My 1980's C8 has proven to be an outstanding performer and would hold it's own against anything in its'class and would love to see how such a scope would compare in a head to head detailed match up. Thoughts?

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mdowns
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5587769 - 12/24/12 09:29 PM

I once had another very good c8 like yours. At the same time I owned a 7" mak.The planetary views provided by the mak were spectacular under steady skies,always better than the c8.Tighter focus with more intricate details visible when set up side by side. The c8 was really a good one often performing very well at 400x, But even with the brighter image it could not stay up with the mak. At that time ,besides those two,I had a 10" meade sct and an antares 4"f15 rfr.The mak always came in at number 1,the c8 second,the 4" rfr third and then the 10" sct.The rfr was handicapped by its smaller aperature,not its performance. The meade suffered from poor contrast levels that always seemed to hide details.

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mdowns
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Re: Maks VS SCTs new [Re: mdowns]
      #5587773 - 12/24/12 09:34 PM

BTW,if you can collimate your sct,you'll be able to collimate your mak.It is more complicated involving say 9 adjustment screws compared to 3.Nonetheless,once you've done it,its relatively simple,just more time consumming.

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azure1961p
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Re: Maks VS SCTs new [Re: mdowns]
      #5587795 - 12/24/12 09:54 PM

Downs,

Interesting comparisons. The way I understand it is the spherical surfaces of the Mak are easier to produce with repeatable precision where as the sct is not. I'm guessing that dished out corrector is where a lot of the extra expense goes into. Might be easier to perfect but possibly a time eater in manufacturing. This is going to be a good thread.

Pete

Edited by azure1961p (12/24/12 09:55 PM)


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Asbytec
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5587824 - 12/24/12 10:20 PM

The interesting difference between the designs is the way they handle spherical aberration. The Schmidt corrector, with an aspheric higher order term, delivers an 'aberrated' wavefront to the spherical primary. Best focus at 0.7D appears to be unaffected while marginal zones are corrected. The marginal wavefront is delayed just a bit so they reflect off the primary very close to a perfect reference sphere centered on best focus. This has the potential for some very good correction. However, I believe the central zones might also be delayed a bit, too, by the thicker central zone on the corrector. So there may be less paraxial correction (covered by the secondary) as the central wavefront lags the reference sphere. If so, that would seem to give a larger P-V error.

The Mak produces a convex wavefront to the spherical primary, and if done correctly, can provide a well corrected wavefront balanced for HSA. (Interestingly, the final wavefront, as I see it, has very similar shape to the Schmidt's higher order surface: the central and marginal zones lead the prefect reference sphere centered on best focus. I believe this offers a little better P-V error.) A Mak cannot completely eliminate HSA, like a good Schmidt corrector can. But the affected portion of the wavefront is negligible, if correcting for the lower order surface approximation is done correctly. In the Mak, all zones, including best focus at 0.7D, have a longer radius resulting from adding aberration of opposite sign (and a longer focal ratio.)

So, both will have some correction error, but the Mak will have some residual HSA since it is impossible to grind a perfect sphere (approximated in the lower order terms, as I understand it.) However, this HSA can be very minimal. So, really, it boils down to how well each scope is made. A good Schmidt can provide better correction to a sloppily made Mak with significant residual higher order aberration. However, a well made, all spherical Mak (of moderate aperture) can provide better images than a sloppy Schmidt surface. Obviously, right?

So, which is easier to make consistently well and smooth? Probably an all Spherical Mak of 6" or less aperture where HSA is not excessive to begin with. Much over 7", and it requires an aspheric term because its' higher order SA becomes exponentially more significant. So, at 6" or less, I would lay bets on the Mak being more consistently good than an equal aperture SCT due to relative ease of laying down a 1/20th wave sphere. (The calculations for Mak radii are the difficult part, grinding to tolerance should be pretty straight forward.) However, once both scopes require an aspheric term, all bets are off. In mass produced models, it will be the luck of the draw. With some hand re-figuring, the higher end Maks can give a better wavefront across most samples for a price. And, it's possible hand figuring a Mak aspheric will be a bit smoother than machine driven Schmidt aspherics.

But, this is nothing a 'premium' SCT could not do, either. Question is, do they? If not, I would give a nod to the Mak. If so, however, all bets are off again. They are both potentially very good designs, the Schmidt has even better potential to correct for SA, as I understand it. So, it probably depends heavily on how well each is made or how lucky you are to have a good one, IMO. (I have a good 6" Mak that seems well balanced for higher order SA and the views are just stunning. But, again, a 6" Mak is in that all spherical sweet zone, and it's probably nothing a good Schmidt cannot deliver. In this case, the discriminating factor might well be the central obstruction.)

I don't want to speak to the EDGE design since I know nothing about them. Heck, I can barely grasp the above, but I think it's at least close to being correct. My two cents, pay pal, please.

Edited by Asbytec (12/24/12 10:38 PM)


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coopman
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Re: Maks VS SCTs new [Re: Asbytec]
      #5588166 - 12/25/12 07:48 AM

Each person is different, of course, but I would find the small FOV of a Mak to be a major issue. I'd have to buy a tracking mount, and probably one with go-to as well, for a f/15 Mak. All of my current mounts are alt-az.

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jrbarnett
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5588279 - 12/25/12 10:23 AM

As mass-produced scopes go, the Gregory Maks are generally easier to fabricate to a given level of quality than an SCT. That said, when you luck out and get a really good SCT (not too common in my experience), the SCT will generally put through a lot more light at a given aperture than the Maks. The multicoatings used on SCTs are much better than the coatings applied to Maks made by the same fabricator (Synta).

So one one hand you have modern coating technology and on the other you have better average optical quality. Tough choice, really.

- Jim


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Eddgie
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5588488 - 12/25/12 01:32 PM

Identical aperture, Identical CO size, and identical quality, they will perform more or less exactly the same.

But these three things are rarely all the same.

If you make the CO smaller (Easy at f/15), or the quality better (think Intes Micro), expect the MCT to perform better on planets but the SCT will have a much wider field capability, and this allows it to perform better as a general use instrument. It is no accident that commercial SCTs are f/10. It is about as fast as the design can be made and still deliver acceptable off axis performance.

I have plotted the MTF curves for the Intes Micro M715 against the C8. The C8 would have to be perfect optically (a sure thing with the Intes Micro, a rare thing with the C8) for the C8 to come in even to the Intes Micro M715.

Not to say that there are not a few perfect C8s out there, but most are not.

But even a very good one will give planetary performance that is similar enough that it will be hard to see the difference.

After owning 4 or 5 dozen scopes, I have come to believe that clear aperture is the easiest way to compare planetary performance on telescopes. The more clear aperture, the better. But quality counts, and when the clear aperture is the same, the scope with the best optical quality will win out.

Both the C8 and the M715 have about the same clear aperture (134mm for the C8 VS 135mm for the M715), but finding C8s that match the quality of the Intes Micro M715 would be difficult. Not impossible. I think there many out there that are this good. But there are far far more out there that are not this good.

But again, for all other observing, the C8 to me would be preferable because of the bigger image scale for the same exit pupil when viewing extended objects, and for the ability to provide a far bigger true field than the M715.

Once again, I will repeat this message... Scopes differ far more in their off axis characteristics than their on axis characteristices, and if you got a really excellent C8, it would equal an M715 on planets, but bet better on just about everything else.

Not bad for the price. Not bad at all.


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gnowellsct
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Re: Maks VS SCTs new [Re: Eddgie]
      #5588687 - 12/25/12 04:58 PM

99% of what we argue about is the 1% of performance that we *might* get if our instruments were all well maintained and the sky was cooperative.

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azure1961p
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Re: Maks VS SCTs new [Re: gnowellsct]
      #5588707 - 12/25/12 05:25 PM

Actually it 5%.

Pete


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orion61

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Re: Maks VS SCTs new [Re: azure1961p]
      #5588929 - 12/25/12 09:33 PM

I love this Thread some very interesting posts and I agree with them all, for the most part. I have one of the Meade
7" Maks. It comes down to QC.. period.. I had one of these before and was not impressed with it, the one I got from escher here is much better. I don't believe he realizes it.
I don't mind the smaller field of view, the added contrast
makes up for it. I simply "like" the view through the Maks.
The Synta 127 (Celestron 127 NexStar SLT) I believe is an instant classic. Planetary views are pretty respectible.
I have an above average C8, an old Orange tube that performs
very well, so the answer to settle this is....
YA GOTTA HAVE EM BOTH....


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vct123
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Re: Maks VS SCTs new [Re: orion61]
      #5589023 - 12/25/12 10:58 PM

I had (2) Intes m703 maks and an m6511 which I found all three to be excellent lunar scopes, probably the best I have owned, but due to the co of similar size to a c8, I found them to be no big deal for planetary detail or similar to the many c8's I have owned depending on the particular sample of sct. I did notice them all to be slightly dimmer compared to other scopes of similar size most likely due to the inferior coatings. They did offer a flatter edge of field but if given the choice I would take a C8 Edge

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RAKing
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5589447 - 12/26/12 10:36 AM

I agree with all the above, more or less.

I have owned half a dozen C8 regular SCT and none of them could hold a candle to my 8 inch f/10 STF-Mirage Deluxe MCT. Some of them were okay on-axis, but the edges were soft and the coma was bad (not so important for planetary). I have owned two C8 Edge and they compare quite well with my Mak, but in the end, the Mak scores better for both optical and mechanical quality.

The Edge requires corrective lenses in the baffle to compete with its assembly line optics, while the Mak just uses smoother 1/10 wave surfaces. My STF has machined front and rear cells, so collimation has stayed perfect since the day it shipped from Moscow. Plus, the focuser mechanics are smoother and more stable on the Mak. (I changed out the Edge focusers for FeatherTouch Micros.) My STF Mak is an f/10, but has a slightly smaller CO than the SCT (30.5 percent). Added bonus: The STF comes with a decent bolt-on dew shield. It's solid and works well enough to make dew straps redundant.

The only knock on the Mak is the cool down time. It take a good two hours to stabilize, but the views are magnificent.

My .02 based on personal expense and experience.

Ron


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orion61

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Re: Maks VS SCTs new [Re: RAKing]
      #5589494 - 12/26/12 11:06 AM

Yes the cool down time on my 7" LX200 is a long time with that 8 lb weight in there. Even when I keep it oin my unheated garage it still takes 45 minutes!
But like the above poster says nothing beats it for
Planetary Except a high $ Apo of similar size.
I'd have to be hard pressed to sell her.
I dont think many Planetary/Double Star viewers will
pick the SCT over a good MCT, My Meade 102 ED
comes close but is dimmer, (there is one for sale in the S&S
thread right now CEAP!)


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Asbytec
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Re: Maks VS SCTs new [Re: orion61]
      #5589539 - 12/26/12 11:29 AM

Shhh!

You know, on cooling...the Mak seems to have a bad reputation. Personally, I have absolutely ZERO OTA thermal issues with a little prep in moderate climates. Conversely, some of my previous larger, more massive SCTs would (at times) present thermals well into the evening even in the tropics. In fairness, that was long before I began to realize how to prep them for observing.

So, point being, since both Maks and SCTs are very similar in their gut (enclosed massive mirror and supporting structure.) I'd guess there is little disparity in cool down across each design given similar conditions. The meniscus is a bit thicker but, much like a refractor objective, it's exposed to open air and can dissipate more readily that the enclosed primary mirror. Both correctors will dew over.

No testing, really, or proof other than anecdotal to support that assertion. Just some application of theory, correct or otherwise. If I were to form a hypothesis for testing, that would be it: both have similar thermal characteristics and it might be proportional to mass (aperture.)


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Darren Drake
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Re: Maks VS SCTs new [Re: Asbytec]
      #5589567 - 12/26/12 11:45 AM

Of course an MNT is a different story over an MCT as the mak newt has a much smaller obstruction and should beat out the other designs all things being equal.

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Darren Drake
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5589711 - 12/26/12 01:01 PM

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...

Edited by Darren Drake (12/26/12 01:06 PM)


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GeneT
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Re: Maks VS SCTs new [Re: Eddgie]
      #5590006 - 12/26/12 05:11 PM

Quote:

Identical aperture, Identical CO size, and identical quality, they will perform more or less exactly the same.
But these three things are rarely all the same.




I agree with this statement. If I was going to buy a SCT, I would pay extra for the Edge HD.


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aolo
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Re: Maks VS SCTs new [Re: GeneT]
      #5590156 - 12/26/12 07:17 PM

Darren,

You reviewed a F/10 LOMO 180 many years back. I happen to have one due to that review. All SCT I've seen are F/10. I've seen MCT between F/10 and F/15. Not apples and apples, but what are your thoughts on the 7" Lomo F/10 MCT vs the C8? Would a 7" f15 Mak may offer compete with a 8" F/10 SCT on Planets and Double Stars?


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Darren Drake
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Re: Maks VS SCTs new [Re: aolo]
      #5590169 - 12/26/12 07:26 PM

Quote:

Darren,

You reviewed a F/10 LOMO 180 many years back. I happen to have one due to that review. All SCT I've seen are F/10. I've seen MCT between F/10 and F/15. Not apples and apples, but what are your thoughts on the 7" Lomo F/10 MCT vs the C8? Would a 7" f15 Mak may offer compete with a 8" F/10 SCT on Planets and Double Stars?




Yes my review of that scope is here on CN. I would suspect that the C8 would beat out the LOMO. It was ok but not great as I recall as I think there was some spherical aberration and the C8 is very good. How does yours perform?


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Darren Drake
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5590425 - 12/26/12 10:34 PM Attachment (48 downloads)

So just how good is my C8? By placing an artificial star in my optically excellent 12 inch dob and aiming the C8 right into the 12 and placing a straight edge in the C8 I was able to get a good null test. It took a bit of patience but I was able to get a good and very revealing pic of the surface of the C8 similar to what Rohr does.

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Darren Drake
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5590431 - 12/26/12 10:38 PM Attachment (70 downloads)

Here is one of the better pics I was able to get. The sensitivity is extremely high. When I put my hand in front of the C8 or the furnace comes on the air currents become very visible and the test is impossible to conduct. The very subtle surface errors that are visible are real as they were repeatedly visible in all my test pics. Overall this is a very good scope.

Edited by Darren Drake (12/26/12 11:35 PM)


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Gord
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5590473 - 12/26/12 11:01 PM

Darren,

Could you elaborate on how you did this? I don't understand the "straight edge" in the C8 part.

Thanks,


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Darren Drake
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Re: Maks VS SCTs new [Re: Gord]
      #5590482 - 12/26/12 11:04 PM

It's a bit long to explain. I did write an article on it here a few years ago. Check it out and maybe that will help.
http://www.cloudynights.com/item.php?item_id=1637


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titanio
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5590902 - 12/27/12 09:54 AM

I prefer Maks to STCs, for me Mak-Newtons are even better. I have had one IM 815 Deluxe, one MN78, One C11, one C8 and I have a MN86 Deluxe and a C9,25 HD. The only SCT that can perform similar or even better than a very nice Mak is the C 9,25 edge HD, I could say it is better than the M815 Deluxe and maybe similar to the MN78. The C8 I had was very nice only with the stars colors the star colors look like originals and very nice, but I didnīt like other thinks. Many STC telescope are goods and many of them are not so goods but they are cheaper. Mak-Cass and Mak-News normally are good or very good but you have to pay extra money for them, moreover you have the guaranty that your telescope will be good and normally a report comes with them.

Regards

Toni


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Illinois
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Re: Maks VS SCTs new [Re: titanio]
      #5593943 - 12/29/12 08:56 AM

I used C8 for years until I got my 180mm Mak-cass and its great for planets and moon! 2700mm I love it! I would like to have a 10 or 12 inch Mak-Cass but $$$$$$$$$$$$$$$$!!!!!!!!!!

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norcalastroguy
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Re: Maks VS SCTs new [Re: Darren Drake]
      #5594035 - 12/29/12 10:02 AM Attachment (33 downloads)

Having owned more scopes than common sense (46 since 2001), I can say in all fairness that a solid well made Mak is the scope to use IF your interest and general purpose is planetary viewing...Not saying you won't of can't appreciate most SCT's for general overall use but let me share 1 experience...The first time I viewed through a Mak I was using my Tak TOA 130, one of the club members next to me had this funny looking little scope with constellations painted all over the OTA, here I'm thinking " what the heck is that thing", little did I understand that a 3.5 questar was going to eat my 130's lunch! One look at Jupiter and the overall view was incredible, prestine, super sharp and overall I was very impressed! That isn't to say my 130 was a slouch, only stating the Maks are very good scope types within a certain view point...I also used a 204 Mak side by side a TOA 130, it was a Bosma ( which makes Ioptron ) and while it was solid for planetary views it really fell short going beyond our solar system and I enjoyed the views in the 130 better ( minimal view conditions / waxing crescent )...Spherical aberration is more inherent with lower f ratios because of the reflection of light rays when they strike the mirror near its edge, in comparison with those that strike nearer the center or get corrected! Even at a 1000x my Meade 16 never once experienced aberration, than again most of your viewing isn't beyond 2 or three hundred power so aberration is held to a minimum...pound for pound you can't beat a solid SCT, OR even a Newtonian, I say go with an SCT BUT get out and use it!

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Napersky
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Re: Maks VS SCTs new [Re: norcalastroguy]
      #5594333 - 12/29/12 12:42 PM

Darren,

Great photo of the null test but I don't know what I am looking for. I see dark shades and lighter places. How do you determine where the zones are and what is good and what is bad.

I really appreciate your collimation of my C8 and the better performance that has resulted from it.

Good thread here on MCT vs SCT. What I have learned is that the MCT can come in longer focal lengths like refractors. How about SCT's I have not seen any f12 or f15 SCTS?

Mark


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Darren Drake
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Re: Maks VS SCTs new [Re: Napersky]
      #5594406 - 12/29/12 01:20 PM

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??


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Denimsky
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Re: Maks VS SCTs new [Re: norcalastroguy]
      #5594498 - 12/29/12 02:06 PM

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.


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maknewtnut
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Re: Maks VS SCTs new [Re: Denimsky]
      #5594677 - 12/29/12 04:12 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.




Agreed. Hopefully just a typo. I love my Maks, but at that aperture range I'll take a quality 90mm refractor to edge out a 3.5" Questar every time.


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Bob Abraham
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Re: Maks VS SCTs new [Re: maknewtnut]
      #5594982 - 12/29/12 07:31 PM

My 3.5" Questar (which is a great scope and which I love... it is an excellent sample) is clearly inferior to a good 4" apo on planets. They are not really in the same ballpark.

With regard to the OP's question, I have compared my 8" TEC Mak to a C8 many times. While they are in the same ballpark, the Mak is quite a lot better on planets.

Bob

P.S. the only 8" scope that has ever beaten my 8" Mak on Jupiter is an 8" Newtonian made by Normand Fullum.

Edited by Bob Abraham (12/29/12 08:08 PM)


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RAKing
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Re: Maks VS SCTs new [Re: Bob Abraham]
      #5595726 - 12/30/12 09:15 AM

Quote:

With regard to the OP's question, I have compared my 8" TEC Mak to a C8 many times. While they are in the same ballpark, the Mak is quite a lot better on planets.

Bob

P.S. the only 8" scope that has ever beaten my 8" Mak on Jupiter is an 8" Newtonian made by Normand Fullum.




In the interest of full disclosure - the only 8 inch scope that has consistently bettered my 8 inch STF-Mirage Mak is my 8 inch f/6 Newtonian. It has a Zambuto mirror and a 3-vane spider to lessen the diffraction spikes.

But since this is the C&C forum, I should also point out that because of my back surgery issues, the Mak whips the Newt's backside every night for ergonomics and comfort.

Ron


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Re: Maks VS SCTs new [Re: Bob Abraham]
      #5595730 - 12/30/12 09:19 AM

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.

Edited by Joe Cepleur (12/31/12 07:35 AM)


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orion61

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Re: Maks VS SCTs new [Re: Denimsky]
      #5595860 - 12/30/12 10:39 AM

I had a 1959 Questar It was beautifully made, but it had horrible SA, Nearly unuseable, It had sit in its case on display for 40 years, A good place for it!

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Re: Maks VS SCTs new [Re: orion61]
      #5595886 - 12/30/12 10:51 AM

Larry, no way! really? Horrible SA?

I just read the Q ad from way back when, the one showing the infamous license plate photo. I thought they were all good and they rejected those that could not exceed Raleigh.


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Re: Maks VS SCTs new [Re: Joe Cepleur]
      #5596461 - 12/30/12 04:13 PM

Hi Joe,

The longer focal length doesn't result in inherently greater clarity. Assuming a sensible optical design, the main factors which define clarity, which I think of in terms of resolution and contrast, are aperture, quality of the optics and obstruction of the pupil (and of course the seeing). 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, and slower optics often have smaller secondary obstructions etc.

Bob

Edited by Bob Abraham (12/30/12 04:39 PM)


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Re: Maks VS SCTs new [Re: Asbytec]
      #5596516 - 12/30/12 04:37 PM

I like to collect older telescopes and in a few cases have picked up scopes with good reputations that show disappointing performance. In some cases it has simply been due to poor fabrication, but in most cases I've found that the apparently poor optics were due to an accumulation of small maintenance issues which piled up over the years.

For example, I have a TEC-6 which has really great optics. But when I first bought it (used) it was showing quite a lot of astigmatism. I know Yuri pretty well and know he would never knowingly ship an obviously astigmatic scope, so I did a little investigating. I ultimately traced the astigmatism to the dew shield being slightly out of round which was pressuring the meniscus cell, which was also overly tightened down. No doubt at some point in its life it the dew shield got stored in such a way that it got bent very slightly and the meniscus was removed by a prior owner for some cleaning and when it was replaced it was tightened a little too much. These issues were trivial to fix and when dealt with the scope went from being ho-hum to being a really fabulous performer.

Anyway, my conclusion after this was that one needs to be cautious about concluding things about the optical quality of older scopes, because previous owners may have done stuff which can degrade the performance of the telescope. I wonder how many "comparos" of different optical designs are compromised by these sorts of factors.

Bob

Quote:

Larry, no way! really? Horrible SA?

I just read the Q ad from way back when, the one showing the infamous license plate photo. I thought they were all good and they rejected those that could not exceed Raleigh.




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Re: Maks VS SCTs new [Re: Joe Cepleur]
      #5596992 - 12/30/12 09:54 PM

Quote:

Longer focal lengths are more tolerant of optical imperfections, making this an apples-to-oranges comparison (or, at least "Red Delicious" to "Granny Smith").





Focal lenght has no bearing on the contrast (sharpness) that an instrument can provide.

Angular resolution is mostly a function of total aperture.

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

Contrast transfer is what is left after the apeture, obstruction, and optical defects take away from the contrast that was present at the target.

The focal lenght or focal ratio have no bearing on image quality. The size of the aperture and the size of the obstruction (and secondary spider vane diffraction) determine the maximum contrast that a system can preserve, and the optical quality determines how much less contrast you will get as compared to the maximum contrast that an aperture can provide.


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Re: Maks VS SCTs new [Re: Bob Abraham]
      #5597219 - 12/31/12 12:21 AM

Makes perfect sense, Bob. Thanks.

Edit: Well, kind of. Not sure what would cause severe SA over time. But, your point is well taken, regardless.

Edited by Asbytec (12/31/12 02:16 AM)


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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.


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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


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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?!


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RAKing
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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


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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


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Gord
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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,


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Darren Drake
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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)


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aa6ww
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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


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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


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Asbytec
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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.


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

Zambuto Mirror referencing Rohr

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


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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


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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.


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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)


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Re: Maks VS SCTs new [Re: Darren Drake]
      #5601347 - 01/02/13 02:26 PM

Ah! Thanks Darren.

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Napersky
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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


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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.

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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)


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bcuddihee
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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

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Jeff B
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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


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Re: Maks VS SCTs new [Re: Jeff B]
      #5603024 - 01/03/13 01:37 PM

Hey buddy, Happy New Year!..tomorrow evening look promising for Hisey.
Any chance.


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Gord
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Re: Maks VS SCTs new [Re: bcuddihee]
      #5603634 - 01/03/13 08:04 PM

That was the first thing I thought of when I saw the image. I've heard of this on some newtonian mirrors, but had never seen these images before from SCT's.

I've never noticed anything on my C14 Edge sample.

Clear skies,


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Re: Maks VS SCTs new [Re: Jeff B]
      #5605269 - 01/04/13 05:39 PM

Quote:

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




From what I've read, it's nothing to do with the primary but an imprint into the corrector's figure from the grooves in the master block used to facilitate the vacuum. Apparently Celestron later changed their master blocks to avoid this problem. Used to be fairly common, even seen in-focus, in the older Celestrons. Newer Celestrons don't have it.

Tanveer.


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