Thread: Newbie: Suggestions for first binoculars?

Originally Posted by Cordite

Repeated, sustained observation requires comfortable binoculars.

Comfortable binoculars have a bright image, not too much perceptible shake, and are not too heavy.

Higher magnification like 10x requires thicker, heavier glass for their lenses to bend light that much, which steals some light. They have a smaller exit pupil which can punish at dusk, when our own pupils may dilate to 5+mm (young eyes 7-8mm!) but the 10x42s will only feed them with a cone of light of 4.2mm. And they have perceptible shake due to the magnification which makes prolonged (handheld) observation a strain.

Don't go above 8x magnification for a combination of all the above reasons.

This puts me squarely in the cheapskate category of course, but the considerations above are basic physics so can't be gotten around by manufacturing a 10x42 to a higher spec. The glass will still be thicker to gain that magnification, the magnification will still cause image shake, and its exit pupil (EP) will remain limited to 4.2mm.

A little table to show you I can do division on a calculator, though the easy ones I did in my head:

10 x 50 EP 5.0mm
10 x 42 EP 4.2mm
8 x 50 EP 6.25mm
8 x 42 EP 5.25 mm
7 x 50 EP 7.14mm
7 x 40 EP 5.7mm
7 x 35 EP 5.0mm
6 x 30 EP 5.0mm

Disclaimer: the best binoculars are the ones you have on your person when you need them, someone else on this forum said that.

Now to turn your argument on its head.

The light that enters the lens is determined by the objective lens size and the losses are pretty much the same for an 8x or 10x magnification, the difference in lens thickness is very little. So the exit pupil might be smaller, but it will be of higher intensity, so the amount of light getting through is the same. Now if your 8x42's have an exit pupil of 5.25 and your eyes at night have a 5mm pupil then you will get losses going into your eyes of at least 1- (5²/5.25²) = 9.3% and more if your line of sight is out by more than 0.125mm from the centre. With 10x42's with a exit pupil of 4.2mm your eye need to be more than 0.4mm from the centre of the exit pupil any light is lost.

Physics!

Originally Posted by gadgetman

Now to turn your argument on its head.

The light that enters the lens is determined by the objective lens size and the losses are pretty much the same for an 8x or 10x magnification, the difference in lens thickness is very little. So the exit pupil might be smaller, but it will be of higher intensity, so the amount of light getting through is the same. Now if your 8x42's have an exit pupil of 5.25 and your eyes at night have a 5mm pupil then you will get losses going into your eyes of at least 1- (5²/5.25²) = 9.3% and more if your line of sight is out by more than 0.125mm from the centre. With 10x42's with a exit pupil of 4.2mm your eye need to be more than 0.4mm from the centre of the exit pupil any light is lost. Physics!

Physics indeed.

In daylight you CAN use say a ridiculously magnifying binocular or monocular of say 25x30, as even with an exit pupil of 30/25 = 1.2mm you will get enough light to see clearly. But what a strain to find that small keyhole of light! Not for prolonged glassing, but fine for just checking something out.

Similarly a pair of 7x50s are comfy to use on the bridge of a ship (no lugging them over hills!) even for a middle aged man with a max pupil diameter of ~5mm. He cannot utilise the 7x50's large exit pupil of 7.14mm, it's just that he can just lift them to his eyes and look without manoeuvring into precise eye alignment. Thus a pair of binos with larger-than-required exit pupils are an advantage not just in very low light, but throughout the day.

Lightness, large exit pupil and wide field of view wins the day every time, but they just don't not go with higher magnification. Can't get both in the same package. Impossible physics in one package.

The solution of carrying some light 7x35s and then using your 3-15x rifle scope for checking out an occasional very distant object works as far as the physics are concerned, with no weight penalty. But it will grate some to use a gun mounted optic for other than aiming though, for obvious reasons of potentially pointing their rifle in the direction of some unwitting passer by, even if unloaded and at a far distance. One might say it dilutes the principle of always pointing a gun in a safe direction. Also, the idea does not work if your rifle scope is a fixed 4x or similar.

The other way to approach it is to use Galilean optics for checking far distant objects. So, say carry a 7x35 bino, and for the occasional far spotting have an extendable type telescope, say 15x or 25x. They're light, compact and reach much further out than any 10x42 or 12x50. But with a narrow FOV they are mainly useful for checking out a specific object, and must be supported as they are usually light weight.

I'd not really go as far as the very heroic monocular (or the Mills bombs) in the kit here ...but the idea is the same: (-:

Originally Posted by Cordite

Physics indeed.

In daylight you CAN use say a ridiculously magnifying binocular or monocular of say 25x30, as even with an exit pupil of 30/25 = 1.2mm you will get enough light to see clearly. But what a strain to find that small keyhole of light! Not for prolonged glassing, but fine for just checking something out.

Similarly a pair of 7x50s are comfy to use on the bridge of a ship (no lugging them over hills!) even for a middle aged man with a max pupil diameter of ~5mm. He cannot utilise the 7x50's large exit pupil of 7.14mm, it's just that he can just lift them to his eyes and look without manoeuvring into precise eye alignment. Thus a pair of binos with larger-than-required exit pupils are an advantage not just in very low light, but throughout the day.

Lightness, large exit pupil and wide field of view wins the day every time, but they just don't not go with higher magnification. Can't get both in the same package. Impossible physics in one package.

The solution of carrying some light 7x35s and then using your 3-15x rifle scope for checking out an occasional very distant object works as far as the physics are concerned, with no weight penalty. But it will grate some to use a gun mounted optic for other than aiming though, for obvious reasons of potentially pointing their rifle in the direction of some unwitting passer by, even if unloaded and at a far distance. One might say it dilutes the principle of always pointing a gun in a safe direction. Also, the idea does not work if your rifle scope is a fixed 4x or similar.

The other way to approach it is to use Galilean optics for checking far distant objects. So, say carry a 7x35 bino, and for the occasional far spotting have an extendable type telescope, say 15x or 25x. They're light, compact and reach much further out than any 10x42 or 12x50. But with a narrow FOV they are mainly useful for checking out a specific object, and must be supported as they are usually light weight.

I'd not really go as far as the very heroic monocular (or the Mills bombs) in the kit here ...but the idea is the same: (-:

Attachment 103182

I have steady hands and have no issues with using 10x binos, but with the 8-20x50 I had at the Toby shoot I mount them in a tripod if the magnification is wound up. I have not had much experience 'glassing' so far, but have had bino's for many years. I compromised and bought a budget pair of 9x36 hunting binos.