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EP recommendations below 10 mm

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#1 Deadlake

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Posted 14 January 2022 - 03:04 AM

Current setup

 

LZOS 130 mm/F6 with reduced tube and FT3545 focuser with 220 mm of back focus.

 

BV Max Bright II, with T2 BBHS mirror diagonal

 

EP’s, 10 mm UFF, 17.5 mm Tak LE, 24 mm UFF’s.

 

I was out last night, first time I had a chance to use BV’s and was looking at the moon. Well not much choice given it was in charge.

 

Happy with the setup as no GPC required. 
 

Any idea of what high magnification options there are, how small could I realistically go? I'd also like to use BV’s on the planet's come the summer.
 

I know using a Barlow is one option, the other is insert a GPC and see what happens, however that can be a lot of faff in the dark.

 

 Thanks 


Edited by Deadlake, 14 January 2022 - 07:39 AM.

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#2 noisejammer

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Posted 14 January 2022 - 06:49 AM

Since you have binoviewers with the ClickLock collets, it's really a matter of exit pupil and colour fidelity.

 

I find that working with a 0.6 mm exit pupil is fine but it requires very careful adjustment of the IPD. I haven't measured it but I think we're talking about 0.1-0.2 mm. This requires some care.

 

Achieving colour fidelity at high power requires the use of a Barlow lens or a GPC.

 

Assuming you were going for high powers, I would install the optics from a BARADV in the nosepiece of your diagonal. This produces about 2.3-2.4x at the focal plane so the f/ ratio is around f/14. To achieve a 0.6mm exit pupil, this would imply eyepieces with a focal length of ~8-9 mm and you're getting close to the maximum your scope can usefully deliver.

 

If you chose a 1.25x GPC instead, the effective f/ ratio is f/7.5. I have no problems using a pair of Pentax 5XW's (nominally 220x) in my f/7.3 scope.


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#3 betacygni

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Posted 14 January 2022 - 10:47 AM

I generally don’t recommend going much below 10mm on binoviewers, as the shorter you go the more merging issues you’re likely to have (longer focal length eyepieces merge much easier). I have 3 sets of binoviewers, all start giving me merging issues sub about 8mm. While people report success with shorter focal length eyepieces, there is still risk of subtle eye strain issues. For example I can merge still at short focal lengths, but when looking up from binoviewers they give me momentary double vision of stars (meaning my brain was have to work hard to merge, which temporarily throws off naked eye vision).

The better option is using a glasspath or barlow ahead of the binoviewers. This not only solves the potential merging issue, but will give a better quality high power view as all prisms, including those in binoviewers, will function better and show less aberrations at longer effective focal ratios. The only real advantage of skipping a barlow/glasspath and achieving focus natively is the wider FOV potential, optically it’s inferior.

#4 betacygni

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Posted 14 January 2022 - 11:02 AM

Forgot to address the issue of fiddling with barlows in the dark. I do nearly all my observing in the 0.5mm to 2mm exit pupil range, which is easily and best achieved with longer focal lengths as above, with a barlow or glasspath. Only rarely do I want or need to go very low power, so the barlow setup is my default, I will only fiddle with removing it and going native on my scope when I want the really large extra pupils, again which is rare.

Edited by betacygni, 14 January 2022 - 11:04 AM.


#5 Sarkikos

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Posted 14 January 2022 - 12:59 PM

I recommend a pair of 8mm Paradigms.  I had good results with 8 and 12mm Paradigms in a Burgess Binoviewer in a 10" f/4.7 Dob with a 1.9X OC.  This was my setup when I sketched Jupiter.  One of these sketches is my avatar.

 

Mike



#6 Deadlake

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Posted 14 January 2022 - 07:09 PM

Just got back from using a GPC 2.6 with the above set of EP's. They all look good, when looking at the Moon. However adding the GPC to the diagonal needs a T2 extension over the top of the GPC connected to the diagonal otherwise the BV's will not attach.

 

The BV no longer fit in the Baader case, any other T2 plumbing I can use so the BV's and the T2 diagonal fit in the case?

 

I'll dedicate the diagonal to the BV's.
 


Edited by Deadlake, 14 January 2022 - 07:09 PM.


#7 betacygni

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Posted 14 January 2022 - 07:37 PM

You shouldn’t need any extension or anything special to attach the glasspath. It should thread into the T2 diagonal, nesting in the T2 male opening at top of diagonal, and not add any height. Then binoviewers will thread onto that still exposed male T2 thread on top of diagonal. See photo on baader website here:

https://assets.baade...miciprisma.jpeg

Also be sure your 2.6 glasspath is correctly configured for your binoviewer. There is a maxbright version, and the Mark V version which has the optical element reversed. If you have it backwards it will perform very poorly.

Edited by betacygni, 14 January 2022 - 07:42 PM.

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#8 Deadlake

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Posted Yesterday, 02:39 PM

Thanks that worked great. If I wanted more magnification with a GPC 2.6 then I presume no smaller then 8 mm EP’s or go with a Barlow?



#9 rob.0919

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Posted Yesterday, 05:34 PM

Hi Martin,

 

I currently max out with a 2.6x GPC and a pair of APM 12mm flat fields. (thats 212x in my 140mm refractor which i find more than enough for our conditions)

These 12mm are discontinued but are quite nice in the bino with their twist up eyecups.

 

I only use Baader prisms with my bino (Mk 5) and have 2  : one with the 2.6x permenently residing in it.

So i tend to use the other prism with no gpc for lower powers, then for planetary etc swap the prism over

which saves fiddling around in the dark. I also have the 1.25x and 1.7x GPCs but don't use them so much.

 

I'm using 24, 19, 15 and 12mm eyepiece focal lengths so have a wide range of magnifications available.

 

50528690177_72d2669a42_c.jpg


Edited by rob.0919, Yesterday, 05:34 PM.



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