"Paul Saunders" <[email hidden]> wrote in message
news:[email hidden]...
| ste® wrote:
|
| >> Patrick reckons the 7th.
| >
| > What does he know?! ;-)
|
| Look at the charts for yourself, it's clearly closest to the Pleiades on
| the 7th.
| http://www.spaceweather.com/images2004/31dec04/skymap_north.gif
|
| "GREEN COMET: Tonight, Comet Machholz is gliding by the Pleiades. The
| blue star cluster and the green comet are only 2 degrees apart--a
| beautiful sight! Although a telescope is recommended, you can see them
| with the unaided eye. Step outside around 9 p.m. and look south"
| http://www.spaceweather.com/
|
| Nice pic too.
Yes, that's what yours should have been like! ;-)
| >> Actually I did get one in focus at 300mm
|
| > Glad you got something. What was your problem? Don't you just focus
| > on infinity and point away?
|
| Pray tell, how do I focus on infinity with a cheapo lens that has no
| distance scale? (As you know it focuses past infinity) I've mentioned
| this problem before, that's why I need lenses with distance scales
| (which equate to better quality lenses anyway).
When I took my star photos, I auto-focused on the moon then switched it to
manual focus. I'm pretty sure that was your advice too. On a moonless or
cloudy night, I would have tried to have focus on the most distant object I
could see (assuming there was something light in a distance).
| But even having a distance scale with an infinity mark doesn't solve the
| problem completely, since the actual focusing point varies with
| temperature (that's why they're designed to focus past infinity). In
| the snow on Mynydd Du recently I remember auto-focusing on distant
| summits (i.e. Pen y Fan) and noticing that the lens had focused way past
| the infinity mark.
I'm surprised that you haven't yet prepared a table of infinity marks
against temperatures! You could go out and focus on the moon and note the
temperature and focusing position! Hard work though... ;-)
| Anyway, using my 24-85 lens, which does have a distance scale I set it
| to infinity and it was acceptably in focus. I then went the other side
| of the house and manually focused on some distant street lights, came
| back and tried again. This time it had focused slightly less than
| infinity I think, and the result was slightly sharper (compared in BBP).
|
| Under normal circumstances setting it to infinity and using a mid to
| small aperture would ensure that infinity would be within the depth of
| field of the lens, however, in this case I had to use the widest
| aperture, and an ISO of 1600, in order to keep the shutter speed fast
| enough to prevent motion in the stars (1 sec in the case of the long
| telephoto), and as you know, depth of field is extremely narrow with a
| long tele so accurate focusing is critical.
|
| Actually, I focused manually on the Pleiades for the long tele shots
| since I could just make them out in the dim viewfinder, but it wasn't
| easy. For the wider shots I couldn't see the stars clearly enough.
Yes, I realise why it's a problem. This is where a viewfinder magnifier
would also come in handy, to help manual focus on distant and small objects.
| The problem with focusing in the dark is that not only will the auto
| focus not work, but that's when manual focusing is hardest too. It's
| also when you need to use a wide aperture, because it's dark! Using the
| distance scale and setting smaller apertures for greater DOF is one
| solution, which can result in very long exposures, but with stars it
| would obviously result in trails.
Oh well, like you've said before, you're never going to get great
astro-photography without some a specialist setup.
| > Thanks for that. I'll have a look on the next clear night and see if
| > I can make it out.
|
| Well tonight's the night. Try to get a pic if you have clear skies.
| Look south at 9pm, SE earlier, SW later.
It's very cloudy, cold, and windy tonight. Around here it is anyway.
| > Pleiades looks familiar as I have often noticed a cluster of stars
| > like that (unless there are lots of them, in which case I might have
| > been looking at anything!).
|
| Well there are other clusters, but that's the most distinctive. Look
| for the roughly V shaped Hyades nearby.
|
| > But to be honest, I'm not that hot on
| > locating stars.
|
| Now is the best time of year to learn. Start with Orion as your main
| reference point(probably the most recognisable constellation after the
| Plough), which is usually somewhere in the south (SE to SW), then find
| your way to other constellations from there. The small map in the link
| above is a good starting point. Gemini is above Orion to the left and
| Taurus above and to the right.
Thanks for the hinters Paul.
| > My only way of finding the North Star is to take a
| > long exposure and see which one the start 'circle' around! :-) (I
| > know, you've probably sent me links with easy to follow diagrams etc,
| > but I never have those diagrams with me on clear nights...)
|
| So carry them with you! I'd recommend the Collins Gem Guide - The Night
| Sky, a small pocket sized book, if they still make it, or something
| similar.
|
| I also have a small plastic rotating wheel skymap on which you can set
| the time and date which shows the entire sky, and is very good for an
| overview of exactly what's visible, don't know where you can buy those
| though.
Yes, don't worry, I'll sort it out. It's going to at least be important for
me to find the north star and see sky charts to work out its position in
relation to nice landscape scenes. That's the type of night photo I'd like
to look for next.
| > One point about using a 50mm 1.8 lens though Paul - the 1.8 is great
| > (these shots were taken at midnight, and some of the others I've got
| > from a 10-15 second exposure look like daylight); however, it's just
| > not wide enough for good night-sky photos (IMO), and personally, I'd
| > want something much wider for general landscape shots which feature
| > star trails (depending on the composition of course).
|
| Yes, with a DSLR a 50mm lens is more of a portrait lens than a standard,
| and a 35mm wide-angle is now a standard, so you'd need a 24mm lens to
| give you the rough equivalent of a 35mm (38mm actually), i.e. a moderate
| wide-angle. Fast 24mm lenses are not cheap though, A 28mm may be more
| practical, but that's only equivalent to 45mm, which is practically a
| standard lens, and both of Canon's models are only f2.8.
|
| I still think the Sigma 17-50mm f2.8 is probably the best buy if you
| want a good compromise between wide angle and wide aperture, plus it's a
| zoom. Not too pricey either, around £320 I think.
|
| If you really do want a fast wide fixed lens then Sigma do a 20, 24 and
| 28 at f1.8. The 20 would be equivalent to 32, which is quite
| reasonable. They also do a 14 (22 equiv) at f2.8.
| http://www.sigmaphoto.com/html/fixed.htm
Possibly a good lens, but nooo, not another lens! :-) I'm now working on
the assumption that in order to buy more camera equipment, I must make money
from the hobby first. We'll see!
| Paul
Ste
