Adaptive Optics for STL questions

[Paul Haese]

I am looking at obtaining an Adaptive Optics unit for my STL11K and have a few questions.

1. Do I need a guide camera for this unit? Images I have seen of the unit suggest not, but I would like that cleared up.

2. If no guide camera am I still guiding via the guide sensor in the camera?

3. Or is it better to have an OAG in the mix?

I sort of know the basic idea of how these units work but need to know exactly what is involved prior to purchase.

[rally]

Paul,

I am assuming you are talking about an SBIG unit ?
You already have the guide camera in the STL - you use that.

If you are doing NarrowBand and can't guide or correct due to faint stars then you could use a remote guide head after the AO but before the filter wheel, using an OAG body.

So you can do it either way.

Its really a question of back spacing, adapters, extra gear and budget !

Rally

[Paul Haese]

Thanks Rally. Yes I am planning on the SBIG unit.

Looks like I will need an OAG for imaging with the STL for narrow band.

It will give me tight stars though. Back focus is not really a problem I have plenty of that.

[bert]

The only commercial oag for the aol setup is a moag.

The only guide cameras you can use are sbig cameras with an i2c port or as rally says a remote guide head.

I was using a moag aol combo, but it chewed too much backfocus. Now I use the internal guide chip and a rotator. I don't do narrowband, but if it floats your boat, the internal guider ain't gunna be much chop.

Brett

[Paul Haese]

Thanks Brett,

what about blue guiding? Is this problematic? Not done that yet. I was thinking maybe in future I will be doing narrow band and broad band combinations with that camera and the RC12.

So it looks like for now to be a non issue??? Blue not with standing.

[rally]

Paul,

That will depend on the star you choose.

If its a small dim star or not very bright blue then you would have a problem, since the exposure is short.
Its not like you can rely on good tracking and a long guide exposure !

[Paul Haese]

Well I guess good tracking depends on how accurate I get my PA and PEC. Both need some work to get it more accurate, that will have to happen during moon lit nights, but clear nights are in short supply at present. Protrack would help too.

Imaging at long focal lengths though will require some guide corrects. :)

[strongmanmike]

Why do you want adaptive optics..??

With that PME and careful setup I just can't see the real benefit...? :shrug:

Mike

[Bassnut]

Brett's right.

IMO forget the internal guide chip for all but lum, AO is marginal at the best of times (but a killer for the rare times there is bright enough guide star) filters kill it. OAG is the only way. And with a rotator, that's essential.

Go away Mike, FLI not doing AO doesn't make useless ;). It's the only way to beat seeing short of a remote dark site.

[Paul Haese]

Even with the mighty PME (which has had the Haese maintenance schedule ;)) I think that the RC12 will need just that added umph. Maybe not initially but maybe to produce that cracking image. Maybe not but I think Martin Pugh uses AO on his 14" RCOS. Maybe I just don't need it. :shrug:

[Paul Haese]

OK Fred, that makes sense. OAG it is then. So maybe all I need is the remote guide head and a MOAG as you guys suggest.

Thanks for all the advice guys. Appreciate the imput.

[Paul Haese]

Yeah good point Ernie. Will save some dough too for a while.

[bert]

Heres my theory on ao...

The luminance data carries 90% the fine details in an image. So that where you want the ao to work.

I don't have an issue with colours with ao with the internal guider. Think about it this way: you may have 3 second guide exposures with the ao through filters. You may think that is no benefit over conventional guiding, but in reality it is. To do a correction with normal guiding, you need to move 60 odd kilos to make the correction and have associated issues with moving that mass. With ao guiding you only move a prism in the optical path. So which do you think will end up with optimal results? AO.

To throw some more info in the mix:

A rotator with the internal guider is better than a oag and rgh without a rotator for multiple target automated imaging (lrgb). I had the choice and I went with the rotator, after trying the oag option, due to limited back focus.

As for fli and ao, they are looking at it and I talked for a good hour or so with Greg from fli about it. Its just not on the top of their list right now.

It was mentioned in the thread to get a moag without ao. Thats a bad idea, it designed for that purpose only and is not made to work without the aol, I do not even think adapters can be bought for the telescope side. A mmoag is made for this purpose, but it will not work with the aol.

[Paul Haese]

Good points Brett. I saw on the OPT site that MOAG with AO fits all together.

Plenty to think about.

[gregbradley]

I haven't used an AO but plan to later this year.

Even with excellent PME tracking and spot on guiding you can see there is a certain amount of averaging of the random corrections that adds up to a wider star than the original focus images at longer focal length.

On a night of good seeing perhap the AO's benefit may not be that great but on an average or poor night it may make a difference.

2-3 weeks ago in my area the seeing was sensational. I took some images of a galaxy and they were some of the best I have seen from my CDK17 rig. Stars really tight and lots of faint details in the galaxy (image not published yet).

Last week was some poor seeing. I took some more galaxy images. They look like they are out of focus by comparison. I should post 2 sample images - one in good seeing, one in poor seeing both are in focus. Its an amazing difference.

Anything that reduces that is a worthwhile improvement. I am looking at a Starlight Express unit.

Greg.

[Paul Haese]

Greg, seeing is not such an issue for me at Clayton. The seeing has proven this year to be quite good with my planetary images of Mars and Saturn being quite good. However I guess like you whatever can gain just a little more detail and sharpness has got to be worth it.

There is a lot to consider now.

[Peter Ward]

AO works. It works even better with the about to be released STT series that has the guide chip in front of the filters...;)

[stevous67]

The SBIG remote guide head is not as sensitive as say the SX Lodestar, so you definitely need a rotator. Especially for isolated galaxy shots. From experience, and with a longer focal length, you need the MOAG and a rotator. I've been happy with the TAK CAA. But this will be useless when remote imaging (if you do that).

The AOL works, and those who don't see the point either have shorter focal lengths or simply don't understand what the AOL does. The RC12 will be sensitive to even the most gentle breeze, and when doing +20min exposures, the AOL will save the sub, when guiding at 2hz or faster.

I can also say that the Maxim tools for the AOL are terrific. It takes only 30-40sec to calibrate the mount, and about 20-30sec to cal the AOL (if that). Only an annoying tilt in my system affects my star shapes in one corner, otherwise, the AOL ensures my stars are tight and round every time.

Here's an example from last Friday night, and I image in Melbourne, so significant light pollution too:

NGC6188 (http://www.mpas.asn.au/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=1954&g2_serialNumber=4)

As mentioned above, back focus must be calculated to ensure you can still reach focus with everything added in.

Good luck :thumbsup:,

Steve

[JohnH]

For me I find this is the real benefit - at regular guide exposures with AO I get better guiding, it just works - every time. I think this is because you only have to move a few grams of glass instead of 20Kg plus of scope and gear. Backlash anyone?

Then agin , if you can get up to 5-10Hz+ guide rates you can start to tighten the FWHM as well...

On the bad side is loss of flexibility/compatibility with flateners and the like due to the AO unit.

[strongmanmike]

Oh I undestand how the AO works and it is sure to be of benifit to some, it's just that I see so many high quality high res images being done with RC's on PME's that don't use AO in the mix, that's all :)

Mike

[Terry B]

I like my AO unit. It certainly guides better than the guidescope alone due to differential flexure. I sometimes use a combination of both. I will guide with the guide scope and use the AO unit for fine control. This is just because I'm lazy and don't want to change the cableing around.:D

[strongmanmike]

Yeh, fair enough I guess... :)

Mike

[multiweb]

:eyepop: That's a real corker Steve. :thumbsup:

[stevous67]

Yes that is true, but I suppose it also has something to do with the fact that people have different tastes for different brands of cameras as they do for cars. And not all brands of cameras have supported AO units, and this would contribute to this fact. The AO is not a magical weapon, but it does help to mitigate certain factors that can otherwise ruin a sub exposure.

Cheers,

Steve

[rat156]

Hi Paul,

I have an AOL, ST11K, MOAG, RGH etc, even have a 10"RC and a PMX, sound familiar?

Recently I have run into back focus issues with the RC10C, with this scope you have to get as close to the optimal 6" back focus as possible or the stars at the edge of the (quite large) ST11k chip are not round. So I have had to forgo the MOAG/RGH and use the internal guide chip. Sometime you get lucky and there's a nice guide star in the field somewhere, though it can limit the framing of the object somewhat. I also used to have a rotator, that went too in search of back focus.

AO is essential IMHO for long focal length imaging, even with the best mount available, AO works and makes imaging so much easier, just use it any way you can. You can get away with longer guiding images on the colour subs, but try to get 5-15Hz for the luminance, it helps to really bring out the best in your imaging system.

I have the MOAG/RGH and adapters sitting in a box in the obs at the moment, I was going to sell it, but am keeping it for a little while just incase I can fit it in somehow. You're welcome to borrow it if you want to try it out, just PM me and I'll arrange to have it posted over.

Cheers
Stuart

[Poita]

I've often wondered if a variation of dlp technology could be used for 'cheap' adaptive optics on a pixel by pixel level.
http://www.dlp.com/technology/how-dlp-works/

[Paul Haese]

Hmmm now that is food for thought.

Perhaps what I will doo for now is get the RC imaging, then get the MOAG and AO with remote guide head and that will show me the difference and I will have a great appreciation.

Thanks all for the assistance, I really appreciate everyones thoughts.