Starlight Xpress AO unit

[allan gould]

Im thinking of getting a starlight express ao unit to fit with my QSI583WSG camera. I phoned the SX dealer here in Australia but got no reponse to my questions regarding attachment to the QSI, as I see there is some difference between the normal OAG sold by SX and the QSI583WSG. The dealer was quite able to sell one but no technical knowledge offered.
Is there anyone in this forum that has an SX AO unit and can advise re attachment to a QSI583WSG camera?
And would it be worth the effort.
Thanks for any help
Allan

[naskies (Dave)]

SX sells two versions of the AO-LF. The QSI version should be identical to the standard version, except that it doesn't come with the OAG (since the WSG already has one built in). By the way, the photo for the QSI version on optcorp.com is incorrect, i.e. the OAG isn't included.

http://www.optcorp.com/sx-sxv-ao-sxv...ve-optics.html

http://www.optcorp.com/sx-sxv-aoqsi-...g-cameras.html

The AO-LF comes with a T adapters (and something else that I can't remember, SCT thread maybe?) for both the scope and camera sides. The adapters use the same coupling system as other SX devices, and the AO unit itself is also threaded at around 72 mm (from memory - I'd have to check to be sure). You'll also need a Lodestar guide camera to be able to use it in MaximDL.

It's been exceptionally useful for me, since I can image at high resolution using a cheap EQ6: round stars even at 0.67''/pixel. My recent images (Cat's Paw, NGC 1763, plus others not posted) were 60 min subs at 1.36''/pixel, all with nice round stars thanks to AO. It can also chase low frequency seeing and wind quite effectively.

[gregbradley]

Is that the large format AO unit Dave?

I am looking at getting one for my CDK imaging train on the 16803 Proline.

Greg.

[naskies (Dave)]

Yep, I have the "Large Format" version... but the clear aperture is only 37 mm (APS sized sensors) so I don't think it'll work effectively with your 16803 PL?

[gregbradley]

Originally Posted by naskies

Yep, I have the "Large Format" version... but the clear aperture is only 37 mm (APS sized sensors) so I don't think it'll work effectively with your 16803 PL?

The promo for it says it has a 60mm clear aperture for full frame? 16803 needs something like a 54mm aperture.

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

Perhaps you have the regular unit which has 37mm clear aperture.

Greg.

[naskies (Dave)]

Hmmm my mistake sorry, I was going by the OptCorp description rather than direct measurement.

What I was trying to say is that the AO unit sits a fair distance in front of the sensor (i.e. in front of the OAG and FW) so depending upon f-ratio I'd imagine that you'd need a larger clear aperture than say for your filters in order not to block the light cone. I have heard other 16803 users say that the AO-LF isn't big enough for that chip, so it might be worth checking with SX?

[gregbradley]

Thanks for the tip. I will clarify that point.

Yes I noticed Opt's site has the AO LF clear aperture incorrectly specified.

Greg.

[clive milne]

Bizarrely, the version that has the lf designation (which stands for large format) is the smaller of the two. It does however come with an off axis guider. You will need to use a Lodestar to make it work.
c

[gregbradley]

Originally Posted by clive milne

Bizarrely, the version that has the lf designation (which stands for large format) is the smaller of the two. It does however come with an off axis guider. You will need to use a Lodestar to make it work.
c

Its just an error on the OPT site. If you go to the Starlight Express site it is correctly specified. The Large Format is the one with the 60mm aperture.

Perhaps the latest version of PHD allows you to use another guide camera.

Greg.

[naskies (Dave)]

My SX AO-LF was in my camp fridge for the past two weeks (attached to the main camera to shoot darks), but the run finished today and so I was able to double check the measurements.

The clear aperture is indeed 60 mm, but it's substantially reduced by the standard adapter plates and adapters that shipped with my unit: T-thread and STL on the camera scope, and T-thread and SCT on the scope side. Apologies for any confusion, Greg.

To get the full 60 mm aperture, you'll need to find M72 threaded adapters for both sides of the AO-LF unit.

[gregbradley]

You were doing darks for 2 weeks?? Or only part of the time?

Time to get yourself a FLI camera. They almost don't need darks.

STL11 is a great camera but very very noisy. So I understand the need for accurate darks.

I emailed Terry and he told me I would likely get some vignetting but it should flat out. I think I will go down this road in the near future as my CDK17 cries to me at night wanting an AO. I've been promising it one for a while now so now it does not believe me!!

Greg.

[RickS (Rick)]

Even FLI can't make a Kodak/Trusense sensor noiseless, Greg Dave is imaging with a KAF-8300.

I did an experiment with some narrowband data from my KAF-16803 at -30C and processed with and without darks. The integration using darks showed several percent better SNR. I get a few more percent from overscan calibration. Add a bit more for careful tweaking of rejection and scaling algorithms and now you're talking about an easily visible improvement.

Darks may be optional with the new Sony sensors. Mike S certainly seems to think so...

Cheers,
Rick.

[naskies (Dave)]

Greg, I've captured a nice dark library at -5, -10, -15, and -20 deg C with 50 x 60 min subs at 1x1 binning with overscan. Based on my overscan test data, scaling darks down works better - and I shoot 60 min subs for NB. The temperatures covers the ranges I actively use (yes - I would love FLI's superior cooling). This should cover my imaging needs (LRGB & NB) for the next few months.

Like Rick, I'm also trying to take an evidence-based approach with my imaging process. Good calibration results in better SNR with my data as well. I've also discovered that performing overscan reduces my empirically measured read noise by 1-2%. I'm very much in favour of following the "anything that gives me measurable SNR improvement without extra dark sky time = good" approach.

I think an AO unit will definitely benefit your imaging on the CDK17. Finding a bright guide star won't be an issue on a 17-inch scope!

[clive milne]

Originally Posted by naskies

Finding a bright guide star won't be an issue on a 17-inch scope!

Guide star availability for a given area of imaging sensor is more or less proportional to the square of the inverse of the focal ratio.

Aperture has little to do with it..

fwiw
~c

[Bassnut (Fred)]

Originally Posted by gregbradley

You were doing darks for 2 weeks?? Or only part of the time?

Time to get yourself a FLI camera. They almost don't need darks.

STL11 is a great camera but very very noisy. So I understand the need for accurate darks.

I emailed Terry and he told me I would likely get some vignetting but it should flat out. I think I will go down this road in the near future as my CDK17 cries to me at night wanting an AO. I've been promising it one for a while now so now it does not believe me!!

Greg.

Actually, its seems unfortunate you got "lumbered" with an FLI now that your thinking of AO Greg .

SBIG STLX would have made AO a snack with a lot less money (and back focus) .

[naskies (Dave)]

Originally Posted by clive milne

Guide star availability for a given area of imaging sensor is more or less proportional to the square of the inverse of the focal ratio.

Aperture has little to do with it..

fwiw
~c

Perhaps that's true for conventional guiding, but star brightness is important for AO guiding since it's often the limiting factor in determining the maximum tracking rate. All else being equal, the same star with a larger aperture scope will give either a higher ADU count, or a shorter exposure for the same ADU count (therefore higher tracking rate).

If a rotator is used and the position angle of the main camera isn't important (e.g. square chip), then guide star availability will be significantly affected both by the angle of the guide chip relative to the axis of rotation (i.e. whether the long vs short axis is tangential to the axis for non-square guide chips), and by the distance of the guide chip from the axis of rotation (greater distances sweep a larger area during a full rotation).

[clive milne]

Originally Posted by naskies

All else being equal, the same star with a larger aperture scope will give either a higher ADU count, or a shorter exposure for the same ADU count (therefore higher tracking rate).

Dave, if you double the aperture of the scope and keep the focal ratio the same, the guide stars will indeed be 4x brighter.... however, because the image scale is increased by a factor of 2x, you will have to increase the guiding chip area by a factor of 4x to capture them or accept that there will be only a 1/4 of the number to choose from. The corollary to this is that if you halve the aperture, your selection of guide stars changes in so much as you have 4x the number of guide stars rendered at 1/4 the apparent brightness....some of the new ones coming in to the field however, will be on average 4 x brighter. ergo, large telescopes don't render star field richer, just more resolved.

[gregbradley]

Originally Posted by RickS

Even FLI can't make a Kodak/Trusense sensor noiseless, Greg Dave is imaging with a KAF-8300.

I did an experiment with some narrowband data from my KAF-16803 at -30C and processed with and without darks. The integration using darks showed several percent better SNR. I get a few more percent from overscan calibration. Add a bit more for careful tweaking of rejection and scaling algorithms and now you're talking about an easily visible improvement.

Darks may be optional with the new Sony sensors. Mike S certainly seems to think so...

Cheers,
Rick.

Speaking of that, what rejection parameters have you found workable? I tend to only use hot and cold pixel rejection and have noticed that helps. I have not noticed the other rejections to help at all unless I am simply using the wrong settings.

Greg.

[gregbradley]

Originally Posted by Bassnut

Actually, its seems unfortunate you got "lumbered" with an FLI now that your thinking of AO Greg .

SBIG STLX would have made AO a snack with a lot less money (and back focus) .

That's funny Fred. Yes there is some truth to that in that FLI do not do autoguiding which is annoying. It leaves only Starlight Express unit as an option and frankly I am bit nervous about that. But as far cost goes I don't see your argument there. 65mm filters from Astrodon are really expensive ($2750 or so) plus add in 65mm narrowbands and the extra adds up even more. Plus I think the STXL costs more than a Proline don't they? Backfocus - yes true. SBIG is defintely a nicely competitive system now. They definitely were lagging before but it seems they have a matching camera now but with more autoguiding solutions. Mind you the MMOAG is not really a problem. It works well. Competition is good.

Greg.

[Bassnut (Fred)]

Using OPT as a reference. A FLI proline 11002 is about $500 more than an STXL 11002, and An FLI micro 6303 is about $400 more than a STXL 6303. It doesnt appear that FLI make a proline 6303 anymore. SBIG dont do a 16803 in STXL. Interesting aside, FLI seem to be pushing electronic shutters, mechanical is an option on most models these days. I dont know what the implications are, interesting.

Im not knocking FLI, itelescope loves em, excellent reliability and support apparently, but they are more expensive than SBIG and as you say not flash in the self guide/AO department, if thats of interest.