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7mm Exit Pupils. Specifically how dark do your skies need to be?

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20 replies to this topic

#1 Eric.TB

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Posted 12 January 2018 - 10:31 PM

I live in a yellow zone on the Bortle scale. Will a 7X50 appear washed out from an area this bright? Not interested in the whole "your pupil may not utilize the full 7mm exit pupil" thing, I'm just curious how dark your sky needs to be to use one of these, and not get a totally washed out image.


Edited by Eric.TB, 12 January 2018 - 10:33 PM.


#2 havasman

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Posted 12 January 2018 - 10:39 PM

‚ÄčAs is often the case, that very simple Q has a more complex answer than you might anticipate. Much depends on the relationship of that 7mm exit pupil to your eye's largest pupil diameter or its diameter under the given viewing conditions.

 

Best is to try it & see, then seek out better conditions & try it again.


Edited by havasman, 12 January 2018 - 10:40 PM.

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#3 Asbytec

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Posted 12 January 2018 - 10:40 PM

As dark as you can stand it? smile.gif

 

I dunno, a yellow zone is not bad. Remember, when your binos image the scene, they gather light not only from the object, but from the sky as well. The scene is brighter, but contrast between the image and the sky is unchanged. So, your objects images should be brighter as well. But, if the yellow zone sky is too bright, try green or blue? If available. Otherwise, yellow is not bad, IMO. 


Edited by Asbytec, 12 January 2018 - 10:41 PM.

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#4 Jon Isaacs

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Posted 12 January 2018 - 10:41 PM

I use 7 mm exit pupils from my red zone backyard and see more than I do at the same magnification but with 5 mm exit pupils.

 

As to whether it's totally washed out..  I am seeing more. 

 

Jon


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#5 Augustus

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Posted 12 January 2018 - 10:43 PM

I'm in a red zone. My eyes dilate to about 8-8.5mm (I'm young though). I find that a 7mm exit pupil causes some level of washing-out, but not enough to lose all that much detail. 5-6mm is much better for general viewing for me.

 

A yellow zone is dark enough that I wouldn't worry about the background being washed out, however. Stellafane is in a yellow zone......



#6 SMark

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Posted 13 January 2018 - 01:03 AM

I use 7 mm exit pupils from my red zone backyard and see more than I do at the same magnification but with 5 mm exit pupils.

 

As to whether it's totally washed out..  I am seeing more. 

 

Jon

My feelings exactly. I am also in a red zone and very much enjoy a 7mm exit pupil. Last year I made regular comparisons between 5mm, 6mm, & 7mm exit pupil binoculars, and I always preferred the 7mm views.


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#7 GlennLeDrew

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Posted 13 January 2018 - 01:41 AM

If your iris dilates up to 7mm, a 7mm exit pupil will have the image as 'washed out' as when seen by the unaided eye. If you're one of the rarer creatures for whom the iris expands to larger than 7mm, a 7mm exit pupil will have the sky a little darker, or less 'washed out' than as seen by the unaided eye.

 

Contrary to somewhat common thinking, an urban sky is still dark enough to cause one's iris to dilate to maximal. Only when notably bright light sources, or awfully brightly lit scenery, falls within one's field of vision might your irises contract somewhat.

 

For given magnification, it does not hurt to have an exit pupil as large as or larger than one's iris. Even though the sky is made brighter by a larger exit pupil, so too are the objects seen through the sky glow. While intrinsic contrast is not altered, the brighter scene results in a relatively smaller contribution by visual system noise, which does improve the detection of slightly subtler contrast.

 

The darker sky rendered by a smaller exit pupil (at given magnification) is principally an aesthetic benefit, but with a small cost in reduced contrast discrimination and general reduction in depth of penetration (when limiting to more typical binocular-sized exit pupils.)


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#8 KennyJ

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Posted 13 January 2018 - 04:12 AM

Thankfully, to me a "totally washed out image" is something I've only ever witnessed whilst sitting in my car in the middle of an automatic car wash process!

 

Kenny


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#9 Tony Flanders

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Posted 13 January 2018 - 06:01 AM

I never have a sensation of a "totally washed-out image" in any binoculars, no matter how bright the skies are. That includes a fair amount of observing in Manhattan.

 

Conversely, the sky never appears dark to me through any instrument with an exit pupil of 3 mm or bigger, no matter how little light pollution there is. That includes some observations far from the nearest town in Chile's Atacama Desert.


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#10 earlyriser

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Posted 13 January 2018 - 07:13 AM

Is the exit pupil being reduced by increasing the magnification, or reducing the aperture? You'll see more with a 7x50 than a 7x35. But a 10x50 will go deeper than the 7x50. 


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#11 Jon Isaacs

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Posted 13 January 2018 - 08:05 AM

Is the exit pupil being reduced by increasing the magnification, or reducing the aperture? You'll see more with a 7x50 than a 7x35. But a 10x50 will go deeper than the 7x50. 

 

The question here is about whether or not a 7 mm exit pupil seems washed out,  it's not about getting the most out of 50 mm binoculars.. 

 

Regarding Kenny's "washed out image", from the movie "Oh God" starring George Burns as God and John Denver as a reluctant super market manager. 

 

https://youtu.be/puXiyRw_L6g

 

Jon


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#12 Albie

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Posted 13 January 2018 - 10:39 AM

One of my first decent quality binocular was a made in japan  7x50 Celestron Ultima with the pebbled fake leather . They seemed light and well balanced in the hands and had a reasonably sharp field of view . Comfortable to use. At the time most of my viewing was from my suburban back yard so the views were a little washed out  but when you took them outside of the city the views were wonderful , lots of pinpoint stars against a black background .  I ended up returning them because of the washed out view in the yard . That was a big mistake  because I wish I still had them .



#13 Mr. Bill

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Posted 13 January 2018 - 11:58 AM

Large exit pupils (relative to pupil size) means you can move your eyes around in the field of view without blackouts, especially noticeable during daytime.


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#14 Eric.TB

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Posted 13 January 2018 - 01:37 PM

If I had a nickel for each time I have read that a 7mm exit pupil will provide an image that is "washed out" due to the sky being too bright, I  would be buying a 7X50 WX!


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#15 andycknight

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Posted 13 January 2018 - 02:11 PM

earlyriser, on 13 Jan 2018 - 12:13 PM, said:

Is the exit pupil being reduced by increasing the magnification, or reducing the aperture? You'll see more with a 7x50 than a 7x35. But a 10x50 will go deeper than the 7x50. 

This is not easy to answer. The best I can say is:

 

My 10x50's clearly show fainter stars than the 7x50's. In addition smaller objects e.g. M57 are easier to see in the 10x50's.

 

However a very large object that fills the view is often easier detected in the 7x50's, since the lower magnification puts some black sky around it.

 

I have also noticed (using both Binoculars and Telescopes) that a larger exit pupil (given the same aperture) can sometimes resolve faint diffuse nebulae better.

 

With regards to bright or dark skies - Obviously I can see far more under darker skies, but the best magnification depends on both the object and conditions (experimentation as opposed to prediction is normally the answer).

 

However this is my eye's - as they say YMMV...

 

Regards

 

Andy.



#16 Littlegreenman

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Posted 13 January 2018 - 09:54 PM

 

Is the exit pupil being reduced by increasing the magnification, or reducing the aperture? You'll see more with a 7x50 than a 7x35. But a 10x50 will go deeper than the 7x50. 

 

The question here is about whether or not a 7 mm exit pupil seems washed out,  it's not about getting the most out of 50 mm binoculars.. 

 

Regarding Kenny's "washed out image", from the movie "Oh God" starring George Burns as God and John Denver as a reluctant super market manager. 

 

https://youtu.be/puXiyRw_L6g

 

Jon

 

Thanks Jon. I gotta watch that movie again.

One of my favorite scenes, according to my memory, badly paraphrased....

Denver character: You're God? [referring to his mundane appearance]

Burns/ God. Yes. I know. [tugging his sweater] First they said I was dead. Then they said I was a cloud of gas. I didn't like that at all.


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#17 edwincjones

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Posted 14 January 2018 - 06:18 AM

Thankfully, to me a "totally washed out image" is something I've only ever witnessed whilst sitting in my car in the middle of an automatic car wash process!

 

Kenny

 

A 7mm pupil exit still works, regardless of pupil size and LP;

although many do not, I like the extra light.

 

edj


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#18 edwincjones

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Posted 14 January 2018 - 09:53 AM

If they offered large binoculars with choice of CF or IF,

price being equal, I would probably go for CF

but doubt I would pay much more.

 

edj


Edited by edwincjones, 14 January 2018 - 09:54 AM.

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#19 Eric.TB

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Posted 14 January 2018 - 11:50 AM

If they offered large binoculars with choice of CF or IF,

price being equal, I would probably go for CF

but doubt I would pay much more.

 

edj

Wrong thread I think..........



#20 Jon Isaacs

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Posted 14 January 2018 - 12:01 PM

 

If they offered large binoculars with choice of CF or IF,

price being equal, I would probably go for CF

but doubt I would pay much more.

 

edj

Wrong thread I think..........

 

 

If they're the wrong thread, IF eyepieces won't focus and the CF thumb wheel won't turn..   :)

 

Sorry but I just couldn't resist.. 

 

Jon


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#21 Jawaid I. Abbasi

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Posted 14 January 2018 - 06:33 PM

 

 

If they offered large binoculars with choice of CF or IF,

price being equal, I would probably go for CF

but doubt I would pay much more.

 

edj

Wrong thread I think..........

 

 

If they're the wrong thread, IF eyepieces won't focus and the CF thumb wheel won't turn..   smile.gif

 

Sorry but I just couldn't resist.. 

 

Jon

 

I love your sense of humor lol.gif .




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