Magnification

[r.t.swing]

Why is there a limit to magnification in say the UK on any particular scope? Say 200x For a 250px. (I gleamed that from another thread.)

[LukeSkywatcher]

There's 2 reasons:

1/The maths/physics of the scope (focal length,size of mirror,EP size).

2/ The weather (the worse the weather conditions,seeing,transparency etc) the more magnification you use on the scope the poor conditions are also magnified at the EP and the images are degraded.

On the rare nights when conditions are very good, you can push the magnification of the scope a bit more then usual because the better "seeing" conditions allow this to happen.

[r.t.swing]

Thanks, I assume the weather conditions here are not of the greatest.

[r.t.swing]

Out of curiosity, does temperature have any effect?

[LukeSkywatcher]

Out of curiosity, does temperature have any effect?

Yep. The air is constantly moving. There are warm and cold currents flowing past all the time. Warm currents tent to make the image less stable and objects appear to "boil" or twinkle. Cold air is much calmer and usually allows more stable images.

[r.t.swing]

So winter is better in general then summer? When not raining or cloudy

[LukeSkywatcher]

Many people think so. They love the cold crisp clear air.

[ollypenrice]

Well... Damian Peach is perhaps the best planetary imager in the world. He goes to Barbados. It is not particularly clear, often the opposite, with a significant haze. It is also warm. But the key thing is that it is stable. The air temperature lowers slowly and consitently as the altitude rises. What mucks up the 'seeing' (the turbulence) are sudden changes in temperature at different altitudes.

Where I live (SE France, close to the Alps but still in Provence) we get excellent transparency, ideal for the deep sky, but the seeing is often fairly disturbed until the land has given up its heat. This means our best planetary viewing is in the second half of the night. I think this is pretty common. In winter this happens more quickly, obviously enough.

So for high magnification you need good seeing (associated with thermal stability) and this is very consistently better when the transparency is imperfect.

Wind is a killer, not only because it jiggles your telescope but because it creates sudden temperature gradients.

In any event, to get beyond 300x anywhere, in any scope on earth, is rare.

Olly

[perrin6]

I use 440X for looking at very close double stars (sub 1 arcsecond) but I have to wait patiently for the occasional moment every 10 seconds say, to glimpse the 2 stars so it's possible to use very high powers in unstable conditions. I have been reading about William Herschel in the superb 'Age of wonder' book and he often used 900X and even.....wait for it.........6000X on occasion !!! Believe it or don't.

[LukeSkywatcher]

Where I live (SE France, close to the Alps but still in Provence) we get excellent transparency, ideal for the deep sky, but the seeing is often fairly disturbed until the land has given up its heat. This means our best planetary viewing is in the second half of the night. I think this is pretty common. In winter this happens more quickly, obviously enough

I could NOT agree more. Some of the most perfect viewing "seeing" i have had is between 4-6am (a couple of hours before dawn). The earth has given up as much of its heat as it is going to before starting to warm again and conditions are absolutely PERFECT.

But more then that................there is something so peaceful and humbling about that time of the day. You really feel at one with the universe,nature etc. Its a "magical" time of the day. Its made even better on those days of the month when at that time of day there is a thin cresent Moon hanging in the sky.