175 replies to this topic

[stubeeef]

I hope to have a 20"SST/Ostahowski f/3.4 in about 12 mo.

 

This summer I should have a unique 10" NMT/Pegasus f/3.4 DOB 

 

I've owned a 12" Orion dob that has been in pieces as I tried to repair the dead goto system.

 

Got an AT130 f/7 that sits too much because, as a DOB lover, I hate equatorial mounts. Has some nice planet views, a super value no question. Just not a KILLER at f/7.

 

Been thinking about a Sky-Watcher Skymax 180 f/15 but not many reviews here on CN.

 

I've reached out to Moonraker about his 150 Mak in development, turns out he's recovering from some illnesses and the Mak is new for him-gonna be awhile. Just love his work though.

 

SO-back to the purpose- what do you suggest for a Planet Killer?

Edited by stubeeef, 16 January 2020 - 10:22 PM.

[Eddgie]

Get a cheap 10" dob.

 

Pull the mirror and send it off to a professional mirror refinisher and have them bring it up to a high Strehl level.

 

Put a high quality secondary mirror in it.

 

Put boundary layer cooling fans on it. 

 

Even an 8" f/6 will work well for this, but the 10" will be better.

 

A 10" Apo would be good even better... Yeah.  

Edited by Eddgie, 16 January 2020 - 10:44 PM.

[bridgman]

My first thought was "an alt-az mount for the AT130"

[stubeeef]

Been looking at some, but f/7 vs f/15....there is a difference

[SteveG]

Get a cheap 10" dob.

 

Pull the mirror and send it off to a professional mirror refinisher and have them bring it up to a high Strehl level.

 

Put a high quality secondary mirror in it.

 

Put boundary layer cooling fans on it. 

 

Even an 8" f/6 will work well for this, but the 10" will be better.

 

A 10" Apo would be good even better... Yeah.  

 

This ^

[clivemilne]

 

Want a Planet killer-suggest some

Shell, Monsanto, Rio Tinto... Take your pick. 

[Galicapernistein]

The slower the scope, the better. I had a Discovery 10 F5.6 that gave great planetary views, but it couldn’t compete with my 8” F9 when it came to high power views. With 3.5 mm and 5mm eyepieces, I can comfortably view objects at high power all night long. And not once have I ever observed a planet with my 8” and thought, the image isn’t bright enough. Barlows are useful with fast scopes, but a 2x barlow will not perform nearly as well as a scope with twice the F ratio.

Edited by Galicapernistein, 17 January 2020 - 08:00 AM.

[bobhen]

Get a cheap 10" dob.

 

Pull the mirror and send it off to a professional mirror refinisher and have them bring it up to a high Strehl level.

 

Put a high quality secondary mirror in it.

 

Put boundary layer cooling fans on it. 

 

Even an 8" f/6 will work well for this, but the 10" will be better.

 

A 10" Apo would be good even better... Yeah.  

With limited budget then the above.

 

It’s all about the quality of the primary. Whether its F5 or F8 doesn’t matter. If the mirror is 1/10 wave it is 1/10 wave.

 

Consider Zambuto Optical for a primary.

 

You also might want to consider some type of tracking mount to keep the planet centered while you observe or image.

GEM
Alt/Az with drive motors
Poncet tracking platform

 

Other designs also have pluses but custom or high quality optics are expensive and for lunar/planetary, above all else, you need very high quality optics.

 

250mm Mewlon (Takahashi)
180mm and above apo refractors from the top makers (TEC, APM, AP used)
200mm and above Maks (AP APM)

 

Bob

[Jeff Morgan]

Got an AT130 f/7 that sits too much because, as a DOB lover, I hate equatorial mounts. Has some nice planet views, a super value no question. Just not a KILLER at f/7.

 

Sounds like you largely have made the reflector decisions, so instead I'll comment on this portion, if somewhat off-topic.

 

To revive your 130mm refractor, the TTS Panther is a fabulous alt-az GOTO mount. I replaced my Losmandy G11 with one. Same load capacity, 27 pounds lighter, no leveling, no polar alignment, and much better ergonomics.

[a__l]

It’s all about the quality of the primary. Whether its F5 or F8 doesn’t matter. If the mirror is 1/10 wave it is 1/10 wave.

 

 

I think closer to 1/8 limit

But it has to be real. Regardless of the manufacturer and its advertising promotion.

Edited by a__l, 17 January 2020 - 10:20 AM.

[stubeeef]

OK so 1 restomod 10" Dob

 

Any SCT or MAK lovers? 

 

What about f/12 or 1/15? Dimmer yes, but we're talking planets here.

Edited by stubeeef, 17 January 2020 - 11:11 AM.

[bobhen]

OK so 1 restomod 10" Dob

 

Any SCT or MAK lovers? 

 

What about f/12 or 1/15? Dimmer yes, but we're talking planets here.

You said planet “killer”. You can’t get an off-the-shelf SCT that fits that definition.

 

For Maks and SCTs you need to purchase limited run or custom made examples and they cost money. For example: there’s a $4,500 8” used Orion UK Mak on astro-mart with a great test report and a 20% obstruction, if you want a Mak.

 

Yes commercial SCTs can deliver fine planetary views but they will never be as good or take high magnification like some other choices so they are not planet “killers”.

 

Again, it’s all about getting very high quality (not mass produced) optics no matter what design you pick.

 

Bob

[Pinbout]

... what do you suggest for a Planet Killer?

move to the SW

Edited by Pinbout, 17 January 2020 - 12:08 PM.

[Volvonium]

I guess it depends what defines a planet killer?   

 

I would think a 20" Ostahowski f/3.4 would be a fine instrument for planetary observation once cooled and well collimated... 20" of well figured aperture would pretty much kill anything you throw at it.

 

I have to admit that even though I have a 16" f/4.5 scope with an Ostahowski mirror, I'm still working on an 8" f/~8.7 dob specifically for planetary use.   The 8" f/8.7 I have isn't necessarily because I think it would be better than my 16" for planetary...I'm building it just because I can, and out of sheer curiosity about how long focal ratio reflectors operate (all of my experience is with F/6 and shorter reflectors).   I'm using an old thick Pyrex mirror that I still need to get tested and maybe refigured, but I assume it'll do well in the planetary arena.   

 

I have a vintage C8 SCT which in theory should be great for planetary, but I have mixed feelings about how SCTs perform in relation to refractors and the big aperture of reflectors.

[Auburn80]

@Eddgie and others, that's what I want to do with my 10".

Who exactly performs a test/re-figure? I haven't had much luck finding one . . .

Edited by Auburn80, 17 January 2020 - 02:21 PM.

[SeattleScott]

Tak TOE and Vixen HR series offer very short FL eyepieces with comfortable ER, so F7 versus F15 shouldn’t really matter unless you are trying to utilize specific eyepieces you already have.

That said the AT130 isn’t a premium brand, so if you really want top tier, and are willing to pay for it, you can do better. I would think your huge Dobs would be great, but not much depth of focus at those F ratios, and maybe you don’t want to pull out a giant Dob to look at planets.

Scott

Edited by SeattleScott, 17 January 2020 - 02:29 PM.

[bobhen]

I guess it depends what defines a planet killer?   

 

I would think a 20" Ostahowski f/3.4 would be a fine instrument for planetary observation once cooled and well collimated... 20" of well figured aperture would pretty much kill anything you throw at it.

 

No place in the United Sates will a 20-inch telescope ever resolve to its full potential.

 

On few nights and in the best locations like south FL. a 12 to 16-inch will have a chance but in most locations just getting sub arcsecond seeing is rare. And not only do you need that seeing but the planets need to be high or at zenith or the seeing will be compromised even more.

 

For example…
"At the William Herschel Telescope site in the Canary Islands, even this superb viewing location (second best in the northern Hemisphere) has many nights of relatively poor seeing: the distribution is positively skewed, and at this excellent site, a 10-inch telescope will be seeing limited on 9 out of 10 nights.”

 

Bob

[Volvonium]

@Eddgie and others, that's what I want to do with my 10".

Who exactly performs a test/re-figure? I haven't had much luck finding one . . .

 

That's a good question.  I know that Optic Wave Labs will offer free testing of mirrors and they do offer fairly affordable coating and refiguring services, but Cary had a handful of very vocal customers who had negative experiences a year or so ago.  In spite of the bad press he's gotten, I'm considering using him/OWL for my small budget 8" project since I figure that he must have had enough happy but silent customers to stay in business and improve his facilities. 

 

I know for a fact that Ostahowski will not touch mass produced mirrors for coating/refiguring and he is constantly booked.   When I inquired with him some time around Fall last year about recoating/refiguring my GSO 16" mirror, he advised me that he's very hesitant to touch mass produced mirrors and when I subsequently asked about making a brand new mirror for me, he was cagey about providing any kind of pricing and quickly told me he was completely booked and to ask again in the Winter, ceasing all communication with me thereafter, without addressing my pricing questions.  I had the sense that because I told him I was still relatively new to the hobby, that "if I had to ask, it was probably more than I could afford".  I was ready to put a 50% downpayment on whatever he quoted me but it never came.  I was lucky to find my used 16" Ostahowski mirror a couple months later, but I have to admit that I felt very let down to get blown off, since I came to revere him after reading/researching so much about him and the other ace opticians in this hobby (Fullum, Zambuto, Lockwood, etc).  I still respect the sheer quality of his work, but I think the volume of demand he's seeing is a big stressor.  I'm not sure that he even works on anything under 12".

Edited by Volvonium, 17 January 2020 - 02:48 PM.

[Auburn80]

Thanks V. I got similar impressions re: OWL.
I did speak with Osta about a 12 and had a good experience - a set price and expected delivery. Sorry your experience was different.

[stubeeef]

Volvonium, If TO said he was swamped- HE WAS SWAMPED.

 

I would email him via his website and set up a time he can talk. An absolute encyclopedia of been there done that knowledge.

 

I encourage people to periodically check his SPECIALS page. Unbelievable finds, and he will send you the test data-like he says-he doesnt sell seconds of anything.

 

Yep thinking of a SW 150 or 180 MAK, 150 is f/12 and 180 is f/15

 

so 150 f/12 or 44% more aperture at f/15

 

Anyone using f/12-15 scope now on planets?

Edited by stubeeef, 18 January 2020 - 09:48 AM.

[Volvonium]

Volvonium, If TO said he was swamped- HE WAS SWAMPED.

 

I would email him via his website and set up a time he can talk. An absolute encyclopedia of been there done that knowledge.

 

I encourage people to periodically check his SPECIALS page. Unbelievable finds, and he will send you the test date-like he says-he doesnt sell seconds of anything.

 

Yep thinking of a SW 150 or 180 MAK, 150 is f/12 and 180 is f/15

 

Yeah, I got the distinct impression that he had so much work on his plate at the time that it was very stressful to even consider adding anything else to it.  I only communicated with him over email and I wouldn't be surprised if he's more of a over the phone person rather than email.  

[stubeeef]

Sounds out of the box, but I bought a 10" from Pegasus Optics and had TO test and coat it.

 

He did a double pass on it and was very complimentary of it and wanted to know who made it. I also had TO pick out a secondary for it after coating it.

 

Theres another more affordable option. The scope is in line with Ryan at NMT to be built so I cant tell you anything about the mirror other than TOs compliments.

[stubeeef]

So anyone here using a f/12 -f/15 reflector?

 

I haven't seen much in my search for Skymax 180 on CN

[macdonjh]

stubeeef, another option if you don't want to afford premium recommendations and want a slow scope for this application is the AT classical Cassegrain.

[Keith Rivich]

Not really sure what to suggest but my 25" kicks butt on the moon and planets. Barring going for such a big scope my 8" f/9 Parks newt on a platform is a close second.