Do you Really need a 2" Filter?

Considering the size of the cone of light coming into my 12" dob, is the full diameter of a 2" filter necessary? One would think that an adapter to accept a 1.25" filter would be all that is required. There are probably scenarios where this wouldn't work, but for my EPs, I wonder? Consider a 40mm Paragon with an F4.9 12" dob. Do I really need all that much filter?

By the way, I just got a 2" OIII filter.

Judson Mitchell said:

Considering the size of the cone of light coming into my 12" dob, is the full diameter of a 2" filter necessary? One would think that an adapter to accept a 1.25" filter would be all that is required. There are probably scenarios where this wouldn't work, but for my EPs, I wonder? Consider a 40mm Paragon with an F4.9 12" dob. Do I really need all that much filter?

By the way, I just got a 2" OIII filter.

Judson:

A good question. One problem with 2 inch filters is that they don't work well with 1.25 inch eyepieces...

Here's a solution to using 1.25 inch filters with 2 inch eyepieces...

Instead of threading em on the filter housings, just place them over the eyelens on the out side. With care, there is no damage and since most 2 inch eyepieces have lots of eye relief, it does work...

Jon

If you use a Siebert Power Mag Wheel, the answer is no as only the central portion of the cone of light is used and it has a 1.25" nosepiece. I use my 2" filters in the JMI focuser extension tube, Click-Lock nosepiece, eyepiece turret nosepiece, or 2" diagonal nosepiece, etc. I rarely screw them onto an EP.

Some filters should not be turned around and used in the output of the EP, such as nebular filters with front reflection coatings.

40mm Paragon yields too large an exit pupil with an f/4.9 Dob (without using a 2" Barlow). 27mm Pan would give you about all the exit pupil you could use.

I believe the Hyperion/Stratus EP's have 1.25" filter threads as they are Barlowed internally.