High end GEM vs Mid range + AO?

[Docrob (Rob)]

Just wanted people general thoughts. It seems to me that with adaptive optics like SBIGs AO-X https://www.sbig.com/products/adaptive-optics/ao-x/ now being available at the ~$2,000 mark has the game has changed in terms of the relative value of a high end mount? As well as compensating for seeing and atmospheric effects AO can also iron out a degree of error in mount gears etc.

How do people think the combination of a mid range mount like the Skywatcher EQ8 plus adaptive optics for ~$6,500 compares to a high end mount like a paramount MX at ~$13,000 without AO? Is AO a "cheap" way to get a whole lot of extra mount for your money?

[Bassnut (Fred)]

Well, thats a good big question Ive often pondered myself.

Having tried those combinations:

AO really sings with bright guide stars, more than mag 5 so you can chase seeing. Suitable brighter than mag 5 stars in just the right guiding spot are rare and definitely require a rotator for composition, you wont just randomly get lucky without a rotator.

Whats left is regular guiding at say 1-3 secs, AO or via mount, same diff exposure/correction speed wise. AO would require less mount moving and be more accurate. Corrections within the AOs span dont suffer PE.

IMO, the MX (set up well) without AO would be preferable for many reasons generally for day to day imaging reliability and convienience, but if you want to produce that once a year rare killer image with lots of planning and patience then AO is the go.

I think thats a bit extreme though and risky. A better plan is to go with an MX and later add AO when funds allow.

[frolinmod]

Is the Paramount MX AUS$13000 even though it's US$9000 in the US? Bummer.

[rogerg (Roger)]

The number of times I can't find a star bright enough to guide on using 15s guide exposures, I'd hate to rely on finding one for AO use for every image. There's just too many objects I'd have to pass up on. At least with the PME I can get such objects any old time I want with 180s exposures and 300s if I am more particular about it. (0.84"/pixel, fl=2180mm)

The thought of always having the hassle of AO vs having a mount which "just works" doesn't draw comparison for me

[Geoff45 (Geoff)]

I have to use an AO unit(Starlight Xpress) with my G8 at 770mm focal length to get consistent results. The g8 can never decide whether to be perfect or hopeless. With my AP900 I get round stars at 2500mm focal length. Nevertheless, someone with the same setup as mine says that he gets slightly better FWHM by using an AO unit, even though he gets round stars without it. Anecdotal evidence is that an AO unit will always improve things. It turns crap into acceptable and it turns good into excellent.
Geoff

[Geoff45 (Geoff)]

Originally Posted by Docrob

Is AO a "cheap" way to get a whole lot of extra mount for your money?

Yes, but it gets extra for every mount, even the high end ones.
Geoff

[Peter Ward]

Mount first.....(second and third)

P.S.

$US 9000 costs about $A 10,600 from most banks...now add 10% GST.

Put it in a 100 Kg container and ship across the Pacific.

Add GST to the shipping.

Pay customs, and pay an import broker to get it across our borders.

$A13K for $US 9K of green money.... such a rip-off !

[netwolf]

I would think the better mount is the best option if you can afford it.
A used tak NJP or MX or AP900 maybe more affordable.

This chap get some great results with an SX AO unit on LX200 12'.
The thing I like about the SX unit is it can be used with non SX cameras.

http://astroanarchy.blogspot.fi/sear...20%28SXV-AO%29

[Peter Ward]

Sorry about my previous post....then again...no

AO works.

The caveat is: they are designed to correct (slow) seeing, not crappy tracking.

I've said it before...but I guess one more time won't hurt...

The best optics in the world will not deliver a sharp image when mounted on a wobbly/inaccurate mount.

Get your foundations right and the rest is a piece of cake

[Peter.M]

Originally Posted by Peter Ward

The caveat is: they are designed to correct (slow) seeing, not crappy tracking.

Get your foundations right and the rest is a piece of cake

I would argue that seeing and high periodic error (smooth) would equally be corrected with an AO. Infact the SX AO example has been a pet hate of mine since I looked at it.

http://www.sxccd.com/sxv-ao-lf

Who wants to spend 2 grand on an AO and not polar align their terrible mount?

Not that I don't think a great mount is the way to go, mounts are mostly simple mechanical creatures and I think If I had the money I would rather a reliable low PE mount than another thing to troubleshoot.

[Peter Ward]

Originally Posted by Peter.M

I would argue that seeing and high periodic error (smooth) would equally be corrected with an AO.........

Last time I looked, with an average quality mount, an AO has to contend with ragged tracking and seeing (I noted note the still eggy, albeit "corrected" stars on the SX web site)

The SBIG AO-X is the largest aperture AO (off the shelf) currently available on the planet, and sure, will run $US 2K ++ .

If you have less CCD acreage in mind, AO-8T is available at half the price.

[Terry B]

Originally Posted by rogerg

The number of times I can't find a star bright enough to guide on using 15s guide exposures, I'd hate to rely on finding one for AO use for every image. There's just too many objects I'd have to pass up on. At least with the PME I can get such objects any old time I want with 180s exposures and 300s if I am more particular about it. (0.84"/pixel, fl=2180mm)

The thought of always having the hassle of AO vs having a mount which "just works" doesn't draw comparison for me

I find it amazing that you would need a 15 sec exposure to guide. With my 200mm scope and the guide chip on my ST10 I can guide at 2 secs on a mag 12 star through a green filter. Maybe 4 secs using a blue filter.
Guiding with my spectrograph on a C11 using an STi guider I will always have a star to guide on with a 3 sec exposure and mostly I can use 0.5 sec if I want to.

I use my AO sometimes with my NJP mount but only if I want particularly tight stars with a dim target star in a crouded field. It certainly will achieve this better than regular guiding even with my reasonably good quality mount. For my normal targets of variable stars or spectra this is not usually a requirement. Pretty pic imaging is a bit different though.

[rogerg (Roger)]

Originally Posted by Terry B

I find it amazing that you would need a 15 sec exposure to guide. With my 200mm scope and the guide chip on my ST10 I can guide at 2 secs on a mag 12 star through a green filter. Maybe 4 secs using a blue filter.
Guiding with my spectrograph on a C11 using an STi guider I will always have a star to guide on with a 3 sec exposure and mostly I can use 0.5 sec if I want to.

I use my AO sometimes with my NJP mount but only if I want particularly tight stars with a dim target star in a crouded field. It certainly will achieve this better than regular guiding even with my reasonably good quality mount. For my normal targets of variable stars or spectra this is not usually a requirement. Pretty pic imaging is a bit different though.

There is often a guide star allowing exposures shorter than 2s, but there's also often not Most of my preferred targets are galaxies which tend to exist away from the dense star regions of the Milky Way and I find the FOV of the guider on my ST8-XME often won't have a star shown in TheSkyX and also in reality when I do a 5s exposure. So getting a minimum of 700ADU on a star for guiding can be a challenge.