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Showdown at the Horsehead Corral

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#1 Sarkikos

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Posted 12 January 2013 - 02:03 PM

I recently took my 10" f/4.8 Dob to a yellow zone site to bag H400 objects. At first there were patchy clouds across the sky. But by 7:30 PM a strong west wind started blowing all those clouds away. The sky was transparent at least until the Moon appeared over the trees at about 1 AM. After finding and observing a couple dozen H400's, I decided to give the Horsehead Nebula (B33) a try before I headed home. I've tried to tease out B33 several times before at this site, but have never been successful. This night would be different.

The night was very transparent with poor seeing, as Clear Sky Chart had predicted. I swung the Dob over to Alnitak, Zeta Orionis. Attaching a spacing ring onto my 2" twist-lock adapter, I screwed a Lumicon H-Beta filter onto the end and slipped it all into the focuser. This setup would allow me to try several 1.25" eyepieces on B33 without having to remove the filter - and without hitting the filter with the end of an eyepiece.

The eyepieces I used were a UO Abbe Ortho 25, BGO 18, Brandon 24, Sterling Plossl 25.1 and XW20, in that order. I tried to select eyepieces that were somewhere around 24mm focal length - to give me about a 5mm exit pupil for my f4.8 Dob - as suggested by Barabara Wilson in this thread:

The Magic Horse Head Eyepiece

The following Megastar chart of the area posted by RolandosCY in another thread helped me tremenously in finding the Horsehead.

Bound and determined : Horsehead thru a ten..BUT..

This was the first night I recall ever seeing IC 434. Common sense would suggest that if you cannot see IC 434, you cannot see the Horsehead. So I always look for IC 434 first. If I don't see it, I don't bother looking for B33. That night IC 434 was fairly easy to see, though not as obvious as NGC 2024 northeast of Alnitak.

Many previous nights I could see NGC 2024 easily, but had no sign of IC 434. Now IC 434 looked like a faint wedge beginning west of Alnitak and extending southeast to a point. The area immediately to the east of IC 434 was clearly darker than that to the west. I used the Megastar chart to locate the Horsehead, situating it on the east edge of IC 434, south of an arc of four stars.

I also kept in mind that the apparent size of the Horsehead is about the same as the dark central area of NGC 2024. I glanced up at 2024 to get a check on the size of its central dark nebula before hunting the Horsehead. Of course, when actually trying to catch the Horsehead, I was careful to keep Alnitak and NGC 2024 out of the field of view.

The first eyepiece in the focuser was my UO Abbe Ortho 25. This was also the first eyepiece that ever showed me the Horsehead. I threw my DarkSky Apparel hood over my head to enhance my dark adaptation. I could just barely make out a slightly darker notch where the Horsehead was supposed to be. Bingo! Next I put in my BGO 18. As expected for an eyepiece with somewhat better coatings - fully multicoated instead of just multicoated - the Horsehead was somewhat easier to tease out from IC 434. (The higher magnification and narrower exit pupil may have helped a bit, too.)

Then I tried my Brandon 24mm. Mine has the amber coatings, which are supposed to be an improvement upon the older, bluish coatings. As expected given the Brandon's reputation, the Horsehead appeared more distinct than in either the UO Abbe Ortho 25 or the BGO 18. But the improvement over the BGO was subtle.

Next in goes my humble and inexpensive Sterling Plossl 25.1mm. Surprise! Best so far in show! The Horsehead was much more prominent than in the Brandon 24. Not a subtle improvement, but an obvious one. The large dark nebula immediately east of IC 434 was darker than in any of the other eyepieces. The outline of IC 434 was easier to tease out. And the Horsehead itself was a much more distinct notch in IC 434. At times, for an instant now and then, I could see a fairly clear outline of the Horsehead and even catch a glimpse of the snout. Very impressive, especially for an eyepiece which only cost me about $45 new!

Finally I tried my new acquisition, an XW 20mm. It has a 70 degree AFOV, so I had to be extra careful to keep Alnitak out of the field. This forced me to view the Horsehead rather close to the edge of the field, which probably had an negative effect on the view. But in any case, the XW 20 showed the Horsehead well. However, I would give it second place to the Sterling Plossl. Maybe if I'd used an XW closer to the magical 24mm, it would have performed better. But you gotta run the horses you've got.

I regret that I did not think to try my Televue Plossl 25mm on the Horsehead. That eyepiece never left the stable except to prime my Paracorr when going after the H400 objects. Neither did I use the Paracorr in viewing the Horsehead.

Here is a rundown of the eyepieces I used, showing their focal lengths, coatings, AFOV, and the TFOV, magnification and exit pupil in my 10" f/4.8 Dob, as well as my overall grade of their performance on the Horsehead Nebula (B33).

Eyepiece________Coating_____Mag______EP_____AFOV_____TFOV_____Grade

UO 25mm_________MC_______48x_______5.2_____47________59________C

BGO 18mm________FMC______67x_______3.8_____42________37________C+

Brandon 24mm_____FC_______50x_______5.0_____44________53________B

Sterling 25.1mm____FMC_____48x_______5.2_____58________73________A

XW 20mm_________FMC_____60x_______4.2_____70________70________B+

MC = Multi-Coated
FC = Fully Coated
FMC = Fully Multi-Coated
EP = Exit Pupil in mm
AFOV = Apparent Field of View in degrees
TFOV = True Field of View in arcminutes

One consequence of this comparo for me has been that I've taken the UO Abbe Ortho 25mm out of my deep sky eyepiece case. I have a pair of these. I'll keep them for binoviewing planets and the Moon, but not for viewing DSO. And I've decided to keep all my Sterling Plossls - 12.5 to 25mm - in the case for deep sky observing.

Clear Skies
Mike

#2 BillP

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Posted 12 January 2013 - 02:31 PM

:waytogo: :waytogo:
Great report!! And yup...those Sterlings are a surprising bunch. Just wish they made a 9mm or 8mm.

#3 DaveJ

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Posted 12 January 2013 - 04:26 PM

Next in goes my humble and inexpensive Sterling Plossl 25.1mm. Surprise! Best so far in show!


<sigh> That's all I can stands, I can't stands no more! (in my best Popeye voice) I just ordered a pair of the 25mm Sterling Plossls from Smart Astronomy. I need two more eyepieces like another hole in the head, but a fellow can only take so much.

#4 precaud

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Posted 12 January 2013 - 04:45 PM

FYI, the Sterlings are 15% off from Smart via their eBay store since Jan 1.

I just got the 12.5 and 25mm this week, only had a 25mm Orion plossl to compare directly with, and was blown away by the magnitude of the improvement in contrast and sharpness. Not subtle at all, even to these untrained ageing eyes. Not only darker darks, but lots of gradations and detail in the dark... like a lower noise floor in audio terms. And stars focussed down to much finer points. Very impressive.

#5 Mike B

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Posted 12 January 2013 - 04:51 PM

Aren't they also available from CN's sponsor, Astronomics, with a different label for the same $$? (i see no 25mm there, tho) Then there's always the CN discount to sweeten that...
;)

#6 DaveJ

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Posted 12 January 2013 - 05:05 PM

FYI, the Sterlings are 15% off from Smart via their eBay store since Jan 1.


Darn it! Where were you an hour ago?! I see the eBay ad here. I guess I could have saved $13.48 plus a better deal on shipping, too.

#7 GlennLeDrew

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Posted 12 January 2013 - 06:50 PM

Did you alternate back and forth over a period of time? Or at least once go back to the earlier, poorer performing eyepieces, so as to verify it was more than merely an improvement in dark adaptation?

#8 Istytray

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Posted 12 January 2013 - 06:55 PM

Great shootout! That Sterling 25mm now has me very interested. :thinking:

#9 Mike W

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Posted 12 January 2013 - 06:59 PM

I'd like to see a comparison between the Sterling and the Televue!

#10 mgwhittle

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Posted 12 January 2013 - 07:19 PM

I'd like to see a comparison between the Sterling and the Televue!


Here you go http://www.cloudynig...hp?item_id=2729

Excellent review by BillP

#11 wky46

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Posted 12 January 2013 - 09:06 PM

5 yrs. ago I could make out the notch (averted) in my 10" without any filter, but now I can't (with any EP). Hopefully just poorer transparency but you've given me another reason to try out a H-Beta filter on it ( I'm good on EP's ;)) Nice report and glad you found a good'n.... Phil`

#12 Sarkikos

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Posted 13 January 2013 - 01:09 AM

Glenn,

Did you alternate back and forth over a period of time? Or at least once go back to the earlier, poorer performing eyepieces, so as to verify it was more than merely an improvement in dark adaptation?


I was wondering when someone would ask these questions ... but I was pretty sure it was going to be you to ask them! :poke:

Well, the answer to both questions is, no, I didn't. :grin: My primary purpose that night was to bag H400 objects. I was able to locate and observe 25 more of them. Hunting for the Horsehead, and then comparing how it looked in different eyepieces, was a sideshow for trick ponies, not acts for the center ring. Besides, 25 mph gusts and temps in the mid-20's do not encourage exhaustive scientific controls. My observations are what they are.

However, I did spend nearly an hour on the Horsehead and the five eyepieces. For me, that is an enormous investment of time on any object that is not a planet or the Moon. I didn't start observing the Horsehead until about 10:45 pm, so my eyes had been dark adapting for over four hours. Also, over the course of my observations of the Horsehead, the sky was consistently transparent.

And for what it's worth, at the beginning of each observation with each new eyepiece, I would get my bearings by going back to Zeta Orionis (my Dob does not track). Even through an O-III filter, I'm sure this reset my eyes to an adequate base-line level of dark adaptation. Then, before I started viewing the Horsehead again with each eyepiece, I put the Dark Apparel hood back over my head to help my eyes dark adapt better and to shield them from ambient light.

I'm confident my report gives a good representation of the relative ability of these five eyepieces to present an image of the Horsehead Nebula. I've already made changes in my deep sky line-up of eyepieces based on the results.

Mike

#13 Sarkikos

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Posted 13 January 2013 - 01:23 AM

Mark,

I'd like to see a comparison between the Sterling and the Televue!


Here you go http://www.cloudynig...hp?item_id=2729

Excellent review by BillP


Thanks for linking to Bill's excellent comparison. I'd forgotten about that article. And since his comparison was among 24mm-26mm eyepieces, it is apropos to my own comparo of eyepieces for the Horsehead.

The objects that Bill viewed which come closest to the Horsehead - a dark nebula against a faint "bright" nebula - would be M31 and M42. The ZAO-I took an A for those objects, but the Sterling 25mm had a solid B. Second place went to the Meade 5k SWA 24mm, which got a B+. Ironically, I have one in my equipment case, but didn't think to try it on the Horsehead. Next time, I will.

Not surprising to me after my comparo, the Brandon 24 and the UO Abbe Ortho 25 only received C's in this category in Bill's comparison. My Brandon 24 got a C+, but I don't expect the results to completely agree. After all, the Horsehead is a somewhat different critter from the Andromeda Galaxy or the Great Nebula in Orion.

Bill gave the Televue Plossl 25mm a grade of C for M42/M31. So I'm not too disappointed that I forget to bring out my own TV Plossl for the Horsehead. Though I do wish I'd brought out the Meade 5k SWA.

Mike

#14 Sarkikos

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Posted 13 January 2013 - 01:35 AM

FYI, the Sterlings are 15% off from Smart via their eBay store since Jan 1.


I already have one of each of the Sterlings from 12.5 to 25mm. They are now resting securely in my deep-sky case.

I thought about getting another 25mm to make a bino pair. But I already have plenty of bino pairs. Besides, I only binoview the planets and the Moon. I monoview DSO, because I like to get the highest level of transmission I can when hunting for the faint fuzzies. So one Sterling 25mm will be sufficient for my purpose. I've got pairs of Brandons, Paradigms, BGOs, UO's and TV Plossls for the binoviewer.

:grin:
Mike

#15 BillP

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Posted 13 January 2013 - 01:11 PM

... I did spend nearly an hour on the Horsehead and the five eyepieces. For me, that is an enormous investment of time on any object that is not a planet or the Moon. I didn't start observing the Horsehead until about 10:45 pm, so my eyes had been dark adapting for over four hours. Also, over the course of my observations of the Horsehead, the sky was consistently transparent.

And for what it's worth, at the beginning of each observation with each new eyepiece, I would get my bearings by going back to Zeta Orionis (my Dob does not track). Even through an O-III filter, I'm sure this reset my eyes to an adequate base-line level of dark adaptation. Then, before I started viewing the Horsehead again with each eyepiece, I put the Dark Apparel hood back over my head to help my eyes dark adapt better and to shield them from ambient light.


Excellent approach :waytogo: :waytogo: The Horsehead is a real challenge object. That being said, it will IMO reveal subtle differences between eyepieces more readily as you are working at the limits of their capabilities. Really and excellent and valuable shootout. You should put this is a review format and submit to CN to institutionalize it better than a thread can ever do. We need more reports and comparisons like this IMO for targets other than the planets. I'm not a dark-site observer and just view from home. As such, the Horsehead is one object that I have still not seen...even after all these years of observing. I have tried many times but never have had the pleasure of seeing it. So I really loved this review as got to see it through other's eyes :bow:

#16 Sarkikos

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Posted 13 January 2013 - 02:00 PM

Thanks. I got lucky this year because I've had more opportunities to observe. Usually the last observing session at my dark site is in November. I can deal with temps down to the '20's there, since I can take breaks in my vehicle. But any chance of ice on the field will keep me home. I might even be able to go back around New Moon in February or March! Most years I'm stuck here in red zone suburbia from Turkey Day to Tax Time.

I've thought about submitting articles but have never done it. Maybe I'll look into that and finally submit something.

Mike

#17 Jeff Morgan

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Posted 13 January 2013 - 05:25 PM

Nice post and links Mike, I will have to obtain a couple of BGO's.

#18 Sarkikos

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Posted 13 January 2013 - 05:31 PM

Happy Birthday, Bill!

:thewave: :band: :banjodance: :bounce:

#19 GeneT

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Posted 13 January 2013 - 08:44 PM

These direct comparisons are both very interesting and helpful. :applause:

#20 Starman81

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Posted 13 January 2013 - 11:53 PM

Nice shootout Mike! I like the idea of twist-lock adapter + spacer ring + filter for easily cycling in different eyepieces.

#21 Sarkikos

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Posted 14 January 2013 - 07:01 AM

Yes, I try to avoid screwing filters on and off, especially at a dark site.

That's why I have filters preloaded in my 1.25"-filter wheel before I leave the house. Although there are 2"-filter wheels, I never thought they'd be useful in a Dob. I'd probably have to put a Barlow or Barlow lens cell in the neck of the wheel so the eyepieces would come to focus. That would shorten the effective focal length of the eyepieces, increasing the power and negating the advantage of using 2" eyepieces. Would not make sense to me. :shrug:

But if you're going to switch out eyepieces and keep the same filter, screwing the filter onto an adapter makes sense.

Mike

#22 Dave Ittner

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Posted 14 January 2013 - 11:52 AM

Dumb question .... why would the spacer ring be needed in the configuration you mentioned above?

#23 Sarkikos

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Posted 14 January 2013 - 12:00 PM

I wasn't absolutely certain that the ring would be needed. But on the other hand, there was the chance that the end of one of the eyepieces could contact the filter and damage the filter or the eyepiece or both. Why waste time trying every possible eyepiece I might use in order to determine if any might be long enough to hit the filter? The less I have to worry about and the less time I waste at the dark site the better.

Mike

#24 Scanning4Comets

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Posted 14 January 2013 - 02:45 PM

I use a 2" extension tube and leave my filters on it. Then when I want to use the filter I just grab the extension tube and plop the eyepiece in it and put both in the focuser....I can reach focus using this and my eyepieces with the twist lock adapters on all of them. All I have to do is rack the focuser almost all of the way in.

I can also reach focus with the twist lock adapters which are permanently on 3 of my eyepieces w/o the extension tubes. All I have to do here is rack my focuser almost all of the way out. :cool:

It literally takes seconds to do this, and I would rather do this than screw filters onto eyepiece or adapter threads.

However, a 2" filter wheel would be a lot better than both methods! Just turn the wheel to see filtered / unfiltered views!

#25 Sarkikos

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Posted 14 January 2013 - 10:33 PM

I've come close to buying a used 2" filter wheel. But I never do because I remember I'd have to bump up the magnification with a Barlow or Barlow lens cell in order to come to focus in my Dobs. What's the point of using a low-power wide-field eyepiece if you have to double the magnification in order to use it? Then it's no longer a low-power wide-field (TFOV). I might as well stick to 1.25" eyepieces in a 1.25"-filter wheel.

Mike






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