Jupiter
Last night a very bright star was risng over a neighbour's house out the front, so I wandered outside with the telescope (much swearing) and set it up outside.
The telescope came with three different eyepieces. There was one marked '20mm', one marked '10mm' and one called 'Barlow' which doubles the magnification of one of the other two.
The numbers in millimetres are the focal lengths of the eyepieces, and different focal lengths give different magnifications. You can work out the magnification using a small formula:
My telescope has a focal length of 900mm, and so the 10mm eyepiece gives about 90x magnification, and the 20mm eyepiece gives 45x magnification (i.e. a smaller image and bigger area of sky, so useful for 'wider' objects).
With the 10mm eyepiece, and the prevailing atmospheric conditions, Jupiter was a very bright disk the size of a lentil, with a line of small dots either side of it - Jupiter's moons. It was very bright indeed, so bright it was difficult to make out much detail, but I saw a couple of faint stripes of the cloud belts.
It's an awesome feeling to see an actual planet, in real life, rather than just watching it on TV. A bit like bumping into Stephen Fry or Richard Ayoade in the street or something. Or maybe it's a bit like having a 'free entry' ticket to the wider universe.
You can add filters to the telescope. Whereas in my last post on the topic I mentioned that lack of light makes things look a bit grey and faint, with bright objects like planets it will sometimes pay to filter out some of the light in order to be able to see detail properly.
A couple of weeks ago I found that this is expecially true of the full moon: when photographing it I had to use similar settings to those I would use during the day in order to get any detail. For astronomers, one cannot adjust the ISO or shutter speed of the telescope (the hole is always open), so one uses filters to block out the light.
You can purchase Moon Filters, as well as filters designed for specific planets (Venus filters etc.) and even light-pollution filters.
Back to the eyepieces and magnifications. Using only the formula above, one would have quite reasonably thought that one could just purchase eyepieces with progressively shorter focal lengths in order to get progressively higher magnifications. This is partially true, however the image will start to deteriorate after a certain point, getting grainier and crappier as you go on.
Each telescope has a 'maximum effective power', above which images start to look pretty dreadful (assuming you can see them at all). This is worked out from the aperture ('width of hole') of the telescope, doubling it by two-and-a-bit. You can work out a conservative estimate using the following formula:
So I could probably get a reasonable 260x magnification, perhaps as much as 320x at a pinch. Therefore a 2mm eyepiece, yielding a 450x magnification would be a pointless expense, but a 5mm (yielding 180x) may be worth a punt, tegether with a neutral density moon filter...
Years ago, if anyone ever told me I'd consider spending £30-odd to make a white dot look a bit bigger I'd've laughed in their face.
The telescope came with three different eyepieces. There was one marked '20mm', one marked '10mm' and one called 'Barlow' which doubles the magnification of one of the other two.
The numbers in millimetres are the focal lengths of the eyepieces, and different focal lengths give different magnifications. You can work out the magnification using a small formula:
magnification = telescope focal length in mm ÷ eyepiece focal length in mm
My telescope has a focal length of 900mm, and so the 10mm eyepiece gives about 90x magnification, and the 20mm eyepiece gives 45x magnification (i.e. a smaller image and bigger area of sky, so useful for 'wider' objects).
With the 10mm eyepiece, and the prevailing atmospheric conditions, Jupiter was a very bright disk the size of a lentil, with a line of small dots either side of it - Jupiter's moons. It was very bright indeed, so bright it was difficult to make out much detail, but I saw a couple of faint stripes of the cloud belts.
It's an awesome feeling to see an actual planet, in real life, rather than just watching it on TV. A bit like bumping into Stephen Fry or Richard Ayoade in the street or something. Or maybe it's a bit like having a 'free entry' ticket to the wider universe.
You can add filters to the telescope. Whereas in my last post on the topic I mentioned that lack of light makes things look a bit grey and faint, with bright objects like planets it will sometimes pay to filter out some of the light in order to be able to see detail properly.
A couple of weeks ago I found that this is expecially true of the full moon: when photographing it I had to use similar settings to those I would use during the day in order to get any detail. For astronomers, one cannot adjust the ISO or shutter speed of the telescope (the hole is always open), so one uses filters to block out the light.
You can purchase Moon Filters, as well as filters designed for specific planets (Venus filters etc.) and even light-pollution filters.
Back to the eyepieces and magnifications. Using only the formula above, one would have quite reasonably thought that one could just purchase eyepieces with progressively shorter focal lengths in order to get progressively higher magnifications. This is partially true, however the image will start to deteriorate after a certain point, getting grainier and crappier as you go on.
Each telescope has a 'maximum effective power', above which images start to look pretty dreadful (assuming you can see them at all). This is worked out from the aperture ('width of hole') of the telescope, doubling it by two-and-a-bit. You can work out a conservative estimate using the following formula:
maximum effective power of telescope = telescope aperture in mm × 2~2.5
So I could probably get a reasonable 260x magnification, perhaps as much as 320x at a pinch. Therefore a 2mm eyepiece, yielding a 450x magnification would be a pointless expense, but a 5mm (yielding 180x) may be worth a punt, tegether with a neutral density moon filter...
Years ago, if anyone ever told me I'd consider spending £30-odd to make a white dot look a bit bigger I'd've laughed in their face.
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