Casual star gazing

[nowty]

Saturn's up tonight too.

To the right and a bit lower than Jupiter.

[Joeboy]

Saturn's up tonight too.

To the right and a bit lower than Jupiter.

Excellent, will have a look. Thanks!

[Bugtownboy]

Are you in the path of the partial eclipse tomorrow, Joe ?

Obviously don’t use the bino’s to look at it

I think you could use ‘lenses’ to project onto a white card or get the welders mask out

[Oldgreybeard]

This thread has had me rummaging around in the loft, as I knew I had a pair of (fairly useless for boat use) binoculars, bought many years ago in error. I've found them, a pair of Pentax model 5810, 16 x 50, 4° field of view binos. They were far too high a magnification level for use on a small boat, so they've been tucked away in their original case, with lens caps fitted, for around 30 years. Would they be any use for star gazing, I wonder?

[Joeboy]

This thread has had me rummaging around in the loft, as I knew I had a pair of (fairly useless for boat use) binoculars, bought many years ago in error. I've found them, a pair of Pentax model 5810, 16 x 50, 4° field of view binos. They were far too high a magnification level for use on a small boat, so they've been tucked away in their original case, with lens caps fitted, for around 30 years. Would they be any use for star gazing, I wonder?

Only one way to find out OGB! A bit of heat haze but could clearly see the four largest moons (Io, Europa, Ganymede, and Callisto) and two horizontal bands on Jupiter. Pretty excellent!

[Stinsy]

This thread has had me rummaging around in the loft, as I knew I had a pair of (fairly useless for boat use) binoculars, bought many years ago in error. I've found them, a pair of Pentax model 5810, 16 x 50, 4° field of view binos. They were far too high a magnification level for use on a small boat, so they've been tucked away in their original case, with lens caps fitted, for around 30 years. Would they be any use for star gazing, I wonder?

16x is way too much for boat use. But perfect for stargazing, particularly it you can rig up a tripod.

[spread-tee]

16 is a pretty high power for a 50mm objective, you may find that there isn't really enough light gathering power for faint objects. Planets and the Moon will be great if you can hold them steady enough, my guess is that they were designed with bird spotting or similar in mind.

Desp

[John_S]

In dim light, which stargazing is, you need to maximise the light getting into the eye. Young adult eyes can dilate to an entrance diameter of 8mm but this deceases with age to around 6mm at 60 although 7mm is possible for some 60 yearolds

To match this with a telescope or binoculars, you divide the diameter of the front lens by the magnification. Eg 50mm*7 binoculars give an exit diameter of7.1 or 40*8 give 5mm. That is why sailors usually go for 50mm*7 as it is the right balance of hand hold ability and large exit diameter to match the dilated pupil diameter in poor light conditions.

Thus for star gazing you really need an exit diameter of at least 6mm. Trouble is, as the magnification goes up you need a bigger front lens diameter which adds weight and cost and reduces handheld ability.

I hope this helps in choosing your stargazing binoculars.

[John_S]

Just seen Desp's post. 16*50mm gives a 3mm exit diameter. Binos with an optimum 6mm or larger exit diameter will let 4 times as much light through to the eye pupil.
John