something interesting for double star observers

[Perseus_m45]

I came across this article tonight . Maybe worth really looking into.. 

http://www.cityastronomy.com/58-filter.htm

what do you guys think?

                                         mike h

[cotterless45]

Interesting.

For shorter achros, Neil English is keen on a fringe killer and an 82a light blue filter. Mind you this for f5. Having just picked up a similar scope , I have noticed very little ca, not enough to worry about .

http://neilenglish.net/gallus-beastie-i-the-skywatcher-shorttube-80-achromat/

After reading a few reviews, I use a Baader Semi Apo 2" filter in the f8 Cr6. This gives more neutral views and is better for picking out companions next to the glare of brightness and splitting tight companions. Certainly any tester stars have come up ok.

Maybe this is a matter of personal choice for your eyesight. I don't have much to compare locally as folk tend to wander off if you're looking at double stars !

Certainly there's very little ca in the Vixen 90 and 102, being up at f10.

One thing that I wouldn't recommend is spending massive amounts of money on an apo for observing. With the filter that works you'll get the same results.

I'd thoroughly recommend the semi apo in the diagonal,

Nick.

[chiltonstar]

I've used a variety of filters to remove the violet and red fringes round brighter stars with my long-focus 4" achromat (it's f13, not the problem is pretty small). I didn't see any difference between a Wratten green filter and a borrowed Baader fringe-killer to be honest. With my ED80 (f7.5), there is very little chromatic aberration, even with a bright star such as Vega.

Chris

[Perseus_m45]

so Chris you have already tried a Wratten green? How long ago ?

[chiltonstar]

so Chris you have already tried a Wratten green? How long ago ?

When I first acquired my 4" achro objective (Vixen) and made a frac tube and mount for it (early 1980s) I bought a number of coloured filters, as was the norm at the time for planetary observing. The Wratten green was part of the basic set.

Chris

[Perseus_m45]

I'm doing some changing around in the shed but after that i'm going to try some filters and maybe write up a little report .

                                                                                                                                                   mike h

[Marki]

Thanks for the link, Mike. Be interested in reading your report once you've done your filter testing. I remembered I have a Baader neodymium (moon and skyglow) filter knocking around in my "astro odds and ends" box (shows how long since I used it) - I wonder if something like that be useful for those big magnitude contrast doubles.

[Perseus_m45]

Thanks for the link, Mike. Be interested in reading your report once you've done your filter testing. I remembered I have a Baader neodymium (moon and skyglow) filter knocking around in my "astro odds and ends" box (shows how long since I used it) - I wonder if something like that be useful for those big magnitude contrast doubles.

well Mark the only way we can tell is giving it a go..I have to see what filters I have now!!!

                                                                                                                              mike h

[chiltonstar]

well Mark the only way we can tell is giving it a go..I have to see what filters I have now!!!

                                                                                                                              mike h

Worth adding perhaps that "fringe-killer" style filters don't give too much of a colour issue, whereas a "simple" colour filter like the Wratten green may sharpen the image by removing violet and cyan fringes, but will make everything green of course. Alright for doubles certainly or the Moon, but not perfect for planets.

Chris