First Look at EDG 7x42 (1 Viewer)

This design has been a problem on the Zeiss FLs. I have Nikon 8x32 LXs and the diopter system works flawlessly, my Zeiss spent last summer in Germany at age 6....months.

Bob,

I'll offer some speculation about this, but I'm far from certain about what I'm saying. Maybe somebody knows for sure.

A simple focusing system that works by varying the distance between the objective and the eyepiece also changes magnification at the same time. Close focus has higher magnification than distant focus. I believe (but I'm not certain) that a properly designed internal focusing system that uses a moving focusing element between a fixed objective and eyepiece changes focus without changing magnification. If the diopter adjustment works by shifting the position of the internal focusing lens in one barrel then there will be no change in the magnification of that barrel at any setting of the diopter adjustment, but if the position of the eyepiece is changed then the magnification of that barrel will increase or decrease relative to the other barrel. It's similar to what happens when you change the distance between a Barlow element and an eyepiece. The farther the Barlow element is placed from the eyepiece the higher the magnification. So, I think the one advantage of the new diopter adjustment system is that it doesn't compromise the magnification match between the two barrels.

Henry

Henry,

Thank you kindly for the review. I have yet to get my hands around an EDG but look forward to eventually...especially the 7x42.

... I believe (but I'm not certain) that a properly designed internal focusing system that uses a moving focusing element between a fixed objective and eyepiece changes focus without changing magnification.

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Henry,

For several reasons I would doubt this. Basically, in order to assist the eye to focus an image on the retina, any binocular is required to add power, and in so doing departs from its afocal state of zero diopters. The amount of power (in diopters) is determined by the distance of the object. If the eyes differ in their requirements, this is handled by the so-called (differential) diopter adjustment, but image magnification changes occur at the retina regardless of the focusing (i.e., diopter control) mechanism designed into the instrument. As I understand it, the moving focus element is optically bundled with either the objective or eyepiece, negating the need to physically move either cell. This minimizes the masses that have to be handled by the racking mechanism, but, the analysis of effective magnification at the eye remains the same.

I'd be more than happy to be corrected if this is not accurate.

Regards,
Ed

Ed,

I made that statement because I've been unable to measure (using Kimmo Absetz' technique) ANY significant repeatable change in magnification at distances between 7' and 100' in the three binoculars I've tried that use focusing lenses, while every binocular I've measured that focuses by varying the distance between eyepiece and objective shows a very obvious change in magnification (4-5%) over that same range.

I don't think it's impossible to design a telescope to maintain consistent magnification at different distances. One way that comes to mind is to use a zoom ocular that changes focal length in response to focuser movement. I'll try to borrow a friend's 10x42 LX and measure its magnification at different settings of the diopter adjustment.

Henry

Henry, Ed;

At first reading of this, I thought Elkcub was probably right. But thinking of it and re-reading both posts, I think Henry is probably more correct. And like Henry and Ed, my opinions are strictly opinions and supposition. I think the first clue for me fell in Ed’s statement “ negating the need to physically move either cell”.

If we assume a 10x bino with a 200 mm focal length and 20 mm eyepiece focal length then using a collimator approximation of focal length offset for different distances on the objective side (a’=(f^2+zf)/z where a’ is the focused distance and z is the focal plane offset, f is the focal length) then the focusing lens is used to bring the desired object into focus at the focal plane when focused on the objective side. If the image is allowed to form behind or in front of the focal point, then the eyepiece, or other element, on the eyepiece side has to be moved to bring the object into focus. If the focused image is brought to the focal plane by a focusing lens, then the fixed ratio remains (200/20). If the focus is allowed to remain behind or in front of the focal plane, then the eyepiece will have to move to bring that object in focus and change the ratio of the focal lengths. For example (strictly assumed and made up numbers) if we change from infinity focus to an object focus of 10 m then the change of focal length will be around 4 mm, if focused at the focal plane then 200/20 ratio would still apply but If allowed to be 4 mm behind the focal plane, then focal ratio would be approximately 204/20 or 10.2x. I will be the first to admit that I do not know what would happen to the image size at the focal plane and how that may relate to final image size. Most of my power checking has been done at infinity focus.

Another thought, maybe totally incorrect, is that the image presented by the binocular is a collimated (therefore infinity focused) image at the exit pupil and is presented to match the pupil diameter, whether to an eye or a camera system, and not a refractive diopter correction of the image, as with corrective lenses.

Another thought. Adding the diopter correction to the CF wheel probably allows you to add offset to the focusing lenses by simply adding a little offset to the thread position of the focus drive thread without need of any additional diopter components.

I am a little under the weather right now, but when I get to feeling like setting up the test bench I will check some of the modern CF bins at infinity and about 2 or 3 meters. I have checked some IF binos in the past and know that increases of .3 to .5x are common, even at moderate distances.

Best to all.
Ron

Henry/Ron,

I yield to empirical data, although I'm ignorant of Kimmo's method. Apparently, by altering the focal length of the objective one can compensate for the increase in overall magnification that normally results from moving fixed components. Very good. |:d|

Ed

Ron,

Your thinking got me to put this together. If the focusing element is considered part of the objective, then by reducing its focal length one also brings the image away from the field lens of the ocular as if the objective were physically moved. By virtue of its shorter focal length, however, magnification of the instrument is reduced, thereby offsetting the increase associated with moving a fixed focal length objective. Now that I think about it, it's a pure geometric tradeoff, and makes perfect sense, — so long as I do all the talking.

Hope you're feeling better.

Ed

Hi Ed;

Having a little bout with Gout and do not feel like doing much that requires moving. Thanks for your thoughts.

Henry;
Sorry, I must have missed your post 25 while doing my post. I just now noticed it and since you have already done the measurements, I do not see any point duplicating your efforts.

Have a good day.
Ron

Ron/Henry,

Are you satisfied with the explanation of how/why it works? Incidentally, this is also consistent with how EdZ computes the magnification for conventional binoculars.

Thanks for the insight, Henry. Chalk up another one for observation.

Ed

Ron,

Hope you will be feeling better soon. I would be happy to see more magnification vs distance measurements of binos that use focusing lenses. My results are based on only three binoculars (Swaro 8.5x42 EL, Zeiss 8x42 and 8x56 FL) Your photographic method should be more accurate than my visual one.

Ed,

Both yours and Ron's thinking seems plausible to me, but it would be nice to have confirmation. Observationally, one worrisome loose end is Edz's tests of some inexpensive roof prism binoculars with focusing lenses that indicated large changes in magnification with distance (using the same measurement technique that I used). Unfortunately, there doesn't seem to be much readily available information about these internal focusing systems.

Henry

Henry;
I will do some testing in the near future. My 2 most accurate magnification tests involve the photo method, with which you are familiar, and a method using the measured angles in the AFOV. Also, I limit my tests to about the center 1 degree, or less, of field to avoid off axis problems. I have seen Kimmo's method before, but will have to find it again since I have forgotton the details.

Another question, do you have any idea of the internal focusing system, whether they use plus or minus lenses, a combination, even direction of travel, or any information. All I have seen is a couple of cut-a-way views and am simply guessing at the function. I can not believe that they would stick a simple positive lens in the light train without matching the other highly corrected optics somehow.

Like you, I would like a lot more information before forming much of an opinion. All of my thoughts above where based on conjecture of how I thought this might work, by no means meant as how it actually works.

Have a good day.
Ron

Surveyor said:

Henry;
I will do some testing in the near future. My 2 most accurate magnification tests involve the photo method, with which you are familiar, and a method using the measured angles in the AFOV. Also, I limit my tests to about the center 1 degree, or less, of field to avoid off axis problems. I have seen Kimmo's method before, but will have to find it again since I have forgotton the details.

Another question, do you have any idea of the internal focusing system, whether they use plus or minus lenses, a combination, even direction of travel, or any information. All I have seen is a couple of cut-a-way views and am simply guessing at the function. I can not believe that they would stick a simple positive lens in the light train without matching the other highly corrected optics somehow.

Like you, I would like a lot more information before forming much of an opinion. All of my thoughts above where based on conjecture of how I thought this might work, by no means meant as how it actually works.

Have a good day.
Ron

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Ron,

I've been reading your posts and others with great interest, but as this debate unfolded I kept wondering, surely these guys realize that even if there is a measurable difference in magnification between the barrels in a binocular using on-the-barrel right diopter focus (or left, my Nikon 8-16x40 XL Zooms had a left diopter focus), the user is unable to see that difference.

Either the magnification difference is below the threshold of the user's ability to distinguish it (I'll say at least most users since I can see gross barrel distortion in the full sized LX's and most people cannot), or our brains have the ability to adjust for the difference.

All my binoculars have diopter focus adjustment rings on one barrel, and I've never detected any difference in image size, and I notice even subtle differences between sides (if the focus is slightly off, for example). I've handed my binoculars to a friend, whose eyes have significantly different diopters values than my own, and I advised him to adjust the diopter settings, but he said, No, it's fine, I can see okay (yeah, through one eye!).

When I bought a 10x42 LX, I noticed a contrast difference between the two barrels, and when I looked down the objectives, I could see the less contrasty side had significantly paler coatings than the other side, which confirmed my observations. The dealer I bought them from didn't notice the difference until I asked him to look down the objective end and notice the difference in coatings as I had done.

So people's eyes and perceptions are different, and
I'm not saying that because I don't see a difference in magnification between the two barrels in my binoculars that it doesn't exist, but rather that the point is moot unless you are able to detect that difference "in the field" rather than only on the test bench.

Brock

Hi Brock;
This discussion was started when Ceaser asked why Nikon changed from the side position to the center position and we were just guessing the reason might be to get the diopter adjustment on the objective side of the system instead of the eyepiece end, which may lead to a more constant power from far to near focus. It really does not matter about the actual diopter control, but rather where the focusing elements are in the train. Now, we are just curious if the position of the focusing elements contribute to a more uniform power through out the focus range.

I do not routinely test binoculars, I only start looking when my perception is that they are somehow lacking of my expectations. When collimation or power, for example, get off by a little I start perceiving a loss of contrast, followed by an image softness or sweet spot less than expected. I may not visually recognize image size or an offset difference as such, but notice other shortcomings in the image quality. After all, the eyes see what is there and the brain tries to smooth things out for us. Most of the time (85 to 90%) the problem is simply collimation, but I have found others. There may be no defect that you can attribute to any one thing; maybe just a duller view than you think you ought to get for your money. Sometimes it is just a matter of wondering if I got what I paid for. Sometimes just to compare one bino to another.

BTW, thanks for the Nikon lead awhile back. It helped greatly.

Have a good day.

Ron

Brock,

The true geek never considers these practical matters! But if you must, here's a worst case scenario.

Imagine a binocular that barely meets spec for magnification matching between the barrels. In the old JIS tolerances that would be 1.5%. This binocular is bought by someone who requires 6 or 7 diopters of compensation. Applying that much correction increases the difference to (let's say) 3%, throwing the binocular out of spec. Not likely that would happen very often, but it is possible and the owner would probably, at the least, feel a vague sense of discomfort. Of course if this same binocular had been bought by someone needing 6 or 7 diopters of correction in the other direction (or the other eye) the diopter adjustment would have perfectly compensated for the original difference. If you don't need much diopter correction all of this is irrelevant.

Henry

Ron,

I think all of these focusing elements are negative, similar to Barlow lenses. In binoculars I've only seen singlets illustrated. In spotting scopes they are usually doublets. Movement is forward toward the fixed objective elements for distant focus and back toward the eyepiece for close focus.

Henry

Thanks Henry, I will have to set around and draw some pictures tonight.

Henry, Brock;

An irrelevant story. Some time back I read Kimmo’s review of pocket bins where he rated the Nikon LXL above the Ultravid. I did not remember mine that way so I went and rounded them up for a visual comparison. I had three 8x20 Ultravids and one 8x20 LXL. Visually, I was able to rate them 1, 2, 3 and 4. The BL’s were best, followed by a BR, then the LXL and lastly, the other BR Ultravid. The only check I made was to measure the collimation of the four units. I did not write the first two down but I do remember they were very well collimated, under 5 minutes vertical and 10 minutes horz. The LXL measured 5’ vert. and 25’ horz. while the BR’s were 17’ vert. and 5’ horz., 5 times better horizontally which the eyes can accommodate but over 3 times in the vertical, which the eyes can not accommodate. The ISO rejection limit for vertical collimation is 30' for standard bins and 20' for High Performance bins, so all were in tolerance. There may have been other faults but the point is that, in my opinion anyway, there does not have to be a visible difference between barrels for the image to suffer noticeably.

Best to all.
Ron

henry link said:

...

Ed,

Both yours and Ron's thinking seems plausible to me, but it would be nice to have confirmation. Observationally, one worrisome loose end is Edz's tests of some inexpensive roof prism binoculars with focusing lenses that indicated large changes in magnification with distance (using the same measurement technique that I used). Unfortunately, there doesn't seem to be much readily available information about these internal focusing systems.

Henry

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Henry/Ron,

Please describe Kimmo's method to measure changes in magnification.

A calculation EdZ described some time ago on BF was simply to add the distance the objective is moved in mm (i.e., to focus on a near object) to its fixed focal length and then divide by the focal length of the eyepiece. Leaving out nodal points and all that jazz, it turns out this corresponds quite well with the expected magnified image size on the retina. I confirmed this by comparing his calculations to those of a famous optician (who will remain nameless), who gave me a numerical example of how he would work the practical image size problem.

Using that simple model as a starting point, it is clear that if the primary function of the focusing lens is to change the focal length of the objective, then by shortening it the internal image made by the objective is moved, but the distance between the objective and the eyepiece remains constant. Hence, the image size on the retina is also constant, independent of the movement of the focusing lens. (Of course, the same basic reasoning applies if the focusing lens is used to change the FL of the eyepiece.)

It may well be that not all focusing lens systems are designed equal, however, or that what is thought to be one is really not.

Ed

Surveyor said:

Thanks Henry, I will have to set around and draw some pictures tonight.

Henry, Brock;

An irrelevant story. Some time back I read Kimmo’s review of pocket bins where he rated the Nikon LXL above the Ultravid. I did not remember mine that way so I went and rounded them up for a visual comparison. I had three 8x20 Ultravids and one 8x20 LXL. Visually, I was able to rate them 1, 2, 3 and 4. The BL’s were best, followed by a BR, then the LXL and lastly, the other BR Ultravid. The only check I made was to measure the collimation of the four units. I did not write the first two down but I do remember they were very well collimated, under 5 minutes vertical and 10 minutes horz. The LXL measured 5’ vert. and 25’ horz. while the BR’s were 17’ vert. and 5’ horz., 5 times better horizontally which the eyes can accommodate but over 3 times in the vertical, which the eyes can not accommodate. The ISO rejection limit for vertical collimation is 30' for standard bins and 20' for High Performance bins, so all were in tolerance. There may have been other faults but the point is that, in my opinion anyway, there does not have to be a visible difference between barrels for the image to suffer noticeably.

Best to all.
Ron

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Ron,

Yes, very interesting. I would only add that ISO limits refer to manufacturing tolerances. They do not say that differences can't perceived (even unconsciously) within the tolerance zone.

Ed

Ed;
Ever so true. I can tolerate about the max in the two horizontal directions but about 10 or 12' vertical is my limit, after that I can perceive the difference. I had a cheap Nikon that was around 45' vertical and was truly awful. Sent them back and was like a new/different instrument when they got back.

Have a good day.
Ron