Henry,
I've altered my post in light of the deletion. I'll be very interested to hear what you find.
David
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Eye relief changes with different lighting? (1 Viewer)
- Thread starter justabirdwatcher
- Start date
Henry,
I've altered my post in light of the deletion. I'll be very interested to hear what you find.
David
Don't forget the pupil of the eye is an aperture stop in the complete optical train and effectively changes a number of optical parameters, like resolution, CA, and other aberrations, and glare. Until the OP mentioned it, I hadn't considered that the apparent ER might be another one. Just trying to understand how and why.
David
I have noticed something similar, but the opposite to the OP. The poorer the light, eg. before sunrise, the more finicky most of my binoculars are with regard to eye placement, eye cup extension, focus and so on. This must be related to the eye stopping up in low light. As it gets brighter the eye stops down, depth of field increases and everything becomes easier.
With regard to eye relief, not only is there reduced depth of field, but the eye performance is worse in poorer light, both because of a faster f ratio and 'sensor' and processor (brain, eye).
One, I think, has to consider also the size and curvature of the eyeball and cornea and the position of the iris.
With glasses, there is the prescription, usually different for each eye.
The thickness of the glass, the position of the glass, along the axis, up and down, sideways, and tilt.
The refractive index of the glass.
Although, maybe seemingly different, I wondered a few days ago why the aircraft photos I took had such poor resolution.
I was using a compact Canon G15, which I find to be excellent in low light. f/1.8-f/2.8 lens.
The exposures 1/1600 second f/2.8 ISO 80.
Today was clear, but late at 15.15 UT winter day.
G15 12 megapixel? photos 1/2000 second f/2.8 ISO 80 Sky.
28-140 equivalent fl plus 4x digital zoom.
Actual fl 30.5mm plus 4x digital zoom.
Canon A720IS, my normal camera which always takes good aircraft photos.
8 megapixel, even smaller sensor than G15 and older processor. 2007, f/2.8-4.8 lens.
1/640 second f/4.8 ISO 80. Same sky position as photos with G15.
35-210 equivalent fl plus 4x digital zoom.
Actual fl 34.8mm plus 4x digital zoom.
So why are the aircraft photos much poorer in the more modern G15 with later processor.
I think that it is because the lens is optimsed for low light and at f/2.8 is much faster than the more modest f/4.8 of the older Canon A720.
For aircraft, one can read birds, as the Canon A720 IS takes excellent photos of flying birds.
Both cameras have optical viewfinders with good centration, so even with 4x digital zoom the birds are well in frame using the optical viewfinder.
The difference to me is surprising and I think that the whole optical system has to be considered regarding binoculars and the eye regarding eye relief in good and poor light.
One, I think, has to consider also the size and curvature of the eyeball and cornea and the position of the iris.
With glasses, there is the prescription, usually different for each eye.
The thickness of the glass, the position of the glass, along the axis, up and down, sideways, and tilt.
The refractive index of the glass.
Although, maybe seemingly different, I wondered a few days ago why the aircraft photos I took had such poor resolution.
I was using a compact Canon G15, which I find to be excellent in low light. f/1.8-f/2.8 lens.
The exposures 1/1600 second f/2.8 ISO 80.
Today was clear, but late at 15.15 UT winter day.
G15 12 megapixel? photos 1/2000 second f/2.8 ISO 80 Sky.
28-140 equivalent fl plus 4x digital zoom.
Actual fl 30.5mm plus 4x digital zoom.
Canon A720IS, my normal camera which always takes good aircraft photos.
8 megapixel, even smaller sensor than G15 and older processor. 2007, f/2.8-4.8 lens.
1/640 second f/4.8 ISO 80. Same sky position as photos with G15.
35-210 equivalent fl plus 4x digital zoom.
Actual fl 34.8mm plus 4x digital zoom.
So why are the aircraft photos much poorer in the more modern G15 with later processor.
I think that it is because the lens is optimsed for low light and at f/2.8 is much faster than the more modest f/4.8 of the older Canon A720.
For aircraft, one can read birds, as the Canon A720 IS takes excellent photos of flying birds.
Both cameras have optical viewfinders with good centration, so even with 4x digital zoom the birds are well in frame using the optical viewfinder.
The difference to me is surprising and I think that the whole optical system has to be considered regarding binoculars and the eye regarding eye relief in good and poor light.
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David
I am going to stick my neck out and speculate that the G15 isn't optimised for the f2.8 stop at all and that like many lenses it is just not at its best when wide open.
Your older camera may be at some theoretical disadvantages but its less ambitious f stop may in fact have been more within its comfort zone and would have given you a little more depth of field which could also have helped.
Possibly.
Lee
Lee,
You are correct in a way.
But both lenses are in fact wide open at the tele lens setting, not stopped down.
Both cameras have superb very fast autofocus in the daytime, and are working at 'infinity'.
They lock onto far aircraft almost instantly.
In fact these cameras have only a limited, say ten? focus positions, not a continuous range of focus.
One of these positions is near 'infinity'.
Stars are sharp at night and in focus.
I don't think that either camera needs depth of focus, as they both focus accurately on 'infinity' very quickly in the daytime.
What I find remarkable about the G15 is that it takes whole constellation photos automatically on Programme at 1 second at f/1.8, at the wide setting, with many stars fainter than those seen with the unaided eyes shown. Possibly at 1600 or 3200 ISO.
That is why the poor daytime resolution surprised me.
The Sony A7S is much more remarkable and shows stars more than 4 magnitudes or more than 40 times fainter than those seen with unaided eyes, with exposures of 1/13th second at 51,000 or 102,000 ISO using a Samyang 85mm lens at f/1.4.
The lens has to be manual focus to accurately focus on stars.
The viewfinder shows numerous stars when no stars at all are visible to the unaided eyes in a light polluted sky.
Modern cameras are remarkable.
160 ASA film used to be very fast when I was young. Kodachrome was about 6 or 12 ASA.
You are correct in a way.
But both lenses are in fact wide open at the tele lens setting, not stopped down.
Both cameras have superb very fast autofocus in the daytime, and are working at 'infinity'.
They lock onto far aircraft almost instantly.
In fact these cameras have only a limited, say ten? focus positions, not a continuous range of focus.
One of these positions is near 'infinity'.
Stars are sharp at night and in focus.
I don't think that either camera needs depth of focus, as they both focus accurately on 'infinity' very quickly in the daytime.
What I find remarkable about the G15 is that it takes whole constellation photos automatically on Programme at 1 second at f/1.8, at the wide setting, with many stars fainter than those seen with the unaided eyes shown. Possibly at 1600 or 3200 ISO.
That is why the poor daytime resolution surprised me.
The Sony A7S is much more remarkable and shows stars more than 4 magnitudes or more than 40 times fainter than those seen with unaided eyes, with exposures of 1/13th second at 51,000 or 102,000 ISO using a Samyang 85mm lens at f/1.4.
The lens has to be manual focus to accurately focus on stars.
The viewfinder shows numerous stars when no stars at all are visible to the unaided eyes in a light polluted sky.
Modern cameras are remarkable.
160 ASA film used to be very fast when I was young. Kodachrome was about 6 or 12 ASA.
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David
The G15 is doing an amazing job then with the stars. Do you think this kind of imaging is easier on the camera because the subject itself (stars on a black background) is very rich in contrast? The detail on an aircraft in daylight is probably much more subtle and have much less natural contrast. And the infinity of space allows a huge depth of field even with the lens wide open whereas a plane in the sky might not be quite in focus and there might not be the depth of field to capture it.
Lee
The G15 is doing an amazing job then with the stars. Do you think this kind of imaging is easier on the camera because the subject itself (stars on a black background) is very rich in contrast? The detail on an aircraft in daylight is probably much more subtle and have much less natural contrast. And the infinity of space allows a huge depth of field even with the lens wide open whereas a plane in the sky might not be quite in focus and there might not be the depth of field to capture it.
Lee
Hi Lee.
I think it is that stars are very high contrast point sources basically.
The aircraft are in focus, but I think it is just that at f/2.8 the lens performance is just poor.
Also the G15 processor seems to have a job dealing with the aircraft.
The old A720 processor seems to do a better job and its lens is possibly better and only working at f/4.8.
I think that a similar situation occurs with our eyes where stopped down performance is much better.
What I think is surprising is how good some old cameras are.
The Konica Minolta Z5 and Z6 took cracking photos. 5 and 6mp??
The Canon A650 IS (G9 with 4 AAs) took amazing photos. 12mp.
I have A2 size prints that are excellent.
The proviso is that lighting must be good, the lens stopped down. Minimum ISO and very steady handholding helped by IS.
Framing must be good with no cropping.
I prefer lower pixel count and larger pixels over high pixel count.
With film, the 110 sized Minolta zoom Mk2 was quite amazing. The lens was reportedly one of the best ever made.
The 1964 Olympus Pen D2 32mm f/1.9 lens, half frame film camera took such good photos that two out of three rolls of 72 prints per roll were stolen from me.
Although the bird photos made with these small sensors and small film sizes are good at smaller sizes, say 8x6 inches or A4, they cannot compete with a good full frame or APS camera.
Obviously, the really good large photos need a better larger camera.
But the Sony A7S and other Sony cameras are quite small.
I think it is that stars are very high contrast point sources basically.
The aircraft are in focus, but I think it is just that at f/2.8 the lens performance is just poor.
Also the G15 processor seems to have a job dealing with the aircraft.
The old A720 processor seems to do a better job and its lens is possibly better and only working at f/4.8.
I think that a similar situation occurs with our eyes where stopped down performance is much better.
What I think is surprising is how good some old cameras are.
The Konica Minolta Z5 and Z6 took cracking photos. 5 and 6mp??
The Canon A650 IS (G9 with 4 AAs) took amazing photos. 12mp.
I have A2 size prints that are excellent.
The proviso is that lighting must be good, the lens stopped down. Minimum ISO and very steady handholding helped by IS.
Framing must be good with no cropping.
I prefer lower pixel count and larger pixels over high pixel count.
With film, the 110 sized Minolta zoom Mk2 was quite amazing. The lens was reportedly one of the best ever made.
The 1964 Olympus Pen D2 32mm f/1.9 lens, half frame film camera took such good photos that two out of three rolls of 72 prints per roll were stolen from me.
Although the bird photos made with these small sensors and small film sizes are good at smaller sizes, say 8x6 inches or A4, they cannot compete with a good full frame or APS camera.
Obviously, the really good large photos need a better larger camera.
But the Sony A7S and other Sony cameras are quite small.
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henry link
Well-known member
David,
I've had a little time to play around with this. Like, you I do measure a slight reduction in eye relief if I stop down my 8x56 FL to 15mm.
I wondered if changing the position of the aperture stop might have some effect, since the 15mm stop had to be about 15mm in front of the objective, so I set up an improvised telescope with a 15mm aperture stop placed about 20mm behind a 30mm objective. Quick and dirty measurements of eye relief with and without the stop suggest the ER measures longer rather than shorter with the stop placed behind the objective. I'm not 100% sure about that.
Henry
I've had a little time to play around with this. Like, you I do measure a slight reduction in eye relief if I stop down my 8x56 FL to 15mm.
I wondered if changing the position of the aperture stop might have some effect, since the 15mm stop had to be about 15mm in front of the objective, so I set up an improvised telescope with a 15mm aperture stop placed about 20mm behind a 30mm objective. Quick and dirty measurements of eye relief with and without the stop suggest the ER measures longer rather than shorter with the stop placed behind the objective. I'm not 100% sure about that.
Henry
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Thanks Henry,
An interesting line of thought. The profile of the EP is product of combination of the objective cluster and the eyepiece aberrations so the stop position might well contribute to the overall difference. I believe it affects the level of pincushion distortion, so it seems a possibility. I don't have much in the way of optical components to play with, but I'll see if I can devise something over the weekend.
I did a further test on an 8x42, which I regard as being relatively critical for eye positioning, compared to the 10x42 I posted earlier. The difference between the full aperture and 2mm ERs was greater, but there was less variation with angle of view. Still pondering on the significance.
Cheers,
David
Attachments
Henry,
I used the dismantled components of a damaged 70mm Canon spotting scope to see if I could figure anything out.
The scope design had a objective doublet and a Smyth element in frot of the prism, which increased the effective focal distance, and a 20x eyepiece.
Again using two flash lights, I checked out the apparent ER for the full objective, and also masked down to 20mm and 2mm. I then repeated it with the same masks behind the objective, and then once checked again with the Smyth lens in it's usual position.
At full aperture, with and without the Smyth lens, the ER was 18.5mm. When stopped down with the two masks, with and without the Smyth lens the ER was 18.0mm. With such a small difference I rechecked the values several times, and couldn't spot any suggestion at all of the increase in ER you found when stopped down.
One difference between the scope and the two binoculars I tested seems to be the sophistication of the eyepiece. From the reflections it appeared the scope eyepiece only had three elements, whereas the two binoculars may have had 5, both with some level of field flattening.
There are too many variables in these comparison to draw any firm conclusions, but it seems that the scope and binoculars with the least ER difference between the full aperture and stopped down are rather more forgiving on eye positioning that my 8x42 with a 3mm difference. However it could well be that apparent difference with angle of view and presence or absences of flattening elements might be part of the story as well. Just a few samples can't paint a full picture and these results could be misleading of course, but it has revealed another intriguing dimension to optical design!
David
I used the dismantled components of a damaged 70mm Canon spotting scope to see if I could figure anything out.
The scope design had a objective doublet and a Smyth element in frot of the prism, which increased the effective focal distance, and a 20x eyepiece.
Again using two flash lights, I checked out the apparent ER for the full objective, and also masked down to 20mm and 2mm. I then repeated it with the same masks behind the objective, and then once checked again with the Smyth lens in it's usual position.
At full aperture, with and without the Smyth lens, the ER was 18.5mm. When stopped down with the two masks, with and without the Smyth lens the ER was 18.0mm. With such a small difference I rechecked the values several times, and couldn't spot any suggestion at all of the increase in ER you found when stopped down.
One difference between the scope and the two binoculars I tested seems to be the sophistication of the eyepiece. From the reflections it appeared the scope eyepiece only had three elements, whereas the two binoculars may have had 5, both with some level of field flattening.
There are too many variables in these comparison to draw any firm conclusions, but it seems that the scope and binoculars with the least ER difference between the full aperture and stopped down are rather more forgiving on eye positioning that my 8x42 with a 3mm difference. However it could well be that apparent difference with angle of view and presence or absences of flattening elements might be part of the story as well. Just a few samples can't paint a full picture and these results could be misleading of course, but it has revealed another intriguing dimension to optical design!
David
Alexis Powell
Natural history enthusiast
I have found (consistently over many years) that to get an unvignetted view through bins, they have to be held very slightly closer to my eyes in bright light as compared to using them in low light. Many shops have low indoor light, so when trying bins for having enough eye relief for glasses, it is important to be able to take them outside into sun or bright overcast daytime lighting.
--AP
--AP
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Alexis,
Like you, I find the apparent ER is generally shorter in bright light than it is when it's dim. It's something that I find rather variable though and is particularly problematic in certain binoculars. This is the opposite to what is described in the original post.
In #5 Henry suggests the cause might be spherical aberration of the exit pupil as illustrated by the ray diagram of the Nagler eyepiece. I know this was a topic that was debated here and elsewhere extensively long before I joined the forum, and I probably don't understand it as well as I should, but that diagram shows a change of ER with the angle of view, and explains why you get kidney beaning at the edges. It does not explain the apparent ER with light levels, though I wouldn't be surprised if the causes are related.
I've now looked at three binoculars and the dismantled spotting scope. In all four the apparent ER is shorter when the stopped down than it is at full aperture, but the difference is quite variable and ranged between 0.5mm and 3mm. However, only one showed a significant shift with the angle of view and that seems to be in the opposite direction to that shown by the Nagler.
Perhaps it would be no surprise that the binocular with the 3mm shift between the small and large pupil size is the one that gives me most ER problems in changeable light. However, it is also the one that is most prone to blackouts when trying to examine the edge of the view. It is not the one that showed the apparent change in ER with angle of view. The one that did is much more forgiving.
The explanation for these differences is beyond my knowledge of optics, but the take home message seems to be clear. Like you said, make sure you check the ER is sufficient in bright conditions. I would add that you should also check for problems viewing the edge of the field at the same time.
David
Like you, I find the apparent ER is generally shorter in bright light than it is when it's dim. It's something that I find rather variable though and is particularly problematic in certain binoculars. This is the opposite to what is described in the original post.
In #5 Henry suggests the cause might be spherical aberration of the exit pupil as illustrated by the ray diagram of the Nagler eyepiece. I know this was a topic that was debated here and elsewhere extensively long before I joined the forum, and I probably don't understand it as well as I should, but that diagram shows a change of ER with the angle of view, and explains why you get kidney beaning at the edges. It does not explain the apparent ER with light levels, though I wouldn't be surprised if the causes are related.
I've now looked at three binoculars and the dismantled spotting scope. In all four the apparent ER is shorter when the stopped down than it is at full aperture, but the difference is quite variable and ranged between 0.5mm and 3mm. However, only one showed a significant shift with the angle of view and that seems to be in the opposite direction to that shown by the Nagler.
Perhaps it would be no surprise that the binocular with the 3mm shift between the small and large pupil size is the one that gives me most ER problems in changeable light. However, it is also the one that is most prone to blackouts when trying to examine the edge of the view. It is not the one that showed the apparent change in ER with angle of view. The one that did is much more forgiving.
The explanation for these differences is beyond my knowledge of optics, but the take home message seems to be clear. Like you said, make sure you check the ER is sufficient in bright conditions. I would add that you should also check for problems viewing the edge of the field at the same time.
David
justabirdwatcher
Well-known member
That's so odd to me that it is exactly the opposite in my case. At least, with the binoculars I am presently using (a high quality Kamakura 8x42 optic rebranded by Cabelas).
