Seeing Faint From Urban Skies

Seeing Faint From Urban Skies

Postby kdrake » Sat Dec 30, 2017 10:18 pm

The use of nebular filters for visual use was started in the early '80s and around 1986 they became available to the amateur community. I got my first look through some of them at the 1986 Texas Star Party when Jack Marling of Lumicon approached me on the upper observing field. He introduced himself and asked if I wanted to try to observe some planetary nebulae that may have only been seen by a handful of people. He was carrying some marked up charts from the Atlas Stellarum. He proceeded to hunt down, using my 10" f/5.6 Dob a PN in the far southern sky - Henize 2-37. There was simply nothing visible in the FOV other than a couple of 10th magnitude and a sprinkling of much fainter stars. We were looking very low in the south, on our knees. What he then did was screw a filter into the eyepiece. The field became dramatically darker and some of the stars had taken on some color. In the field was a small round glow, ~30" in size where nothing was b4. We continued to observe Abell 34, Kohoutek 1-22, & Abell 33. I made drawings of several of these on May 8 using my own newly purchased 2" filter in my 32mm widefield eyepiece.

An interesting note on K1-22 is that Tokou Nakamoto is credited with the 1st visual sighting on 2/1/87 using a 14" f/6 reflector 4 miles east of Saddleback Butte State Park, California. My drawing was made on 5/8/86 at 5:10am from Prude Ranch. Jack Marling and his OIII filter was the only reason I saw this obscure planetary nebula.
Now onto why I'm writing this post. The use of narrow band filters can truly enhance your view of some objects even from partially light polluted zones. I've included a drawing I made of the eastern portion of the Veil Nebula. Three drawings are comparing the detail visible using no filter, a UHC filter & an OIII filter. My suggestion is that if you have not added these tools to your visual arsenal, do so soon.

Image

Kenneth (drako) Drake
Willis, Texas
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Re: Seeing Faint From Urban Skies

Postby lauren-herrington » Tue Feb 06, 2018 2:34 pm

Great story and excellent sketches, Drako! (MD-MotOC,CotDC)

I have three nebula filters; a Meade #908 narrowband, a Meade #908B broadband, and a Celestron #94126A LPR. I haven't experienced the kind of dramatic differences portrayed in your sketch. I remember observing the Veil at the dark site near the zenith, and the filters helped increase the contrast with the background very slightly, but it didn't really seem to extend any farther with the filter than without. "Blinking" with a filter did help Steve to see it when he hadn't been able to before, though. And I recall another time when using my narrowband filter actually made the view of NGC 2438 in M46 significantly worse. (Then when I went to take the filter off, I discovered that the rather badly-cut threads had gotten stuck, and in trying to get it un-stuck I partially unscrewed the barrel of my 13mm Ethos... cue panic.)

But, I should also say that I think it's my filters that are the problem, and not filters in general: I got mine used for $10 apiece. "You get what you pay for"!

I did encounter one case recently where using my filters helped the view somewhat, while observing the Little Dumbbell in my backyard. I hope you'll forgive my long, rambling log. I narrated it into a voice recorder as I observed, and tried to record many details about the performance of the various filters, since I'm still trying to figure out myself what kind of use I can make out of them.



Telescope: Zhumell Z12 12" Dob
Eyepieces: 13mm Ethos (115x), 6mm Plössl (250x)
Seeing: Good
Transparency: Excellent
Location: Spring, TX (Bortle 9, typical NELM 5.2-5.5 -- I've got some more data for the NELM thread, just haven't gotten time to put it together yet!)
Transcript: "Observed the Little Dumbbell nebula with the Ethos 13mm and the 6mm Plössl. The best view is to be had in the 6mm Plössl, though the image is more comfortable in the 13mm, somewhat unsurprisingly. The crampedness and difficulty of tracking with the 6mm is outweighed by the better view.

In the 13mm it appears as a very faint, elongated, diffuse path of haze, elongated from about, say, 8:30 to 2:30 in the eyepiece field of view.

In the 6mm, it's visible as having some detail. There seems to be a brighter knot on the righthand side, and then a slightly brighter part on the lefthand side, so it has a bit of a double-lobed appearance.

Back with the Ethos 13mm, the use of LPR, broadband nebula, and narrowband nebula filters all improved the view. I blinked the filters, and the LPR and broadband filters gave a little bit better view than the narrowband (the narrowband had strong reflections that were distracting when blinking). That showed the bilobed nature in the Ethos 13mm, similar to the view in the 6mm, however it was brighter-or, well, the contrast was better.

Adding an LPR filter to the 6mm also improves the view. The nebula appears with much better contrast, now more obviously standing out from the background rather than being "very faint, you need to be looking carefully to pick it up"... it could [now] be picked up in a sweep. The bilobed appearance continues, one lobe, the brightest and largest, in the upper right, a smaller, fainter lobe in the lower left. It can also have an appearance somewhat like... well, I guess, a dumbbell, but with extensions from the tips, arcing inward and down. They don't meet, they only arc out a bit. It's sorta like- imagine a cartoon image of a dumbbell being thrown through the air. The cartoonist would probably draw little aerodynamic lines coming off the edge of it to imply motion. It's like that. Switching the LPR filter out for a broadband nebula filter, the background become a bit brighter, but the view seems both blurrier and more detailed at the same time. I suppose it's because of the brighter background: the edges of the nebula are less well defined, but in the center, there's now the visual impression of mottling. Nothing that I can pin down, nothing strong- just there. Swapping the broadband filter out for a narrowband nebula filter definitely does not help the view. There now seems to be imperfections over the field, as though some parts are filtered more than others; dark and light blotches. The nebula itself did not gain any detail and seems to have maybe lost a bit of contrast..... well, ok, I think I might need to revise my statement of "did not seem to gain any detail". The lower tip of the barbell now seems to have a bit of that extension that was glimpsed earlier, curling around towards the right. That extension, or at least in the area of that extension, there's now some nebulosity, so perhaps it did help. Aesthetically the view is worse, but detail-wise it might be better.

I should mention, it does help to cup my hands over the eyepiece so that extraneous light is shielded, definitely an improvement. It does not help to put one filter on the eyepiece and blink with another. I tried the LPR and broadband together, and the broadband and narrowband together."



Clear Skies!
Lauren Herrington
Youth Director

---

New astronomer? Have a question? Feel free to contact me! I'd love to help.

Zhumell 12" Dobsonian
Orion XT8 8" Dobsonian
Various ATM projects at differing stages of functionality (completion? what's that?)
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Re: Seeing Faint From Urban Skies

Postby kdrake » Tue Feb 20, 2018 12:32 am

Nice bunch of notes. Especially on the filter comparison. The one thing I find confusing is the directions in the description - towards the right, upper right, inward and down. I know those words mean a lot to you and any drawing you have made but what works for those trying to look at it and orient ourselves need east, west and so on. Also another thing that helps is size and distance estimates. I know that all of that does not really matter for a personal visual impression but others trying to reference your notes can benefit. And on that note, did you see the eclipse visual impression by Cindy Krach in the December Reflector! Wow!
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