Off axis solar filter

I have seen off axis filters advertised and am curious about the pros and cons. I have a home made 10 inch dob and finding a filter large enough to fit the 12.25 inch tube will be cost prohibative for me, however I could construct a housing to fit the tube and incorporate a smaller filter off axis at an affordable price.

Is this doable and would the performance be acceptable?

What size off axis filter would be needed for a 10 inch mirror? I have in my head that a 4inch diameter filter would be adequate.......

Thanks.

Leslie

4" should be just fine. Another thing you can do is to measure the distance between the edge of the secondary out to the inside edge of the tube. This number will be the biggest you can go if you want no obstruction. The Baader Solar Film works great for these type of applications.


Robert W.

I would suggest getting some of the Baader astrosolar film and making the filter yourself. It isn't very expensive so you could even experiment with a full aperture version. Under most conditions I would think that the off axis 4" or so setup would work better. The main thing with the Baader film is that you don't stretch it when making the filter, you leave it loose (just secure to the cell well so it doesn't come off !) I have found that the image with the Baader film is superior to any glass filter I have looked through.

Joplin

This goes without saying, but I'm going to say it anyway. Whatever you do, MAKE SURE THAT YOU HAVE A FOOLPROOF METHOD TO KEEP THE FILTER ON THE END OF THE TUBE. For obvious reasons, it must not be allowed to fall off, blow off, get knocked off, be pried off, etc. etc. etc. And remember that it is darn near impossible to make something foolproof, because fools are too ingenious!

Doug