Quote:
Originally Posted by Eden
G'day Peter,
Thanks a lot for your feedback. Your comments in another thread were what prompted me to get the ONAG in the first place and I'm very glad that I did. 
I pondered the idea of a motorized stage myself, but I can think of several reasons why it could potentially cause more problems than it would solve. Your ICX825-based camera is an excellent solution, since it offers basically twice the effective resolution than the cameras I mentioned and has a good pixel size and high sensitivity in the NIR. What is the readout speed like for a full frame? For what it offers I think it's quite reasonably priced but wished that ATIK had used the smaller-form factor for it.
I don't do unattended pier flips at this stage but I can see why it could be a problem on some targets, especially at longer focal lengths. I can't however see how it would be any less of a problem on -- for example -- a single-head OAG setup. A dual-head OAG could get the same star after a pier flip, but for the price it goes for plus the cost of two guiding cameras, an ONAG with larger guiding sensor and if necessary, a focal reducer, would be better IMHO. |
I have had a ONAG XT in combination with an stl11k and AOL for some time, in fact I think I got mine from the first bunch.
I only do remote automated imaging, so my comments will be based on that slant.
A motorised stage I think is not great value. I think the better option is to either use a larger format sensor (think ST10 for crazy sensitivity) or a focal reducer for the guide port.
I use a Sbig remote guide head for guiding with a cheap Bintel .5x 1.25 inch focal reducer and a custom adapter to fit the 1.25 filter thread to the t-thread. That not only increases Signal to noise but also increases the field of view. Innovations foresight has an IR optimised adjustable focal reducer but I have not used it.
I love the ONAG and it works well for me, (I have used both an moag and a mmoag in the past) but the HUGE advantage of the ONAG over conventional OAG is the ability to use a larger format camera as a guider. Most OAG's will only illuminate some thing like a 1/3 format sensor. With the onag you can use any camera that uses a t/thread or 1.25 nosepiece and know that the fov will be completely illuminated. This makes guide star selections less of a hassle, especially when AO is used as you need a brighter star for faster guiding. Thats without the benefits of the IR characteristics.
I have never had an issue getting guide star even at f11.