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Possible Magnitude with 15x70?


LoopyLunar
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It partly depends on what your sky is like in the first place. I'd estimate an improvement of perhaps up to 7 magnitudes over what you can see with the naked eye.

Perhaps the easiest way to do it though is to use Stellarium or something similar to find a few stars of varying magnitudes near the zenith see which ones you can find.

James

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Mag 11 ought to be easy, mag 12 possible with a reasonably dark sky & full dark adaptation. That applies to stars - for galaxies, comets etc. the quoted mag is "integrated" (what the thing would look like if all the light was concentrated to a point) but the light is spread over a considerable area, making them much harder to see than a star of the same magnitude. For instance, the California Nebula (NGC 1499) is about mag. 4 but is really hard to see with any scope!

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You should get just under 6 magnitudes gain (for people over 35, with 5mm pupils) or 5 if you are young enough to have a 7mm pupil (fully dilated). The latter is easy to compute: the aperture has gone up by a factor of 10, so the surface area by a factor of 100, which is precisely 5 magnitudes. In the case of 5mm pupils, the difference in area is a factor of two higher, which is just under one magnitude (0.75 to be more precise) or a total magnitude gain of 5.75.

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You should get just under 6 magnitudes gain

Don't forget to allow for the light losses in the instrument ... probably of the order of 30 to 40 percent with budget bins & likely over 10 percent even in the best instruments, there is a lot of glass and many surfaces in a pair of binoculars.

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You should get just under 6 magnitudes gain (for people over 35, with 5mm pupils) or 5 if you are young enough to have a 7mm pupil (fully dilated). The latter is easy to compute: the aperture has gone up by a factor of 10, so the surface area by a factor of 100, which is precisely 5 magnitudes. In the case of 5mm pupils, the difference in area is a factor of two higher, which is just under one magnitude (0.75 to be more precise) or a total magnitude gain of 5.75.

I knew I should have done it that way. I'd just read somewhere about the increase in magnitude being something like 5 x log10( aperture area / pupil area ) though, so I did it the hard way instead :)

James

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Besides the light loss due to the complexity of the light path through binoculars (many surfaces, lenses and prisms), and accounting for the quality of those optics where the lesser can lose a substantial amount of light, also account for how adept the binocular is at resolving the object. While 70mm objective lenses may give an adaquate gain so as to transmit sufficient light to see an object of a certain magnitude, if the object is small, it may simply be obscured by the inability of the optics to resolve the object. So even if the object is theoretically bright enough to be seen, it won't be discernable if it's too small.

I evaluated the Celestron 15x70 binocular which may be very similar to the Revelation. I found the optical quality appalling but there are some useful features. I also thought that the binoculars were appropriately priced so while they dashed my hopes that aperture would "win," I found them comparable to other binocular in the same price range. My older Nikon 10x21 pocket binoculars are in the same price range. The Nikons were slightly dimmer but had a little better image quality. I tried some Canon 8x25's that outdid the 15x70's in every way except magnification (but they cost something like 5 times as much). So while the 15x70's aperture was mostly wasted through the mangling of the poor quality optics, there were some advantages to 15x over 8 or 10x, particularly on viewing the moon and planets. There are also advantages to lower magnification if it can give you a wider field of view. The Steiner 7x50 gives a wonderfully wide field of view. 15x almost requires a tripod or lying on your back or some other creative method of holding them. It's much easier to hand-hold 7x, although image stabilization is still useful even at 8x and if the binocular are heavy like the 7x50, the image may be reasonably stable, but they're still heavy. The 15x70's I tried were remarkably light for their size, only slightly heavier than higher quality 7x50's.

Another thing to note about the 15x70's is that it is quite easy to twist them out of alignment because they have almost no frame between the optical tubes. Most of the time they spring back into reasonable alignment but these are not high precision instruments. They're big and cheap.

For binocular, I suggest looking at the Pleides and examining the fainter sisters. There are nine brightest stars, two "parents" and their seven daughters. Can you see and resolve the nine? There is a map and list of magnitudes here:

http://en.wikipedia.org/wiki/Pleiades_(star_cluster)

If you can see and resolve the 10th star, Sterope II, the binocular is useful. It's magnitude 6.41 and 0.04 degrees (or 144 arc seconds) from Sterope.

If you can see that, try the Trapezium in M42. At magnitude 4, it's quite easy to see, but it's only 47 seconds of arc across. I can see four of its stars at 20x, it would be a challenge to pick them apart at 15x (I don't have anything 15x at the moment).

If you can report that you see M1 clearly in the bins, I might want to buy them from you. It's magnitude 8.4 and about 6x4 arc minutes across. Honestly, if you can see that, go for M109 in the dipper. At 10.6, you should be able to see it if you believe "the numbers."

Don't be frustrated by what the 15x70's can't do, whether it's seeing a faint smudge like M1 or picking apart a tiny speck. There's no point in it other than fun. Enjoy the big bins for what they easily do, rather than be frustraed for what they can barely do.

Edited by BenM
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As an optical astronomer by training, I must qualify BenM's remarks somewhat. The 15x70 binoculars are what we consider flux-buckets: large-aperture, low magnification optical systems suitable for rapid surveying of large areas of the sky, without the need for high resolution. At an exit pupil of 4.4 mm they are never going to produce the full resolving power of a 70 mm achromat. So long as the point-spread-function of the optics falls within one cluster of rods on the retina, no light loss is incurred.

I have observed the Pleiades (in which I was able to see 11 stars at least with the naked eye as a youngster) with my parents' Olympus 10x50 binoculars, and sketched masses of stars in the cluster. My Omegon 15x70 show more. In fact, the view is much more similar to that obtained with a 70 mm f/10 achromat at school.

Of course the image quality of the APM 80 mm APO is better, and can see deeper into space, but simply in terms of light grasp the 15x70 completely thrash good quality 10x50 binoculars. Last summer I compared the two side by side, and several deep-sky objects clearly visible in the 15x70 binoculars were invisible in the 10x50.

The Celestron/Revelation/Omegon 15x70 are not top of the line optical systems, and there are occasional dud ones, but calling them appalling is well beyond the mark.

Edited by michael.h.f.wilkinson
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I have a pair of Helios Apollo 15x70s which I bought effectively as my travel scope and also for a quick peek at home. I use them with a heavy duty Manfrotto monopod (this has small tripod legs for optional use which are excellent) along with a Triton pistol grip ball joint head. This system is compact, quick to set up and really good optically. That said, it costs around £450 new to buy so you'd expect that it would be. These binoculars literally create a different sky compared with the 10x50 Pentaxs I had previously. Whilst the Pentax were good, the 15s create a completely different impact and everything looks bigger and better.

I have not used the Revelation / Celestron ones but a lot of experienced people that use good quality scopes and optics suggest they are pretty good and for the money excellent. I think the point here is that the quality control is variable and it seems that only by buying through a supplier who checks them before dispatch and through a courier that cares will you get a decent pair.

BUT all that said, the original question was about magnitudes and not a specific pair of bins. As brianb points out the key is to appreciate what magnitude means for each object. Personally, I wouldn't look at it in this way but see what objects you are likely to be able to observe with your bins.

There are some showpiece objects that just look better in 15s than a scope. M44 and 45 spring to mind as do the Sword and the Belt of Orion which idividually fit wonderfully into the field of a pair of 15s.

There are several binocular lists of objects too, just google 'binocular observing list' and there are loads of options. I can almost guarantee you won't get bored. A dark sky will definitely help and then try and find the same things at home once you know where they are (assuming of course that you don't live at a dark site). With Comet Hartley last year, I had no chance of seeing this from my home site until I found it easily at a dark site (it was bordering on naked eye there once you knew where it was). Back home I thin looked again and just found it in my light polluted skies.

Edited by Moonshane
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...

The Celestron/Revelation/Omegon 15x70 are not top of the line optical systems, and there are occasional dud ones, but calling them appalling is well beyond the mark.

I completely agree with everything you said about 15x70 binoculars with regard to the plain optical physics and in comparison to 70mm acrhomats etc.

The Celestron 15x70 was selling for $48 (that's 30 GBP) in December through Amazon.com. This is the binocular I evaluated. It may not be the same as Revelation or Omegnon, but it was appalling. I compared it to my Nikon 10x21's and all I could say was it was a little brighter and had higher magnification. Around the same time I was using Steiner 7x50 Commander XP's, and on a subject like the Pleides, there was no comparison whatsover unless you put some well-used vinyl safety goggles over the Steiners. Maybe it's down to sample variation, but a lot of people that buy these, they might have a budget under 60 quid and haven't tried anything good before and how could they tell?

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I completely agree with everything you said about 15x70 binoculars with regard to the plain optical physics and in comparison to 70mm acrhomats etc.

The Celestron 15x70 was selling for $48 (that's 30 GBP) in December through Amazon.com. This is the binocular I evaluated. It may not be the same as Revelation or Omegnon, but it was appalling. I compared it to my Nikon 10x21's and all I could say was it was a little brighter and had higher magnification. Around the same time I was using Steiner 7x50 Commander XP's, and on a subject like the Pleides, there was no comparison whatsover unless you put some well-used vinyl safety goggles over the Steiners. Maybe it's down to sample variation, but a lot of people that buy these, they might have a budget under 60 quid and haven't tried anything good before and how could they tell?

You may well have had a dud one. I first got a Celestron Skymaster 15x70, and it was completely mis-collimated. The shop was out of this type so they offered the Omegon as a replacement. This was a great deal better. I think corners are cut in quality control.

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Hi Michael

I bet your really happy with the replacements, My friend has a pair of Omeron and I liked them very much

Doug

Essex

Actually, the Omegon is the exact duplicate of the Revelation, as far as I can see, and both are near Celestron clones (only the rubber on the prism housing differs slightly). The second set did have a very slight misalignment issue, which was solved (accidentally) as I related here. They are now fine, except that I never really get used to central focusing.

I do frequently compare the 16x70 finder and 15x70 bins on the same object, and the finder (built from a cheap little F/5 achromat) definitely is sharper and (very slightly) brighter. There is certainly room for improvement.

I am looking at a replacement APM 15x70, which has individual focusing, and is filled with dry nitrogen to prevent internal fogging. However, these are four times the price of the Omegon, so the latter are very good value for money.

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