Interchanging binoviewer and single eyepieces

[AlentejoSkies]

Hi,

Just taken delivery of a mint used William Optics binoviewer (Thanks Wayne!) and it's wonderful.

I want to use it for now on my homebuilt 6 inch f/8 dob. I have no problem with cutting the OTA a bit shorter, but I wondered how people manage to combine binoviewer and single eyepieces. If I move the primary up 100mm I can use the binoviewer with the supplied 20mm eyepieces, but will have no way of reaching focus without it. I can add the 1.5x Barlow to the binoviewers, meaning I only need to find 50mm, or increase Barlow power by stacking a couple of units, to make it almost parfocal with single eyepieces, but rather inelegant, and only high power.

Do you binoviewer experts out there shorten the OTA and use extension tubes when not using the binoviewer? Or always use the binoviewer and buy two of every eyepiece?

Focuser is GSO single speed Crayford with 32mm total travel.

Thanks for any advice,

Douglas

[Tris]

For me binoviewing was a one way trip and I never went back to single eyepieces again because I see so much better and am so much more comfortable using two eyes. My Denk bino has a powerswitch, but to be honest, I don't even use that very much. It's just as easy to change to different eyepieces on the few occasions I want to zoom in or out. 

[Louis D]

Make sure to recalculate how much of your primary rays won't be reflected by your secondary when you shorten your tube.  It might not be an issue if it was sized to illuminate a 2" eyepiece and you'll only be using 1.25" eyepieces with no larger than a 23mm field stop (these binoviewers have a 22-23mm clear aperture).

[AlentejoSkies]

Ouch, thank you Louis D, there is an issue... I need to re-check the calculations but it seems like the fully illuminated field falls to almost zero. And I need to think a bit about the effect of that - or maybe just try it out. I think that I will try it out for a while as things are, moving the primary temporarily and if I still like it as much after a few months as I do now, start redesigning. At the moment it seems like the advantage of the brain having two images to work with is so significant that it's worth rebuilding specifically to make that work as well as I can. A one-way trip indeed!

[MrBill]

I use the Williams binos all the time for planetary and lunar viewing, so I shortened my trusses a bit so that they just come into focus with the 1.6x barlow attachment mounted on them and the focuser nearly all the way in.  With my focuser I can still get regular eyepieces to come into focus with the focuser most of the way out.  Honestly though, the solution I've found is that I have one scope pretty much dedicated to lunar / planetary that the binos live in and another scope for DSO's where I use 2" wide field eyepieces.

Since I only use the binos for solar system viewing there's no problem with keeping the barlow unit in line, I mainly use 15mm and 12mm pairs of eyepieces with them, sometime on rare occasions some 10mm.

They are a real godsend for me.  I have terrible floaters these days which really interfere with high power viewing but with the binos they just disappear as my brain fuses the two images and filters them out, it's like magic.

[brantuk]

Like MrBill - I only use my bv's in scopes with a large range of focus like sct's or maks and certain fracs. They only come to focus in some (not all) of my fracs, and I wouldn't mod a newt to make them fit - certainly not by sawing tubes or moving mirrors - and in dobs they'll create all sorts of balance issues.

That's not to say you can't or shouldn't go modding your gear - if you like tinkering then why not - I just like the idea of having one or two dedicated scopes I can use the bv's with. As well as being ideal for planets/moon - bv's can also produce some pretty stunning "3D like" star fields when dso hunting.

[AlentejoSkies]

Experimenting again last night, got some fantastic views of Jupiter at about 180x using two stacked 1.6x barlows. It's the only combination I have that reaches focus. Tantalising that I can't try lower magnifications without making some modifications. I am very tempted to move the primary up a bit...

My second scope, the first refractor, coming next month with 80mm focuser travel will give a bit more freedom to play around. I think with a 1.25 " prism diagonal I should reach focus with no barlow, and see how those 3D star fields look like.

It was a really calm night last night, which contributed a lot to the great view, but it was also very noticeable that I was staying at the eyepiece much longer and enjoying it more with the two eyes.

[Tris]

I was out last night too and Jupiter did look fine, even through intermittent this cloud. The bino was faultless, and so comfortable and relaxing. I was playing with Starry Night and Meade Autostar on the laptop. I wonder if I actually prefer the Meade programme for guiding the scope? It seems easier on the eyes at night.

My 'scope seems to lose alignment slightly and "synching never really seems to work very well. I've found a new (to me) way of aligning the scope during a session. Just slew it to Jupiter or similar, then loosten the knobs, and put J in the middle. Job done. The 'scope thinks it is pointing at Jupiter, and it is pointing at Jupiter.  Obvious, really - but I'm a slow learner.