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What makes a particular Bino good for astronomy?

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#1 jself24

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Posted 13 December 2010 - 12:37 PM

I notice some manufactures will list models that they recommend for Astronomy use. What makes one pair suitable for astronomy while the next one with similar specs is not?

I'm looking for a decent pair of all around binos - probably 50/50 daytime and Astronomy use. I'm thinking of this pair but they are not noted as being good for astronomy:

http://www.opticspla...lars-d5085.html

I want them to be 100% handheld. I'm afraid to go to 10x as I don't have the steadiest of hands. I used a pair of Vortex Viper 8x42s and was blown away. They are quite a bit more expensive than the diamondbacks and they are listed as recommended for Astronomy. I'm just not sure what the difference would be related to Astronomy. Wouldn't the 50mm obj actually be better?

#2 KennyJ

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Posted 13 December 2010 - 12:49 PM

Hi John ,

There are long - standing traditional opinions that large aperture and large exit pupils are preferable for astronomy .

For hand - held binoculars , I think you can safely relegate those two features to fourth and third places respectively , in favour of hand - holdability with respect to magnification and sheer size .

In other words , if you find 8x a magnification significantly easier to hold steady than 10x , then a 8 x 42 should work just fine , without giving up too much compared to a 8 x 50 .

8 x 42 is also an excellent " all - round " combination , particularly with centre - focus , as opposed to individual focus arrangement , which is admittedly a very rare feature anyway with 8 x 42s .

Kenny

#3 Roadbike

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Posted 13 December 2010 - 01:14 PM

Hi. An 8x40 or 8x42 binocular will give very nice views in both situations. Because you will be using them half the time night sky viewing I would suggest that you also look at porro prism binoculars. You might find the porro prisms deliver more sharply focused objects in the night sky. Vixen makes some interesting models and Nikon has some in their moderately priced Extreme series.

#4 BillC

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Posted 13 December 2010 - 01:27 PM

Aperture and quality.

Bill

#5 pcad

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Posted 13 December 2010 - 02:12 PM

An exit pupil between 4mm and 7mm depending on you and the conditions you observe in.

Good quality as BillC says. Good optics to get pinpoint stars and good collimation to prevent double vision.

Using binoculars for astronomy will make these quality issues much more obvious than using them for terrestrial viewing.

Tremors will also be much more noticable at night. Even with 7x you'll see more with a monopod or tripod. That's why the stabilised binoculars are so popular for astronomy.

With roof prisms there may be a little spiking that wouldn't be there with Porro prisms. If the roof's are good quality you may not notice a difference.

#6 Obx

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Posted 14 December 2010 - 04:33 PM

All else being equal, I find 8x40 (or 8x42) to be the best all-around binocular.

#7 Andresin150

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Posted 14 December 2010 - 04:38 PM

In my humble experience, assuming good optics, I found anything near 2º to 3º TFOV frame my subjects of interest the best way.

#8 Andresin150

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Posted 14 December 2010 - 04:39 PM

and also and AFOV of 60º or more is preferable.

#9 hallelujah

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Posted 14 December 2010 - 04:53 PM

http://www.cloudynig...sb=5&o=all&vc=1

http://www.cloudynig...sb/5/o/all/vc/1

#10 charen

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Posted 14 December 2010 - 05:37 PM

As with most things in life a good guide is cost. There are exceptions but it is a good rule. The majority of entry level binos just don’t make good astro binoculars. My most used two hand held binos are 1/ Bushnell Elite 8x43 - lightweight, Japanese made, now discontinued and 2/ Minox BD 10x58 ED. Solid build but truly excellent optics esp. for astro use. Also sadly discontinued.
With roofs they do have to be of a high optical quality to avoid spiking.
The water proof 8x and 10x 40mm and 50 mm series from Pentax and Nikon are solid performing affordable porro prism binoculars as others have said.
The old saying 'don’t look through a binocular you can’t afford' is very true.


Chris

#11 F.Meiresonne

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Posted 14 December 2010 - 06:00 PM

To me brightness, contrast ,and a sharp wide field together with appropriate eyerelief for the ease of viewing.
These are 4 important criteria IMHO wich makes a good astro bino

#12 EdZ

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Posted 14 December 2010 - 06:41 PM

What makes a particular Bino good for astronomy?



A respectable amount of aperture. Astronomy includes many faint objects and you should optimize the use of aperture to see those objects. Daytime viewing is far different in that maximum powers of 7x, 8x or sometimes 10x, coupled with daylight constricted eye pupils, result in maximum usable apertures of perhaps no more than 40mm. That's a bare minimum for astronomy. For serious binocular astonomy 50mm to 70mm is vastly more useful. For serious deep sky observing 80mm is not uncommon.

Sufficient power to actually see the objects you are looking for. Perhaps all you ever want to do is scan the sky at low power. Then for you that good astonomy binocular could be 8x. But there are many objects that are not seen reasonably at 8x. It could be 10x or 12x for many open clusters and some larger galaxies. Once you turn your gaze to fainter galaxies, planetary nebula small distant clusters and closer double stars a good astronomy binocular could be 15x or 20x or more.

Flat field. A field flattener corrects the binocular image by removing curvature. That is extremely beneficial for astronomy. The goal is to see as much of the field of view sharply defined or having pinpoint stars as much across the field of view as possible. While there are still other aberrations that may be present, the biggest offender as you move further away from the center of the view is curvature. A well designed field flattener takes that problem away.

Good optics, or minimum of all the remaining aberrations. Until you've seen thru binoculars that truly show pinpoint stars, you won't know what excellent image quality is. Astronomy is not forgiving at all to optics with aberrations. Cheap optics often suffer from curvature (see field flattener) spherical aberration and astigmatism. Both these other aberrations give you that feeling that you just can't ever get to best focus and they can destroy that pinpoint image quality.

High contrast. Another of the most important aspects of good optics can only be experienced. There's a number of things that can be going on in cheap optics that destroy contrast by either allowing light to bounce around inside or by scattering light or by the inability to concentrate light to its smallest spot. Poorly coated optics, shiny internal surfaces and poorly baffled insides, poorly polished lenses, poorly corrected chromatic aberration and poor correction for spherical aberration and astigmatism all destroy contrast. Once you see real good contrast in a higher quality optic, you'll know it. That's a good astronomy binocular. Generally you don't find good contrast in an optic that failed to properly address the other issues above.

A field of view that matches your style of viewing. If you are that sky scanner above, maybe you need 7° or 8°. But your power choice is going to have a deciding factor on the size of your field of view. In general, a good 60-65° Afov will provide you everything you need. That's 6.5° at 10x, 5°+ at 12x, 3°+ at 20x. There are exceptions, in that design limitations limit some binoculars.

Your choice of exclusive hand holding or desire to tripod mount can limit your size choices above. If you choose to mount, then all options are open. If you desire handheld, then a 10x limit is recommended. Sure 12x is doable and some people will say they can hold 15x or even 20x. But they are not what I would consider "good" for handheld astronomy.

The binocular needs to "fit" the user. If you don't like the way the eyepieces fit your face, or it's too heavy, or it doesn't have enough diopter adjustment for your extreme perscription, or you wear glasses and it doesn't have enough eye relief, or any number of things, you are not going to be happy with that binocular. A good astronomy binocular fits you like a good pair of shoes.

Along the same lines as "fit", know your personal optics, your eyes. If you have eyes that do not dilate to greater than 5mm, then don't buy a 10x70 binocular with a 7mm exit pupil. That is not a good astronomy binocular for you.

All that, wrapped up in a good quality mechanical housing that will give you years of service with no worrys.

edz

#13 AV in CMH

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Posted 14 December 2010 - 09:37 PM

Great reply Edz.

Your post would be a great addition to the best of series.

#14 Zdee

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Posted 15 December 2010 - 05:06 AM

Great reply Edz.

Your post would be a great addition to the best of series.


I'll second that.

#15 Andresin150

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Posted 15 December 2010 - 10:34 AM

Now, that summarizes all! :waytogo:

#16 Wes James

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Posted 15 December 2010 - 01:35 PM

Wow, I have to agree, EdZ- yours was a superb reply... and I agree, should not get lost in the pages of the forum. Should be preserved.

#17 RichD

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Posted 15 December 2010 - 01:48 PM

Ditto!

#18 EdZ

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Posted 15 December 2010 - 02:50 PM

this thread linked to
Best Of Binoculars - First Binocular Purchase? Questions?

best place i could think of.
edz

#19 hallelujah

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Posted 15 December 2010 - 04:12 PM

this thread linked to
Best Of Binoculars - First Binocular Purchase? Questions?

best place i could think of.
edz


It's included in the second link that I posted above. :waytogo:






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