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Equipment Discussions >> Binoculars

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mv1612
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Reged: 08/11/09

Re: 7x35 binoculars for viewing the stars? new [Re: mv1612]
      #5561694 - 12/08/12 11:36 PM

A found some surprising comments about the Celestrons here and here

but with big quality control issues unfortunately...

Edited by mv1612 (12/09/12 05:19 AM)


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KennyJ
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Re: 7x35 binoculars for viewing the stars? new [Re: mv1612]
      #5561889 - 12/09/12 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


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David E
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Re: 7x35 binoculars for viewing the stars? new [Re: mv1612]
      #5561913 - 12/09/12 06:27 AM

Quote:

"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.


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steveyo
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Re: 7x35 binoculars for viewing the stars? new [Re: David E]
      #5561949 - 12/09/12 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.


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Tony Flanders
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Re: 7x35 binoculars for viewing the stars? new [Re: Plan9]
      #5562148 - 12/09/12 10:26 AM

Quote:

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.


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mv1612
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Reged: 08/11/09

Re: 7x35 binoculars for viewing the stars? new [Re: Tony Flanders]
      #5562195 - 12/09/12 10:56 AM

Quote:

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?


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KennyJ
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Re: 7x35 binoculars for viewing the stars? new [Re: mv1612]
      #5562219 - 12/09/12 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


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Tony Flanders
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Re: 7x35 binoculars for viewing the stars? new [Re: mv1612]
      #5562488 - 12/09/12 01:47 PM

Quote:

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.


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David E
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Re: 7x35 binoculars for viewing the stars? new [Re: David E]
      #5562620 - 12/09/12 03:08 PM Attachment (15 downloads)

Quote:

Quote:

"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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Mark9473
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Re: 7x35 binoculars for viewing the stars? new [Re: Tony Flanders]
      #5562671 - 12/09/12 03:42 PM

Quote:

Quote:

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




Are you holding magnification or aperture constant?




Neither.
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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Jay_Bird
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Re: 7x35 binoculars for viewing the stars? new [Re: Mark9473]
      #5562694 - 12/09/12 03:54 PM

Please be careful of falling into over-analysis...

You need a good-value binocular that your daughter can use:

- Yosemite have narrow close IPD, most other binos don't
- Yosemite good mix of build and optics for money (coming from people here who know more than I do)
- true field of view 6x or 8x about the same, 7.5 - 8 degrees makes finding things easy
- 6x might be easier for child to hold steady - think about this factor...

Dad, were you looking for a bino as well? You could try the 8x30 or an 8x40-42 for yourself.

I am content when camping to use 6.5x21 or 6x25 for extended observing, and see all the brighter Messier objects, great views of the moon, Pleiades Hyades Beehive Perseus or Orion are wonderful with these, Jupiter's moons, wider/brighter/colorful double stars (try Omicron Cygni next summer!) and so on. My Dad's WW2 6x42 large binos and my Uncle's old 6x25 compacts both show more lunar detail than you'd think, your daughter can spot a lot of features. Your library may have the old "Exploring the Moon through Binoculars" by Cherrington, and you can use virtual moon atlas VMA without zzoming in much to be a binocular moon map. The milestone 1st version of Binocular Astronomy by Crossen and Tirion (Craig Crossen posts here) said you could see 1/2 the 100's of described objects with 7x35; I bet very close to half can be found with 30mm.

Cabela's may have the Yosemites' for under $80 and free shipping over $99 at the moment. You could get the 6x and 8x and share, that way dad doesn't have a pair of binos that daughter can't use too...

If you live near some sporting / hunting stores, you might be able to try the Yosemites in person

Don't get too caught up in this spec or that spec vs. the overall package, or your objective...


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mv1612
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Reged: 08/11/09

Re: 7x35 binoculars for viewing the stars? new [Re: Jay_Bird]
      #5562957 - 12/09/12 06:45 PM

>> 6x might be easier for child to hold steady

You're right, never thought about that...

I live in Canada, so free shipping from US doesn't apply, unfortunately...

>> Please be careful of falling into over-analysis...

You're right, I think I have all the elements to decide. Well, almost, I still have one last question. It's about those two Leupolds and two Kowas, both reputable companies... They have identical specifications, probably exactly the same design. Could I assume that optically they are very very close, so that I would decide which one to buy based on other considerations, like whether I can try them or not before buying, or the cost of shipping and taxes to Canada... this kind of stuff ?

Thanks, Virgil.

Edited by mv1612 (12/09/12 07:54 PM)


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ronharper
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Re: 7x35 binoculars for viewing the stars? new [Re: mv1612]
      #5563118 - 12/09/12 08:54 PM

The Y eyecups do not hold adjustment well. I have not used the K, but comparative reviews say their eyecups do. No other significant difference.
Ron


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Jon Isaacs
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Re: 7x35 binoculars for viewing the stars? new [Re: Tony Flanders]
      #5563582 - 12/10/12 05:36 AM

Quote:



Tony wrote:

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.




Quote:


Mark had written:

The point is, Tony, not that 8x30 shows you more than 6x30 - which is true - but that an 8x30 has a rather small exit pupil compared to e.g. 8x40 or 8x50 binoculars.




Binocular exit pupils are always difficult to evaluate.. in terms of sharpness, one is never seeing the Airy disk so any increase in magnification for a fixed aperture will result in a "sharper view" but with the major assumption that the binocular is rock solid steady.

Jon


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FrankKD
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Re: 7x35 binoculars for viewing the stars? new [Re: Jon Isaacs]
      #5564068 - 12/10/12 12:21 PM

Since Cabelas came up I thought I would mention that they, too, have their own version of the Yosemite binocular. Not sure what the name of it is/was but they were just on sale for $50 with the regular price being around $80 for the 8x30 configuration.

http://www.cabelas.com/product/Hunting/Optics/Binoculars%7C/pc/104791680/c/10...
The only reason I know is they are on my "wish list" for the future Mrs. for Xmas.

Edited by FrankKD (12/10/12 12:35 PM)


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mv1612
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Reged: 08/11/09

Re: 7x35 binoculars for viewing the stars? new [Re: FrankKD]
      #5564365 - 12/10/12 03:19 PM

Thanks, good to know...

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faackanders2
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Re: 7x35 binoculars for viewing the stars? new [Re: mv1612]
      #5565002 - 12/10/12 10:17 PM

inexpensive, low power and light weight for kids is best.
Inexpensive, so you don't have a heart attack when they put fingers on lenses, drop, or break them. Simply replace when broken.


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mv1612
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Reged: 08/11/09

Re: 7x35 binoculars for viewing the stars? new [Re: faackanders2]
      #5567480 - 12/12/12 12:26 PM

Hello again,

I ordered today the Kowa YF 6x30 et 8x30 from B&H. At $11 shipping and $14 duties and taxes, total for the two, I think it's a good deal. It's just that the 8x30 was not in stock and I told them to ship them together, so I guess I'll have to wait a bit.

Could you tell me what to check when I get them? They are my first binoculars and I want to make sure that I'm able to detect any problems they might have.

Thanks, Virgil.


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Jay_Bird
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Re: 7x35 binoculars for viewing the stars? new [Re: mv1612]
      #5567688 - 12/12/12 02:18 PM

Congratulations!

Best of Binocular forum is one of the pinned threads here, there's useful info there.

If you haven't used binoculars a lot, practice with eye placement behind eyelens, the extending eyecups help when set right, and getting IPD just right between eyes.

Defocusing one side with the diopter adjustment allows for a quick alignment check - the sharp star seen by one eye should be centered in the blurry star seen by the other eye.


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ronharper
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Re: 7x35 binoculars for viewing the stars? new [Re: Jay_Bird]
      #5568464 - 12/12/12 11:31 PM

Sharing a binocular can drive you nuts. Also, guiding another binocular user through the sky star by star is a wonderful way to share it. Smart move getting two. I hope you'll report how ya'll like the Kowas.
Ron


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