View Single Post
  #25  
Old 15-02-2015, 12:15 PM
gaston (Gaston)
Registered User

gaston is offline
 
Join Date: Oct 2011
Location: Glenmoore, PA, USA
Posts: 46
Hi Greg,

I used 850nm for my calculation because it is the average value on the NIR range accessible for most guiding cameras.
This wavelength range starts around 750nm (the ONAG's cut off wavelength) and ends around 950nm, the silicon sensor upper wavelength limit.
For the same reason 550nm is usually used as the average wavelength for the visible range.
This is just a first, but good, order approximation, since for more precise values we would have to integrate (weighted average) the seeing effect with the sensor quantum efficiency versus wavelengths.
By definition the UV range starts below 400nm , down to 10nm. The lower end of most silicon sensors (CCD/CMOS) is around 300nm, which means they can see some UV light.

The ONAG reflects typcially 98% of the light from 350nm to 750nm, above 750nm the relection is less than few percents, below 350nm it is not specified. However color one shot cameras, or LRGB filters with monochrome cameras, usuly cut most of the UV, below 370nm, and NIR, above 650nm. Although the ONAG will remove most of the light energy above 750nm, you may still want o consider removing NIR above 650nm or so, as well as UV below 400nm, for the imaging camera using filters, yet as I pointed out above most cameras or filter sets will do just that.
Using wavelength above 750nm only for guiding using the ONAG will provide smoother tracking, with a marginal lost in SNR.
Having a wide FOV for guiding at, and near, the optical axis associated with a large guider chip provides a unique opportunity for using multi-star (constellation) guiding, for superior performances, which is now available in Maxim DL 6 for instance, just a beginning though.

Although the ONAG option with a large guiding camera seems expensive at first, and I do understand that, it should be compared with other set-ups, such as a good OAG and a rotator alternative (+ a guider). Good quality mechanics and optics are never cheap, especially in relatively small quantity.
Beside the ONAG offers a very large FOV, access to multi-star guiding (with a large chip guider) using one scope, and the only unique real time auto-focus solution in the market (Sharplock), which solves yet another challenge.

Having the main camera vertical is obviously unusual. Yet it may offer a more compact mechanical solution limiting the distance from the scope visual back and the imaging camera, which impacts the gravity center and reduce torque coming for lever arm.
I never experience any balance problem related to this configuration.
Reply With Quote