Quote:
Originally Posted by gaston
I used 850nm has the average wavelength in NIR to make the calculation simple, assuming the filter is a high pass with a cut off wavelength at 750nm (ONAG) and the sensor (silicon based) is limited around 950nm. To get a more precise answer one should integrate the sensor spectral sensitivity (QE) and the star power spectrum too. But this is a good enough approximation.
Here is further information in NIR for guiding:
http://www.innovationsforesight.com/...-infrared-nir/
I would avoid a NIR NB filter since you will loose too much energy, you are better off with a high pass filter as described above.
P.S: As a simple rule of thumb, the reduction in back focus coming from a window inside the optical path(like the camera or an AO) is a third of the its thickness, roughly. This means a 3mm thick window would decrease the back focus (relative to the mechanical one) by about 1mm. |
In my opinion, the image comparison on your site is misleading. While it shows a marked improvement, the first image is guided horribly, stars are not even round in the first place. Secondly, is the only difference between the two setups the NIR guiding? Who is to say, this is not an example of how well SBIGS AO works since that is mentioned in the text.