UHC versus O-III filter

[Astro_Baby]

Some people asked me awahile back how the O-III filter was working out. At the the time the weather and other pressing priorities hadn't given me much chance to use the filter and give any opnion.

Last night, wonder of wonders the sky was clear, good transparance and stable atmospherics, which, combined with a decent dark sky site allowed me to get the O-III in use.

In the interim I have acquired firts shout on a UHC filter which was also taken with me.

Bothe filters are Sky-Watcher supplied ones.

Last night I tried the two filters out against two targets. The Ring and the Dumbbell Nebula. All tests with with a Sky-Watcher Ultrawide 26mm EP and a Baader Hyperion 13mm EP fitted to a Sky-Watcher 200P F5 reflector.

Heres my verdict........

M57 - The Ring Nebula

With no filter in at all the ring can be a bit tough to locate. Nestled in among other bright stars I found without GoTo it was a tough target. Once found the ring shows as a faint greyish smoke ring.

With the O-III filter the ring shows up better against the background sky. Other stars are muted down and the sky goes jet black. M57 shows throough the O-III a greenish a hue. Prolonged observation hinted at some red coloring in the outer section of the ring but I wouldnt swear that this wasnt wishful thinking or seeing things. Would the ring be easier to locate ? My verdict would be no. It will show better once your there but I cant say it would be easier to find. Focus suffers with the O-III and its hard to get accurate focus I found as the few stars that shine through the filter are so dulled down. O-III filters generally work better (I am told) in larger scopes and perhaps 8" is pushing the limits.

The UHC filter did better. less color was evident in the ring with ring retaining a greyish color, perhaps a small tinge of green. The background sky was jet black again but surrounding stars were less affected. This made focusing a bit easier. I doubt finding the ring would be easier with the UHC and the view was very similar I felt in overall aethetics to the non filtered view.

Verdict - the O-III to produced some colors which hinted at photographic images but at the cost of clarity. Rather like an out of focus color picture versuse a sharper black and white one.

M27 - The Dumbbell Nebula

With no filter in use the Dumbbell resembles a grey puff of smoke. Larger to the eye than M57 the Dumbell appears as a rather diffuse cotton wool ball.

With the UHC filter in place the filaments within the nebula were more readily observable and the nebula exhibited more of its dumbbell shape (persoanlly I always think it looks more like an hour glass) and exhibited a pronounced greenish hue tending to yellow in some places after a while observing. Contract gain was very high with the bacground turned jet black and the few stars in the background dulled down.

The O-III filter produced a darker more contrasted image but the contrast was so high I personally found that there was too much loss of detail for the O-III to be acceptable for this object.

A larger scope may have fared better.

Verdict - Against a more diffuse target the UHC appeared to perform better than the O-III filter. The O-III produced such a high contrast image that it was rather like viewing a televison with the color and contrast turned to maximum.

Overall verdict - I personally found on balance the UHC to be the better choice between the filters. My view may be slanted because of the relatively small size of the scope and the limited targets.

I have a sneaking suspicion that against a target like the Orion Nebula the O-III would provide better views owing to its more aggressive cut-off and the brighter general background which may swamp the UHC filter.

As ever with astronomy equipment its horses for courses. I'll keep both filters personally but if I had to choose one it would be the UHC.

[ashenlight]

Thank you for doing this AB - really great reading. I'll be getting my hands on some filters soon, it'll be interesting to see how I get on with my 5" - I'm not holding my breath but it'll be interesting at the very least.

[Andrew*]

Hi AB,

Great review. OIIIs really aren't for everybody as they are very harsh. In some cases, though, the extra contrast of the OIII can really go the extra mile.

The UHC filter is very versatile and comfortable to use.

Thanks for that!

Andrew

[Merlin66]

What you effectively seeing is the limited light at the various wavelengths.

There are strong OIII and some SII (in the red) so the UHT would show both whereas the OIII only shows the green wavelengths.

[mike-h]

Hi, I have the SW UHC filter too (I bought it a couple of months ago).

I was disappointed to find that I prefered the non-filtered view on M57 when under a dark sky in Wales.

However, I used it last night in my light polluted garden for the 1st time and it really made both M57 and M27 appear brighter and easier to see.

Be interesting to try it on M42 in Winter

When choosing between the UHC and OIII I liked the fact that the UHC doesnt dull the surrounding stars too much.

Mike H

p.s. so far I do think that you forfeit a bit of sharpness for the extra contrast though.

[part timer]

I use both of these on my 6" newt and at first I too found the the 0III a bit much. BUT I have since found that there are quite a few objects where it really shows detail that the UHC just can't. The added contrast really does make a difference.

That said if only one filter is possible then I agree that the UHC is probably the best bet.

[Beulah]

Good review, Astrobaby, thank you for taking the time to write it.

I would definetely agree with your findings, especially as I have the same apeture reflector, albeit on a Dobsonian mount.

You have tipped the balance for me in favour of getting a UHC filter as part of the observing arsenal.....

I had more luck with the Dumbbell Nebula - the shape became more defined.

For a small/medium scope, the 0III filter seems to fare incredibly well with the Veil Nebula. It's worth having one just for that. Breathtaking.

I recommend you try the 0III on the Owl Nebula - it seemed to define the shape a little more to the point where one of the eyes was just visible.

[bish]

Thanks for the review Astro_Baby. I was thinking about whether to get an OIII or UHC for my scope. I wasn't sure if my scope would be big enough but it seems that part timer has been using them with a 6" scope.

[Doc]

Very good report Mel and pretty much hits the nail on the head concerning the O111.

I haven't tried a UHC one as yet but have tried a Baader O111 filter. I completely agree about the difficulty in focusing and I found myself wandering off to a brighter star to refocus before looking at the nebula in question.

The baader is pretty strong and such as delivers a very strong green tint which to my eyes was off putting, so much so I found myself hesitating to use it.

When I did I found it increased the contrast of M27 and M57 and they did appear brighter and more detailed but did not appear natural due to the green tint.

By using the blinking technique some nebs did appear and disappear so in this instance it did work as these were unseen without the filter.

Is it worth the money I'm still not sure but I will eventually get the UHC as well as I think any serious astronomer shouldn't be without these.

I look forward to one day trying these with a widefield eyepiece such as a Nagler 31mm and under dark skies as I'm sure the Veil Nebula will pop out in all it's glory with a O111.

It's just under mediocre skies and inferior eyepieces the O111 does not excell in my book.

[Beulah]

I look forward to one day trying these with a widefield eyepiece such as a Nagler 31mm and under dark skies as I'm sure the Veil Nebula will pop out in all it's glory with a O111.

Popped into the focuser of your 16" Lightbridge, you'll need smelling salts, afterwards. You must report your findings when that day comes!!

[Doc]

Popped into the focuser of your 16" Lightbridge, you'll need smelling salts, afterwards. You must report your findings when that day comes!!

That day shouldn't be to far off I hope.

[albedo0.39]

Nice report Astrobaby and thanks for taking such time to detail all the findings

I'm (sort of) pleased you cam away with the result you did becasue it's now sealed the fate of when / who's UHC filter to get for my LB. Mick got the O-III and I'm looking forward to a back to back review at Salisbury (green stars cannot wait !)

Any recommendations for a general purposes UHC ?

Thanks

[Doc]

If you can afford it Steve get the Baader.

[mdstuart]

I have the OIII and generally I think well that just dulls the stars and does not add any detail. That was until I tried NGC 6781 in Aquila. It is a faint planetary neb and it was alomost non existant without the OIII.

Try it Astrobaby and see what you think. You need a dark sky and perhaps your 13mm ep as its quite small.

Good luck

Mark

[Doc]

Never seen NGC6781 Mark whats it like and how does it compare in the O111?

[ZOG]

Great report Mel, I have the Baader OIII filter and I agree it really darkens the background making the brighter stars a violet colour. I don't use the filter to search for objects, I tend to locate them in a widefield EP and then use the filter, usually in my 13mm to view them, with mixed results really. M42 is awesome through it but M57 tends to fade a bit.

A case of horses for courses I think.

[AndyBooth]

I looked at both M27 and the veil last night with both a UTC and a OIII.

The OIII won hands down, the dumbell outer area was only visible in the OIII.

I was using a 12" dob.

The veil was only just visible against the skyglow in the UTC, but was breathtaking in the OIII. The sky background becomes a lot darker, but you lose some of the faint stars.

[callump]

Would be helpful to know which brands of UHC and OIII filters you are comparing - different brands have different passbands, and some are better than others.

In fact there is some variation within batches within a brand too, but thats a bit more difficult to tell apart.

Maurice Gavin did some interesting testing a few years back:

wpo-spectroscope tests deepsky/OIII filters

/callump

[Astro_Baby]

The ones I compared with both Sky-Watcher supplied ones. They came with the band pass graphs but I am too dim to really understand what they are all about :). I can only go with my eyeballs really - math not being a strong point with me.

[AndyBooth]

Both mine are Baader products.

[mdstuart]

Doc, 6781 is a patch that looks like a small gibeous moon in the OIII but is almost invisible without it.

[Doc]

Interesting Mark....

Btw Callump mines a Baader Narrowband O111

[Astro_Baby]

I have heard the Baader filters are more aggressive than the Sky-Watcher/Orion ones.

I guess what would be interesting would be a comparive test between say Sky-Watcher, Baader and Lumicon.

[Astro_Baby]

ps to get that report I suffered terribly you know. It was c-o-l-d out there, the dew was atrocious and I was so intent on what I was doing I didn't spot how cold I was. Frozen stiff by the time I finished up I can tell you and I still had to pack the scope up, drive for 2 hours and then lug the scope up 8 flights oif stairs and unpack it all to let it dry out after the dew attack.

But I shrugged it all off to bring you SGL folk the eyewitness report.

None of this lounging about in a comfy obs with some imaging kit and a warm computer and comfy slippers- its rough and tough out there on a lonely hillside with just the stars as company

I'm thinking of an electrically heated suit for winter .

[Doc]

ps to get that report I suffered terribly you know. It was c-o-l-d out there, the dew was atrocious and I was so intent on what I was doing I didn't spot how cold I was. Frozen stiff by the time I finished up I can tell you and I still had to pack the scope up, drive for 2 hours and then lug the scope up 8 flights oif stairs and unpack it all to let it dry out after the dew attack.

But I shrugged it all off to bring you SGL folk the eyewitness report.

None of this lounging about in a comfy obs with some imaging kit and a warm computer and comfy slippers- its rough and tough out there on a lonely hillside with just the stars as company

I'm thinking of an electrically heated suit for winter .

Sounds like fun to me.