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Deep-sky binoviewer - contrast vs light loss

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#1 Astrojensen

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Posted 17 September 2010 - 02:34 PM

Hi

Monday evening was very clear here, so I went outside with my 63mm Zeiss Telemator and Baader Maxbright (+1.25x corrector, 1050mm total focal length), in order to observe some deep-sky objects for an hour or so, before hitting the sack.

I observed several objects, all of them old friends, like M13, which showed strong granularity at 105x and M92, which also showed hints of granulation. The Veil nebula was faintly visible at 26x and the double cluster was stunning at the same power.

But what really amazed me was M31 and M33. I observed both at 26x, using my 40mm TS Superview eyepieces. The field is around 1.5 degrees wide and both M31 and the two companions were all inside the field, but just barely. That's fairly ordinary, but what surprised me was that NGC 205 was dimly visible with averted vision! I normally have great difficulty picking it out, but it was not all that hard with binoviewer, though it wasn't exactly easy, of course, but easier than in mono mode. I have looked for it countless times, so just picking it out like that *with a binoviewer* greatly surprised me, considering the well-known light loss. I verified the position of the glow I observed and there is no question it was NGC 205.

I then turned to M33 and even at 26x, I could pick out NGC 604 as a tiny glow. It was easier at 42x and 58x was even better, but 105x was too much. I was also impressed by how well M33 stood out at 26x. I will definitely spend time on this galaxy when it gets higher.

*

I am very surprised by these observations, as well as those I've done earlier with the 85mm Zeiss apo on small galaxies. It seems contrast really is even better in bino mode vs mono mode and that this is actually preferable on deep-sky objects, even if they're faint threshold objects. It seems the bino holds up to mono mode, by having better contrast and ergonomics, even though the mono view is brighter. I should definitely do a direct comparison one day, something which is made a bit easier by the fact that I own two 63mm Zeiss scopes and lots of eyepieces, making comparisons at identical powers possible, as well as different ones. Trouble is, I tend to be so entranced by the bino views, I forget everything else...

I would be interested in hearing your opinion on this matter, that is, if you personally find that the improved contrast makes up for the light loss.


Clear skies!
Thomas, Denmark

#2 GlennLeDrew

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Posted 17 September 2010 - 02:57 PM

From a purely numbers standpoint, the 50% light loss is partially made up for by the gain in signal to noise of 41%.

To my mind, this would imply that there is a real loss in detection ability at the lower end of image brightness and contrast. To get there, one may need to use quite small exit pupils of, say, 1mm. Have you tried this out? I'd be interested in your results!

It would be interesting to do controlled experiments along the lines of Blackwell's 1946 study. I've often ruminated on the idea of setting up in a dark room a large screen which can be uniformly illuminated by a dimmable light source, and then projecting upon it a variety of sized spots of controllable intensity. In this way I could determine thereshold contrast levels for one- and two-eyed observation.

#3 Astrojensen

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Posted 18 September 2010 - 10:54 AM

Hi Glenn

From a purely numbers standpoint, the 50% light loss is partially made up for by the gain in signal to noise of 41%.

To my mind, this would imply that there is a real loss in detection ability at the lower end of image brightness and contrast.


I quite agree, but then the question appears, as to what is more important in the detection of faint objects: Brightness or contrast. I find it highly probable that to a certain limit, having a fainter but more contrasty image allows one to see just as faint objects - or indeed even fainter ones - by having a better S/N ratio. Perhaps it is possible to calculate this?

To get there, one may need to use quite small exit pupils of, say, 1mm. Have you tried this out? I'd be interested in your results!



Yes. As I mentioned in my first message in this thread, I have used powers up to 105x on my 63mm on deep-sky objects, with binoviewer. When using mono mode, I've been going up to 210x on small, bright objects. When binoviewing, I often use up to 58x on normal galaxies, using 18mm orthos. In mono mode, I often used 84x on galaxies. I generally get the same results with bino as with mono: To see the faintest objects, you need to go to 1mm exit pupil or in some cases, even less.

I know very well that since a binoviewer on a telescope essentially means that the aperture is reduced to 0.7x the normal, the power should also be reduced, to mimick a 1mm exit pupil on a smaller scope. The exit pupil with binoviewer should be 1.4mm to mimick a 1mm exit pupil on the simulated smaller scope. However, there is much improvement to be gained in the detection of faint stars by going much higher than this. M13, for example, shows very strong granularity at 105x on my binoviewed 63mm Telemator, better than at lower powers.

But I am not sure, which provides the best deep-sky views of galaxies etc,: The 25mm eyepieces, giving very nearly 1.4mm exit pupil at 42x, or the 18mm's giving nearly 1mm at 58x. I will need to do some very careful comparisons between them to find out. Lower powers, giving 2mm exit pupils or more, are giving fabulously sharp and contrasty views. I am thinking about getting a cheap 100mm f/5 achromat, just so that I can reach low powers with binoviewer. The biggest problem would be chromatic abberation. For this reason, I have considered newtonians, but then other problems arise (coma, central obstruction, etc).

It would be interesting to do controlled experiments along the lines of Blackwell's 1946 study. I've often ruminated on the idea of setting up in a dark room a large screen which can be uniformly illuminated by a dimmable light source, and then projecting upon it a variety of sized spots of controllable intensity. In this way I could determine thereshold contrast levels for one- and two-eyed observation.



I would be extremely interested in knowing the results of such an experiment.


Clear skies!
Thomas, Denmark

#4 davidpitre

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Posted 19 September 2010 - 03:04 PM



It would be interesting to do controlled experiments along the lines of Blackwell's 1946 study. I've often ruminated on the idea of setting up in a dark room a large screen which can be uniformly illuminated by a dimmable light source, and then projecting upon it a variety of sized spots of controllable intensity. In this way I could determine thereshold contrast levels for one- and two-eyed observation.


This would be a fantastic experiment!

#5 JustaBoy

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Posted 26 December 2013 - 11:56 AM

Hi All,

Sorry for dredging this old post up, but since members come and go, I was wondering if anyone else had anything to add to this?

I'm very interested - Thanks!

#6 Eddgie

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Posted 26 December 2013 - 12:18 PM

I have not done any of the testing mentioned, but in general terms, I agree with the OP in that the supposed light loss caused by binoviewers does not seem to have the same effect as the often quoted .7 apeture brightness would suggest if one does excatly what Astrojensen suggests, which is to use slightly less power when binoviewing as when monoviewing.

For most targets this has worked well for me. I tend to use slighly less power when using binoviewers and in general, I feel as if for deep sky extended targets (Nebula and Galaxies), I feel as if I am able to detect things as well as with monovision, and in many cases, even though the view is less magnified, I feel as if I get more detail.

For example, Planetary Nebula for me personally are always better in binoviewers than they were in mono, even though I am using a bit less power (and sometimes far less power because it just seems easier to resolve detail in the binoviewers).

There is one place though that the difference is apparent to me.

For dense clusters (Globular or regular, but dense clusters like M11) I do notice that I don't have quite the same limiting magnitude.

M13 for example does not seem quite as resolved.

But I still vastly prefer the view though binoviewers because the depth is so much more pronounced.

So, while I feel that in some instances there is a slight penalty, for me personally, the use of two eyes just makes most targets far more beautiful to me.

I am now doing almost 100% of my observing using binoviewers. While it may very well be that I am loosing a tiny bit of limiting magnitude, the quality of the views just seem better to me.

And the 110mm f/refractor has been a complete rebirth for my interest in small refractors.

The low power wide field views in the SV110 have been nothing short of spectacular. For every target I have revisited, I enjoyed the view so much more than with my 100mm f/9ED and my TV 101. Big clusters are totally amazing in the binoviewers. All of them.

I had given up on using small refractors but the binoviewers have completely changed the game, and now using my small refractor is actually enjoyable to me, where in the past, it has always been just a bit to disappointing to me.

#7 faackanders2

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Posted 26 December 2013 - 04:23 PM

In my 17.5" f4.1 Dob, I have the opposite effect. Dim objects can only be seen in mono view. Brighter objects are required for bino view. In binoview mode I always look for objects in lowest LL power mode (1x for normal Newtonian OCS, 0.87x for newer 45mm clear aperture Multipurpose OCS", or 1.8/1.4= 1.29x est for lesser used Multiplier OCS.) I amlost aways use 24mm Panoptics, but sometimes use 14mm 82 AFOV ES when the panoptics dew or ice over.

I uses to almost always binoview till 100 AFOV eyepieces came out and I fell in love with those.

#8 GlennLeDrew

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Posted 26 December 2013 - 07:59 PM

Thomas's original question, which asked whether it's brightness or contrast which is more important, can be answered, "contrast" when it comes to extended objects at least. The eye is primarily a contrast detector, and its huge dynamic range results in a 50% diminution in image brightness being a not so egregious loss.

Now, near the threshold of detection when contrast is very low and the sky is quite dark (as made so by a small exit pupil), the advantage seems to shift to the brighter view delivered in mono mode. That is, if the small object size doses not permit to back off on magnification and thereby regain image surface brightness. Failing that, an increase in aperture which provides the required magnification *and* retention of image brightness is in order.

#9 Allan Wade

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Posted 26 December 2013 - 08:57 PM

I have just started using the BinoTron, and have not had them nearly long enough to start making firm judgements yet. However, a couple of things I have observed so far.

I have to use a filter when looking at the near full moon in mono mode. The brightness is borderline painful for me. I don't use a filter with the bino. This indicates to me that some light loss is occurring in the bino.

Observing NGC253 Sculptor Galaxy was as pleasing, if not more so, in the BinoTron. The contrast was better and I could see more detail in the dust lanes than observing through the Delos. This was the opposite to what I was expecting, but tends to agree with some of the comments in this thread.

#10 swampdog

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Posted 30 December 2013 - 03:26 PM

Interesting idea this contrast vs. light loss. An experiment I do from time to time, with the sct+gem mount (because of available focuser travel) is to swap out bino/diagonal combo, to directly bino to visual back. Then I might try same thing in mono mode, all the while using same mm ep's, if I have them. Conclusion?...Yes, lower powers are more pleasing in binos, from magnification factors, aside from that, it's six of one & half a dozen of the other, so for me, it reinforces the idea that while a shorter path in general, is good, but also you want to keep it simple, sturdy, & user friendly.

#11 jgraham

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Posted 03 January 2014 - 07:54 PM

Last summer I spent quite a while out with my 10" SCT observing deepsky objects with a monocular as per usual. Just for yucks I mounted up my binoviewers with the idea that I would just take a quick peek before bringing my gear back inside. The absence of eye strain was so nice I just had to start over and revisit everything that just looked at with my monocular. I was surprised that I didn't notice any loss in brightness, the view was just so comfortable. I now use my binoviewer most of the time when I'm observing, the exception being when I want to use my 2" eyepieces.

#12 Sorny

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Posted 03 January 2014 - 11:02 PM

The only times I observe without the binoviewer now is when I need more mag than my bino pair gives, or a larger TFOV (and big exit pupil) that I get with my big ol' 55mm Plossl.

Most nights, there is no changing eyepieces at all. Just flip a switch and refocus...

#13 t.r.

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Posted 06 January 2014 - 09:22 AM

This is the biggest hurdle for newcomers to binoviewing to accept...YES, there is a light loss in the binoviewer, HOWEVER the increase in perceived contrast due to binocular summation makes up for a large part of it and the added bonus is the comfort in using two eyes! The only reasons I go back to monoviewing are to reach a limiting magnitude or for grab-n-go quick sessions. Binoviewing on all categories of objects is just so much better to me!

#14 Mark9473

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Posted 06 January 2014 - 12:30 PM

This is the biggest hurdle for newcomers to binoviewing to accept...YES, there is a light loss in the binoviewer, HOWEVER the increase in perceived contrast due to binocular summation makes up for a large part of it

Well, it doesn't for me. Not for any open or globular star cluster.

#15 Astrojensen

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Posted 07 January 2014 - 02:53 PM

Well, it doesn't for me. Not for any open or globular star cluster.



Funny, I find those to work particularly well in a binoviewer. Obviously the scope must be large enough to have a little extra light to spare in case of the globulars and have a focal length short enough in case of the larger open clusters. M13 in my C8 with binoviewer, running at around 300x in very good seeing was a sight to behold. Truly excellent.

We all have different tastes and expectations when it comes to visual observing. It is very important to note this. What works well for me might be a dull, boring view for others.


Clear skies!
Thomas, Denmark

#16 George N

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Posted 09 January 2014 - 10:42 PM

For my eyes, my bino-viewer does cut back on DSO brightness when used on 5 & 6 inch scopes (Newt & APOs), so I generally only use the bino with these scopes for solar/lunar/planetary viewing.

When used with my 20-inch Dob, or Kopernik Observatory's 20-inch F/8 RC Cass, I don't notice much if any reduction in brightness. The only observational reasons I would not use a bino on those scopes is when I need a very wide field, or when observing galaxy cluster/groups (dimmer than 13.5 magnitude). The latter are a frequent target when I observe from a very dark location. In this case I'm pushing the Dob as deep as it goes, and I believe that mono is the way to go.

#17 GlennLeDrew

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Posted 10 January 2014 - 04:40 AM

A BV does not have some 'magical' quality that selectively dims the image more on small apertures. No matter the aperture, the ratio of light loss introduced by a BV is *constant*. This is important to bear in mind.

There are two reasons why it *appears* the BV dims the image more so on smaller scopes.

1) The object is already dim and/or small, and so gets uncomfortably close to the threshold of visibility.

2) One is trying to compensate for the smaller image scale by not decreasing magnification in step with the aperture ( i.e., decreasing the exit pupil), and thereby dimming the view.

If one bears in mind the role of the exit pupil, objects which are suitable for the smaller aperture are quite well seen with a BV attached. If the aperture is halved, the smallest objects are doubled in size, and the faint limit is brightened by 1.5 magnitudes. Do not push the instrument beyond its limits, and all is fine.

#18 Astrojensen

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Posted 10 January 2014 - 05:28 AM

Beat me to it, Glenn. However, the light loss you quote is exaggerated. You lose 0.8 magnitude by splitting the light in half, but you gain 0.4 magnitude (or a little less) by the S/N increase from doubling the signal. Effectively, you lose about 0.4 - 0.5 magnitude. (EDIT: As you have already pointed out above in your first post in this thread...! Duh! moment there for me.)

I've found that even a 63mm scope works fine on deep-sky objects with a binoviewer, as long as you keep the magnification down on the faint stuff or keep to the relatively bright stuff if you want to use some magnification. As a rule of thumb, if it is visible in a telescope in mono mode with 0.8x the aperture, it's fair game in a binoviewer.

Contrast detection is enhanced, as is ergonomics, so in many cases you actually end up seeing MORE with the bino than with a single eyepiece. But the bino MUST be able to work at low magnifications, preferably without a barlow.


Clear skies!
Thomas, Denmark

#19 Mark9473

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Posted 10 January 2014 - 05:46 AM

Next time you look at M37 with a binoviewer in your 63mm, please take the time to compare the mono view and let us know if you can convince yourself you saw more stars in the binoviewer.

#20 Astrojensen

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Posted 10 January 2014 - 08:36 AM

I wasn't clear enough, it seems. Of course I will see fewer stars. I did point out that there would be a net loss in light grasp, didn't I?

But on deep-sky targets where the detection of details depend strongly on how contrasty they appear, such as details in galaxies, the binoviewer can best the view of the single eyepiece. At least for me.

Here's a drawing of M106, made with the binoviewer on my 63mm Zeiss:

Posted Image

And here's one of M51:

Posted Image


Clear skies!
Thomas, Denmark

#21 GlennLeDrew

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Posted 10 January 2014 - 09:07 AM

Thomas,
Methinks thou didst read too swiftly. I did not imply a halving of area. I stated that a halving of aperture is a dimming by 1.5 magnitudes. If we have a 12" scope, what aperture is half that? Why, 6" of course. And so the light collecting area is 1/4, and the magnitude equivalent is 1.5. :grin:

#22 Astrojensen

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Posted 10 January 2014 - 01:57 PM

Eeerhm - guess I am still a little confused about it... But I think I get that it was just an example of how a smaller scope affects what's being seen and it had no *direct* relation to the binoviewer discussion?


Clear skies!
Thomas, Denmark

#23 GlennLeDrew

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Posted 10 January 2014 - 02:57 PM

Yes, it's more fundamental 'background' info on how use a telescope on dim objects, with OR without a BV attached. I was stressing that smaller apertures are fine when appropriate objects are viewed.

The number of comments which have it that smaller apertures are not suitable for BV use due to the dimming puzzle me. A BV-equipped scope is just like a true binocular. Both instruments are defined by the same laws if optics. If a Binocular can be used down to quite small apertures, so can a BV. The very same brightness offset as exists between some huge true bino and a same-aperture BV/scope applies for all other aperture regimes.

If we accept that a 10" true bino and, say, an 11" scope w/BV are equivalent in terms of image brightness, then it's the case that a 3" bino and a 3.3" scope w/BV are equivalent. Or 1" and 1.1".

#24 Astrojensen

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Posted 10 January 2014 - 03:23 PM

I was stressing that smaller apertures are fine when appropriate objects are viewed.


Absolutely. Viewing 11th mag galaxies in a 60mm is the same as observing 16th mag galaxies in a 24". You just got fewer to choose from... And a lot fewer objects that do appear very bright in the eyepiece.

The number of comments which have it that smaller apertures are not suitable for BV use due to the dimming puzzle me. A BV-equipped scope is just like a true binocular. Both instruments are defined by the same laws if optics. If a Binocular can be used down to quite small apertures, so can a BV. The very same brightness offset as exists between some huge true bino and a same-aperture BV/scope applies for all other aperture regimes.


Totally agree, but I offer an explanation: People don't know how to make the binoviewer work at low magnification. This dims the view uncomfortably. The situation is made worse by the fact that many large scopes are often very fast f/ratio (big dobs certainly are) and thus have a much better starting point, if a barlow is needed to reach focus, since the final f/ratio is still not all that slow.

If we accept that a 10" true bino and, say, an 11" scope w/BV are equivalent in terms of image brightness, then it's the case that a 3" bino and a 3.3" scope w/BV are equivalent. Or 1" and 1.1".



A scope with binoviewer needs to be 1.4x the aperture of a true binocular telescope to show the same brightness in the eyepiece. But it will be far more compact and easy to manage. It will not be able to go to as low magnifications as the true binocular telescope or show as wide a true field.

A 14" with binoviewer is the same as a true 10" binoscope; a 100mm is the same as a 70mm; a 11.2" is the equivalent of an 8" binocular, etc.


Clear skies!
Thomas, Denmark

#25 GlennLeDrew

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Posted 10 January 2014 - 04:05 PM

Thomas,
If one were viewing through a BV with just one eye, then the 1.414 ratio (and its reciprocal, 0.707) on aperture would certainly apply. Integrating two signals, however, regains some of that loss, which when applied to the two dimmed images gets you back up in equivalent aperture an additional 1.189 times in aperture. And so for a 10" with BV, the one-eyed equivalent aperture is 7.07", and with two eyes on the case it becomes 7.707 * 1.189 = 9.16".






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