Resolution 32 vs. 50 (1 Viewer)

[Binastro]

Hi Arthur,

Nortons, my constant friend since I was 16.

Now I use later expanded editions.

It should be " not'.

Arcseconds not arcminutes.

This is the Dawes limit for white double stars of equal brightness.
With a 6 inch telescope the stars are 6th magnitude, so I suppose a 1 inch telescope needs stars of 2nd magnitude and a 2 inch telescope magnitude 3.5.
But this is at night.

During the day using artificial stars these separations are better at about 2/3 the night vision figures.

But some observers do considerably better by examining the high magnification star discs.
Sir William Herschel used magnifications of 250x, 450x and 900x to examine star images with his 6.3 inch speculum mirror scope.

With binoculars one needs to double or triple the 10x magnification, to say 20x or 30x before getting near the limit of resolution.

A 25mm telescope needs about 25x before a person with 20/15 vision gets close to the resolution limit.

A 50mm 50x.

Someone with 20/8 vision might begin to get near the resolution limit of a 10x25mm telescope.

But binoculars are considerably worse as they are so fast.

Tenex,
My finances, and now my old eyes have not had the privilege of using a SF 42 or NL 32.

My 8x32 BA resolves well, but I have some problems now with finding perfect focus due to tired eyes.

The Minolta 8x23 Autofocus binocular is very sharp in bright light looking at people's faces at 10 metres walking down the street.
I cannot get anywhere close to this resolution with any standard binocular, except an IS binocular.
The Canon 10x42L is very sharp with or without IS.

Some Soviet era binoculars are very sharp but are based on old Zeiss designs that have somewhat bloated star images.

Regards,
B.

 

[kimmik]

I wish there was a thread titled:

How to get 20/8 vision

 

[Jefrs]

By convention magnification is proportional to a 50mm focal length, which is nominal our eye field of view. Thus 10x is 10 x 50 = 500mm
Aperture value (the F-Number) is defined as focal length divided by iris diameter (the objective). Aperture is a dimensionless ratio proportional to the amount of light let through irrespective of lens diameter and focal length.
Thus 10x50 bins, 500/50= f/10, and 10x25 bins, 500/25= f/20. Which is two stops. One stop is twice as bright, two stops four times.
So a larger objective should be brighter and clearer.

 

[ReinierB]

By convention magnification is proportional to a 50mm focal length, which is nominal our eye field of view. Thus 10x is 10 x 50 = 500mm
Aperture value (the F-Number) is defined as focal length divided by iris diameter (the objective). Aperture is a dimensionless ratio proportional to the amount of light let through irrespective of lens diameter and focal length.
Thus 10x50 bins, 500/50= f/10, and 10x25 bins, 500/25= f/20. Which is two stops. One stop is twice as bright, two stops four times.
So a larger objective should be brighter and clearer.

What do you mean with stop? Why is it two stops in this example?

 

[kimmik]

I think he is confusing photography with binoculars.

Also 50mm being “1x” in photography is referring to 35mm format film.

50mm lens on a phone camera sensor…. Is no longer “1x”

Edit: and before anyone confuses the subject further, 50mm lens is not the same as “50mm equivalent” lens. The latter takes into account sensor size aka crop factor.

 

[William Lewis]

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.

That's 2 great binoculars. You won't notice a huge difference in daytime by going for a 50mm (eg leica ultravid) or 54mm (eg zeiss HT) or 56mm objectives.

The only time you will really notice a significant change is if your using them in low light, the objective just gathers the light so a larger one will gather more and for a set magnification also lead to a larger exit pupil.

The resolution difference is quite subtle in daytime and only really apparent at long range providing there's good "seeing" i.e less atmospheric disturbance, heat haze etc.

As I tend to have only one main birding binocular that I use when I go out specifically birdwatching I like it to be good in all conditions and the SLC 8x56 fits the brief. Of a weekend or on holiday when i might use binoculars I take my 8x32 porro with me pretty much everywhere. With you current line up you've got all the bases covered except a really low light specialist tool - a 7x42 or 8x56 will cover you very well for that.

 

[Binastro]

Post #23.

The standard film full frame format is 24mm x 36mm.
The standard lens is the same as the diagonal of the full frame format i.e. 43mm not 50mm.

There are so-called standard lenses of 42mm, 50mm, 52mm, 55mm and 58mm.
The longer focal lengths were to make it easier to design fast lenses that cleared the mirror on a film SLR camera.
With computer design and new glass types 50mm became the 'standard' lens.

There are also 24x32mm and 24x34mm full frame formats.

Also the 24mm x 24m Robot camera standard frame.

Early Kodak cameras had circular images.

Medium format cameras with nominal 6cm square and 6x7cm had standard lenses of about 80mm.
The actual image size was slightly smaller than the nominal values.

This has nothing to do with telescopes or binoculars.

The field size of these depends on the eyepiece design and type of binocular and varies from less than 20 degrees apparent field of view to about 100 degrees field of view, sometimes 120 degrees or larger.

A stop in photography is a doubling or halving of light passing through the camera lens.
This is the square root of 2 as far as lens markings is concerned.
an f/1.4 lens passes twice as much as an f/2 lens.
However, it isn't that simple as vignetting means that the edge and corners of most fast lenses is not as bright as the centre of the image.

The aperture of a telescope or binocular is the dimension of the clear opening at the front, i.e. the objective. Usually measured in mm or inches.

The diameter of an objective is by convention the actual glass size of the objective when removed from its cell.

For instance a Leica Apo Televid 77mm has an actual aperture of about 75.5mm.

The Steiner 15x80 binocular has a clear aperture of about 77mm.

With 500mm f/8 mirror lenses the aperture varies from 62mm to about 77mm as some makers compensate for the loss of light by the central obstruction.

A T-stop is used in movie lenses that compensates for the actual transmission of the lens.

Regards,
B.

 

[Scott98]

This resolution issue is not complicated, the resolution is directly related to the aperture (size of the objective lens) and that is the only factor that determines the resolving ability of the lens.

Think of television and "High def" - increased resolution is higher def. Going from 32 to 50mm is like going from 1080 to 2K or 4K hi-def TV's. There is finer-grain detail in the higher-def image. At low power you may not see it, just like a small television. You'll notice it more in a big-screen TV just like you will at higher magnification through a scope or bino.

 

[ReinierB]

That's 2 great binoculars. You won't notice a huge difference in daytime by going for a 50mm (eg leica ultravid) or 54mm (eg zeiss HT) or 56mm objectives.

The only time you will really notice a significant change is if your using them in low light, the objective just gathers the light so a larger one will gather more and for a set magnification also lead to a larger exit pupil.

The resolution difference is quite subtle in daytime and only really apparent at long range providing there's good "seeing" i.e less atmospheric disturbance, heat haze etc.

As I tend to have only one main birding binocular that I use when I go out specifically birdwatching I like it to be good in all conditions and the SLC 8x56 fits the brief. Of a weekend or on holiday when i might use binoculars I take my 8x32 porro with me pretty much everywhere. With you current line up you've got all the bases covered except a really low light specialist tool - a 7x42 or 8x56 will cover you very well for that.

Thanks! I was hoping the SLC 8x42 is good enough in low light, and I actually, I think it is pretty good. Will a 7x42 really outperform the 8x42 due to the EP of 6 instead of 5.25?
What I noticed is that the 8x42 is brighter in low light, but with the 10x32 I still see more detail. I was watching red deer at twilight/night and could see the chandlers with the 10x32 but bearly with the 8x42. So that made me curious a 10x50 or 12x50 would be a better addition. Especially when the view will have more resolution/pop/details than the NL 10x32...
I already have a lightweight... but on the cases lightweight doesn't matter, I was thinking a 50mm would be more "immersive".

 

[ReinierB]

Ps. I do not have a (good) scope and don't really like walking around with them... that's why 12 power attracts me.

 

[William Lewis]

This resolution issue is not complicated, the resolution is directly related to the aperture (size of the objective lens) and that is the only factor that determines the resolving ability of the lens.

Think of television and "High def" - increased resolution is higher def. Going from 32 to 50mm is like going from 1080 to 2K or 4K hi-def TV's. There is finer-grain detail in the higher-def image. At low power you may not see it, just like a small television. You'll notice it more in a big-screen TV just like you will at higher magnification through a scope or bino.

I'm no expert as mentioned but I'm not massively convinced by this - in a terrestrial and pratical sense at least.

For very faint light, i.e when using my 8 inch dobsonian then yes a larger aperture will resolve more detail at higher magnifications all else being equal. In binoculars though this comes with many compromises, size and weight being the biggest concern but also the quality of the lenses, prisms, coatings and baffles used playing a big role as well as needing larger or more of these for larger lenses.

Also larger lenses generally mean more aberrations, it's harder to make larger pieces of glass perfectly hence why most large telescopes are reflecting ones, this isn't really practical in binoculars, just for alignment reasons amongst others.

So yes in absolute terms you can say that larger lenses will have a higher resolution but in practical terms this is not always the case. There's a limit to how much detail can be perceived by the human visual system through the pupil as well - this is less than what most binoculars supply.

 

[LucaPCP]

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)

I tend to think that the answer to this question would matter only if you mounted the binoculars on a tripod. If you hand-hold them, I do not think the lens size is the limiting factor to perceivable sharpness.

 

[tenex]

These discussions easily go off the rails when people start making inappropriate comparisons with photography or astronomy... or just hasty mistakes.

By convention magnification is proportional to a 50mm focal length, which is nominal our eye field of view. Thus 10x is 10 x 50 = 500mm.
Aperture value (the F-Number) is defined as focal length divided by iris diameter (the objective). Aperture is a dimensionless ratio proportional to the amount of light let through irrespective of lens diameter and focal length.
Thus 10x50 bins, 500/50= f/10, and 10x25 bins, 500/25= f/20. Which is two stops. One stop is twice as bright, two stops four times.
So a larger objective should be brighter and clearer.

No, 10x50 binoculars do not have 500mm focal length, so the following calculations are all false. The focal length of a binocular or telescope objective must simply be measured, or deduced from the f/ratio of a scope stated by the manufacturer, or estimated from the likely focal length of a binocular eyepiece.

This resolution issue is not complicated, the resolution is directly related to the aperture (size of the objective lens) and that is the only factor that determines the resolving ability of the lens.

This is true only of diffraction limits in telescopes, as has already been said, twice.

I was hoping the SLC 8x42 is good enough in low light, and I actually, I think it is pretty good.

It is. 50mm is a big improvement on 32, but a smaller one on 42.

What I noticed is that the 8x42 is brighter in low light, but with the 10x32 I still see more detail.

Now you're getting into the question of "better at what". There's the matter of overall brightness where aperture rules (up to one's pupil dilation), but magnification also helps to see detail if that's what you're after. This is why the (still simplistic) "twilight factor" attempts to include both.

Ps. I do not have a (good) scope and don't really like walking around with them... that's why 12 power attracts me.

If you don't intend to carry a scope, you may enjoy a 12 or even 15x binocular instead. It's hardly a full substitute, but the best one can practically do.

 

[Jefrs]

These discussions easily go off the rails when people start making inappropriate comparisons with cameras or telescopes... or just hasty mistakes.


No, 10x50 binoculars do not have 500mm focal length, so the following calculations are all false. The focal length of a binocular or telescope objective must simply be measured, or deduced from the f/ratio of a scope stated by the manufacturer, or estimated from the likely focal length of a binocular eyepiece.


This is true only of diffraction limits in telescopes, as has already been said, twice.


It is. 50mm is a big improvement on 32, but a smaller one on 42.


Now you're getting into the question of "better at what". There's a question of overall brightness where aperture rules (up to one's pupil dilation), but magnification also helps to see detail if that's what you're after. This is why the (still simplistic) "twilight factor" attempts to include both.


If you don't intend to carry a scope, you may enjoy a 12 or even 15x binocular instead. It's hardly a full substitute, but the best one can practically do.

Actually what I said was just dredging up what I learnt in the optics module of physics at college about a million years ago. However no less than Nikon repeat it here - Nikon | Sport Optics | Magnification (Binocular)
And I quote from that, "The effect of 8x binoculars is equivalent to that you can obtain by using a 400mm (50mm x 8 = 400mm) lens." They are of course taking full frame camera lens.

With astro telescopes and some spotting scopes with interchangeable or zoom eyepieces/ocular it is confused by the primary or objective, and eyepiece or ocular having separate focal lengths. To get the magnification there we divide the primary focal length by the eyepiece focal length e.g. 1000mm/6mm = 167x (and 167x50 = 8,750mm "equivalent"). It's all a bit academic when we slap a camera on the end, we have to recalculate with the crop factor.

Or, to describe a crocodile, "It is shaped, sir, like itself, and it is as broad as it hath breadth. It is just so high as it is, and moves with its own organs. It lives by that which nourisheth it, and, the elements once out of it, it transmigrates." (Shakespeare)

In other words, it is what it is.

 

[kimmik]

Actually what I said was just dredging up what I learnt in the optics module of physics at college about a million years ago. However no less than Nikon repeat it here - Nikon | Sport Optics | Magnification (Binocular)
And I quote from that, "The effect of 8x binoculars is equivalent to that you can obtain by using a 400mm (50mm x 8 = 400mm) lens." They are of course taking full frame camera lens.

With astro telescopes and some spotting scopes with interchangeable or zoom eyepieces/ocular it is confused by the primary or objective, and eyepiece or ocular having separate focal lengths. To get the magnification there we divide the primary focal length by the eyepiece focal length e.g. 1000mm/6mm = 167x (and 167x50 = 8,750mm "equivalent"). It's all a bit academic when we slap a camera on the end, we have to recalculate with the crop factor.

Or, to describe a crocodile, "It is shaped, sir, like itself, and it is as broad as it hath breadth. It is just so high as it is, and moves with its own organs. It lives by that which nourisheth it, and, the elements once out of it, it transmigrates." (Shakespeare)

In other words, it is what it is.

Equivalent is not equals…

400mm lens on 35mm format sensor, is not 400mm binoculars.

Please do not try to confuse the topic further.

 

[tenex]

Actually what I said was just dredging up what I learnt in the optics module of physics at college about a million years ago. However no less than Nikon repeat it here - Nikon | Sport Optics | Magnification (Binocular)
And I quote from that, "The effect of 8x binoculars is equivalent to that you can obtain by using a 400mm (50mm x 8 = 400mm) lens."

The "effect" Nikon are talking about here is magnification, as you might gather from the page title, not brightness/speed which you were trying to apply it to. But I don't pretend to be able to guess exactly where you went wrong, that's up to you to figure out.

I don't believe I've ever read Antony and Cleopatra though, so thanks for the lovely quote, whatever it may mean here.

 

[Jefrs]

The "effect" Nikon are talking about here is magnification, as you might gather from the page title, not brightness/speed which you were trying to apply it to. But I don't pretend to be able to guess exactly where you went wrong, that's up to you to figure out.

I don't believe I've ever read Anthony and Cleopatra though, so thanks for the lovely Shakespeare quote, whatever it may mean here.

Same applies - effective focal length divided by iris diameter. It's all rather simple really. The formulae can be worked backwards and forwards, rearranged.
You might care to notice that the objective diameters of binocular progress in roughly one-stop series, 25, 32, 42, 50 etc ad naus - i.e. 28 to 40 is one stop, 25 to 50 is two stops.
The relative brightness (not the f-number but proportional to it) is again given by Nikon further down that page, Nikon | Sport Optics | Relative brightness
But this is only true if the magnification remains the same, do note they will get dimmer with higher magnification, this then is the f-number proportional to light transmission.

Binoculars are what they are, you buy the ones you like most. Don't get bogged down with the numbers. Ye cannae change the laws of physics anyway.

“Reality is that which, when you stop believing in it, doesn't go away.” Philip K Dick

 

[kimmik]

Your analogies may work superficially but they are taking many mental shortcuts that ignore real physics. Many here have pointed this out to you but sadly to no avail.

 

[Maljunulo]

A 12” telescope gathers more light than a 6” telescope, and has greater resolution no matter what eyepiece you use.

Light gathering and resolution are invariant.

The image gets dimmer as the magnification is increased, but the instrument does not gather less light.

 

[tenex]

Same applies - effective focal length divided by iris diameter. It's all rather simple really.

It's rather simple if you understand what the focal length actually is, as in this case you do not. A binocular is an afocal instrument, it doesn't have a focal length as a camera lens does. Its objective and eyepiece each do, but those require some investigation. The focal ratio tends to be around f/4, or even a bit faster. Not f/10 or f/20 which are frankly ridiculous; the tubes would be a meter long. You really have no idea what you're talking about.