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Onag
Just few comments.
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.
Clear skies!
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