I'd like an "f" please Bob.....

[Flying Eye]

Is it me, or are we short of focal length number for binoculars?

How would we get this info for other calculations we might wish to make?

[BinocularSky]

As a rule of thumb, the objectives are usually around f/4.5 to f/5. There are larger f-ratios, but these tend to be in the very specialist stuff (the Takahashi Astronomer and Miyauchi Saturn lurch to mind).

[Flying Eye]

Thanks Steve, since I'm going to try using a-focal web cams on the non dioptre side, I was just wondering if they might go a bit deeper sky (with stacking) than the eye can easily detect!

I know I'm being cheeky going after that, but sometimes you just have to try things, well, I find I do!

From what I have been reading, I think longer would have been nicer but there may be almost enough in there for a surprise or two.

[Merlin66]

I use binocular lenses as cheap collimator lens in spectroscopes. The 50mm aperture lenses are usually 180mm focal length.

[BinocularSky]

The 50mm aperture lenses are usually 180mm focal length.

Sheesh! That's only a tad over f/3.5 -- no eyepieces work well at that short an f-ratio -- no wonder the budget ones are stopped down (by internal gubbins) to an effective aperture of around 42mm!

[Flying Eye]

I use binocular lenses as cheap collimator lens in spectroscopes. The 50mm aperture lenses are usually 180mm focal length.

Thanks for that, filed it for later, as I'm sure it could come in handy not too far down the road!

[Flying Eye]

Sheesh! That's only a tad over f/3.5 -- no eyepieces work well at that short an f-ratio -- no wonder the budget ones are stopped down (by internal gubbins) to an effective aperture of around 42mm!

Interesting,

That begs the question as to whether 42 mm is a good/practical upper size for binoc' purchase consideration? Unless they stop those down even further and we are also avoiding lens edges that may no be quite as wonderful as the rest of the glass?

[Merlin66]

Hmmmm

This thread made me think....

If the bino's are usually around f4 and the one's I've pulled apart seem to only use Kellner type eyepieces.....

1. Why is their performance so acceptable????

2. Why are not more Kellners used as low power eyepieces on f4+ telescopes

Interesting.....

[Flying Eye]

Hmmmm

This thread made me think....

If the bino's are usually around f4 and the one's I've pulled apart seem to only use Kellner type eyepieces.....

1. Why is their performance so acceptable????

2. Why are not more Kellners used as low power eyepieces on f4+ telescopes

Interesting.....

Yes, quite, and right now, I have an MS Cinema webcam lashed to my cheap and cheerful Bresser compact binos, a-focal, and very rough and ready it all is too, as I'm just tinkering to see what happens next.

Thing is, that is appearing to largely outperform a Fuji 9600s with a raynox 2020Pro telecon for the same distance of shot. On top of this the fuji has way better resolution, but the shots at 100% are very interesting (to me at least!) So rather than move up to a DSLR I'm going to tinker further.

I just know I've stumbled into the beginnings of something here, but I have no real idea what it is, yet! I sure do aim to find out if I possibly can though.

There is something pretty odd about a binocular optics chain and it does all sorts of interesting things.

[BinocularSky]

Hmmmm

This thread made me think....

If the bino's are usually around f4 and the one's I've pulled apart seem to only use Kellner type eyepieces.....

1. Why is their performance so acceptable????

2. Why are not more Kellners used as low power eyepieces on f4+ telescopes

Interesting.....

Indeed. It flies in the face of what we think we "know". I feel some experiments coming on...