Testing scopes and binoculars (1 Viewer)

what test chart would you recommend for testing optics?

http://www.edmundoptics.com/testing-targets/test-targets/

The Edmund Resolving Power Chart looks suitable, but maybe a bit big for testing indoors,
if you want to test on about 10 m/20 yards?

I have several of the test charts on that page: the Edmund Resolving Power Chart, the Pocket USAF Optical Test Pattern, the 1951 USAF Contrast Resolution Target and a 1951 USAF glass slide.

The limitation with all of them except the glass slide is the printing quality. Mine are old and apparently better than recent ones, but even mine are useless beyond Group +2. Group +3 is printed on them, but too fuzzy to be accurate. The glass slide is perfect through Group +7.

I think the 1951 USAF pattern works fine for scopes as long as the smallest resolvable line pairs are magnified enough to be easily seen. Usually that's a magnification equal to something between 1 and 1.5 times the scope aperture in millimeters. I don't think it works so well for low magnification binocular testing because the elements are crammed too close together when the smallest visible line pairs are at or near the limit of eyesight acuity. The NBS 1963A Resolution Target looks to me like it would be better for binoculars at normal magnification, but I've never actually gotten around to ordering one.

Hi Henry,

I have the Edmund Resolving Power Chart and it is not very useful. -2,-1 are ok 0 not very good at all forget below that. The big thing with this chart ordering off of Edmund was shipping was very high, something like $18. I bought older Gurley charts off Ebay that were very good and would go down to Group +3 element 6. I have the "cheaper" glass slide from fellow in China off Ebay. I am afraid I have not set it up yet. Surveyor has one of these and I did get one off him preplanned type of thing.
http://www.ebay.com/itm/1951-USAF-G...037?pt=LH_DefaultDomain_0&hash=item1c39e679b5

thanks for your replies,
I guess it all depends on the distance…

I did some calculations and realized that using my cell phone's display might work,
At 15 meters I think I could reach 1 arc second (not quite the limit but)
the phone display have 1280 pixels/94 mm,
but I guess that is RGB-dots..so I'm not sure,

or is my calculations wrong and crazy?

used this calculator:

http://www.1728.org/angsize.htm

Here is a test chart from a file a BF-member did which you can print.... http://www.birdforum.net/showpost.ph...04&postcount=2

Anders

Binoseeker said:

Here is a test chart from a file a BF-member did which you can print.... http://www.birdforum.net/showpost.ph...04&postcount=2

Anders

Click to expand...

thanks, but link seems to be broken,
could you fix it?

It seems i can't copy the link info correctly, if you make an advanced search for a post made by Atomic Chicken on Saturday 23rd October 2004, 12:30
then you find it.

Anders

Binoseeker said:

It seems i can't copy the link info correctly, if you make an advanced search for a post made by Atomic Chicken on Saturday 23rd October 2004, 12:30
then you find it.

Anders

Click to expand...

thanks,
I found the thread:
(post number 2)

http://www.birdforum.net/showthread.php?t=25004

I did some testing with my own computer rendered test chart that I created for my mobile phone.

The result is that my ED50 + 20x eye piece can resolve 3.06 arcseconds,
Does that seem reasonable?

Pixel size on my cellphone is about 0,07427 mm or 342 ppi (1280x720 pixels on a 4.3 inch screen)

At 5 meters I could resolve single lines for the finest pattern (L=1)
see the attached the test chart:

important that the chart is displayed at original size on the screen when testing,
and not resized.

Vespo,

A couple of comments, intended as encouragement, not critique.

With resolution testing, it is useful or even essential to define your goals. If you wish to do tests which will yield a precise figure for the performance of the scope you are testing, one that would be replicable by a qualified lab testing the same scope, you are facing a rather tough challenge. For that, you need to have a target of the quality of the Edmunds glass slide Henry mentioned in his post, and will have to have a test setup where you have precisely known illumination levels and either a long enough test distance or a collimating lens between the target and the scope so that you can focus the scope to infinity.

In addition, you need to make sure there is absolutely no heat haze, the scope to be tested has reached thermal equilibrium within the test environment, and that you can reach an exit pupil as small as Henry mentioned. The last condition requires either an eyepiece that, in practice, reaches magnifications between 90-150x, which are available only for very few spotting scopes, or a booster behind the eyepiece.

If your goal is not to put a number on the resolving power of the scope but to "just" evaluate its performance on more practical terms and to compare it with another scope you have at hand at the same time, the task becomes much easier. Now you only need to have a target which has patterns smaller than even the best scope could resolve at the distances you use it at, and to take care of the conditions I spelled out in the second paragraph above.

You can also set up a test procedure for your home which is not lab-calibrated but is repeatable, and results you get from such a setup will allow you to compare different scopes you have tested at different times.

One more thing. When you are able to compare two or more scopes directly with one another, a very good and sensitive test, providing you have a test target, is to choose a pattern to be resolved and move the scope further and further away from the target until you can just barely resolve that pattern. If you do this to two scopes at a time (set to identical magnification, maximum usually), going back and forth between them, you will very easily see which one is better as it will resolve the target from a longer distance. On a typical test pattern, the target sizes are gradated in steps of about 15%, whereas by adjusting the distance, at lets say 20 m distance 10 cm will be a difference of 0.5%, so you can see that much smaller differences become detectable. Also here you need to be careful about conditions. Outdoors especially, light levels are changing all the time and heat haze is very unpredictable and influential, so you really need to be able to go between the scopes that are being compared in a matter of few seconds, and to make sure you don't jump to conclusions. Once you have determined that B is better than A, you can compare B to C in a similar way, etc. This way you will come up with a reliable ranking.

Wishing you an interesting learning process.

Kimmo

kimmo:

thanks for your advice!

My intention is definitely not scientific though it would be nice to know that the
methods are not completely crazy and out of order…


What I wondered was if 3.1 arc seconds would be realistic with a 50mm at 20x?
Since I have no references it's not easy to evaluate the absolute results.
Dave's limit is 1.3 for D=50mm, but I guess it's not a linear increase with magnification?
But looking at this graph it seems very low...

http://www.tvwg.nl/testrapporten/telescoop/images/ATX-04.jpg

Since the pixel size in the smartphone is well defined, (and quite small in newer models)
and it's illuminated evenly. My thought is that it might be better than a home-made-printed res. chart

At 15 meters one should be able to test for 1 arc second, and at 20 m about 0,8 arc seconds,
(with the finest pattern L=1)
Good enough for testing scopes?

As you suggest, changing distance to the test chart seems to be the easiest and most precise way.
Testing with booster I think might be overkill for me.
But I understand that it is "standard" for serious tests.

What is your view of the correlation of indoor tests at shorter distance in perfect air with real
resolution in the field? Does better lenses handle difficult field conditions better? Things that won't show in a simple indoor test like mine? And also, sometimes you actually see less with high mag than low mag in the field…due to air movement etc. So I guess it's complicated…and it gets even worse when you learn more about it…

After some more measurements (in a slightly better test environment) I could get down to 2.5 arc seconds for the ED50. Distance is then 6.2 meters. To get down to 1.9 arc seconds the distance should be 8 meters. Of course it might be my eye sight that is the limitation here...

According to this diagram:

http://www.tvwg.nl/testrapporten/telescoop/images/ATX-04.jpg

resolution is equal at 30x for all scope apertures (ATX is the example scope).

Isn't that a bit strange? Bigger should be better even at lower
apertures, as shown in Kimmos test:

http://www.lintuvaruste.fi/hinnasto/optiikkaarvostelu/optics_5_Smallscopes_GB.shtml

Just brief comments on the two resolution graphs. In Jan's graph, if you look at his curve for the human eye with visus 1.5, at 30x it does not separate from the resolution results for those three scopes, so in effect the scopes are here limited by his eyesight. My eyesight back when I did the test you linked might have been slightly better, although not by much. That might explain some of the difference.

Another factor, which explains more, is the way the tests were conducted. As far as I know, Jan M did his from a fixed distance, whereby resolution results would correspond to the steps in the chart used. For the curve drawn, he would have interpolated both for magnification and for resolution. I used the distance adjustment method, so the interpolation is different. Both of us have measured at marked magnification settings only.

A third factor is that judging by the ultimate resolution figures, the individual sample of the ATX 95 Jan M tested was not a very good one. It resolved about as well as the best Kowa 883's in his tests.

Kimmo

updated the test chart since it was a bit to much of the line pattern which made me dizzy…

Also added some bars for easier focusing. Bars could also be used for checking CA.

2.5 arc seconds may have been a bit too positive result, with the new chart I get 2.8.

Dave's limit for 50mm aperture is 2.32 arc seconds.

So maybe 2.8 is not a completely insane value.

Optometrists simply use a sans-serif font and call the resolution 1/5 of the font height.
It doesn't matter much to get finer than that. (put another way, it takes 5x5 'pixels' in the eye
to recognize all the letters and numbers)

You always have to be careful you are not limiting on the eye's 30-60 arc-second apparent limit.
60 is far more common than 30.

Putting a low-power monocular on the eyepiece helps tremendously, I find,
although you do have to pour on more light to focus well.

2.8 arc-seconds is possible. If it's at 20x, doing better would probably be
pointless to the human eye. Most cameras would have trouble around there as well,
unless you pushed the aperture and power up. It isn't practical to ask more from
50mm.....it gets quite dim at 40x, and most cameras suffer more than your eyes
from the noise. I have learned that pushing for power alone achieves nothing
without added brightness, so aperture brings both naturally. Prime quality
comes at 1/2-2/3 of aperture(ap. in mm vs power), it seems,
and things go downhill fast after that. 50x at 50mm doesn't give what you expect.
I'd rather catch a 25x50mm photo and post-process it to get a better quality
shot than 50x. Same for eyes. If you want resolution, there are two reasons
for going large, and you can't get around them both.

Some people obsess over exit pupil. It is a handy obsession, because it brings
brightness, dim-level contrast (lack of noise), saturation, and resolution...
if you force the objective size up for the power.

seems valid,
50-60x in an 65mm scopes is not of much use,
up to about 40x seem to look ok to me,
I always have preferred lower mag binos/scopes.
Stability, resolution, brightness, and mirage tolerance are all important factors,
and I have pretty good eye sight so I doesn't seem to need the high
magnification that much, I guess when my eye sight start to drop more mag
can be of interest.

I've taken to looking at the devilishly small font (with low contrast)
on a "Sweet 'n' Low" sweetener package lately. The 'resolution'
is 1/5 of the font height, optometrists say. At about 2-4 arc-seconds
you realize....if you blew it up more it would be grainy and dim.
That and....2-4 arc-sec is really amazing.