How to get sharp star photos...

if you mean sharpness relating to the startrail then you need to depress shutter speed depending on what focal length you are on. for wide angle lens, i wouldn't go above 15sec strictly if you really don't like trails at all. even at 20sec trails can bee seen depending on which side of sky you are shooting.

If you are talking about more of sharpness of star images even when it's not trailed. it's going to be one of two things or both sometimes. 1. stars may not be in focus. 2.wide open aperture your lens gives you softened image. In second case, it depends on the lens quality. Most of the lenses with very wide aperture give you a bit softened image at wide open aperture compared to the closed aperture. closing up one step down your aperture value can give you more clear and sharp image.

A lot of lenses seem to give very sharp clear image around aperture value 7-8 but this wouldn't be feasible setting in landscape astrophotography. stepping down 1.4 down to 2.8 or 3.5ish might be better in terms of looking at the shape and sharpness of stars (even the coma gets better in closed aperture)

thanboora wrote in post #17065495
A lot of lenses seem to give very sharp clear image around aperture value 7-8 but this wouldn't be feasible setting in landscape astrophotography. stepping down 1.4 down to 2.8 or 3.5ish might be better in terms of looking at the shape and sharpness of stars (even the coma gets better in closed aperture)

A good modern lens shouldn't suffer too much when used wide open. Focal Pro allows you to test your lenses sharpness at varying apertures.

Here's my 10-22. Amazingly enough, it's sharpest wide-open.

hollis_f wrote in post #17065422
Afraid not. While the idea of hyperfocal distance sounds like a magical panacea for all focussing problems - it isn't.

The theory of 'depth of field' and 'hyperfocal distance' depends on the concepts of 'acceptable blur' and 'circle of confusion'.

Your lens can only perfectly focus light from a single plane (for a well-designed rectilinear lens). Light coming from objects in front of, or behind, that plane will be blurred - with the degree of blur becoming greater the further the object is from the plane of focus.

A depth of field calculator (like the one to which you've linked) works by deciding how much blur would be too small to notice on your particular camera (i.e., when it's smaller than the circle of confusion). Objects close enough to the plane of focus will produce 'acceptable blur'. The depth of field extends from the closest of these object to the farthest.

The hyperfocal distance is calculated as the closest distance to enable the depth of field to extend to infinity. Which does sound perfect for astro work (hey, if our subjects aren't at infinity - what is?). But remember, objects at the edge of the depth of field are just barely 'acceptably' blurred - but they're still blurred. And the degree of blurring that seems 'acceptable' when shooting landscapes really doesn't produce a result that's 'acceptable' for the bright points of light we expect to see when shooting stars.

I went through this procedure when I first started to shoot stars. I soon discovered that depth of field and all associated concepts just didn't apply to stars. The only way to get sharp images, without using fancy tools, is to do it manually. The development of LiveView and twisty LCD screen with x10 magnification has made this a lot easier.

LightView, for me, is hard to see at night, not saying it doesn't work, but I myself have a hard time with it, (Canon 6d screen to small?) Thanks for your input, I do want to say when adding foreground objects that hyperfocal seems to have its place, this is what I managed last night using it, kinda of. I auto focused to the foreground (daughter held a flashlight to the foreground so that the camera could focus on it, then she shut the flash light off during exposure, it was DARK out there), locked the setting, recomposed and took the shot. I'm almost entirely convinced that if I had closed it down a couple stops the stars would've come out a lot sharper. Gonna try the LiveView again though, thanks. (20 seconds, f/2.8 ISO6400)

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Nice to see this thread still breathing I will actually be attempting some more milky way shots and star trails in the coming weeks. So will be nice to post my latest attempts compared to what I initially attempted 3 years ago!

Tony_Stark wrote in post #17081097
Nice to see this thread still breathing I will actually be attempting some more milky way shots and star trails in the coming weeks. So will be nice to post my latest attempts compared to what I initially attempted 3 years ago!

Hope it works out, I'd join ya but the moon has decided to come out and play.. Don't know what's worse that or light pollution.