ONAG - How does it work question?

[g__day (Matthew)]

Peter,

I saw your mention to a custom made focuser made by Gary Jarrett; can you please pass some information along please and if possible add some more detailed pictures that better show what you've utilised.

When I had to first match my OAG's primary camera and guide camera I first focused the main camera using a Bhatinov mask on a bright star, then I centred the guide camera on Jupiter and used the Bhatinov mask on it to best focus the guide camera. Only Juptier was bright enough to give me a diffraction pattern I could use. It was a total PITA but eventually got it sorted. I wish that this pain was avoided if you are forking out for over $1,000 gear - that they had gone to the effort to simply at least thread the guide camera extension tube. I suggested this to Foresight Innovation well over a year ago - ponder if this idea has progressed far?

Secondly agree totally with Greg - much easier to guide at full, long focal length with an OAG / ONAG - side by side or saddled gear is so much harder to manage guiding with in my experience due to mirror shift / flop and or differential flexure. Even a minute amount kills you.

[PRejto (Peter)]

Hi Matthew,

I certainly don't disagree with you or Greg about OAG guiding. Of course it works better in any situation (but with more difficulty). I was only indicating that I would guess that most wouldn't bother with OAG for short focal lengths.

As for the focuser..... The one I'm using is based on the design for the QSI camera. This video completely describes the focuser. Gary just built for me a small inserted adapter with c threads at the bottom. He has said that later models might be a bit different to fit different guide cameras or mounting solutions. Anyone wanting one of these will find Gary very accommodating in searching for individual solutions.

https://m.youtube.com/watch?v=YX-nyWe0qp0

Peter

[mldee (Mike)]

Originally Posted by gregbradley

OAG always leaves guide scopes for dead. I use both. Sometimes I get great guiding with a guide scope, other times not so great. Apart from the adapter universe needed sometimes for various camera/scope setups with MMOAGs/OAGs it is a very accurate guiding tool.

Greg.

Well, as usual, testing doesn't come easy. Thought I'd put the DSI II Mono on the guide port, and the QHY8 PRO OSC on the imaging port, and see how it went with the Megrez 80mm refractor on the azeq6.

First, the two USB hubs got cantankerous, making both cameras misbehave. 5v back feed problem to cure tomorrow.
Second, the Megrez Crayford decided it was all too hard and refused to cooperate. Time to fix the lock screw tomorrow.
Maybe then.......

Plan is to start modestly using the mono DSI. Center the scope on a fairly populated sky area, Mioplacidous looks like the optimum spot for my setup, then take a 2s shot from the imaging port, changeover the DSI to the guide port and take another, so we can all compare the difference between optical and NIR results with the same camera.

Well, that's the plan anyway, clouds permitting.

[PRejto (Peter)]

Sounds like an interesting experiment, but what exactly are you trying to prove?

Obviously the camera only receiving IR will shower fewer and dimmer stars. The way I look at this is that it is the only way the ONAG concept can work. Clearly OAG vs ONAG gives winners in both camps. For the ONAG the main advantage is the large star field and ease of finding a guide star. For brightness of guide star, OAG wins. With a large aperture scope the difference in brightness perhaps becomes moot. This is why I'm curious to see if you can use the ONAG with only 80mm aperture. As I said a while back, I had trouble with 140mm, but 180mm is working great.

Peter

[mldee (Mike)]

Originally Posted by PRejto

Sounds like an interesting experiment, but what exactly are you trying to prove?

Obviously the camera only receiving IR will shower fewer and dimmer stars. The way I look at this is that it is the only way the ONAG concept can work. Clearly OAG vs ONAG gives winners in both camps. For the ONAG the main advantage is the large star field and ease of finding a guide star. For brightness of guide star, OAG wins. With a large aperture scope the difference in brightness perhaps becomes moot. This is why I'm curious to see if you can use the ONAG with only 80mm aperture. As I said a while back, I had trouble with 140mm, but 180mm is working great.

Peter

Not really trying to prove anything, just want to satisfy myself of the pluses and minuses, if any, of the onag, and to share the results with any interested IIS onlookers. I also want to see how my quite modest scopes and mount handle onag, and when, if necessary, using a separate guide scope may be more effective, or even no guiding at all.

I guess it's called a learning curve.

[E_ri_k (Erik)]

I have been using an ONAG on my RC10 for almost 2 years. I think its fantastic. It's so easy to find a guide star. Although I had to upgrade my guide camera to a Lodestar, because my QHY5 wasn't picking up enough IR.

I don't mind being able to slide the guide camera around on the 2 axis's, it helps sometimes when there are not many stars in the FOV, or to centre one. It is a bit annoying though to have to tighten all the screws up when you're done.

I'm interested in trying out the Sharplock too.

Erik

[gregbradley]

It looks like an interesting device and the Sharplock could make it worthwhile all by itself if it works well.

Greg.

[gaston (Gaston)]

I thought you maybe glad and interested to know that all ONAG (SC and XT) models come now with a helical focuser for the guider.

Also OPTEC is going to release in few weeks a beta version of a new software, known as Focuslock, which implements the SharpLock technology for any applications supporting ASCOM devices, such as Maxim-DL, The Sky X, PHD, ...

A quick comment on NIR guiding. The seeing (FWHM, or HFD) drops as the 6/5th power of the wavelength. This means that between 500nm (mid visible) to 800nm (mid ONAG NIR guiding range) the seeing improves by about 70%.
Since there is less star wander the tracking is smoother, but also the guide star is tighter, leading to a better SNR, which offsets partially the drop in flux, if any, while using NIR starlight only.
More than 70% of the main sequence stars have surface temperature below 3700K, radiating a lot of NIR (for further information on this matter you can visit http://www.innovationsforesight.com/...-infrared-nir/).

Clear skies!

[PRejto (Peter)]

Hi Gaston,

Thanks for this update!

I'm very anxious to try the new Optec focusing software! I've been reluctant to abandon guiding in TSX just to use Sharplock so this is a potentially great solution!

Peter

PS. Yes, the new design of you web pages looks great and I appreciated the interesting article on critical focus. I looked around for a picture and specifications on the helical focuser but could not see it. Is it possible to see any photos?

[Eden (Brett)]

The new Innovations Foresight website looks great! Now to wait until Winter finally hits so that I can take SharpLock for a proper test-drive in the field.

[gaston (Gaston)]

Good point Peter.

I have added a picture and some information about the new ONAG helical focuser for the guiding camera.

Here is the link:

http://www.innovationsforesight.com/...s-guider-onag/

Thanks for the feedback!

[g__day (Matthew)]

Woo hoo for the helical focuser - remind me again who first requested that add on to you guys !

http://www.cloudynights.com/topic/35...s-guider-onag/ Dec 2011

Are there mechanical aids to precision (almost micro focus the guide camera) - like a threaded tube moving the guide camera in / out a few microns at a time?

[gaston (Gaston)]

It took a bit longer than I have anticipated to release this new focuser feature, therefore I'll like to thank you all for your patience and overall for your suggestions and comments, which eventually made possible this.
It is the result of your useful feedback.

[PRejto (Peter)]

Originally Posted by gaston

Good point Peter.

I have added a picture and some information about the new ONAG helical focuser for the guiding camera.

Here is the link:

http://www.innovationsforesight.com/...s-guider-onag/

Thanks for the feedback!

Thanks Gaston.

Now comes my obvious question. Is it possible to retrofit my existing ONAG with the new focuser?

Peter

[gaston (Gaston)]

Yes there is a retrofit kit available now for any ONAG using the traditional drawtube focuser.
Any new model (SC and XT) comes with the helical focuser in standard.

Here is a link to the kit:

http://www.innovationsforesight.com/...-retrofit-kit/