28 replies to this topic

[GazingSkyward]

Would I recommend the ONAG?  Absolutely.  The benefits of near-infrared guiding on-axis are not simply theoretical, you can see them right there in your guide camera images and in the results that you take home at dawn.

Click here to view the article

[Ricky]

Excellent review!

[WalterG]

What an amazing review!  I immediately went to their website but then sticker shock hit me!  Do you know another off-axis guider that comes in second place that you would suggest?  

[james7ca]

Walter, this is an ON-Axis Guider not off-axis. In any case, I think (but am not certain) that Innovations Foresight is the only company that makes such a unit (at least for amateur astrophotographers).

[orlyandico]

the Innovations Foresight ONAG is indeed a bit steeply priced, which motivated me to make my own:

 

http://orlygoingthir...xis-guider.html

 

However "my own" is much less robust and less flexible than the ONAG.  I eventually gave up on it (a better mount made OAG unnecessary).

[Corsica]

Walter, this is an ON-Axis Guider not off-axis. In any case, I think (but am not certain) that Innovations Foresight is the only company that makes such a unit (at least for amateur astrophotographers).

 

The ONAG is a trade mark and unique patent pending technology from Innovations Foresight.

It is designed and made of high quality components to insure diffraction limited images. Custom high performance dichroic mirrors are expensive to make, they use many inferential coating layers, which is a much more complex process than standard optical AR and reflection coatings (used for traditional  lenses and reflector mirrors).

The devil is on the details, as usual, and the ONAG is the results of many years of experience on this matter.

As with any new technology cost is higher initially, however  good quality OAGs are close in price range, yet we are working hard to offer the ONAG at economical feasible and competitive price, without compromising its performances and unique features.

The ONAG does not require any rotator which usually add some extra load, back focus and cost in the setup, also the associated patent pending real time auto-focus (SharpLock) technology provides an unique solution to handle critical focus without any interruption of the image session.

[Corsica]

the Innovations Foresight ONAG is indeed a bit steeply priced, which motivated me to make my own:

 

http://orlygoingthir...xis-guider.html

 

However "my own" is much less robust and less flexible than the ONAG.  I eventually gave up on it (a better mount made OAG unnecessary).

 

 

A good mount is always better, but more pricy too.

With a high end mount, on a permanent setup, and a good pointing/tracking model such as Tpoint/ProTrack you can achieve unguided exposure for few minutes, depending of the target location, seeing and setup.

Longer exposure times, such as 10 to 30 minutes are more challenging and usually require some active guiding, even professional astronomers are guiding.

As a rule of thumb you want to keep your rms tracking error at, or below, a quarter of the current FWHM seeing, which means that good seeing could require rms tracking errors as low as 0.2" to 0.3".

[orlyandico]

I must add to my previous post.

 

I am currently not using the home-made on-axis guider.  There were too many problems with it, e.g. no way to move the guide camera, there was astigmatism even in the main camera, a horrendous amount of vignetting..  and adjusting focus on both the guider and main camera was very problematic.

 

In short - it was good as an intellectual exercise (and to exercise my ATM DIY skills), but not really viable for anyone serious about imaging.

[bsavoie]

Astronomy is wide open.. there is always a place where reality can be better appreciated. That is the fun of it. Astronomy is where hardware, software, and beauty connect.

 

I read your home-made on-axis guider whey you were first interested in it.. I am also happy that you do not give up. Your lessons learned will be key to some future approach that will be successful. Yesterday I bought a ADM Accessories MAX-M Guidescope Aiming Device. I am going to wade into this branch of astronomy that uses cameras.. In long - it is a good ongoing intellectual exercise. The future will break the bondage of high costs for all of us.

 

Bill

[juan manuel o]

great information, I see you have a z-EQ6 pro, I am very interested in purchasing a mount like that, you could help me by giving me a review of this mount also want to check that you can work in less than 3 ° latitude, and if I could send photographs would appreciate it! most of all in which is the minimum latitude, greetings and best wishes !!

[GazingSkyward]

Thanks to everyone for your feedback about this article, much appreciated!

 

As promised, I will be road-testing the ONAG SharpLock™ auto-focus feature in the coming weeks, so stay tuned for that.

[GazingSkyward]

great information, I see you have a z-EQ6 pro, I am very interested in purchasing a mount like that, you could help me by giving me a review of this mount also want to check that you can work in less than 3 ° latitude, and if I could send photographs would appreciate it! most of all in which is the minimum latitude, greetings and best wishes !!

 

Hi Juan,

 

Although the AZ-EQ6-GT has been on the market for a couple of years now, a few people have asked me to review this excellent mount and I will endeavor to do so in the coming weeks.  Unfortunately I can't answer your question regarding the operation of that mount below 3 degrees latitude, that is something you would want to ask Skywatcher.

[Fernando134]

Looking forward to your AZEQ6GT review!

 

Regards, Fernando

[John Jennings]

I understand about the advantages of On Axis Guiding as far as the flexure issues etc, but why can't I just place a near infrared filter on my external guide scope to guide in the near infrared, with a camera that's IR sensitive?

 

That would seem to help any guiding system not just the ONAG based on the comments in the article.

 

John Jennings

[Corsica]

I understand about the advantages of On Axis Guiding as far as the flexure issues etc, but why can't I just place a near infrared filter on my external guide scope to guide in the near infrared, with a camera that's IR sensitive?

 

That would seem to help any guiding system not just the ONAG based on the comments in the article.

 

John Jennings

 

Fundamentally this is correct. The NIR seeing effect (around 850nm) is close to 70% less than in the visible (550nm).

 

Here few comments:

There is a drop of the star signal level using only NIR versus using the visible + NIR (the all sensor spectral range).

This is a function of the star surface temperature (class) and the guider chip sensitivity versus wavelength.

Class M stars have surface temperatures, lower than 3700K therefore they radiate a lot of NIR. They are also quite common, since more than 76% of the main sequence stars are from class M.

With a classical Sony ICX429AL chip (used in the lodestar, the X2 version has a new generation of the Sony Exview chip, whcihis twice more sensitive now, chip QE improves all the time driven by the security camera market), the above signal level drop is about 50%, or near -0.8 magnitude. However it is not has bad as it may seem since there is less seeing induced guide star star wander in NIR your star signal level, relatively speaking, is usually better since the starlight is not as much as spread in NIR than in visible under seeing limited conditions.

 

Also with an ONAG you have wide FOV to find a guider star, which significantly increases the probability to find a suitable one. You are closer the the optical axis where the optical aberrations are minimum, those features help to offsets the signal drop.
An OGA by nature looks far of axis, especially with large ships, it is not uncommon to experience some coma, field curvature, ..., depending of the scope, and also some diffraction issues from the small pick up prism. Using a NIR filter maybe more challenging in term of SNR with an OAG.

Guidescopes do not have such limitations but they have others, beside differential flexure, they exhibit a smaller aperture D, 80mm is common, and this is an important figure of merit in term of SNR.

Since a star is a point source (a plane wave), the level of energy collected is a function of D squared, not a function of F/# like for an extended object.

Therefore a 11" (D=280mm) scope collects roughly  (280/80)^2=12x more starlight than a typical guidescope (80mm), this is a +2.7 magnitude gain in guide star selection for the same exposure time and SNR. This is valid for an OAG, ONAG, or self-guided cameras.

 

Also to benefice of a NIR filter for guiding you need to have a steep filter transition at the cut-off wavelength. This usually requires using interference filters, not die based filters.

 

But beside the above arguments, using NIR for guiding will help by reducing the seeing effect on the auto-guiding process.

 

Seeing a is a complex beast. Usually it is made of various temporal and spacial components coming from different layers of the Earth atmosphere. The guide star wander due to the seeing is only correlated with the other part of an image in a very small area surrounding it, few arc-second across, known as the isoplanatic angle, or patch.

Therefore it is not uncommon for the auto-guider and related software to "chase" the seeing while using short exposures (few seconds or less).

 

If such short exposures are needed indeed, using NIR will significantly help. Another approach is to use longer guider exposures, every time it is possible, to average out the seeing. You have to watch your polar alignment, and you may need to use a model of your setup to correct in real time the tracking rate (King's rate), such as Tpoint/ProTrack.

[John Jennings]

Corsica,

 

Thanks for your detailed synopsis. I fortunately have a good mount and optical system. I image with an AP1200GTO, C14 Hyperstar f/2, QHY12, Orion 120mm dia + QHY5LII external guidescope. My main/guide scope are are rigidly attached with a bulletproof monster Andy Homeyer cradle.

 

I have a remote observatory in the dark skies of New Mexico with good seeing. I typically get  0.02 - 0.03 arc/secs RMS guiding with my system using MaximDL. I know this system pretty well and have been imaging with the mount and HyperStar since 2007, and with the mount/C14 since 2000.  I've recently started using Astro-Physics APCC with atmospheric tracking correction and good modeling. I've been acquiring 10 minute unguided images at 600 mm FL down to low declinations that look better than my guided images sometimes. (poor seeing)  I'm sure as I tweak my polar alignment, I will get longer duration unguided images at the lower declinations. Just goes to show you the uncertainty of accurate guiding in less than perfect conditions. (Why I would like to use NIR guiding)

 

Many successful refractor imagers use external guidescopes successfully. These days it's fairly easy to mount them without a large amount of flexure and the main scopes are also fairly short focal length systems too which makes guide requirements easier for automated imaging instead of using a pick off mirror OAG etc. (This depends on image train deflection too)  Of course my system suffers from mirror flop, but I've made major modifications to minimize.

 

However, I'm always looking for guiding upgrades. Since I already use an external guide scope with fairly decent aperture, I'm getting very good FOV for guiding and use CCDAutopilot for unattended imaging. Only on rare occasions in guide star poor regions do I have an issue. Obviously using an NIR ONAG with a larger Cass or RC would be better with NIR ONAG guiding. When I start to image at prime focus on the C14 again, it seems very logical. However I'm currently in the same boat as many refractor imagers with smaller apertures that would suffer from reduced signal with a NIR ONAG solution. I have to use an external guide scope because of the HyperStar system and my camera combo.

 

With my external guide scope configured with an NIR filter, it seems to me that I will obviously loose a fair amount of stars for guiding. Since I perform completely automated imaging runs it seems I might have to make some target selection restrictions to prevent guide star acquisition failures during an automated run. With my current system, I'm successful 95% of the time. I originally chose the larger 120 mm external guide scope system of guiding instead of camera pickoff OAG to get better automated guide star selection and performance in the first place. Based on your calculations ((120mm/80mm)^2 = 2.25), my 120mm is already acquiring 2.25 times the light as a typical 80 mm guidescope system. 

 

Question: Am I correct in thinking that since there is an approximate loss of 50% signal level based on your comments, that my external 120mm guide scope with an NIR filter would translate close to guiding with an 80mm refractor (no nir filter) with the advantages of guiding in the NIR. ((2.25/2) = 1.125)

 

 

John Jennings

[Corsica]

Corsica,

 

Thanks for your detailed synopsis. I fortunately have a good mount and optical system. I image with an AP1200GTO, C14 Hyperstar f/2, QHY12, Orion 120mm dia + QHY5LII external guidescope. My main/guide scope are are rigidly attached with a bulletproof monster Andy Homeyer cradle.

 

I have a remote observatory in the dark skies of New Mexico with good seeing. I typically get  0.02 - 0.03 arc/secs RMS guiding with my system using MaximDL. I know this system pretty well and have been imaging with the mount and HyperStar since 2007, and with the mount/C14 since 2000.  I've recently started using Astro-Physics APCC with atmospheric tracking correction and good modeling. I've been acquiring 10 minute unguided images at 600 mm FL down to low declinations that look better than my guided images sometimes. (poor seeing)  I'm sure as I tweak my polar alignment, I will get longer duration unguided images at the lower declinations. Just goes to show you the uncertainty of accurate guiding in less than perfect conditions. (Why I would like to use NIR guiding)

 

Many successful refractor imagers use external guidescopes successfully. These days it's fairly easy to mount them without a large amount of flexure and the main scopes are also fairly short focal length systems too which makes guide requirements easier for automated imaging instead of using a pick off mirror OAG etc. (This depends on image train deflection too)  Of course my system suffers from mirror flop, but I've made major modifications to minimize.

 

However, I'm always looking for guiding upgrades. Since I already use an external guide scope with fairly decent aperture, I'm getting very good FOV for guiding and use CCDAutopilot for unattended imaging. Only on rare occasions in guide star poor regions do I have an issue. Obviously using an NIR ONAG with a larger Cass or RC would be better with NIR ONAG guiding. When I start to image at prime focus on the C14 again, it seems very logical. However I'm currently in the same boat as many refractor imagers with smaller apertures that would suffer from reduced signal with a NIR ONAG solution. I have to use an external guide scope because of the HyperStar system and my camera combo.

 

With my external guide scope configured with an NIR filter, it seems to me that I will obviously loose a fair amount of stars for guiding. Since I perform completely automated imaging runs it seems I might have to make some target selection restrictions to prevent guide star acquisition failures during an automated run. With my current system, I'm successful 95% of the time. I originally chose the larger 120 mm external guide scope system of guiding instead of camera pickoff OAG to get better automated guide star selection and performance in the first place. Based on your calculations ((120mm/80mm)^2 = 2.25), my 120mm is already acquiring 2.25 times the light as a typical 80 mm guidescope system. 

 

Question: Am I correct in thinking that since there is an approximate loss of 50% signal level based on your comments, that my external 120mm guide scope with an NIR filter would translate close to guiding with an 80mm refractor (no nir filter) with the advantages of guiding in the NIR. ((2.25/2) = 1.125)

 

 

John Jennings

 

John,

 

The apparent guidescope aperture D (assuming 120mm nominal), for a 50% drop of signal would be given by 120*sqrt(2) = 85mm.

Since (120/85)^2 = 2, the dependency is on the squared root of the drop.

 

The guide star FWHM and HFD due to the seeing (star wander) decreases with longer wavelengths. The net result is that the central peak and HFD carry more energy (higher amplitude, better Strehll's ratio), if you are seeing limited which is usually the case with large aperture scopes (>3").

You may have a gain in SNR up to 50% in NIR, depending of your local seeing, exposure time, and scope aperture.

From experience part of the NIR 50% signal drop is offset by a better NIR seeing and a resulting tighter guide star.

Most of the ONAG users have experience very little change in their ability to find a guide star.

[John Jennings]

Corsica, 

 

That's encouraging for my setup.  Good point about central peak and HFD carrying more energy. I'm kind of excited about trying NIR out. At first with an external guider, and then maybe with a Foresight NIR ONAG system when shooting at prime focus with the secondary in place. Most of my improvements over the years have been incremental.

 

Thanks again for the info.

 

https://sites.google...gapastronomer1/

 

John Jennings

[Corsica]

John,

 

If you have a good mount and tracking using a model as I understand you have, I would recommend to try using long guiding exposures as much as you can, like 30 seconds or more. Basically your maximum exposure time will be limited by the left over drift, since no model and mount are perfect, but it could be very small, depending of the position of the target above the horizon.

With long enough guiding exposure you are averaging out the seeing (in NIR and/or visible), which means that the guide star centroid is essentially seeing free. Of course you still have the starlight energy spread from the star wander, this is where NIR may be useful. Yet with long exposures finding a suitable guide star with a good enough SNR is seldom an issue for most targets and apertures any way.

 

Many people try to guide with too short exposures to deal with the guide star drift in my opinion, they would be better off, with most today's mount (and PEC), with longer ones and a good pointing/tracking model, at least for a permanent setup.

Making a good model takes some time and commitment, but it pays back. Too short guiding exposures increases the risk of chasing the seeing, especially in the visible wavelengths. Even when using NIR this remains a concern since the guide star wander isoplanatic patch is usually quite small, few arc-seconds across.

 

On the other hand using a multi-star (constellation) guiding strategy offers an unique interesting and promising alternative. You will average out the seeing by using several stars across the scope FOV, which also improve the SNR, the resulting guiding information is essential correlated with your setup error, not the seeing anymore, at least not its contribution related to small isoplanatic angles (upper Earth atmosphere effects).

 

Maxim DL version 6 offers such capability, other are coming soon. The only way to use constellation guiding with the same scope than imaging is the ONAG technology using a guider having a large chip to access a wide FOV without any part in motion.

[John Jennings]

Corsica,

 

I have tried to stay with 4 second guide exposures through the years with my system in order to not chase seeing. I have not experimented with long exposures with APPC, but will give it a try. I have a significant FOV with my external guide scope system and have tried multi-star guiding as implemented in MaximDL6, but have not found any consistent improvements to guiding so far. In some cases it appears to perform worse and others better. This could be due to the implementation by MaximDL and/or the combination of my system. I was excited when MaximDL6 implemented multi-star guiding, but have not kept up to see if others are having better success. Since Maxim's algorithm is proprietary and feedback is limited, it's difficult to analyze the issues with it.

 

The biggest advancement for me as an AP mount user seems to be with APCC's refraction correction and a good pointing model for my system. I just turn off guiding when the seeing is not great. Six minute subs are no sweat unguided at most declinations tested so far. I have tested up to 10 minutes a few times with no problems. Of course, guiding at the lower declinations is a harder test and most difficult usually due to the air mass refraction errors, but with APPC tracking correction, that part is minimized. It really makes you appreciate how tentative auto guiding is and that we are mostly chasing long period mount tracking errors and not seeing like a lot of folks think. The seeing issues just get in the way of good auto guiding while trying to correct for mount tracking errors. I guess that's why the new generation of quality mounts with hi-res shaft encoders used with programs like APPC and ProTrack are so incredible. 

 

I think your suggestion of long guide exposures like 20-30 seconds with APPC enabled may be a good strategy in order to correct for any polar mis-alignment drift or mount mechanical errors in long exposures. I do not have shaft encoders on my 15 year old AP1200GTO so it is an open loop system. Of course AP's new series of mounts have that as an expensive option and integrates feedback into their adjusted rates. A new mount with shaft encoders are above my dollar limit. APCC can only tell my mount to track at the corrected rates, but with no closed loop polar and dec shaft encoder feedback, it can't guarantee positional accuracy. (I think its close) I don't think APCC checks the Dec and Polar drive motor's encoder for position feedback, but I could be wrong about that.  And I guess there is always the image rotation component that can not be corrected with guiding or APCC. I'm not sure how significant that would be. I guess it could be pretty small. My mount was aligned with PEMPRO, but believe it could be adjusted better by performing alignments on both sides of the meridian, although Dec and RA alignment is always a compromise.

 

John Jennings

[ccdmaker]

the Innovations Foresight ONAG is indeed a bit steeply priced, which motivated me to make my own:

 

http://orlygoingthir...xis-guider.html

 

However "my own" is much less robust and less flexible than the ONAG.  I eventually gave up on it (a better mount made OAG unnecessary).

Loved that article - it's always fun when you do it on your own. When are you going to strip down a Canon ultrasonic lens and use those motors to build your own AO?

[PRejto]

I have been using an ONAG on my TEC140 and TEC180 for some time now. It is an impressive product and now even better with the new helical focuser for the guide camera. I'm using an ATIK 414EX to guide. An expensive solution but gives an impressive FOV. Also, very recently I have auditioned SharpLock using MaximDL. It works as advertised once set up and the system understood. In the future I think I will be using SL and the new Optec solution FocusLock (essentially SL engine that allows for a large number of capture programs like TSX). If anyone is interested I can publish some of my observations using SL.

 

Peter

[Corsica]

Following Peter's post I'll like to update on the FocusLock status, it is now live.

You can download and try the beta version till August 31 2015.

 

http://www.innovatio...-download-beta/

 

Any comments and feedback are most welcome.

[PRejto]

In case anybody is interested, this is a demo video I put together for a talk I gave last week to the imaging group of the New South Wales Astronomical Society on Optec's FocusLock which I used entirely for my image of NGC 1532. It's a bit long mostly because I was taking long guide exposures. If short guide exposures are used it is considerably faster. In reality it is of no consequence as camera focus changes are quite slow. It only matters for the purpose of demonstrating. The exciting thing is that this focus system is coming to the Lodestar guide camera + OAG, so no ONAG required. This will be released in April at NEAF.

 

https://www.youtube....h?v=UtgBTVEImZg

 

Peter

 

I took this image (ca 26 hours) entirely with FocusLock:

 

http://www.astrobin.com/full/240667/0/

 

The background music is performed by my partner, Bernadette Harvey, playing the Australian composer Ross Edwards' "Night Mantras."

Edited by PRejto, 04 March 2016 - 02:33 PM.

[Corsica]

In case anybody is interested, this is a demo video I put together for a talk I gave last week to the imaging group of the New South Wales Astronomical Society on Optec's FocusLock which I used entirely for my image of NGC 1532. It's a bit long mostly because I was taking long guide exposures. If short guide exposures are used it is considerably faster. In reality it is of no consequence as camera focus changes are quite slow. It only matters for the purpose of demonstrating. The exciting thing is that this focus system is coming to the Lodestar guide camera + OAG, so no ONAG required. This will be released in April at NEAF.

 

https://www.youtube....eature=youtu.be

 

Peter

 

I took this image (ca 26 hours) entirely with FocusLock:

 

http://www.astrobin.com/full/240667/0/

 

The background music is performed by my partner, Bernadette Harvey, playing the Australian composer Ross Edwards' "Night Mantras."

Peter,

 

I think the youtube video link is not correct.

 

Now it is, I have updated the link in this post as well, thanks Peter

Edited by Corsica, 04 March 2016 - 08:06 AM.