PHD Guide with SXV-AO

[Gert]

Hello All,

I am searching for info about SXV-AO usage with PHD guide.

I have the camera optical train with ASI2600MM, ZWO filter-wheel and OAG with ASI290MM guide camera. Scopes are C14EHD or Planewave12. Yes, the 2600 sensor will be oversampled. Either will use binning or reducer optics. Mount is AP1200. Capturing software NINA.

• My concern to using non-SX camera for the guider. Are there features / performance results that are lost when not using SX guide cameras with the SXV-AO (I plan on the 'new' USB version) I would like to use my ASI290MM. What about guide frequency, (multi) star selection, ROI selection (less frame area to download -> faster cadence?)
  
• Is all operational handling done in PHD guide? Or is some special SX software needed ? (other than driver)
• Is any AO control handed upstream to NINA for imaging control? I.e. bumping the mount in between exposures? (assuming that the mount runs clean for the sub exposure time?)
• SXV-AO does not have ASCOM, right? So PHD guide controls it via native driver. Any issues or missed capabilities due to that?
  

My apologies, some bullet item might be more suited for SX or NINA group (and I will go there as well) but I would like to start discussion here as well.

Feedback or user reviews are welcome.

Thanks & Clear Skies,

Gert

[ChrisR Oz]

Hi Gert,

I use the SX-AO (plus SX filter wheel and compact OAG) with my EdgeHD 8 with 0.7x reducer and ZWO cameras, 120MM as guide camera and 294MC Pro for imaging. Both the 120MM and the SX AO work very well through PHD2 with control (e.g. dithering) from SharpCap, which reads the 294MC. The AO and PHD2 have reined in the AVX mount, which is too close to its weight limit, getting down to 0.5” total RMS guiding. Calibration is easy, after using the wizard for setting up a new profile, done in 2 stages to calibrate the AO then mount. It seemed to need calibration twice the first time.

Using the 120MM as guide camera did require the CS adaptor that came with the camera with the addition of a spacer to stop it jamming against the locking screw. But then work well. This does lengthen the guide distance, so I needed a couple of shims to extend the imaging camera distance to match.

I find it works best with 2x2 binning on the 120 MM and 0.5 second exposures. Now it’s pretty much set and forget, just works …

Cheers, Chris.

[Gert]

Hi Chris,

Thank you for your info. That's very encouraging to see that someone has gained experience with this type of setup.

A question for you: Do you use the ROI option in PHD? Using a small ROI of i.e. 100x100 pixel (I think the size can be configured) the frame down load rate could be significantly improved.  You write that you use 0.5sec exposures that would be 2Hz guide rate which is already quite good. One thing that I don't see mentioned enough is the huge reduction in inertial mass that has to be moved when changing from guiding the scope to guiding a small piece of glass! Have you ever wanted to achieve higher guide rates? (Of course given a bright enough star!) ?? I would be wondering if a guiding ROI would enable that? (Alas this eliminates the multi-star guiding in PHD ... are you using that?)

I'm also doing planetary imaging with Firecapture and with a ASI290MC USB3 ROI 600x480 I get >200fps. Not saying to do the same in PHD guiding, but it could be opening a trend. :-)

Thanks & Clear Skies,

Gert

PS still wanting to ping the NINA group for their support for PHD with AO.

[bw_m...@earthlink.net]

I think you should probably read some background info on AO guiding and why using very short exposure times isn’t a good idea:

 

https://openphdguiding.org/man-dev/Supplemental_Info.htm#AO_Devices

 

Lucky imaging works ok with streaming video devices and planetary imaging because you may discard 90% of the images with no loss other than time.  “Lucky guiding” is a really bad idea.

 

Bruce

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[Gert]

Hi Bruce,

Going back to original development of Benoit Schillings and Brad Willis for the what became the SBIG AO7 the developers showed guide rates of 10Hz providing measurable improvement.

https://diffractionlimited.com/product/ao-8a/

https://cdn.diffractionlimited.com/downloads/legacy/ao7manual.pdf

https://davidastro.com/sbig-ao-8-adaptative-optics/

Quote : 

"Other data gathered by Brad Wallis of JPL (Brad Wallis and Benoit Schillings developed the prototype for the original AO-7) show the the effect of rapid corrections on poor seeing. 

At 1 Hz the larger, slower component is reduced, but the amplitude of the jitter remains about the same:

However, at a 5Hz correction rate, the faster jitter is reduced:

And at a 10 Hz correction rate, significant improvement is seen:

The improvement in stellar profiles can also be seen at corrections above 1 Hz.  First by looking at the non-AO guided image: And comparing the non-AO guided image to the AO guided image there is again significant improvement in the FWHM of the star profile: Telescope mounts cannot correct faster than about once per second. 

The 10Hz rate of the AO will clearly result in improved resolution under the right conditions."

Main advantage point of AO (i.e in amateur realm active optics, not adaptive optics) is reducing inertia from 100s of pounds to grams. I've been using ABIG AO for >15years and never used AOG or guide scope or had a guide cable to the mount that could snag.

Now SBIG is captive tech and going to SXV-AO is a desirable path.

Cheers & Clear Skies,

Gert

[bw_m...@earthlink.net]

I’m well aware of this, it’s old information, and my opinion stands – based largely on conversations with active, top-quality imagers who aren’t involved in flogging a product. At the image scales where any of this matters much, you are likely to find 10^th magnitude stars few and far between and the benefits of multi-star guiding will be lost.  But you should do what you want.

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/d203c77a-161a-470f-b669-450717bed6ddn%40googlegroups.com.

[ChrisR Oz]

Hi Gerd,

The problem is having enough SNR on available guide stars to go below 0.5s. The 2x2 binning helps. But the 120 MM pixel size is a limit. I’ll soon have a 174MM with larger pixels, which will give me a factor of about 2.5x (again using 2x2 binning) light collection and a 4x larger area to find better stars. This will help enormously. 

As Bruce alludes to, you don’t want to chase “seeing”. But there are a lot of successful imagers on Cloudy Nights who swear by 0.5s especially to tame the AVX. As for faster, that is interesting territory that I will be exploring with the 174MM, It would be useful if the AO could help reduce the effects of thermal effects close to the ground from roofs and roads nearby. A simple tilt window AO can’t really help with perturbations from higher altitudes. The greater sensitivity and better guide star choice will help explore exposures around 0.2s.

Cheers, Chris.

[ChrisR Oz]

Sorry, I forgot to mention that I don’t use the ROI feature as yet. At 0.5s it’s not really needed. It does help around 0.1s exposure.

[Pict...@earthlink.net]

Chris, it will be very interesting to read about the results of your investigation into higher guide rates.  My own experience with the SXV-AO is that higher frequency guide rates resulted in significantly improved RMS values.  My assumption is that RMS values are a valid measure of guiding quality.  Unfortunately the guider I was using was not capable of always acquiring suitable guide stars at higher guide rates.  In order to achieve more reliable guide star acquisition, I have since replaced my guider with one that has a much larger sensor.  This has eliminated guide star acquisition as a problem provided that I am using guide exposures of several seconds and sometimes it enables multi-star guiding as well.  Unfortunately the resulting RMS values are now poor.  It is possible that some of this is due to other causes since I have not only replaced the guide camera, but the computer as well and that brought along a number of its own challenges.  I have not yet had an opportunity to see if I can improve my results via various adjustments, nor have I attempted shorter guide exposures.  My nighttime imaging has been very limited lately.

I am well aware of the belief that a higher guide rate only results in "chasing the seeing" and that it is better to use guide exposures of several seconds.  That is why I have initially used guide exposures of several seconds.  As I mentioned above, that has enabled multi-star guiding in some cases, but you can imagine my disappointment to see that my RMS values are now significantly worse than previously.

While it may be true that for many imagers guide exposures of several seconds yield better results, it may not be universally true.  For example, I believe that local topography can significantly affect atmospheric turbulence and thus seeing.  Airflow where I live is most certainly not laminar.  It would be helpful to see data from imagers that included their locations and, if possible, characteristics of the airflow along the directions of images taken.

Thank you for sharing the link to the article you referenced.  I will read it to see what I can learn.  My interest is not in proving one school of thought is right or wrong; my interest is in understanding how to achieve the best results I can and what are the factors that I can control that will enable me to do that.  I am guessing that is probably what we all want.

Manning B

[Gert]

Hello All,

Let's not call it AO to prevent false advertising of trying to deal with seeing on amateur level . Let's call it 'parallel plate guiding' = PPG. Compare vs. 'full mount guiding' =

FMG. From a purely mechanical and operational point PPG has clear advantages.

1. No differential flexure i.e. as in guide scopes vs OTA
2. Eliminate extra weight of guide scope
3. Significant reduction in weight / inertia of moving parts
4. No backlash when reversing guide direction as in DEC backlash and it's various efforts in compensating it in software
5. Elimination of control cable camera to mount

#1 & #2 can also be achieved in OAG

But #3 to #5 are unique feature of PPG.

In my own experience once I moved to SBIG ST10 cam & AO8 in 2000 for my 13' F4 Newtonian I first removed the guide scope and never looked back. The mount can run 'open loop' just tracking and not pulses issued to either axis. Even if PPG is disputed to perform in higher guide cadence the remaining advantages and simplicity of process are making a no-brainer decision for me.

Now over time the SBIG solution failed to move beyond a captive technology. Nobody today wants closed drivers, captive control software, choice of cameras etc.

So SXV-AO with ZWO / QHY / SX / ATIK  / etc camera ASCOM mount driver and guiding support is the way to go. Just wish more vendors would start competing in PPG market.

Clear Skies,

Gert

[ChrisR Oz]

Hi Gert,

I don’t mind the term AO, (Adaptive Optic) as the tip/tilt are just the first order Zernicke terms anyway. SX actually call it an “Active Optic” to avoid any controversy.

Hi Manning,

I have a similar experience with excellent results in May and less so since. Most nights the AO is earning its keep wrestling with air movement, which catches the dew shield on the OTA. Hopefully, September may see some quieter air here and I can explore what the AO can do more. I am waiting on a larger guide camera too (ASI 174MM). Which one are you going for? Larger area and also larger pixels will both help.

Cheers, Chris.

[Brian Valente]

Hi Gert

I have had good results with both SBIG (earlier) and SX AO (more recently) and agree it would be nice to see more entrants into the market here

Regarding PHD settings, you might consider a strategy i used successfully in the past using the auto exposure and related target SNR settings

You could set your auto exposure to as low as .01 sec (although that's probably too low) and a reasonable max exposure for AO (1 second?) and PHD will automatically adjust the exposure until it hits the target SNR. IIRC correctly it does this continuously, so it's not like it picks an exposure time and sticks with it.

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/9d719f73-2d0a-4c4b-911f-afdf06d76dedn%40googlegroups.com.

--

Brian 

Brian Valente

astro portfolio https://www.brianvalentephotography.com/astrophotography/

portfolio brianvalentephotography.com 

astrobin https://www.astrobin.com/users/bvalente/

[Pict...@earthlink.net]

Gert, I am puzzled by your request: "Let's not call it AO ...".  The Starlight Xpress product name is "SXV-AO-USB".  I simply referred to the product I use as SXV-AO.  (There is/was a non- USB version also).  That was my only reference to "AO".

Manning B

[Pict...@earthlink.net]

Hi Chris,

I bought the ASI 183MM.  It has a 15.9mm diagonal sensor, much larger than the Lodestar X2 which I previously used.  And, the price is about the same.  The ASI 183MM has small pixels (2.4 microns), but I bin it 3 x 3.  I don't use ROI guiding.  I also use an ONAG to guide and with the ASI 183 MM I no longer have the problem of not finding a guide star in the FOV.  The ONAG does have an adjustable stage the guide camera is attached to, but moving the stage is a manual process which doesn't work for automating the system. 

Manning B

[Pict...@earthlink.net]

Hi Brian,

I used to use Auto Exposure when I was using the Lodestar X2.  Then PHD2 came out with multi-star guiding and it seemed like Auto Exposure was a sure way to reduce multi-star to single star.  As I mentioned previously, based on recommendations I have read here, I switched to a fixed exposure of several seconds when I bought the ASI 183MM guide camera, but that doesn't seem to be working out well for me.  I haven't had an opportunity yet to try auto exposure with my new guide camera.  I thought I would try reducing the number of variables and see if I could first get reliable guide star acquisition by using a fixed longer guide exposure and also see if I could exploit multi-star guiding.  Both of those goals are achievable with the ASI 183 MM guide camera.  Unfortunately, the end result thus far has been reliable, but poorer, not better guiding.  Hopefully, I can find a way to get both reliable and better guiding.

This forum is a great way to share individual experience and learn from others.

Manning B

[ChrisR Oz]

Hi Manning,

The 174MM has 5.9 micron pixels and at 2x2 binning then effective 11 micron pixels will provide improved sensitivity. I am exploiting the capability of PHD2 for sub-pixel precision.

Hi Brian,

I will give the auto exposure idea a try when I can - sounds interesting.

Cheers, Chris.

[Gert]

Hi Manning,

I wasn't referring to your post actually. :-) Rather to earlier discussion where the naming 'AO' alludes to making a claim of correcting seeing (by use of high frame rate) In context of that discussion I wanted to point out that naming the product 'AO' (and SBIG and SX are both 'guilty' of that) is inferring a functionality that is not there in these products. It should be called a 'guiding tool that doesn't have to move the whole scope around'. But that doesn't make for a catchy acronym 'GTTDHTMTWSA' :-)

Cheers,

Gert

[Salaam Al-Shaksy]

Hi 

I am keen to learn more about using an SX AO with PHD2. Where do I find clear instructions/guidance on this?

Best, Salaam

[oliv...@gmail.com]

Hi Gert

My 2 cents about the ´´over sampling’’ myth

You may not get any improvement at all with a reducer and it could even be counter-productive.

For instance, look at the PW reducer specifications in detail. You will see that the spots diagrams are not smaller with the reducer, thought there should be due to the shorter F/D ratio. This means you would loose resolution.

Additionally it is much more difficult to get the sensor perfectly parallel with the focal plane, the backfocus is very short (so you can’t fit the SXV AO, I tried…) and more vigneting…and it is expensive.

at the other hand the PW optics is excellent without reducer, the F/D 8 ration is still pretty workable with the 2600 sensor.

At my side, after having used the CDK12.5 with and without reducer, and with the SXV-AO, I am currently using a CDk17 without reducer and the QHY600 (same sensor in 24*36 format) with my team. Have a look to Arnaud’s Peel Astrobin Galery (who is the best PI expert of our team) and compare pictures with other CDK 17/20 that are using the reducer and the same sensor.

Besides, we are using PHD2 and smooth guiding on top of the absolute encoders of the L500 while others are using the reducer and no guiding…

At the end we keep luminance raws only under 1,6’´

And what I said for the CDK is also valid for the vast majority of reducers.

Clear skies

Olivier 

Le 24 mars 2023 à 00:23, Salaam Al-Shaksy <sala...@gmail.com> a écrit :

Hi 

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/02acc341-16b5-43ad-be84-65e4f82819aan%40googlegroups.com.

[bw_m...@earthlink.net]

Salaam, it looks to me like you have hi-jacked someone else’s thread and now we have a mess.  Would you please create a new conversation on the forum and ask your question that way.

 

Regards,

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/02acc341-16b5-43ad-be84-65e4f82819aan%40googlegroups.com.