Resolution 32 vs. 50 (1 Viewer)

[ReinierB]

Good day,

I have people heard saying that a 10x50 has more resolution compared to, let's say, a 10x32 because of the lens diameter. Is that true? And if that is true, how will you notice that?
Let's say it is a very bright day, will the 10x50 outperform a 10x32 if you spot an object far away in regard of the resolution? Will the 50's show more pixels / show a sharper image?
I just wonder...
(NL Pure 10x32 vs. EL 10x50)

 

[Binastro]

Hi Reinier,

The answer mostly depends on the observer's eyesight.

One could say that on a bright day the pupil size is about 2.5mm, so both binoculars are working as 10x25s.
So the performance is equal.

However at f/4 the focal lengths are 200mm and 128mm.

Stopped down to 25mm the larger binocular is working at f/8, the smaller binocular at f/5.
So the resolution of the larger binocular is probably better.
And the eyepieces have focal lengths of 20mm and 12.8mm.
So the larger binocular probably has more eye relief.

Also the larger binocular may be steadier because it is heavier and longer.

It is likely the larger binocular resolves better, but neither binocular has enough magnification to resolve near the limit for its size unless one has exceptional eyesight and the binocular has exceptional optics.

Regards,
B.

 

[ReinierB]

I am sorry, what do mean with f/4, f/5 and f/8?
Thanks for your reply anyway!

 

[Conndomat]

I am sorry, what do mean with f/4, f/5 and f/8?

...is the ratio of the lens opening to the focal length!

Example 50mm. opening, 200mm. focal length = f/4
Example 50mm. opening, 250mm. focal length = f/5...etc.

Andreas

 

[Binastro]

The focal length of a telescope or binocular objective divided by the aperture gives the focal ratio or f number.

So, if the focal length of a short focus instrument objective front lens like a binocular is 200mm and the aperture 50mm then 200 divided by 50 is 4.
Or f/4.

f/4 is simple to use although some binoculars are nearer f/3.6.
At these fast focal ratios the aberrations or optical faults are more apparent than with slow optical systems like f/8.

Because the pupil size of the eye is small in bright sunshine not all of the aperture is used.
The instrument is stopped down.

A hand held binocular suffers from hand tremor.
Any Canon IS binocular from 8x upwards will likely resolve better than either the Swarovski 10x50 or 10x32.

The focal length of a lens is the distance from the lens to the focus point of the lens using something distant such as the Moon.

Regards,
B.

 

[William Lewis]

I'm no expert but I notice a difference with my SLC 8x56 in resolving details compared to 32's. This was especially apparent when I was on top of the great orm this summer looking down on the villages along the Welsh coast, I've never had a binocular reveal so much fine detail at range. It's much less apparent at "normal" distances and also less apparent in darker conditions - despite the high transmission and large exit pupil.

I think the conventional wisdom is that binocular resolving power as long as it's of good quality even with a 20mm objective is beyond what human eyesight can perceive though, so what do I know!

What I also find interesting is that generally the mechanics and glass before the eye piece of binoculars, again using the SLC 56 as an example are I believe similar regardless of the magnification - the SLC has 8x 10x and 15x magnifications but it's just the eye pieces that set the mag. So I suppose the detail is there that the 15x mag can resolve in the 8x, it's just too small to see.

The other factor to consider is that with a larger aperture for a fixed magnification you also get a larger exit pupil, in use this means that if your pupils are smaller than the exit pupil, if properly aligned you will only be seeing the image produced by the central parts of the lenses which generally means less aberrations. Again I'm no expert so will hope Henry may chime in, especially as I haven't heard from him for a while!

P.s top thread, I love a technical quandary!

 

[Scott98]

The larger-aperture binoculars are resolving more detail in the image, the debatable part is whether your eyes can detect it. At low power of 7 or 10x the theoretical limit of eyes says maybe you can't see a difference. For me, more aperture is always better - I see a "richer" image - just more alive and vibrant-looking.

Of course hanging a 56mm binocular off your neck for a 3-hour walk in the woods is not practical for most, and bearing the weight isn't much better with a chest or shoulder harness either. I'll keep my 10x56 mostly for astronomy but also for a special thrill anytime I want to carry them along for a short session with more distant terrestrial targets

 

[tenex]

I agree that this resolution difference due to objective size is most easily noticed in fine detail at great distances, rather than in typical birding. What I don't understand is why the effect is more obvious in some cases than others. In particular, the EII 8x30 seems to perform surprisingly well for its size. And it can't have an unusually slow focal ratio, with those dimensions.

 

[William Lewis]

I agree that this resolution difference due to objective size is most easily noticed in fine detail at great distances, rather than in typical birding. What I don't understand is why the effect is more obvious in some cases than others. In particular, the EII 8x30 seems to perform surprisingly well for its size. And it can't have an unusually slow focal ratio, with those dimensions.

I might suspect transmission plays a role. So habichts are known as very high transmission glass and in the 8x30 (prism leak aside) one of the sharpest of the genre. So hypothetically in good light a higher transmission glass will let through more light to your pupil, shrinking it and therefore stopping down the binocular so again it's only using the central part of the optics?

 

[Binastro]

There is definitely a difference in resolution with binoculars because of the quality of the optics and the design.

I find in particular the following samples of binoculars that have I tried are very good. Nikon E II 8x30, Conquest HD 10x42, Canon 10x30 IS (IS off), the Foton 5x25 (actually 35mm objectives), Hensoldt 16x56, Zeiss 20x60S.

Some binoculars have mushy expanded star images and don't resolve well at night but are very good in the day. Probably more to do with handling and balance.

B.

 

[kimmik]

SLC 8x56 is centrally slightly sharper than EL 8x32.

Most noticeable when darker and you use the full exit pupil.

SLC 8x56 will always get the job done.

 

[yarrellii]

All this thread is a very interesting read, I hope more forum members will continue to contribute with more hints and clues.

What I don't understand is why the effect is more obvious in some cases than others. In particular, the EII 8x30 seems to perform surprisingly well for its size. And it can't have an unusually slow focal ratio, with those dimensions.

Off topic, I know, but other surprising fact about the 8x30 EII (for me, at least) is the ease of view, how natural, easy and fast is to find a perfect view, with no trace of blackout even with a "humble" exit pupil of just 3,75 mm, compared to the 5,25 mm of a "classic" 8x42 that it's usually regarded as offering a more comfortable, less finicky and "easier" view. I wonder this every single time I use the small EII 8x30.

 

[Maljunulo]

Many of the things mentioned are not resolution.

 

[ReinierB]

So most of you agree that bigger oculars (or bigger exit pupils?) result in higher resolution/more details/more immersive view... but I still don't understand why. At bright daylight the pupil is just 2,5mm or so. A 10x25 should be as immersive as a 10x50 I would say?

I think I noticed it too with the CL 10x30 I had. It was not really comfortable watching far away. I prefered the 8x42 for that, which its strange because it is a 8 power. The 10x32 is already way better. Also because of the bigger fov I think.

Bigger oculars or bigger exit pupil... what is the most important for an immersive and more detailed view?

 

[William Lewis]

So most of you agree that bigger oculars (or bigger exit pupils?) result in higher resolution/more details/more immersive view... but I still don't understand why. At bright daylight the pupil is just 2,5mm or so. A 10x25 should be as immersive as a 10x50 I would say?

I think I noticed it too with the CL 10x30 I had. It was not really comfortable watching far away. I prefered the 8x42 for that, which its strange because it is a 8 power. The 10x32 is already way better. Also because of the bigger fov I think.

Bigger oculars or bigger exit pupil... what is the most important for an immersive and more detailed view?

Bigger oculars and bigger exit pupil are the same thing for a given magnification. Exit pupil is just aperture divided by magnification. I think I may have mentioned that in your previous thread "8x42 vs. 10x50 dawn/twilight".

What are you using at present?

 

[Binastro]

Oculars usually refer to eyepieces., the rear lenses.

Objectives are the front lenses.

As I said earlier, bigger objectives mean longer focus objectives and with a 2.5mm pupil size, a much slower system with less aberrations.

A 10x25 probably has objectives of 100mm focal length.

With a 10x50 the objectives are nearer 200mm focal length.

With the 10x50 eye placement is easier and the whole system is slower.

B.

 

[Pinewood]

Hello,

I found an old edition of Norton's Star Atlas on line. It provided the following information for telescopes:

A telescope with an objective of 1 inch can separate double stars of 4.56' displacement.
A telescope with an objective of 1.5 inches can separate double star 3.04' displacement.
A telescope with an objective of 2 inches was separate double stars 2.28' displacement.

1 inch is close to 25mm, 1.5 inches is close to 37.5mm, 2 inches is 50.8 cm.

The lower the displacement the higher the resolution.

Whether one can see the difference with a 10x binocular is another question.

Stay safe,
Arthur

 

[tenex]

It provided the following information for telescopes:

That has to do with diffraction limits which binoculars are not approaching.

So most of you agree that bigger oculars (or bigger exit pupils?) result in higher resolution/more details/more immersive view... but I still don't understand why

Let's leave out "immersive" which is a separate issue and harder to define. To expand on what B. said above, resolution is limited by a variety of optical aberrations due to varying wavelengths of light, deficiencies in curvature of lenses, etc. The shorter the focal length of the objective, the more the light rays are refracted, with greater aberrations. So larger objectives with gentler curvature tend to perform better, especially when stopped down further by your daylight pupil.

[Edit] Now that I think about it, one could still have a longer focal length with a small objective, like SF 42 or NL 32 and even more so if desired. Binastro, you didn't list these as examples of exceptional resolution... have you tried them?

 

[ReinierB]

Bigger oculars and bigger exit pupil are the same thing for a given magnification. Exit pupil is just aperture divided by magnification. I think I may have mentioned that in your previous thread "8x42 vs. 10x50 dawn/twilight".

What are you using at present?

Exactly. Now I think a 10x50 is better at twilight, because of the bigger lenses, although the exit pupil is about the same or even bigger on a 8x42.

I have a SLC 8x42 and Nl Pure 10x32.

 

[ReinierB]

So the length of the binoculars play a rolex as well. Interesting. I will reread everything you wrote and try to understand it all. It is a bit technical now and more complicated than I thought.

I appreciate your comments!