Beginner Kit Lenses and Basic Astrophotography

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Vectorially

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I see a lot of entry-level mirrorless cameras advertised with f/3.5–f/5.6 kit lenses with typically something like f = 15mm–55mm.

As I understand it, to take pictures of the night sky you should have as wide a lens as possible and focus around infinity. However, for lenses with the specification above, focusing near infinity will mean a relatively long focal length at or near the max of the lens and so correspondingly a relatively small aperture, e.g. f/5.6.

Will f/5.6 be good enough to get decent shots of the night sky, albeit with a very limited field of view, as long as the shutter time is long enough, e.g. 15–20 secs at ISO 1600?
 
Vectorially said:
However, for lenses with the specification above, focusing near infinity will mean a relatively long focal length at or near the max of the lens and so correspondingly a relatively small aperture, e.g. f/5.6.
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I might be missing your point but I don't understand the above. Why would focusing at infinity mean you have to use the long end of the range of a zoom lens?

For the odd star shots I take I use an f3.5-f5.6, 18-55mm kit lens usually set at 18mm.

Dave
 
It appears from your question that you may be confused about lenses and all the numbers / specifications.
Saying that a 15mm-55mm focal length lens has an aperture specification of f/3.5-f/5.6 means that the largest aperture achievable on that lens is f/3.5 when the lens is set to 15mm focal length and f/5.6 when the lens is set to 55mm focal length. Note that these are the largest apertures and you can always set a smaller aperture of f/8, f/11 etc.
The focal length of 15mm will give a wide field of view while longer focal lengths give smaller fields of view albeit with larger magnification, no matter what the focal length you can set the focusing distance at infinity.
So if you want the widest field of view set the focal length to 15mm, if you want the maximum light set the aperture to f/3.5, set the focus distance to infinity and choose the shutter speed and ISO accordingly.
Aplogies if you know all this and I have misunderstood your question.
 
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Yes, sorry I'm clearly confused and haven't quite grasped the connection between focal length, focusing and zoom. I had thought that, by zooming one was increasing the focal length, which I understood to be (in simple terms) the distance from the first lens element to the node where all light beams coincide. :(:help:
 
How the pictures come out depend on how much light you collect. The kit lens needs to be kept open for a long time to collect enough light so needs to be kept stationary on a tripod and likely the stars will move. Good for star trail photos. To get pictures of stars that are sharp you’ll need a lens with aperture f2.8 or less. Samyang 24 f1.4 is a good choice and not too expensive, note it’s manual focus only though.
 
newbie1 said:
How the pictures come out depend on how much light you collect. The kit lens needs to be kept open for a long time to collect enough light so needs to be kept stationary on a tripod and likely the stars will move. Good for star trail photos. To get pictures of stars that are sharp you’ll need a lens with aperture f2.8 or less. Samyang 24 f1.4 is a good choice and not too expensive, note it’s manual focus only though.
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Thanks. Unfortunately too much light pollution where I am – see my 'First Attempt' share thread.
 
It’s possible to get filters that help somewhat with light pollution, but much better to get out of the city once you have practiced the technique.
 
It doesn’t have to be, but it can be! My gear for Astro costs...well you don’t want to know...
 
have to say agree with above, not expensive at all, my main night lens for my olympus EM5 Mk2 is the Samyang manual focus, F2 and 12mm (24mm) and it cost under £200 new.
 
A others have said, of course you can focus at infinity with the lens at its widest angle. Focus and zoom are different functions. I successfully took star trail photographs with my DX 18-55 kit lens set at 18mm, f3.5, iso 3200 in my back garden in a heavily light polluted area on a windy night. Is it a great photo? not really as it was just a preliminary experiment with no great composition involved, but I was actually quite shocked when I got a result that was half way acceptible with equipment and location that falls far short of the ideal. Much also relies on image stacking and post processing. I can't wait to go and try it somewhere darker. Of course star trails are arguably the least demanding form of astrophotography but it just goes to show that it is well worth just going out and having a go with the kit you already have.

Startrail edited.jpg
 
Well done on your experiment! Hope to see more in due course.

What shutter (bulb?) speed did you use? My photo in the 'First Attempt' share thread was at f/3.5 15mm (virtually the same as yours) ISO 200 for 20 secs - much less exposure/senstivity, I'm guessing, than your photo given your star trails. I think your "heavily light-polluted" back garden must be significantly less polluted than my area because even at ISO 400 & 20 secs my sky looks like a mid-summer morning - light blue with pin-point stars just about visible. At ISO 800 (again 20 secs) the result really does look like it was taken at noon at some Italian getaway in mid-June. ISO 3200 would just turn out creamy white all round.
 
Vectorially said:
Well done on your experiment! Hope to see more in due course.

What shutter (bulb?) speed did you use? My photo in the 'First Attempt' share thread was at f/3.5 15mm (virtually the same as yours) ISO 200 for 20 secs - much less exposure/senstivity, I'm guessing, than your photo given your star trails. I think your "heavily light-polluted" back garden must be significantly less polluted than my area because even at ISO 400 & 20 secs my sky looks like a mid-summer morning - light blue with pin-point stars just about visible. At ISO 800 (again 20 secs) the result really does look like it was taken at noon at some Italian getaway in mid-June. ISO 3200 would just turn out creamy white all round.
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It does sound like your area is even worse than ours, although it is best to make sure there is no moon too. Following advice I found on the net I tried 30s exposures with 15 second gaps. I attach an unprocessed image. Next time I'll try taking the iso down a notch, and reducing the gap to 10 seconds or less.

unprocessed_5011.jpg
 
If I'm shooting star trails I don't leave any gaps between shots - you run the risk of ending up with dashed star trails (unless that's what you want)
 
hunnymonster said:
If I'm shooting star trails I don't leave any gaps between shots - you run the risk of ending up with dashed star trails (unless that's what you want)
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Yes, I understand that, but the advice is also to give your sensor a chance to cool down to reduce noise so I went with the suggested gap. I have more experiments planned but with our current weather, it's going to take a while! Also, I'd pinned my hopes on the Starstax smoothing function.
 
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In my experience, the shorter the gaps the better and didn’t have any problems with heat. At night time it’s usually pretty cool especially this time of year.
 
newbie1 said:
In my experience, the shorter the gaps the better and didn’t have any problems with heat. At night time it’s usually pretty cool especially this time of year.
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Same here. Eliminating heat effects in the sensor is the purpose of the dark/flat frames at start & end of the shoot is it not?
 
For seamless star trails, an old film camera with a fast lens and ISO400+ film is the way to go! No limit on how long the shutter stays open and no sensor heat build-up.
 
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