jermng
professor emeritus
Reged: 08/29/05
Posts: 665
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Hi,
I've been thinking of getting a 15x70 for a while now and there's one on sale for a pretty good price locally so I was thinking of grabbing it ...
But as you can see, I've already got a 12x50 .... Will the 15x70 make a big difference or would it be better to save the money and go for something bigger? I mean, it's only a 3x increase in magnification although the 70mm diameter does look attractive ... =)
Would waiting for something like a 20x80 be more worthwhile?
I live in VERY light polluted skies ... and love hunting and sweeping the sky for star clusters with binos .. I use the scope for other stuff ... =)
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Jeremy Ng
Along the Equator with -
C8 OTA
C6R OTA
TMB 80/480
Orion Skyview Pro Mount w/Intelliscope Upgrade
AstroSlew I Alt-Az mount
Minolta Activa 12x50WA
Olympus 7x35 DPS
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Swedpat
Pooh-Bah
Reged: 02/18/05
Posts: 1144
Loc: Boden, Sweden, Scandinavia
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Hi Jeremy,
I am not the real expert in this matter, but I would consider the step from 12x50 to 15x70 quite close. You are going to clearly notice the improvement but it isn't tremendous. I would go for something which results in at least twice the gain of the performance. If I,m right they use to measure the performance of stargazing with multiply the magnification and aperture. According to this the 12x50 = 600 and 15x70 = 1050.
Therefore I think a step from 10x50 (500) to 15x70 (1050) or 12x50 (600) to 16/20x80 (1280/1600) is more justified. But that is my opinion.
Regards, Patric
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*2,3x40 Constellation View Wide-Bino
*Leupold Katmai 6x32
*Nikon Sporter I 8x36
*Swarovski SLCNew 7x42B
*Bresser (Lidl) 10x50
*Oberwerk 11x70
*Stellarvue SV50 spottingscope
*Meade 5000 26mm Plössl, Vixen LV 10/5mm
Psalm 19:2
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Sarah88
sage
Reged: 11/18/05
Posts: 354
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Well the 70mm will gather twice as much light as 50mm, and will have a slightly bigger exit pupil.
You won't get a big jump in the image size - but you will get a noticeable jump in image brightness, and the ability to pick out dimmer fuzzies, and more detail in the brighter ones.
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ED100, OD250L
15x70, 10x50, 7x50
54.7N 2.7W
Edited by Sarah88 (01/26/06 01:08 PM)
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SaberScorpX
Post Laureate
Reged: 01/12/05
Posts: 4224
Loc: illinois, usa
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re: I've been thinking of getting a 15x70 for a while now and there's one on sale for a pretty good price locally so I was thinking of grabbing it...
Hi Jeremy-
While the 15x70 will make a noticable difference, I would not expect a 'big' difference (especially from your very light-polluted skies).
IMO, the next 'big' step in magnification would be an 18-20x binocular.
Still, 'locally' is a word that stands out for me.
By all means, give them a try. Be sure the dealer has a decent return policy.
In either case, the 15s or 20s will also require a tripod for anything more than casual viewing.
Stephen Saber
PAC/Astronomical League
http://www.geocities.com/saberscorpx/home.html
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jermng
professor emeritus
Reged: 08/29/05
Posts: 665
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Thanks for your suggestions ... =)
I'll probably wait for a good 20x80 though the price jump seems to be pretty significant ... =)
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Jeremy Ng
Along the Equator with -
C8 OTA
C6R OTA
TMB 80/480
Orion Skyview Pro Mount w/Intelliscope Upgrade
AstroSlew I Alt-Az mount
Minolta Activa 12x50WA
Olympus 7x35 DPS
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 18806
Loc: Cumberland, R I , USA42N71.4W
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The gains due to aperture are not nearly as great as the formula mag x aperture would indicate. A far more realistic scale is magnification times the square root of aperture.
In fact, you can break it down even further.
If your primary targets are stars and clusters, then magnification has 3to 4 times the weight of aperture on the scale.
If you are observing from light poluted skies then you need to add magnification equally as you increase aperture and keep exit pupil at your optimum.
The only thing I'd caution about jumping all the way from a 12x50 to a 20x80 is the dramatic loss of filed of view. Whereas you can still get 4.25° in a 15x70, when you go up to a 20x80, there are few binoculars on the market over 3.0°.
One more comment, a mediocre 15x70 is not much of a step up at all from a very good 12x50. So take quality into consideration.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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Glassthrower
Vendor - Galactic Stone & Ironworks
Reged: 04/07/05
Posts: 17931
Loc: Oort Cloud 9
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Quote:
The only thing I'd caution about jumping all the way from a 12x50 to a 20x80 is the dramatic loss of filed of view. Whereas you can still get 4.25° in a 15x70, when you go up to a 20x80, there are few binoculars on the market over 3.0°.
A very important thing to consider. Especially if the user favors open clusters - some sprawling clusters like Alpha Persei are difficult to squeeze into a 15x70, let alone a 20x80 or 25x100 field. I have viewed through a 12x50 Barska and my own 15x70 Skymaster, I can say for certain that the difference in image scale is noticeable, albeit slight. Brightness was much more noticeable on M42, BUT, the Barska had Bk-7 prisms, so the direct comparison of brightness is not totally fair versus the Bak-4 15x70's.
I think the key thing here is, like Stephen said, the 15x70's are LOCAL and on sale. At least you'd get a good price and a chance to try them out before buying, and perhaps return for a refund later if necessary. Something to think about.
Also, the 15x70 bino is going to be somewhat heavier and bulkier.
Good luck
MikeG
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Michael Gilmer - Member of the Meteoritical Society & Collector of Falling Stars.
☄ ⒼⒶⓁⒶⒸⓉⒾⒸ ⓈⓉⓄⓃⒺ ☞ www.galactic-stone.com
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Erik D
Post Laureate
Reged: 04/28/03
Posts: 4066
Loc: Central New Jersey, USA
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Jermey,
I do not own a 15X70 binocular but I do have 10X40, 12X50, 12X60 and 20X80 binoculars(2). I see very little difference in limiting magnitude when I switch between 12X50 roof prism and 12X60 porro prism binos even though the 60mm have 44% more light collecting area.
I see a noticeable gain in brightness and star count when I switch from 12X60 to 20X80 binos. The same for 18X50 IS bino to 20X80. (from my magnitude 4.5-5 backyard)
I would guess 85%+ of observers would want to mount 15X70s. Not sure which State/Country you are located. If you are in the USA the price difference between the 3.0 lb Oberwerk 15X70 and 3.6 lb 20X80 LW is $50 USD:
http://bigbinoculars.com/compare.asp?sortby=size
You can mount either one on just about any fluid head. I believe FOV of the 20X80 LW is ~3.5 deg perhaps a bit more. The 20X80 Standard is 3.2 deg. Enough to frame most open clusters nicely.
On a dark night M44.45 and the double cluster are nice in 12X60s, Magnificent in 20X80s!
Erik D
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Mark9473
Postmaster
Reged: 07/21/05
Posts: 6459
Loc: 51°N 4°E
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I'm a big fan of the 'binocular performance index': magnification squared times diameter (OK, I know this is a simplification. But it's good enough: for 12x50 the BFI is 7,200, for 15x70 it's 15,750. So as a first approximation you'll see twice as much.
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Mark
Leica 8x20; Nikon 7x35; Vixen 8x42; Orion 15x63; Docter 15x60
WO Megrez II 80 FD / APM 107mm f/6.5 / Mewlon 210 on DM-6 + Berlebach Planet
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KennyJ
The British Flash
Reged: 04/27/03
Posts: 20139
Loc: Lancashire UK
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I think EdZ's formula of multiplying the square root of the objective diameter by the magnification produces more realistic comparisons than Mark's idea of magnification squared times diameter .
There is a HUGE difference in the comparitive results of the two different formulae .
Whilst Mark's makes it appear the 15 x 70 will show more than TWICE as much as a 12 x 50 , Ed's produces the more realistic ( to my mind , eyes and experiences ) differential , whereby the 12 x 50 is showing approximately TWO THIRDS of the 15 x 70 .
Having ( incredibly co - incidentally ) literally just spent the best part of two hours comparing the views around
M42 and M45 through 12 x 60s and 15 x 70s of roughly equal optical quality ( Oberwerk and Helios respectively ) while the experience is fresh in my mind , I would have to say that the 12 x 60 probably showed AT LEAST 75% of what the 15 x 70s did , admittedly in what would probably struggle to attain a 5 /10 on the Pickering scale , or any other scale for that matter :-)
Just MY humble impressions , of course .
To be fair , the views through BOTH were quite impressive , and might even have been ENJOYABLE , had I not been trying to concentrate more on COMPARING the various QUALITIES of what I could see , rather than simply lying back and actually ENJOYING and RELAXING .
While I'm at it , I'll give another plug for the neck monopod !
No -- it's NOT as stable as any kind of tripod / mount , or as enjoyable to smoothly pan with , but the increased concentration factor of actually feeling quite COMFORTABLE , dressed for the arctic and laying back on a recliner , beats standing and craning the neck any time for me .
And just NOT having to lift these tired old arms after a hard day's work ( even to handle the handles of the 501 head ) is PRICELESS :-)
Craig Simmons must be in seventh heaven when he's sat in his creations :-)
Regards , Kenny
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Milton Wilcox R.I.P
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Mark9473
Postmaster
Reged: 07/21/05
Posts: 6459
Loc: 51°N 4°E
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Kenny... interesting...
Using mag^2 * diameter on my 8,5x44 and 20x80 binoculars, would have a 10x difference between the two, which I always considered appropriate for how the difference "felt" to me.
Your alternative would put the difference at a factor 3. Difficult to judge... Probably my examples are too widely separated.
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Mark
Leica 8x20; Nikon 7x35; Vixen 8x42; Orion 15x63; Docter 15x60
WO Megrez II 80 FD / APM 107mm f/6.5 / Mewlon 210 on DM-6 + Berlebach Planet
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Rick
Post Laureate
Reged: 04/12/05
Posts: 3285
Loc: Tokyo, Japan
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Quote:
If you are observing from light poluted skies then you need to add magnification equally as you increase aperture and keep exit pupil at your optimum.
The only thing I'd caution about jumping all the way from a 12x50 to a 20x80 is the dramatic loss of filed of view.
I'm somewhat in agreement here in that the more important spec for me when considering buying a new bino (or even a long focal length, low power telescope eyepiece) would be FOV and how it fits into my overall astro kit. I look for a FOV 30-50% more or less than what I have now. An exception might be if the new bino brings a higher mag at about the same FOV as the current bino or is of a higher quality, both in consideration of the next important spec, exit pupil.
Exit pupil would be the next factor and in my Tokyo skies 3-4mm seems to provide the best view. If I had dark skies for most of my viewing I'd consider 5-7mm exit pupil binos optimum.
If you give priority to these factors, then mag and apperature take care of themselves.
cheers,
Rick
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 18806
Loc: Cumberland, R I , USA42N71.4W
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Quote:
Kenny... interesting...
Using mag^2 * diameter on my 8,5x44 and 20x80 binoculars, would have a 10x difference between the two, which I always considered appropriate for how the difference "felt" to me.
Your alternative would put the difference at a factor 3. Difficult to judge... Probably my examples are too widely separated.
Actually I agree it is difficult to judge, but it's not impossible to prove. I believe I have the proof which supports the Adler Index (mag x sqrt aperture). Based on the studies I've published on Binocular LM gains, the jump from 8.5x44 to 20x80 would be this.
A gain in magnification from 8.5x to 20x would increase LM by 1.1 magnitude or slightly more than 2.5x.
A gain in aperture area from 44sqrd to 80sqrd would produce a gain in LM of 0.5 magnitude or a gain of a little more than 1x.
Therefore the total gain in light gathering as measured by gain in LM is just a little over 3.5x. The Adler Index agrees almost exactly with that result.
Gains in contrast detection would probably be greater, but ten times as great? I don't think so. To get a 10x increase in LM you would need to jump up by about 2.5 magnitudes. You can't even get a jump that big by going from an 8x42 up to a 25x100.
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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jermng
professor emeritus
Reged: 08/29/05
Posts: 665
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Wow .... this is getting into a scientific discussion ... and I'm learning ALOT from it. Thanks to all! =)
I'll probably wait for a good pair of 20x80s or something larger in that range to be available locally before I get one. =)
Been getting interested in Binos lately cos of the amazing views just around the region of Saggitarius and Scorpius (mid last year).... Can't imagine what I'll see when I look through the rest of the sky! =)
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Jeremy Ng
Along the Equator with -
C8 OTA
C6R OTA
TMB 80/480
Orion Skyview Pro Mount w/Intelliscope Upgrade
AstroSlew I Alt-Az mount
Minolta Activa 12x50WA
Olympus 7x35 DPS
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DJB
Carpal Tunnel
Reged: 02/23/05
Posts: 1742
Loc: Lisle NY
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Hi Jeremy,
So many good points made by so many so good! I would simply add that you stated "VERY light polluted skys."
This would indicate to me that the 12x50 and the 20x80 exit pupils are more similar. And, yes, the FOV on the 20x80 is somewhat limited, but I think you are leaning "that way" anyway.
I would opt for the 20x80, but, then again, that's what I would do--perhaps you would not.
I suspect that you may have several extremely good nights throughout the year, as I, and this may just save the day/night for you.
Regards,
Dave.
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Mark9473
Postmaster
Reged: 07/21/05
Posts: 6459
Loc: 51°N 4°E
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Ed, your examples of light gain indeed seem to prove the Adler Index correct, BUT along with 3.5x deeper limiting magnitude, the 20x80 give 2.35x more resolution than the 8,5x44 ... and 3.5x2.35 = 8.
I know there's probably no scientific basis for what I just did, but if you tell me that my recent view of M37 under an exceptional sky (for my site), resolving somewhere between 50 and 100 stars in the 20x80s, is just 3 times 'better' than what I would have seen with the 8,5x44s, then quite frankly I'm not buying it...
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Mark
Leica 8x20; Nikon 7x35; Vixen 8x42; Orion 15x63; Docter 15x60
WO Megrez II 80 FD / APM 107mm f/6.5 / Mewlon 210 on DM-6 + Berlebach Planet
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