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Whilst waiting for my 2" visual OIII filter.....


geoflewis
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Actually I was intending to image Mars last night, but the seeing was terrible, even for the Moon, so I gave up around 9:30 and closed the observatory....

What has this to do with visual OIII filters...? Well I got back from Kelling Heath on Saturday, at which star party, despite the mostly cloudy skies, I had the opportunity to discuss with some highly experienced observers which are the best filters for observing the Veil, Crescent, et al, plus some excellent views of the same through a suberb 24" dob. The consensus was that the Astronomik OIII was probably the best value currently on the market, so I ordered one on Sunday....

(NB there was also a concensus that the original Lumicon OIII was previous the filter of choice, but that the current version is not so good - I do have an original 1.25" Lumicon OIII, but only fairly narrrow (40-45 AFOV) 1.25" eyepieces, that don't play well on larger targets with my C14.

Looking out again around midnight the skies looked fairly pristine, the Moon had set and I thought, 'well let's see what I can observe with my 2" Explore Scientific UHC filter', not least because the views from Kelling suggested that a UHC filter worked better on some targets, e.g. NGC281 (Packman), than the OIII. The Packman was my first target and the ES OIII paired with my ES 68/40 gave a lovely view, pretty much filling the eyepiece. The dark region denoting the Packman mouth was easily seen with DV, but AV teased out more structure and once I allowed my eye to 'rest' rather than strain to see, this was a delightful experience, with general luminosity visible all around the main target.

Next up was the Veil complex, which I had previously viewed a few weeks ago with the same rig under astonomical twilight with disappointing results. I starting with NGC 6960 (Witch's Broom), the now much darker skies revealing much more nebulosity, with the brush end resolved into 3 forks and the twisted handle above the star 52 Cyg clearly seen. Over to NGCs 6992 & 6995 (Eastern Veil) with the latter 'Network Nebula' showing a fair amount of structure, which bodes will for the arrival of the OIII filter, if as suggested the views will be much improved over the UHC. I tried for Pickering's Triangle, but other than a couple of knots of nebulosity (perhaps NGCs 6974 & 6979) nothing definite was seen.

NGC 6888 (Crescent) was next up and again the UHC performed fairly well with the main curve seen, but no additional structure - will the OIII reveal more?

After those 3 main targets I kind of hopped around to see what was up. The Blue Snowball (NGC 7662) was very bright, but small with the 68/40 eyepiece and probably deserved higher magnification, but I was on a roll with the 2" UHC so moved on to M27 (Dumbell) which was huge in comparison and a lovely sight. I tried for ICs 59 and 63 adjacent to Gamma Cas, but did not see anything, so not being an experienced visual observer I don't know if they are visible targets and with which filters.

Now I tried to experiment with & without the UHC on a couple of big galaxies, M31 and M33. I was surprised how much was visible through the filter, but far better views were obtained without it. M31's major dust lane was visible and the entire region around the core was bright - hardly surprising given the FOV of the C14, with trips to M32 and M110 using the keypad, further endorsing just how large is this galaxy...!!

M33 was a delight with the major spiral arms easily seen, giving an oval appearance to the galaxy, which filled (plus maybe a bit more) the FOV.

Before closing the observatory at around 3:00am, I swapped over to my 4" APO to take a look at the entire Veil complex in a single FOV - a lovely sight that I anticipate will be further enhanced with the Astronomic OIII.

With the much larger FOV of the 4" APO, last up was a visit to NGC7000 (North America Nebula) which looked great, with the bright 'Cygnus Wall' / 'Mexico' region trailing away from the larger 'continental' region, followed by a brief look at IC5070 (Pelican Nebula).

Needless to say, as soon as a moonless, clear sky permits, I'll be revisiting some of these targets with the OIII filter, which BTW arrived this morning whilst I was catching up on my beauty sleep after a possibly too rare (I'm mostly an imager), but hugely enjoyable visual obersevring session, ?.

Cheers, Geof

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Your skies sound like they are lovely Geoff. Using an old style Lumicon OIII in my 14" the other night, it seems I managed to pick out more detail in, say, the Crescent and Pickering's triangle, but could not say that I had a clear split of the Witch's broom into three. It was a definite two with something elae there but only with averted imagination ;). Our skies were mag 20.8, I suspect yours were better, so hopefully that is a very positive sign for the performance you should get from the Astronomik when it arrives.

I guess you also need the 40mm eyepiece to give you a big enough exit pupil to get the maximum from the filtered views? Ever considered a 55mm Plossl in the C14? Might be fun :)

Great session and lovely report, thanks.

 

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5 minutes ago, Stu said:

Your skies sound like they are lovely Geoff. Using an old style Lumicon OIII in my 14" the other night, it seems I managed to pick out more detail in, say, the Crescent and Pickering's triangle, but could not say that I had a clear split of the Witch's broom into three. It was a definite two with something elae there but only with averted imagination ;). Our skies were mag 20.8, I suspect yours were better, so hopefully that is a very positive sign for the performance you should get from the Astronomik when it arrives.

I guess you also need the 40mm eyepiece to give you a big enough exit pupil to get the maximum from the filtered views? Ever considered a 55mm Plossl in the C14? Might be fun :)

Great session and lovely report, thanks.

 

Thanks Stu,

At 20.8 I'm not sure that my skies are any better than yours, but other than an iPhone DSM app I don't have a device for accurate measurement. I used to submit readings to the DSM project with the app until the project closed a couple of years ago and often got readings in the mid 21s. The range would be from lower 20s to upper 21s, BUT this is just an iPhone app so likely not particularly accurate. Like you the brush end of the Witch's Broom was a pretty easy 2 split, but I'm confident of seeing a third with AV. I don't have much of an eyepiece collection, most old cheapies from some years ago. Since getting my C14 I've stuggled with the narrow FOV for larger nebulae, with even M42 far too big for my old Meade 40mm (AFOV ~40 deg), so earlier this year I did a bit of research and invested in the ES 68/40. I did consider a 55mm Plossl, but opted for the larger image of the 68/40, certainly it gtave me all of M42 in the FOV making that target very enjoyable again without having to nudge the mount to see all of it. Next up was the UHC filter, but I now know that I also need the OIII. If I continue to do more visual as well as imaging then I suspect extending the range of eyepieces will become necessary....., but I need to see how I get on with what I have plus lots to learn from experienced visual observers......!! I moved to Norfolk from surburban Surrey a couple of years ago primarily for darker skies for imaging, but I've been blown away by how much more I can see aty the eyepiece, so somehow have to manage my astro budget across both AP and visual to get the best (well maybe not the best) of both ??

Cheers, Geof

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1 minute ago, geoflewis said:

Like you the brush end of the Witch's Broom was a pretty easy 2 split, but I'm confident of seeing a third with AV.

Good stuff, maybe not so different then.

20.8 was at our dark site, Surrey is where I am so as you will know around 19.1 is about as good as it gets here without heading south :(

If you do end up doing more visual with the OIII in the C14, at f10 you may find the 5.5mm exit pupil from a 55mm gives you a brighter filtered image despite not much more field of view.

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1 minute ago, Stu said:

Good stuff, maybe not so different then.

20.8 was at our dark site, Surrey is where I am so as you will know around 19.1 is about as good as it gets here without heading south :(

If you do end up doing more visual with the OIII in the C14, at f10 you may find the 5.5mm exit pupil from a 55mm gives you a brighter filtered image despite not much more field of view.

My home at Frimley was more 16-18, not sure I ever saw 19, though we did observe from Alice Holt Forest south of Farnham, which maybe was slightly darker. Certainly visual observing of anything other than bright targets was sorely compromised, with even M42, bathed as it was in orange Aldershot LP, a pale shadow of what I now see from Norfolk.

Thanks for the advice on the 55mm, definitely something to keep in mind.

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5 minutes ago, geoflewis said:

My home at Frimley was more 16-18, not sure I ever saw 19, though we did observe from Alice Holt Forest south of Farnham, which maybe was slightly darker. Certainly visual observing of anything other than bright targets was sorely compromised, with even M42, bathed as it was in orange Aldershot LP, a pale shadow of what I now see from Norfolk.

Thanks for the advice on the 55mm, definitely something to keep in mind.

19 is near Esher, I think the LED lights have improved things by about 0.5 mag. Still nothing like your Norfolk skies though, glad you are enjoying them

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