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Ships and Stars

Binoviewing the Horsehead and Flame Nebula

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Hi all, a bit of a long-winded one here but hopefully interesting.

Clear moonless skies yesterday, so set off late afternoon for my dark sky site, somewhere between 21.90 and 21.92 supposedly (Note: would like to obtain SQM-L for actual at-the-time readings, seemed to be a bit more early evening LP on the horizon this time, but still exceptionally dark).

I always forget to bring something. Well… this time it was nothing less than my finderscope, I had it with all my gear going out the door, but left it tucked against the sofa… needless to say, this made alignment with a 2m tall, 2000mm focal length 500p an absolute nightmare in windy conditions, and it took ages to find my alignment stars in the EP (21E is the widest I currently have) and I really struggled to achieve a proper alignment for much of the evening which greatly curtailed the number of stops I made, but on the upside, I spent more time studying the targets I did acquire.

Anyway, soldering on, I had 25-30mph gusts for the first few hours so I moved my van to act as a windblock but the wind kept veering north until it finally died down. Thought scope was going over a few times, and that weighs a good 75kg. If I unlocked the clutches, it would freely weathervane around!

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First stop – IC 405 Flaming Star nebula, 21E & Astronomik OIII – excellent – nebulosity just seemed to keep going out out out, away from the central area.

Blue Snowball NGC 7662– Leica Zoom and TV 2X Powermate – got to around 300-350x before view came apart, but nice to pay a visit.

Bubble Nebula & M52/NGC 7510 – 21E again, very nice.

M1 Crab Nebula – I understand this is a lot fainter than when it was first catalogued, still, an easy one to spot and good nebulosity under these conditions.

M31,32,33, M110 (M31 naked eye) – binoviewers! Awesome. Can only recommend. Please see notes on slightly unusual 40mm eyepiece choices below.

M36,38, NGC 1893 – lovely star clusters in the neighbourhood of IC 405

M42 – always a must see. Tried the Trapezium Cluster at 350x to 450x, got the four stars sharply at lower mag, couldn’t get more at higher mag, sky wasn’t having it. The nebulosity around M42 just kept going and going and going… best views with 21E and no filter, OIII was good to excellent, but in the end, preferred without filter.

Double Cluster (naked eye & 12x70 binos).

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Horsehead B33, IC 434, NGC 2023, Flame Nebula NGC 2024 – I spent a lot of time last night doing a few eyepiece experiments on the famous B33 Horse Head and Flame Nebula – the Flame I sort of forgot last time in my obsessive quest for the HH, so gave NGC 2024 due admiration this time. This is only the second time I have seen B33, but the views were even better last night.

I finally slewed on target with the 21E and OIII. Right after Alnitak came in the FOV, I noticed the Flame was immediately visible with direct vision, so I figured this was a good sign.

I then swapped to a 27mm Orion (fittingly) ‘Flat Edge’ EP with Astronomik Hb filter and moved down to B33. It was immediately apparent with direct vision, just a huge dark bulge jutting out into IC434. Excellent!

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Crazily enough, I’ve wanted to try B33 for some time through binoviewers (or a binoviewer). I assumed that in a 20” dob, splitting the light still roughly equals using a 14” binoscope, plenty of aperture under these dark skies. I imagine someone out there has tried binoviewers on the Horsehead, but I haven’t read any reports or comments about binoviewing the HH online, so gave it a shot - I broke out the WO with 1.6GPC which goes in a Baader clicklock 2” to 1.25” adapter straight into the focuser to get the BV as close as possible to the secondary to reach focus.

BV eyepiece choice – this is where it gets kind of interesting. I used 40mm 1.25” Revelation plossls that cost me a whopping £22 each from Telescope House on special.

Why 40mm EPs in an f4 scope, especially for very faint DSOs? A fellow SGL member (thank you again @jetstream!) pointed out before there is a ‘false exit pupil’ dynamic whereby the BV splits the light and reduces the exit pupil area by 50%, if I understood correctly. With 40mm EPs at 1.6x in a 508mm f4 dob with 2000mm focal length, this gives me 80x mag and twin exit pupils of 4.49mm, not the usual 6.35mm that a single 40mm ep (with 1.6x GPC) would normally provide. By the way, the 40mm would give 10.6mm exit pupil with no barlow on its own.

I realise the FOV is probably only around 40deg but it gives a low 80x magnification which is close to what the bbastrodesigns visual detection calculator recommends for some of the fainter DSOs (85x) in my scope. FOV doesn’t matter for the HH in my opinion anyway, as I want Alnitak well out of the picture, so to speak.

Here’s what I came up with:

Binoviewer ‘false’ exit pupil:

(508x508)/2 = 129032

Squrt129032= 359.2102448427661

Therefore, a pair of 40mm eyepieces with a 1.6 barlow in a binoviewer is not an individual 6.35mm exit pupil (508mm/80x mag = 6.35mm), it is actually 359.21/80 when split, which equals a 4.49mm exit pupil for each eye.

Roughly calculated…

40mm EP with 1.6x barlow = 80x   = 4.49mm exit pupil.

40mm EP with 2.0x barlow = 100x = 3.592mm exit pupil

32mm EP with 1.6x barlow = 100x = 3.592mm exit pupil

32mm EP with 2.0x barlow = 125x = 2.874mm exit pupil

25mm EP with 1.6x barlow = 128x = 2.806mm exit pupil

20mm EP with 1.6x barlow = 160x = 2.245 mm exit pupil

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So did binoviewers work on the Horsehead?

Absolutely 100% yes! I saw the Horsehead with both direct and averted vision through binoviewers with as Hb filter on the nosepiece, no maybes or buts, a definite hit, and could see IC434 running along the dark dust cloud. I couldn’t quite make out the small notch for the nose, but was really close.  The windy conditions actually made it a little easier to see at times as it shook the scope during the gentler gusts, kicking in some averted vision, but I'd still prefer it calm.

The only drawback is the massive amount of eye-relief from the 1.6x barlowed 40mm EPs, which must be huge as I had to hold my head well back from the eyepieces. This meant eye placement was critical and extremely limited. I want to try 32mm EPs next, those are in the post along with some 25mm EPs and a solitary 42mm 70 deg finder EP. 

One thing I found a necessity for the best views of the really faint stuff - a hood or towel over your head, even under starlight. The huge increase in contrast and ease of viewing seems to far outstrip most other factors such as particular make of eyepiece, coatings, etc. The boost in contrast was substantial. I have a down parka with a big hood that has an integral wire brim which I gently fold around the EP or binoviewers. The more incoming light you can block out completely, even reflected from the ground below, the better. The stars were bright enough I could see my feet and walk around easily once dark adapted. Those small but annoying LEDs from the GOTO unit, dew controller etc etc were all covered up with a raincoat. Total darkness is the goal, aside from what’s coming out of the eyepiece. That makes a big difference in my book and really lets me focus on what's in the glass.

I later tried the UHC filter in the BVs and managed to see the HH with direct and averted vision. Here, averted vision was definitely better and things were quite washed out and really lacking a lot of contrast at this stage in comparison to the Hb filter.

Next trick was dropping in the 20mm WO eyepieces, but too much mag (160x I think) for binoviewers and things just turned inky black with the Hb, perhaps I should have tried the UHC here.

Which was better – a single EP or BVs?

Both! Really interesting, both have pros and cons.

I later switched to a single 17.5mm Morpheus and got a really contrasty view of the HH with Hb filter. It loomed large in the eyepiece and was immediately unmistakable. I didn’t quite get the nose detail, but the huge lump projecting out into IC434 at 114x was near impossible to miss.

Considering I only have bog standard binoviewers with ultra-low end eyepieces and a small 1.25” nosepiece which projects well into the large light cone coming out of an f4 dob, I was really impressed. It had reduced contrast and a slight reduction in overall brightness in comparison to using a single EP, but was this was largely countered by greatly reduced eye-strain and the benefits of binocular vision. I would say there was no more detail with either set-up, maybe a slight edge to the 17.5 Morpheus or 27mm Flat Edge, but being able to see the HH directly with both eyes was a genuine pleasure I will remember for a very long time.

I think with some large bore Denks/powerswitch or some crazy Siebert binoviewers, higher-contrast EPs and the 45mm OCA for fast dobs, this would match or exceed the solitary Morpheus views. By the way, I wish Baader made 2” wide-field Morpheus EPs!

Flame nebula was wonderful with the binoviewers, not as contrasty as the single Morpheus, but great to scan across. Hb filter worked better than OIII here. The Hb on the Morpheus was also excellent, probably the best view there of the lot.  I really like the Flame Nebula, especially with the dark lane in the middle, a nice one to admire.

One thing I note – I don’t think Orion ever gets very high in the sky here at my latitude (57-ish). Viewing from very dark/excellent skies further south (La Palma! Morocco? Alps?) must be excellent.

The site I use in the Cairngorms is very dark indeed and supposedly 21.90 to 21.92SQM according to the LP map. However, I noticed considerable skyglow on the horizon, right under Orion as a matter of fact, so not sure where this is coming from, perhaps from the Central Belt starting some 70-80 miles away. Not sure some of this wasn’t zodiacal glow either, but not 100% on that. Either way, it was definitely excellent overall sky darkness, winds and turbulence in the atmosphere aside which limited magnification and seeing, but if Orion was another 10deg up, it would make a noticeable difference.

Once the scope was packed around 2am, I spent about 20 minutes with my trusty 12x70 Cometrons just taking everything in. Any trace LP visible on the horizon had dimmed a fair bit and the sky was just absolutely incredible. I started at one end of the Milky Way with the binos and did transects across until I had rapidly covered all it. I lost count of how many star clusters and double stars, etc I saw, an excellent way to end the night, despite the self-inflicted finderscope problems and strong gusts which swept through for much of the early evening.

Thanks for reading and feedback welcome…👍

Edited by Ships and Stars
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Great read again @Ships and Stars Sounds like you managed plenty of targets but still had the time to spend on each one.  Looking around with the binos must have been awesome too!

There was a comedy picture of a Skyliner 200P next to a tabletop Dob recently... it's how a picture your 500P next to a 200P 😁

Edited by geeklee
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There is always something that gets forgotten, regardless of how much detailed items you may have packed. However a superb and varied session Robert with an interesting comparison when using binoviewers. My quite exposed site was surprisingly wind free last night, good plan to use the van as a wind break. IC 405 is a nice target and as you mention, it is easy to slip into observing many of the close by open clusters contained within Auriga. I did not observe M42 and M43 until much later keeping with the particular dimmer subjects, when I did focus attention on the Orion Nebula, the intensity of colour and bright expansive nebulosity was very impactful.

Skyglow when you are least expecting it can be alarming and vary throughout the session. At my location there is some in the south east, but as transparency improved it diminished, Newcastle Airport is the culprit which is stupidly lit up, at least the area is not in a flight path zone, just instead the occasional shooting star.   

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15 minutes ago, geeklee said:

Great read again @Ships and Stars Sounds like you managed plenty of targets but still had the time to spend on each one.  Looking around with the binos must have been awesome too!

There was a comedy picture of a Skyliner 200P next to a tabletop Dob recently... it's how a picture your 500P next to a 200P 😁

Thanks Lee, that's at least the second time I've left the finderscope at home, argh! I have a telrad but there's no place to mount the base so that's going on my smaller 'grab and go' dob (when I get one). 

Just the 12x70s bins were amazing, star cluster after star cluster out there!

I'm definitely keeping the 500p but will be looking soon for a 10"-14" dob to play around with after my 200p newt on EQ5 is sold. Looking for one that's scratched and generally beat up but optically ok, preferably a flex-tube. The 500p can be a handful to set up just for quick sessions (e.g. under an hour or two).

Cheers!

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The maximum field stop the 1.25” binoviewers is not very generous. I was looking at larger binocular options and went with a conventional type over a split system. Even with all that loss it’s interesting to hear you still had a good view. Binocular viewing has a noticable benefit over mono. https://www.bbastrodesigns.com/30/30 inch binoscope.html  It’s just hard to obtain, though interesting to see that this might be about to change (if you have a 3D printer). https://analogsky.co

 

peter 

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4 minutes ago, scarp15 said:

There is always something that gets forgotten, regardless of how much detailed items you may have packed. However a superb and varied session Robert with an interesting comparison when using binoviewers. My quite exposed site was surprisingly wind free last night, good plan to use the van as a wind break. IC 405 is a nice target and as you mention, it is easy to slip into observing many of the close by open clusters contained within Auriga. I did not observe M42 and M43 until much later keeping with the particular dimmer subjects, when I did focus attention on the Orion Nebula, the intensity of colour and bright expansive nebulosity was very impactful.

Skyglow when you are least expecting it can be alarming and vary throughout the session. At my location there is some in the south east, but as transparency improved it diminished, Newcastle Airport is the culprit which is stupidly lit up, at least the area is not in a flight path zone, just instead the occasional shooting star.   

I usually leave my step ladder or finderscope at home, must be some kind of record 🤣 That ate into a lot of time last night managing without that. The skyglow was a bit alarming and I'm fairly certain now it was distant LP as it seemed to dim markedly late into the evening and wee hours.  There are lots of interesting sights around IC 405, I could spend a while just on that area. Doubt binoviewers will replace my single eyepiece collection, but was happy with how they turned out last night, if I have the money someday and a pair of Denks/Earthwins or maybe Sieberts pops up for sale, I may have to try that. Moving the van around was a necessity, it got a bit bad for a while last night with the wind, thought it would be a show stopper! That caught me a bit off guard.

Next time out I want to try for more galaxies, I was using Dubhe as one of my alignment stars last night, and kept sweeping past tiny galaxies trying to find Dubhe without the finderscope! I was all over the place, haha. Got there eventually. 

Hope there are more clear nights for everyone soon!

 

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11 minutes ago, PeterW said:

The maximum field stop the 1.25” binoviewers is not very generous. I was looking at larger binocular options and went with a conventional type over a split system. Even with all that loss it’s interesting to hear you still had a good view. Binocular viewing has a noticable benefit over mono. https://www.bbastrodesigns.com/30/30 inch binoscope.html  It’s just hard to obtain, though interesting to see that this might be about to change (if you have a 3D printer). https://analogsky.co

 

peter 

Ah yes I probably had a FOV of something like 38-40deg max, haha, not the greatest. I bought the cheapest EPs I could find for this test, they aren't too bad actually, fully coated and blackened where it counts, but the Morpheus and TV stuff is noticeably more contrasty.  The WO binoviewers have the standard 20 or 21mm fieldstop, so any EP over 25mm I believe vignettes. The bigger BVs like TV and Denk, Baader maxbright have 25mm on up to 27mm I think.

I now get eye strain really easily in my right eye (my main viewing eye) so keep flipping back and forth but need to refocus slightly each time, so the binocular view is something I will probably be doing more and more of. Must check out these links, thanks for sending those along.

Thanks Peter!

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1 hour ago, PeterW said:

 It’s just hard to obtain, though interesting to see that this might be about to change (if you have a 3D printer). https://analogsky.co

 

peter 

Just had a look at the analogsky website Peter, these designs look very interesting and I dare say, possibly affordable!

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On 19/01/2020 at 09:07, Ships and Stars said:

Absolutely 100% yes! I saw the Horsehead with both direct and averted vision through binoviewers with as Hb filter

Congrats!

Quite a feat actually, seeing the HH with binoviewers and you are right on the money with the 40mm EP's!  One of my best ever views of the Leo triplet was with the Binotron27's and 32mm TV plossls at f4.8.

Great report and keep the great observing S&S!

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10 hours ago, jetstream said:

Congrats!

Quite a feat actually, seeing the HH with binoviewers and you are right on the money with the 40mm EP's!  One of my best ever views of the Leo triplet was with the Binotron27's and 32mm TV plossls at f4.8.

Great report and keep the great observing S&S!

Thanks Gerry!

I feel like I achieved something here. Not to constantly butter everyone up with tons of accolades 🤣, but I only managed this with the help of you and Scarp and everyone else who has replied to my many and varied posts here on SGL. I've learned a lot and am still learning by leaps and bounds. I will have to take another keen astronomer with me next time to verify that one can binoview the HH under the right conditions/aperture. Someone may well have already done this, but I've never found any online accounts of people binoviewing the HH (someone in the states saw it through a pair of large observation binoculars and then there's the particularly interesting account of the fellow down in the Florida Keys who saw it (or detected it) with 12x70s binos/Hb filters apparently!). I'm sure someone out in Nevada or Texas or Western Australia with a giant 30-32"+ has seen B33 with binoviewers, but haven't read about it. 

This particular dark sky site is about as good as it gets in my neck of the woods, I reckon it's the darkest place within reasonable driving distance of home, even for a weekend. The only disconcerting thing is some obvious skyglow on the horizon from the central belt of Scotland starting about 50-60 miles away (which happens to be right below Orion), but I guess that shows how dark it is there. By 2am when the LP on the horizon was down a bit it was just amazing, and I'm not even sure seeing and transparency were close to optimal (the wind was one clue). Besides a thunderous Milky Way, the sky was ink black and the stars were just intense points of light.

Anything much darker in a Bortle 1/22.00SQM environment would require a trip to a few select places on the West Coast of Scotland, or even a ferry trip to the Outer Hebrides for the ultimate conditions here. 

Exit pupil was never something I paid much attention to until everyone kept bringing it up, haha. I think it made all the difference viewing the HH with the 40mm EPs - I wouldn't have known about the false exit pupil dynamic until you pointed me to the CN post (last time I'll mention this, I promise!)

Next time out there I want to try the 32mm EPs - I ended up ordering 3 sets of plossls (40/32/25) and a 42mm 70deg 'finder' eyepiece for not much money from Telescope House on discount, so that's quenched my binoviewer madness for the immediate future 👍

Maybe you can give the HH a whirl sometime with the 24" and the binotrons/Hb/UHC/NPB! I'm also sold on using a large hood to seal out all extraneous light and getting in the most comfortable position I can and relaxing. My ladder (a freebie, was left by previous homeowner!) has a small platform and a handle on top so I can lean against it in relative comfort.

PS the binoviewers on M31 & Co was a treat, really good - need to do a direct comparison with single EP viewing next time. I'll have to go for the Leo Triplet next time and the Virgo Galaxy Cluster, been wanting to chase these.

I await your next post - my 'grab and go' dob is on the way after selling my smaller Newt/EQ mount yesterday, so waiting in anticipation for that as well. Hopefully that's me sorted on the scope/EP frontier for a good long while!

Cheers!

 

 

Edited by Ships and Stars
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That is a good point concerning using a large hood, this is something I haven't tried, I know that some on here with stray light situations use this method. I might take my hooded down jacket next time rather than my old down, non hooded, smock. Comfortable posture or seated position and becoming relaxed when at the eyepiece, is definitely beneficial, never forget my astro chair, only problem with it being black, I do from time to time stumble straight into it.  

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I got a purpose made good which works well, but suffers from gravity when I look at the zenith through binoculars... good flocking and stray light shields can also help stop stray photons going where they shouldn’t.... unlikely unneccessary in the caingorms!

Peter

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I find a hood helps even in very dark conditions if chasing the faint stuff. Might add more detail to brighter DSOs as well.  Even under 21.9 skies, once fully adapted, I can see the general surroundings and hills and move around carefully without a torch, part of that might be central belt LP, but I reckon a lot is simply from the Milky Way! Iain - I bought some glow in the dark tape - would be ideal for your chair! Peter - there was a small company in the states that made a Monk's hood vest thingy just for astronomy, had large pockets for eyepieces and an absolutely massive hood, haha, function over fashion!

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Yes its quite easy to read the landscape when you are dark adapted, just off in the far distance occasionally there might appear a flare or two, Otterburn military training camp, not directly encountered any pursuing squaddies so far, at least whilst out stargazing. 

Aye glow in the dark tape, I probably have some spare luminous tent guy line around. However perversely it does ensure that I keep my wits about me, when I have the odd stumbling gaff with the chair. No harm done, walking into an open car door or particularly open car boot door has much worse momentary consequences as I have discovered. 

Yep flocking what you can of the inner and painting other parts with Krylon Ultra Flat Black paint can do no harm. 

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I got my observing good from Russia! I use a large forward facing bumbag for holding stuff, but a coat with insulated deep pockets would be better. I  have a box of long life glow in the dark plastic “fish pond rocks”, they are good for marking stuff. I also made some custom clip on dim rid cr2032 powered leds that I pop in sealable plastic bags and use to mark stuff too.

PEter

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10 hours ago, Ships and Stars said:

I feel like I achieved something here.

You sure did! My hat is off to you, S&S!

10 hours ago, Ships and Stars said:

 I think it made all the difference viewing the HH with the 40mm EPs -

Yes, me too. I put a lot of thought into this years ago but never followed up past the 32mm's- just too much to see and try out. I did realize that there is definitely something to the false exit pupil theory and while the experts were bantering back and forth I was trying out things. Spectacular views of certain DSO, brighter ones. The Needle galaxy is another example. I must try at f4 when I get a chance. M42 is beyond belief as well...

Keep up the great observing!

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20 minutes ago, jetstream said:

 

Keep up the great observing!

Thanks Gerry! Seems like everyone over here was desperate for a few decent, clear nights, some good observation reports coming in at last. Hope it's ok your way.

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11 minutes ago, Ships and Stars said:

Thanks Gerry! Seems like everyone over here was desperate for a few decent, clear nights, some good observation reports coming in at last. Hope it's ok your way.

Your welcome!

Here is my obs spot with chair to view naked eye. Some nice meteors coming across lately.

 

IMG_4590.JPG

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9 minutes ago, jetstream said:

Your welcome!

Here is my obs spot with chair to view naked eye. Some nice meteors coming across lately.

 

IMG_4590.JPG

That looks excellent!!

 

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On 21/01/2020 at 23:15, geoflewis said:

Just found this thread, what a cracking read - all of it, but especially the OP by @Ships and Stars

Thanks Geof! I spent a lot of time that night just trying to do an alignment and waiting for the wind to drop at times, but the binoviewer experiment was really interesting, I'd been wanting to try BVs on the fainter objects for some time under good conditions. They are not a replacement for single EP viewing, but do provide a different sort of view with stereo vision, less contrast, but more information, if that makes sense? Next time I'd like to try them on the Virgo Galaxy Cluster and Markarian's Chain etc.  

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This is a really excellent and interesting report- thanks for sharing. Reports like this really help to give ideas for improving observing experiences...

I'm very interested in your BV experience- I have a WO set, presumably the same as yours, but I can only bring it to focus on my 14" by using x1.6 and x2 Barlows. I've been pondering replacing the focuser with a low profile model to get more inward travel- I think you've just provided the final bit of inspiration for me to go ahead with that.

It's also interesting to read about your 40mm experience. I've got 2 Meade 40mm super plossls- but I tried them in the BVs once and it was like looking down a couple of tunnels- not a good view at all. Perhaps if I can go to using the 1.6x Barlow only this will improve.

Finally- I'm going to look into getting an observing hood!

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Depending on the scope focal ratio and the prism size you could be losing a lot of light in the system. I looked at binoviewers and the limited prism size restricted me to (something like) 24mm diameter field stop eyepieces.

Peter

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I use a Binotron 27 with a 45mm OCS for use with steeper light cones. Some say the clear aperture is not 27mm... well the prisms are but the powerswitch is a bit restrictive in 2 modes. Using the center (IIRC) position there is no aperture reduction.

So any 1.25" eyepiece is not vignetted in the center powerswitch position.

Will this translate into real world DSO gains over S&S's system? I would like to think so but would not bet on it....

I can say this- the Binotron 27's on the moon using the 15" give the most fantastic, jaw dropping views I've had and the jaw continually drops- for years now. I believe the Binotron 27's approach if not equal Zeiss Mark 5 optical quality in a much user friendly package- and as we all know its the system that counts espc with binoviewers- a couple of niggles here and there will drag them down fast. ie eyepiece alignment, focuser sag, bino collimation, etc etc the there is the typical GPC issues.

When I purchased the Binotrons I put them in thre focuser, merged for the first time in under a minute and had fantastic views, right out of the box.

S&S has achieved a superb observation with his set up- the HH.

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6 hours ago, Whistlin Bob said:

I have a WO set, presumably the same as yours, but I can only bring it to focus on my 14" by using x1.6 and x2 Barlows. I've been pondering replacing the focuser with a low profile model to get more inward travel- I think you've just provided the final bit of inspiration for me to go ahead with that.

It's also interesting to read about your 40mm experience. I've got 2 Meade 40mm super plossls- but I tried them in the BVs once and it was like looking down a couple of tunnels- not a good view at all. Perhaps if I can go to using the 1.6x Barlow only this will improve.

Finally- I'm going to look into getting an observing hood!

I indeed have the WO binoviewers, but I use a Baader clicklock adaptor to insert the 1.25" nose right into my SW focuser without using the standard adaptor which sticks out maybe 25 or 30mm - that adds a fair bit of inward travel. I looked at the low profile focusers and that would add another 30-40mm inward travel (estimated, not 100% on that), so that should allow you to use just the 1.6x barlow, but try a flush-mount 1.25" adaptor first - might do the trick! You are right about the very restricted FOV with the 40mm plossls, I was using those mainly for exit pupil and target mag (80x). There is a mile of eye relief, so a pair of 32mm EPs might be more comfortable and practical, but worth a shot with the 40's on faint DSOs and see if you have any luck!

5 hours ago, PeterW said:

Depending on the scope focal ratio and the prism size you could be losing a lot of light in the system. I looked at binoviewers and the limited prism size restricted me to (something like) 24mm diameter field stop eyepieces.

Peter

I'm using standard WO binoviewers which are basically the same as all the lower end BVs on the market I believe, so the prism and clear aperture are going to be basic fare. My 500p is f4 so apparently there is quite a large light cone coming out of the focuser. Considering the 1.25" nosepiece is right the way in to allow focus, I am probably missing a fair bit of light there, and some loss from within the binoviewer body/prism itself - the question is how much, and if light loss is concentrated around the periphery of the FOV, or across it. Having said all of that, as Gerry mentions, it could be fairly negligible! Perhaps just a few percent? Or less than 10%? Have to do more research on that, but if I had the money right now, I'd just get some Binotrons and the 45mm OCS (sorry, think I was calling it an OCA earlier!). But I'll play around with the WO setup and my cheap plossls a bit more and see what I can squeeze from them. I'll have to ask the fellow in Croatia who supercharges BVs and see if he has calculated it, and how he would set up BVs specifically for faint DSOs? (same goal as any object though - as much light as possible is the desired result). Lots of details to consider here.

1 hour ago, jetstream said:

I use a Binotron 27 with a 45mm OCS for use with steeper light cones. Some say the clear aperture is not 27mm... well the prisms are but the powerswitch is a bit restrictive in 2 modes. Using the center (IIRC) position there is no aperture reduction.

So any 1.25" eyepiece is not vignetted in the center powerswitch position.

Will this translate into real world DSO gains over S&S's system? I would like to think so but would not bet on it....

I can say this- the Binotron 27's on the moon using the 15" give the most fantastic, jaw dropping views I've had and the jaw continually drops- for years now. I believe the Binotron 27's approach if not equal Zeiss Mark 5 optical quality in a much user friendly package- and as we all know its the system that counts espc with binoviewers- a couple of niggles here and there will drag them down fast. ie eyepiece alignment, focuser sag, bino collimation, etc etc the there is the typical GPC issues.

When I purchased the Binotrons I put them in thre focuser, merged for the first time in under a minute and had fantastic views, right out of the box.

S&S has achieved a superb observation with his set up- the HH.

If I ever make it to a star party and someone has the Binotrons, I'd like to do a rough comparison between the Binotrons/45mm OCS and standard WO binoviewers regarding brightness - it may not be a huge difference, but the Binotrons must give a noticeable boost!

The 40mm plossls are really only the means to an end - detecting the HH. I'll have to try the 32mm plossls next time I have the big dob at my dark site, am hoping eye-relief is greatly reduced. 

I figure that splitting the light from a 20" dob would equal a 14" dob for each eye, minus some light loss from the BV mirrors themselves, so under really good conditions it would be like using a 12"-13" binoscope to view the HH - entirely plausible! Again, I think getting the right exit pupil is critical here, but at the expense of FOV which is frankly terrible unless you are concentrating on planetary nebula or small galaxies, etc. Dropping to 32mm plossls reduces the exit pupil almost a full mm, would be interesting to see what effect that has. I need a good night again with all three pairs of plossls. So many tests, so little time! Making slow progress though. 

A lot to digest here! Thanks all!

Edited by Ships and Stars
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