Jump to content


Photo

William Optics Binoviewer Back Focus

  • Please log in to reply
19 replies to this topic

#1 Tom Polakis

Tom Polakis

    Surveyor 1

  • *****
  • Posts: 1644
  • Joined: 20 Dec 2004
  • Loc: Tempe, Arizona

Posted 31 December 2013 - 02:47 PM

I am looking at the cheapie William Optics 1 1/4" binoviewer that sells with a pair of eyepieces. A support person at OPT told me that the added back focus is 4.5 inches, which means that it is unlikely to reach focus with my refractor. I understand that the provided Barlow doesn't do much to improve this situation. Has anybody tried different Barlows with better results for reducing the back focus problem? If so, can you estimate the added back focus? Thanks.

Tom

#2 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 12533
  • Joined: 01 Feb 2006

Posted 31 December 2013 - 05:22 PM

Actually, the included .6x Barlow has allowed many people to reach focus in refractors that can reach focus with a 2" diagonal, but only when the 2" diagonal is removed and replaced with a 1.25" diagonal.

The light path though a 2" diagonal including the eyepeice holder is usually about 130mm.

The ligth path though a 1.25" diagonal is only 75mm typically (including the eyepeice holder).

So, part of the savings is achieved by the .6 barlow, and part is achieved by the 1.25" diagonal.

And many people do report reaching focus with the 2" diagonal in place!

So, depending on the amount of in-travel you have now (if you are using a 2" diagonal" it is possible that you might get the 1.6x to work, but almost certian that you will get the BV to work if you put in a 1.25" diagonal.

And a few peopel have even reached focus without the 1.6 by using a 1.25" diagonal, but I have not managed to do that.

I was able to reach focus in a refractor with the Maxbright Binoviewer and the T2 Prism without a GPC as well.

Anyway, if you are using a 2" diagonal but have a 1.25" diagonal as well, chances are, you will be able to get the 1.35" to work.

If your scope was not designed to work with 2" diagonals, all bets are off.

But most refractors made in the last 10 years were designed to work with a 2" diagonal, so hopefully you will be OK.

#3 Ant78

Ant78

    Explorer 1

  • *****
  • Posts: 99
  • Joined: 23 Sep 2011

Posted 31 December 2013 - 07:32 PM

I am in the same situation, same bino viewers but 4" refractor F8, would like to use them with my 2" everbrite diagonal but just cant get to focus..

#4 Dubboy

Dubboy

    Vanguard

  • *****
  • Posts: 2464
  • Joined: 05 Jul 2005
  • Loc: Western Kentucky

Posted 31 December 2013 - 07:42 PM

I am looking at the cheapie William Optics 1 1/4" binoviewer that sells with a pair of eyepieces. A support person at OPT told me that the added back focus is 4.5 inches, which means that it is unlikely to reach focus with my refractor. I understand that the provided Barlow doesn't do much to improve this situation. Has anybody tried different Barlows with better results for reducing the back focus problem? If so, can you estimate the added back focus? Thanks.

Tom


Hi Tom,
I just purchased a W.O. Binoviewer to use with my AT106LE f6.5
I can reach focus with a 1 1/4 diagonal and the included 1.6x barlow. If I use my 2" diagonal with a 2x barlow lens on the binoviewer ,it will also reach focus. Hope this helps
Don

#5 Messyone

Messyone

    Viking 1

  • -----
  • Posts: 536
  • Joined: 02 May 2012
  • Loc: Down Under

Posted 01 January 2014 - 02:32 AM

I can use my refractor with WO's and no OCS. With a standard Synta 6" f8 and my 6" f12 Istar ATM (which I made to use bino's without the OCS) I use a GSO focuser and 1.25" Prism diagonal, Long Pern in my case. No cutting of the f8 tube was needed. I had to grind the lip off a GSO 2-1.25" adaptor so it would slide all the way in the focuser.
After doing all that the only object I look at without the OCS is the Sun with 28mm RKE's…. beautiful.
I prefer the 1.25" diagonal as it holds the Bino's better than a 2" dialectic GSO I have.
To reach focus with a 2" diagonal needs the 1.6 OCS.
To use the f12 and f8 mono I have to add a 50mm extension tube as the GSO focusers have a 50mm draw tube. If I had a 4" draw tube the extension would not be needed.
My 10" Newt is set up the same way i.e. with or without the 50mm extension tube for mono or bino viewing.
Matt

#6 Tom Polakis

Tom Polakis

    Surveyor 1

  • *****
  • Posts: 1644
  • Joined: 20 Dec 2004
  • Loc: Tempe, Arizona

Posted 01 January 2014 - 12:56 PM

Thanks for the replies, all. I'll go ahead and order a 1 1/4" diagonal as well. I am only going to use this setup for moon and planets, so the light loss with a cheap diagonal and binoviewer is not of concern, as long as I get full aperture.

Tom

#7 Tom Polakis

Tom Polakis

    Surveyor 1

  • *****
  • Posts: 1644
  • Joined: 20 Dec 2004
  • Loc: Tempe, Arizona

Posted 08 January 2014 - 09:34 AM

I received the WO binoviewer and a 1 1/4" diagonal, and got a chance to look at the moon and Jupiter last night under partly to mostly cloudy skies. I was impressed enough with the build quality of the binoviewer, although one of the lenses is rattling around in one of the provided eyepieces.

I put the binoviewer with no Barlow in my ED 127 refractor, and not surprisingly, it bottomed out before reaching focus. The provided 1.6x Barlow did not improve matters, which led me to wonder why it is even included. Fortunately, I have three Barlows, 2x, 2.5x, and 5x, and all of them easily reach focus. For even more magnification, I increased the projection distance by placing the 5x Barlow upstream of the diagonal.

This won't be news to anybody reading this forum, but the views are outstanding! I instantly sensed not only how much more relaxing the observing was, but how much more detail I was seeing. Even though the seeing was fairly soft, I was pushing the magnification to 240x, and seeing exceptional detail inside Tycho, and very different discs to the four Galilean moons. Even better news was learning that the binoviewer works in my 10-inch Newtonian. By the time it had cooled, the clouds slammed shut.

I'm really looking forward to future lunar and planetary views, and to looking at the sun with this setup through a solar wedge.

Tom

#8 seawolfe

seawolfe

    Viking 1

  • -----
  • Posts: 907
  • Joined: 26 Jun 2013
  • Loc: N 47.11.23 W 122.20.18

Posted 08 January 2014 - 09:41 AM

I enjoy my WO binoviewers as well. Did you get the kit with the small barlow? I've tried it and it does help a little. Mainly though, I use my 2 inch 2X Orion barlow since I always keep my 2 inch diagonal on my Edge 8".

I really like using the binoviewers to look at the Moon, Jupiter and Saturn. I've tried it a bit on the Orion nebula, but usually go back to one EP for other things.

#9 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 12533
  • Joined: 01 Feb 2006

Posted 08 January 2014 - 09:49 AM

Ah, happy to hear that you enjoyed the views.

It seems that most people that start with the moon as one of their first targets has a very positive experience.

And yes, one of the major benefits of binoviewing is how relaxed you can be. Two eyes working together simply allow you to be far more comfortable than with one eye.

While many think the dimming is go much for deep sky, I personally find it to be very easy to deal with by simply backing down one step in magnification, but in your case, the need for barlows makes this hard.

Are you using a 2" diagonal?

If so, going to a 1.25" diagonal will buy you 50mm of in-travel, and with the 1.6x GPC, my bet is that you reach focus.

If you measure the amount of in-travel you have, you might be able to reach focus with the Maxbright and T2 diagonal using the 1.25X GPC, or (fingers crossed) even without a GPC.

But start by measuing how much in-focus there is in the refractor. The Maxbright Bino Owner's manual (free PDF) has the instructions on how to do this.

And remember, if you can reach focus with a Maxbright without a GPC, you may be able to get a wider true field than using a bino with a big prism because if the bino with a big prism (Mark V for example) reqires a GPC or a more powerful GPC, you can actually get the same true field with the less expensive Maxbright.

Happy to hear that your initial experience was so positive though, and look forward to your ongoing reports!

#10 Tom Polakis

Tom Polakis

    Surveyor 1

  • *****
  • Posts: 1644
  • Joined: 20 Dec 2004
  • Loc: Tempe, Arizona

Posted 08 January 2014 - 12:46 PM

Are you using a 2" diagonal?



No, I took the advice posted here, and got a 1 1/4" diagonal in the same order. I am still a good inch away from achieving focus with the provided 1.6x Barlow. Not really a problem, since I already have three Barlows, all of which reach focus.

I have little desire to use it (or any binoviewers) for deep-sky viewing, since the light loss by splitting the beam even in a perfect system is unacceptable in my experience. It's more than worth it for the Solar System views, though!

Tom

#11 Tom Polakis

Tom Polakis

    Surveyor 1

  • *****
  • Posts: 1644
  • Joined: 20 Dec 2004
  • Loc: Tempe, Arizona

Posted 08 January 2014 - 05:52 PM

Today I looked at the sun in white light and H-alpha, and am again quite blown away by just how much more detail I am seeing. With both filters, the detail around the giant sunspot group is exceptional. I feel more the fool for not getting a binoviewer about ten years ago, when they were becoming popular.

Tom

#12 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 12533
  • Joined: 01 Feb 2006

Posted 08 January 2014 - 07:05 PM

This is why I started a post specificlly to encourage trying solar with their BV.

I was simply shocked at how much more detail I was able to see with them than I had gotten in the past when Mono-viewing.

I now do more solar white light than anything else..

Of course it is winter.. LOL.

#13 SkyGibbon

SkyGibbon

    Mariner 2

  • -----
  • Posts: 204
  • Joined: 09 Feb 2013
  • Loc: Las Vegas, Nevada

Posted 08 January 2014 - 09:31 PM

You can try extending the 1.6x corrector a little farther away from the nosepiece. That has enabled me to come to focus on a newt with these. I used two empty filter rings, screwed together, to achieve this. It will give you a tad more mag.

To be honest, I only binoview the moon, Sun, and planets, so I just put the b-viewers straight into the focuser drawtube on my refractors, and bypass any diagonal. Never have issues with coming to focus this way, and just use an extender if need be. Then again I am only 5' 10", so if I raise my mount up, and use my viewing chair, things aren't too difficult to view near the zenith.

I actually prefer not using a diagonal in my refractors. I could care less about orientation with the things I view with them. The moon and sun look outstanding in my Z-71 with these, using this method. Could only imagine stepping up in b-viewer class.

#14 axle01

axle01

    Mariner 2

  • *****
  • Posts: 218
  • Joined: 26 Jan 2013
  • Loc: Townsville Nth Qld Australia

Posted 09 January 2014 - 01:22 AM

By replacing the focuser on a refractor with a Moonlite brand will that help with in focus.

I have just sent off the measurements of my focuser to Ron at Moonlite and hopefully his focuser is a bit shorter than the original on a SW102.

Alan

#15 axle01

axle01

    Mariner 2

  • *****
  • Posts: 218
  • Joined: 26 Jan 2013
  • Loc: Townsville Nth Qld Australia

Posted 09 January 2014 - 01:26 AM


I just put the b-viewers straight into the focuser drawtube on my refractors, and bypass any diagonal.

I actually prefer not using a diagonal in my refractors.


That would be good if Baader made a straight through Wedge instead of a diagonal.

Alan

#16 csrlice12

csrlice12

    Voyager 1

  • *****
  • Posts: 10557
  • Joined: 22 May 2012
  • Loc: Denver, CO

Posted 17 January 2014 - 02:59 PM

While not cheap, its not overly expensive either, Seibert Optics makes a diagonal for binoviewers that allows you to use the binoviewer without any barlows, screw on or otherwise.

#17 junomike

junomike

    Surveyor 1

  • *****
  • Posts: 1823
  • Joined: 07 Sep 2009
  • Loc: Ontario

Posted 17 January 2014 - 04:02 PM

While not cheap, its not overly expensive either, Seibert Optics makes a diagonal for binoviewers that allows you to use the binoviewer without any barlows, screw on or otherwise.



This isn't totally correct! I had that gadget (which I called the non-OCS Prism) and It worked great in my AT111EDT. However there still wasn't enough in-focus in a friends SW 120ED with the Siebert Prism and thus, he still had to use an OCS.

It's best to measure the back focus of the telescope first and then subtract the optical path of the Binoviewers + Siebert Prism.

Mike

#18 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 12533
  • Joined: 01 Feb 2006

Posted 18 January 2014 - 10:16 AM

This isn't totally correct! I had that gadget (which I called the non-OCS Prism) and It worked great in my AT111EDT. However there still wasn't enough in-focus in a friends SW 120ED with the Siebert Prism and thus, he still had to use an OCS.


True. Not everyone will reach focus with this or the Maxbrighht BV with a T2 Prism.

The Maxbright / T2 prism with a 1.25x GPC though will reach focus in almost any telescope that will come to focus with a 2" diagonal.

The Baader stuff seems expensive, but Baader really has engineered the best "Entry Level" binoviewr on the market.

With the 1.25X GPC. most refractors are going to reach focus.

Expensive though, and for testing the water, a used WO or similar with 1.6x GPC is a great way to try binoviewing and learn about preferences for upgrading...

#19 stevew

stevew

    Now I've done it

  • -----
  • Posts: 4294
  • Joined: 03 Mar 2006
  • Loc: British Columbia Canada

Posted 19 January 2014 - 03:44 PM

Ed, Does the binnoviewer work in your HD Edge C8 with out any barlows or extensions?
I've never owned a binnoviewer, and now you have me very curious about them.
Steve

#20 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 12533
  • Joined: 01 Feb 2006

Posted 19 January 2014 - 04:01 PM

Yes, all binoviewers will work with an SCT with no Balow or GPC.

My advice though is to try to keep the light path short.

Using a 2" diagonal in my EdgeHD 8" resulted in quite a bit of aperture loss.

This is OK for general observng, but for planets, you would want to use a Barlow for best result. This will allow you to move the mirror further back so that the baffles do not restrict the light cone.

With a system like the Maxbright, you can get the T2 Prism which helps keep the power as low as possible and if you keep it really short, you don't even need a barlow for planets.

Denkmeier also has a special diagonal that can be used to do the same thing, and in high power mode, you are esentially using a barlow, so again, no or little apeture loss when you do planets where you need full apeture for best contrast.

But pretty much any binoviewer will focus in an EdgeHD 8". Keep the back focus as short as possible to get the best result.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics