On Axis Guiding vs Adaptive optics

[Rodd]

I am considering a Innovations Foresight on axis guiding unit or an SBIG AO-8 adaptive optics unit. 

1) On-Axis Guiding.  Splits the near IR off and uses that for guiding--IR is not used in imaging.  Works like an OAG, but it allows for continual real time focus correction during subs--no more stopping an exposure and tweeking focus--it maintains focus during the exposures.  It improves guiding and reduces time spent on focusing.  Expense is high (over $1,500 and maybe over $2,500--depends on what is needed and I'm not sure--there are many adapters and spacers in the kit)

2) SBIG AO-8 "adaptive optics" unit-I have the STT-8300 and use Maxim DL so using the AO-8 unit would be easy. It uses a tilt mirror to make millesecond guide corrections that is supposed to improve guiding, substantially reducing FWHM.  It does not improve focus, and it seems to me that it would complicate focus as the exposure must be stopped, then started in traditional fashion and the AO-8 unit is one more layer of hardware that must be restarted, calibrated and maintained.

Does anybody know anything about either of these technologies?  Both impact back focus and add weight and length to the optical train--though the AO-8 unit less so (about 2") and it weights 1.4 pounds.  It is also cheaper at $795.  Which would be more likely to improve my images?

 

Thanks.

 

Rodd

[Rodd]

I guess the goal is to compare the On-AG and SBIG AO-8 to my self guiding filter wheel.  3 methods of guiding.  Which is best?

[ChrisLX200]

On-axis guiding is similar to off-axis guiding in the way it works (guide camera senses movement and sends corrections to mount) but by using a cold mirror and guiding on the actual image it avoids any issue of there being differential flexure in the system. However, it still requires the mount itself to make the corrections (with all the inherant limitations of doing that). Adaptive optics systems on the other hand make corrections independant of the mount at a [potentially] faster rate so in theory at least that system offers more promise. The on-axis system requires the imaging camera to be fitted at 90deg to the optical axis (the guide camera replaces it as the straight-through sensor) which I just don't like the idea of with a heavy camera.

None of these systems are a 'plug and play' improvement if that's what you were thinking, they all need setting up correctly and tweaking to get the best out of them.

ChrisH

[swag72]

I used an Active Optics unit for a few months - I honestly didn't find it beneficial. It took a lot of time to set up correctly and I lost many nights worth of imaging due to glitches and the like. In principle it sounds great, but I was finding that when used in conjunction with an OAG I was struggling to find guide stars bright enough to allow anything shorter in exposure than about 2s........ so that negated the 0.1s exposure that they were suggesting made a real difference.

I would never bother with one.... so perhaps there's better alternatives out there.

[Rodd]

2 minutes ago, swag72 said:

I used an Active Optics unit for a few months - I honestly didn't find it beneficial. It took a lot of time to set up correctly and I lost many nights worth of imaging due to glitches and the like. In principle it sounds great, but I was finding that when used in conjunction with an OAG I was struggling to find guide stars bright enough to allow anything shorter in exposure than about 2s........ so that negated the 0.1s exposure that they were suggesting made a real difference.

I would never bother with one.... so perhaps there's better alternatives out there.

Thanks--I kind of suspected the trouble would outweigh the benefit.  Learning anything new impinges on imaging time.  I have the components to install to allow for autofocus--but I have to install them and learn how to make it work--meanwhile I only have about 6 hours of decent darkness and I don't want to break down to install them.  Choices. 

[Rodd]

24 minutes ago, ChrisLX200 said:

On-axis guiding is similar to off-axis guiding in the way it works (guide camera senses movement and sends corrections to mount) but by using a cold mirror and guiding on the actual image it avoids any issue of there being differential flexure in the system. However, it still requires the mount itself to make the corrections (with all the inherant limitations of doing that). Adaptive optics systems on the other hand make corrections independant of the mount at a [potentially] faster rate so in theory at least that system offers more promise. The on-axis system requires the imaging camera to be fitted at 90deg to the optical axis (the guide camera replaces it as the straight-through sensor) which I just don't like the idea of with a heavy camera.

None of these systems are a 'plug and play' improvement if that's what you were thinking, they all need setting up correctly and tweaking to get the best out of them.

ChrisH

According to Innovations Foresight--I think they have a new version that no longer has to be at a right angle.  The thing I like about the on axis guiding is the focusing in real time without having to stop teh sub--it maintains correct focus always.  But your right--not plug and play for sure.

[ollypenrice]

I don't think this technological approach is what your images need. I would concentrate on getting lots of data, nicely in focus and well guided, (you seem to have this nailed) and then settle down to learn the gentle art of processing.

Olly

[Rodd]

5 minutes ago, ollypenrice said:

I don't think this technological approach is what your images need. I would concentrate on getting lots of data, nicely in focus and well guided, (you seem to have this nailed) and then settle down to learn the gentle art of processing.

Olly

Thanks Olly--I appreciate the compliment.  You are probably right in that the thing my images need MOST is not guiding or focus related.  However, it seems that both of these things--getting the best guiding and focus possible are variables that are much easier to eliminate than good processing--at least with good hardware.  With  FWHM values above the local seeing (I assume--no way to confirm) and eccentricity values considerably above .42 (the accepted target),  the best processing will eventually hit that proverbial wall.  However, it is a matter of degree--which I as a novice have not the ability to gauge.  I assume you feel that improved processing will provide greater improvement at this stage than an improvement in focus/guiding.  No doubt because my focus/guiding is much better than my processing.   It is good news on a couple of fronts.  1) I haven't been spinning my wheels on acquisition, and 2) it will save me $$$ (at least until my processing improves)

 

Thanks

Rodd

[ian_bird]

I had an SX AO on my 10" RCT. On the one occasion I got it working - it worked well.

Now I follow Olly's advice (stretched I will admit beyond what Olly would suggest) and use a guide scope welded to the top rail of the RCT. I am using a reducer now which drops the focal length from 2000mm to 1300mm - but with this setup I am getting results as good as the AO produced.

And here is the rub - with a fraction of the grief.

If I lived somewhere like Olly does - I would play around with the AO - because I love the idea. But I don't live somewhere like Olly does - so I go with what works.

Cheers

Ian

[Rodd]

13 hours ago, ian_bird said:

I had an SX AO on my 10" RCT. On the one occasion I got it working - it worked well.

Now I follow Olly's advice (stretched I will admit beyond what Olly would suggest) and use a guide scope welded to the top rail of the RCT. I am using a reducer now which drops the focal length from 2000mm to 1300mm - but with this setup I am getting results as good as the AO produced.

And here is the rub - with a fraction of the grief.

If I lived somewhere like Olly does - I would play around with the AO - because I love the idea. But I don't live somewhere like Olly does - so I go with what works.

Cheers

Ian

I thought that the AO unit was supposed to help with atmospheric disturbance--that's what they claim, anyway.  It would seem that the AO unit would be more suited to a poorer observing location than Olly's.  What was the difficult part of getting it to work?

 

Thanks--Rodd