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The InBetween

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#1 Shorty Barlow

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Posted 13 December 2024 - 06:22 PM

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Over about the past ten years I have utilised a variety of eyepiece pairs with my William Optics e-bino-p binoviewer. I finally reduced this to eight pairs.

 

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I use these predominantly with three particular scopes: 127 mm SW Maksutov-Cassegrain, 102 mm Altair Starwave (ED doublet) and my 80ED Evostar. Although it’s worth pointing out that the BV was originally purchased for use with my 235 mm SCT. The refractors require the 2x Barlow BV nosepiece to achieve focus, effectively halving the focal length of the eyepieces deployed.

 

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Overall these give me an exit pupil range of between around 2.5 mm to 0.5 mm. Useful enough for mostly lunar/planetary observing with a possibility of some DSO’s. In my experience any telescopes used in conjunction with prismatic binoviewers require focal ratios of between f/12 to f/15. Whether this is achieved with Barlows/glass path correctors or not is irrelevant. Any instrument with a focal ratio much faster than about f/10 to f/12 may have difficulty focusing with certain focal length eyepieces. Also, as many regular stereo viewers discover, lower magnifications than usual are often preferable. Apparently the objective size in millimetres is the ideal magnification limit. No greater detail will be observed at higher magnifications than this figure (1 mm exit pupil).

 

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For example; my 80mm Evostar will not produce any better resolution at magnifications above 80x. It may be easier to discern detail at higher magnifications, but the resolution of 1.45 arc seconds (Dawes’ Limit) will not be better; as I understand it. 

 

BV Eyepiece Pairs:

 

1/ 32 mm BCO

 

2/ 25 mm Ohi (Astro Hutech) orthoscopic

 

3/ 20 mm WO SWAN

 

4/ 15 mm TV Plossl

 

5/ 12 mm GSO Plossl

 

6/ 10 mm SvBony aspheric

 

7/ 8 mm TV Plossl

 

8/ 6 mm SvBony WA

 

I had some concerns about the 12mm GSO Plossls after recently witnessing some odd bright and distracting diffraction rings with them when observing Saturn in the vicinity of a bright Moon. There’s nothing fundamentally wrong with the GSO’s but I’ve seen this effect before with them and similar with  some cheap Japanese Plossls (the rubbish Starbase ‘orthoscopic’ Plossls manufactured by the equally rubbish *Kubota Corporation). Not all Plossls are equal and many actually have slightly differently designed elements. Even the appellation ‘Plossl’ is arbitrary. My 15mm Tele Vue Plossls didn’t suffer the same aberration as the others. I also possess a pair of SvBony 10mm 60° aspherics. These are pretty decent, but having plastic housings, and also deploying a polymer element, I wondered about their longevity and eventual replacement.

 

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The aspherics can also often display some chromatic aberration. As I already have a 10mm BCO, essentially all I needed was a second BCO for a 10 mm replacement eyepiece pair. In the end I decided to split the difference and acquire a second 11 mm TV Plossl, effectively replacing both the aspherics and the GSO Plossls. The exit pupils and magnifications are all incredibly similar and I can simplify my collection down to seven bino pairs.

 

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Unfortunately I do not get on with TV eyeguards. When folded down the eyecap will not fit back over them. I don’t generally use the 11 mm’s with the eyeguards folded up in their default position. As I have a spacko right hand that is not easy for me to manipulate in the dark (particularly when I’m stressed out and swear a lot lol). The answer is to pull the guards off, as I don’t need them. The problem then is that the eyecap will be too big to fit back on the eye lens end. In a fit of creative genius (lol) I realised the TV end cap will fit perfectly as an eye lens cap. The TV field lens end caps are difficult for me to remove ‘in field’ as they tend to stick in the cold or damp.

 

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So, I replaced them with slightly looser generic end caps. Problem solved. Compared to the 12 mm GSO’s the 9.1 mm wide 11 mm TV field stop seems slightly bigger. Both Plossl makes have an 8 mm eye relief. I don’t miss the eyeguards at all. Daylight trials at 109x (80ED Evostar) with the 11 mm TV’s are extremely promising, with a wide field stop, excellent colour separation, acuity, and contrast. The EP’s are easily merged and compare well with the 12 mm GSO’s. The barrels fit smoothly into the dioptres with no problems. It was worth paying four times as much as the GSO’s (probably). OK, I’ll readily admit I’m a bit of a TV fanboi. I’m looking forward to using these babes in the night.

 

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*Although, to be fair to the Kubota Corporation, they mainly manufacture tractors, combine harvesters, rice transplanters and vending machines. I don’t know whether they are also rubbish products or not (I personally wouldn’t trust them).


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#2 Highburymark

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Posted 15 December 2024 - 11:24 AM

The 11mm TeleVue Plossls are brutally sharp and bright, I agree. I bought a pair of 12.5mm Tak TPLs with the intention of selling the TV Plossls, but I don’t seem to be able to let them go - they’ve been with me ever since I started solar Ha binoviewing and I’ve enjoyed many spectacular sessions with them - even at 140x they are as good as it gets for solar.
Good solution with your new eyeguards - these eyepieces are worth going the extra mile for.
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#3 betacygni

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Posted 15 December 2024 - 12:24 PM

I find myself very picky with eyeguards as well. In fact I’ll often Frankenstein eyeguards from other eyepieces to my preferred eyepiece. The donors are usually the Baader classic orthos, as I really like batwing eyeguards binoviewing, and their small diameter fit many plossls/brandons/orthos (assuming they have a lip on the top edge).
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#4 Shorty Barlow

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Posted 15 December 2024 - 12:31 PM

The 11mm TeleVue Plossls are brutally sharp and bright, I agree. I bought a pair of 12.5mm Tak TPLs with the intention of selling the TV Plossls, but I don’t seem to be able to let them go - they’ve been with me ever since I started solar Ha binoviewing and I’ve enjoyed many spectacular sessions with them - even at 140x they are as good as it gets for solar.
Good solution with your new eyeguards - these eyepieces are worth going the extra mile for.

There's at least ten years between buying the two 11 mm TV's. I have a complete set of TV Plossls, although I acquired two 15 mm years ago. 

 

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They're very difficult to beat indeed.

 

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The eyeguards were not such a problem with the 8's and 15 mm's.

 

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Until I had a brainwave with the 11's lol.


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#5 Shorty Barlow

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Posted 15 December 2024 - 12:39 PM

I find myself very picky with eyeguards as well. In fact I’ll often Frankenstein eyeguards from other eyepieces to my preferred eyepiece. The donors are usually the Baader classic orthos, as I really like batwing eyeguards binoviewing, and their small diameter fit many plossls/brandons/orthos (assuming they have a lip on the top edge).

I was tempted to Frankenstein the GSO guards, but in the end decided to go commando.

 

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I'm partially paralysed in my right hand so I got bored fiddling with the dioptres and the BCO batwings. Inevitably I 86'd them and went commando with them as well. 


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#6 Shorty Barlow

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Posted 15 December 2024 - 01:14 PM

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SvBony's and original 11 mm TV with eyeguard.

 

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#7 Shorty Barlow

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Posted 17 December 2024 - 10:55 AM

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The 11 mm TV's.

 

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1.25" Baader BBHS Zeiss spec prism with twist lock.

 

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BV with two prism diagonals: Top, the BBHS Baader Zeiss. Below, BBHS Baader Zeiss Amici prism.

 

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25mm AH (Ohi) orthoscopics plus BBHS prism.

 

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#8 Shorty Barlow

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Posted 27 January 2025 - 04:45 PM

I finally got first light on the TV 11 mm Plossls & the William Optics BV. On Saturday I had an early morning session (02:40-04:15 GMT) with my 72ED. It was like looking into a Spring sky. Leo was due south. I saw Mars (in mono) at 140x with the 72 mm Evostar. Although it was much smaller than portrayed in the file below, I could just make out the Syrtis Major plateau. A  Lumicon #8 Wratten helped greatly. It has good transmission for a small aperture. Both bright polar features were visible. I'm assuming the northern one was the NPH. The south may have been actual snow.   

 

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I'd originally decided on the Friday evening with the 102 mm Altair Starwave but the weather put a stop to that. Saturday evening the Starwave did get out. I decided to try the BV on Mars. I had tried earlier in mono with a 7 mm Nagler/2x TV Barlow plus TV Mars filter. The results were not inspiring. So I went with the BV. I swapped the TV Everbright mirror for a Baader BBHS prism plus a Baader Neodymium filter in the diagonal nose.

 

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Naturally Mars was the first target, 178.5x with the 8 mm TV's. Unfortunately the conditions were not so hot & I switched to the Big Lebowski of Jupiter, inevitably replacing the field tested 8's for the untried 11's for around 130x.

 

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I was seriously impressed! The detail was most excellent. I've heard the 11 mm TV Plossls described as 'aggressively sharp'. It's not hyperbole, considering the seeing conditions weren't optimal.

 

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The Galilean moons were well defined discs revealing individual colour. Jovian surface detail was virtually breathtaking and the ice in the White Russian was ... I could see the GRS!

 

The Dude would abide!

 

https://youtu.be/z92bykaeV4o


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#9 Highburymark

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Posted 29 January 2025 - 02:28 PM

I dig your style man. TV Plossls in a binoviewer really tie the view together.
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#10 Shorty Barlow

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Posted 29 January 2025 - 07:22 PM

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Well, there has been a TV decal on my BV case for several years. I thought I may as well put some TV's in it. lol


Edited by Shorty Barlow, 29 January 2025 - 07:38 PM.



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