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Old Wednesday 11th January 2017, 20:49   #1
DadraFromFrance
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Legend M 10x42 - quick test

I tried, the week before christmas, le Legend M serie 10x42. Great binoculars !

PRO
- A very very good transparancy (incredible in this price range !)
- Very sharp at the center (and good in the border). Better than the L serie and the Elite I tried the same day.
- Good weight balance and confortable oculars eye cups
- Good color reproduction and very good CA control
- Price in US...

CONS
- Focuser a little stiff.
- Not very light weight
- Price in France...

A new french binoculars book ("Observer avec des jumelles") is available. The authors are serious and famous for their astronomics test in a popular astronomic review ("Ciel et Espace").
The internet site (in french) : http://www.astrophotography.fr/wp/

The Lengend M 10x42 have a very good score (31/40) and the Zeiss SF the best of the test (38/40). Here the page for the Zeiss SF and the Bushnell Legend M 10x42.
96% and 91% is the transparancy mesure line (in the green value) respectively for the SF and Legend M.
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Old Wednesday 11th January 2017, 21:38   #2
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Thanks for the observations. I have tried the L and M. Perhaps it was the samples on the day but I felt the L was a fraction sharper in the centre and preferred the lighter weight, but can understand that many will prefer the flatter view of the M.

I had a close look at the images you attached and the testing method and scoring on the link you gave. Maybe something is lost in the google translation, but I'm stuggling to understand what they have done. I do quite a bit of resolution testing myself as you know, and the differences in the images look rather surprising. I might well have misunderstood something. Do you have any further information that might help?

David

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Old Wednesday 11th January 2017, 22:58   #3
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Difficult for me to explain : I'm not an optical specialist and my english is so so...
For optical resolution, the notation is in corrélation with the human's eye resolution ( = 1' arc minute).

Scale for notation (center) :

Less than 5’ =0/5

From 5’ to 3’ = 1/5

From 2’ to 1,4’ = 2/5

From 1,3’ to 1,1’ à = 3/5

From 1’ to 0,7’ = 4/5

Best than 0,7’ = 5/5

The sample of Serie M i tried was notably better than the L (luminosity and borders). Sample variation ?

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Old Wednesday 11th January 2017, 23:47   #4
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Leaving aside the mystery of how they did the test, it seems you read the info it the same way as I did. Taking a wild guess, I suppose the 1 arcminute reference they are referring to is the instrument resolution multiplied by magnification. In my opinion a rather flawed and meaningless calculation, but others seem happy to use it. The ISO 14133-2 standard means that from 2006 the majority of binoculars above a €250 threshold will score around the 5/5 threshold or better. The photos look quite bizarre with this in mind. The difference between a fairly average binocular and the very best is about three steps on the chart. Unfortunately even a score of 5/5 doesn't ensure the binocular isn't limiting for users with excellent eyesight.

What I've seen is extremely short on information so my guesswork might be wrong.

Borders yes, but I didn't spot any difference on luminosity. I feel that is almost impossible to judge outside a lab so who knows? I'm sure both Bushnells are going to seem quite attractive at US prices.

David

Last edited by typo : Thursday 12th January 2017 at 05:02.
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Old Thursday 12th January 2017, 08:08   #5
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I had another look at those test chart images this morning. I'd hazard a guess that the middle chart photo is an edge shot and the Zeiss is obviously better. I presume one of the other two, probably the top, is centre resolution. Which ever it is, the Bushnell matches the Zeiss (which doesn't surprise me) and should have been scored the same. If I understand the scoring correctly, that means both would be better than 4.2 arcseconds which is very respectable. I presume the other image is CA, but again in either set I can't see a difference, so the scores should be the same.

If I've interpreted it correctly, it looks to me like the Bushnell should have been scored at least a couple of points higher from those images.

David
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Old Thursday 12th January 2017, 08:21   #6
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Thanks for the report, Dadra. I was pretty impressed with the 8x42 M, mainly for the optics. The focuser should lighten with use, but any play in the focuser will likely remain.
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Old Thursday 12th January 2017, 14:47   #7
james holdsworth
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Quote:
Originally Posted by typo View Post
I had another look at those test chart images this morning. I'd hazard a guess that the middle chart photo is an edge shot and the Zeiss is obviously better. I presume one of the other two, probably the top, is centre resolution. Which ever it is, the Bushnell matches the Zeiss (which doesn't surprise me) and should have been scored the same. If I understand the scoring correctly, that means both would be better than 4.2 arcseconds which is very respectable. I presume the other image is CA, but again in either set I can't see a difference, so the scores should be the same.

If I've interpreted it correctly, it looks to me like the Bushnell should have been scored at least a couple of points higher from those images.

David

I don't think you can judge anything from those thumbnails - if you go to the actual test of the M, the photos are of higher quality and resolution. For example, the CA test in the thumbnail really shows nothing but the actual test pic clearly shows quite a bit of blue / purple edge fringing.
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Old Thursday 12th January 2017, 15:55   #8
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James you might be right the original may be better, but where did you find the Legend M? I've only foumd the Legend L.

David
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Old Thursday 12th January 2017, 18:14   #9
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James you might be right the original may be better, but where did you find the Legend M? I've only foumd the Legend L.

David

My mistake, it was a test of the L, not the M.
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Old Friday 13th January 2017, 07:50   #10
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Quote:
Originally Posted by typo View Post
I had another look at those test chart images this morning. I'd hazard a guess that the middle chart photo is an edge shot and the Zeiss is obviously better. I presume one of the other two, probably the top, is centre resolution. Which ever it is, the Bushnell matches the Zeiss (which doesn't surprise me) and should have been scored the same. If I understand the scoring correctly, that means both would be better than 4.2 arcseconds which is very respectable. I presume the other image is CA, but again in either set I can't see a difference, so the scores should be the same.

If I've interpreted it correctly, it looks to me like the Bushnell should have been scored at least a couple of points higher from those images.

David
It's difficult to have a clear view on the pics/thumbnails and yes, the two shots are the center and the border...
I tried the SF and the Legend M and L (and the news Nikon Manarch HG) in the same time. You are right : in the center, the sharpeness could appear similar. SF borders are a little bit better.
I repeat : CA control and luminosity are incredible in the Legend M, a notch better than the L serie...
I think the 945g for the Legend M is a bit surevaluated (in hand SF and Legend M seem ti me similar).
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Old Friday 13th January 2017, 13:50   #11
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Bushnell give a single weight specification for all three E, L, and M models which I'm quite sure is wrong. The M certainly felt a lot heavier than the L, but I'd agree, 945g doesn't sound right.

David
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Old Friday 13th January 2017, 14:43   #12
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I'd also like to know more about how these test images were made.

Group 5/element 5 on the USAF chart is comprised of some very tiny lines; 114 per mm or 57 line pairs per mm. In order for a binocular with 4" of resolution (measured in line pairs) to resolve such fine lines the chart would have to be about one meter from the binocular.

The axial CA image appears to be the same chart at a much greater distance (or at much lower magnification?) and also overexposed compared to the resolution image, presumably to enhance the visibility of the color fringes. I can't really see the point of that since the CA is quite readily visible in the resolution image.

Henry
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Old Friday 13th January 2017, 17:23   #13
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Henry,

I noted the same thing.

A bit of a guess, but I've seen illustrations of commercial test platforms where the schematics suggest the test target is back illuminated by a collimated light source and imaged via a lens that appears to correct for infinity. In which case the binocular would be infinity focussed but the actual target distance is only 1m or so. I suspect this auxillary lens would have it's own CA contribution. It would then make some sense to miss out the lens and use 3 to 4m and close focus the binoculars instead.

One thing I find puzzling about this possibility is that, given the likely cost of the optical test bench and imaging system why they haven't gone the whole hog and used commercial MTF analysis package and a slant edge instead? I'd agree, it would be useful to know more.

David
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Old Saturday 14th January 2017, 08:22   #14
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Henry,

If you can persuade Google Books to let you see page 135 onwards of 'The Optical Transfer Function of Imaging Systems' by Thomas Williams it shows various configuration for testing both focal and afocal test systems. The nomenclature is a bit different to the illustration I saw before.

David
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Old Saturday 14th January 2017, 21:15   #15
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Thanks David,

I couldn't persuade Google to take me beyond page 90, but I have seen illustrations like that before. I've tried using one of my astronomical refractors as a collimating lens with a backlit USAF glass slide placed at the end of the focusing tube. It works fine with the binocular under test (focused at infinity) easily reaching focus on the chart at less than a meter from the telescope objective. Of course, it's still necessary to use an examination scope behind the binocular eyepiece to see the full resolution. Problem is I don't know how to derive arc second resolution from the resolvable LPs/mm on the chart when it's used that way, so I haven't pursued it. I'm sure you are right that they must be using a set-up with a collimating lens and presumably an auxiliary scope.

Henry

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Old Sunday 15th January 2017, 18:05   #16
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Henry,

I think Ron (Surveyor) would know how to calculate the arc second resolution for your setup. However, I found some setup instructions form my earlier correspondence with Ron which might explain what to do and I'll paraphrase them here:

"The most important part of the setup is to get the target behind the collimating lens to true infinity focus. This is easiest done by focusing a telescope to infinity outside, and fixing the focus so that it remains at this infinity setting (tape, glue, welding, naive hope that it stays where you left it etc.). Now, place your collimating lens (your astro refractor or magnifying glass or whatever you are using) close to your infinity focused instrument and move your resolution target back and forth at the guesstimated focal plane of the collimating lens until you have best focus at the infinity focused telescope's eyepiece. Once you have found your best focus, you are done and have found the optimum distance between the collimator lens and the test target, which should be the collimating lens (telescope, if you use a refractor) focal length.

When doing your math for resolution, the distance (to target) is always the (collimating) lens focal length, regardless of how far the test optic is from the lens."

The above is an edited version of Ron's instructions. If you were to do a couple of tests with this setup again and do the math this way, and then check against results you get from "open chart" testing (without a collimator lens and infinity focus) with the same binocular or telescope, you would be able to see if the derivation is plausible for your setup. If it were, then the results should be repeatable as long as you kept the distance between the target and the collimator constant, and that should be easy enough to maintain even with a jury-rigged setup at least to a precision of a millimeter or two. If your refractor focal length is in the 500-800mm range, that would be plenty precise enough.

Kimmo
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Old Sunday 15th January 2017, 21:45   #17
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Thanks Kimmo,

I was blindly groping for something like that, probably half remembering instructions that Ron sent me. The forum could certainly use more of his knowledge. I noticed he was signed in about a week ago. Too bad he has nearly stopped posting.

Henry
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Old Monday 16th January 2017, 07:56   #18
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I have played around with the objective doublet from an inexpensive scope and figured it would work, but felt that lens wasn't up to the job optically. The main reason I haven't persued it though is that I don't have a suitable imaging imaging system.

Obiously it's important to have a long enough camera lens. It does depend on the sensor but would need to be at least 300mm and 500mm would be better (real, not equivalent). That's f/60 or less with long exposures and that needs good vibration isolation. All the electronic trickery on the camera, like noise reduction, sharpening and gamma correction needs to be switched off and of course you still need the analysis package for the image. Using colour adds another level of complexity as well. Not a trivial undertaking.

It's well beyond my budget and I suspect that of most here.

David
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Old Monday 16th January 2017, 13:46   #19
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Hi David,

I agree that it's much more difficult to make an accurate image of a binocular's resolution than it is to accurately see the resolution through an examination scope placed behind the eyepiece. I posted about my experience using a 600mm lens here:

http://www.birdforum.net/showpost.ph...1&postcount=17

I would add that focus was extremely critical. In the end, to arrive at the best focus, I made many photos as I racked through focus in tiny increments. Vibration was also a problem. I used the camera self timer, but even then some photos were ruined by the slap of the camera mirror.

Henry
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Old Monday 16th January 2017, 15:40   #20
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Henry,

I recall the post. I should have asked at the time if the scope had a dedicated SLR mount or some other coupling mechanism? I suspect alignment was challenging.

In a project quite unrelated to this, I initially used a SLR whith a mirror lock and remote 'live' viewing via a cable connection to a computer and monitor. Unfortunately we couldn't turn off all the onboard image processing or remove the antialiasing filter. We switched to using industrial/scientific cameras which were totally under computer control, practically more suited to this kind of job, and produced a much higher quality output (in scientific terms). I still have a couple of the cameras, but no suitable lens unfortunately. That's just the start of the shopping list!

David

Last edited by typo : Monday 16th January 2017 at 17:05.
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Old Tuesday 17th January 2017, 14:08   #21
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Henry,

I recall the post. I should have asked at the time if the scope had a dedicated SLR mount or some other coupling mechanism?

David
I use a simple prime focus adapter. It's just a 2" tube that slides into the scope focuser with male T threads at the back end to accept the camera.

Sounds like your camera would be much better for this. I don't know how to do anything about my camera's output or internal settings. All I can do is shoot RAW images and compare them to the what I see at the examination scope's eyepiece.

Henry
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Old Tuesday 17th January 2017, 16:08   #22
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Tanks Henry,

I hadn't thought of a draw tube type arrangement. I do have extension tubes for the industrial camera that might be made to work with one scope objective, and a second one that could work as the collimator. I really like to get the components rail mounted if I can. It would make life so much easier.

It's not unusual for cameras to have an options for remote control and viewing. Might be worth looking into?

David
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Old Sunday 5th March 2017, 06:13   #23
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Thanks David,

I couldn't persuade Google to take me beyond page 90, but I have seen illustrations like that before. I've tried using one of my astronomical refractors as a collimating lens with a backlit USAF glass slide placed at the end of the focusing tube. It works fine with the binocular under test (focused at infinity) easily reaching focus on the chart at less than a meter from the telescope objective. Of course, it's still necessary to use an examination scope behind the binocular eyepiece to see the full resolution. Problem is I don't know how to derive arc second resolution from the resolvable LPs/mm on the chart when it's used that way, so I haven't pursued it. I'm sure you are right that they must be using a set-up with a collimating lens and presumably an auxiliary scope.

Henry
Hi Henry, been awhile.

The math for the distance for using a collimating lens is the same as for regular distance to a paper target but using the focal length of the collimating lens. The atan (reciprocal of the lines per mm divided by the distance in meters).

I have attached the ISO page for a resolution collimator and a picture of the one I built that has a 400 mm objective.

I have used a five inch +/- 450 mm lens but it is in the open and not lighted per spec and does not yield good results. You might try a good backlight with a frosted glass diffuser in a dark room and see how close you get.

Lighting is very critical. My home built collimator has a frosted glass diffuser and I use a collimated light source as the ISO diagram shows and get very good results but I can take the glass diffuser out and use an integrating sphere, which gives an almost perfect diffuse light source (also expensive) and get a measurable improvement in my readings. Don’t recommend spending the money for the sphere, all you really want is reproducible results.

Setting the USAF target at the focal point of the collimating lens is critical to accuracy, in your case I would recommend using the K&E double collimator since, unless way out of adjustment, both sides are infinity focus, you can verify that by looking at distant objects outside and comparing one side to the other. Also the grid at the focal point has a 5 minute apparent angle, a rough check against your USAF target.

I have attached a spreadsheet for simple conversion for you. Change the focal length or distance to target in column B, change the resolved group in column C. As a check column G should be the same lines per mm as your standard USAF target.

Let me know of any other questions.

Ron
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Old Monday 6th March 2017, 13:48   #24
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Hi Ron,

Thanks for the tips. I've downloaded the spreadsheet and the ISO page. What can we do to coax you into bringing your trove of knowledge here more often?

Henry
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Old Wednesday 8th March 2017, 05:33   #25
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An odd thing, the apparent distance of something viewed through a collimator. Thanks, RonE.

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