Hello,
Following in C.Buil's footsteps, these cloudy days I've rehearsed the properties of an old second hand Nikon 135mm. F2.8 objective in my Piera observatory NOU_T echelle.
The Nikon 135mm. F2.8 has 5 optical elements so is simple and it weighs 435grams, only 35grams more than the Nikon 85mm. F1.8 that I used actually.
At the moment the tests and theoretical results are satisfactory, and the RELCO light map
is focused much more better than the Nikon 85mm. one that needs a balanced focus Orders commitment.
Nikon 135mm. F2.8 pros and cons,
More and average order resolution R=10500 in contrast to R = 8500.
Very weight Fits files, 101925KB with the ASI2600MM.
More longer integration times due a more long focal point, but I can't precise
why because it has better focusing.
On the other hand, theoretically Nikkor 85mm. F1.8 is faster than the 135mm. F2.8 and with sufficient resolution for the analysts work studies, so I don't know if it is worth keeping this last one that needs to spend more time and gets minus stellar magnitude.
You can see this test daylight graphic made on the desk and its R values and download some integration Fits from,
https://drive.google.com/file/d/1ReQTHG ... sp=sharingCheers, J.Guarro.