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I used a 25mm 720nm IR filter and a 760nm IR filter. I see the ONAG uses 850nm so there's a difference there.
Your mention of the UV is interesting as well. So yes my test is not matching the specs of the ONAG so perhaps there's nothing to be concluded from it.
The imaging camera has these NIR and UV bands filtered out by the dichroic mirror of the ONAG - is that right?
That could also be useful for me in that I find my Trius 694 being so sensitive to IR and probably UV that I get star bloat in some images from brighter stars which per the theory here on ONAG and different types of stars output points the finger at too much NIR and UV affecting my images at times.
If I understand this thread correctly then the ideal setup would be:
1. An ONAG guider.
2. A high sensitivity and larger guide camera ideally a Sony ICX style chip which seem to be the highest QE lowest noise CCDs at the moment.
3. An AO unit before the camera.
So the advantages of the ONAG then are:
1. Better guiding.
2. More guide stars as your guide camera is able to see the same scene as your imaging camera so if you select a guide star closest to the object you are imaging you minimise the seeing differences between patches of sky.
3. Reduces IR/UV that is getting through to your imaging camera also resulting in potentially tighter stars.
4. Ability to select brighter guide stars to enable faster AO corrections thus optimising AO performance.
So an ONAG with a small ICX674 based guide camera, an AO unit like an SBIG or Starlight Express, the continuous focusing system could result in nailing down 2 of the more difficult and troublesome areas of astrophotography - the seeing / guiding as well as obtaining critical focus.
The disadvantages of an ONAG are:
1. Cost.
2. Extra weight.
3. Takes up a lot of backfocus.
4. Having your camera vertical (does this cause balance problems on heavy cameras?) possible cable tangle.
5. Does it reduce the amount of light that arrives at your imaging camera? (I though dichroic mirrors had some loss like the Sony translucent mirror technology they use in their A900 camera - that loses 10%).
By the way this is an excellent thread and we could be talking here about the next step forward in an imaging system which I know I am ready for.
Greg.
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