Manual focus to infinity

mel.b

I'm heading off to hopefully see & photograph the aurora next weekend. From my reading, using manual focus set to infinity is the best. Looking at my lens (Sigma 17-70) i can see a little dot that doesn't move and I can line up the infinity symbol with that and it does seem to be in focus so I am presuming that is where it should be?

I've read about taping it to keep it in place, however my zoom ring is right next to the focus ring, so I wouldn't be able to tape it?

John mac

i wouldn't rely on using the symbol alone , it can be off a tiny bit ,
best is to manually focus on a bright star , taping it there is a good tip , ,
you will prob be using the wide end of the zoom so tape shouldn't be a issue.
best to refocus in the field ,
*** practice before you go . ***

if you have your camera set to back button focusing you might be able to focus on a distant object that will give you infinity . without having to set to manual ..

magicbastarder

are you going to be shooting wide open?
if not, focus becomes a little easier as the depth of field will deepen.

uck51js9zml2yt

Speaking of aurora. What aperture is recommended?

ED E

Riley Curved Mango wrote: »

Speaking of aurora. What aperture is recommended?

Its a big trade off depending on setup. Too long and its movements soften it, too open and you lose DoF.

mel.b

So while the dog was having a run around the park tonight I had a go at trying to manual focus. Ignore the fact that camera isn't level :rolleyes:
Have I got these in focus?

This one I used the live view and zoomed in on the seat. I used my head torch to light it up. 4 sec, f2.8 iso 1600


This is another . 6 sec, f2.8, iso 1600


This one, the trees look soft to me? Am i correct in thinking, if I focus on the stars then anything in the foreground will be OOF? So I'm better to focus on something in the foreground, but maybe 20-30m away and then everything after that will be in focus?

John mac

there's no photos attached ..

mel.b

John mac wrote: »

there's no photos attached ..

Hmmm...I can see them

uck51js9zml2yt

mel.b wrote: »

Hmmm...I can see them

so can I

mel.b

Riley Curved Mango wrote: »

so can I

That's good! Did I get them in focus ok?

.Longshanks.

mel.b wrote: »

That's good! Did I get them in focus ok?

All 3 seems to be slightly out.
Use live view. Magnify as much as possible.
Good rule of thumb is to dial back from infinity by ¼ to ½ mm