SKYMAX - 180

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SKYMAX - 180

Postby james s » Fri Jan 21, 2011 9:13 pm

Hi everyone,

So, on the back cover of your new Sky at Night Magazine is (amongst others) a SKYMAX-180 Mak.

This lovely thing is an F/15 with a 7.1inch aperture primarily designed for observing solar system objects and detailed lunar observing...

Can anyone suggest where the equilibrium is between aperture and F ratio for viewing solar system objects? e.g. my dob is and F/5 and is a bit fast and wide for Jupiter at the moment and the atmosphere shows a wobble...would this SKYMAX-180 be similarly affected by atmosphere - being that it's a particularly big Mak?

If one were to buy a Mak for solar system observing in the UK what's the crowning aperture size that will give good viewing most of the time without being wobbled very much by the atmos?

Thanks in advance to all advice/comments received.



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RE: SKYMAX - 180

Postby brianb » Sat Jan 22, 2011 3:20 am

Sites vary.

Maks are compact and light for their aperture but the thick corrector plate makes them exceptionally slow to cool. They're not perfect planetary scopes any more than any other design is ... optical quality is probably 20% of the equation, design 5% and site selection 75%.

The very best planetary work is carried out by people with good sites, and the "weapons of choice" tend to be 11" or 14" SCTs or relatively slow Newtonians with apertures in the 12"+ class.

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RE: SKYMAX - 180

Postby james s » Sat Jan 22, 2011 7:46 am

Thanks Brianb

Yes, I've read that Maks have extended cool down times.
The Dob can take anything from 20mins to an hour to cool off - by which time sometimes the clouds come over...

Would a 127 Mak take much longer than this to cool down?


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RE: SKYMAX - 180

Postby brianb » Sat Jan 22, 2011 10:50 am

[quote]The Dob can take anything from 20mins to an hour to cool off - by which time sometimes the clouds come over...

Would a 127 Mak take much longer than this to cool down? [/quote]
In my experience a ETX 125 takes 2-3 hours. A Newtonian of similar aperture will likely cool in 10-15 minutes - without fan assistance - and fan assistance is much easier to add to a Newtonian / Dobsonian tube, in fact they tend to come with the fittings if not the actual fan assembly, which is only a cheap PC type.

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RE: SKYMAX - 180

Postby kevinrowsell » Tue Feb 01, 2011 3:33 pm

[quote] A Newtonian of similar aperture will likely cool in 10-15 minutes - without fan assistance [/quote]

The mirror of a Newtonian of that aperture will not have cooled down in that time. OK, collimation by a non-expert may give a bigger difference than the flexture of the mirror as it cools, but the primary mirror of a Mak is a pretty effective radiator, I don't think 2-3 hours is right unless you're talking quite extreme differences in temperature.

Talking of which, any ideas how to best keep an (expensive) larger scope "outside" but safe from both theft and, more continually, damp? The case for a Meade SCT looks like it should handle being in an outhouse fine, but the skywatcher case for the 180mm Mak doesn't look robust enough. Or would I be being a worry-wart?
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RE: SKYMAX - 180

Postby russ1970 » Wed Mar 02, 2011 11:30 am

[quote]ORIGINAL: brianb

[quote]The Dob can take anything from 20mins to an hour to cool off - by which time sometimes the clouds come over...

Would a 127 Mak take much longer than this to cool down? [/quote]
In my experience a ETX 125 takes 2-3 hours. A Newtonian of similar aperture will likely cool in 10-15 minutes - without fan assistance - and fan assistance is much easier to add to a Newtonian / Dobsonian tube, in fact they tend to come with the fittings if not the actual fan assembly, which is only a cheap PC type.


[/quote]

2-3 hours sounds about right for a Mak that is stored indoors and coming from a warm house to a very cold outdoors. But if stored outdoors, a shed or garage or relatively cold conservatory, the cool down will be much faster.

Maks also hold collimation much better than either an SCT or Newt. Another possible consideration. And their secondary obstruction is also smaller, especially on an F15 model. Not sure about the Skymax 180 but my Intes had an obstruction of 25%. Compare this to 35% for an SCT. It makes no real difference for imaging but should help for visual.
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RE: SKYMAX - 180

Postby brianb » Wed Mar 02, 2011 12:03 pm

[quote]secondary obstruction is also smaller[/quote]
Makes no noticeable difference for visual up to about 30% ... above that there is a definite contrast loss. The main factors for contrast are (1) good seeing, (2) accurate collimation, (3) optical quality, (4) cleanliness of surfaces and (5) central obstruction - in that order.

One thing that should be noted is that [i]all[/i] scopes with obsturctions in the aperture (however small) can have issues with very low powers, the obstruction is projected into the exit pupil. And scopes where the light passes through the tube more times tend to suffer from cooling issues / tube currents more than scopes where the light passes through the tube fewer times ... [i]real[/i] advantages for the refractor, and for Newtonians over Maks/SCTs ...

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RE: SKYMAX - 180

Postby dave.b » Thu Mar 03, 2011 10:30 pm

I saw the SkyMAX 180 at Astrofest this year. It looked impressive at first glance but on thinking why I decided that it was its size that looked impressive. But note that an 8" F10 SCT would be shorter, however, I believe the SkyMAX 180 is cheaper than say the Celestron C8 (but please check coz I'm going from memory here).

Dave B.
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RE: SKYMAX - 180

Postby philip pugh » Fri Mar 04, 2011 2:20 pm

Wish they gave one away free with the mag!
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