Big SCT or Big Dob & EQ Platform?

[Cath]

except my spare pennies go to repairing my car.

Keeping my car going is also my local big black hole

[JB80]

There is one point that you've completely overlooked Jake..... you've just moved house and every spare penny you thought you had will go into redecorating.

sorry to depress you mate. I'm in the same boat, except my spare pennies go to repairing my car.

Lee

In going through our budget to buy a house it turns out I could of afforded something like this quite some time ago.

I didn't work it out soon enough though because now we will have no money left and as you say what will come in is already slated for a new kitchen, floor, etc...

It's going to be a while yet.

[SnakeyJ]

There is one point that you've completely overlooked Jake..... you've just moved house and every spare penny you thought you had will go into redecorating.

sorry to depress you mate. I'm in the same boat, except my spare pennies go to repairing my car.

Lee

More of a change of tenancy, so the decorating costs are minimal and diy effort is focused on the obs.       One of the more appealing factors with the dob/eq platform was that it removed the requirement for substantial pier and foundation (though I have already constructed this part and designed it to be bolt on and below ground level so it can be easilly concealed below ground level for the next move).      However, there are some decent looking third party tripod options (like altair's starbase) that could be perfectly acceptable in a small obs, provided you were working from a warm room or remotely to minimise any vibration and the trip hazzard!   And, for planetary purposes this 600kg+ of concrete in the ground is certainly overkill.

The RC and cassegrain options certainly look possible, but neither are as 'compact' as the SCT alternatives.    The SCTs also offer the advantage of a closed environment to keep the dust and bugs away from the optics, though with the penalty of being slower to reach thermal equillibrium (this being less of a problem in a static unheated observatory).    At worst a constantly running dessicant dehumidifier could be adding 3-6C to the ambient external temperature, which means cool down times are not irrelevant in an obs, though far less of a problem than bringing the OTA out of a heated house which could be 18 degrees above ambient in UK winter.

[DrRobin]

Jake,

Even though my C11 is housed in an obs I still need to run the scope and extractor fans for at least 30 minutes to get rid of tube currents and if it has been a hot day even longer.  You can really see the difference if I rush it, apart from the focus changes the fine detail just isn't there whilst there are tube currents.

A truss tube RC is no different to a truss tube dob in respect of dust and most have a cap to cover the primary.  Or you can get a flexible side, which also helps cut down on stray light.

An RC, although longer than an SCT, will still be shorter than a dob.

Robin

[JamesF]

Regarding the RC...  I thought they had curved fields by definition?  Not sufficiently curved to be an issue for planetary imaging, but don't they need a corrector to obtain a flat field?

James

[SnakeyJ]

On the other hand.... with a bigger and more expensive mount the RC's would not be a one trick pony and could offer impressive deep sky performance, with a good reducer

Though I think I'm being drawn back towards a big SCT on an EQ8, the extra load capacity would allow for future ambition and a small apo co-mounted for wider field.    Beyond the planetary, I think the C14/ASI174M + 0.63 reducer could provide quite reasonable performance for the brighter planetary nebs, small galaxies, comets and supernovas at 30-120s exposures.

[cgarry]

When I build an obsy I am keen to co-mount my SW Esprit 120 scope with my C14 for widefield views.  I wonder if the Mesu 200 would be up to the job...

Cheers,

Chris

[SnakeyJ]

Regarding the RC...  I thought they had curved fields by definition?  Not sufficiently curved to be an issue for planetary imaging, but don't they need a corrector to obtain a flat field?

James

The limited data at Teleskop Services, states big corrected flat field without need for additional correctors - http://www.teleskop-express.de/shop/product_info.php/language/en/info/p6685_TS-16-inch-f-8-Ritchey-Chretien-Astrograph---carbon-truss-tube.html

The specs at Lunatico, describe a fully illuminated image circle of 60mm, natively corrected to APS 35mm and fully corrected with their 3" FF - http://tienda.lunatico.es/16-f/8-GSO-RC-Truss-Astrograph-Carbon-tube.

I think Mr Penrice might love this, if only it could be made with a clear optical window to eliminate those pesky diffraction spikes!   Though sure there's a good work around for this in Pixinsight

[SnakeyJ]

When I build an obsy I am keen to co-mount my SW Esprit 120 scope with my C14 for widefield views.  I wonder if the Mesu 200 would be up to the job...

Cheers,

Chris

From all I hear the Mesu/Sitech and would be a superb choice, provided you didn't want to fully automate the obs and run it remotely.    

[Pete Presland]

I can not add much to the C14s v 16" dob debate, but when i sold my 10" newt a few years back i didnt think i would regret it. I am pretty sure tthough it would probably out perform my C9.25 though for planetary imaging.

[DarkD]

I went through the same reflection in recent years ... A break of almost 5 years during which I have sought the best setup for imaging and visual. In priority for planetary imaging and observation, but not exclusively.
First condition, the diameter. No less than 350mm ... I have had a CG11, a 300mm ultra compact dobson, and already observed in larger instruments, so I wanted to "upgrade" in diameter.
For me, a prerequisite for high resolution is high optical and mechanical quality. A lowest possible obstruction and maximum contrast.
I decided for a 16-inch, but no way to put it on an equatorial mount (too expensive, too bulky and difficult to transport - I know it's not your case).

An equatorial platform ? No because i find it too restrictive (and raises the eypiece). So, the AltAz solution is the option that I finally chosen ... For planetary imaging, fast cameras can compose most of the time with the field rotation. For deep sky a field rotator solve the problem.
I now use for 4 months a 16" Newton truss at FD/4 made by SkyVision. Motorized and goto with SkyCommander and Servocat, all transportbale with a wheelbarrow.

I am ready to observe in less than 15 minutes, and can take it under better skies if needed.

So if money is not an option, as you said, I would think about such a solution. I don't have an observatory in may garden, don't want it.

This is just my own experience and not the truth

I'm imaging jupiter since last month and my first results are encouraging if one can say...

see here for an example

Michel

[Cath]

From all I hear the Mesu/Sitech and would be a superb choice, provided you didn't want to fully automate the obs and run it remotely.    

Would Jake think full automation is a desirable goal ?

[SnakeyJ]

Would Jake think full automation is a desirable goal ?

Not for me Cath, too expensive and unless you lived a fair distance from the obs, probably unnecessary. I'm quite happy to open up and switch on, then close up at the end of the session. Though eventually a warm room would be nice, maybe with a bunk where I could catch a few Zzzs while the data was being captured!

[Cath]

<wipes brow>

[astroman001]

Hi all and Neil in particular.

I have made the transition from C8 to C11 and recently from the C11 to a C14. I bought a second hand C14 OTA for £2000 and a CGE mount for £1300. The pair work well together. The other transition I made between C11 and C14 was to mount the C14t permanently on a pier in a roll off roof obsy. This makes cool down not such an issue and helps keep collimation consistent for long periods. Once you have mastered the basics of planetary imaging, collimation and seeing are the main factors. I have to say that I star check my C14 regularly on camera and it has not needed an adjustment for at least 3 months now.

When the seeing allows, aperture rules. The C14 delivers much better images than the C11. Also for DSO viewing, what was hard to see with the C11 is easy with the C14. 

I can't comment on the large Dob vs C14, but when sorted the C14 is an excellent all round scope.

Hope this helps.

Best regards

Peter

[neil phillips]

Hi all and Neil in particular.

I have made the transition from C8 to C11 and recently from the C11 to a C14. I bought a second hand C14 OTA for £2000 and a CGE mount for £1300. The pair work well together. The other transition I made between C11 and C14 was to mount the C14t permanently on a pier in a roll off roof obsy. This makes cool down not such an issue and helps keep collimation consistent for long periods. Once you have mastered the basics of planetary imaging, collimation and seeing are the main factors. I have to say that I star check my C14 regularly on camera and it has not needed an adjustment for at least 3 months now.

When the seeing allows, aperture rules. The C14 delivers much better images than the C11. Also for DSO viewing, what was hard to see with the C11 is easy with the C14. 

I can't comment on the large Dob vs C14, but when sorted the C14 is an excellent all round scope.

Hope this helps.

Best regards

Peter

I kept thinking of you Peter. Because your transition has been somewhat smoother than some I have seen switching to bigger scopes. Me included. Though not sure a 12"  SW is a great comparison of switching,  as there are numerous problems with those setups. Only twice has it seemed to perform.

But all the hallmarks of blur are apparent often when switching to large optics. And I am not convinced in some cases its as simple as cooldown. or just thermal problems.

 Though of course cooldown will be a important issue. as will thermal issues

 I think those that have problems, should try to leave the scope out for long periods to see what effects it has.

I have done numerous things to see whats happening with mine. For the most part. No matter what I do, The blur factor is stronger than with my Orion. One suspects worse optics. Yet on one night, briefly it seemed to do great.  I may get the optics tested at some point.

I think in cases of switching to large optics, the foot print of what is going to be got in the longterm, is established quite early. For those that don't seem to do that well. Often things stay like that generally. While others seem to be more consistent Pete R for example.

I keep trying to get a night like I had with the SW, I have to try for longer to figure this stuff out. But when the smaller scope is sharper 90% of the time. I get little incentive to do so.

That's not true for everyone of course. But for a unlucky few, it certainly seems to be.

Switching to large optics does not always go well. For some like you peter, it seems to work well, for others the images are no better than what can be got with 250mm optics. In some cases  considerably worse.  Its a conundrum that doesn't always seem to be predictable.

[michael.h.f.wilkinson]

I gather RC designs typically sport very big secondaries (50% CO by diameter is common), SCTs have some 32% CO. That makes the SCT better for planetary given the same optical figure!! A well designed Newtonian will have even smaller CO, so in principle could outperform the SCT. Having said that, SCTs seem to hold collimation better, which can save hassle.

[michael.h.f.wilkinson]

Oh, and then there is this beast:

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p6628_Orion-UK-300mm-f-12-Planeten-Cassegrain---Abschattung-nur-75mm.html

Looks impressive, but the price looks intimidating

[neil phillips]

Oh, and then there is this beast:

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p6628_Orion-UK-300mm-f-12-Planeten-Cassegrain---Abschattung-nur-75mm.html

Looks impressive, but the price looks intimidating

Never seen that before. the potential would be immense

what a design. Better than a RC for planetary. Cooldown would behave more like a Newt. but so would dewing. Heater of somekind would likely have to be fitted to remove dew once settled.

Wonder why I hadn't seen this scope before.

[SnakeyJ]

Never seen that before. the potential would be immense

what a design. Better than a RC for planetary. Cooldown would behave more like a Newt. but so would dewing. Heater of somekind would likely have to be fitted to remove dew once settled.

Wonder why I hadn't seen this scope before.

Wowzer, that looks very interesting indeed, but the price!    Not quite the same, but I found an interesting thread here, talking about a custom OO 12" DK build for planetary @ Roger Vine's Scopeviews site http://www.scopeviews.co.uk/OrionOptics12inchDK.htm - this is an excellent site and recommended reading material BTW

Edit - odd that this model does not get a mention on OO's site, perhaps a discontinued line?