Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Intes Scopes?

This topic has been archived. This means that you cannot reply to this topic.
27 replies to this topic

#1 Tim2723

Tim2723

    The Moon Guy

  • *****
  • topic starter
  • Posts: 5765
  • Joined: 19 Feb 2004

Posted 18 June 2004 - 02:46 PM

I'm thinking of an Intes Micro M715 7" F/15 MAK for my lifetime lunar scope. It's only $2500 (OTA only), but my SVP mount would carry the weight (about 18 pounds), until I I could save for a Losmondy. It's not a whole lot more than the TV102 I've been secretly eyeing (and not that much more than the new transmission in my van that sucked up the money this time!).

Anybody got a good reason I shouldn't dream the dream? If somebody knows better, PLEASE talk me out of it!

#2 BluewaterObserva

BluewaterObserva

    Fly Me to the Moon

  • ***--
  • Posts: 5809
  • Joined: 18 May 2004

Posted 18 June 2004 - 03:07 PM

Only to say, go for the 8" if you can!!!!

They are very sweet scopes.

#3 matt

matt

    Vendor (Scopemania)

  • *****
  • Posts: 10991
  • Joined: 28 Jul 2003

Posted 18 June 2004 - 03:34 PM

I guess you could even look at planets with it!

However, regarding the cost of the intes scopes, there is a gap between the 5" and 6" (justifiable for the purchaser), and a HUGE gap between the 6" and 7" (less justified imho). Either you want only one scope and go for the 7", or you plan to have a large aperture instrument for deep sky and you could stay with the 6". However, if this is your dream scope and you know you won't be looking back, GO FOR IT! :waytogo:

#4 Tim2723

Tim2723

    The Moon Guy

  • *****
  • topic starter
  • Posts: 5765
  • Joined: 19 Feb 2004

Posted 18 June 2004 - 05:10 PM

No, this scope will be dedicated to lunar work 99% of the time, and will replace my 6" f/8 Newt. Deep sky, a very limited interest for me, would fall into the 10"-12" Dob catagory anyway (waiting to see what the Celestron 12's are like).

I can't go the 9", but I can't find an 8" listed. Bluewater, were you thinking of the 9"?

#5 PJF

PJF

    Viking 1

  • -----
  • Posts: 667
  • Joined: 06 May 2004

Posted 18 June 2004 - 06:23 PM

You can see details of the Intes-Micro 815 here:
http://www.brayimagi...s/IM-M.html#815
(as well as many of the others in the range)
It's very expensive, and I'm betting pretty heavy and pretty *bleep* good.

Unless you have a specific need for a (relatively) compact 7" scope, a better alternative for lunar/planetary is the Intes-Micro MN78 Maksutov-Newtonian. This has a tiny central obstruction, and to all intents and purposes will perform as well a 7" apo refractor.
http://www.brayimagi...IM-MN.html#MN78
It's a great performer, but not nearly as user friendly as a Mak. We're talking estate car transport.

Another 7" Mak worthy of serious consideration is the Mirage 180. Chris Garvey at Bray Imaging keeps prompting me to get one, and in my case profit isn't his motive. He really raves about them (and he rates the 715 highly too). The only thing stopping me is lack of money.

#6 Guest_**DONOTDELETE**_*

Guest_**DONOTDELETE**_*
  • -----

Posted 18 June 2004 - 06:38 PM

Have you looked at the Clavius 166 and Takahshi Mewlons? Both seem to be optimized for high power use, and within the same size range. I'm particularly interested in the Clavius - it only weighs 10.6 lb!

#7 Rammysherriff

Rammysherriff

    Surveyor 1

  • -----
  • Posts: 1967
  • Joined: 26 Mar 2004

Posted 20 June 2004 - 03:13 AM

I have looked at the Intes Micro/Moscow products in depth now (online). They seem very well thought out, come with loads of useful extras BUT the central obstruction for what I would their planetary scopes ( ie f12 and higher)seems quite large - 34% in one case.

So will this lower contrast significantly despite all the good efforts with internal baffling, dew shield etc? It draws me back to Orion's OMC200 that has 22% central obstruction.

The only draw back I see with the OMC is that it is a whopping f20; now as we're talking about a scope dedicated to looking at planetary objects, perhaps I can learn to cope with that...

#8 wilash

wilash

    Fairy Godmother

  • *****
  • Posts: 5746
  • Joined: 30 Sep 2003

Posted 20 June 2004 - 03:44 AM

So will this lower contrast significantly despite all the good efforts with internal baffling, dew shield etc?


No.

#9 Gary BEAL

Gary BEAL

    Surveyor 1

  • *****
  • Posts: 1566
  • Joined: 10 May 2003

Posted 20 June 2004 - 03:55 AM

My money is with PJF, I would opt for the Mak/Newt line in preference to the Mak/Cass, UNLESS portability or mount size is the major issue. I have heard very good for the M715, albeit with collimation issues out of the box, but still prefer the all round abilities of the Maksutov Newton designs. The MN66 is a stunner, and I am now onto an MN76, a homebrew one though.
Can't lose either way though.
Gary

#10 Rammysherriff

Rammysherriff

    Surveyor 1

  • -----
  • Posts: 1967
  • Joined: 26 Mar 2004

Posted 20 June 2004 - 06:21 AM

So will this lower contrast significantly despite all the good efforts with internal baffling, dew shield etc?


No.


I am grateful for the advice, but why do many of my fellow Newtonian users have an aversion to large central obstructions and say they lower contrast? I am not nitpicking, I am genuinely unsure whether I have read something incorrectly, or whether I fail to understand the technical issues.

Gary - a MakNewt is tempting, but I am seeking a long focal length, a specialised planetary scope. I have my eye on a 300mm f4 Newt elsewhere for lightcatching!

#11 Rammysherriff

Rammysherriff

    Surveyor 1

  • -----
  • Posts: 1967
  • Joined: 26 Mar 2004

Posted 20 June 2004 - 06:24 AM

although I have just notice the Alter M715 has only a 24% central obstruction, and has suddenly leaped back up to favourite again :o

#12 Tim2723

Tim2723

    The Moon Guy

  • *****
  • topic starter
  • Posts: 5765
  • Joined: 19 Feb 2004

Posted 20 June 2004 - 08:24 AM

Yes, I understand from the Intes web site that the M715 was put into production based on the success of a longer FL model of the M710 built for a custom order. Its smaller obstruction attracted me as well.

As goes the large central obstruction argument, I understand that any obstructed design will scatter more light than a refractor, and I suppose the thinking is that the larger the secondary, the worse it should be. I can only say that I've studied the Moon through a short focus 12.5" Newtonian with a secondary the size of a tea plate and was still bowled over by the detail. Probably owing to the sheer resolving power of that huge mirror.

As to the Maksutov Newtonian designs: I desire a scope that has the eyepiece at the 'right end'. I'm currently using a classical Newtonian, but find that I need to be seated at the EP (a special need). I'm also limited to a weight range that will mate with a G-5 size mount. The larger G-6 and similars are far too massive for my situation. Of course, budget is always a consideration. For US$2500 I can consider an APO refractor in the 4" class or a compound scope in the 7"-8" range. I'm opting for greater aperture. I'm not discontent with the 6" aperture, since my usual one arc-second skys seldom support a larger glass, but I'm hoping for a bit more aperture to have some 'head room' in the mix.

#13 wilash

wilash

    Fairy Godmother

  • *****
  • Posts: 5746
  • Joined: 30 Sep 2003

Posted 20 June 2004 - 09:37 AM

So will this lower contrast significantly despite all the good efforts with internal baffling, dew shield etc?


No.


I am grateful for the advice, but why do many of my fellow Newtonian users have an aversion to large central obstructions and say they lower contrast? I am not nitpicking, I am genuinely unsure whether I have read something incorrectly, or whether I fail to understand the technical issues.


The important word is "significantly." If a central obstruction of 30% to 35% was really that bad, why do so many people buy SCTs. Yes, the size of the central obstruction does affect contrast, but the results have hardly left amateur astronomers in agreement to how significant it is. Even the MTF plots that are used are very misleading. Most of the discussion over central obstruction is nitpicking. Some of it is imagination. The real problem is that image quality results from multiple factors and the size of the central obstruction is just one of them.

Maks give great images. While they have a central obstruction, they also control abberations very well. Every scope is a compromise. They all have strengths and weaknesses. Buy the best tool for your purposes. Maks have very good reputations because they perform well.

#14 PJF

PJF

    Viking 1

  • -----
  • Posts: 667
  • Joined: 06 May 2004

Posted 20 June 2004 - 11:28 AM

The important word is "significantly." If a central obstruction of 30% to 35% was really that bad, why do so many people buy SCTs.


Well, because resolution of low-level contrast isn't a significant concern to them. As you say, all instruments are a compromise, and the primary reason SCTs are so popular is because the appealing aspect of their compromise is compactness and low weight for the aperture on offer.

Another way of looking at it would be:
"If the large central obstruction of SCTs isn't really that bad, why do keen planetary/lunar observers spend a fortune on apochromatic refractors; or struggle with long focus Newtonians?"
They could just get themselves a comfy C8 for 850 bucks and be done with it, but they don't. I don't think it is accurate to say that they are nitpicking or imagining things.

Tim2723 is looking for a lifetime lunar-dedicated scope. I think that context puts the very real image degradation due to a large central obstruction firmly within the realm of 'significant'.

#15 Tim2723

Tim2723

    The Moon Guy

  • *****
  • topic starter
  • Posts: 5765
  • Joined: 19 Feb 2004

Posted 20 June 2004 - 12:02 PM

Thanks Peter, that was one of the better arguments I've heard. I didn't want to get into the 'central obstruction' debate, so I stayed away with my answer above.

If one is a generalist observer, or even a dedicated deep space fan who spends little observing time with the Moon and planets, it's very easy to be impressed by the views from any large scope. Likewise, go from an 80mm refractor to even a mediocre 8" mirror and the increase in details alone will knock many a sock off! But to one who spends the majority of time in the shallow sky, it takes more than just seeing more bands in Jupiter. For instance, such an observer might spend several nights watching a particular festoon develop. This takes a different tool.

Indeed it is niether nitpicking nor imagination, but a different facet of the hobby requiring appropriate technology and specialization.

#16 Rammysherriff

Rammysherriff

    Surveyor 1

  • -----
  • Posts: 1967
  • Joined: 26 Mar 2004

Posted 20 June 2004 - 06:34 PM

Thankyou Tim and also Peter and Wilash;

I apologise for raising the obstruction issue, but your comments have expanded my understanding of an area that is new to me.

From looking at the various designs and specifications, it seems that the longer the focal length, the smaller the secondary obstruction; is it designed to be that way to improve contrast due to it's specialist use, or is it a function of the increased focal length? Ie, the f10 types are quite ok with 34% (they get used as GP scopes), but jump up to a specialised f15, and 22% to 24% is used.

I can see the point that the larger the obstruction, the scattering effect will depend upon the circumference of that obstruction, but also that good baffling and secondary design can minimise this effect; also that other factors in design can also affect the final product just as much. The effect on light gathering is not important as we would be looking at bright things with it.

It's a fascinating area; how long would a refractor or a Newtonian be to make f15, unless it was as narrow as a gun barrel? And how much does it then cost to make the refractor big enough to still gather light, or how do you do the same thing with a Newt and stop the tube from sagging?

One thing is sure - somthing easy to use will get more use!

Thankyou everyone; I think I will be going for the 715, and I hope we are very happy together!!

#17 wilash

wilash

    Fairy Godmother

  • *****
  • Posts: 5746
  • Joined: 30 Sep 2003

Posted 20 June 2004 - 06:59 PM

Another way of looking at it would be:
"If the large central obstruction of SCTs isn't really that bad, why do keen planetary/lunar observers spend a fortune on apochromatic refractors; or struggle with long focus Newtonians?"
They could just get themselves a comfy C8 for 850 bucks and be done with it, but they don't. I don't think it is accurate to say that they are nitpicking or imagining things.


Well, some don't spend a lot of money on apochromatic refractors. It is hard to beat a C-14 on the planets or even an 11" SCT. And how many people who view the planets use a scope with a large central obstruction compared to those who don't? Do we have any numbers? Or does this statement come from "common" wisdom like the best binoculars for astronomy are 7X50s.

Now I have heard that the contrast of an obstructed scope is equal to a smaller unbstructed scope. To work out the relative size simply subtract the diameter of the obstruction from the aperture to determine the equivalent size of an unobstructed scope. I have seen this theory many times and it is nonsense. It is too simplistic. There are far more factors involved than simply the central obstruction. Or do you think my 80mm refractor has the same contrast as my 5" Mak? (It does not by the way, the Mak is superior to it.)

I have also seen the use of MTF curves as some kind of proof. The curves deal only with central obstruction and not optical quality - for example the affect of chromatic abberation on an image. Nor do they deal with optical designs, or do you feel there would be no difference in an image from an 8" f/10 SCT, MCT, or Newtonian with the same central obstruction. They do not show the affects of aperture either. MTF curves cannot predict visual response to an image.

If this is a lunar scope, then there is less of a problem with the central obstuction because of target brightness and contrast. A larger obstruction may not be significant at all. Aperture and optical quality would be a greater factor.

Now if you place two 7" Maks side by side, one an f/10 and the other an f/15, how much difference would there be? If the scopes could not be compared directly, would you notice the difference? Is there a "significant" jump in contrast, or a negligible difference in contrast? Would there be anything you could see in one, you couldn't see in the other? It seems to me that you can spend a great time worrying over slight differences, rather than enjoying the view of the moon. If you really want the best 7" scope, buy a APO from TMB - but you would probably end up worrying about chromatic abberation.

As far as imagination goes, yes there are plenty of conclusions in amateur astronomy based on personal biases rather than fact.

#18 Guest_**DONOTDELETE**_*

Guest_**DONOTDELETE**_*
  • -----

Posted 20 June 2004 - 07:59 PM

I have also seen the use of MTF curves as some kind of proof. The curves deal only with central obstruction and not optical quality - for example the affect of chromatic abberation on an image. Nor do they deal with optical designs, or do you feel there would be no difference in an image from an 8" f/10 SCT, MCT, or Newtonian with the same central obstruction. They do not show the affects of aperture either. MTF curves cannot predict visual response to an image.

I'm not sure if I accept that. Optical design is usually taken into account when calculating the MTF. So is aperture. Imperfection of the optics is usually not considered, but for high-end telescopes (say, 1/6 wave wavefront error or Strehl ratio of 0.96), the diffraction limit should be useful analysis.

Here's the MTF of a 6" scope with 33% obstruction. I modeled it as a Newtonian to eliminate any on-axis aberrations. Horizontal axis is spatial frequency in cycles per mm. I modeled it with a 1000mm focal length, so 100 cycles/mm corresponds to 2 arcsec cycle. Blue line is on-axis, green is 2 arcminutes off-axis, and red is 0.1 degrees off-axis.

Attached Thumbnails

  • 130445-150-33.gif


#19 Guest_**DONOTDELETE**_*

Guest_**DONOTDELETE**_*
  • -----

Posted 20 June 2004 - 08:00 PM

And here's a 6" with 20% obstruction. The contrast at 2-arcsec is about 15% higher.

Attached Thumbnails

  • 130446-150-20.gif


#20 Guest_**DONOTDELETE**_*

Guest_**DONOTDELETE**_*
  • -----

Posted 20 June 2004 - 08:07 PM

However it's also easy to show that even an obstructed telescope is better than a smaller aperture unobstructed telescope. Here's the MTF of a 4" unobstructed telescope. Note the horizontal axis scale is different. At all spatial frequencies it is worse than the 33% obstructed 6" telescope.

Attached Thumbnails

  • 130451-100-0.gif


#21 PJF

PJF

    Viking 1

  • -----
  • Posts: 667
  • Joined: 06 May 2004

Posted 20 June 2004 - 08:48 PM

And how many people who view the planets use a scope with a large central obstruction compared to those who don't? Do we have any numbers?

You keep going on about the numbers - but they are irrelevant. It's like saying more people drive VW Golf GTIs than Lotus Sevens, so therefore VW Golfs go round the bends just as well Lotus Sevens. The reality is, more people drive the Golf because they can also use it to do the shopping and take the kids to school. It's a good all-rounder that can give a happy driving experience, but for proper grins you need the proper device - the Lotus.

The simple fact is that a smaller central obstruction is significantly better than a larger one (all else being equal) in the area under discussion (yes, there is low level contrast on the Moon). I agree that CO size isn't the only important factor - but so what?

#22 wilash

wilash

    Fairy Godmother

  • *****
  • Posts: 5746
  • Joined: 30 Sep 2003

Posted 20 June 2004 - 09:10 PM

That is very interesting Ken. And one of the best examples I've seen. Most just show two curve to show the affect of the central obstruction without reference to actual spacial response.

But here again, these are limited. Would an SCT and MCT or even your Mewlon have the same plots? How does focal ratio change this? (MTF is associated with resolving power which changes with focal ratio.) What would the off-axis plots look like - most of the image is off-axis. And how do the radial and tangental off-axis data compare? And last but not least, how does this affect the image you see; an MTF curve can show differences that are not perceptable.

Ken this is not a criticism of you - I'm very grateful for this data and I think MTF data is very revealing, but the interpretation is not that simple. Also these are theoritical plots, they do not necessarily show how a particular instrument will perform.

My problem is that theory can suggest affects specific specification have on an optical system, but they do not look at all the factors in the opitical system as a whole. For example resolving power and contrast are not mutually inclusive. You can maximize a system for one or the other, but not both at the same time. The Japanese tend to like resolution over contrast, the the Germans favor it the other way around. A little bit if information does not tell the whole story.

#23 Tim2723

Tim2723

    The Moon Guy

  • *****
  • topic starter
  • Posts: 5765
  • Joined: 19 Feb 2004

Posted 20 June 2004 - 09:36 PM

Wilash,

Thank you for your responses.

The planetary observer must cope with his fair share of low-level contrast as well as distinguishing delicate linear features, a problem seldom encountered elsewhere. The deep sky observer deals with point sources and broad, diffuse objects yes, but distinct fine lines? Seldom if ever.

Your MAK most likely outperforms your 80mm refractor due to its greater aperture and other factors, not because it is an obstructed design. You've said nothing of their comparative quality, so aperture is the only criterion given.

As to your disparagment of 'common wisdom', I prefer to think of it as 'collective experience'. Sadly, a very great number of us must rely on this collective experience as well as the physics and math involved in order to guide our decisions. Not everyone has the advantage of trying any given piece of equipment before slogging ahead. This is one of the greater purposes of Cloudy Nights in the first place.

As goes general recommendations such as 50mm binoculars for astronomy, this is offered not only based on the experience of vast numbers of observers, but for a great many good reasons, not the least of which is to avoid endless paralysis by analysis.

If you'll kindly revisit my original post and my subsequent amplifications, you will see that there is no need to enter into the 'obstruction vs. contrast' argument again, as I've based my decision on many factors, possibly the least of which is central obstruction.

Can you offer an opinion on the quality of the Intes M715; its build quality, optics, warranty, etc? That's what I'm looking to the experts for.

#24 wilash

wilash

    Fairy Godmother

  • *****
  • Posts: 5746
  • Joined: 30 Sep 2003

Posted 20 June 2004 - 10:03 PM

If you'll kindly revisit my original post and my subsequent amplifications, you will see that there is no need to enter into the 'obstruction vs. contrast' argument again, as I've based my decision on many factors, possibly the least of which is central obstruction.



I'm sorry I brought the subject up. I was just answering a question Simon raised. I will confine myself to your original post.:slap:

I have a different model from Intes Micro - M503. The scope arrived dirty - metal filings in the OTA. The coatings on the miniscus are softer than usual optical coatings. Intes Mirco will from time to time change the accessories included with their scopes without informing you when you purchase it. Good luck.

#25 Rammysherriff

Rammysherriff

    Surveyor 1

  • -----
  • Posts: 1967
  • Joined: 26 Mar 2004

Posted 21 June 2004 - 04:07 AM

I in turn apologise for bringing the obstruction debate up and provoking the debate, but thank you for your very informed comments, as understanding this issue is important to me before I splash my cash.

May I join Tim in asking for any user reports of the Intes 715, and if we want to argue the obstruction issue, I would gladly start a new thread.


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics