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Refractor-like views?

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#1 RGM

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Posted 12 October 2013 - 08:33 AM

This is a question for those that use binos in their refractors. I have an older Denk Standard binoviewer. It is at least 10 years old. The model I have came with a single arm power switch for reducer mode.

I can reach focus in my 5" Istar without an OCS, and I do not use the reduction mode, just straight through. The binoviewer is wonderful to use, BUT..., it does not provide as pin-point stars as mono viewing does. The stars are just "mushy" enough to bother me.

Thinking about upgrading to something better. Are there any binoviewers that do not degrade the star image? I am looking to retain the "diamond dust on velvet" view.

Thanks

#2 mikey cee

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Posted 12 October 2013 - 09:39 AM

Don't know about your Denks. Sounds like something is amiss. My WO's in my 10" refractor are sharp right up to 815x with tight doubles. Of course this is dependent on seeing conditions this time of year. Yes a lot of my nights produce fuzzy stars but it is not the bino's fault. ;) Mike

#3 Astrojensen

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Posted 12 October 2013 - 09:53 AM

I have the same experience as Mike. My Baader Maxbrights are as sharp as the scope I am using them in, seeing depending, of course. I see no difference in sharpness between mono and bino.

But often, when I am using the same magnifications in both modes, I am able to resolve more in bino mode, and that can make the seeing more noticeable. The solution is to lower the magnification a bit, usually to 70% of mono mode. This provides me with the same level of brightness and detail as in mono, but with increased contrast, due to the binocular vision, and lowers the seeing sensitivity.


Clear skies!
Thomas, Denmark

#4 RGM

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Posted 12 October 2013 - 12:00 PM

Mikey and Thomas, I have done comparisons just minutes apart, at the same magnificatiion, and can see a difference. I bought my Denks early in their developement, and maybe the quality has improved. I guess that is my question. Would buying a more modern bino give me an improvement.

Observing under the jet stream is something I have to deal with. I will take more time, over more nights, and try to nail down if the seeing has more of an impact on the binos than on mono viewing. Maybe under good/rare/great conditions the binos will deliver the views I am after.

#5 Astrojensen

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Posted 12 October 2013 - 01:35 PM

If in doubt, compare the views in mono, by using just one side of the binoviewer. Compare both sides, to determine, that one side isn't worse than the other. If it's still unsharper than in real mono mode, then you can expect a notable difference by changing to a higher quality binoviewer.


Clear skies!
Thomas, Denmark

#6 GlennLeDrew

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Posted 12 October 2013 - 01:52 PM

You can try this sensitive test for quality. Hold the BV in front of a bino or finder scope. This could be done during the day, or at night using distant street lights. It doesn't matter if the BV's aperture is much smaller than the testing instrument's objective; just mask off any aperture which might allow light not from the BV to enter. To make the comparison meaningful, make a mask whose opening is no larger than the BV's clear aperture. In this way you will retain the same exit pupil for both views.

At 6-10X, this test is more sensitive to optical error in the BV than during normal use on the scope. You are utilizing the *full aperture* of *all* surfaces for every image point in the field. If the BV imposed, say, a 1/2 wave error, at 6X this would appear as though it were 3 waves. If the view with the BV in place is not noticeably inferior to the masked down view without, the BV is likely not at fault.

Naturally, do this test through both sides, aiming through the eyepiece barrels. And for curiosity's sake you could flip the BV around, aiming into the front barrel. You will have two overlapping images, for which very distant lights or stars (e.g., the Pleiades) would make a better target.

#7 Astrojensen

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Posted 12 October 2013 - 02:24 PM

Hi Glenn

I had completely forgot about that test. The Moon makes an excellent target for it. By masking one half of the bino, you can check for image quality, and by using both halves, you can check for image merging. I use an 8x30 finderscope. By using the Moon, which is close to 30' in diameter, you can estimate the prism misalignment.


Clear skies!
Thomas, Denmark

#8 tonyt

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Posted 12 October 2013 - 07:31 PM

I've been out the last 3 nights with my Denk Binotron in the ED127 comparing views to mono in the refractor and mono in an 8" Edge, the subject being the Moon. I haven't been able to see any disadvantage to the binoviewers with or without the powerswitch although unstable conditions haven't let go to higher magnification.
The one noticeable difference is the extra comfort of using two eyes, especially trying to pick out fine detail.

I haven't used my WO set for a little while; they seem very good too but with a bit less contrast, probably due to lesser baffling inside the bino.

#9 urassner

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Posted 13 October 2013 - 08:37 AM

I use a Denk II with D14s mostly on the moon and planets, also occasionally on M13 ( my backyard has a lot of light pollution) and never have the feeling that the image is degraded compared to mono viewing with an XW eyepiece. I am using a 6 inch refractor.

#10 RGM

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Posted 13 October 2013 - 09:06 AM

Thanks for the input from everyone. I was also out last night, and spent a lot more time trying to find out why I see a difference. I think I may have found the problem.

Over the past year I have switched my mono eyepiece collection to long eyerelief because of my 60 year old eyes. I now use Panoptics and XWs for all mono viewing with my eyeglasses and this has greatly improved the quality of the view.

In bino, I am still viewing without eyeglasses, beacause of the limited eyerelief of my bino eyepiece collection. Last night I tried bino viewing with glasses at the expense of a smaller FOV, but immediately noticed an improvement. The views were in fact similar to mono.

So, it looks like my 19Pans and 13T6s will have to be replaced with 20mm eyerelief alternatives. I will start a separate thread to address this question.






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