OOUK newts with binoviewers?

[Mike73]

I tried binoviewers a few years ago in a 180 Mak which was enough to prove just how good binoviewers are for planetary and lunar observing and I'd like to try them again but in my OOUK VX12L for the upcoming Jupiter and Mars opposition.

Has anyone on here tried BV's in a OOUK newt? 

The VX12L has a low profile focuser, I have to use a 2" extension just to make any of my EP's come to focus. Will it just be a case of taking that extension out to make the BV's come to focus (because of the extra in focus BV's require)?

How do I work out the focal length with BV's in place so I know what EP's I should pick?

Baader maxbrights or WO BV's? I've read the Maxbrights are slightly better but are they worth the extra considering they are only going to be used for the planets and moon?

[Avocette]

I don't have an OOUK scope but for my SW 12" Flextube I reduce the truss length by 10cm to bring my WO binoviewers to focus with the supplied 20mm EPs. It could be quite frustrating if BVs don't quite focus with your fixed tube design!

I toyed with getting Maxbrights but reckoned that the marginal benefit against the WO BVs was offset by the 12" light grab especially for lunar and planetary.

[John]

I tried a pair of the William Optics ones with my 12" F/5.3 newt Mike.

I seem to recall I needed the barlow attachment but they worked OK. I didn't get on with them but thats for different reasons than the scope. I couldn't get them to focus in either of my refractors.

[Mike73]

I tried a pair of the William Optics ones with my 12" F/5.3 newt Mike.

I seem to recall I needed the barlow attachment but they worked OK. I didn't get on with them but thats for different reasons than the scope. I couldn't get them to focus in either of my refractors.

Thanks John.

Yes I kinda thought the supplied x1.6 would help and thats reassuring to know that it will come to focus at least!

I had a similar problem with my WO's but only one eye would come to focus properly, now I'm not sure whether it was user error in me not setting the BV's up correctly or something else??

WO state they have a 20mm clear aperture but the Maxbrights state 23mm, does this just effect the view brightness or is it actually robbing you of resolution?

Lots of questions.  

[niallk]

Just a side comment: my 2.5x Powermate allows me to focus my Maxbrights in my 15" without trimming poles, whereas I couldn't with my Baader 2.5x GPC - which is what I use in my 250px to reach focus.

Not sure if the telecentric nature of a PM might be useful here in the context of binoviewers(?): I only mention it as if you have one, it might save on the added cost of a GPC - €95 from TS for a Baader.

I have a notion some day of having a second set of truss poles for low power binoviewing of DSOs.

[Stu]

The optical path length for Baader Maxbrights is quoted at 110mm so it looks like you would still need a Barlow to reach focus.

TS seem to quote path lengths on many of their bits of kit which is very handy.

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p482_Baader-Maxbright-Binokularansatz-mit-1-25x-GWK---1-25--Adapter.html

If you are using them for lunar and planetary then this is not really an issue, it means you could use longer focal length, more comfortable eyepieces whilst still achieving good mag levels.

I never really got my head around working out the effective focal length with the Barlow but in theory if you know the path length of the BVs and the power of the Barlow it's possible to calculate it.

Like John, I never really got on with binoviewers despite trying three pairs! William Optics, Maxbrights and finally a pair of Denks. The Denks were by far the best and easiest to use, I found collimation of the images difficult in the others, the Denks just worked. Still didn't enjoy them though

[niallk]

Televue have a chart of mag vs focus position for PMs - I think this is relevant to their use when binoviewing, and means you see less magnification. There's a fair chance I'm misinterpreting though...

http://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_app#.VhoetIlwbqA

[Stu]

Televue have a chart of mag vs focus position for PMs - I think this is relevant to their use when binoviewing, and means you see less magnification. There's a fair chance I'm misinterpreting though...

http://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_app#.VhoetIlwbqA

My understanding is that Barlows are used rather than PMs when you need to push the focal point out enough to achieve focus. The issue with Barlows is that the magnification increases with distance from the eyepiece so a x2 Barlow attached to a BV gives for more than that compared with when used just with an eye piece. Do PMs push the focal point out in the same way as Barlows (he says falling off the edge of his cliff of ignorance )

[John]

.... PMs push the focal point out in the same way as Barlows (he says falling off the edge of his cliff of ignorance )

I'm teetering on the brink of the same cliff but I think Powermates and TeleXtenders don't move the focal point.

[Stu]

I'm teetering on the brink of the same cliff but I think Powermates and TeleXtenders don't move the focal point.

That was my understanding too, but......

[Mike73]

Thanks for the help guys.

Looking at this the only inward travel I will need is 31mm which should be no problem with the 2" extension removed.

Stu I have looked at Denks but that a lot of money considering I'm perfectly happy with mono viewing for DSO's. Apart from the focus issue I really did enjoy using BV's on Jupiter though, no more cheek cramp from prolonged squinting. 

[Stu]

Thanks for the help guys.

Looking at this the only inward travel I will need is 31mm which should be no problem with the 2" extension removed.

Stu I have looked at Denks but that a lot of money considering I'm perfectly happy with mono viewing for DSO's. Apart from the focus issue I really did enjoy using BV's on Jupiter though, no more cheek cramp from prolonged squinting.

That looks correct with the 2" GPC fitted yes. Just need to work out if that just gives X1.7 or whether it gives more when fitted to the BV. It's very easy to end up with too much mag.

I got a nice used pair or Denks for around £300, sold them for the same. I found the need to adjust the eyepiece positions to get good collimation at high power a right pain on both the other pairs I had, but maybe that's just me!!

[Peter Drew]

Hope their's space for me on that "cliff" . I thought that power mates moved the focal point but didn't increase the magnification beyond their native prescription. 

[Stu]

Hope their's space for me on that "cliff" . I thought that power mates moved the focal point but didn't increase the magnification beyond their native prescription.

It's ok Peter, as we each fall over the edge it creates room for the next

I'm sure you know far more about this than we do, so please step back from the precipice and leave this to us true ignorants

[JED-E3]

If you have an eyepiece correctly focused, take it out and put a powermate in front of it will still be focused however they do move the focal point, basically if the powermate is 'inside' of focus it pushes the focal point outwards. 

It's easy to see in practice if you rack your focuser inward and then lift the eyepiece out of the powermate until it comes to focus.

This is certainly the case with the 2.5x Powermate, I use one with a binoviewer quite often.

James.

[John]

Some interesting stuff on Powermates there

I'll try and get back up the cliff somehow !

[Stu]

If you have an eyepiece correctly focused, take it out and put a powermate in front of it will still be focused however they do move the focal point, basically if the powermate is 'inside' of focus it pushes the focal point outwards.

It's easy to see in practice if you rack your focuser inward and then lift the eyepiece out of the powermate until it comes to focus.

This is certainly the case with the 2.5x Powermate, I use one with a binoviewer quite often.

James.

If I read that correctly it just means that the PM acts as if it wasn't there ie it only pushes the focal point out far enough to take account of its own length. Is that right?

A Barlow must push it out further in order to be used in the way it is to create more infocus? Yes/no?

Desperately clawing at the base of the cliff whilst the tide comes in.....

[JED-E3]

If I read that correctly it just means that the PM acts as if it wasn't there ie it only pushes the focal point out far enough to take account of its own length. Is that right?

A Barlow must push it out further in order to be used in the way it is to create more infocus? Yes/no?

Desperately clawing at the base of the cliff whilst the tide comes in.....

It only pushes the focal point out far enough to account for its own length when at the correct focus point for the eyepiece used.

I just checked with my 2.5x PM, I focused it and then racked the focuser in 5mm then lifted the eyepiece out of the PM and it was 25mm up before it came into focus again. It's this effect that is useful when binoviewing.

I can't visualise how a ray trace of this would look compared to a barlow, though I'd be interested to see it, I just know that it works.

James.

[Stu]

It only pushes the focal point out far enough to account for its own length when at the correct focus point for the eyepiece used.

I just checked with my 2.5x PM, I focused it and then racked the focuser in 5mm then lifted the eyepiece out of the PM and it was 25mm up before it came into focus again. It's this effect that is useful when binoviewing.

I can't visualise how a ray trace of this would look compared to a barlow, though I'd be interested to see it, I just know that it works.

James.

Thanks James