The council has thoughtfully provided a 10 gigawatt fluoro streetlight outside my observing site. Attached are the effects of various filters. I placed a Baader diffraction grating in front of a 70 mm zoom lens at F/10 on a Canon EOS 20D, and took 1/10 sec shots.
The top panel is with no filter. The zero order image is on the left as a reference, and the 1st order blazed image is on the right. You can see that the lamp doesn't helpfully produce a nice sodium D or mercury line, but has an almost continuous spectrum.
A Baader Neodymium filter obligingly removes the entirety of the yellow image, but leaves the other colours more or less unchanged. When looking at say Eta Carinae nebula the filter has no subjectively detectable effect good or bad. My guess is that if I lived under a sodium lamp, it would be of great benefit, but is of no use to me.
An Astronomik CLS filter severely attenated everything, but blocked orange, yellow, and violet completely. The blue of H-beta, the cyan of O-III, and the red of H-alpha are therefore selectively enhanced. Greens are suppressed but not eliminated. Subjectively, I find it increases the contrast of Eta Carinae by an appreciable and worthwhile but not miraculous amount. In my 16" Dob, the Homonculus nebula disappears.
Finally, an Astronomic UHC filter savagely cut everything except the colours associated with H-beta, O-III, H-alpha, and some nearby colours, especially nearby reds were allowed through. Subjectively, I find this filter magnificent for Eta Carinae and Lagoon from a light polluted site. The Homonculus is again utterly gone.
In conclusion, a UHC filter seems the best of the three in the presence of rather wide-band light pollution. Thank you Penrith Council.
Changing the topic very slightly, from a light polluted site where it is so bright you can read, I find an O-III filter to be far superior to a UHC on most planetaries (eg Blue Planetary, Dumbbell, Scutum Planetary), whereas the UHC is superior on general emission nebulae like Lagoon and Eta Carinae nebula. At a wild guess, I would say that this is because H-beta, CN, and perhaps H-alpha are all getting through the UHC and helping. The only exception is that the Helix is very slightly easier with the UHC. My wild guess is that this is because it is so faint that, unable to light adapt under a 6 gigawatt street lamp, I just run out of photons with the O-III.
Astronomik UHC passes more Ha than Lumicon Ha .
Lumicon DSF looks superior to both if you want Ha too.
Want to cut Hg emission bands at 405, 436, 546 and 579 nm
and airglow at 558 nm ,
and Na emission bands at 570, 583 ,600 and 617 nm. Lumicon Deep Sky Filter fits the bill and still passes broad bands.
If you look at your narrow band filters they are effectively like a mirror to all but the narrow pass band intended to pass through it. This means that ambient light gets reflected straight back to your eyeball. Covering your head with a jacket or cloth can help enormously here.
I've seen when using my astronomik UHC-E that if I use it without wearing a hooded jumper or having something covering the rest of the eyepiece, any stray light that enters the the eyepiece can cause really garish reflections within the eyepiece due to the reflectivity of the filter. However with a hooded jumper covering the EP from stray light it performs wonderfully.
In addition, using the UCH with a red filter provides some really stunning views of nebula from light polluted areas.
The council has thoughtfully provided a 10 gigawatt fluoro streetlight outside my observing site.
Mike BJ
Not very considerate of them, interesting results with the various filters..... of course the best filtration is lead, preferably from the barrel of a high powered rifle will reduce the amount of emmitted light every time.
on the topic has anyone read/seen a baader uhc-s in action, i was thinking of purchasing one
thanks daniel
I guess i am asking is it in the same league as the astronomics or lumicon, or a step below. the bintel guys suggested the orion ultrablock was a class below
I have both. The Baader is mechanically flimsy - the soft (aluminium ??) thread is easily damaged. The Astronomik is far superior mechanically. I also personally greatly prefer the Astronomik visually. Others may see it differently.
I have both. The Baader is mechanically flimsy - the soft (aluminium ??) thread is easily damaged. The Astronomik is far superior mechanically. I also personally greatly prefer the Astronomik visually. Others may see it differently.
Didn't want this to be about brand vs brand, more about some pretty coloured pictures showing intuitively how street lights can have a fairly wide spectrum thus defeating a simple "light pollution" filter, whereas a nebula (UHC) filter does a lot more.
But the main difference I see between the Baader UHC-S and Astronomik UHC is that the former lets through more nonspecific blue. Thus the Astronomik view is slightly darker, but more contrasty.
Next time it is clear again, I must try the Baader vs the Astronomik on the Trifid nebula. It is just conceivable that the otherwise annoying "blue leak" might let one see more of the reflection nebula, without losing too much contrast in the emission nebula. (An O-III filter, as expected, completely blocks the reflection nebula part).
sculptor, when you prefer the astronom visually does it let more lightthru?
thanks dan
I have three astronomik filters and have had two baader filters. As far as build is concerned the Astronomic filters leave the Baader's in the dust. Visually I am happy with my UHC filter; though I dont do much visual these days.
EDIT ** Sorry to continue the brand comparison. I think you have done a great test by actually displaying the spectrum through each filter. A top and interesting piece of work.
What do people think of the Orion Ultrablock? Price-wise it's a good bit cheaper than even the UHC-E Astronomik filter, at least in 2" form, and I have to wonder, with my cheap eyepieces and cheap telescope, whether the difference would be noticeable. I could afford the 1.25" Astronomik UHC-E, but I've been DSO observing mostly with my 2" 26mm GSO eyepiece, and I don't think I'll be able to afford a quality replacement soon.
pneuman I thought the same, was advised by bintel it blocks a bit much and the uhc filters are better. have just purchased a baader uhc-s, which blocks slightly less than a ordinary uhc,
bought from HK for $100 http://www.tan14.com/gears.htm
pneuman I thought the same, was advised by bintel it blocks a bit much and the uhc filters are better. have just purchased a baader uhc-s, which blocks slightly less than a ordinary uhc,
bought from HK for $100 http://www.tan14.com/gears.htm
They've some good stuff.
I like that CD1 + MT1 portable tracker - would be great as a grab and go kit for short work trips and overseas trips (when you don't to and wont want to tote about a full GEM & tripod and all the paraphenia, when you're travelling light).
At moment I have a EQ1-mini with a basic RA drive for that and it's OK for short exposures with a wide lens, but a pain polar aligning and leveling.
will reduce the amount of emmitted light every time.
