20x80, 25x70 or 15x70?

[Xenoyia]

Hi, my mother is into astronomy and for Christmas I've been thinking about getting her some binoculars for stargazing purposes.

All 3 of the listed (20x80, 25x70, 15x70 celestron skymasters) are within my budget and we do have a tripod, but being able to use them without a tripod would be ideal.

What kind of things would she be able to see with each of them and overall, which one do you think is the best?

[baggywrinkle]

How old is your mother? The ones you list are good sized bins but even on a tripod getting to see objects at higher declinations can be back breaking. Plus it would have to be a very steady tripod to prevent wobble.

They would be hard to hand hold.

Think along the lines that the 20x80 are the near equivalent to an ED80 refractor.

Better off going for a lighter pair with a good field of view, say 10x40, they are lighter and can be hand held while lying back in a comortable camping chair.

[rowan46]

get her some 10x50 or 8x42 i am pretty sure that she will struggle hand held on all the 3 you mentioned and personally I find extended astro viewing through binoculars on a tripod uncomfortable. those with 45 degree or 90 degree eyepieces are pretty comfortable but they are a fair way out of your budget.

[Xenoyia]

She is not weak. She can lift 5lbs for a long time so that isn't an issue.

We already have a pair of 10x50, and I'm just looking to upgrade that.

[rowan46]

As to what you can see with binoculars look at binocular sky's website. a fair few of the brighter larger meesiers are possible jupiters moons can be seen (no detail though) the moon is nice and cruising though the milky way is very enjoyable with binoculars

[rowan46]

She is not weak. She can lift 5lbs for a long time so that isn't an issue.

We already have a pair of 10x50, and I'm just looking to upgrade that.

i forgot to say welcome but I don't think we meant to say that she was weak its just that with the increased magnification and decreased field of view the natural jitters that we all have are very much amplified.

[BinocularSky]

She is not weak. She can lift 5lbs for a long time so that isn't an issue.

It's not a case of being able to lift, but of being able to hold steadily. Try this experiment: Albireo is a nice easy object when it gets dark at this time of year. See if she can split it (i.e. detect that it is a double star) and see markedly differently coloured components with your 10x50. If she can do this easily, she has half a chance of being able to hand-hold a 15x70 usefully steadily very briefly. If she can't, you really ought to be considering upgrading your 10x50 to something lighter and of better optical quality, and probably slightly less magnification.

[Charic]

Hello.........

How old is your Mother ? again its not a chat up line! I`m interested because as a Younger person, eyes dilate at night (the black pupils widen) to let in the lower light levels in order to see. As we get older, pupil size can get slightly smaller. Is it possible to measure your Mothers pupils at night time, whilst your out next time observing. If you can measure the width, it can help in your next choice of Binoculars?

All Binoculars if held aloft at arms length, looking at the sky/daylight, you will see a small circle of light exiting the eyepiece. That light is known as the Exit Pupil Size. If for example your Mothers eyes measure 5mm dilation at night, then a pair of 7x50 binoculars would give an exit pupil size of 50/7= 7.14mm of light `width` which exceeds the width of your Mothers eyes of 5mm, therefore wasting the light gathering power of the binoculars. Your 25x70 would give an exit pupil size of only 2.8mm. too little light maybe. By trying to match the exit pupil size of the ocular to the eye, you will get better light transmission into the eye, which gives as bright an image, that is possible with the optics in use. In the past I used to have some Helios `Stellar` 20x80. They were heavy, could have been better with a support of some kind (I used a wall?) but they only had an exit pupil size of 4mm and being of high magnification, reduces the field of view, So high maginication magnifies hand-shake, reduces the field of view, so you only see one star at a time instead of the whole constallation, and a darker view?

So my advice is to measure the eyes, purchase something that has an exit pupil of similar dimensions (like for like offers the best transfer of light) for brighter viewing, and a decent field of view. The rest comes down to price.

Dividing the objective lens by the magnification produces the exit pupil size, so a pair of 10x50 has 50/10=5mm of exit pupil or in my case 7x50 have 50/7=7.14mm of exit pupil (brighter /wider view than the 10x50 for me.

I can see the blurr of the Andromeda M31 Galaxy with my 7x50` (if i use Averted vision, a technique for viewing faint objects, not by looking directly at the object, but looking a little off to the side, while continuing to concentrate on that object, things can appear sharper!) it does for me.I dont see M31 with naked eye. Also the wide view is just great for sitting back in the recliner and scanning the skies. Amazing how many satelites can be seen with binoculars, which are invisible to the naked eye., and the Milky way is just awash with stars.

Hope this helps with your decision making. take care.

[BinocularSky]

So my advice is to measure the eyes, purchase something that has an exit pupil of similar dimensions (like for like offers the best transfer of light)

That is theoretically correct, but does not take into account:

* Sky brightness: this is reduced by increasing magnification, thereby increasing the contrast and, hence, visibility of point objects.

* Increased magnification makes more objects visible.

* If the exit pupil is an exact match to the eye's pupil, eye placement becomes critical; a smaller exit pupil relaxes this a bit.

My pupils open to just over 6mm; none of my astronomical binoculars has an exit pupil of greater than 4.7mm.

Dividing the objective lens by the magnification produces the exit pupil size, so a pair of 10x50 has 50/10=5mm of exit pupil or in my case 7x50 have 50/7=7.14mm of exit pupil

Again, theoretically correct, but is confounded by the manufacturers of budget binoculars. Have you actually measured the exit pupil of yours? The design may have changed, but it used to be a mere 6mm -- this is because, in order to reduce aberrations, the binocular wass stopped down internally, giving it an effective aperture of 42mm.

IMHO there are maybe half a dozen objects that I sometimes find easier in a 7x50 than in a 10x50; the increased contrast and magnification win almost every time. Again IMHO, the only astronomical reason to prefer 7x to 10x is if you cannot hold 10x sufficiently steadily. I also think it makes sense, if you are going to 7x or 8x, to also go down to 40 or 42mm aperture so as to benefit from the reduced weight.

(As an aside, there used to be a fashion for 7x50 for astronomy. This was due in part to 7x50 being favoured as a low-light binocular in most navies. A large part of the reason is that, on the heaving bridge of a ship, a 7x50 is a heck of a lot easier to use than a 10x50. But the "7x50 is better" passed into mythology and the rest, as they say, is history...)

[Charic]

BinocularSky....constructive criticism? I dont profess to being the authority on the subject. Forums are for gleaning other users, hands-on experience.

Technical issues you`ll find on the Internet or from the manufacturers.

Pupil size is not fixed throughout your observing session, but you still need to get as much light as possible into the eyes, and matching the optics to your eye is still the way forward.

The `Visual Instruments` title at http://en.wikipedia.org/wiki/Exit_pupil for example, says exactly what I was trying to say, only in more detail. I didnt give wrong or misguided information!

Ive also physically re-measured my (old)Bresser Hunter 7x50, and no, they havent changed in any way, their still exactly 7mm as stated.

Xenoyia..... sorry for this in your post. If my advice is criticised in any way, right or wrong, i`ll respond and correct if necessary. But this is my view from experience, which is what your looking for. The text could have been added as a note, rather than pull me up? After all, were only trying to help you make a decision for yourself, we shouldnt be criticising.

BinocularSky.... If I have the wrong end of the stick then resolved, but thats how I read the reply!

take care.

[Viewmaster]

...................................Make her a 4 inch f4 with 25mm eyepiece, which I have just made, and she can sit in the garden and see the all wonders above in comfort. Here's a picky of my Astronomer Royal with mine.

[BinocularSky]

Forums are for gleaning other users, hands-on experience.

Technical issues you`ll find on the Internet or from the manufacturers.

Umm -- I think you'll find that quite a few technical issues are discussed in these forums (which, incidentally, are part of the internet .)

Ive also physically re-measured my (old)Bresser Hunter 7x50, and no, they havent changed in any way, their still exactly 7mm as stated.

Interesting. Would you be willing to share your method of measurement?

As my opinions (for that is all they are) on the relative merits of 10x50, 7x50 and 8x40 appear to be unwelcome in some quarters, perhaps those expressed by binocular experts like Ed Zarenski, Bill Cook and others here and here may be of interest. Also a good paper on limiting mag in binoculars here (the 12x50 and 10x50 data can at least be qualitatively extrapolated to 7x50).

Nice! Reminiscent of:

(clicky, in case you want more info...)

[Mr Spock]

I'd go with the 15x70. The 25x is too high a magnification to hold steady and the 80mm's are bigger than you think.

[michael.h.f.wilkinson]

Of the three mentioned, 15x70 is easiest to use. Note that the cheap ones are often badly collimated out of the box, and many are closer to 63-64mm. My more expensive Helios 15x70 clearly outperform the cheaper Omegon and TS ones I have used. A better pair of 10x50s might be a good alternative in terms of ease of use. The 80mm ones are much bulkier and heavier, with the notable exception of the Vixen Arc (also sold as Opticron) 20x80 (or 16x80). The Vixen 20x80 I had a look through during my summer vacation was slightly lighter than my 15x70, and yet solid as a rock. These Vixen bins are not cheap at all, however!

[Viewmaster]

Thanks Steve for that clicky link which lead me to your site.

A very good read there.

[Tinker1947]

Its not the magnification but light gathering power, whats the point in magnifying something you can see.......20 X 80 would be my buy, i generally use 8 X 42 though.....

[Charic]

I know this is a very old thread,  that someone has just revived, but reading back on the comments I made to Stephen Tonkin  (Binocular Sky) I'm quite shocked to be honest,  that I misinterpreted, misread  and replied the way I did?

I was not being criticised or pulled up in in anyway whatsoever!  why I believed I was, I don't know?

Too late to adjust or edit now, so better late than never,

@Stephen Tonkin    Sorry.

[BinocularSky]

Charic, long since forgotten, and I also don't find it in any way strange that the rest of humanity doesn't share all (or even any) of my opinions. (But thanks anyway...  )