Horsehead hunting 2" vs 1.25" H-beta filter\eyepiece combos

[mandragara]

Hi,

I'm up in the Blue Mountains with a 12" f/5 Dob and want to try and see the Horsehead this season.

I own a 30mm 82deg ES eyepiece and was thinking of getting a 2" Astronomik H-beta filter to use with it ($300 at Bintel).

However, it dawned on me that I could also just get a 1.25" filter for $150 and hunt down a TeleVue 32mm Plossl to use it with for about the same price as the 2" filter. Currently my longest FL 1.25" eyepiece is a 24mm 68deg ES but I think I want the bigger exit pupil.

Do you think the extra FOV from the 30mm 82deg + 2" filter would improve my odds of seeing the Horsehead? Or would I be better off looking through a narrower FOV made of TeleVue glass?

I already have a 1.25" Astronomik O-III and UHC and a Kson brand 2" O-III filter.

[astro744]

You get a 1 deg field with either 32mm/50, 24/68 or 40/43 eyepiece and as you say the higher exit pupil is desirable for the horse head but so is a very dark sky. You don’t necessarily need the wider field as 1 deg. is more than enough.

It comes down to how much you want to spend and what other targets you may want to observe with h-beta with the wider 2” eyepiece. Astronomik filters are very good, not familiar with the Kson brand.

I went through this a few years ago (not specifically h-beta) and invested in 1.25” filters of various brands until I found my preference and then invested in 2” of that brand. What surprised me was the variation between brands of the same type of filter but overall all impressed. I have Tele Vue (1st gen, no h-beta), Lumicon, Astronomik, Thousand Oaks.

The horse head when you finally see it is black on black and not as the show piece that other nebular are such as Eta Carina with 2” O-III or veil nebular with the same and of course M42 in all three filters.

I’d get the astronomik 1.25” and see if you like H-beta on other targets too. M42 looks different with H-beta. I use 1.25” filters with 1.25” eyepieces and 2” filters with 2”eyepieces. Seems obvious but.... some people buy 2” only and screw onto the bottom of their 2”-1,25” adapter. I DO NOT recommend this approach as you risk damaging your 2” filter if your eyepiece has a long barrel or you’ve left a filter on a 1.25” eyepiece. Even Tele Vue don’t provide for this option as they deliberately do not thread their 2”-1.25” adapters and if it’s good enough for them it’s good enough for me.

[N1]

B33 sure is a fun object - to hunt, and then to finally see.

As others have said, you do not need 2" EPs or filters. In fact, a wide view will often include Alnitak, which I find a bit distracting and which is the reason I prefer Plössls or Abbe orthos for this particular target. Any eyepieces with modern coatings and/or little glass will help though. So will clean mirrors.



For your interest, I saw the object without filter through 8" a few years ago (https://www.iceinspace.com.au/forum/showthread.php?t=141218) and again with a 12" dob last month observing at 1,000m asl, also no filter. Having been to the Blue Mountains, I think it's doable from there too. Perhaps try that before spending the big dollars on a one-trick pony (see what I did there) filter...

[Don Pensack]

2" is the universal size. It fits the front of a 2" diagonal, it fits 2" eyepieces, and it fits the bottom of most 1.25" to 2" adapters so is usable with 1.25" eyepieces. It threads on the front of coma correctors and many/most 2" barlows.

[ausastronomer]

Hi Richard,

There's a few things to get in order to observe the Horsehead (B33) in "threshold" sized telescopes. A 12" Telescope is borderline under most conditions, but it is doable when it all comes together. In fact when everything is favourable it has been observed by people in telescopes down to 4"; but that isn't the norm. The Astronomik UHC filter, while not quite as good as a H-Beta on B33, will certainly help a lot. I wouldn't race out and buy a H-Beta filter in the hope of seeing the Horsehead, because the telescope is borderline in any case and you won't use the H-Beta on many other targets at all. About 15 or 16 years ago Glenn Dawes (another experienced observer) and myself spent about 2 hours trying to find the Horsehead in a 10" telescope under pretty good skies at a South Pacific Star Party without success.

Here's a checklist of things to steer you in the right direction to achieving success with your 12" scope

1) Dark Skies
2) Darker Skies (I doubt Blue Mountains will cut it, go West)
3) Give yourself at least an hour after full dark, to get properly dark adapted. Don't look at bright targets like Jupiter/Saturn. etc and then jump to the Horsehead. That won't work. Stay away from bright things for a good while before you try for B33.
4) Clean Mirror
5) Astronomik UHC Filter
6) Well cooled and collimated telescope
7) A "decent" eyepiece giving an exit pupil of 3mm to 4mm. In your scope that's a 15mm to 20mm eyepiece. The smaller exit pupil improves contrast and is far more important than a wider FOV.
8) If you can see the Flame Nebula (NGC 2024) there's a reasonable chance you will be able to see the Horsehead (B33). If you can't see the Flame, don't waste your time on the Horsehead.
8) Use Alnitak (ζ Orionis), with averted vision, to orient yourself and figure where you need to look for the Flame and the Horsehead and then push Alnitak out of the FOV. You won't see anything whilever Alnitak is in the FOV unless you have a 20" or larger telescope.
9) It's very dim and unimpressive as a visual target. The Horsehead (B33) is actually a dark nebula in front of a bright emission nebula (IC434) which creates the visual appearance of the Horsehead. Unfortunately IC434 isn't so bright in average amateur telescopes and is barely visible above the background sky brightness, which makes the Horsehead very difficult to see. In my 14" telescope it appears as a barely discernable "notch" against the background nebula, which itself is very difficult to detect.

Now here's the rub and why "some" people might not ever see it. IC434 emits it's light towards the red end of the spectrum. People with a low sensitivity to red light just cannot see IC434, which means they won't see the Horsehead. One of my very skilled observing buddies is in this category. He can't see it in a 25" telescope.

Here is a link to an image which shows the relative positions of The Horsehead and the Flame in relation to Alnitak (https://en.wikipedia.org/wiki/Flame_Nebula#/media/File:Spectacular_visible_light_wide-field_view_of_region_of_Orion's_Bel t_and_the_Flame_Nebula.jpg)

Good Luck !!

Cheers
John B

[By.Jove]

Hi Richard, I have seen it a few years ago from Shipley Plateau (near Blackheath), using a 10" with a 2" low power eyepiece - and no filters. It's tricky to find though. I found it using an EQ6, by calibrating the GOTO position on Alnitak and then offsetting from it. As John suggested you have to get Alnitak OUT of the field of view, and it is essential to let your eye properly dark adapt.

Good luck chasing the horsie.

[Stonius]

The horsehead is one of those objects you 'detect' rather than 'see', if you take my meaning. It's a very low contrast extended object. If you think you see it, wobble the telescope a little. If it moves, it's a real detection.

Markus

[Allan]

You will never regret buying 2” format filters. The same can’t be said for 1.25” filters as they are a lot more limiting in their use. I would bite the bullet and pay the extra if you can.

The Horsehead is not a difficult target provided, you have access to some impressively dark skies. It does become very easy to see with experience. I do tend to check in on it a lot during the season.

In the 32” it’s an impressive showpiece object, with dark and light mottling in the Horsehead and bright streaks of nebulosity running through IC434 in the background.

Under Bortle 5 it’s not too difficult in the 16”. I never tried under Bortle 5 with my 12”, but it would be just out of reach. Under Bortle 1, 21 Ethos, Lumicon H-beta and the 12” it’s pretty easy to see. But like I said, I look at it a lot, and that helps. Just get yourself somewhere really dark and keep trying and practicing until you get it. Take someone else along who has seen it if you can, that’s probably your best asset.

My astro property gets into the SQM 22.0 range and I could see the Horsehead in my TV76 at that site. So it’s not a tough object once you’ve got a lot of experience with it.

[Stonius]

Interesting run-down there Allan. I tend to find the horsehead difficult, but definitely do-able in my 16". I've had some people look through and not be able to see it, where others can. I'd love to see it in dark skies with a 32", that would be mind-blowing!


I think you're right about having seen it makes it easier to detect the next time because you know what to expect.



I'm curious, with your experience, if there are other objects you'd put in a similar category for detection difficulty - as in, all but impossible in 12", do-able in 16" and quite detailed in 32"? If you feel like sharing, of course.



Cheers,
Markus

[glend]

John pretty much covered the approach. The Horsehead can be found but as Allan pointed out a very dark site is a prerequisite. As indicated it is black on slightly less black, so knowing exactly where to look helps enormously. Obviously good vision is important. Also "averted vision" can sometimes find it when looking directly at it doesn't. I recall looking at it at Chaffey Dam dark site, with my 16" Dob, and not being really sure till I looked slightly away, where I had better light/dark perception.
Despite the challenge that the Horsehead represents visually, it is easy to video image with a plain colour high frame rate camera; but the human eye lacks the ability to build an image over time. If you want to try EAA, where you use a high frame rate camera and software like Sharpcap, it will jump right out of the screen at you as Sharpcap stacks frames (which no human eye can do). In my opinion, being of advanced years and not so good eyesight now, it is much more rewarding seeing it through EAA in real time.

[N1]

That would indeed be interesting to see - an object where 2.7x the image scale at the same brightness makes the difference between "all but impossible" and "quite detailed". I've never observed anything like that.

[Don Pensack]

Here is a list of H-Beta targets, most of which are faint:
1. IC 434 (HORSEHEAD NEBULA)
2. NGC 1499 (CALIFORNIA NEBULA, naked eye and RFT)
3. M43 (part of the Great Orion Nebula)
4. IC 5146 (COCOON NEBULA in Cygnus)
5. M20 (TRIFID NEBULA, main section)
6. NGC 2327 (diffuse nebula in Monoceros)
7. IC 405 (the FLAMING STAR NEBULA in Auriga)
8. IC 417 (diffuse Nebula in Auriga)
9. IC 1283 (diffuse Nebula in Sagittarius)
10. IC 1318 GAMMA CYGNI NEBULA (diffuse nebula in Cygnus)
11. IC 2177: SEAGULL NEBULA (Diffuse Nebula, Monoceros)
12. IC 5076 (diffuse nebula, Cygnus)
13. PK64+5.1 "CAMPBELL'S HYDROGEN STAR" Cygnus (PNG 64.7+5.0)
14. Sh2-157a (small round nebula inside larger Sh2-157, Cassiopeia)
15. Sh2-235 (diffuse nebula in Auriga).
16. Sh2-276 "BARNARD'S LOOP" (diffuse nebula in Orion, naked eye)
17. IC 2162 (diffuse nebula in northern Orion)
18 Sh2-254 (diffuse nebula in northern Orion near IC 2162)
19. Sh2-256-7 (diffuse nebula in northern Orion near IC 2162)
20. vdB93 (Gum-1) (diffuse nebula in Monoceros near IC 2177)
21. Lambda Orionis nebular complex (very large, naked-eye)
22. Sh2-273 "Cone" Nebula portion south of cluster NGC 2264

A list of objects at the limit of 12.5" and easier with larger apertures would number in the thousands, so not practical to answer.
There is a galaxy cluster in Corona Borealis at a bit over a billion light years that would be a good candidate, since larger apertures will see more galaxies.
There are a lot of galaxy clusters in the Southern sky that would qualify as well, like Abell 838 in Hydra at 675 million light years, or Abell 2448 in Aquarius at a distance of 1.1 billion light years.
There are many many such across the entire sky.
The limit depends as much on darkness of sky as it does on aperture.
15th magnitude galaxies are within reach in a 12.5" in dark skies, but 13th magnitude galaxies are tough in light polluted suburbs.

[astro744]

A dark sky will of course improve views of galaxies but are you also saying a H-Beta filter will improve or further improve views of galaxies and galaxy clusters? None of the objects you listed are galaxies.

The original Lumicon H-Beta filter was marketed as the Horsehead nebula filter but it does so much more. Objects that are viewed best with UHC look different in O-III which is UHC minus H-Beta and also look different in H-Beta which is UHC minus O-III. I find a H-Beta filter presents a different view of an object I would normally use an O-III filter for provided the object is emitting in H-Beta too.

I didn't think any line filter was good for galaxies.

[Don Pensack]

Oh, no.
I was merely talking about Horsehead and faint nebulae near the limit with the list of H-ß objects.

No filter will help with galaxies except gasoline--you put it in your car and drive your scope to darker skies.
I wasn't thinking about galaxies with the list of faint nebulae.

I mentioned galaxies because objects near the limit will mostly be faint nebulae and faint galaxies. Sorry for the confusion. Perhaps it should have been 2 separate answers.

[Stonius]

Thanks Don, I wan't expecting an entire list!


I've attempted some of them - California Neb was a fail for me last time I tried, but I think with B33 one has the advantage of the contrast of the dark horsehead. Also, the California nebula is pretty low on our horizon (15 degrees) here which affects transparency.


I've never seen Barnard's loop naked eye, or Lambda Orionis but to be fair, I'm often busy chasing easier targets (which is also the reason I'm yet to experiment much with the Abell's - too busy in Fornax and Virgo).


By the looks of it the cone nebula should similarly be naked eye under the right conditions - the blackwater skies imaging toolbox would seem to render them at a similar surface brightness.


To clarify, are we talking *naked eye*, or naked eye with UHC filter?



Cheers, I look forward to working through some of the challenges on your list!


Markus

[Allan]

I had over 50 people at my property once and many/most had never seen the Horsehead. So I just lined them up on the 32” and one after the other they all got to see it. For many, they realised they had been looking right at it for 30 years without ever seeing it. IC434 is very bright and detailed in the 32”, so the Horsehead sticks out easily against it.

The Cone nebula is a good example of a target that is tough even in the 32”. I never saw it in my 12”. Don has good eyes and some higher altitude sites, so he might have seen it in his 12.5”. But he would be one of the few humans to do it in that size scope.

My favourite success I’ve had with the 32” is observing the solar system moons. I’ve visually seen 29 moons in the 32”. While 19 or 20 moons would be the limit for a 12”.

[Don Pensack]

Those are all through a telescope. A couple are visible to the Naked eye, but otherwise, I meant through a telescope.

[ausastronomer]

Hi Markus,

This comes down to what I mentioned previously about each individual observers own eyes sensitivity to the higher wavelengths of red light.

Cheers
John B

[ausastronomer]

Allan,

While the Cone Nebula is a very challenging target in most amateur telescopes, it should be fairly routine in a 32" scope under Bortle 1 skies, particularly so, if you use a H-Beta filter. I've observed it at Ozsky, in all of the scopes we take to Ozsky from 14" to 30" at different times. It certainly isn't easy. One night we spent a good bit of time on it in my 18" scope. 3 of us could see it fairly comfortably with a UHC filter (Andrew Murrell, myself and Lance Humphries), yet another 1/2 a dozen people, including some experienced observers like Alan Dyer, could not see it. Hartung regularly observed it in his 12" scope, with a H-Beta filter. I would say it's definitely tougher than the Horsehead, but achievable in 12" scopes by skilled observers under ideal conditions. The planetary nebula that Andrew Murrell discovered (Murrell 1) is certainly a lot tougher and James Peirce, Andrew Murrell and I have observed that in James's 16" scope from Coonabarabran. The Cone Nebula certainly isn't a beginners target in a 12" scope, but I know at least 6 people personally who would be capable of it. I can guarantee you the worldwide list extends far beyond Don.

Cheers,
John B

[Don Pensack]

I didn't mean to imply all those H-ß objects were easy or even visible to a 12.5" aperture.
I mentioned the 12.5" aperture because the original post wanted a list of objects at the edge of visibility for that aperture, and there are just too many thousands of objects to make such a list. Most are not H-ß objects, of course.
He was also mentioning an H-ß filter, so I gave him a list of faint targets at the edge of visibility using that filter. B33, the Horsehead, is one such.
My list is northern hemisphere-biased, and a southern list would contain many objects not visible up north. You guys would know best what objects to add to the list of H-ß objects in deep southern skies.

Observer experience counts, of course, but I think light pollution is the biggest factor keeping observers from going faint. If you have truly dark skies, it's amazing what can actually be seen with modest apertures.

[Stonius]

I guess the other aspect of all this is the discussion of filters and conditions. My filter passes Ha, Hb and OII, so it's fairly broad - possibly making the detection of the horsehead more difficult compared to more specialised H-beta ONLY filters.


And even among Hb filters some are broader than others, with different peak transmission data. Am I correct in thinking that Lumicon is the go-to these days?



I've seen the horsehead through my 16" using the above-mentioned UHC filter, and in the same night, completely failed to see it through a 40" telescope (unfiltered) most likely because the sky had moved (as it does) and the horsehead was swimming in horizon muck.


I can imagine that it may well be in reach of a 12" instrument under good conditions , especially near meridian-crossing, with a quality dedicated H-beta filter.


Thanks Don. Now I have gear-lust again :lol::help::lol:


Markus

[Don Pensack]

Lumicon doesn't currently make an H-ß filter since 2016.
The Go-To H-ß filters are Astronomik H-ß (since 2017) and TeleVue (since 2018). I had an Orion that measured 'very good', but variability in manufacturing means you might not get as good a filter, so caveat emptor.

At high altitude at 35°N, I see the Horsehead in the 12.5" without a filter, and a filter makes it easy. The main issue I had in finding it originally was that I was looking for something small, and it's about the same size as M2.

[Allan]

I guess our eyes are target specific. I can tell you have trouble with the Horsehead. I would rate it a fairly basic observation in a 10” at SPSP. I’ve seen it there in my 5” refractor unfiltered. Even in my 3” refractor with a h-beta under Bortle 1 the Horsehead was a nice positive observation. The Cone is a significant step up from the Horsehead in difficulty.

[ausastronomer]

Our eyes are target specific for certain, as different people have different sensitivity to different wavelengths of light. That's an absolute given!

I don't know that I have that much trouble with the Horsehead. I've probably observed it close to, if not more than, 200 times over the past 40 years, which is when I gained access to telescopes 12" and over. For the 10 years I observed prior to that with smaller telescopes, I never bothered trying to observe it, as I had other programs I was focused on. I've probably only ever tried to observe it in a telescope under 12" less than 5 times. As nice as small refractors are, and they do give an aesthetically nice image, they don't have the light grasp, or resolution that I want to use these days. To be totally honest I spend very little time with telescopes under 14" these days. Even my 10" SDM, as nice as it is, generally only gets used for lunar and planetary observation, which is why I got Peter to build it. Ill be observing under Bortle 2 skies December new moon and will try for the Horsehead in my friends new 5" Triplet APO with a H-Beta filter.

Cheers
John B

[Stonius]

Is there a way for the home user to measure this and generate a sensitivity curve for their own eyes? I'd be curious to be able to test in a setting that is not dependent on other variables such as transparency, filters, etc...


It's kind of a good thing to know, same as knowing your maximum pupil dilation.



Has anyone done this?


Markus

[ausastronomer]

Hi Markus,

I don't think this would be something easy to do at home. I may be wrong. It would be very easy to do in a laboratory that could emit light at various wavelengths and measure the response. Similar to doing a hearing test where they measure your ability to detect sound at a whole range of wavelengths and measure the lowest db level you are able to detect each of those frequencies.

I know its a real life thing because I have seen instances under very good conditions with large aperture, where a couple of observers have been able to observe the horsehead unfiltered very easily, yet a couple of other very experienced observers have not been able to detect it at all, due to their own eyes inability to detect the high red wavelengths emitted by IC434. However, on targets which emit at lower frequencies, they can go just as deep as the others.

Cheers
John B