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Equipment Discussions >> Cats & Casses

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Darren Drake
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
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
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
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
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
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
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
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
sage


Reged: 02/15/09

Loc: Alicante, Spain
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
Carpal Tunnel


Reged: 12/18/06

Loc: near Dixon, Illinois USA
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
newbie
*****

Reged: 06/07/12

Loc: CA USA
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
Carpal Tunnel
*****

Reged: 01/27/10

Loc: Chicagoland
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
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
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
professor emeritus


Reged: 01/21/07

Loc: BC, Canada
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
Member
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Reged: 10/08/06

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
sage


Reged: 05/17/05

Loc: Toronto, ON, Canada
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
Postmaster
*****

Reged: 12/28/07

Loc: West of the D.C. Nebula
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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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
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

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
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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Asbytec
Guy in a furry hat
*****

Reged: 08/08/07

Loc: La Union, PI
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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Bob Abraham
sage


Reged: 05/17/05

Loc: Toronto, ON, Canada
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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Bob Abraham
sage


Reged: 05/17/05

Loc: Toronto, ON, Canada
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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Eddgie
Postmaster
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Reged: 02/01/06

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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Asbytec
Guy in a furry hat
*****

Reged: 08/08/07

Loc: La Union, PI
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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