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binoviewing vs mono

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#1 Ebbisham

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Posted 01 January 2014 - 07:02 PM

I just noticed than when comparing my mono viewing habits with the bino eps i always seem to step back when going bino.
I usualy find that a 8mm TV plossl gives me the best and stable views of Jupiter and the moon in mono mode. When changing to my Baader maxbright i either find a pair of 25mm TV plossl with a GPC 2.6 (mag 2.5 from what i read here) or a pair of 15mm TV plossl with a GPC 1.7 (really a x1.5)as the best pick before the image starts to loose and get soft and unstable. Both combos result in an effective 10mm ep.
does this have to do with the loss of light in a binoviewer or is it just me :) .

#2 Eddgie

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Posted 01 January 2014 - 09:09 PM

I think that it is in fact the dimming.

Anyone that has read many of my posts on planetary observing will tell you this I believe that image brightness is very important factor in getting the best view, and that to small an exit pupil, and the eye will start to loose contrast, and to me the dimming is essentially the same as using too small an exit pupil.

I see the same thing that you do. I cannot use the same high powers when binoviewing that I use in monovision.

I have to lower down one step.

But even though the image is smaller (and brighter of course) both eyes working togetheter still allow me to see more than with the higher power in monovision.

My result then, matches yours. I noticed it with every binoviewer I have used (so I don't think it is anything to do with your binoviewer quality), my very best observations are typically done with a bit less power, but even though the target is smaller, I still feel like I get more detail and all details are easier to see.

#3 faackanders2

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Posted 01 January 2014 - 09:22 PM

For a Newtonian, the binoviewer system naturally increases magnification so obviously a lower powered eyepiece works better when binoviewing.

Binoviewers work better on bright object. Some dim objects require monoviewing to see. Some large and/or multiple objects require wider mono TFOV 2" eyepieces to see more and/or all of the objects.

P.S. With my 17.1" f4.1 Dob the plannets are never dim. That might be why I use filters often, because the dimming of the filter actuaally has a beneficial effect on very bright planets.

#4 Eddgie

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Posted 01 January 2014 - 11:04 PM

I am not aware that a binoviewer increases magnification in Newts unless you use a GPC or Barlow.

In SCTs and MCTs with moving mirrors, they do increase magnification, but not in Newts without the use of a GPC or Barlow.

#5 faackanders2

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Posted 01 January 2014 - 11:40 PM

I am not aware that a binoviewer increases magnification in Newts unless you use a GPC or Barlow.

In SCTs and MCTs with moving mirrors, they do increase magnification, but not in Newts without the use of a GPC or Barlow.


The extra length of the binoviewer increases focal length of the system and power is increased. I had to get an additional reducer power switch to get to 1x power (normal eyepiece mono power) in LL mode with 1.4x newtonian OCS.
Only with the advent of 45mm clear aperture 1.2x multipurpose OCS, was I able to be 0.84x (lower than 1x).
So all my other 8 of 9=3x3 power switch options are > 1x barlow equivqlents. And if i put the 1.3x multiplier OCS on all 9 power options , even LL are > 1x.
I have a slit tube discovery Dob, and chose to keep mirror and secondary positions as received, so the system would work as designed in mono mode.

I believe all others that have newtonians with original unshortened trusses have the same >1x multiplier unless they have the recently discontinued reducer power switch.

#6 GlennLeDrew

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Posted 02 January 2014 - 05:44 AM

Just to be doubly sure, the BV *by itself* does not alter the effective focal length of the telescope.

On such scopes as Newts and refractors, the BV with no auxiliary optics does not alter the focal length. On a Cass it will, because of the altered distance forced upon the primary/secondary in order to push the focus farther out.

As to the efficacy of using a somewhat lesser magnification than in mono mode... There are two reasons for this.

1) The increase in signal to noise afforded by two eyes does seem to permit resolving somewhat finer detail.
2) The image dimming, while partially made up for when the two images are integrated, could make for a slight reduction in the visual system's resolving power. And a dimmer image at smaller exit pupils is less pleasing, too.

So by going to a slightly smaller exit pupil/lower magnification, image surface brightness is regained, but the better resolution afforded by two eyes makes up for the reduced image scale. But if magnification is reduced by more than perhaps 20%, such a compensation may not be realized.

#7 Eddgie

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Posted 02 January 2014 - 09:05 AM

The binoviewer by itself does not change the focal lenght of reflectors.

Only for moving mirror systems with negative power secondaries.

Any magnificaiton you get with your newt was because of the extra elements you used, not because of the bino.

A newt with shorthend poles will work at stated focal lenght.

The OCS allows the newt to reach focus without a GPC.

Same for refractors. My refractor works at stated focal lenght with binoviewres.

If you add GPCs, that is what increases the magnifcation, not the bino itself.

#8 dmgriff

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Posted 02 January 2014 - 05:50 PM

I believe there should be a lot of info in the archives on this general topic of eps and bvs for optimal results.

As I recall, 17mm plossls with oca was a good performer in those posts.

My experience with reflectors and bvs supports this general combo for merging images, etc.

Good viewing,

Dave

#9 faackanders2

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Posted 02 January 2014 - 08:48 PM

What is GPC?

#10 Ebbisham

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Posted 02 January 2014 - 11:17 PM

a glas path corrector IIRC developed by Rolad Christen for the Mark V. Acts as a barlow but also cleans up the effect all the glas in a binoviewer has on the image.

#11 Eddgie

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Posted 03 January 2014 - 09:43 AM

Ebbisham has nailed it, but I will add a little.

Because the binoviwer uses prisms, a fast light cone can start to seperate and show chromatic aberration because of these prisms.

The Glass Path Corrector is designed to cancel this error out and to shorten the light path.

A Balow that doubles the focal ratio will do much the same thing but only at 2X or greater.

If one desires to get the least magnification possible and can reach focus without the GPC, then it is not really required for general observing, but the binoviewer will induce CA in fast telescopes.

For example, I tried Solar White Light with my SV110ED. Even though I could reach focus without the GPC, I was shocked to see how bad the CA was.

I put in the 1.25 GPC and the improvement was pretty dramatic. There was still a tiny amount of CA, but that was coming from the scope itself.

So, I use the GPC for planets and solar, but I remove it for DSO and wide field observing.

Again, if you use a 2X Barlow or a slow scope like an SCT, you may not see the result, but with a fast scope, expect the see CA without a properly designed GPC.

#12 faackanders2

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Posted 03 January 2014 - 11:38 PM

Ebbisham has nailed it, but I will add a little.

Because the binoviwer uses prisms, a fast light cone can start to seperate and show chromatic aberration because of these prisms.

The Glass Path Corrector is designed to cancel this error out and to shorten the light path.

A Balow that doubles the focal ratio will do much the same thing but only at 2X or greater.

If one desires to get the least magnification possible and can reach focus without the GPC, then it is not really required for general observing, but the binoviewer will induce CA in fast telescopes.

For example, I tried Solar White Light with my SV110ED. Even though I could reach focus without the GPC, I was shocked to see how bad the CA was.

I put in the 1.25 GPC and the improvement was pretty dramatic. There was still a tiny amount of CA, but that was coming from the scope itself.

So, I use the GPC for planets and solar, but I remove it for DSO and wide field observing.

Again, if you use a 2X Barlow or a slow scope like an SCT, you may not see the result, but with a fast scope, expect the see CA without a properly designed GPC.


Would the Denk OCS act as a GPS? would using powerswitches make CA worse? I have only had issues with the very highest power HH (prototype part) and very lowest power (LL) on bright Jupiter with heavy 10mm Etos eyepieces (system potentially too heavy for focuser)

#13 Eddgie

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Posted 04 January 2014 - 09:27 AM

I do not know if the Denkmeier GPC was specifically designed to ofset CA or not, but since the Denk front element is bascially a 2x Barlow, the light cone from it is not all that steep.

The most important element would be the low power reducer arm becasuse this will make the light cone fastser.

But this is also the low power element, so at low powers, CA will not be as noticable or as important.

And straight though, the front OCS is working and that is somehthing like 2.3x, so even an f/5 telescope light cone will hit the BV body at f/10, yes?

I have useed two Denkmeier powerswitch systems and have not noticed CA.

Now if you used an a la carte bino head in a fast refractor, my guess is that you would have CA without a GPC.

But these are all just guesses. I don't know what steps Denk has taken to deal with the issue, but for the low power arm, it probably does not make any difference, and straigh though and high powers are running behind the 2X GPC with a very shallow light cone.

#14 faackanders2

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Posted 04 January 2014 - 09:31 PM

I do not know if the Denkmeier GPC was specifically designed to ofset CA or not, but since the Denk front element is bascially a 2x Barlow, the light cone from it is not all that steep.

The most important element would be the low power reducer arm becasuse this will make the light cone fastser.

But this is also the low power element, so at low powers, CA will not be as noticable or as important.

And straight though, the front OCS is working and that is somehthing like 2.3x, so even an f/5 telescope light cone will hit the BV body at f/10, yes?

I have useed two Denkmeier powerswitch systems and have not noticed CA.

Now if you used an a la carte bino head in a fast refractor, my guess is that you would have CA without a GPC.

But these are all just guesses. I don't know what steps Denk has taken to deal with the issue, but for the low power arm, it probably does not make any difference, and straigh though and high powers are running behind the 2X GPC with a very shallow light cone.


In my scope straight through w/ both powers switch lenses pulled out MM/MH is 2.3x (Multipurpose), 2.5x (Newtonian) and 3.2x (Miltiplier OCS).
For finder mode w/ both powers switch lenses pushed in on left side out LL/LL is 0.87x (Multipurpose), 1.0x (Newtonian) and 1.3x (Miltiplier OCS). I really do like this mode alot, and am surprised Russ discontinued it.
rarely used high power mode w/ both powers switch lenses pushed in on left side out RM/HH is 3.3*0.87x (Multipurpose), 3.3x (Newtonian) and 3.3*1.3=4.3x est (Miltiplier OCS). The HH option was my requested prototype, not pre tested, and not guaranteed.
All other power switch combinations are between these limits.






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