Making a solar filter for the Evo 8

[wellsi]

Hello all

I want to make a solar filter for my Evolution 8.  I have an A4 sheet of Baader Planetarium solar foil and a spare dust cap for the telescope. I bought the spare cap so I can cut a hole in and fix the solar foil onto a firm tight fitting filter cap.

My question is whether I cut a 2 inch hole towards one edge of the cap, as I’ve seen on some solar filters? This would only allow light through the single hole between the edge of the tube and the centre reflector mirror. Alternatively do I cut a large 6 inch hole that spans most of the lens covering the centre reflector?   Does anyone have any advice on the differences or advantages of either design?

Cheers,

Ian

[michael.h.f.wilkinson]

I personally have always used a full size solar filter in front of the C8 I have. I have not really seen benefits from the tiny 63mm off-axis filters I have seen

[ArmyAirForce]

As with most aspects of astronomy, aperture is key, and the larger aperture, the better the detail.

I started with an off axis filter, about 95mm diameter on my 8 inch reflector. 95mm was the largest size I could get between the side wall and secondary mirror.

 

 

It worked well, but when photographing the Sun, the off axis mask gave the effect that the Sun was itself Sun-lit from one side.

 

 

I learned to cure this by positioning the Sun not in the middle of my DSLR camera sensor, but off towards one corner where the bright spot was most even.

 

Last year, I made a new almost full aperture mask, about 190mm out of a 200mm wide sheet. I also made a full aperture mask for my Evo 80ED scope. Ilumination is far more even with the full aperture mask, and taking flats would improve things further.

 

[wellsi]

Thank you gents.

Very informative. Stephen, grateful for the photos; I see exactly what you mean about the off-centre lighting.

Much appreciated

Ian