Vignetting issues with the Meade F6.3 Focal Reducer
I get so few imaging opportunities that up until now I've not looked at setup issues and just grabbed as many images as I could.
Recently I've noticed some significant vignetting issues that I would like to solve.
I use a 10 inch LX200 with a JMI NGFS focuser and a Meade F6.3 focal reducer. The imaging camera is a Starlight Xpress SXV-H9.
This is what I have found so far:-
Usual imaging configuration as I believe many other people use:-
LX200 then NGFS then F6.3FR then extension tube then CCD camera.
Below is a typical image and flat from this setup. Please note, changing the extension tube length varies the FL but the 'Donut' remains!
Alternate imaging configuration:-
LX200 then F6.3FR then NGFS then extension tube then CCD camera.
Below is a typical image and flat from this setup.
In my opinion the alternate configuration gives a much better result and I would say is a typical vignetted field.
I do not understand why placing the FR after the NGFS has such a severe effect. I have also tried the JMI large format adapter which made no difference. In both configuration I have tried to keep the FR to CCD distance to about 90mm.
My questions therefore are:
What causes the 'Donut' vignetting of the first