Baader OIII filters for visual?

[Franklin]

My scopes are all small refractors and I have been using a Baader UHC-S filter for some time and it definitely works. Over the winter I placed the UHC-S in a filter wheel and switched back and forth from filter to no filter on M42 and the difference in contrast was very noticable. Now that nebula filters are my new friend I have picked up a Baader OIII and was just wondering what the differences between the different bandwidths is and what they mean in actual visual terms. From the Baader website I see that the visual OIII has a 10nm bandwidth and they also do a CCD OIII filter at 8.5nm bandwidth. However, the OIII I have which I bought used, must be an older one as it's called a Baader OIII visual 8nm. Is there going to be much difference for visual use between 10nm and 8nm? Or am I splitting hairs?

[Davesellars]

I'd not heard of that one...  I have the Baader 10nm Visual which I bought quite a few years ago which is a narrower band than my Astronomik OIII (can't remember the exact figure for this now... somewhere around 12nm possibly) and there is noticable difference between the two.  The Baader I use pretty much exclusively in the 12" dob and very occasionally in the 120ST but with this it really needs to be an object with significant OIII and also use in the region of a 25 or 32mm eyepiece to get a large exit pupil.  For smaller apertures the Astronomik works much better for me.   I have a feeling that 8nm will be far too narrow for small apertures unless you're in pristine skies and using an eyepiece to give a large exit pupil.

Edited April 9, 2022 by Davesellars

[Louis D]

Theoretically, as long as the passband is perfectly centered on the emission line(s), the narrower passband filters should simply exclude more stray light increasing contrast.

However, you run into the problem that there are two OIII emission lines, a brighter one at 500.7nm and a secondary one at 495.5nm.  Most visual OIII filters attempt to pass both while most ultra-narrowband imaging filters only pass the former.  It would be great if the filter could pass each with a 3nm passband, but that's not really possible as the two passbands would be touching at their bases, and it would be super expensive to manufacture.  Instead, most use a 12nm to 15nm passband for visual to pick up both bands to increase the signal being fed into the eye at the expense of passing more sky glow noise.

[Franklin]

Thanks for the replies and the graphic explains all. With the 8nm bandwidth, the filter may cut out some of the OIII at 495.5nm. I'll just have to experiment and see if it's too dim. I have a TV Bandmate OIII which seems to work but I don't know what the specs are for that one.

[PeterC65]

I have the Astronomik UHC filter which has a slightly narrower 500nm passband than the Baader UHC-S and a 650nm passband that extends beyond 700nm, but I expect the two perform similarly. It makes a big difference on nebulae with the 127mm Mak, less so with the 72mm Apo, and is my most useful filter.

I've been considering adding an Astronomik OIII filter (12nm passband at 500nm) but haven't done so yet as the passband is much narrower than the UHC filter and I'm concerned that the reduced light transmission will make it unusable for visual, even with the 127mm Mak. @Franklin, have you tried your 8nm OIII filter with a small aperture refractor, was it beneficial when compared with the UHC filter, and if so, on which targets?

I would like to see the Veil Nebulae and have been thinking that an OIII filter might be useful for this target.

[PeterC65]

19 minutes ago, Franklin said:

I have a TV Bandmate OIII which seems to work but I don't know what the specs are for that one.

The TV Bandmate OIII looks like it has a 12nm passband (see here) and is almost identical to the Astronomik OIII.

[Franklin]

7 minutes ago, PeterC65 said:

have you tried your 8nm OIII filter with a small aperture refractor, was it beneficial when compared with the UHC filter, and if so, on which targets?

Not yet Peter but will update when I do. Using a long focal length eyepiece to keep the exit pupil as large as possible should help. I was under the impression that it's generally best to stick with UHC when using small scopes, my largest scope is 100mm, but I've read on here and on other sites that the OIII can be used with smaller scopes. My widest field eyepiece in the 1.25" size is the 24pan, so i'll be giving the filter a go with that when the skies permit.

[Franklin]

4 minutes ago, PeterC65 said:

The TV Bandmate OIII looks like it has a 12nm passband (see here)

That's interesting, the specs for the filter on FLOs site are the specs for the TV zoom eyepiece???

[Whistlin Bob]

Sounds like you've already got the right plan- that is definitely worth trying out. Was just going to flag that I've got the same filter that I originally bought for imaging, and it works really well in 8" and 14" Newts for visual. I know that's not quite the same use case, but planetary nebulae are awesome in it and I get great views of The Veil as well.

[PeterC65]

5 hours ago, Franklin said:

I was under the impression that it's generally best to stick with UHC when using small scopes, my largest scope is 100mm, but I've read on here and on other sites that the OIII can be used with smaller scopes. My widest field eyepiece in the 1.25" size is the 24pan, so i'll be giving the filter a go with that when the skies permit.

That was also my impression, but the UHC filter is so useful that I've been wondering whether the OIII might also be useful for certain nebulae. My scopes are on the smaller aperture side but I've recently added a 150mm reflector and that should give me more light to possibly accommodate the OIII filter.

5 hours ago, Franklin said:

That's interesting, the specs for the filter on FLOs site are the specs for the TV zoom eyepiece???

Yes, the text does seem to be for a zoom eyepiece! But they seem to have the filter spectrum right.

How do you rate the TV OIII compared with the Baader UHC-S? It has a similar spec to the Astronomik OIII that I've been considering,

 

[Franklin]

8 minutes ago, PeterC65 said:

How do you rate the TV OIII compared with the Baader UHC-S? It has a similar spec to the Astronomik OIII that I've been considering,

 

The Baader UHC-S has been my goto nebula filter and to be honest I'm not really that experienced with these kinds of filters. I was drawn to the UHC-S because it is more of a broadband than other UHCs and doesn't dim the stars so much, having limited aperture and not so good skies. But on the other hand it doesn't create as much contrast as the narrower type. The OIII bandmate makes the sky darker and stars dimmer but when looking at the M42 I could definitly see more detail in the arching wings of the nebula. It extended slightly further, so these filters do work. I would love to get a large dob out to a dark sky on a moonless night and give these nebula filters a try.

[Louis D]

8 hours ago, PeterC65 said:

The TV Bandmate OIII looks like it has a 12nm passband (see here) and is almost identical to the Astronomik OIII.

Not surprising.  It says right on the linked webpage:

Designed and manufactured exclusively for Tele Vue by Astronomik. 

[Louis D]

8 hours ago, Franklin said:

the OIII can be used with smaller scopes.

Indeed.  It's exit pupil based.  The problem with smaller scopes is image scale.  At the preferred exit pupil, the nebula image will be smaller than in a larger aperture telescope.  If you're willing to live with a smaller image scale, the OIII will work fine in smaller scopes.  In fact, you might be able to detect large nebula regions thanks to the wider field of view at larger exit pupils.  By contrast in larger aperture scopes, you just can't get the magnification down low enough to do edge detection on these same regions.  You end up looking straight through them as if they were mere sky glow.  You might detect them with careful sweeping of the area, but detailed observing would be difficult.

[Zermelo]

On 09/04/2022 at 13:43, PeterC65 said:

I would like to see the Veil Nebulae and have been thinking that an OIII filter might be useful for this target

I have the Astronomic UHC and an OVL OIII.

With a 150mm reflector in Bortle 4, I found that I couldn't see the Veil at all without a filter. I found the Eastern Veil before the Western, when I got the UHC. After I bought the OIII, I found that with a 6mm exit pupil the nebula looked the same with both, but with a 2.4mm pupil it was a bit better in the UHC.

 

 

[PeterC65]

49 minutes ago, Zermelo said:

I have the Astronomic UHC and an OVL OIII.

With a 150mm reflector in Bortle 4, I found that I couldn't see the Veil at all without a filter. I found the Eastern Veil before the Western, when I got the UHC. After I bought the OIII, I found that with a 6mm exit pupil the nebula looked the same with both, but with a 2.4mm pupil it was a bit better in the UHC.

 

 

So no benefit of going for OIII over UHC with the Veil and 150mm of aperture.

Are there any targets where you have found the view through the OIII to be better than through the UHC, with any of your scopes?

[Zermelo]

10 hours ago, PeterC65 said:

So no benefit of going for OIII over UHC with the Veil and 150mm of aperture.

Are there any targets where you have found the view through the OIII to be better than through the UHC, with any of your scopes?

That was my conclusion so far on the Veil, though I will revisit it in the light of the very interesting post from @Stephen Waldee above.

I don't recall seeing anything better, or different, with the OIII so far. That could be down to my skies, the more restrictive filtering of the OIII combined with the modest aperture, sub-optimal choice of exit pupil, or perhaps the OVL performance not being quite as good as Astronomik, Lumicon, etc.

I've not been very scientific in my observing so far, I just offer the above as my thoughts at the moment to anyone in a similar position. I do need to experiment more with exit pupil, and I'll have a look at Stephen's links when I get chance. I think the Astronomik UHC was worth the money (though it cost more than my first eyepieces!); so far, I haven't seen much extra value from the OIII. I remember seeing threads previously, along the lines of "I can afford to get only one filter at the moment, should I go for UHC or OIII?" and the responses were split about equal.

[Stu]

22 hours ago, PeterC65 said:

So no benefit of going for OIII over UHC with the Veil and 150mm of aperture.

Are there any targets where you have found the view through the OIII to be better than through the UHC, with any of your scopes?

I don’t think OVL vs Astronomik is a fair comparison. An Astronomik OIII would likely perform much better than the OVL. In my experience the Lumicon OIII gives better contrast on the Veil than a Lumicon UHC. I do think these types of filters are worth spending cash on to get the best performance ie narrow bandpass and high transmission. Astronomik, and by definition Televue seem to be the best out there currently, although I think the latest Lumicons are back to being good too though not sure. Mine are old but excellent.

This is an oft posted link to some excellent camparisons between filters on a range of targets.

https://www.prairieastronomyclub.org/filter-performance-comparisons-for-some-common-nebulae/

[PeterC65]

It seems there are mixed opinions about the benefit of an OIII filter over a UHC filter when used with a smaller aperture scope. As is often the case, I guess I will have to see for myself, so I have just ordered an Astronomik OIII filter from FLO to go alongside my Astronomik UHC filter.

I would love to see the whole of the Veil Nebula through my 72mm APO which certainly has the required field of view, and maybe with the OIII filter it might be possible.

[Stu]

16 minutes ago, PeterC65 said:

I would love to see the whole of the Veil Nebula through my 72mm APO which certainly has the required field of view, and maybe with the OIII filter it might be possible.

Under good skies it certainly is possible. You need good dark adaptation of course, and preferably mag 21 or better skies, but I’ve done it on a few occasions with good results. I used to think it needed a four inch scope but that’s definitely not the case.

There is a brief description of the views in this report in comparison with the far more detailed close up views in a 14” dob.
 

[Zermelo]

37 minutes ago, PeterC65 said:

It seems there are mixed opinions about the benefit of an OIII filter over a UHC filter when used with a smaller aperture scope. As is often the case, I guess I will have to see for myself, so I have just ordered an Astronomik OIII filter from FLO to go alongside my Astronomik UHC filter.

I would love to see the whole of the Veil Nebula through my 72mm APO which certainly has the required field of view, and maybe with the OIII filter it might be possible.

I'll be very interested in your findings.

[PeterC65]

5 hours ago, Zermelo said:

I'll be very interested in your findings.

I'll let you know. It will be late summer before the Veil is visible again from here though.

[jetstream]

On 09/04/2022 at 08:54, Franklin said:

I was under the impression that it's generally best to stick with UHC when using small scopes,

This is not true- a top quality OIII works well in small scopes, just have to play with the mag.IMHO.

[BGazing]

Filters work irrespective of the aperture as long as you use a correct exit pupil.

I used UHC and OIII in my 71mm refractor to see the whole of the bigger nebulas (Veil and N. America).

[PeterC65]

I've been meaning to post about my experience with the Astronomik UHC and OIII filters on the Veil Nebula but have been preoccupied with EEVA for the last few months. Last night I did a comparative test with the East Veil via EEVA between the Baader Skyglow, Astronomik UHC and Astronomik OIII filters, and none. I was using short 8s exposures and 20 staked frames, although the image didn't change much beyond the first minute, so this was close to live. These are snapshots from the live stacks from last night ...

With no filter ...

With the Baader Skyglow ...

With the Astronomik UHC ...

With the Astronomik OIII ...

As expected, the UHC filter makes a big difference and for me this is the best view of the Veil. The OIII filter does bring out more detail in the structure I think, and it greatly reduces the brightness of everything in the background, including the stars, but it also turns everything green / blue! This may not be so apparent when observing visually as I hope to do soon.

I did the same test with M27, with similar results, although the OIII filter seemed less effective at releasing structural detail with this target.

 

[Louis D]

Is the red Hα?  You'll have to compare visually to see if it shows up at all to the human eye with the UHC filter.