Binoviewer, ep choice

[Stu]

I'm considering getting another binoviewer, having sold mine a while ago. Would probably get the WO one.

Main use would be with my 106mm apo, f6.7 and I think probably for high power viewing, particularly planetary.

I have a very annoying floater in my observing eye at high power and am thinking this may help.

Best high power views I get currently are with a 3 to 6 nagler zoom, giving up to x230.

My question, what ep's would you suggest to give similar magnifications in the binoviewer? I've thought about another 7mm BGO but that would not be high enough power. Could I use my power mate and still reach focus?

Thoughts appreciated

Cheers

Stu

[nightfisher]

If you get on well with ortho`s short eye relief then how about KK circle T 5mm or a pair of celestron xcel-lx

[Andrew*]

Why not get another 3-6mm zoom? Or is that out of budget?

[Stu]

I did think about that but at £ 340 it its definitely out of budget unfortunately. Even second hand that's too much.

Jules, I'll have a look at the Celestrons, might be a good option.

I think somewhere around 4mm or 3.5 mm gives optimum max magnification so maybe a barlowed 7mm. I think the bino viewer comes with a x1.6 barlow type lens, not sure how good this is?

Cheers

Stu

[angusb1]

How about sterling plossls? 4mm or 6mm would be about £20 each and should work quite well at f6.7. With the 6mms and a 2x barlow you would equal the highest power of the zoom you have, without, you equal the lowest power.

[E621Keith]

How about getting one of those Baader glass path corrector or put a barlow ahead of you binoviewer to give it a magnification boost, and then get a second 7mm BGO?

[Andrew*]

A 1.6x Barlow screwed on the end of a binoviewer acts at about 3x magnification because the optical distance from the eyepiece is so long.

Andrew

[Stu]

Thanks all for the suggestions. I think I'll maybe try another 7mm BGO. Andrew, I assume the x1.6 included with the bino viewer will give x1.6 rather than x3 for a barlow as you suggest? This would give me just over 4mm which would be a good high power

Stu

[Naemeth]

As Andrew says, the distance the light has to travel in the Binoviewer through the Barlow and into each eyepiece means your apparent magnification is increased a lot. As the WO Binoviewers already come with 20mm eyepieces, try using this thread over on Cloudy Nights to try and work out the magnification in your scope, and then you can work out what focal length EPs you will need.

I'm fairly sure that the Binoviewer, as it acts like a Barlow will increase eye relief, so Plossl's or Ortho's may be the only way to go in order to have your eyes close.

[Stu]

Many thanks! Appreciated

Stu

[Stu]

To update, this has proved to be a bit of a journey of discovery which I am enjoying in a slightly pained way!

I have bought a pair of Baader Maxbrights and have been having fun getting them to focus due to the limited back focus in the Astrotech. I have now succeeded, using a shorter diagonal which has T2 threads and makes for a much more solid connection to the binoviewer. I have two 25mm Celestron X-Cel LX ep's which seem pretty good and can reach focus using a x1.7 Baader Glass Path Corrector which seems to give the necessary focus travel without introducing too much CA as I had been getting with a barlow.

I had some excellent views of the moon last night, got round to setting the Sphinx mount up which gave me a nice stable platform to experiment on.

Main remaining problem, I also have a couple of 7mm BGO'S and whilst they focus ok and give a useable magnification, the collimation is way out with them. Not sure if it is production differences between the ep's bought at different times? There is one more adjustment I can try from the instructions which involves loosening the ep holders and correcting the collimation this way. Will give that a go and report back.

Does anyone have experience of this? May post this question separately to get more answers later.

Cheers

Stu

[angusb1]

The shorter the focal length of the EP the more they will show inaccuracies in collimation of the binoviewer. The same miscollimation does not show up in the longer FL 25mm EPs. I guess you have tried rotating the EPs one at a time in the holders to see if you can correct for the miscollimation that way. If you manage to get it sorted this way you can mark both 7mm EPs so you can put them straight in next time with the correct rotation.

[Stu]

Hi Angusb1, thanks for the reply. Yes, I tried rotating the ep's with no joy. I suspect that means the ep's are ok and that it is the binoviewers that are out. On the Maxbright you can apparently collimate by loosening the screws which hold the ep holders so I'll give this a go and see where I get to.

cheers

Stu