An accessible test for comparing binoculars of different magnifications. (1 Viewer)

[Torchepot]

Apart from the topic of which make of binocular is better than which, the other issue which frequently promotes debate is which magnification is best.

Often it is the comparative resolving power of 7x 8x and 10x binoculars which concerns people. It's been said that a lower power binocular will show more detail than a 10x because the higher power induces more shake when used handheld.

In January last year Kimmo posted a very interesting test on the comparative resolution of binoculars on the Canon sub-forum (but comparing the handheld resolution of different magnifications wasn't the primary focus of his test).

I tried a few different ways to compare the only two binoculars I had to hand - an 8x32 Leica and a 10x42 Swarovski and soon got a bit disillusioned. I found that comparing the two mounted on a tripod gave me the clearest proof that (at least with these two) the 10x could resolve finer detail than the 8x. No surprise there - greater magnification should show better detail. Handheld the difference was more difficult to quantify - both binoculars were subject to shake and trying to judge the resolution was influenced by a number of factors.

I believe that resolution is measurable within fine margins - but most of us don't own high quality resolution charts or have the experience to get the most out of them. I wanted to find a simple test that would enable someone to compare binoculars of different magnification.

I tried resolution charts, bank notes and printed text of various font sizes but found that the more I used them the same problems cropped up.

Knowing what you are looking at in advance can convince the mind that you are seeing it, also when looking at text, the mind is very good at recognizing the shape of words even if the individual letters are not discernable. I noticed that foreign words were a better test. The other thing that I struggled with was prejudice! Wanting one binocular to out-perform another can make you try that little bit harder.

On an earlier post Binastro mentioned the idea of producing groups of random letters in various sizes as an alternative to resolution charts. It's taken me an age but I finally got round to trying it out.

I produced an A4 chart of text using a random word generator to form groups of four letters, these are arranged from font size 14 to 34 and are in "optician's chart" font.

The method I ended up with is to attach the chart (on a clipboard) to a stake which I placed at a distance of 30 metres (or 100 feet). Ideally for the actual test you need a second person who should stand next to you with an identical copy of the sheet. Then you simply start reading the chart aloud from the largest font upwards and the second person checks off the letters. As soon as you reach a line which you are struggling with you stop. Then swap optics and repeat.

Although this test seems very straightforward and got round some of the problems that my previous efforts encountered - particularly familiarity and prejudice, it did throw up a couple of interesting issues.

Two of us tried the test and I have no idea if we are typical but we both found that we could read the letters with the 10x binoculars at several font sizes smaller than with the 8x.

What was interesting was that we could momentarily read smaller fonts, sometimes two sizes or more smaller and then "lose" them again. So the smallest size of font that we could comfortably read straight off without hesitation or mistakes was 36 for the 8x and 28 for the 10x but we could get glimpses of 30 or even 28 with the 8s and 26 with 10s.

Trying the binoculars mounted on a tripod produced 18 comfortably with the 10s and glimpses of 16 and with the 8s 24 comfortably with glimpses of 22.

One other odd thing with the 10 mounted on the tripod was that I could read the first and last letter in each "word" on the smallest line 14 but not read the letters between them.

This is very much a subjective test - I'm not drawing too many conclusions from it - and I look forward to some decent weather to repeat it and see if the results are the same.

I would also really like to try other binoculars against each other.

I would be very interested in other people's results using this test, and any thoughts on ways to refine or improve it.

One thing I want to try is a new chart using single letters instead of groups (more like an optician's chart).

I'll post the chart separately as I can't attach the file using this tablet.

 

[Torchepot]

Test Chart

Binocular Test Chart

 

[fstop]

Here's a Snellen eye chart, but it needs to be printed 11x17 I think. I think you have done a very interesting comparison and appreciate that you have shared it. I wonder if part of the disparity between the central and end acuity is due to FOV, especially since the sharpest vision is the central area of the eye. Although it really has nothing to do with your test of the 2 binoculars, have you considered used porro type binoculars for the sake of comparison? I'm looking forward to seeing what you -and others, come up with.
http://www.hometrainingtools.com/media/reference/CM-SNELLPA.pdf

 

[Torchepot]

Thanks for the chart fstop, something curious - I noticed that it only uses 10 different letters, 9 of which are repeated. I wonder if there's a reason for that? I've recently had to undergo a whole series of eye tests and have some more coming up. I recall that seperating the C, O, G & Q caused me problems when at the limits also some other pairs of letters like E&F M&N B&R U&V.

The font I used is called the Snellen font so is meant to be the same. It might be worth excluding some letters from the next chart, I L and J could be candidates. I also wondered if I should print the chart in Bold but I thought that would simply make it slightly easier, though it does look even more like an eye chart. I do want to try and retain the A4 format for ease of use.

Unfortunately out here I only have the 2 pairs of binoculars, I'm hoping that some of the members with other binoculars will contribute. It would be interesting to see how porros compare. I wasn't really thinking about comparing binoculars of the same magnification against each other, though maybe trying an 10x32 against a 42 or 50 might be interesting.

If I was in the U.K. I would like to try a chart at one of the retail stores and run through a top notch 7x42, 8x32, 8.5x42 and 10x50. It would also be good to compare 8x42 with 10x42 as they are the most popular choices.

Some lucky BFers probably wouldn't need to go to a store to try this!

 

[Torchepot]

fstop just reread your post and realise that I could have worded my first post better. When reading the chart through the binoculars I should have said that each block is centred in the binocular field - i.e. I'm following the text with the centre field, not leaving the binoculars centred on the first line.

 

[kabsetz]

Torch,

Thanks for sharing this. I'm not at all surprised by your results. In all of the comparison testings I've done, higher magnification has showed more detail than lower mag also handheld, and this holds also for 15x binoculars. Same results also whenever there's been a friend trying the same, but I have never tested this with a larger sample of viewers, so cannot say whether or not there would be widely different types of people with respect to image shake and how it influences the viewers' ability to observe and process detail.

The notion that one could see more detail handheld with lower magnification is, in my view, more of an urban legend (or field legend) of sorts, based on careless assumptions. There has been testing done by the militaries, with results suggesting a useful upper limit to handheld magnification, and I don't dispute these findings as such, as handheld viewing with very high magnifications and a severely shaking image is very unpleasant and stressful, and if you are forced to do it for a long period of time, it is quite possible that eventually you become unable to utilize the magnification advantage completely. I also don't deny diminishing returns, but maintain that the returns do not diminish as fast as often is said.

With respect to the chart itself, I don't think we should get too hung up on exact target sizings, contrast levels or print scales. What matters is repeatability for the tester, so consistency should be maintained in order to compare different test sessions with one another. Having one constant reference binocular is one good way of attaining this.

Since the viewer's eyes are one of the most important variables between testers and constants for one single tester, we will never get this test so repeatable between testers and binoculars that you could ever expect the exact results obtained by one tester to be repeated by another no matter how accurately the chart, light levels, distances etc. are standardized. Relative results a tester gets between different binoculars will nevertheless be meaningful and valuable.

I think that once I have some more time at hand, I'll print out your chart and see what kinds of results it gives.

Kimmo

 

[Binastro]

The letters at the end and middle differences may be due to crowding.
With sunspots much smaller ones are seen centrally than near the limb using safe filters and unaided eyes.

I definitely see fainter stars sometimes with 8x25 compared to 10x25, But this is not resolution but a good indicator how steadiness improves the view at lower magnifications.

I also see more detail up to 20x binoculars hand held than lower magnification, but momentary glimpses. The eye is good at retaining images. I can recognise aircraft with 1/100 second glimpses.

My optometrist uses the O on the test chart to test my astigmatism. I can repeatedly fix this to +/- 1.25 deg even though my astigmatism is small.

I don't think you should exclude difficult letters. The whole point is to make the test difficult.

My cousin read car number plates at double my best distance. He must have had 20/8 vision.

 

[Binastro]

If you really want to make it difficult, turn the test chart upside down.

But this might only test your ability to read upside down letters.

 

[Binastro]

There is a difference in being able to recognise isolated letters and letters in words, even meaningless words.
This is because adjacent letters heavily influence the readability of letters within words.

 

[Torchepot]

Hi Kimmo

Thanks for my new title - I do seem to spend a lot of time in the dark!

I'm really hoping that other people try this test - particularly devotees of 7 and 8x binoculars. One of the advantages of this kind of comparative test is that the conditions don't have to be the same from one tester to another because the difference between the optics on test are what's interesting. If for example one of the binoculars was unable to satisfactorily resolve even the largest font at 30metres it's simply a matter of taking a step or two until it does and then comparing the 2nd binocular from the same distance.

I am sure there is an increase in discomfort with increased magnification, at what point that adversely affects observable resolution may well be different for different people. I also think that some people get used to using a certain magnification and may find it hard to accept the different experience of higher or lower magnification.

I think you're right about not getting too hung up on producing the perfect chart. For the moment this seems to work O.K. so probably no need to agonise over every detail. I may try a version with the letters spaced out singly though just out of curiosity.

If people do try the test I hope some will also try the chart with the binoculars tripod mounted. It's a bit more fiddly and for me at least quite an unfamiliar experience but it does take a lot more variables out of the test. If they can be mounted on two tripods side by side any difference in comparative resolution should be quite apparent. It also serves as a base line of potential resolution for a binocular to then compare to that handheld. I look forward to any results that you get when you get some time.

Hi Binastro

Hope you don't mind me stealing your idea! I think you're right about not making the test easier but I also don't want to put people off by making it harder. Something about the simplicity of an optician's chart test appeals, I've found that reading it aloud helps too - it's much harder to cheat! and it's fairly obvious when the limit is reached.

All the best

Torchey

 

[Binastro]

I know of people who memorised the opticians chart to get a job or even to serve in the armed forces.

Also I suspect that some phenomenal glimpses of faint stars at altitude, i.e. 14,000 ft might have had the benefit of an oxygen bottle.

I used to hyperventilate sometimes to see faint stars. Not a good idea.

The idea of the alternative chart is free to use.

 

[Torchepot]

Just noticed a mistake in the chart, here's a new one.

 

[elkcub]

...

Two of us tried the test and I have no idea if we are typical but we both found that we could read the letters with the 10x binoculars at several font sizes smaller than with the 8x.

What was interesting was that we could momentarily read smaller fonts, sometimes two sizes or more smaller and then "lose" them again. So the smallest size of font that we could comfortably read straight off without hesitation or mistakes was 36 for the 8x and 28 for the 10x but we could get glimpses of 30 or even 28 with the 8s and 26 with 10s.

Trying the binoculars mounted on a tripod produced 18 comfortably with the 10s and glimpses of 16 and with the 8s 24 comfortably with glimpses of 22.

One other odd thing with the 10 mounted on the tripod was that I could read the first and last letter in each "word" on the smallest line 14 but not read the letters between them.

...

One thing I want to try is a new chart using single letters instead of groups (more like an optician's chart).

I'll post the chart separately as I can't attach the file using this tablet.

Hi Torchepot,

You've done interesting work here, particularly noting the "odd thing" in the highlighted sentence, although I doubt that it's limited to just the 10x. You might want to review modern test chart design before constructing your next version. There are several known spacing, sequence, and letter-specific effects that go into an optimal design. In the end, it might be more practical to just buy one that suites your fancy.

Ed

 

[Torchepot]

Thanks Ed,

That's a really interesting link. It's going to take me while to work my way through it. I like some of their charts and would be happy to try them - or indeed if anyone designed a different one. The thing about a chart in PDF format on A4 paper though is that it's easy for anyone to print one off and try it - and it's free!

Today I made a new chart with single letters spaced evenly and printed off a Bold version too. The Bold chart looks a lot more like an optician's chart but is a bit easier to read so I added a line of smaller (12) point font. If the rain stops for long enough tomorrow I'll give it a go and if it's an improvement I'll post it.

All the best

Torchey

 

[Hermann]

The notion that one could see more detail handheld with lower magnification is, in my view, more of an urban legend (or field legend) of sorts, based on careless assumptions.

I agree. You always see more at higher magnifications, even though the benefits of using higher magnifications seem to more or less disappear once you get above a certain level. I seem to reach that level at about 15x magnification. I can see more details at 15x than at, say, 10x or 12x magnification, handheld, but once I get above 15x I don't seem to get more detail consistently.

There has been testing done by the militaries, with results suggesting a useful upper limit to handheld magnification, and I don't dispute these findings as such, as handheld viewing with very high magnifications and a severely shaking image is very unpleasant and stressful, and if you are forced to do it for a long period of time, it is quite possible that eventually you become unable to utilize the magnification advantage completely.

I think you mentioned something important here - "a severely shaking image is very unpleasant and stressful". That's the point, I think. If I'm out birding all day, high magnifications *are* stressful and unpleasant, and I find I'm getting tired far more quickly. For me the upper limit is usually 10x magnification. I'm fine with higher magnifications "for a quick look", but not for birding all day. Even 10x can be a bit high, especially when I'm birding in difficult terrain in the mountains or on a windy day at the coast. 8x magnification with a large enough exit pupil (>/= 5mm) may well me my personal "sweet spot", even though there are always times when I long for 10x magnification.

In real life there's of course another consideration that comes into play here: With high magnifications the depth of field isn't really very large, that does make things difficult for instance when birding at a migration hotspot with lots of songbirds in the bushes. In that case high magnifications also don't work all that well in my experience.

Hermann