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Old Thursday 6th July 2017, 21:40   #76
kabsetz
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Rathaus,

Could we just all appreciate each others' different contributions and approaches, and use our own preferred source criticism standards privately without attempting to impose them onto others. To me your post read like you might not have a clear idea about the kind of testing Henry does and procedures he uses. Reading some of the threads he linked will show you how simple means can be used to glean lots of valuable information.

Much of the value of Birdforum optics discussions come from fruitful exchange of ideas, experiences, experiments and testing methods & procedures.

Respectfully,

Kimmo
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Old Friday 7th July 2017, 00:46   #77
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Henry,

You made the claim that it is "really not that difficult to plot and measure field curvature", and I am simply asking you to articulate and to explain to us how you might do this, including your methodology.
In order to reasonably justify your statement, I do consider this to be the simplest of requests.

Rathaus
Henry,

With all respect, I still await your proper response to this simple request.

I doubt you will be able to respond appropriately because I believe that you cannot.
- it is my opinion that any attempt to reveal your methodology will show it to be based in descriptive and subjective terminology and descriptive self determined points of reference.

Let it be clear - My point is not intended to denigrate any interesting work or observations which you have made, but to highlight the fact that you, just like everybody else I have read on this forum including myself, are operating from an ultimately subjective viewpoint.

Cheers,

Rathaus
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Old Friday 7th July 2017, 04:25   #78
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Even for someone like me using amateur methods it's really not that difficult to "plot and measure" field curvature and off-axis astigmatism in diopters, using star points, grid patterns and the binocular's diopter adjustment. Distortion patterns are also easily photographed.

Henry
Hi Rathaus;

Henry has already given all the information you need to measure field curvature in the paragraph quoted. All you need is a flat target that covers the field of view and some way to measure diopter (this can be converted to meters if needed).

For the amateur the following are useful for measuring diopter:

The diopter control of the binocular.

Calibrating the focus knob in degrees per diopter or diopter per degree, need a paper scale to read degree or diopter change.

A set of retinoscopy or a set of regular optical trial lenses.

Not really in the amateur realm but readily available (I have a couple) is a professional dioptometer, but these are expensive.

All you need to do is focus the center of the image as best you can then use whatever dioptometer determining device you have to focus the off axis point of interest and note the difference.

I know Henry has used all the above methods, he has a dioptometer but I do not know if, or how much, he uses it. Those are best used on a bench, not really suitable for field use.

Attached are some images I did many years ago for a review of the then new Zen Ray 7x36 ED2.

One good objective/repeatable measurement is worth a great many subjective guesses. Henry does far more of this type of work than I do.

Hope this satisfies your questions.
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Old Friday 7th July 2017, 09:37   #79
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Okay, so let's say one measures the image quality of two binoculars keeping magnification, FOV and other things equal. Binocular A is found to have zero field curvature and B shows positive curvature. Can we conclude that A will be perceived as "flatter" when in use, or that it's a better view? Possibly not.

Being "visual instruments," the two binoculars are clearly intended to be used with human eyes, which have near-spherical biological receptor surfaces (i.e., retinas). The "tests," however, are invariably done using a flat receptor surface (e.g. camera film or sensor). Assuming that the instrument designers' intended optimization was to make the image coincident with the retina, however, then its measured curvature should match the eye's Petzval curvature.* This would be consistent with how forward-looking biological eyes evolved, and would seem to produce more "natural" perceptions.

Looked at it from this perspective, the ideal field curvature for a visual instrument may not be obtained by eliminating it, but rather shaping it to match the human eye. Along these lines I would submit that the Leica NV, like my Swaro 4x42 SLC, probably do an outstanding job matching the image to the eye's Petzval surface without the need for a flattener lens. But, of course, I have no way of verifying this without knowing exactly what curvature the designers had in mind.

Ed

* The instrument's curvature necessarily involves coupling it with an eye model, of which there are several to pick from.
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Old Friday 7th July 2017, 10:09   #80
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Okay, so let's say one measures the image quality of two binoculars keeping magnification, FOV and other things equal. Binocular A is found to have zero field curvature and B shows positive curvature. Can we conclude that A will be perceived as "flatter" when in use, or that it's a better view? Possibly not.

Being "visual instruments," the two binoculars are clearly intended to be used with human eyes, which have near-spherical biological receptor surfaces (i.e., retinas). The "tests," however, are invariably done using a flat receptor surface (e.g. camera film or sensor). Assuming that the instrument designers' intended optimization was to make the image coincident with the retina, however, then its measured curvature should match the eye's Petzval curvature.* This would be consistent with how forward-looking biological eyes evolved, and would seem to produce more "natural" perceptions.

Looked at it from this perspective, the ideal field curvature for a visual instrument may not be obtained by eliminating it, but rather shaping it to match the human eye. Along these lines I would submit that the Leica NV, like my Swaro 4x42 SLC, probably do an outstanding job matching the image to the eye's Petzval surface without the need for a flattener lens. But, of course, I have no way of verifying this without knowing exactly what curvature the designers had in mind.

Ed

* The instrument's curvature necessarily involves coupling it with an eye model, of which there are several to pick from.
Thats a fascinating idea Ed. Thanks for sharing.

On the general question of technical analysis of how a binocular performs optically versus subjective descriptions, I believe we need both and on Bird Forum we get both.

However, I wonder how many of the 151,000 + members that Bird Forum has can make good use of highly technical analyses of binos' optics. For example a description of Swarovski's moustache distortion pattern might make it sound as though the bins would be awful to look through and of course they are the most popular premium bins out there. Nor, when folks ask what bins should I buy for X $/, or when they want advice about whether bino A is 'better' than bino B do they say, 'make sure your answer is in arc-seconds and includes photos of star tests'. Nor should we forget that many people get tons of nature observation pleasure from the most under-performing of binos.

And yet those technical investigations are vital if we want to know what is going on if a bino has some problem or undesirable characteristic.

I will quote Kimmo here when he says: Much of the value of Birdforum optics discussions come from fruitful exchange of ideas, experiences, experiments and testing methods & procedures.

I totally agree with him that there is room on here and value to be had from all approaches.

Lee
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Old Friday 7th July 2017, 12:18   #81
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Thats a fascinating idea Ed. Thanks for sharing.

On the general question of technical analysis of how a binocular performs optically versus subjective descriptions, I believe we need both and on Bird Forum we get both.

However, I wonder how many of the 151,000 + members that Bird Forum has can make good use of highly technical analyses of binos' optics. For example a description of Swarovski's moustache distortion pattern might make it sound as though the bins would be awful to look through and of course they are the most popular premium bins out there. Nor, when folks ask what bins should I buy for X $/, or when they want advice about whether bino A is 'better' than bino B do they say, 'make sure your answer is in arc-seconds and includes photos of star tests'. Nor should we forget that many people get tons of nature observation pleasure from the most under-performing of binos.

And yet those technical investigations are vital if we want to know what is going on if a bino has some problem or undesirable characteristic.

I will quote Kimmo here when he says: Much of the value of Birdforum optics discussions come from fruitful exchange of ideas, experiences, experiments and testing methods & procedures.

I totally agree with him that there is room on here and value to be had from all approaches.

Lee
Lee, Great post with an outstanding summary.
I think that one of my faults is that I expect a purely technical approach to be "absolutely ruthlessly technical"...when this is infact unreasonable and often impossible (though, the challenge is potentially very exciting).
I can see that Elk has written a really profound post and I'm trying my best to get into the right headspace to fully decipher it...but I've come down with the flu and I'm watching Blackadder with a fever and the walls are all wobbly.
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Old Friday 7th July 2017, 15:10   #82
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Originally Posted by Troubador View Post

However, I wonder how many of the 151,000 + members that Bird Forum has can make good use of highly technical analyses of binos' optics.
Lee
I personally find it extremely boring, and at that point I lose interest in the thread.
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Old Friday 7th July 2017, 15:31   #83
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Thanks, Ron. Of course, since you're the only one here with a real optical lab at home, I think you're the only one who could really satisfy Rathaus' requirements.

I have to disagree with Ed's idea that the field curvature of a binocular should be tailored to match the eye. I think the field curvature of the collimated light that exits the eyepiece should be tailored to match the field curvature of the collimated light that falls on the eye (or a camera) without a binocular in front, which is to say the binocular should ideally have zero field curvature. That allows the eye or the camera to exhibit whatever field curvature they normally have without a binocular in front of them.

Rathaus, when you're feeling up to it here are some instructions for measuring the astigmatism and field curvature of your Swarovski 8x30 Habicht using only a sheet of lined writing paper. The thin low contrast lines of writing paper are ideal for this purpose because they quickly disappear if they are not well focused. You'll need to use eyeglasses that correct your own astigmatism if you have it.

Cut two squares of the paper containing 6 or 7 lines. Butt them together with one set of lines vertical and the other set horizontal and mount them on a brightly lit wall that you can see from about 7 or 8 meters way. Examine the lines at the very edge of the field (3:00 or 6:00) using only the right side eyepiece with the diopter adjustment. On this binocular there is a 1 diopter separation between the little dots on the diopter adjustment (just take my word for it).

You'll notice that the vertical and horizontal lines can't be focused simultaneously at the very edge. One set of lines is at the sagittal focus and the other set is the tangential focus. Because of astigmatism the two foci follow divergent curves. Bring the set of vertical lines to best focus at the field edge using the center focus knob. Now, move the vertical lines to the field center and refocus using the diopter adjustment. Now just count the number of dots it took to refocus. That's the difference in diopters between the central and the edge focus. Reset to zero and repeat the procedure with the horizontal lines. You'll notice that you have to turn the diopter knob in the opposite direction this time. Add the two numbers together and you have the total astigmatism at the field edge.

Field curvature doesn't have much meaning when there is a lot of astigmatism, but you can determine how far off the mid-point between the sagittal and tangental foci is from the center field focal plane. For instance, if the total is 9 diopters of astigmatism and you moved the knob 4 diopters in one direction and 5 diopters in the other direction you know the midpoint is 0.5 diopters from the central focal plane. That sounds good for field curvature, but because of the high astigmatism it looks bad.

If you have a binocular with low astigmatism, like the Nikon 8x32 SE, you'll find that both the vertical and horizontal lines can be focused almost simultaneously at the edge. Then it's a simple matter to measure the field curvature by refocusing at the center and reading the diopter scale.

Sorry, I won't have time for any more long posts during the next week.

Henry

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Old Friday 7th July 2017, 16:26   #84
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Gads, jg, that one forced me out of lurkdom!

Ed and others:
I appreciate the technical posts and do read the forums for it. Ain't alone, am sure...
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Old Friday 7th July 2017, 17:15   #85
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I will quote Kimmo here when he says: Much of the value of Birdforum optics discussions come from fruitful exchange of ideas, experiences, experiments and testing methods & procedures.

I totally agree with him that there is room on here and value to be had from all approaches.

Lee
Agreed.

I don't have enough interest in audio anymore to read audiophile magazines, but I recall that "Stereophile" used to have a lab guy named John Atkinson who tested equipment and presented his results alongside the subjective reviews. Sometimes loudspeakers with wildly inaccurate measured frequency response would get the highest praise from the subjective reviewer. The fault lines were similar to what we have here, but I recall that the battles between subjective and objective audio reviewers were more bitterly contentious in those days and probably still are. Believe it or not I fought on the Subjective side in that war.

It all brings to mind Sayre's Law: https://en.wikipedia.org/wiki/Sayre%27s_law


Henry

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Old Friday 7th July 2017, 17:25   #86
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Exclamation

Well, I'm glad everyone is playing nice again!

FWIW Rathaus, some of the tone of your questioning to Henry didn't come across so well to me - I'm sure it went a bit skewiff from what you intended - I'm not going to go so far as to say it was rude or uncharitable, but from one Aussie (pronounced Ozzie for the benefit of the rest of the world - not! Aussy :) to another, take it from me mate, it was a bit un-Australian.

Henry goes a long way to measure, and objectively quantify field characteristics, photographing grids and high contrast targets, dioptric measurement etc, and he has generously and helpfully detailed his methods many times. As he freely admits, he wants nuffin' to do with the subjective quagmire once eyeballs are incorporated.

Henry gave me one of the best tips ever to assess binoculars by eye, and that was to turn them *rs* about and look through the objective end - thus minimizing the distortions due to one's own eyeballs. Tip for the forum .... if we'd all do this there'd be a lot less he said / she said, and more relevant apples to apples comparisons.

I disagree a bit with Henry's conclusion that the field curvature of the collimated light leaving the eyepiece should match that of the source. The view through something like Canon's IS models f'rinstance looks like something out of the book 'Flatland' to me. I'm not going to go so far as to totally lob in Ed's camp, coz the Swaro SLC doesn't thrill me as much as it does for him. My eyesight is fairly middle of the road according to the tests on Holger Merlitz's page, which I would urge everyone to try out - so I'm not overly susceptible to rolling ball.

However, from what I have read, it's precisely this seeming 'goldilocks' field design that goes toward the NV's widely reported enhanced '3D effect' for what is after all, just an in-line roof prism design (did we ever get to the bottom of whether one of the prisms was rotated 90 as one of the cutouts appeared to show? - without such, there's definitely no chance for any enhanced dof as somewhat spuriously claimed by the advertising bunkum - it's merely greater perceived stereopsis ).

That's the genius of the NV - they have definitely struck upon a pleasing field prescription which takes some account of the petzval curvature of the eye. Provided you have enough focal accommodation to utilize this, it is definitely going to appear more natural than some flat field designs, and that's before things get complicated by over correction of rectilinear and angular magnification distortion in some designs too.

In another thread Kimmo attributes this 3D effect and pleasing view, majorly to the NV's great glare control, contrast, colour saturation, relatively clean aberration free view, and sharpness, as well as the field curvature prescription and nicely compromised mild pincushioning toward the edges.

Without having seen it, but just collating everyone's reports, I tend to think it's the field curvature and distortion prescription that is the major source of this more life like view, but that the other things are definitely essential icing on the cake which are critical to the perception.


Chosun
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Old Friday 7th July 2017, 23:30   #87
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...I have to disagree with Ed's idea that the field curvature of a binocular should be tailored to match the eye. I think the field curvature of the collimated light that exits the eyepiece should be tailored to match the field curvature of the collimated light that falls on the eye (or a camera) without a binocular in front, which is to say the binocular should ideally have zero field curvature. That allows the eye or the camera to exhibit whatever field curvature they normally have without a binocular in front of them.
Henry,

I don't mean to be argumentative, but I'm having a hard time understanding what is mean by "... the field curvature of the collimated light that exits the eyepiece" or "... the field curvature of the collimated light that falls on the eye (or a camera)." It's also been mentioned in earlier posts.

Field curvature, and other aberrations, refer to images on a focal surface, not to the light that enters or exits the instrument. Since a telescope/binocular is afocal by design, standing alone it does not produce any image at a finite distance, so the concept of aberrations is devoid of meaning. Only when used in conjunction with an eye or a camera, does the combined optical system (telescope+eye) or (telescope+camera) produce images in the former case on a curved surface, and in the latter on a flat surface. "Image quality" refers to the amount by which rays miss their paraxial (ideal) image points, and improving the quality is an effort to reduce those errors to zero.

What I'm calling into question is the notion that flat-surface image assessment methods can be used to evaluate curved-surface image quality with any validity, particularly if we're dealing with image projections over a large 60-80 degree sensor area on a spherical cap (i.e., the retina). Pretty much every optics book I've read skirts the issue as if were the proverbial elephant in the room. Perhaps my texts are not advanced enough, although the issue is at least touched upon in Yuhao Wang's 2014 dissertation "Advanced Theory of Field Curvature." Specifically,

Quote:
2.5.2 Curved Film and Curved Detector
Instead of correcting field curvature, a curved film or detector with the radius matching the Petzval radius can solve the field curvature problem. The most common optical system with a curved detector plane is the human eye. Field curvature is not a large problem for the human eye because the retina could auto-adjust its curvature biologically [i.e., via evolution]. (My insert)
Now I don't pretend to understand the subject to any great extent, but if telescope images are corrected for flat image planes, then that plane would have to lie tangent to the retinal sphere or intersect with it. In either case, the implications for defocus blur would be most unfavorable, which may partially explain why I'm allergic to (most) binoculars with field flatteners. Logic suggests that the correction should be made to match the eye's Petzval curvature.

I'm not wedded to this conclusion, particularly if someone were to lay out a different but plausible optical explanation.

Ed
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Old Saturday 8th July 2017, 00:42   #88
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Hi Ed,

I'd didn't think you'd take that lying down and I completely agree that field curvature doesn't exist in the light that normally falls on the eye, which is why I assigned it a value of zero. My point is that correcting the field curvature in an optical device placed before our eyes simply maintains that non-existance. The eye experiences the focus for laterally separated objects at the same distance exactly as it it does when no optical device is in front of it. What is unnatural is finding that the field curvature of an optical device prevents two objects at the same distance, but one in the center of the field and the other 20 or 30 off-axis, from coming to the same focus as they would if we were looking through a hollow tube.

Henry

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Old Saturday 8th July 2017, 03:36   #89
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Appropriate Decorum

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I personally find it extremely boring, and at that point I lose interest in the thread.
Whether one finds it spellbinding or boring, where is the decorum? Last time a thread hijacking took place this severely, a moderator split off the pontification to it's own separate thread.
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Old Saturday 8th July 2017, 03:52   #90
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Whether one finds it spellbinding or boring, where is the decorum? Last time a thread hijacking took place this severely, a moderator split off the pontification to it's own separate thread.
I agree... Original subject has been ignored. Good taste and common courtesy thrown out the window. Someone searching for info on the Noctivid gets THIS??
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Old Saturday 8th July 2017, 04:51   #91
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I'm sorry that you feel that way guys, I don't think anyone has deliberately tried to hijack the thread in bad taste (although some of the unintentional personal stuff could've been headed that way IMHO, which was the reason I posted - to bring it back from the edge ....) or disrespected the original post.

Bird Forum (particularly the optics forum) has always allowed some 'latitude' for exploration provided it is good natured. I for one, welcome the additional technical information, and I'm grateful to those who contribute it.

I also welcome the way the OP so thoroughly structured the initial post to offer some guidance.

I believe the exploration of the parts of the original post focusing on questions 8, 9. (Expectations), and 14. ('3D effect'), and 16. (Other comments) is due to the way OTT marketing guff put forward by Leica, and the very real 'pleasing' field characteristics people are mostly seeing with them.

Folks are curious is all ........


Chosun

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Old Saturday 8th July 2017, 05:44   #92
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Whether on finds it spellbinding or boring, where is the decorum? Last time a thread hijacking took place this severely, a moderator split off the pontification to it's own separate thread.
When the OP himself questions the decorum of the participants on his own thread that's a show-stopper for me.

Ed
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Old Saturday 8th July 2017, 09:09   #93
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Agreed.

I don't have enough interest in audio anymore to read audiophile magazines, but I recall that "Stereophile" used to have a lab guy named John Atkinson who tested equipment and presented his results alongside the subjective reviews. Sometimes loudspeakers with wildly inaccurate measured frequency response would get the highest praise from the subjective reviewer. The fault lines were similar to what we have here, but I recall that the battles between subjective and objective audio reviewers were more bitterly contentious in those days and probably still are. Believe it or not I fought on the Subjective side in that war.

It all brings to mind Sayre's Law: https://en.wikipedia.org/wiki/Sayre%27s_law


Henry
And Henry, who could forget the oft-repeated phrase following the changing of any component in the sound-chain, even something as lowly as the brand of fuse in the plug: 'It was as if a veil had been lifted between me and the music'.

Lee
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Old Saturday 8th July 2017, 12:30   #94
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Hi Ed
Post 87.

Telescope plus eye is not the same a telescope plus camera.

Telescope plus eye is similar to telescope plus camera lens plus camera.

I think my original camera, a Kodak 127 Brownie, had a curved film plane, using maybe just a meniscus lens? As did maybe the Purma Plus. I'll check.
The Purma Plus had 3 speeds controlled by a gravity shutter rotating the camera through 2 times 90 degrees (3 positions).

Schmidt cameras had curved film planes as did possibly some Maksutov cameras??
One had to hold the film against a curved plate.
This was a nuisance as only one frame at a time could be taken.

I notice that the Celestron 300mm f/1.5 Schmidt camera seems to have a flat plane, at least the Epoch version.
But again I am not sure.

The Zoomar 180mm f/1.3 lens clearly has a curved field at the film plane. It was designed for movie 35mm, i.e half frame 35mm, when it is sharp wide open.
On full frame 35mm the edges and corners are soft at f/1.3 due to film curvature and possibly other aberrations.

I suspect there may be curved digital sensors for military devices, but I don't know of any.

For me with little accommodation, I don't mind curved fields with binoculars, but I can only focus on parts of the image without changing focus. Looking centrally they are usually O.K.

I just had an eye test, and as suspected one eye is now 20/20 although the other eye is better.
But I am pleased I still see well unless my eyes are tired.
Strange thing is that my reading glasses are the same but I need new computer glasses ( 67 to70 cm) and new T.V. glasses (1.95m)

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Old Saturday 8th July 2017, 15:15   #95
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I'd have no problem with the moderators dumping or moving everything after post #24.
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Old Saturday 8th July 2017, 16:08   #96
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Ditto.
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Old Saturday 8th July 2017, 17:17   #97
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When the OP himself questions the decorum of the participants on his own thread that's a show-stopper for me.

Ed
As a relative newbie I'd like to say that I for one have found this thread fascinating and informative. I think, as Chosun has pointed out, that the discussion does pertain to parts of the OP's list of questions, and I find that very often the most interesting information on internet forums is revealed as a consequence of tangential discussions. It's also very normal for tensions to arise occasionally between forum members, but I think that's fine (within certain limits) as long as the discussion stays on track and renewed respect is shown by the parties involved - as it has. It would be a shame, IMHO, to delete any part of this thread. Just my 2 cents......
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Old Saturday 8th July 2017, 18:04   #98
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It looks to me like almost everything from post #25 is on the subject of "flat-fields". All of it could be moved to a new thread with a title something like "Is a Flat Field Desirable? (from Leica Thread 'Owners: How Are your Leica...') ".

Henry

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Old Saturday 8th July 2017, 18:22   #99
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Quote:
Originally Posted by henry link View Post
It looks to me like almost everything from post #25 is on the subject of "flat-fields". All of it could be moved to a new thread with a title something like "Is a Flat Field Desirable (from Leica Thread 'Owners: How Are your Leica...')".

Henry
That would be a good solution. It would certainly be a shame to lose everything since post 25.
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Old Saturday 8th July 2017, 19:07   #100
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I agree.

Ed
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