I've done some experimenting with binoviewing due to some of the issues.
I don't have a 180mm Mak, but do have a Bresser 127mm. I have used two different binoviewers on the Mak, a 6" F/6 DOB and a 100 and 80mm refractors.
Here is some of what I found, with help from Eddgie on the merging issue, that may be of use/interest to others. On some of the things, I have no idea why they act as they do. Anyway...
1. I have an Astromania binoviewer. It is the exact same as the Arcturus. I was having a lot of merging problems and couldn't merge stars at all. The smaller the object the harder it is to merge. I thought it was collimation/alignment of the binoviewer, but Eddgie told me the real issue and I was able to get them to work.
The problem with the Arcturus and other moderately priced binoviewers is the eyepiece holders. The way they are constructed getting the eyepieces centered and aligned is difficult.
First off, I use only eyepieces with no undercuts. The two Plossl 32mm EPs that came with the viewer and three other sets I have are Meade Series 4000 Plossls and none have undercuts. This helps.
The other and very important thing I did was to arrive at a way so as not have the eyepiece holders and their collets throw the centering and alignment off. One thing, so far worked for me.
When I put the eyepieces in the holder tubes I tighten the collets so that they just touch the eyepiece barrels. And that is, just touch. Tightening the collets was the problem with my binoviewer.
By just touching the eyepiece barrels, the collets center the eyepieces well enough but don't tilt them. The eyepieces essentially sit, by gravity, on the interior stop ring and are well aligned. I've been able to merge stars at all powers as well as everything else.
Having the eyepieces like this requires that the binoviewer itself is not tilted to a degree where the EPs will fall out or move. With an Alt-Az this is no problem. With an EQ mount the binoviewer should always be adjusted to be as vertical as possible.
This has worked wonders for me for merging and I suspect it would for others having the problem also.
2. I have several nose piece Barlows I use. Two came with the binoviewer, a 2.88X and a 3X. Additionally, I took the front Barlow assembly off a 2X and 3X Shorty Meade Barlows, so I just had the lens with its cell. The 2x threads into the front silver nosepiece of the binoviewer. I had to modify the 3x by attaching it to an empty filter holder, and it too will thread into the silver nose piece.
Also, I have a 1.9X Burgess Barlow attachment and a 2X William Optics attachment.
All these will work with my refractors and the Mak. The two Meade Barlow's will work with my DOB, and there is an important reason for this.
All the Barlow nose pieces except for the Meade pieces, require the binoviewer to move inward a substantial distance to focus. This is normal and a problem with most Newtonians. There isn't enough in-focus travel to reach focus with Newts. There is enough for the refractors and the Mak.
But, using the Meade 2X and 3X pieces the Binoviewer/Barlow combination focus right about at the point where mono eyepieces do!
So in this configuration, the binoviewer works fine and focuses in the DOB. Also, the focus of the binoviewer is very close to the optimum spot of the Mak.
Why? I haven't any idea.
In all situations I don't notice any vignetting. I don't, however use any wide angle eyepieces, just the Plossls mentioned before.
3. Finally, using these different nose piece Barlows works well giving great sharp images, high contrast and little scatter. I only view the planets and the moon. There is no good DSO observing where I live. Anyway, most who use binoviewers say, monoviewing is best for DSOs especially with a wide angle and premium eyepiece.
But, I've found that the stated magnification stamped on the nose-piece/Bralows is not what you get using them in a binoviewer. It seems the actual magnification is higher, significantly so with the 3X Meade. I don't know what each nose-piece Barlow gives, but I will be doing drift timing tests to find out.
Both Meade nose-piece Barlows seem to be significantly more magnification than stated, but all the Barlows are apparently more.
I have to say that not using a Barlow at all with the Mak or using the Burgess and William Optics nosepiece-Barlows, which do shift the focal point from the Mak's nominal position does not seem to have any negative effect on the quality of the view. And there is no visible vignetting.
These are just my observations with the binoviewer. everything was done, trial and error. At this point, binoviewing the moon and planets and double stars is superior in all instances over monovision.
Thanks. Hope this is helpful.
Edited by Joe1950, 05 September 2019 - 09:24 AM.