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First binoviewer - some questions

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#1 HTJ


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Posted 06 January 2013 - 04:40 PM


I am strongly considering getting a binoviewer. Main usage will probably be for planetary and globs with my 100ED.

I leaning heavily towards the Baader Maxbright. The opinions on this forum seem to rate it quite well, it is relatively affordable, and with the T2 diagonal, it seems to reduce the in-focus issues significantly. I do have a lot of questions regarding it and acquiring a binoviewer is a daunting task. Here goes:

I understand that the Glass Path Corrector not only changes the back-focus and focal-length, but also corrects for the prism in the binoviewers. However how usable is the field without these, if I want some wide-field views? (the 21 mm field stop has its limitations, but still).

Does the GPC function as a barlow wrt. changing eye relief and exit pupil or is more like a telecentric extender?

Will the view vignette more without a GPC? (this related to the previous question somewhat depending on how a GPC changes the light cone).

How long time does it roughly take to switch a GPC, and how troublesome is it compared to switching eyepieces?

Will the view seem to dim faster when going up in magnifications? (This probably depends a lot on the target and person, but I'd like to hear people experiences).

The regular T2 Maxbright diagonal seems to get recommended over the Zeiss version. However AFAICT the Zeiss version is actually cheaper - at least here in Europe. Am I missing something? There is also a prism, which is cheaper, but I assume this is not what I want.

Will my regular focuser on the 100ED by enough? It does not have issues at all when pointing towards zenith with a 2" diagonal and the Hyperion 36, which was the heaviest setup I had. I know some people have had issues and changed it, but does anyone have it working with it?

Eyepices. Groan...

Do people use multiple GPCs or eyepiece sets?

I understand that long focal length is better than shorter, as the angular separation becomes larger and merging becomes more difficult / strained. However how big a problem is this? Can I use relatively short EPs, like 10 mm for planetary (with the 1.25 GPC) without to much fuss, or would it be better to go for a 1.7 GPC and a longer focal length eyepieces.

I'd like a set of eyepieces close to 21 mm field stop, but cannot really make up my mind. Ideally I'd like something like my XW 7/10, which has excellent ergonomic, sharpness, and scatter control. I've been playing around with my XW and a binocular, and I think my IPD should be okay and same with nose room. However they are heavy and expensive, making it a relatively expensive experiment (which I know has failed for some). The LVW 22 will vignette and the LVW 17 does not have the stellar reputation that the 22 has (though still good). I don't really get along with the regular Hyperions for some reason. I've considered the ES68 20 mm. I have the 24 mm and while it draws beautifully it has some form of radial distortion (not sure which), which bothers me somewhat. It only takes a very small movement with my eye to feel like I'm drunk or dizzy. I'd like to avoid to narrow FOVs (I do appreciate abbe orthos, but it feel like I am looking through a straw). Suggestions accepted :-).

Thanks for reading though :-).

#2 Moonglum


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Posted 06 January 2013 - 06:52 PM

Hi and welcome.
The field is totally usable without a corrector for low and medium power.
The GPC functions as a barlow changing eye-relief and exit pupil, yah.
The view will vignette in maxbrights with something like 24 Pans, fieldstop 27, but not 25 Televue Plossls. Just don't barlow any Televue plossls with any GPC as these combos all vignette pretty bad. Antares Elites don't vignette with GPC but there can be some unwanted reflections with these.
It is indeed a pain to switch GPC's in the field, unfortunately, it is much easier to have multiple sets of eyepieces if you like to change magnification often.
With your scope I would aim to have two mags for planetary and the moon, 120X and 150X. Beyond 150X I think the view is gonna dim too much with binos. Play with the math and the 1.25x and 1.5x(it's mis-labeled 1.7X) and start with a pair of the new 10mm Baader Classic Orthos, readily available there and reported to be excellent price quality wise.They have 50* field which is fine for hand-tracking even at 150X. You could likely even bino a pair of 6mm BCO's if you had too, but I would start with 10's if possible.

#3 Eddgie


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Posted 06 January 2013 - 11:38 PM

The regular T2 Maxbright diagonal seems to get recommended over the Zeiss version. However AFAICT the Zeiss version is actually cheaper - at least here in Europe. Am I missing something? There is also a prism, which is cheaper, but I assume this is not what I want.

As far as I know, there are four different prism diagonals that Baader sells.

One is a 2" Prism. Very expensive, and not at all good for bino application. I don't even know if they make this anymore.

One is an Amici prism (Alpine Astro in the US lists the part number of this as AMICI-DX1) and while I am sure that it is better than most Amici prism diagonals, I would not use it becuase these diagonals can have spikes on bright stars.

There is a Baader diagonal with Ziess Prism. Alpine Astro in the US lists this as part number T2-01B, and in the US, retails for $259. But you need to be careful with this because this is just for the prism itself. You also need a nose piece, which is purchased seperately.

Then there is the Baader Maxbright (T2-01C) with the non-Ziess prism. Retail price in US is $129. Once again, this is without a nose.

The T2-01C is the one I use. I suppose the Zeiss prism might be a bit better, but I can't see that the standard prism is in any way inferior to the best mirror diagonals I own. The T2-01C also has a 3mm shorter light path than the Zeiss prism unit. This doesn't sound like much, but it often means the difference between reaching focus and not reaching focus, or having to go from a 1.25x GPC to the 1.7x GPC.

And on th GPCs, if you need it to reach focus, then you have to use it always. The 1.25x GPS also can give 1.5x by using it in between the nose and the front of the diagonal but if you can't reach focus with that, then you need to use the 1.7x in front of the diagonal that gives more like 2X. Again, another good reason to keep the light path short.

The Maxbrights are fairly light, but if you have trouble with a 2" diagonal and a hyperion, then you might have issues with the Maxbright/T2 and two eyepieces. This likely weighs a bit more than a single 2" diagonal and a Hyperion.

My advice is to download the Maxbright Owner's Guide. Alpine Astro has it available on their web site. This will tell you how to measure your back focus so you can select the right OCS.

Hope this helps.

#4 HTJ


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Posted 12 January 2013 - 02:06 PM

Hi, just wanted to say thanks for the replies (busy week at work this week), it cleared up a lot of things.

I will try and do some measuring for back-focus to find out which GPC I make it work with.

Unfortunately the Baader T2 Prism seem be sold out everywhere right now. I might go for the mirror instead, despite having a slightly longer optical length, but I'll have to measure and calculate a bit first.

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