MaxBright II BW colour fringing - is it expected?

[AlcorAlly]

I recently got MaxBright II binoviewer for Christmas and I'm really enjoying the immersive views  

The center of the field is nice and sharp, however on the edges there's a noticeable amount of false colour. Is that expected? I'm using it with a 1.7GPC, 32mm Baader prism, and 18mm BCOs. The telescope is Takahashi 76DCU.

The false colour on the edges is especially obvious when observing Jupiter. The planet is sharp when it's in the center of the field but when approaching the edge it has yellow and blue fringing, just like the rook on the image above:

I tried swapping one of the BCO for my 24mm Panoptic but the colour is still there, although it's less noticeable due to lower magnification.

Is this type of aberration normal and expected? 

I really like the BW otherwise, so hopefully there's nothing wrong and it's just a small trade-off one has to make to enjoy BW. 

Edited December 14, 2023 by AlcorAlly
typo

[globular]

First thing to check is that you have the GPC correctly oriented.  The convex face of the GPC should point towards the object / away from the binoviewer.  The GPC should help correct colour fringing - but if positioned incorrectly it can make it worse.

Edited December 14, 2023 by globular

[bosun21]

Yep, I’m guessing you have the GPC mounted wrong. Have you fitted it in your diagonal or the binoviewer itself? As already stated the convex lens must be orientated towards the telescope.

[AlcorAlly]

4 minutes ago, bosun21 said:

Have you fitted it in your diagonal or the binoviewer itself?

In the diagonal. As per instruction on the GPC. But I'm going to check again if the convex lens is facing the right way (I thought it was!)

[Highburymark]

There’s some confusion about the orientation of GPC lenses with the MBII - I was used to inserting the 1.7x GPC in the BV body with the Baader MkV, but had to turn that around with the MBII - ie GPC pointing away from the scope. That’s almost certainly the problem here. You should be ok using a prism diagonal with that scope, though they’re not advised for faster refractors - ie below F/7

[Highburymark]

7 minutes ago, AlcorAlly said:

In the diagonal. As per instruction on the GPC. But I'm going to check again if the convex lens is facing the right way (I thought it was!)

That’s the orientation I’m using with the MBII and 1.7x for best views, but my GPC is quite old - maybe Baader flipped the lenses for newer GPCs?

[globular]

2 hours ago, Highburymark said:

That’s the orientation I’m using with the MBII and 1.7x for best views, but my GPC is quite old - maybe Baader flipped the lenses for newer GPCs?

Bader make two versions of the 1.7x GPC, one facing the binoviewer and one facing away.  Which ever one you have you can turn it into the other one by removing, flipping and reinserting the lens within the housing. 

In other words the key is not whether you put it in the bino or the diagonal, but whether the lens is orientated correctly within the housing for your choice of bino or diagonal placement.

[AlcorAlly]

I confirmed which side was concave by placing a small ball on it. 

The concave side is interfacing with the BW. The convex side is facing the diagonal.

To the best of my knowledge the GPC is placed correctly.

[AlcorAlly]

Thanks to everyone who tried to help with my fringing problem. After some experimenting last night I concluded it was the BCO eyepieces causing it. I tried my one TV Delite in the BW – something I initially overlooked due to its very short focal length. It worked well and was sharp and distortion free to the edge.

The BCOs are excellent, and considering their price, I really can't complain. But it's good to know they're the main cause of fringing in my setup. Thought I'd share my conclusion here in case it's helpful for someone else in the future.

Edited December 16, 2023 by AlcorAlly

[bosun21]

33 minutes ago, AlcorAlly said:

Thanks to everyone who tried to help with my fringing problem. After some experimenting last night I concluded it was the BCO eyepieces causing it. I tried my one TV Delite in the BW – something I initially overlooked due to its very short focal length. It worked well and was sharp and distortion free to the edge.

The BCOs are excellent, and considering their price, I really can't complain. But it's good to know they're the main cause of fringing in my setup. Thought I'd share my conclusion here in case it's helpful for someone else in the future.

I found that the BCO's were excellent in my MBII binoviewer. I always used the 18mm ones as part of my session.