Best Diagonal for Binoviewer

[Thewalkingastronomer]

I have a Denk binoviewer which I use in my LZOS 105/650. At the moment I use it with a standard Baader prism diagonal but I do notice a bit of CA with it on brighter objects (this is more pronounced in mono but I still there in binoviewer). I think this may be due to how fast my scope is so am looking to get a new diagonal. Now the choice is between the Zeiss prism or the BBHS mirror. I don't have issues with focus so don't need the prism for the shorter light path so was wondering if anyone has any experience of using either in a similar set up to help me decide!

 

Thanks Adam

Edited February 15, 2020 by Thewalkingastronomer
Gratuitous picture of setup!

[mikeDnight]

Could it be lateral colour you're noticing caused by the ultrawide angle eyepieces? If you can try a pair of orthoscopics in your binoviewer, you may be able to see if its the eyepieces causing the colour you're seeing rather than the prism. Just a thought!

[Captain Scarlet]

I also have an LZOS 105/650, and on it I very recently directly compared a Baader Zeiss prism diagonal with a revelation dielectric mirror diagonal. Not with a binoviewer though, just single eyepiece (TV Delos). I used Venus during late afternoon as the target.

The Zeiss prism diagonal showed significant CA, the revelation mirror absolutely none. It was as simple as that.

More recent still, on my Intes Mak, f/10 (as opposed to f/6.2 for the LZOS), there was no discernible difference (no detectable CA) between the two diagonals. Both 2”. 

Cheers, Magnus.

 

Edited February 15, 2020 by Captain Magenta

[Paz]

8 hours ago, Thewalkingastronomer said:

 

I can't help with the question but will say that's a very fine set up!

[Space Hopper]

I believe what you are seeing is sphero-chromatism rather than chromatic aberration as such.

And this is primarily caused by the binoviewer as it has much bigger prisms. The prism diagonal will add a little but a much lessor extent.

With the Baader bino's the GPC's counter this issue. As well as giving extra lightpath they also correct the sphero-chromatism. 

They are also designed by refractor guru Roland Christen who knows a thing or two.

Looking at your system, i'm not too sure what the way forward is ?  You may be able to fit a Baader GPC into your diagonal, but that may tie you in to quite a high power ?

Do you have access to a Denkmeier Powerswitch ? This may be what you need.

 

Question : do you find this an issue only when high power viewing or is it there when using lower powers as well ?

I can use my own bino natively (i only use prisms btw) and i don't notice it (spherochromatism) when low power viewing. Maybe thats my 52 yr old eyes !  High power, using higher power eyepieces is a different story.

On something like Jupiter, its immediately noticeable, and not nice. But pop in a gpc, and its gone.

Beautiful looking scope btw  ; i love the Feathertouch on it. I have something similar, but it doesn't look as sweet as that ! 😃

 

 

Edited February 15, 2020 by Space Hopper

[Thewalkingastronomer]

8 hours ago, Space Hopper said:

I believe what you are seeing is sphero-chromatism rather than chromatic aberration as such.

And this is primarily caused by the binoviewer as it has much bigger prisms. The prism diagonal will add a little but a much lessor extent.

With the Baader bino's the GPC's counter this issue. As well as giving extra lightpath they also correct the sphero-chromatism. 

They are also designed by refractor guru Roland Christen who knows a thing or two.

Looking at your system, i'm not too sure what the way forward is ?  You may be able to fit a Baader GPC into your diagonal, but that may tie you in to quite a high power ?

Do you have access to a Denkmeier Powerswitch ? This may be what you need.

 

Question : do you find this an issue only when high power viewing or is it there when using lower powers as well ?

I can use my own bino natively (i only use prisms btw) and i don't notice it (spherochromatism) when low power viewing. Maybe thats my 52 yr old eyes !  High power, using higher power eyepieces is a different story.

On something like Jupiter, its immediately noticeable, and not nice. But pop in a gpc, and its gone.

Beautiful looking scope btw  ; i love the Feathertouch on it. I have something similar, but it doesn't look as sweet as that ! 😃

 

 

Thanks SH, it is something I do notice when using the Baader prism on it's own so I wondered if it's due to the quality of the diagonal (hence if an upgrade to the Zeiss version would remedy the situation a bit). It's definitely something I only notice on brighter objects but don't see it to such an extent if using my William optics dielectric diagonal. I guess as most people seem to use prism's with binoviewers I wondered if there was another reason other than shortening the light path. Both the potential choice of diagonls are pretty much the same cost so perhaps I'll toss a coin! 

[Thewalkingastronomer]

11 hours ago, Captain Magenta said:

I also have an LZOS 105/650, and on it I very recently directly compared a Baader Zeiss prism diagonal with a revelation dielectric mirror diagonal. Not with a binoviewer though, just single eyepiece (TV Delos). I used Venus during late afternoon as the target.

The Zeiss prism diagonal showed significant CA, the revelation mirror absolutely none. It was as simple as that.

More recent still, on my Intes Mak, f/10 (as opposed to f/6.2 for the LZOS), there was no discernible difference (no detectable CA) between the two diagonals. Both 2”. 

Cheers, Magnus.

 

Thanks Magnus, I'd read the fast f ratio of these scope's does cause the prism to introduce some CA and like you I see none in mono using a William optics dielectric so perhaps I'll get the BBHS

[Stu]

5 minutes ago, Thewalkingastronomer said:

Thanks Magnus, I'd read the fast f ratio of these scope's does cause the prism to introduce some CA and like you I see none in mono using a William optics dielectric so perhaps I'll get the BBHS

Given the choice between Zeiss prism and BBHS, I would go with the mirror due to the speed of your scope and ot avoids any doubt as to whether this is causing issues or not. I have one and enjoy it alot.

As Spacehopper asked, do you use a GPC in your binoviewer? Even just a x1.25 would be worth trying; minimal impact on magnification and should correct the colour errors from the binoviewer. I tend to use mine for high power solar and lunar viewing mainly so always have a GPC in place. I prefer single eyepieces for low power observing.

[Space Hopper]

Like i said, its not the diagonal thats the issue. You could buy every diagonal on the market to no avail.

Its the binoviewer. There are several prisms in there. I'd say 90% of the SC you are seeing is caused by the binoviewer.

Its the nature of the beast.

[Stu]

8 minutes ago, Space Hopper said:

Like i said, its not the diagonal thats the issue. You could buy every diagonal on the market to no avail.

Largely true, but the prism can introduce some CA when used in fast scopes such as the one the OP has, so if the objective is to make the system as good as possible, a mirror diagonal makes more sense.

[Space Hopper]

He could, but if he wants to use the scope with the Denk, he'll still need to deal with the bino induced spherochromatism.

Stu : i'd not considered the 105/650 F6.2 that fast a scope to be an issue, but evidently it is ?

I have no such issues in my larger scope with prism and bino sans gpc for low power / wide fields and thats F7.

I will test my own 105/650 with various combos and see if i can replicate what he's seeing.

[Thewalkingastronomer]

Following all the helpful advice I've put in an order for a BBHS diagonal as feel given how fast my scope is and with the light path not a worry that'll be the best option for me (oh and another 14mm Morpheus to use in it!).

 

Thanks Adam

[Space Hopper]

Let us know how it performs if you would, both with bino & cyclops.

I take it the BBHS is the mirror version ?

I use 3 diagonals ; all Baader.

2 are the Zeiss spec prisms ; one has a 2.6x gpc permanently occupying it, the other without.

The other is a Baader Amici (not the megabucks one)

All 3 diagonals perform very well.

 

[Thewalkingastronomer]

Got a chance to use the BBHS mirror diagonal last night and with a bit of wind, the transparency was very good.  In use with the Denks I definitely observed a notable reduction in CA (relative to the prism) on brighter star's and in mono what CA I'd noted with the prism was completely gone. Perhaps it was the new gear bias but I had one of more memorable views of M42 with a Morpheus 4.5mm and even managed to resolve some stars in NGC 2158 which is a first in a 4" scope (which of course I'll attribute to the new diagonal!). Looking forward to some planet's reaching a more palatable elevation so I can put it's through it's paces on lower contrast features.

As an aside, the 14mm Morpheus might well be the best eyepieces I've ever used in a binoviewer, very comfortable and easy to see the full FOV.

Thanks Adam

Edited February 21, 2020 by Thewalkingastronomer