Thank you very much for sharing your excellent DIY measurement and analysis ideas!
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Does the Head Rest help on the NL 8x42? (1 Viewer)
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This is a matter of taste. I've used the Canon 12x36 IS III and I own the Nikon 10x25 IS. Both are ok but I prefer the optical quality, ergonomics, wide field, etc, of a classic excellent binocular.
But make me a NL Pure 10x32 IS and I may change my mind.
PeterPS
Well-Known Member
Rigorous analysis, it reads as a paper in a semitechnical journal, thanks for it. The generality of the results, however, may be questioned:
-you used a DIY rest, and not all forehead rests are equal
-you collected time series data over a rather short interval (less than 1min, after you eliminated the transients); analysis of data collected over longer intervals (3-5min or even longer) might lead to different conclusions.
-the results can be expected to depend a lot on the user, as well as on the scenario (such as using the binos after climbing a hill).
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davewilletts
Member
1. I like to think that the forehead rest was pretty good - not a lashed together job. See the attached photos.
2. You are right, but I struggle to maintain good pointing without ANY glitches for much longer. Averaging of several runs could be done, but there seems to be little point in view of the lack of any obvious dramatic improvement with use of the rest.
3. Again you are right, but I suspect that the relative performance changes between rest/no rest, and sitting/standing, are much the same for most users. And of course after exercise everything degrades, but I try to avoid birdwatching after vigorous exercise!
2. You are right, but I struggle to maintain good pointing without ANY glitches for much longer. Averaging of several runs could be done, but there seems to be little point in view of the lack of any obvious dramatic improvement with use of the rest.
3. Again you are right, but I suspect that the relative performance changes between rest/no rest, and sitting/standing, are much the same for most users. And of course after exercise everything degrades, but I try to avoid birdwatching after vigorous exercise!
davewilletts
Member
I broadly agree. However it could be argued that the improvement in pitch pointing when sitting is marginally worth having, at the inconvenience of the protruding rest.
'Are you sure the benefit you see why sitting and using the forehead rest was not just because you were sitting? How did you isolate the benefit of the forehead rest and sitting?' - I am not quite sure what you mean by isolate: the comparison was between measurements taken while sitting, with or without the forehead rest.
I should have pointed out that I do not use spectacles, and that the binos were pressed well into my eye sockets to steady them. And really I have implied too much accuracy in the table - a single digit after the decimal point probably still exaggerates the precision, given the lack of averaging several 'runs' and possible onset of fatigue.
'Are you sure the benefit you see why sitting and using the forehead rest was not just because you were sitting? How did you isolate the benefit of the forehead rest and sitting?' - I am not quite sure what you mean by isolate: the comparison was between measurements taken while sitting, with or without the forehead rest.
I should have pointed out that I do not use spectacles, and that the binos were pressed well into my eye sockets to steady them. And really I have implied too much accuracy in the table - a single digit after the decimal point probably still exaggerates the precision, given the lack of averaging several 'runs' and possible onset of fatigue.
Nice pictures! That is a pretty nice forehead rest you fabricated. Looks almost the Swarovski one!
Hi Dave,
Thanks a lot for sharing method and results of your experiment!
Is the 200 Hz sample rate a necessity? I found an an App "SensorRecord", and it only reads the gyro at 100 Hz, so I wonder if that's good enough. Do you have an URL (or the publisher's name) for the SensorData app you mentioned? I get ambiguous results from the Playstore based on the name alone.
How do you think about translational acceleration data? I vaguely wonder if it can be used to cross-check the rotational data, or maybe add something to the evaluation.
That's interesting ... my own forehead rest did seem to improve accuracy noticably even when standing, but I didn't actually take any measurements (though I toyed with the idea). How far above the eyes does your rest contact the forehead? I wonder if that makes a difference for the results. On the other hand, maybe the fact that I was using the binoculars with glasses makes a greater difference ...
Regards,
Henning
Thanks a lot for sharing method and results of your experiment!
Is the 200 Hz sample rate a necessity? I found an an App "SensorRecord", and it only reads the gyro at 100 Hz, so I wonder if that's good enough. Do you have an URL (or the publisher's name) for the SensorData app you mentioned? I get ambiguous results from the Playstore based on the name alone.
How do you think about translational acceleration data? I vaguely wonder if it can be used to cross-check the rotational data, or maybe add something to the evaluation.
That's interesting ... my own forehead rest did seem to improve accuracy noticably even when standing, but I didn't actually take any measurements (though I toyed with the idea). How far above the eyes does your rest contact the forehead? I wonder if that makes a difference for the results. On the other hand, maybe the fact that I was using the binoculars with glasses makes a greater difference ...
Regards,
Henning
Regarding the sampling rate of analogue-digital converters: Shannon's sampling theorem [2] always applies, which means that the sampling frequency must be at least 2x as large as the highest signal frequency (here, human tremor). To avoid errors, A/D converters [1] have low-pass filters that are not ideal, so it is not only their cut-off frequency that matters but also their order. A 1st order low pass achieves - 20 db per frequency decade.
Tiefpass – Wikipedia
Now you could look for data sheets of IS binoculars, see which frequencies are important. I would then suggest >= 3-fold sampling frequency because of non-ideal low pass filters of AD converters of the gyro sensor.
Imho, a sensible evaluation programme should determine the sampling rate of the A/D converter of the gyro sensor. The A/D converter can only provide data according to its design and specifications. Why change it? Users of A/D converters need to know which signal frequencies they can be used for. For this purpose, the manufacturer specifies the maximum sampling rate and filter data on the cut-off frequency. Gyro sensors in smartphones are now a combination of analogue sensor and A/D converter. Therefore, one "only" has to consider the specs of the combination.
If an evaluation programme does not comply with these specs and omits intermediate values, Shannon's sampling theorem is violated. The evaluation programme with user input may at most configure the A/D converter (and filter parameter). The user must then think along with it. Therefore Mr. Shannon. ;-)
In "short": I wouldn't change anything about sampling rates - but check:
1. does the "app" match the specs of the sensor-A/D converter combination? Does it read out all the data? Omitting values can easily lead to the violation of the sampling theorem!
2. does the A/D conversion of the gyro sensor comply with the sampling theorem for measuring hand tremor? Is this digital measuring instrument suitable for the measurement project?
3. For the visual data display: You need about 10 measured values for 1 harmonic signal period. For non-harmonic signals, which can be composed of several harmonic signals, the highest signal frequency (periond duration T = 1/f ) counts.
On rotation and translation: Translations of binoculars imho lead to far less image shift than rotations. For this purpose, imagine the extension of an aeroplane or ship in relation to binoculars in order to estimate the different effects of angular changes due to rotation versus translation.
Roll-Nick-Gier-Winkel – Wikipedia
Gierachse – Wikipedia
In total, the movement of rigid bodies (or individual parts in the case of deformations) can be described mathematically with 6 degrees of freedom, 3 translations and 3 rotations in an xyz coordinate system. This then results in simple and therefore elegant matrix equations.
Edit:
I better attach a links.
[1]
Analog-to-digital converter - Wikipedia
https://en.wikipedia.org/wiki/Nyquist–Shannon_sampling_theorem
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It may sound like a smart-ass, but 2 tips anyway:
1. you have cut off transients/spikes. Further "outliers" of measured values can be "smoothed" by means of numerical mathematics programs and polynomial interpolation, visualise measured values and "play" with parameters of the polynomial, compare polynomial with measured value visualisation. This is halfway suitable for displaying measured oscillations.
2. the overall result (jitter + drift) can be decomposed into several harmonic signals by Fourier transformation (DFT, FFT) and try to subtract the "drift functions". As well as other signals that appear faulty. At the end, put the individual functions together again.
3. Presumably, mathematics programmes also offer ready-made filter functions (band pass) whose parameters can be changed. Is then basically the same as 2.
Statisticians have different methods than technicians. ;-)
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davewilletts
Member
I broadly agree. However it could be argued that the improvement in pitch pointing when sitting is marginally worth having, at the inconvenience of the protruding rest.
'Are you sure the benefit you see why sitting and using the forehead rest was not just because you were sitting? How did you isolate the benefit of the forehead rest and sitting?' - I am not quite sure what you mean by isolate: the comparison was between measurements taken while sitting, with or without the forehead rest.
I should have pointed out that I do not use spectacles, and that the binos were pressed well into my eye sockets to steady them. And really I have implied too much accuracy in the table - a single digit after the decimal point probably still exaggerates the precision, given the lack of averaging several 'runs' and possible onset of fatigue.
1. I have only removed the huge transients which result from picking the binoculars up and putting them down, since it is very difficult to start and stop the recording process while looking at a 'target'. I have not doctored the steady observation data at all.
2. Plainly the spectrum can be obtained, as was done for the angular rate data, but I don't know what the gyro drift features were to correct for them. The large 'human factors' effects like fatigue and cramp suggest that it is not worth massaging this data to death; I was looking for obvious features.
In this context, I am just thinking about what to do with the (high) signal frequencies and acceleration amplitudes caused by impulses. Pulses are generated by the impact of the binoculars or the forehead support on the head. Press as firmly as possible? Unpleasant. What effect does this have on the measurement objective (purpose): indirect comparison of image displacement via accelerations, not comparison of accelerations per se.
Is pressing on really feasible in practice and how do impulses distort the evaluation of accelerations when bins with forehead rest not pressing on? I think we should finally think about this. Thinking is not so fast for me. ;-)
In any case, an interesting experiment that stimulates thought. Thanks again for this!
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davewilletts
Member
Hi Henning
I don't think I have got the hang of using the reply feature in this forum!
The app I used was Sensordata 1.8.2.0 APK and it seems to be associated with com.matlabgeeks.gaitanalyzer. The 200 Hz sample rate is the default, a much lower rate would be adequate because the shake is limited to low frequencies, nothing much above 20 Hz, so a 40 Hz or more sampling rate would be fine (Shannon's theorem). I chose this app because the first I tried - name forgotten - only read out rates to a precision of 0.1 rad/s which was inadequate for the job.
I don't believe translational data would add anything, as explained at length by Jessie 66.
My rest contacts a patch of my forehead about 4 cm wide by 3 cm high, from the brow upwards; some detail is in the photos.
Wearing glasses may well make a difference too.
Regards
Dave
Regarding post #152:
Another simply DIY method, I think a better method, as there are fewer possibilities for error (direct results, no rotation/translation derivation from acceleration values):
www.cloudynights.com
(post #58)
Addendum:
I thought about the evaluation distortion caused by impulses: The forehead support is damped with a soft material, impulses hardly occur. People who wear glasses can generate impulses by lightly hitting the eyecups against the glasses, which only lead to slight rotations/image shifts but with high accelerations. This falsifies evaluations of the image shift via accelerations. The low-pass filter of the A/D converter of the gyro sensor counteracts this somewhat, but it is difficult to predict to what extent. Distorting, because higher accelerations with low rotations can also occur when trembling movements of the eyecups are slowed down by the eye sockets. I see the main problem of the method in quickly decelerated movements with low rotation and thus low image shift. I think a direct method (see link above) is better.
Nevertheless, I like the unusual use of sensors from readily available devices for measurements elsewhere.
Another simply DIY method, I think a better method, as there are fewer possibilities for error (direct results, no rotation/translation derivation from acceleration values):
Binocular Resolution Testing w/USAF Charts - Page 3 - Binoculars - Cloudy Nights
Page 3 of 4 - Binocular Resolution Testing w/USAF Charts - posted in Binoculars: When testing the central vision of an eye we use a 10 deg field. This is measured from the center of fixation. This results in a 20 deg edge to edge field. Photopic acuity drops off rapidly after that. There is a...
Addendum:
I thought about the evaluation distortion caused by impulses: The forehead support is damped with a soft material, impulses hardly occur. People who wear glasses can generate impulses by lightly hitting the eyecups against the glasses, which only lead to slight rotations/image shifts but with high accelerations. This falsifies evaluations of the image shift via accelerations. The low-pass filter of the A/D converter of the gyro sensor counteracts this somewhat, but it is difficult to predict to what extent. Distorting, because higher accelerations with low rotations can also occur when trembling movements of the eyecups are slowed down by the eye sockets. I see the main problem of the method in quickly decelerated movements with low rotation and thus low image shift. I think a direct method (see link above) is better.
Nevertheless, I like the unusual use of sensors from readily available devices for measurements elsewhere.
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Jessie. I agree with you. I think resolution testing would be a better way to test the Forehead rest. Why don't you do it? It would be a great experiment! Maybe you could even throw in some IS binoculars to see how they compare.Regarding post #152:
Another simply DIY method, I think a better method, as there are fewer possibilities for error (direct results, no rotation/translation derivation from acceleration values):
(post #58)Binocular Resolution Testing w/USAF Charts - Page 3 - Binoculars - Cloudy Nights
Page 3 of 4 - Binocular Resolution Testing w/USAF Charts - posted in Binoculars: When testing the central vision of an eye we use a 10 deg field. This is measured from the center of fixation. This results in a 20 deg edge to edge field. Photopic acuity drops off rapidly after that. There is a...
Addendum:
I thought about the evaluation distortion caused by impulses: The forehead support is damped with a soft material, impulses hardly occur. People who wear glasses can generate impulses by lightly hitting the eyecups against the glasses, which only lead to slight rotations/image shifts but with high accelerations. This falsifies evaluations of the image shift via accelerations. The low-pass filter of the A/D converter of the gyro sensor counteracts this somewhat, but it is difficult to predict to what extent. Distorting, because higher accelerations with low rotations can also occur when trembling movements of the eyecups are slowed down by the eye sockets. I see the main problem of the method in quickly decelerated movements with low rotation and thus low image shift. I think a direct method (see link above) is better.
Nevertheless, I like the unusual use of sensors from readily available devices for measurements elsewhere.
Dennis, post #155:
I'm not going to test it myself:
1. I don't have Swaro NL, would have to make a makeshift forehead rest for one of my mid-range binoculars.
2. I don't wear glasses, therefore I would have to buy one made with window glass: Analysis of previous posts and historical advertising brochures of vintage porros (thanks to John A. Roberts) [1] shows that forehead rests tend to help spectacle wearers at magnifications >= 10x.
3. if I had a problem with tremor and high magnifications, I would choose IS binoculars and not stopgap solutions like forehead rests.
4. Swarovski has probably carried out meaninful tests with n (n >> 1) people . But do they at least publish or name test results? You should ask Swaro. ;-)
[1] SpectaRoss 8x40: https://www.birdforum.net/threads/does-the-head-rest-help-on-the-nl-8x42.394532/page-2#post-4064720
(1st picture)
I'm not going to test it myself:
1. I don't have Swaro NL, would have to make a makeshift forehead rest for one of my mid-range binoculars.
2. I don't wear glasses, therefore I would have to buy one made with window glass: Analysis of previous posts and historical advertising brochures of vintage porros (thanks to John A. Roberts) [1] shows that forehead rests tend to help spectacle wearers at magnifications >= 10x.
3. if I had a problem with tremor and high magnifications, I would choose IS binoculars and not stopgap solutions like forehead rests.
4. Swarovski has probably carried out meaninful tests with n (n >> 1) people . But do they at least publish or name test results? You should ask Swaro. ;-)
[1] SpectaRoss 8x40: https://www.birdforum.net/threads/does-the-head-rest-help-on-the-nl-8x42.394532/page-2#post-4064720
(1st picture)
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I agree with you on choosing IS binoculars over the forehead rest. I wonder if Swarovski has done any testing of the forehead rest to see if it is actually effective. I think resolution testing is the best way to see if the forehead rest works though. Kimmo where are you?
dave,
Did you try a few different configurations for the headrest? What I mean is that I noticed I would end up with two different settings depending on whether I created a... weld(?) by starting to adjust the FHR and then the eyecups accordingly, and visa versa. This might not make a darn bit of difference, but I did notice different levels of contact, stability, and comfort depending on which part was adjusted first. This may not apply whatsoever since your FHR is not identical to the factory part, but it may? I stumbled on it by accident after trying to use the FHR to float the glass (cups fully collapsed) in front of my face as another user mentioned.
Last bit that might throw a very small variable in there is the flex of the factory part. Swaro wouldn't tell me that they made those posts too long but it sure looks that way considering the matching contours that appear to be designed to accommodate flush fitment between leading edge and the hinge. Without that larger contact area the darn thing has a lot more flex than I'd care for from a $140 part.
Goes without saying, awesome work and thanks for the info!
P.S. holding binos to 1 mil? Never tried to measure, but it's a safe bet that your hands are way steadier than mine!
Did you try a few different configurations for the headrest? What I mean is that I noticed I would end up with two different settings depending on whether I created a... weld(?) by starting to adjust the FHR and then the eyecups accordingly, and visa versa. This might not make a darn bit of difference, but I did notice different levels of contact, stability, and comfort depending on which part was adjusted first. This may not apply whatsoever since your FHR is not identical to the factory part, but it may? I stumbled on it by accident after trying to use the FHR to float the glass (cups fully collapsed) in front of my face as another user mentioned.
Last bit that might throw a very small variable in there is the flex of the factory part. Swaro wouldn't tell me that they made those posts too long but it sure looks that way considering the matching contours that appear to be designed to accommodate flush fitment between leading edge and the hinge. Without that larger contact area the darn thing has a lot more flex than I'd care for from a $140 part.
Goes without saying, awesome work and thanks for the info!
P.S. holding binos to 1 mil? Never tried to measure, but it's a safe bet that your hands are way steadier than mine!
Hi,
My own 3D printed headrest, being mounted on the forward end of the bridge, was quite flexible due to geometry and material choice.
I speculated that might actually be an advantage, by dampening some of the vibrations instead of transferring them.
However, that's just a thought, and it might well be that flex actually affects different geometries in different ways.
Regards,
Henning
My own 3D printed headrest, being mounted on the forward end of the bridge, was quite flexible due to geometry and material choice.
I speculated that might actually be an advantage, by dampening some of the vibrations instead of transferring them.
However, that's just a thought, and it might well be that flex actually affects different geometries in different ways.
Regards,
Henning
I would like to add my experience to this thread. I just received my FRP headrest for my recently purchased 8x42 Nl. I am in my late 70's and have a small amount of old man shake. I wear progressive eye glasses. My first impression was the headrest made little difference in how I could steady my 8x42Nl. Then, I realized I was using the head rest incorrectly. For the best stabilization one must make 3 point contact which includes the headrest, and your glasses firmly against the eyecups. This 3 point contact is like a miniature tripod on your face. My initial trial was with the forehead only, which did nothing for stabilization although it felt haveing my eyeglasses free from conctact with the binocular.
Did the headreast make a big difference for me? To be honest, no. Yet the difference for me was definite. Was it worth $150? Probably not, but when you have already spent 3 grand on these binoculars, what's another $150. Especially when you are talking about minute improvements in alpha optics, minute improvements often come at a higher cost.
Did the headreast make a big difference for me? To be honest, no. Yet the difference for me was definite. Was it worth $150? Probably not, but when you have already spent 3 grand on these binoculars, what's another $150. Especially when you are talking about minute improvements in alpha optics, minute improvements often come at a higher cost.
Hi,
Ah, good idea to mention that explicitely!
I'm using it in the same way, and just like you, I feel the headrest (of my own design, on a pair of Nikons) improve stability a bit.
(I have used my smartphone's gyroscope to capture a recording of the shake with and without headrest, but haven't gotten around to evaluating the raw data yet.)
Regards,
Henning
Ah, good idea to mention that explicitely!
I'm using it in the same way, and just like you, I feel the headrest (of my own design, on a pair of Nikons) improve stability a bit.
(I have used my smartphone's gyroscope to capture a recording of the shake with and without headrest, but haven't gotten around to evaluating the raw data yet.)
Regards,
Henning
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