There was a solid write up about ONAG in cloudy nights; I think its a product I will buy into once (when) I become cashed up again. The price I gather for base set-up is around $1,000.
The only question I had was how easy is it to precisely focus the guide camera to the primary camera?
My challenge precision focusing the guide camera to the primary camera using an Lumicon OAG - required focusing the primary using a Bhatinov mask - primary using Rigel, guider using Jupiter! Only Jupiter was big and bright enough to let me see the diffraction pattern! Precision focusing the guider wasn't fun at all because the OAG didn't had a threaded tube mechanism to allow the guide camera to be adjusted by fractions of a mm at a time.
I think anyone designing ONAG or OAG should correct this by allowing a micro focus arrangement for at least one of the cameras attached to their rig! All it needed was a threaded sliding inner tube!
thanks for the ideas for attaining focus , i may have to emply one of those? i have been in conversation with Gaston in the pM's but i thought i might share a few points here. i will be getting a custom made adapter made for my setup. i went to the web site to order the gear, i found it a tad cumbersome and no PAYPAL available or was it international friendly for the address. i have brought this up with the company and they will apparently rectify this issue. As you may deduce i am ordering the On axis guider - it is the only clear way i can see to use the 14" in the 2.3m sirius dome. I am currently awaiting an email with the paypal link to complete the order
Keen to know how it goes for you! I am stunned folk go through all this effort to split and align the optics - then forget how challenging focusing the second camera is! Even if you simply threaded the outside of a tube and put a larger threaded tube over it and a seperate lock nut - the outside tube would simply very slow slide up or down as you rotated it - this would give the guide camera something to rest against and it would make micro focusing adjustment trival.
I reckon that idea would add less than $2 to the cost and add heaps to the functionality! Maybe suggest it to Gascon!
Matt et al,
I've been using ONAG for the past five years. I use a modified Vixen flip-mirror body where the mirror is replaced by a 92T/4R beamsplitter plate.
I now use a Lodestar guide camera and it works 100% on my C11 with the spectroscope.
I have a Baader helical focuser available on the guide port but to be honest it never really gets used. Once the target object is brought to a focus (Batihov mask etc) it's so simple to "ease" the guide camera into focus. You only have to do this once, so its a "Set and Forget" arrangement.
Being able to guide on axis and select any star in the guide FOV is great, for my spectroscopy, but if you're imaging faint fuzzies or nebulae you want to be able to possibly use the whole imaging field to find a suitable guide star...you can't do that unless the guide camera CCD chip is the same size as the imaging chip (unreasonable?) or be able to move the guide camera radially in the housing to look around the field.
Does this make sense?
All in all, it's an easy system to set up and use. The total cost of my 2" ONAG was $120.
How challenging was it maching the beam splitter to fit into the Meade cell and be precisely aligned? As a ONAG for $120 sounds a wonderful poor mans option! Do you have a more detailed how to guide to make one?
It's very simple:
1. Use on Vixen Flip mirror body.
2. Remove the mirror from the flip plate
3. Drill a 12mm hole central in the flip plate
4. Place a microscope slide (!) (or if you want to spend $$$ buy a pellicle and use that) using double sided tape on the front of the flip plate.
5. Re-assemble - job done!
I do have some images - they were used in the book "Astronomical Spectroscopy for Amateurs" to illustrate this guider. I'll see it I can upload them.
Works very well; I use them for guiding my spectroscopes with a Lodestar....
The PAYPAL option is back on the Innovations Foresight website.
The focusing of the ONAG guider port is done with a compression ring and a sliding drawtube. The design is made for easy focusing, so far user experiences and mine have shown it is simple and fast to do (see Ken feedback on the website for instance).
As Merlin66 wrote you do it once for a given set-up. However any feedback and suggestion is very welcome and I will certainly consider those options to improve the ONAG.
As far as the beam splitter is concern it is useful to make some precisions here.
They are different types of beam splitters, the “classical” one splits the incoming light beam (all wavelengths) in two parts which share the total energy. They are specified as xR/yT where x is the amount of energy reflected by the BS and y the amount of energy transmitted by it (again across all the wavelengths).
The sum of both is near 100%, often below because the BS itself may absorb some of the energy.
For instance a 50R/50T means you split the light energy budget in 50% for reflection and 50% for transmission.
In order to get as much as possible light (energy) for imaging you will need to have a small amount of light available for guiding. For instance 95T/5R, where the 5% reflection is use for the guider.
However imaging through a BS (unless it very thin, such has pellicle BS) with a tilt of 45 degrees will result in significant image distortion, mainly coma, even on axis, this is may be not a problem for astro-spectrography, but it is not acceptable for imaging.
One way to deal with that is to reverse the concept and use a 5T/95R BS, this time the reflected light (95% in this example) is used for imaging, and the 5% left for guiding. The reflection, much like a star diagonal, using a good mirror (BS in this case) does not exhibit optical aberration, the guide star could suffer from some but this is not a problem for guiding.
Yet a better approach is to use a dichroic BS (ONAG solution, patent pending), this is quite different because you do not split the light energy for every wavelength. You select the wavelength range instead for the splitting.
Here you reflect (better again for imaging) all the visible light (370nm to 750nm) toward the imager and every thing above 750nm, the NIR (near infrared), is used for guiding (see my previous reply on NIR guiding). The ONAG dichroic BS reflect more than 95% of the visible range while allowing more than 90% of the NIR to go through for guiding. From my previous comment on NIR guiding, this give you about 50% of efficiency for the guide star, while a classical BS such as 95R5T will give you only 5%.
Good dichroic BS are much more complex and expensive to make than classical BS (95R5T like) because, like good interferential filters used for imaging, they require complex multi-coating (up to 10 layers) to achieve such wavelength splitting.
Finally the ONAG as an integrated X/Y stage allowing the guider to be moved everywhere in the scope field of view to locate a guide star, this is very handy when your guider uses a small chip.
The ONAG's design took years of experience and learning curve. I made the first prototypes for myself at the time, and I eventually decided to make a product after that many friends have asked me to do so.
There is no short cut to make good quality astrophotography, you need to stick with high quality material, sound concepts, and consider all the aspects of the problem.
Although the concept seems simple enough, the devil is in the details, trust me.
This makes all the difference between average images and great ones.
However this also means more expensive material, optical parts and assembly cost.
Not to mention that the company policy is to make the best and we do not want to outsource in China either.
We could make the product half the price this way, but most likely at the expense of the quality, and the future of small business in our countries…
I also like the idea that this product is made by and for astronomers, and I do value all comments (good and bad), as well as any suggestions to make it better, everything can be improved. I see this as a way to involve the community with the design process.
well some news. I have received the first part of my order - i now have in my hot cloud infested little hands the On axis guider - and its raining - how unusual? yes this was 100 wife dollars (1 wife dollar = 10 real astro dollars)
i will post some pics later when i can get it out safely with no questions asked......
I am really interested in reading your findings on the new gear for your rig h0ughy - please do paste piccys and do a complete review! My guiding is pretty impressive in my OAG - but I hate the coma I see in the right half of the guider's CCD - I lose half my field of view...
So advice - the thing you give to your friends to see if it works!
I think I too will go down this route if you have great experience with this gear. Must start saving now!
PS
Scince buying a modified DSLR hasn't stopped raining or being cloudy for a minute. Why do astronomy purchases always cure droughts?
