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Equipment Discussions >> Cats & Casses

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azure1961p
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: amicus sidera]
      #5825963 - 04/27/13 10:02 AM

The PARKS is relative to the example as a model or example of a typical classic 10" f/5 . True, they haven't advanced in 35 years and much to the detriment of their business. At anyrate being that they are so prevalent (reflectors in this size and speed) and that it shared some specs with the Roland -Vallery Mak the comparison seemed worthwhile and revealing of both pluses and minuses in both systems.

You could make the argument that an optimized 10" newt bridges the gap better but that wouldn't be representative of the common reflector in this size most people seem to own.

Pete


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Eddgie
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: azure1961p]
      #5825999 - 04/27/13 10:29 AM

Quote:

10" f/5 that simply was an unimpressive planetary scope.




You are comparing a telescope that was crafted over a years time by one of the leading optical fabricators on the planet to a telescope that was most likley not.

The CO you site also understates the real obstruction which is more like 28%. This is because the secondary size alone does not constitute the entire obstruction. A very thin vane spider will ad 2" to the obstruction, and this assumes a very thin. Many time, the spiders are made a bit thicker than the minimum so it is possible that 3% is more realitic, which brings the obstruction to something like 29%.

But it gets worse. Often, the focuser tube will extend very slighty into the light path of a Newtonian when using eyepecies with a field stop located far up in the barrle.

We don't know if this was the case for your particular scope, but I have seen it enough to know that it is not at all uncommon. This may add another couple of percent of obstruction.

But the biggest difference here is optical quality.

The AP is without doubt most liklely to be pushing a strehl of .98%.

I have a serious doubt that the Parks is in this stratified quality level.

And finally this. Planetary Observing rarely presents a "Wow" because seing for most of us is simply not that good.

I spend an hour or two glued to my binovierers to get glimpses of detail on planets. I don't just sit down and see it all. It comes and goes.

Were you patient? Or did you just sit down and expect to see pictures like we seen in the solar system imageing forum?

On my best nights, I don't see Jupiter as well as even so-so images taken with cheap planeatry cameras. One has to remember though that the planeatry camera does what I do, but it does it in five minutes. It watches and takes thousands of images, and the software selects the best images and combines them together.

And that is what I do. I sit and I watch, and I wait. And after several dozen moments of steadiness in the images over an hour or two, I do the same thing. I "Stack" these images in my brain, and I wind up with a mental image that shows much of the detail that the CCD camera captured.

But not all. The eye simply is not a sensitive and lacks the resoltuion of a modern CCD camera.

Summary: Your telescope is more obstructed than you think, and there is a huge probability that the quality is not on par with what we can reliably expect to be one of the finest set of optics ever made.

And my hunch is that you did not exercise the patience necessary to do planetary observing to the level your instrument was capable.


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Eddgie
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: Eddgie]
      #5826030 - 04/27/13 10:48 AM Attachment (35 downloads)

I have plotted the two scopes.

The AP was plotted as being perfect optically an that is because we can assume that it is.

The Parks was plotted with a 29% obstruction (to reflect the added diffraction of the spider which I doubt was an optimized thin vane type).

I also plotted the Parks with a single optical defect, which was 1/8th wave of spherical abberation.

Now this represents a mirror of far better than average quality. Most mirrors produced today are not nearly this perfect just on spherical abberation.

Most will have other very small errors like some amount of surface roughness, and usually a very small amount of astigmatism or other on-axis errors.

Usually the only time you get a mirror as good as the one I plotted here is if you pay for a custom mirror.

Anyway, the plot on the right represents the quality of a Newtonian that many of us would be thrilled to have, and my guess is that it represents a level of quality that is above the level that your instrument had.

Notice that at every point on the MTF plot, the AP maintains more of the initial contrast than the Newt.

The CO is the major contributor, but again, I was very kind to the Parks and gave it only a single, minor optical error. The vast marjority of mirrors made today are not this good.

A 10" f/5 reflector could be made to do as well as the AP, but the one you owned could not be expected to come close.


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Eddgie
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: Eddgie]
      #5826041 - 04/27/13 10:58 AM

If you are not famaliar with MTF, the solid red line represents the contrast loss of a perfect, unobstructed aperture 10" in size.

The dotted lines represent the additional amount of contrast lost due to optical quality issues or obstruction.

If you worked down from the top of the chart at .4 on the X axis, you would see that even a perfect 10" unobstructed instrument would loose mybe 47% of the contrast at .4 of its maximum linear resolution.

THe AP would loose an additional 7% or so, for a combined contrast loss of about 56%.

The 10" 29% obstructed with 1/8th wave would loose about 62%. This way you can find out how the scopes would transfer contrast on varius sized details, The left side represents large details, and as you work to the right, smaller sized details.

The .4 line represents detials that would be maybe 3 or 4 Airy Disk diametars of the instrument. In a 10" scope this might be detail taht was 2 or 3 arc seconds in size.

Now if you are looking at Jupiter, and it is 35 arc seconds across, this should give you the idea. We would be looking at medium sized pale ovals as an example. These are difficult contrast targets for a smaller apeture, and at 8" or 9" of good apeture, under good seeing, and with patience, will start to show more reqularly.


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azure1961p
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: Eddgie]
      #5826783 - 04/27/13 05:31 PM

Edd,

I'm at work - I just read through your posts. Can't reply now but I believe the MTF does a fine job of fog lifting here and I appreciate your working through the details in presenting the comparison.

Pete

Edited by azure1961p (04/27/13 05:31 PM)


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azure1961p
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: azure1961p]
      #5827468 - 04/27/13 11:11 PM

Ok off work ...

I've been observing planets for decades. Even as a kid I was the patient observer. Its my natural thing to lose myself in the observation. Over the course of several months with the 10" f/5 (my prior scope being a C8 and prior to that an old orange C8) I really gave it my all. I was very dissatisfied with the performance - even sending it back to Parks saying that while their accompanied ronchi was ruler straight this was not a performer. I began to see traces if astig at the larger exit pupils of low power but that's a side note that obviously wasn't the issue of PARKS. Anyway, Clements is on the phone with me saying "Jupiter ought to look like gangbusters with this mirror" - they sent it back nothing changed. The night I had a local club menber invite me to come over and let him have a look it was all over. Jupiter was up and he had his 10" f/7 Cave and I realized that was what I wanted. I messed with the collimation doing the high power diffraction pattern centering - he messed with it too. I just had it. I sold the beast and was dead set on a scope from Parralax Instruments. Their brochures aeed to embody my wants here and a check was nearly in the mail till Chris at PARKS said " yes we do custom telescope assemblies". That's all it took. - check was in the mail and the weeks passed. When I finally got it the views were a revelation outdoing any instrument Ive ever owned - certainly the 10" f/5. But it wasn't just planetary Ed...

The Orion Nebula was up I swung it there for a gander and saw clearer than any view before the E-F stars in the trap and in mediocre seeing. Those months I had the ten they didn't budge even once. Jupiter now had these flashes of watermark intensity markings that I never noticed before. It was uncanny. Mind you it wasnt a matter of paying extra attention - these things came to me . I wasn't even thinking of the E-F stars and Jupiter was so good it took getting used to. Saturn later on proved equally stunning and I even went headlong into doubles that spring summer and fall - an interest that was always so-so to me. Clements suggested I try doubles with the scope, I was polite and silently scoffed at it. Bootes was riding that spring and it was a nearly year long obsession. I was seeing these text book star patterns the ten never seemed to manage. Instead he rings tended to blur into the disc - wether it was seeing or extra light in the diffraction rings it was a downer. Other 10" scopes at star parties of the f4.5 variety and such left me equally ho-hum. The one that wasnt was a home made 10" F/7 with a PARKS mirror and dang it what a fabulous Saturn!

The other scopes to sum it up were big bright blah images. That uncanny tickle of gossamer details that flutter with the seeing just kind of simplified into something that didn't move me. Eh.

Sometimes I regret having let the 10" go - I lost angular res and some deepsky ability. I wonder what I might have or could have done to make it work but Im happy enough with the carefree, coma free easy collimating f/9 and I leave it there.

Maybe the next time Im at a star party and there's another fast ten Ill give a look see . The images in the f/9 though again were a revelation. If it'd been even a little ho hum Id ve sold it - as it is this was no. 4 in a succession of buying, trying and selling. This one for me was the winner.

Pete

Ps: I've read through all the technicals on MTF. I'm going to rereading it all tomorrow morning when Im fresh. Again thanks.

Edited by azure1961p (04/27/13 11:24 PM)


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azure1961p
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: azure1961p]
      #5827501 - 04/27/13 11:27 PM

Edd,

How ARE you saving those aberrator mtf images - I can't manage this but Id like to be able to save them for comparisons I do.

Thanks.


Pete


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Eddgie
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: azure1961p]
      #5827567 - 04/28/13 12:34 AM

I have to do a FN/Print Screen, then past them into individual MS Paint images, then copy the MTF from one, then past it into the other, then crop the two MTFs.

Aberrator does not allow you to generate more than one MTF at a time.

I did not realize that you had tow different 10" scopes.

My guess was that the f/7 one was more optimized than the f/5 one, but if an f/5 scope were built with a 20% secondary and the optics were of superb quality, then it should do as well as the MCT.

But this would be a custom scope, and the off axis illumination would not be great. But still, you would likely have the same true field capability of the f/14.4 AP, with a bit of coma of course. At the center of the field, the performance should be similar.


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azure1961p
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: Eddgie]
      #5827846 - 04/28/13 07:52 AM

Thanks Edd,

What's a fn/print screen?

I didn't have two ten inch scopes - one was a friends from a local club I spent the evening with another was at a starparty . Sorry for the confusion on description.
Pete

Edited by azure1961p (04/28/13 07:54 AM)


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iluxo
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: amicus sidera]
      #5827875 - 04/28/13 08:27 AM

You're all missing something - you need eyepieces to see anything. It isn't just about CO and MTF.

On the planets I'd much rather use an f/15 Mak with a 10mm eyepiece than struggle with an f/5 Newtonian with any 3.5mm eyepiece you can name (to achieve roughly the same magnification).

Barlows/Powermates etc don't help either.

Edited by iluxo (04/28/13 08:29 AM)


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: azure1961p]
      #5827906 - 04/28/13 08:56 AM

Quote:

The scopes:

10" f/14.6 Mak 23% co
10" f/5 newt 26% co

Ok, no doubt Roland's Mak is corrected to a higher degree than any 10" f/5, too a paracor would eat up the throughput advantage of the newt s simple design but that still makes it seem like the reflector has a fighting chance to match this $10,000 OTA Mak.

So what's going on here? Is Roland really getting 10" f/5 planetary performance? Or is the ability to perfect a maks optics so much better than a similar parabola that no reflector in that size can realistically hope to compete?

Pete




Why would a faster OTA be in the running as a comparable or better planetary instrument?

I have the AP 10" Mak-Cass and a good number of other fine scopes (AP apos, Zeiss APQs, Tak Mewlon 300CR), and have looked through a lot of other's telescopes. Roland's Mak-Cass provides about as close to refractor performance as I've seen. In addition to delivering highly detailed views of the planets (Jupiter & Saturn), it performs well on Lunar features, globular clusters and other DSOs. Thus far, it has given me the best view of M42 (with a Leitz 30 mm 88* AFOV EP). It easily shows the central star of M57, because it can tolerate ridiculously high magnification.

I may be selling a scope or two soon to purchase an FLI CCD camera. My AP Mak-Cass will never leave.


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Eddgie
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: azure1961p]
      #5828013 - 04/28/13 10:15 AM

Function Key, Print Screen Key on your keyboard.

This will make an image of your desktop in your computer clipboard.

Now, when you want to edit it, just open Microsoft Paint and do a "Paste." The image of your desktop will show up in Paint.

I did two different Aberrator images into two different Paint Windows, then cut and pasted the MTF from one to the other, then cropped everything else out.

It is only a little tedious, but I do it so that it is easy to make a side by side comparison for interested people that are interested.

Of course I realize that most people are not at all interested, but as you can see, MTF offers a very visual way of comparing how two different instruments might perform.


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Eddgie
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: JJK]
      #5828020 - 04/28/13 10:21 AM

The speed of an optical system does not really have much bearing on its ability to perform well on planets.

And the reality is that it has to be in the running because not everyone can afford a $10,000 telescope.

And when you could put together a telescope offereing similar performacne with a tracking mount for less than $3000, most people would say that this would indeed be a valid challanger.

The only issue with building an f/5 planetary scope is that the small obstruction required would make it unusable for wider field viewing, but then again, a 10" f/14.4 MCT does not really offer much in the way of wide field viewing either.

Still, if you used a very low profile focuser on the Newtonian, you could potentially have a wider true field than the f/14.4 MCT.

So, similar planetary performance and a wider field of view for maybe 25% of the price.

Sure, one is an AP and one is an Orion Dob with custom mirrors, but if the goal is to see an equal amount of detail on planets, then you can get there with an optimized 10" f/5.


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Jon Isaacs
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: JJK]
      #5828134 - 04/28/13 11:24 AM

Quote:


Why would a faster OTA be in the running as a comparable or better planetary instrument?




A point I think is worth making: The primary mirror of the Mak is in the F/3 realm. Compound scopes are very fast spherical mirrors combined with corrective optics and a magnifying secondary mirror to achieve that slow focal ratio. While the optics may be spherical they are not in the scope in question and one can fabricate a somewhat slower parabola with equal precision.

Jon


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azure1961p
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: iluxo]
      #5828136 - 04/28/13 11:25 AM

Quote:

You're all missing something - you need eyepieces to see anything. It isn't just about CO and MTF.

On the planets I'd much rather use an f/15 Mak with a 10mm eyepiece than struggle with an f/5 Newtonian with any 3.5mm eyepiece you can name (to achieve roughly the same magnification).

Barlows/Powermates etc don't help either.




No they dont. Barlows are cosmetic attachments to make low power oculars feel mighty.

P.


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azure1961p
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: Eddgie]
      #5828140 - 04/28/13 11:29 AM

Quote:

Function Key, Print Screen Key on your keyboard.

This will make an image of your desktop in your computer clipboard.

Now, when you want to edit it, just open Microsoft Paint and do a "Paste." The image of your desktop will show up in Paint.

I did two different Aberrator images into two different Paint Windows, then cut and pasted the MTF from one to the other, then cropped everything else out.

It is only a little tedious, but I do it so that it is easy to make a side by side comparison for interested people that are interested.

Of course I realize that most people are not at all interested, but as you can see, MTF offers a very visual way of comparing how two different instruments might perform.




Im thinking of an overlay here in photoshop where both are visible as one image. I could color shift one to separate it from the other .
Just a thought.

Pete


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Eddgie
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: azure1961p]
      #5828694 - 04/28/13 04:30 PM

Well, that would indeed be better. I don't have photoshop, so my tool was Paint.

When you have had a chance to do one, would you show me what it looks like


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Jon Isaacs
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: azure1961p]
      #5828942 - 04/28/13 07:19 PM

Quote:

Quote:

You're all missing something - you need eyepieces to see anything. It isn't just about CO and MTF.

On the planets I'd much rather use an f/15 Mak with a 10mm eyepiece than struggle with an f/5 Newtonian with any 3.5mm eyepiece you can name (to achieve roughly the same magnification).

Barlows/Powermates etc don't help either.




No they dont. Barlows are cosmetic attachments to make low power oculars feel mighty.

P.




As someone who actually uses F/5 Newtonians for Planetary viewing, Barlows can be an effective tool. It's probably easier to fabricate a high quality Barlow than a high quality 5x magnifying mirror...

Jon


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JJK
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: Eddgie]
      #5829008 - 04/28/13 08:03 PM

Quote:

The speed of an optical system does not really have much bearing on its ability to perform well on planets.

And the reality is that it has to be in the running because not everyone can afford a $10,000 telescope.

And when you could put together a telescope offereing similar performacne with a tracking mount for less than $3000, most people would say that this would indeed be a valid challanger.

The only issue with building an f/5 planetary scope is that the small obstruction required would make it unusable for wider field viewing, but then again, a 10" f/14.4 MCT does not really offer much in the way of wide field viewing either.

Still, if you used a very low profile focuser on the Newtonian, you could potentially have a wider true field than the f/14.4 MCT.

So, similar planetary performance and a wider field of view for maybe 25% of the price.

Sure, one is an AP and one is an Orion Dob with custom mirrors, but if the goal is to see an equal amount of detail on planets, then you can get there with an optimized 10" f/5.




I would expect with faster optics, more care needs to be applied with figuring them.

Also, I doubt that an Orion Newtonian can perform as well as the AP Mak-Cass.


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R L Harris
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Re: Roland's 10" Mak versus a 10" f/5 reflector new [Re: JJK]
      #5829127 - 04/28/13 09:14 PM

I have seen some fantastic views in newtonians in my life time!
I started out in astronomy when I was 14 years old 1972!
ground my first telescope lense when I was 16-1974!
Worked for Celestron !978-1980 as optical Assembler Mainly
worked on C-14!
And have used and built many scopes in my life time!


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