Sharpness and resolution, one subject or two ? (1 Viewer)

Torview · Feb 17, 2015

Apologies if this has been raised before.

I`m asking because when I read all the posts on here, members often declare one optic as being sharper than another and I`m unsure if they mean resolving ability or the way the image looks due to contrast and clarity.

My Ultravid HD looks less sharp than say an SV, but careful observation shows it resolves the finest details just as clearly handheld to my eyes.

I tend to look at the lichens on a neighbouring house roof which I find a good test for detail resolution.

John.

typo · Feb 17, 2015

A can of worms I suspect.8-P

Resolution is an optical property and sharpness a visual perception. However I am normally referring to visual comparison of effective resolution when I use sharpness and try to mention separately properties like contrast and colour contrast. I suspect that's not usually the case.

I don't think I would personally be able to compare effective resolution using lichens on a roof except in extreme cases.

David

Pileatus · Feb 17, 2015

Torview said:
Apologies if this has been raised before.

I`m asking because when I read all the posts on here, members often declare one optic as being sharper than another and I`m unsure if they mean resolving ability or the way the image looks due to contrast and clarity.

My Ultravid HD looks less sharp than say an SV, but careful observation shows it resolves the finest details just as clearly handheld to my eyes.

I tend to look at the lichens on a neighbouring house roof which I find a good test for detail resolution.

John.

The "flat field" of the SV skews perception...at least I think so. Personally, I enjoy the relaxed "flat field" view in my SV better than my old UV view. BUT, you are correct. When carefully examined exotic details show up in both windows in surprising ways. A lot of the discussion over sharpness/resolution/whatever is about one's perception to the entire view. And, just because I enjoy one view more than another doesn't necessarily make it sharper. I may think so but what do I know.

PHA · Feb 17, 2015

Hello Torview

Good! I agree resolution is an objective and mensurable optical property. "Sharpness" a percepción.
I can talk about my experience comparing a former Leica BA and the Zeiss FL I changed for: the Leica BA, great instrument, had the same center (outstanding!) resolution as the FL (and my actual HT, by the way, all 10x42). But the contrast and colours saturation provided by the two Zeiss, really amazing! makes al great difference in sharpness to me.

PHA

typo · Feb 17, 2015

I think we are already stumbling into some of the pitfalls of this topic. Just because two instruments appear to show the same level of detail to the eye it doesn't mean they have the same resolution or even effective resolution.

A binocular as an instrument has a resolution primarily dictated by the full aperture objective. It also has an effective resolution which is dictated by the diameter of the objective corresponding to the diameter of the pupil of the eye when observing. So if your pupil is 2.5mm diameter than the effective aperture with an 8x42 for example is 2.5x8= 20mm. So the effective resolution for 20mm applies.

Those with excellent eyesight might see the 'sharpness' differences due to effective resolution in optimum light conditions on top of other properties. The rest of the time the detail will be limited by the acuity of the user's eyesight as it normally would be for those with more typical eyesight. Then any perceived sharpness differences will be due differences like contrast and colour contrast not effective resolution.

Cheers,

David

Cluster · Feb 17, 2015

I agree that apparent sharpness can be enhanced by boosting the contrast.
It was easy to see when (way back when) printing images in a darkroom from negatives.
The same image could be made to be much sharper or softer, but retained the resolution.
Much the same can be seen in image manipulation applications on the PC.

Inquisitor · Feb 17, 2015

Cluster said:
I agree that apparent sharpness can be enhanced by boosting the contrast.
It was easy to see when (way back when) printing images in a darkroom from negatives.
The same image could be made to be much sharper or softer, but retained the resolution.
Much the same can be seen in image manipulation applications on the PC.

Is this what is going on when two binoculars have similar resolution chart values but one snaps into top focus and the other one oozes into top focus? Simply a difference in contrast?

I hate the feeling of using a low end system and the image starts going the wrong way before I am satisfied with the image. I have always formerly used sharpness/resolution to mean that I can't wish for or perceive the need for finer focus.
That's why I am here, to learn stuff.

OPTIC_NUT · Feb 17, 2015

Cluster said:
I agree that apparent sharpness can be enhanced by boosting the contrast.
It was easy to see when (way back when) printing images in a darkroom from negatives.
The same image could be made to be much sharper or softer, but retained the resolution.
Much the same can be seen in image manipulation applications on the PC.

Precisely, and then some.
To the extent that the contrast affects the slope of the
image edge or dot the eye is detecting, it has a real effect on actual
acuity. You see the difference between dark and light much more than light.

You can see the effect by posting a series of lines in
smaller and smaller font at a distance. As the sun goes down,
you will notice the smallest font you can read gets larger,
rather than most lines disappearing all at once. You can also notice
the increasing cognitive delay time in recognizing the words.

Swedpat · Feb 17, 2015

We can also describe it like relative and absolute resolution. Sharpness(relative resolution) is how sharp the image appears to the eyes. But the resolution is the details we actually are able to see. A bad sharpness demands higher magnification to reveal the same detail. Still, what we see is also depending on the personal eyesight.

OPTIC_NUT · Feb 17, 2015

In doing measurements down past the eye's actual acuity
(with a low-power monocular) I have noticed the following:

That a resolution in the range of an apparent 15-30 arc-seconds
corresponds with a perception of great 'sharpness' and, especially,
a stronger 3D effect that lasts out past 100 yards. I first noticed
the link with a pair of IF 7x35 Manons. I can't read font that low,
but I can see a more precise line, it seems.

That leads me to believe that you can actually extract a greater
precision out of lines or curves than the normal 'dot-to-dot' seperation
figure would suggest. It makes some sense, given how simple the
mathematical job is refining the edge in image processing
(along-axis-filtering or with least squares). One consequence is that
the alignment within each barrel is important. Another is that the focuser
must be extremely stable left/right to get this last bit of apparent 'sharpness'.
Off the shelf or in the shop, I can pick up various great binoculars but then
one pair is suddenly 'all there' for the view. That might be it....the last
bit of alignment. Very smooth focusers are key too. Otherwise, you can't
find the perfect spot.

typo · Feb 17, 2015

Inquisitor said:
Is this what is going on when two binoculars have similar resolution chart values but one snaps into top focus and the other one oozes into top focus? Simply a difference in contrast?

I certainly wouldn't rule out other factors being involved but so far I've found that effective resolution, not resolution, is the key to whether a binocular snaps into focus or not.

David

OPTIC_NUT · Feb 17, 2015

typo said:
I certainly wouldn't rule out other factors being involved but so far I've found that effective resolution, not resolution, is the key to whether a binocular snaps into focus or not.

David

Don't forget mechanical repeatability (focuser slop) and optimum focuser speed.
Some fast focusers on premium binocs I found never quite hit the best spot.
Snapped like a grasshopper, past the target.

oetzi · Feb 17, 2015

Cluster said:
I agree that apparent sharpness can be enhanced by boosting the contrast.
It was easy to see when (way back when) printing images in a darkroom from negatives.
The same image could be made to be much sharper or softer, but retained the resolution.
Much the same can be seen in image manipulation applications on the PC.

thank god we dont experience "grain" when looking through our binos. Another factor which made a negative appear sharper/more contrasty or not
Those were the days!

Pinewood · Feb 17, 2015

oetzi said:
thank god we dont experience "grain" when looking through our binos. Another factor which made a negative appear sharper/more contrasty or not
Those were the days!

Hello Oetzi,

I experience something like grain with uncoated binoculars.

Contrast is measurable. The modulation transfer function, which I do not understand, seems to be measuring tool. Google it.

Happy bird watching,
Arthur Pinewood

WJC · Feb 17, 2015

Torview said:
Apologies if this has been raised before.

I`m asking because when I read all the posts on here, members often declare one optic as being sharper than another and I`m unsure if they mean resolving ability or the way the image looks due to contrast and clarity.

My Ultravid HD looks less sharp than say an SV, but careful observation shows it resolves the finest details just as clearly handheld to my eyes.

I tend to look at the lichens on a neighbouring house roof which I find a good test for detail resolution.

John.

Ya know, there are just some threads that it's better to stay away from.

Bill

OPTIC_NUT · Feb 18, 2015

Pinewood said:
Hello Oetzi,

I experience something like grain with uncoated binoculars.

Contrast is measurable. The modulation transfer function, which I do not understand, seems to be measuring tool. Google it.

Happy bird watching,
Arthur Pinewood

You can see a pebbly 'grain' when the light is very dark.
That's the 'shot noise' of your eye's receptors. Above that level,
all I can imagine is that the uncoated binoculars you looked through had
dust on the field lenses. Pebbly noise with medium brightness is almost
always dust and reflections of it.

The best way to check contrast is to look at "grey level",
how truly black a region next to brighter regions.
For consequences, you can have subtly different shades
and see if you can find the faint letters.
There are excellent camera test patterns that can be applied to binoculars.
A general 'haze' exists when contrast is poor.

ceasar · Feb 18, 2015

typo · Feb 18, 2015

Another go at explaining it.

Those in the UK will know the easiest way to distinguish a Red Kite from a Buzzard at long range is the shape of the tail. It's something with 20/20 (6/6) vision you might be able to distinguish up to about 500m and those with 20/10 up to 1000m on a good day. That's acuity or the resolution of the eye. With a 10x binocular on a tripod those with 20/20 should be able to do it at 5000m with any half decent binocular. It would take an exceptional binocular for those 20/10 to get to 10000m as frequently the effective resolution of the binocular is limiting.

For acuity and resolution we are talking about the limit of detection. Sharpness is different. With the naked eye the distance where the tail distinction is clearest, or sharpest would be much closer, around 70m or 700m with a 10x due to the contrast sensitivity function of the eye. (If I understand it correctly. I don't have any information on how that changes with acuity.)

As MTF has had a mention, the resolution limit is normally quoted in cycles/degree for 5% contrast whereas the figure for 50% contrast is considered a good indicator of perceived sharpness. Binocular aberrations and internal stray light may affect the 50% 'sharpness' readout more significantly than the 5% 'resolution' readout. In camera systems it's common to tweak the sharpness at the expense of resolution but I don't know if this could be applied to binoculars but suspect it might be counterproductive if it was.

So it's possible for a binocular to have a high resolution and poor sharpness and alternatively poor resolution and high sharpness in theory. I can't think of any examples of the latter though. On the whole it appears to me that if you get good effective resolution, good sharpness follows, but undoubtedly colour bias, stray light and other factors play a role as well.

David

Renze de Vries · Feb 18, 2015

Discussions about the terminology we use in evaluating binoculars are important because our evaluations are necessarily subjective, and so we should be as clear and specific as possible.

Here's an older thread where concepts for evaluation are discussed: http://www.birdforum.net/showthread.php?t=218607

This is what I suggested in post #22:

Object Performance

Sharpness (retrieval of fine detail, resolution)
Contrast
Color representation

Field Performance

Brightness
Transparency
Sweet spot
True field of view
Apparent field of view
Depth of field
3D-effect
Color tone (fidelity)
Flare, ghosting
Vignetting

Practical Performance

Balance
Focusing
Eye comfort
Weather performance

Overall Performance

Presence

Note that I don't make a clear distinction between sharpness and resolution. Of course there is a difference, as outlined above, but as we deal here with subjective observation and impressions the concept of sharpness seems more practical.

Renze

Renze de Vries · Feb 19, 2015

John,

Here's an interesting article by Tobias Mennle (he's a BF member as well) on sharpness, contrast and resolution:

http://www.greatestbinoculars.com/allpages/articles/mtf/mtfmysteries.html

Renze

Sharpness and resolution, one subject or two ? (1 Viewer)

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