Maxbright II and eyepiece conundrums...

[cplee42]

I have upgraded my 8" SCT with the Baader 2" click lock diagonal and the Maxbright II Binoviewer with two Baader Morpheus 17.5mm eyepieces. Last night the views of Mars were excellent as where the star clusters (although, since I do not use a focal reducer, I mainly swam amongst them!). The Moon was excellent and, as a sketcher, it is so much easier to observe and draw with two eyes. I had no issues getting focus for my system.

and so...

Question 1: I would like to use the binoviewer at higher mag. I already have the Baader Hyperion 8mm and so I wonder if I have three choices and, if so, which is best? I could buy another Baader 8mm and so have high and low power eyepiece sets for swapping in and out... I could just add a GPC (say 1.7?) and stick with the 17.5 mm pair or I could get a 2" 2x Barlow and similarly stick with just the 17.5mm pair. The prices for these options are not too dissimilar (roughly) but I wonder which would be better for me optically?

Question 2: Mars was very bright and so I sought to reduce this by using the only 2" filter I possess - the variable polarising filter I use for the Moon. I screwed this into the MB II nosepiece and inserted into the 2" diagonal. However the image appeared to have some ghosting and I could not really snap it into easy focus. Is there an optical effect here for splitting the polarised light between the two eyepieces and so confuses the brain vs mono viewing? How will this affect lunar work? To be honest the moon was so "dim" low down last night that I never had a realistic chance to see the polariser in action in the new set up.

Thanks for any thoughts

[Highburymark]

You have a wonderful pair of Morpheus eyepieces, perfect for binoviewing - I’d stick with these and use GPCs and/or barlows for higher powers. I do most of mine with pairs of 24mm and 18.2mm eyepieces, then use 1.7x and 2.6x GPCs and sometimes Barcon barlow for closer views (adding spacers between the BV and barlow to increase power). Be aware though - the 1.7x Baader GPC is only 1.5x in reality.

[Paz]

I'd go for glass path correctors, they are designed to correct [spherical abberation] [prismatic colour fringing] caused by the binoviewers so you get the magnification and an abberation fix all in one. With the right t2 bits and pieces you can use the gpcs and keep the light path as short as possible.

Gpcs are small and take up very little space in your eyepiece case/box.

Edited October 11, 2020 by Paz
correction

[Louis D]

1 hour ago, Paz said:

I'd go for glass path correctors, they are designed to correct spherical abberation caused by the binoviewers so you get the magnification and an abberation fix all in one. With the right t2 bits and pieces you can use the gpcs and keep the light path as short as possible.

Gpcs are small and take up very little space in your eyepiece case/box.

Binoviewers introduce spherochromatism, not spherical aberration.  Basically, GPCs reduce spherochromatism by slowing down the light cone.  Also, increasing power by using GPCs instead of higher powered eyepieces reduces the appearance of collimation issues in the binoviewer.  So, GPCs/OCAs/OCSs are a win/win all the way around.

Binoviewers can introduce spherical aberration indirectly in certain telescope designs such as SCTs by increasing the required back focus to account for the binoviewer's additional optical path length.  This is because SCTs have increasing spherical aberration the further off the designed back focus distance the focal point is moved by moving the mirror to reach focus.  Again, a GPC can return the back focus to the optimal distance to minimize spherical aberration.  However, the SA is not caused by the optics of the binoviewers, only its optical path length.

[Paz]

5 hours ago, Louis D said:

Binoviewers introduce spherochromatism, not spherical aberration.  Basically, GPCs reduce spherochromatism by slowing down the light cone.  Also, increasing power by using GPCs instead of higher powered eyepieces reduces the appearance of collimation issues in the binoviewer.  So, GPCs/OCAs/OCSs are a win/win all the way around.

Binoviewers can introduce spherical aberration indirectly in certain telescope designs such as SCTs by increasing the required back focus to account for the binoviewer's additional optical path length.  This is because SCTs have increasing spherical aberration the further off the designed back focus distance the focal point is moved by moving the mirror to reach focus.  Again, a GPC can return the back focus to the optimal distance to minimize spherical aberration.  However, the SA is not caused by the optics of the binoviewers, only its optical path length.

Thanks for the correction and clarification, I've added a correction to my note.

[cplee42]

OK thanks for the advice on GPC so can I ask is it better to get the 1.25" nose piece and the smaller GPCs vs the 2" GPC which is double the price? I have a 2" nosepiece already and use this with my 17.5mms but adding another £200 for the occasional mag views vs £120 is a consideration.  Will this markedly affect the view? I like the 2" nose partly because it grips nicely in the click lock diagonal but never quite sure if the view thru a 2" diagonal is very different with the bino vs a 1.25" nosepiece...

[omo]

With the Baader T2 1.25 nosepiece the small GPC's can be screwed into it, with the Baader T2 / 2" nosepiece its a push fit with the plastic adaptor ring supplied with the GPC.

If you go for the larger 2" corrector it needs to be able to pass all the way through the clicklock up the focuser tube if you have one on the scope

 

 

Edited October 12, 2020 by omo