Tracking down small planetary nebulae can be a bit of a challenge when they may look just like another star in the starfield, at first glance.
Filter "guru" David Knisely gave me a idea when I read:- "One neat trick for finding tiny planetary nebulae is to "blink" the objects by holding the filter between the eyepiece and the eye. The stars in the field will dim somewhat, but the planetary nebula will remain undimmed, thus standing out from the background stars."
I have a good 2" OIII filter, but that can stay on the filter slide. I bought a cheap GSO 1.25" OIII filter - Andrews had the best price. I searched Bunnings until I found a plastic scrapping spatula - in the paint section, I think. I cut a hole in the centre of the spatula into which I could screw the filter. It was a white spatula, so I sprayed front and rear with matt black paint, then screwed in the filter. I now had a tool with a good sized handle which allowed me to slip the 1.25" filter between my eye and the eyepiece. It will also stand in my heated eyepiece box between uses. The filter surface can be generally kept from coming into contact with anything - apart from my eyelashes? It is easily stored in its own plastic bag in my eyepiece case.
I tried it the other night. I think I was working with a 19mm Panoptic eyepiece. Simply marvellous! I toured planetary nebulae in a sky that had poor transparency (high cloud) and a Quarter Moon! In nearly all cases, blinking the filter allowed the planetary nebula to be readily contrasted with the rest of the field of view. It's a winner!
Possible problems:- If the eye relief of the eyepiece is very small, it may prove difficult to insert the filter between eye and eyepiece and still see enough of the field of view. If the object is very faint, having to pull your eye away from the eyepiece cup may allow too much stray light to enter and you may lose sight of the view - hence I painted the spatula matt black to help. It is likely that the focus changes somewhat with the introduced filter, which may be a problem. I had no problems with these three on my test run. I think the focus change isn't much for this filter, but I will have some eyepieces where the eye relief might be a challenge, and I will struggle with very faint objects unless in very dark surroundings.
Yep, it's a great trick Eric, used it myself plenty of times.
It also works with a 2" filter, holding it in front of the finder, to find the Helix.
Gary
Nice one Erick.
Another neat solution from you! I had been thinking of something similar and perhaps buying a Radian to get more eye relief as a specilist PN eyepiece as I find I always have to tak my eye away to move the filter in, so it isn't a tru blink.
Yep, it's a great trick Eric, used it myself plenty of times.
It also works with a 2" filter, holding it in front of the finder, to find the Helix.
Gary
I have done it with eyepiece only, but I always worried handling filters - especially with gloves. They are certain to head for the dirt! So I have the main 2" filters permanently in a slide and this 1.25" OIII in a holder.
Nice one Erick.
Another neat solution from you! I had been thinking of something similar and perhaps buying a Radian to get more eye relief as a specilist PN eyepiece as I find I always have to tak my eye away to move the filter in, so it isn't a tru blink.
As you'll see from the photo, the filter in tool is a lot narrower than filter held in fingers. As I get the hang of it, I expect I'll only have to pull my eye back a few mm from the eyepiece cup.
