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7x35 binoculars for viewing the stars?

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#26 mv1612

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Posted 08 December 2012 - 11:04 AM

I'm not sure I understand. Exit pupil is directly related to the perceveid brightness of the objects you observe. For example, in a telescope, if you're looking at an extended object, the 7mm EP gives you 100% surface brightness and for example a 5mm EP gives 50% and a 3mm EP gives 18% of what is possible with that particular telescope.

Then of course going with a smaller EP gives you more detail and increases the contrast because a darker background sky is achievable (we're not talking here about completely dark places). Based on this I was thinking that a 5mm EP is better than a 3.75 EP, especially for a child that would theoretically be able to achieve 7mm EP.

Let's put it this way. If I look at the Pleiades, the double cluster, or just the Milky Way, which one of these two binoculars would give me more pleasing views? And let's define pleasing: bright, sharp, spectacular, groupings of stars.

If I try Andromeda galaxy: in which one of these two will it be easier to notice something?

Or is the answer entirely subjective?

I also feel kind of guilty trying to use 30-35mm bins for astronomy, I know I'm streching things here, but it's just my situation for the moment... Thanks for understanding.

Virgil.

#27 mv1612

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Posted 08 December 2012 - 11:11 AM

Another question: in which one of these two will I be able to see fainter stars?

#28 Mark9473

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Posted 08 December 2012 - 11:21 AM

A 7x35 and 8x30, if of equal optical quality, are tied as far as limiting magnitude goes. There are a few targets, notably partially resolved open clusters, where the 8x will show a little bit better resolution. The main disadvantage of 7x in my opinion is that on the Moon you'll see noticeably less detail than at 8x.

#29 Mark9473

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Posted 08 December 2012 - 11:24 AM

If I look at the Pleiades, the double cluster, or just the Milky Way, which one of these two binoculars would give me more pleasing views? And let's define pleasing: bright, sharp, spectacular, groupings of stars.


Pleiades - tied.
Double Cluster - the 8x30 will be better.
Milky Way - the 7x35 will be better especially since it has a much wider FOV.

#30 mv1612

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Posted 08 December 2012 - 11:28 AM

Sorry for the misunderstanding: I was talking about the two Yosemites: 6x30 versus 8x30. Thanks

#31 Mark9473

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Posted 08 December 2012 - 11:40 AM

Well personally I would not get anything below 7x as it will show virtually no resolution on open clusters and far too little detail on the Moon.

#32 Binojunky

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Posted 08 December 2012 - 12:50 PM

Regarding the Yosemite, the odd bad one gets out so if buying be aware that a good return policy is needed also if like me they had to be returned to Leupold from Canada that you will be on the hook for shipping both ways, that makes an inexpensive binocular not such a great bargain, DA.

#33 Tony Flanders

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Posted 08 December 2012 - 06:08 PM

My direct personal experience is that star colours are more vivid with larger exit pupils.


Are you holding magnification or aperture constant?

In general, if you hold magnification constant, larger exit pupils always show more, because they increase the aperture. So 10x50s invariably show more of everything than 10x30s of identical optical quality.

But if you hold aperture constant, larger exit pupils decrease the magnification, and therefore show less. So 7x50s show less than 10x50s.

Star colors are generally more saturated in larger apertures. So 10x50s show more colorful stars than 10x30s. That's a function of aperture, not exit pupil.

#34 Tony Flanders

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Posted 08 December 2012 - 06:11 PM

Another question: in which one of these two will I be able to see fainter stars?


8x30s will show considerably fainter stars than 6x30s. My own 10x30s will show even fainter stars than that. By a fair margin.

For showing stars, the Bishop formula is a pretty good approximation -- multiply the aperture by the magnification. So 8x30s show roughly as many stars as 6x40s.

#35 Tony Flanders

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Posted 08 December 2012 - 06:16 PM

Let's put it this way. If I look at the Pleiades, the double cluster, or just the Milky Way, which one of these two binoculars would give me more pleasing views?

If I try Andromeda galaxy: in which one of these two will it be easier to notice something?

Or is the answer entirely subjective?


No, it's not subjective. 8x30s will show considerably more than 6x30s on each and every one of the subjects that you named. The difference will probably be biggest on the Double Cluster, because of its andundant, close-packed stars.

I also feel kind of guilty trying to use 30-35mm bins for astronomy.


You shouldn't! Many renowned observers have said that 7x35s were their very favorite instruments of all. My favorite binoculars are my image-stabilized 10x30s.

#36 SMark

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Posted 08 December 2012 - 09:05 PM

You can look at my collection below and know that I will be more often taking a 7x35 with me when I go out under the stars. I especially enjoy wide angle binoculars, and the 7x35 configuration typically has the widest angle choices. Wide angle 7x35 star field images can be quite breathtaking.

#37 David E

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Posted 08 December 2012 - 09:14 PM

I think I will still buy the 6x Yosemite. The exit pupil on the 8x is too small if it is to be used for the night sky, I think. I will take a decision as soon as possible...

Thanks for your help, it was invaluable.

Virgil.


I like my 6x Yosemite. I'm really impressed with the color accuracy. It has some whoppin' field curvature, but with some creative focusing and positioning of the brightest stars in the star field, you can get some really nice views. Having used the 6x so much I'm tempted to get and try the 8x version. No, the exit pupil will not be too small for astro-work; I use my 12x36 Canon IS binocs (3mm exit pupil) for astro use all the time.

#38 mv1612

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Posted 08 December 2012 - 10:54 PM

Thanks. Tony, I'm encouraged that the 8x30 shows fainter stars that the 6x30, probably because of a darker background. That's important for me. So I'm leaning towards the 8x30 form factor. Now, in the meantime I've found other binoculars very similar to the Leupolds:

Leupold Yosemite 6x30 8.0deg 482g $80
Leupold Yosemite 8x30 7.4 482 $95
Celestron Nature 8x30 8.2 482 $52
Kowa YF 6x30 8.0 470 $99
Kowa YF 8x30 7.5 473 $105
Vortex Raptor 6.5x32 7.8 490 $120
Vortex Raptor 8.5x32 7.4 490 $130

Why can't I put tabs between those columns? I was trying to show the field of view, weight and price.

All seem to be Bak4 (please correct me if not). Some of them could be clones of another... The Kowa seems to be identical to the Leupold... The Celestron is intriguing, only $55... Probably corners have been cut somewhere, if it's not in the optics I might be tempted. On the other hand, if the Leupolds and Kowas are significantly better than the Celestron, then I'm ready to pay their price. Nice to have alternatives. I try not to fall into "paralysis by analysis", but the reality is that I'm in no rush, it will not be a present for Christmas. Did anyone compare some of these? Thanks...

#39 Plan9

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Posted 08 December 2012 - 10:57 PM

Star colors are generally more saturated in larger apertures. So 10x50s show more colorful stars than 10x30s. That's a function of aperture, not exit pupil.


Tony,

The discussions I've seen about this here state that exit pupil determines brightness (so the same exit pupil for any aperture looks equivalent in brightness, although the limiting magnitude will go up with more aperture). Color perception is related to brightness (cone cells are less sensitive - need more flux), so wouldn't it actually be true that exit pupil determines color perception?

You are right, though, in the sense that you will see more stars in the 10x50 than the 10x30, therefore more of the stars that are colorful. :)

Bill

#40 mv1612

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Posted 08 December 2012 - 10:58 PM

"The whoppin' field curvature" of the 6x30 pushes me also towards the 8x30... Thanks David.

#41 mv1612

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Posted 08 December 2012 - 11:36 PM

A found some surprising comments about the Celestrons here and here

but with big quality control issues unfortunately...

#42 KennyJ

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Posted 09 December 2012 - 05:17 AM

Yes,not only the usual lottery Q.C issues usually associated with binoculars costing no more than around $20US to produce,but those"8x30" Celestrons turned out to be closer to 7x25 in effective specifications.

Kenny

#43 David E

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Posted 09 December 2012 - 06:27 AM

"The whoppin' field curvature" of the 6x30 pushes me also towards the 8x30... Thanks David.


I'm sure the 8x30 will have some too. I would think when you get right down to it, at this price range you won't find perfection. I also have the Vortex 8.5x32 listed in an above post. That's also a very nice pair for the money IMHO. Excellent color correction, and close focus make it great for nature viewing in the back yard. It has some field curvature, but can be focused close to the edge of the field with a sharp view. That Vortex is a roof prism design (straight barrels), and I personally prefer, for extended up in the air viewing, the comfort of the porroprism design. It's just a personal thing, I prefer holding porro's, they seem to fit my hands better. But I've used the Vortex for casual night time astronomy and they work well for their design and price range. It's design though, makes it great for close-up viewing of plants and bugs so I mostly use it for that.

#44 steveyo

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Posted 09 December 2012 - 07:39 AM

This is off the OP's original topic, but as an aside to the AFOV/FOV discussions...

I have the Leupold 8x50mm BX-1 Rogue. They were under $150, and, though I did send them back due to a bad focus knob, the optics of the pair I had were sweet, and the 8x50 FOV is gorgeous. Also, Leupold's cust svc is decent, and I'll be rcving the new pair this week.

#45 Tony Flanders

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Posted 09 December 2012 - 10:26 AM

The discussions I've seen about this here state that exit pupil determines brightness.


That is true, but only for one very specific definition of "brightness."

When you are viewing an extended light source, such as a nebula or a galaxy, the intensity of the image cast on your retina depends entirely on the exit pupil of the instrument that you're using.

However, given the same exit pupil, the image seems subjectively brighter when you use a larger aperture. So, for instance, the galaxy M33 seems considerably brighter in 15x70 binoculars than in 6x30 binoculars. That's because your brain trusts that it's seeing a faint object when many adjacent retinal cells "vote" the same way.

So even though any given retinal cell is stimulated the same viewing M33 through 6x30 and 15x70 binoculars, the overall perception is that it's much brighter through the larger instrument.

In any case, this all breaks down for point sources such as stars. There, the image is theoretically infinitely intense but infinitely small. What that means in practice is that a single retinal cell responds to all the light from a given star regardless of how much or little it's magnified.

So for seeing color in stars, what matters is not the intensity of the light but the total amount gathered, which is a function of aperture and independent of magnification.

#46 mv1612

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Posted 09 December 2012 - 10:56 AM

In any case, this all breaks down for point sources such as stars. There, the image is theoretically infinitely intense but infinitely small. What that means in practice is that a single retinal cell responds to all the light from a given star regardless of how much or little it's magnified.

So for seeing color in stars, what matters is not the intensity of the light but the total amount gathered, which is a function of aperture and independent of magnification.

So if we compare the image of stars in the 6x30 vs 8x30, then:

a) the bright stars will appear equally bright in both (same aperture)
b) I will see fainter stars in the 8x30 because of enhanced contrast with the sky.

Did I understand this correctly?

#47 KennyJ

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Posted 09 December 2012 - 11:08 AM

Enhanced contrast will help,but the higher magnification alone,regardless of aperture or exit-pupil,should enable more fainter stars to be seen.

Kenny

#48 Tony Flanders

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Posted 09 December 2012 - 01:47 PM

So if we compare the image of stars in the 6x30 vs 8x30, then:

a) the bright stars will appear equally bright in both (same aperture)
b) I will see fainter stars in the 8x30 because of enhanced contrast with the sky.


That's more or less correct. But you may well also perceive the bright stars as being brighter in the 8x30s due to the increased contrast. That's a subjective judgment that could easily vary from one person to another.

However, everyone will see fainter stars. So that's objective, not subjective.

#49 David E

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Posted 09 December 2012 - 03:08 PM

"The whoppin' field curvature" of the 6x30 pushes me also towards the 8x30... Thanks David.


I'm sure the 8x30 will have some too. I would think when you get right down to it, at this price range you won't find perfection. I also have the Vortex 8.5x32 listed in an above post.


Correction: Mine is the Spitfire, not the Raptor. The Spitfire is a roof prism design and is discontinued. :(

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#50 Mark9473

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Posted 09 December 2012 - 03:42 PM

My direct personal experience is that star colours are more vivid with larger exit pupils.


Are you holding magnification or aperture constant?


Neither. :grin:
But perhaps let me express myself differently: I found that star colours are more vivid if the sky background is brighter. And yes that also means in twilight or when the Moon is up.

Of course stars cannot be within a certain margin of the limiting magnitude, else they'd be too faint to show colour. So this is where aperture and magnification enter into the game again.






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