Please read if you are about to buy high end bins (1 Viewer)

iporali · May 18, 2004

mike60 said:
I believe that i get more definite 'black out' on bright sunlit days with lots of reflected light than in dimmer conditions using my Zeiss 10x40. Does this stack up technically?

Me too. This is from the astrosurf-link above (the bottom of the page):

"...when the exit pupil is very large and close to the size of eye pupil, looking at the edge of the field your eye pupil will cut off a part of the light cone in the medium field region of the eyepiece. That medium field become dimmer while the center of the field of view is unaffected. You see blackout areas in the field. When the exit pupil is small, the effect is less apparent as your eye pupil can more easily move inside the light cone, this last having more place to browse your eye pupil. The "blackout" effect mainly arises with eyepieces of large eye relief and exit pupil or barlowing a low focal eyepiece as a 35mm."

Ilkka

jebir · May 18, 2004

iporali said:
Me too. This is from the astrosurf-link above (the bottom of the page):

"...when the exit pupil is very large and close to the size of eye pupil, looking at the edge of the field your eye pupil will cut off a part of the light cone in the medium field region of the eyepiece. That medium field become dimmer while the center of the field of view is unaffected. You see blackout areas in the field. When the exit pupil is small, the effect is less apparent as your eye pupil can more easily move inside the light cone, this last having more place to browse your eye pupil. The "blackout" effect mainly arises with eyepieces of large eye relief and exit pupil or barlowing a low focal eyepiece as a 35mm."

Ilkka

So, if I interpret the above correctly, the problem should be due to too large exit pupils and it should not be a big problem in low light when the eyes' pupils are larger.

Hmm... I will definitely have to check this out at different light conditions to figure out what is going on.

Maybe we will have to put ND filters on our SE:s to dilate our pupils :eek!:

Cheers, Jens.

mike60 · May 18, 2004

Ilkka, i didnt follow that at all - must be gaps in my understanding.
I was thinking about this and sketched it out : If the exit pupil is about 4mm, and the eye pupil is say 2mm in bright sunlight, and you misalign the eye pupil centre with the exit pupil centre by only 3 mm, it would result in a complete loss of vision - no overlap. In darkness the eye pupil may be say 6mm, so if you misaligned by the same amount you would still have 2mm overlap, and still get an image - only dimmer. Then i looked at 3mm on my steel ruler - its not much of an error. I wonder if this is the correct way to understand this?

iporali · May 18, 2004

jebir said:
So, if I interpret the above correctly, the problem should be due to too large exit pupils and it should not be a big problem in low light when the eyes' pupils are larger.

Jens & Mike: I hope someone with true knowledge could clear this up (Hello Chris, Jay, Henry, mak...), but yes, that's about how I understand it: the large exit pupil AND eye-relief cause blackouts. The problem with the above explanation is that it does not say that the eye must be closer than the eye-relief (IMO).

To summarize my point:
a) When the eye is farther off than the eye-relief distance, it is the eyepiece that "shadows" the edges of the fov (these light rays form the "peripherial" image) -> narrow field, smaller image, but no blackouts.
b) The eye at the eye-relief distance. Widest view, no blackouts.
c) The eye closer than the eye relief. If the exit pupil is larger than the eye pupil, the edges of the iris cast shadows on the retina. These shaded light rays would form the image in the middle of the fov -> the blackout is a moving blob in the middle of the fov. In such a small distance even small pupil movement has a big impact.

You can demonstrate this with a digiscoping setup if you have a scope with a long eye relief and a camera with a short distance to the entrance pupil (like Canon Digi-Ixus etc.). Put the camera lens on the eyepiece. Move the camera slightly and you should see the blackouts in the LCD screen.

Ilkka

ps. Jens - that's a bizarre thought about using ND-filters... "Could I have my Nikon SEs a little less bright, please?"

Leif · May 18, 2004

AlanFrench said:
I think you have this backwards.

On a bright sunny day, your pupil is open to 2mm or so, so you are only using part of the aperture in any binocular with an exit pupil larger than 2mm. With 10x42s, you are using less than half the aperture. This does not change as we age.

Under dark conditions, a youngster's pupil opens to 7 or 8mm, but as we age the pupil loses its ability to open that wide, and the maximum opening is perhaps 5mm. Us old folks never use the full aperture of a pair of 7x42 binoculars (although some of us appreciate the wide field enought to ignore this issue).

Clear skies, Alan

What you say is rather misleading.

There's an interesting study that was done by an amateur astronomer. I don't think it was done in a proper controlled manner, but it's interesting nonetheless:

http://www.btow.com.au/pdf/agwa/agwa-September-2003.pdf

From this study we see that although on average pupil dilation does indeed reduce with age, the spread is very large, and interestingly many old people have greater pupil dilation than many youngsters. So if you want to know how much your pupil dilates, you should measure it, rather than make an assumption based on age.

Jonathan B. · May 18, 2004

AlanFrench said:
I think you have this backwards.

On a bright sunny day, your pupil is open to 2mm or so, so you are only using part of the aperture in any binocular with an exit pupil larger than 2mm. With 10x42s, you are using less than half the aperture. This does not change as we age.

Under dark conditions, a youngster's pupil opens to 7 or 8mm, but as we age the pupil loses its ability to open that wide, and the maximum opening is perhaps 5mm. Us old folks never use the full aperture of a pair of 7x42 binoculars (although some of us appreciate the wide field enought to ignore this issue).

Clear skies, Alan

I am 51, and this does not hold true for me in the field. I own Leica 8x20 and Nikon SE 8x32, and in direct comparison in open sunlight the image in the Nikon is much brighter, so my pupil is obviously dilated to more than 2.5mm under those conditions. In open shade, my 7x42 is obviously brighter than the 8x32, which suggests that under those conditions my pupil is dilated to more than 4mm.

I wouldn't trust any textbook explanation of pupil dilation in choosing binoculars with regard to the size of their exit pupils.

jebir · May 18, 2004

iporali said:
ps. Jens - that's a bizarre thought about using ND-filters... "Could I have my Nikon SEs a little less bright, please?"

Ilkka,

I tried it today! I went out and tested the "black out" (BO) when viewing under different conditions.

Some observations:

1) When looking at a bright scene (against the sky), the BO came more often than when looking in low light (in a forrest).
2) Using sunglasses eliminated the tendency for BO.
3) Using sunglasses ruined the contrast of the binos even in bright sunlight.
4) When looking on a clear blue featureless sky, no BO ocurred at all.

Regarding the eye-relief and exit pupil combination:
In order to actually see the edge of the exit pupils, I have to hold the binos quite near the eyes in bright light. If I don't, the edge of the FOV becomes diffuse (limited by my own pupils presumably). I have not been able to do the same experiment in low light but I have the feeling that it is less sensitive.

So my conclusions are that when the eyes' pupils becomes comparable in size with the exit pupil, there is a risk of overlap at the edges. Only when looking straight through the binos, there is a clear view. When panning, the eye balls will be moving slightly sideways back-and-forth because my brain can't ignore the features in the scene that is passing and thus the vignetting will set in at each eye-movement and a series of the black outs becomes evident. (No BO occurred when looking at the featureless sky.)

Cheers, Jens.

PS. It was a bizarre and really bad idea to make the SE:s darker - even if the tendency for BO:s was reduced.

andytyle · May 18, 2004

iporali said:
Jens & Mike: I hope someone with true knowledge could clear this up (Hello Chris, Jay, Henry, mak...), but yes, that's about how I understand it: the large exit pupil AND eye-relief cause blackouts. The problem with the above explanation is that it does not say that the eye must be closer than the eye-relief (IMO).

To summarize my point:
a) When the eye is farther off than the eye-relief distance, it is the eyepiece that "shadows" the edges of the fov (these light rays form the "peripherial" image) -> narrow field, smaller image, but no blackouts.
b) The eye at the eye-relief distance. Widest view, no blackouts.
c) The eye closer than the eye relief. If the exit pupil is larger than the eye pupil, the edges of the iris cast shadows on the retina. These shaded light rays would form the image in the middle of the fov -> the blackout is a moving blob in the middle of the fov. In such a small distance even small pupil movement has a big impact.

You can demonstrate this with a digiscoping setup if you have a scope with a long eye relief and a camera with a short distance to the entrance pupil (like Canon Digi-Ixus etc.). Put the camera lens on the eyepiece. Move the camera slightly and you should see the blackouts in the LCD screen.

Ilkka

ps. Jens - that's a bizarre thought about using ND-filters... "Could I have my Nikon SEs a little less bright, please?"

The question of pupil to exit pupil is partly covered in posting #180+ in the 'Scope Survey' thread. When the pupil is smaller than the exit pupil, it places a 'stop' on the effective aperture, and vignettes the image (increasing loss of illumination toward the field edge). If the pupil is the same diameter or larger than the exit pupil, then all the rays from the objective lenses pass through to the retina. The advantage here is full field illumination and maximum resolution that the aperture can deliver. The disadvantage here is (particularly with binoculars with notable chromatic aberration), that the worst of the CA, formed by the periphery of any achromatic lens, is present in the image. At least, when the image is vignetted by having a too small pupil, the light from the lens edge does not pass through the eye's pupil, hence less CA is noted.
If your pupil is smaller than the EP of a 10X42 binocular during daylight (which it is likely to be), then blackouts can be caused by the placement of your eye inside the eye relief position. In other words, if you place your eye too close to an eyepiece with a fair amount of eye relief, you may experience blackouts. What is more, this varies from person to person, and further, the eye relief (or rather, visibility of the field edge) changes with pupil diameter. This essentially means that you don't have to place your eye as close to an eyepiece in order to see the edge of the field at night, as you would during the day. This then leads to the intermittent 'bobbing in and out' of your eye within the eye relief placement, causing these momentary blackouts.

best regards
Chris

oathkeeper · May 18, 2004

Alan,

Thanks. I stand corrected.

Leif · May 18, 2004

Jonathan B. said:
I am 51, and this does not hold true for me in the field. I own Leica 8x20 and Nikon SE 8x32, and in direct comparison in open sunlight the image in the Nikon is much brighter, so my pupil is obviously dilated to more than 2.5mm under those conditions. In open shade, my 7x42 is obviously brighter than the 8x32, which suggests that under those conditions my pupil is dilated to more than 4mm.

I wouldn't trust any textbook explanation of pupil dilation in choosing binoculars with regard to the size of their exit pupils.

Jonathan: Even when your pupils are contracted as in daylight, you will see differences in brightness between binoculars. All other things being equal, increasing the size of the objectives increases contrast, and increasing the magnification lowers the contrast. So although it is often said that in daylight a larger binocular is wasted, you do get more contrast (and resolution) which helps when for example watching distant birds in flight. The small binocular shows a dark blob, the larger one shows some of the colours.

Large eye relief does increase the chance of black outs, but for me anyway, it beats having to press the binocular tight against my face!

iporali · May 19, 2004

jebir said:
I tried it today! I went out and tested the "black out" (BO) when viewing under different conditions.

Some observations:

1) When looking at a bright scene (against the sky), the BO came more often than when looking in low light (in a forrest).
2) Using sunglasses eliminated the tendency for BO.
3) Using sunglasses ruined the contrast of the binos even in bright sunlight.
4) When looking on a clear blue featureless sky, no BO ocurred at all.

Nothing beats good experimental science

I especially liked your observation #3 (you can be sure that I'll try it too, LOL).

Ilkka

Leif · May 19, 2004

jebir said:
3) Using sunglasses ruined the contrast of the binos even in bright sunlight.

iporali said:
Nothing beats good experimental science I especially liked your observation #3 (you can be sure that I'll try it too, LOL).

Ilkka

Ilkka: I have seen quite a few people in the UK wearing sunglasses while viewing through a scope or binoculars!

jebir · May 19, 2004

Leif said:
Ilkka: I have seen quite a few people in the UK wearing sunglasses while viewing through a scope or binoculars!

Leif,

hopefully, their scopes weren't in the +£1000-league (or even much inferior to that). That would be a waste of money.

Unfortunately, I wouldn't be surprised if they were.

Cheers, Jens.

Leif · May 19, 2004

jebir said:
Leif,

hopefully, their scopes weren't in the +£1000-league (or even much inferior to that). That would be a waste of money.

Unfortunately, I wouldn't be surprised if they were.

Cheers, Jens.

Sadly in one case the user was digiscoping with a Leica APO 77 scope and Leica 8x42 Trinovids!

pduxon · May 19, 2004

Leif said:
Sadly in one case the user was digiscoping with a Leica APO 77 scope and Leica 8x42 Trinovids!

More money than sense perhaps? Although I could be accused of that

Edward woodwood · May 19, 2004

sorry boys n girls

me n the boys were birding in shades at the weekend

found a british lifer though (only a thunbergi wag but bloody nice)........and looked pretty cool while doing it

rock n roll B

RCMann · May 19, 2004

Tim Allwood said:
sorry boys n girls

me n the boys were birding in shades at the weekend

found a british lifer though (only a thunbergi wag but bloody nice)........and looked pretty cool while doing it

rock n roll B

What the..? We are truly two countries separated by a common language. I believe the quote above indicates a mixture of birding and drinking, er, dirding and brinking, and seeing something important? Please-don't try this at home.

Leif · May 20, 2004

pduxon said:
More money than sense perhaps? Although I could be accused of that

You must be very rich then. What a crawler eh?

Psst. How's the new scope?

AlanFrench · May 20, 2004

Leif said:
Jonathan: Even when your pupils are contracted as in daylight, you will see differences in brightness between binoculars. All other things being equal, increasing the size of the objectives increases contrast, and increasing the magnification lowers the contrast. So although it is often said that in daylight a larger binocular is wasted, you do get more contrast (and resolution) which helps when for example watching distant birds in flight. The small binocular shows a dark blob, the larger one shows some of the colours.

Large eye relief does increase the chance of black outs, but for me anyway, it beats having to press the binocular tight against my face!

If you are using a pair of 7x42 binoculars, which have a 6mm exit pupil, and your eye is only open to 3mm, you are only using 21mm of the aperture. Stopping down the exit pupil has EXACTLY the same effect as stopping down the aperture. You are really using 7x21 binocluars. The question of resolution is actually rather meaningless, however, since normal birding binoculars are not using a high enough magnification to utilized the potential resolution of the objective.

Clear skies, Alan

BTW, contrast is really a function of optical quality - putting all the light where it belongs in the image.

pduxon · May 20, 2004

Leif said:
You must be very rich then. What a crawler eh?

Psst. How's the new scope?

Rich - moi, the proverbial church mouse.

The new scope? very nice!

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