filter advice

[Mak the Night]

Yes there are confusing reports about filter use, I have tried all my EP's with them from 32mm-3.5mm and can say that the exit pupil issue is real and is about the best way to get things working together for good OIII views. Sorry about your scope FL, I wasn't exactly sure which one you had.

I think there might be something to the "volume of light" (aperture) deal but the main thing is the exit pupil IMHO. You can always try one with the Skymax to see how it works. Reflectors are excellent for filter use, I think it is a myth that refractors are assumed better in this regard.

OK, thanks that's interesting. Although unless I use an EP with a greater f/l than 32mm I'm not sure how I'll get an exit pupil above 2.5mm with the Mak. A 40mm would still only give me a 3.1mm exit pupil.

[YKSE]

It was this bit in the Astronomik blurb that put me off.

'Since enough light must be available to make use of the OIII filter it is best to use this filter with apertures of more than 6" (150mm). Smaller instruments do not gather enough light for meaningful and satisfying astronomical work.' ~ op cit 

That's one of the reason that David Knisely is not very fond Astromik filters if you follow his comments on CN.   and I respectful disagree with that statement too.

a 40mm plossl in your 130m gets close to 5.8mm exit pupil, it should work much better with an OIII than in your mak.

Here's something to read about exit pupil.

[Mak the Night]

That's one of the reason that David Knisely is not very fond Astromik filters if you follow his comments on CN.   and I respectful disagree with that statement too.

a 40mm plossl in your 130m gets close to 5.8mm exit pupil, it should work much better with an OIII than in your mak.

Here's something to read about exit pupil.

OK thanks. I suppose I need a 40mm Plossl now lol! The Explorer is difficult for me to set up and even more so to actually operate, which is why I use the Mak so much. The NexStar Evolution I'm getting soon should be much easier, especially with a GOTO which will enable me to spend more time actually observing than wasting valuable time star hopping. Whoever invented the GOTO deserves the Nobel Prize IMO lol. David Knisely told me that the early Astronomik filters did not have the bandwidth curve like the Lumicon but he believed that if they are getting the curves that they are now claiming in the graphs on their site they may be as effective as the Lumicon inter alia. I know how the brightness of an object diminishes with magnification, I believe the inverse square law comes into play. As I'm an arts graduate advanced maths is beyond me though and I have to take my shoes and socks off to count on my toes. ROTFLMAO

[Dave In Vermont]

Here's another article on exit-pupil size. This one being from the venerable Sky & Telescope Magazine from the US:

http://www.skyandtelescope.com/astronomy-equipment/a-pupil-primer/

Cut & Paste.....

Dave