Nightime shots / infinity focus!?!

[fishtank]

Hi,

I'm fairly new to the world of DSLR photography and am trying to do some night time shots of a tree, with a long shutter speed, so that I can light the tree up with a torch.
The tree is in the dark and it's pitch black, so the autofocus on the camera will not lock onto the tree.

I'm informed that the way to get past this is to use Manual Focus and set this to infinity.

I am able to put the camera onto Manual focus and understand about the focus ring and setting this to the maximum one way or another, I also appreciate that sometimes the focus ring doesn't have to be fully extended in either direction as infinity is sometimes slightly before this.

Is there any secrets / hints that people can give me to help me with achieving these pictures in focus? I struggle to tell, due to the light, whether the tree is in focus, through the viewfinder whether I light it with a torch or not!!!

Please help as this is something that I will not only use once and it's really frustrating me now!!

Thanks

Dan

[EDIT: I am using a Sony a390 with the 18-55mm kit lens]

[ianpinion]

Hi Dan and welcome to the forum.

Just a thought, but have you tried setting the camera up in daylight to get a focus lock, noting the distance shown and marking the point at which you took the test shot from? Then when it's getting dark, set your camera up on exactly the same spot, set the focus to the reading you got earlier and hey presto you should be close.

[OldBoy]

Two ways, either switch your lens to manual focus and focus by hand or, if you can't see to focus then use the torch on the spot you want the focus to be and use focus lock. This will lock the focus on that spot, press the shutter the use the torch to light up the tree and when the preset time on the camera closes the shutter you should get what you want. To take another shot you will need to do the same again.

[Cathus]

get to know how hyperfocal distance works then you will be able to choose settings which get your tree in focus every time, so long as you know roughly how far away from the camera the tree is.

If you have an iPhone or Android phone you can get free hyperfocal distance or depth of field calculators, just put in the lens, aperture & distance & it will tell you how far into the scene to focus to get everything you need sharp.

There's an explanation of hyperfocal distance here

[fishtank]

Hi all, thanks for your replies, I've tried shining the torch on the tree on order to get the camera to focus, so this has failed.
I'm going to try and understand hyperfocal distance i think, I've got an iPhone so it's off to the app store for me!!
Thanks again and let's hope I get some pics for my gallery