6 replies to this topic

[itstom]

Hi-

New to binoviewing with a new to me BW-Optik.

 

The scope is an Explore Scientific 152mm f8 triplet. I didn't like the big hex focuser and installed a Moonlite. I have a couple of different spacers and believe that I can configure this to reach focus without using my 2X barlow.

 

Will this be the preferred way to set things up? It seems that I have seen posts advocating for the use of a barlow in some cases. Also a lot of folks going to great lengths to avoid using any GPC. What conditions determine if I should use the barlow or not?

 

 

I'm waiting on a second 20mm Televue plossl to get delivered for my first serious attempts.

 

Thanks,
Tom

 

[Shorty Barlow]

Hi-

New to binoviewing with a new to me BW-Optik.

 

The scope is an Explore Scientific 152mm f8 triplet. I didn't like the big hex focuser and installed a Moonlite. I have a couple of different spacers and believe that I can configure this to reach focus without using my 2X barlow.

 

Will this be the preferred way to set things up? It seems that I have seen posts advocating for the use of a barlow in some cases. Also a lot of folks going to great lengths to avoid using any GPC. What conditions determine if I should use the barlow or not?

 

 

I'm waiting on a second 20mm Televue plossl to get delivered for my first serious attempts.

 

Thanks,
Tom

Not sure if this helps: https://www.cloudyni...wer/?p=14033363

[photoracer18]

Unless you have a way to shorten the OTA by about 4" best you can do it get a Linear BV or use a Barlow/GPC/OCS to extend the focus. Standard prism BVs extend the focal point about 4 inches farther back roughly. I prefer to use refractors with removeable focuser extensions, pioneered  chiefly by Stellarvue so I do not have to use Barlows or GPCs. I was a beta tester for Denkmeier and was lucky I had a 1.5x Barlow so I could get some refractors to focus.

[balcon3]

There are several reasons people use Barlows with Binoviewers:

 

1) To reach focus (not an issue with your setup apparently)

2) To reach a given magnification with longer focal length eyepieces. Since longer FL eyepieces often have longer eye relief and make for easier holding of the exit pupil, this results in more comfortable viewing.

3) To correct for optical aberrations from the the binoviewer prisms. This is also less of an issue for you at f/8, but for faster scopes the aberrations can be noticeable. 

 

The main reason people don't want to use Barlows with Binoviewers is that it results in a smaller maximum field of view

 

I think for your scope the balance is between #2 above and the the field of view issue. 

 

By the way, the actual magnification of the Barlow depends on where you put it in the light path. If you put it before the Binoviewer, the magnification will be greater than 2x. If you put it before the diagonal it will be even greater. This is for Barlows. For Televue Powermates, it is different.

Edited by balcon3, 19 March 2025 - 07:20 PM.

[TOMDEY]

I also have that telescope and upgraded the 3-inch focuser. With the 3-inch Star Diagonal you can use this 3-inch eyepiece, which makes it a magnificent 40.5X ≈ Rich Field Telescope with a 100^o Apparent Field of View (AFOV) and 2.46^o True Field of View (TFOV) completely free of vignetting.

 

Regarding Binoviewer use --- the Linear is a convenient plug-'n-play, parfocal with the eyepiece alone (no focus shift whatsoever).

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[itstom]

Thanks everyone for your responses. I'll start out with the barlow and my 20mm plossls and see how it goes. If I get about 150X It should be a good place to start.

 

The Linear binoviewer is intriguing, but the scope and Moonlite have kind of wrecked the astro budget for a while.

 

Thanks again,

Tom

[jprideaux]

Yeah, just start out with the equipment that you already have and see what works.  Then later decide if you want to get anything new.

 

Of course the most important thing is being able to reaching focus.  

Then you can start to worry about other things like optimal eye-relief, lower power, higher power, etc.