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Thread: 8x40 vs 7x50

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    Cool 8x40 vs 7x50



    Greetings all, I'm quite new to astronomy or atleast gave it a break for far more decades that I wish to admit to. What got me back into it was my daughter looking skyward through someones old cheapo 8x30 binoculars with oxidized lenses. This lead me to borrow a friends Olympus 8x40s, and then I purchased a pair of Nikon 8x40EX's with which I am very happy.
    I have noticed that 8x40's seem to be somewhat looked down upon for astronomy in favour of 7x50, 10x50, 9x63, or other much larger more expensive binos. When I was reading up on binos I read about exit pupil or the size of the ball of light arriving at your eye, which in the case of 7x50's is 7mm. Now being middle aged I'm informed my pupil wont dilate to more than 5mm (not that I've measured it) So from what I understand the remaining 2mm of light falls on my iris & is wasted. I also had an old pair of 10x50's when I was a teen which weighed a ton and made holding them steady difficult. So I opted for a nice light-weight pair of Nikon 8x40EX's with a nice 5mm exit pupil, and good value for money.
    So have I got one of the best kept secrets in astronomy, or am I missing something??
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    Default

    PS I forgot to mention the 8 degree field of view they have.

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    Hi Tony,
    With all science aside what really matters in binoculars is quality of optics. Also, there are two types of binoculars - in one of them focusing is done by moving eyepieces outside the bino, i other - by shifting elements inside. I've got different vision in my eyes, and find adjusting the first type the heck of a hassle. In moderately priced binos there's just too much "play" in the eyepieces.
    About aperture. 50 mm is normally brighter than 40, however heavier as well. So my answer would be - the best binoculars are the ones from a good brand (Olympus, Nikon, Canon an so on), light enough to hold them steady and comfortable to use. Said that - I've got very good Tactical binoculars (not so well known brand) those satisfy me alright. Just try and choose. My way to try is to look through them at some bright light inside the shop. If I see no color fringes and don't have to strain the eyes after adjusting the eyepieces - good enough for me.

    Clear skies,
    Michael

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    Hi again Michael, looking back at my initial question it sounds a little like an advertisement for nikon which it wasn't supposed to be, it was to highlight 8x40s as a breed. I agree that cheaper binos can have too much play and that some of the cheaper chinese binos might as well be thrown in the bin, but some are good. My main point is, could it be said that for the majority of people 8x40s could be superior to 7x50s because for most people their pupils cant open to 7mm and therefore the extra aperture & weight and cost is wasted. In the same way a person may purchase some 10x70s and be happy with them, but in reality they might as well have purchased 15x70s (both I assume would be mounted) because their eyes cant take advantage of it.

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    Quote Originally Posted by tony884 View Post
    Hi again Michael, looking back at my initial question it sounds a little like an advertisement for nikon which it wasn't supposed to be, it was to highlight 8x40s as a breed. I agree that cheaper binos can have too much play and that some of the cheaper chinese binos might as well be thrown in the bin, but some are good. My main point is, could it be said that for the majority of people 8x40s could be superior to 7x50s because for most people their pupils cant open to 7mm and therefore the extra aperture & weight and cost is wasted. In the same way a person may purchase some 10x70s and be happy with them, but in reality they might as well have purchased 15x70s (both I assume would be mounted) because their eyes cant take advantage of it.
    Hi Tony,
    On the exit pupil issue- it's not as simple as that. You're right - lights may get wasted at CURRENT moment of time. But an eye does not stay still. Nor the hand does. I'd better have some spare field to play with, than "bumping" all the time into the black edge (most important for day and dusk/dawn, of course). And mounted binos are not as versatile as hand-held ones,or a telescope.
    Clear skies,
    Michael
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    So, good, now I understand that the black area to the side will be better, that makes sense, thank you for that. I personally though haven't had any problems with bumping the black area with both 8x40s that I have tried. So, for people thinking of purchasing a pair of binos. All things considered, will the images in a pair a 7x50s be brighter than in a pair of 8x40, or will they be the same due to the extra light of the 7x50s falling on the iris not the pupil? Personally, the 1st time I pointed my friends 8x40s at the night sky I was very surprised how bright they made the sky. Also, the field of view of in both the 8x40s I tried was 8.2 degrees. 7x50s you'd think would be better but is actually worse at approx 5.5 degrees. Everything is always a compromise I know but, they're light-weight, wide field of view, bright images, good value for money. So could 8x40s be, as I suggested before one of astronomy's best kept secrets?

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    Hi Tony,
    I'm not in sales either. And as I said, the best binoculars are the ones you feel yourself comfortable with. For you it's 8X40, for me 10X42, for someone else 25X80. There's no big secret or conspiracy - it's great that everyone can choose what he needs. And if commercials push something at you, it's up to you, mate to sort it out yourself. They don't pay for your interest. Maybe now you see why my fist post started with All science aside...

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    All good mate, all good, I think what interests me a lot is that when you read peoples threads on new binocular purchases, they are quite often opting for quite expensive first choices, I guess trying to avoid making a bad first choice. I guess I just want to assure people that good cheaper choices can be made. I use my binocs probably 6 times as much as my 10'' scope

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    OK Everyone, I've managed to get hold of 3 additional pairs of binos, for a test. A pair of Nikon Action EX 7x50, A pair of Nikon Action EX 12x50, and some older Bushnell 20x50 Instafocus binos. As mentioned my binos are Nikon Action EX 8x40s. I tested them all last night. The sky last night was clear but with a slight haze. I live in Eastern Auckland Eastern suburbs, so to the north-west & west of me is the CBD (Central Business District) and industrial parts of our fair city which is the source of a large amount of light polution. To the east of me is the Pacific Ocean, and south is more rural which both allow darker skies. I think this will allow a reasonably balanced test of these binos abilities. I'm going to handhold them only, no tripods.
    I'm used to my 8x40s, so I will test them last.

    NIKON ACTION EX 7x50. First up are the Binos which I started questioning comparing my binos with, the 7x50s. It hadn't fully got dark when I first checked them out, the first thing you notice with these is their narrower field of view which at 6.4 degrees is much less than my ones. Weight wise there wasn't much difference, slightly heavier but not a big deal for looking through. Indeed the main part of the case is exactly the same as mine. Looking through them the image was nice and stable, but it seemed initially that that mine were better. Then it got dark, as in previous comments you see I've commented on exit pupil, and that for a middle aged person like me much of the light gathering ability of binos like these is wasted as it doesn't fall on the pupil but on the iris. Well forget it, the 7x50s were brighter, much brighter,the images sharper, and sharper across nearly all of the field of view. Looking toward the CBD, the ability of these Binos to suck invisible images out of the milky skies was quite impressive, Looking toward the sea it was the same, these Binos could resolve, images none of the others tested here could see. Looking toward the Southern Cross, I could just squeeze the constellation into its field of view, the jewel box just shined at you, and shined with clarity. I quickly got used to these binos, despite their narrower field of view, Hand holding them was a breeze, everything nice & stable.

    NIKON ACTION EX 12x50. Going from the 7x50s these was interesting, having been surprised with the 7's, the 12's were a bit of a disappointment , the field of view was narrower again, but with them also came shakey images, a failure to resolve images clearly whether from milky or the darker skies. I only have these binos for 1 night, it's probably me but I failed to see the point of these binos, if they had a tripod perhaps, sure they could see jupiters moons wider apart but not a clearly as the 7's. The 8x40s could resolve images better than these and frankly I felt my 8x40s binos were better. Perhaps its my expectation of binos, to me if you want higher magnification, you need a tripod, if you've got to get a tripod out you might as well get a telescope out. 12x magnification doesn't really cut it. Binoculars are for convenience, you want field of view, stable images and resolution. These 12's offered little in these respects, so wouldn't recommend them.

    BUSHNELL 20x50 INSTAFOCUS: Hmmm I'm trying to think of something positive to say about these and picture a useful purpose for them. Sure during the day they were fine, but at night they were hopeless, really hopeless. Dark shakey images, couldn't resolve images, at 20x magnification and approx 3 degrees field of view, you couldn't work out what you were seeing in the sky. Perhaps on a tripod for lunar observation, but as I've said before binos are for convenience. So, best uses, well you could use these say as a door stop, or if you're observing on a windy night with charts, a paper weight. The next problem these have is the instafocus lever, you're constantly fiddling with it trying to get it in focus. I'm sure some marketing person thought of it, trying to come up with a unique selling point, but unfortunately they failed. For daytime use with a tripod, possibly OK. For Lunar observation only, possibly OK. For general astronomical purposes these binos. are hopeless.

    NIKON ACTION EX 8x40: My Binos, looking through these after the 20x50's what a relief, nice bright stable images again. What really scores with these is their field of view, which at 8.2 degrees is the widest here, and nearly 30% wider than the 7's. This makes studying & learning constellations such a joy, you can see so much of the sky. Having looked through the 7x50's though it is obvious that the images aren't as clear across the whole field of view as much as they are with the 7's. Having said that, being able to see so much of it makes them a good choice. The 8's could resolve dim images better than all others except the 7's.

    RATINGS:
    I'm going to give marks out of ten, for these binoculars,and state whether I would recommend these them for astronomical use or not.

    Nikon 7x50 Action EX: 9/10. Recommended: Yes.
    Nikon 12x50 Action EX: 5/10. Recommended: No.
    Nikon 8x40 Action EX: 7/10. Recommended: Yes.
    Bushnell 20x50 Instafocus: 1/10. Recommended: No.

    CONCLUSION:
    I hope you notice that as the magnification goes up, the rating goes down. I also hope you look at the magnification rather than the manufacturer because I read of people who rave about Bushnell 8x42's and some others. For me 7-8x magnification seems about right, and as you read so many times, aperture wins, but remember you have to hold the darn things. For me I'm definitely going to get the 7x50's ASAP.
    These are my personal views I can only test what I have at hand, and hell what do I really know anyway! I suppose I'll get a few adverse comments, but I hope it helps someones decision making.
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    What a fascinating bit of research! The only real way to tell if a binocular is better than another is, of course, to get out there and test the things!

    The fact that for you the 7x50s be the brightest means that you are better with a 7mm exit pupil.

    So I wonder how true it is about the iris shrinking to 5mm by middle age?
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