Can i focus my DSLR on stars in this way??

[neelam]

hi guys yesterday i took around 400 images till dawn to create a time lapse video but unluckily all were out of foucs.i dont know what went wrong.

should i first put the camera on automatic foucus take a shot and then pull the button on lens back to manual focus and then put it on continous shot mode?will it work?

[Psychobilly]

Couple of questions...

What lens are you using?

Are you adjusting Zoom after you have focused?

Your better of focusing on a distant street light and then switching to MF... if you alter the zoom then the focus can change slightly.. and slightly is enough for stars...

Also its worth using a blob of blutack to "lock" the focus ring...as the focus mechanism is so loose on an AF lens it can creep with even the slightest vibration when its set to MF...

When you have "locked" it swing the focus zone across the distant light to make sure your stll focussed if not make tiny manual adjustments witht he blutack in place...

Peter...

[neelam]

i am using the ordinary 18-55 IS kit lense and i am not using zoom.

[neelam]

how much far should the street light be?would 40,50 meters work?

[Psychobilly]

OK I would still go through the distant streetlight approach...

You should be able to get focus Lock on the moon, and the brighter planets ... A street light a few hundred meters away is basically at infinity with a 18-55

You could alwys stop the lens down a stop or two as well this will help and may also improve the star shape around the edges of the image...

Peter...

[Albireo380]

Psychobilly is right, Neelam. Use manual focus on a bright light as far away as possible. Do this using your zoom at "full zoom", then "lock" down the focus with blue tack. Canon lenses often have the "infinity symbol" not quite at the focus point for infinity - so ignore the infinity symbol on the lens. Move to the zoom you want and take a couple of exposures (as said earlier, always stop down the aperture a little from maximum (around a full stop is probably okay, but 1.5 stops is better). Check your initial test shots, adjust the focus minutely if required, and off you go. But check focus every now and then, it is surprising how it the lens can get slightly out of focus during a series of exposures.

Tom

[neelam]

ok so jupiter is out these days.if i can focus on jupiter than does that means its focused on infinity and and other stars in the background will also appear focused?

[Psychobilly]

yes... but a street light a few hundred yards away will be just as good edge of a distant building agaisnt the sky aything that gives enough contrast to get the AF to lock...

[beetlejuice]

I can very rarely get my Canon 400D to focus on the stars; the autofocus system tends to just hunt around looking for focus. As Tom says, the infinity focus is not at the actual infinity point on Canon lenses, so manual focus is the order of the day. Use a bright star, take a few shots and compare. The trouble with this approach is maintaining it. A year or two ago Sky & Telescope published an article about making a focus scale to apply to the lense to achieve this. I'll have a hunt around and post a scan - but not for a couple of weeks as I'm off on my hols to escape light Scottish nights.

[jgs001]

Something to bear in mind... Even if you've nailed focus, tripod mounted long exposures with the IS turned on will come out looking either like you kicked the tripod or OOF stars... The IS will activate and move the correcting element around. Make sure you've turned the IS off. You'll hear the IS when it's active, it sounds a bit like a tearing sound coming from the camera... first time I did this, I thought there was something wrong with the shutter.

You don't mention what camera you're using, but with the IS kit lens, it's likely to be either the 450d or 1000d, in which case, another option to sort out focus, although it's still not that easy, centre a bright star, activate liveview and zoom in all the way (10x), then in MF mode, twist the focus to the infinity end of the movement (it's actually beyond infinity, and I've read that's too allow for thermal changes) and slowly and carefully rotate it back until the star becomes the smallest blob on the screen as possible. Then take a test shot and zoom in all the way. Oddly, the Canon EF 50mm lens has the infinity focus point at the end of the focus travel.