Attack of the filters - 1st light & question

I finally got the Lumicron 2" UHC and 1.25" O-III filters today and the weather holds. Tonight, the purpose was to try out a few objects and not spending my usual quality time on each object.

M57: The donut hole is easier in both filter.

NGC 7000: Finally, I could see the nebula! But I admit that it wasn't as spectacular as I thought it would be. The filter just made the nebula visual and it was still dim. Can't tell if O-III was better but it was surely darker.

NGC 6334 (Cat's Paw Nebula). I reported seeing it a few weeks ago without filter. Tonight, I couldn't see it without filter. But then I didn't try to match the star pattern as I did a few weeks ago to nail its precise spot. UHC brought it out but still very dim. Can't say that I saw it with O-III, too dim.

M8 (Lagoon): Wow, I can now see the northern portion of the nebula with ease via the UHC. The O-III seems to bring out more, but not 100% sure. Then, I notice something strange about the stars (more later).

M17 (Swan): Wow, much more it is visible through the UHC and seems more intense with the O-III.

O-III definitely is dimmer with darker sky background. I couldn't believe I've been "keeping the faith" without filter for more than a year! Lookout Rosette, Witch Head, Flame, etc. nebulae; your days are numbered. However, I can see that it's gonna to take a lot of practice as to how to use the filter.

Here's the strange thing. While looking at M8, I noticed that I couldn't bring the star to focus with the 2" UHC screwed into my 2" TV Everbrite diagonal. So I removed and place it in front of the eyepiece and viola, no problem. I tried with Antares and here's a real strange result. Out of focus cause the star to be elongated into a line on both side of focus when screwed into diagonal. When place into front of the eyepiece, all is ok. This is with the 2" UHC filter. What is wrong? Is the filter defective? With the
O-III filter screwed into my eyepiece, the stars looked fine.

Thanks,
Ron B[ee]

I think the problem you mention is the filter. Here
is possible explanation and test:

When you screw the filter into the Everbright, the
optical beam is about 15 - 20mm in diameter when it
hits the filter -- thats how much of the filter is
being used. But if you just hold the filter in
front of the eyepiece, you are only using about 1 or
2 mm of the filter (size of exit pupil). So my
guess is that the filter glass has some bad
astigmatism on scales like 15 - 20 mm on the glass.

Here's a simple test. Screw the filter into
the Everbrite, put star just outside of focus
(run focusser out) and note which direction the
image is elongated. Now unscrew the filter
exactly 1/4 turn, and repeat the test. If the
problem is the filter, the elongation
direction of the star image should rotate by
90 degrees.

Good luck.