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The Most Beautiful Planetary Images In The World

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#1 Daniel Mounsey

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Posted 20 August 2013 - 01:40 AM

I've been observing pretty solid for two decades. In the past 15 years however, I have tested many telescopes in the field, side by side and it actually became an obsession for me. Bringing photons to a single point is an amazing thing I don't often take for granted, and it takes a very special instrument to do it. In that time, I am deeply grateful to several extremely experienced and talented observers for this.

I have tested numerous achromats and apochromats all the way up and through 6", 7", 8", 9" and 10". In my opinion, apochromats have a cutoff point at 10" with a point of diminishing return on anything larger, due to several factors. Pons always told me that an apochromat beyond 10" is highly unlikely to achieve the spherical correction needed to produce a world class image. Another extremely talented source who I will not name, agreed. There is only so far an apochromat can go and other options have to be considered.

I have also tested numerous high quality reflectors using some of the the finest optics available all the way up to 32". You just never know what a telescope will dish out until that moment occurs, and it's a breathtaking sight if it does. But, based on all the observational experiences I've encountered, these mid size equatorial mounted Newtonian's still reign supreme. This 8" F-10 by Ed Grissom is just a smaller example.

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  • 6035776-Grissom8-F10.jpg


#2 Daniel Mounsey

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Posted 20 August 2013 - 01:42 AM

Ed Grissom's latest 12.5" F6.

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#3 Daniel Mounsey

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Posted 20 August 2013 - 01:44 AM

Fan cell.

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#4 Daniel Mounsey

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Posted 20 August 2013 - 01:50 AM

Mirror cell.

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#5 Erik Bakker

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Posted 20 August 2013 - 01:56 AM

I am with you Daniel. Thanks for sharing the pictures. In which direction do these fans blow for best results at the eyepiece?


#6 Daniel Mounsey

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Posted 20 August 2013 - 01:56 AM

Rear side.

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#7 Daniel Mounsey

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Posted 20 August 2013 - 01:59 AM

Curved spider.

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#8 Daniel Mounsey

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Posted 20 August 2013 - 02:01 AM

Side view.

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#9 Daniel Mounsey

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Posted 20 August 2013 - 02:03 AM

For more. Ed Grissom's Pinball Machine.

#10 Daniel Mounsey

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Posted 20 August 2013 - 02:11 AM

I am with you Daniel. Thanks for sharing the pictures. In which direction do these fans blow for best results at the eyepiece?


Hi Erik,

There is always controversy. I just look and call it like I see it. The most solid views in this configuration are pushing. You can actually feel the air in your face if you stand in front of the OTA. Fans remain on at all times with a slow and steady flow. If pushing has failed, it's because the observer is not using enough fans. The failure to flush the OTA is no different than a small speaker struggling to fill a concert hall with solid sound.

#11 Cotts

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Posted 20 August 2013 - 07:19 AM

I am amazed by the size of that secondary mirror! It must be around 10% of the primary (by diameter). Such a small secondary becomes invisible in the diffraction pattern and turns the scope into a perfectly APOchromatic "Unobstructed" telescope.

I have a 'cousin' of that telescope - my 6" f/8 Intes Mak Newt has a 16% central obstruction and, in careful side-by-side tests with a 1988 6" Astrophysics, no difference could be seen between the diffraction patterns seen in each telescope. Planetary and double star performance is world class. In the case of the MakNewt I think the meniscus lens is an added bonus for two reasons - there is no spider, curved or otherwise to reduce contrast and the tube is completely sealed which removes all that boundary layer difficulty...

There is a price to pay (isn't there always?) for these tiny secondaries, though. Vignetting and the inability to give wide-field views with 68, 82 and 100 degree eyepieces. Specialized telescopes.

Dave

#12 obin robinson

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Posted 20 August 2013 - 08:07 AM

That's one good looking scope! great craftsmanship there!

obin :bow:

#13 kauf

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Posted 20 August 2013 - 08:15 AM

thanks for you sharing with us.
F1O,such a long focus ratio,I think it's very good for the planet and double stars.
I have 203mm, F7.5 reflector,in Dob mount~

#14 maknewtnut

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Posted 20 August 2013 - 09:18 AM

Amen brother. The midsize Newt just flat delivers. DiScuillo used them to produce impressive results. I had my 8" f/7 with a Spooner primary side by side with an APM 8" f/7 apo I could have purchased at cost....I kept my Newtonian.

#15 Jeff Morgan

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Posted 20 August 2013 - 10:12 AM

There is a price to pay (isn't there always?) for these tiny secondaries, though. Vignetting and the inability to give wide-field views with 68, 82 and 100 degree eyepieces. Specialized telescopes.

Dave


Not in the shorter focal lengths certainly. My 10" f/9 used a 1.25" secondary (E&W Optics for you old timers) and it was absolutely fine with the 9 Nagler. Come to think of it, it wasn't too bad with a 38 Erfle either ....

#16 ATM57

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Posted 20 August 2013 - 10:23 AM

Nice instrument. There is something special about a long focal length Newt with a good optic set. I'm still waiting for that "special night" for my 10" F/8 (15% obst) which I just put together a couple of months ago. I have been teased with some good views but the atmosphere has yet to allow me to push much beyond 180-200x.

Scopejunkie

#17 Cotts

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Posted 20 August 2013 - 10:13 PM

There is a price to pay (isn't there always?) for these tiny secondaries, though. Vignetting and the inability to give wide-field views with 68, 82 and 100 degree eyepieces. Specialized telescopes.

Dave


Not in the shorter focal lengths certainly. My 10" f/9 used a 1.25" secondary (E&W Optics for you old timers) and it was absolutely fine with the 9 Nagler. Come to think of it, it wasn't too bad with a 38 Erfle either ....


Well, a 9mm Nagler in a 10" f/9 scope is working at 254x which is very far from wide angle observing. I should have said, "wide-field, low-power" viewing with 68, 82, 100 degree eyepieces.

The 38 Erfle would show some fall-off of field illumination with a secondary that small.

Dave

#18 george golitzin

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Posted 21 August 2013 - 01:01 AM

Love the title in this thread! Not pulling any punches here!

Daniel, you know I bought that 12.5-inch f/6 mirror Pons sold to Don Rothman? I'll never know if it really is a Zambuto, I suppose, since Pons didn't keep any paperwork, but it sure acts like one, and I'm getting some of the most beautiful planetary views ever with it. Jupiter had finished its latest apparition before I got the scope up and running, but the banding on Saturn has been exquisite--it's just a killer mirror. I'm really looking forward to Mars and Jupiter later.

So I completely agree with you--the 12.5-inch f/6 or thereabouts is a real sweet spot for planetary viewing, and I'm sure this scope is a keeper.

-George

#19 Jarad

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Posted 21 August 2013 - 07:34 AM

Regarding vignetting, the longer the f-ratio, the steeper the fall-off is once you go outside the 100% zone. So if you compare a slow scope and a fast scope with similar size 100% zone, the slower scope will drop faster outside that zone. Here are some examples:
10" scope, 12" tube, 1.6" tall focuser
f4: 2.5" secondary, 100% zone = 0.67", 75% zone = 1.64"
f10: 1.5" secondary, 100% zone = 0.78", 75% zone = 1.15"

So the faster scope has a smaller 100% zone, but a wider 75% zone (slower drop-off). The slower one would show significant vignetting at the edge of a 2" widefield eyepiece like a 35 Pan. It will also have a much narrower max TFOV.

Excellent planetary design, but not good for widefield work. Everything is a tradeoff.

Jarad

#20 Jeff B

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Posted 21 August 2013 - 10:00 AM

Nice well thought out viewing machines. I notice that the tube I.D. is considerably larger than the Mirror O.D., effectively putting the mirror in "free space". I suspect this is for thermal reasons as it goes against the idea of putting the focuser as close to the secondary as possible, right?

I've a Fagin 8" F7.5 mirror that's exceptional and gives truly exceptional lunar/planetary views with an E&W 1.5" secondary. My Mathias-Wirth 8" F6 Mak newt with its 16% secondary is aslo exceptional.

However, as Yoda says, "There is another". My D&G 11" F12 D&G achromat has given up some stunning lunar/planetary images (particularly Saturn this year)when used with a properly matched and positioned Chromacor. Yeah, I'm "limited" to an 11" aperture (or 9.5" or 8.5" when using aperture stops). I too have been observing for decades with some truly exceptional scopes, but when the big D&G "shows its stuff", I'm always taken aback. I've seen the same thing recently in a humble 8" F9 achromat with a well matched Chromacor.

But to your point, on an absolute basis, a well done mid-sized (8"-12" in my book) equatorial newt can be smashing period.

Jeff

#21 Jeff Morgan

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Posted 21 August 2013 - 11:16 AM

Well, a 9mm Nagler in a 10" f/9 scope is working at 254x which is very far from wide angle observing. I should have said, "wide-field, low-power" viewing with 68, 82, 100 degree eyepieces.

The 38 Erfle would show some fall-off of field illumination with a secondary that small.

Dave


Some yes. But noticeable? I think you might be basing that on the 70% edge illumination criteria. Fine for imaging, but a widefield visual observer perhaps doesn't need that much. See Alan Adler's August 2000 article on page 123 of Sky & Tel. He suggest a visual observer can be fine with 50% edge illumination, perhaps even 40%.

But using the "conventional wisdom" 70% criteria: Only at the extreme edge. Although I didn't own one at the time (not invented yet!), it would have illuminated a 31 Nagler using the 70% criteria. Attached is a screen shot from Mel Bartel's Secondary Size calculator using the dimensions from that scope.

Twenty years ago minimum diagonal size was all the rage. From the looks of it, I "got away with one". If I were to rebuild that scope today, once I got the central obstruction below 20% I would likely say "good enough". And the thought has occurred to me that I could always keep a smaller "spare" diagonal on-hand for nights I just want the planets.

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  • 6038251-10 f9 Secondary Plot.jpg


#22 Mark Harry

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Posted 21 August 2013 - 11:30 AM

I have a comment about smallish secondaries.There seems to be the desire to use a wide field eyepiece in such a scope; but it seems to me to be counter-productive. The small area of 100% illumination should be used where maximum detail contrast and resolution are provided by such a setup. Use the eyepieces that work well for longer F/D primary mirrors, with the fewest number of glass surfaces- and without the types of glass that bias (attenuate) certain color wavelengths to maintain fidelity. Choose the secondary size that the eyepiece stops of the MOST USED medium-high power settings will cover. The scope will then show amazing views, as mentioned by Daniel and others earlier. Save those wide field EPs for a different scope!!!
:tonofbricks:
M.

#23 dscarpa

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Posted 21 August 2013 - 12:14 PM

Nice scope! The solar system is my 1# and excellent lunar-planetary images are what I should get with my done but a continent away 11" ZOC F/5 Teeter STS with SIPS. I recently got a 5 XO mainly for it and my refractors. David

#24 Jeff Morgan

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Posted 21 August 2013 - 01:58 PM

I have a comment about smallish secondaries.There seems to be the desire to use a wide field eyepiece in such a scope; but it seems to me to be counter-productive. The small area of 100% illumination should be used where maximum detail contrast and resolution are provided by such a setup. Use the eyepieces that work well for longer F/D primary mirrors, with the fewest number of glass surfaces- and without the types of glass that bias (attenuate) certain color wavelengths to maintain fidelity. Choose the secondary size that the eyepiece stops of the MOST USED medium-high power settings will cover. The scope will then show amazing views, as mentioned by Daniel and others earlier. Save those wide field EPs for a different scope!!!
:tonofbricks:
M.


I can see your argument about a "confused purpose" scope.

While the strong suite of such a scope is minimum glass/maximum contrast one still has to be able to get around the sky. Having a finder/star hop eyepiece does have a lot of utility, especially for people not equipped with GOTO. Squeezing out the last few tenths of a degree is pretty handy.

Whether or not that justifies a $500 premium wide field or a $120 war surplus tank periscope eyepiece is of course a matter of taste and finances.

#25 Jeff Morgan

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Posted 21 August 2013 - 01:59 PM

Nice scope! The solar system is my 1# and excellent lunar-planetary images are what I should get with my done but a continent away 11" ZOC F/5 Teeter STS with SIPS. I recently got a 5 XO mainly for it and my refractors. David


Thanks.

BTW, I wondered who got that 5 XO. I was just a bit late on that one .... :bawling:

Congrats!


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