1 reply to this topic

[CLJLF]

I have recently bought a 6" 1200mm f/8 refractor. I know that it is relatively slow for NV use, but it was Â£70. 

 

 

I'm looking to adapt it for my P8079HP, prime focus. The tube is a Gen 1 cascade that has decent performance, but is massive.

 

I have taken off the focuser of the refractor and saw that there's a baffle around 13 cm into the tube. 

 

 

If I remove the focuser, make a custom one with the NV tube, and put a cheap 200mm FL doublet right up against the baffle (Or remove the baffle and put it a bit further in), I believe that I would be able to reduce the focal length (Thus increasing the speed) and decrease the bulkiness of the NV tube by telescoping it into the telescope tube (Wow say that 5 times fast). Something like the diagram below?

 

 

Here is a ray optics simulation (That assumes everything is a thin lens), IDK anything about the maths but it may help illustrate what I wish to do. I found a equation online (That also assumes everything is a thin lens) that the effective focal length is 1/f=1/f1+1/f2-d/f1(f2), which gives me the effective focal length of 685mm, or an F stop of 4.5.

 

 

Will this approach also cause significant vingetting or abberations? I am using a narrowband Ha filter so CA is not an issue, and the sensor is a 25mm diameter circle with around a 17-18 diameter usable area approx.

 

Edited by CLJLF, 20 December 2024 - 04:53 PM.

[slavicek]

I do not see any issue with it. Basically you are adding focal reducer to your scope. People do it all the time for NV (including myself). The only issue with adding focal reducer is reduced light path = one needs more "in travel" in the focuser.

GL.