Setting up Binoviewers

[brantuk]

Hi folks - I need a little help setting up my nice new binoviewers on a WO Megrez 72 (F6) focal length=430mm. I tried to focus down the street, and in the distance - but nothing (with or without the 1.6x barlow).

The only thing I could focus on was a tree in my own front garden 10 ft away - and that was with the focuser turned full in.The moment I pulled it out a bit everything blurred up. Tried adjusting the 20mm ep's in several positions accross the full range of in-focus and out-focus but still nothing

I really thought they'd be plug 'n' play but clearly I've no idea what I'm doing - any help would be much appreciated.

Cheers

[kniclander]

the problem is that the binoviewers add so much length to the optical train that you do not have enough infocus. the solution is to get a more powerful barlow (preferably one where the lens screws off the body) or (and I don't recommend this...) shorten the ota...

problem with the more powerful barlow is that the mag is greatly increased by the distance between the barlow and the e/ps so you can only binoview at high powers. Siebert Optics make some quite expensive adaptors that will make standard binoviewers work at lower mags with most scopes.

[red dwalf]

they should work alot better on your cpc 800 sct,

the pair i borrowed worked amazingly on the Moon

[brantuk]

Thanks for the quick response chaps. Yup I got them primarily for the cpc but wondered what the issue was on the megrez. I only tried it on there cos I saw a WO advert with them attached to a doublet - slightly misrepresented I think but.... whatever. I'll be using the megrez for imaging anyway (I think lol) Thanks again

[martin20]

I had exactly the same problem with the same combination. After much trial and error my eventual solution was to get 1.25inch WO diagonal from FLO. I then screwed the 1.6 barlow to the tube facing end of the diagonal and and used the binoviewer as normal in the other end.

This got me into focus without any problem, although it did increase the magnification.

[brantuk]

Thanks Martin - I'll give that a try - I've been using a 2" dielectric diagonal in the hope of getting as much light as poss through the setup - but I'll certainly give it a go with a 1.25".

Cheers

[brantuk]

Well Martin - first of all sorry for calling you Ian - dunno why - head/finger coordination first thing in the morning or something.

Secondly - you're my hero - it works with a Celestron Starbright 1.25" diagonal. I even have enough focus travel now to adjust it on distant objects - but I'm totally mystified! (not hard to do with me lol).

Why would a smaller diagonal make that much difference? Is it just the larger size of the 2" diagonal pushing it out of focal range? Or is it more subtle than that?

Thanks again Martin

[martin20]

Glad it's sorted.

It's actually not really the size of the diagonal that's made the difference. It's more that, because it's a 1.25inch, the filter thread on the tube facing end is the correct size for the 1.6 barlow. This allows you to get the end of the barlow further into the tube and resolves the in-focus problem.

[Andrew*]

Hi Brantuk,

You may find this thread useful. I found out the magnification achieved with various combinations of barlows and diagonals with a binoviewer. They will not be exact in your WO, due to the different designs, but they will be very close.

Further down the thread is a more accurate result, showing that an eyepiece in the binoviewer in a 1.25" diagonal with the 1.6x barlow on the end, will magnify 5 times as much as the native eyepiece. Therefore a 20mm eyepiece acts as a 4mm eyepiece.

You get more in-focus the further the barlow is from the eyepiece. Also, a smaller diagonal has a shorter light path, so it will bring the eyepiece closer ot the objective = more in-focus. I think there is a huge market for more angled binoviewers, so a diagonal is not needed.

HTH

Andrew

[martin20]

Also, there's a shorter light path through the 1.25" vs the 2" diagonal.

[martin20]

Oops! Didn't spot Andrew's post.

His was much more informative anyway.

[brantuk]

Ahh - it's all making sense now - Thanks Andrew and Martin.

Andrew - did you mean to put a link in there? I'm now itching to see that thread so I can experiment with various combo's of barlows and diagonals.

Cheers Chaps

[Andrew*]

Ooops! Sorry mate. Here it is: http://stargazerslounge.com/equipment-discussion/100507-magnification-factor-barlows-binoviewers.html

[brantuk]

Thanks Andrew

Just been reading it - will have to again cos there's a lot of info there - just the stuff I needed

Thanks again.