cant get sharp images ?

[scottphillips]

im having serious trouble getting sharp images of wide-field star trails, constellations and iss passovers

I have the camera on manual mode, manual focus, f3.5 to let the most light in possible with my lens and iso at 800 for 25 second exposures

here is en example of two images I took a month ago and you can see what i mean by lack of focus and sharpness of the image

any help is appreciated 

thankyou

[andyboy1970]

Try autofocus on Jupiter then switch autofocus off.

[ronin]

Getting good focus will need something like a Bhatinov mask, the sky is too dark to do it by eye.

The widest setting generally produces images that are not sharp, try f/5.6, should be better.

If it is the supplied zoom lens they are not great, seems a good prime lens of 50mm or less 28mm perhaps are better.

[jambouk]

The focus just looks "off" to me (i am using my iphone to view the images).

Bang in focus is very hard to achieve when just using the small screen on the back of a DSLR. Using a Bahtinov mask does make it easier, but it is still hard.

Can you plumb the image feed from the camera into a laptop and get a better [bigger] look at the focus?

James

[sharkmelley]

My trick is illustrated below:

Put the lens in manual focus mode and stick a couple of pieces of masking tape to the focusing ring and the main body of the lens.  Take a series of test shots at different focus points according to the scale you have drawn. View them at max size on the camera LCD to judge which is the sharpest then tape the focusing ring at that focus position (so it doesn't get accidentally knocked).

I actually do it twice - once to judge best focus for the image centre then again to judge best focus for the image corner(s).  The optimum focus will then be somewhere between these extremes.

Mark

[kens]

Are you able to zoom in (electronically - not optically) onto one of the doughnuts and focus on that?