100mm binoculars

[glass]

Would a 100 mm binocular have the same light gathering of a 200 mm telescope? Thanks. 

[Alien 13]

The total surface area of the combined 100 mm objectives would be equivalent to a single optic of around 142 mm, not sure how this works in the real world though and how the brain processes the two images.

Alan 

[Ben the Ignorant]

25 minutes ago, glass said:

Would a 100 mm binocular have the same light gathering of a 200 mm telescope?

No, an objective with 1/2 the diameter collects 1/4 of the light, but the two together take in half the light compared to a 200mm scope. The question is not that straightforward when you pit a binocular against a monocular scope, though. The binocs have the natural contrast and snappy images of a refractor, and when the brain receives the same info from both eyes, it constructs a more vivid sight in the mind's eye.

The monocular scope will reach higher mags, good for high-res, the bino will detach deep-sky targets very well from the sky, good for low-power. Are you interested in an achromatic or apo binocular? Cause the latter will also reach high powers and sharp planetary detail.

[Alfian]

Have a look at this useful article by Ed Zarenski regarding "Binocular Summation".

http://www.cloudynights.com/topic/61467-binocular-vision-summation/#entry792719

This would suggest that taken all factors into account, which Ed Zarenski typically does at length,  a 100 mm bino  would equate to a 118mm scope. 

[glass]

Ben, I have a 100mm APM APO which I am very pleased with. I'm thinking of getting an  Altair Starwave 152mm (used hopefully) and wonder if I could see deeper with the telescope. Higher magnification but less FOV I suppose?

[Ben the Ignorant]

In your case I would stick to the double 100mm apo. As Alien 13 said, it grabs as much light as a single 142mm lens, but focuses it more tightly than an achro, and feeds both eyes. I guesstimate you would need at least a 250mm monocular to make a worthwhile jump from your 100mm apo.

[glass]

 Thanks for all replies. Ben, I don't intend selling the 100 mm, just wondered if there'd be much of an advantage to get the 152 mm Altair as well, which it seems there isn't. Thanks very much for your advice. 

[Peter Drew]

It depends a lot on what you want to look at. For things like M31, M42 or Plieades probably nothing would beat your APM's, but for globulars the superior resolution of the 152 would be an advantage and its marginal extra light grasp would render faint objects on the limit of visibility a little easier to see. Whether this would be enough to justify an additional telescope is in the eye of the observer. 

[BinocularSky]

As a rule of thumb for detecting faint objects, all else being equal (*), I reckon a binocular is equivalent to a monocular aperture approx 1.4x larger, and this tends to accord with empirical evidence. There are at least two kinds of binocular summation when it comes to faint objects: statistical (higher probability of detection with two detectors) and physiological (essentially reduction of neural noise). Remember that vision is not a linear response and a heck of a lot of it has to do with the processing in the brain, not just the response of the rods in your retina.

Magnification also plays a part in rendering things visible; with stars (& resolving clusters) this is obvious: point sources become more intense with larger apertures and higher magnification renders them resolvable, but what about something with low contrast like the Triangulum Galaxy (M33)? It is a rule of optical physics that a passive optical system can only make an extended object fainter, yet it is a heck of a lot easier to detect M33 in a 10x50 binocular than it is with the unaided eye. And easier still with a 16x70, even though it ought to be fainter. Then again, it looks brighter in a 10x70 (if your eyes can take advantage of the exit pupil). Rendering things visible is a function of the instrument (the characteristics of which, in general, we do understand) and the observer's visual system (of which we have a lesser understanding).

* Conclusion: All else is not equal and there is a large variation in instruments and how they are used, and a huge variation in observers - for this reason, I don't think a "strict rule of binocular summation" is a thing.

Oh dear. I didn't mean to add confusion. Honestly. Sorry.

[glass]

Thanks for your opinions. If I come across a real bargain i might take it.

[bertieb]

I just found this study which agrees with the 1.4x increase for point light sources but goes on to suggest that for viewing extended objects that increase may be as much as 1.6 - 1.8x. All to do with the gain in contrast apparently.

http://arieotte-binoscopes.nl/Binocular Summation Factor.pdf

[Physopto]

Reading through this thread one point that I think that has been missed is this.

What is seen or perceived to be seen by the brain adding two optics together compared to only a single view, is this. 

I have had a few pairs of binoculars and several scopes. From 12" Lx 200 , a WO 132mm f7 to my last purchase an 85mm Tak at f5.3.

if I had two 85mm Taks and added them together to make binoculars I would still have f5.3 optics for the brain to assimilate (one for each eye).  Same with two WO 132mm at f7.

For light gathering onto a ccd it is a  different matter.

I don't understand the human physiology of the brain so cannot comment on why. If the Tak or WO binocular idea was used with optics to superimpose the images onto the same ccd then a different matter as image accumulation time would be reduced, by half !!

 

Thoughts anyone ?

Derek

[LukeSkywatcher]

In a nutshell...........NO. Bins and scopes are 2 very different things. Its all about the mechanics and our perception. I have a set of 20x90 bins and they are great, but they come nowhere even close to giving me the same views as with my 200mm scope.

The biggest and best advantage with observing with bins is how the brain perceives the view. The human brain is wired to see things in 3D (or is it 2D stereoscopic). Thats why the view through bins is much more natural and pleasing to us than if we look with one eye through a scope (2D).

Using both eyes while observing with bins allows the brain to register what it does naturally..........depth of field of view.