early morning long exposure question

ronlane · Oct 26, 2012

Got the idea this week to stop on my way to work and take long exposure (30 sec) shots of a landscape, railroad tracks and trees. I got set up and was working with my 18-55mm. I had to take it off autofocus because of the lack of light. I did not get it focused good for my pictures. I was happy with the exposure but it was out of focus.

Does anyone have any suggestions for getting the focus better in a really low light situation when you are having to do it manually?

480sparky · Oct 26, 2012

Take a bright flashlight along.

Bracket your focus.

Big Mike · Oct 26, 2012

Older lenses and most high quality lenses have a distance scale on them so that you can see approximately how far it's focused to by the markings on the lens. Unfortunately, cheaper lenses like the 18-55mm don't have that.

As mentioned, all you need is a bit of light on the spot where you want to focus, so a flashlight might be helpful. Also remember that focus is just a distance (to the lens). So if you need to focus 20 feet away in one direction, but it's too dark...you could focus at 20 feet in another direction and then go back to your original direction.

If your camera has live view, then it probably has exposure simulation (the live view gets darker or brighter as you change the exposure). You might then be able to use the live view to manually focus the lens.

You might also want to read up on Hyper-focal Focusing.

PlanetStarbucks · Oct 26, 2012

There's a couple techniques you can use. Lights are the easiest thing to focus on through the lens in that situation. Another method I've used is to bump up to max ISO and take a test shot to zero in the focus. I'm not a big fan of doing it that way, but it can work. I've found that as I get more familiar with a lens, I start knowing where the focus should be just with aperature. So, shooting in f11...if the scene is 40 feet out I can usually just stick the focus by pulling back a bit from infinity. Think hyperfocusing with more cowboy.

Dao · Oct 26, 2012

Last time when I need to focus in dark area, I use liveview. It was the July 4th fireworks.

- Camera on tripod
- Set the lens to manual focus.
- Turn on the liveview.
- Since the fireworks were shoot from the ships, so I aim at the ship.
- Magnify the image on the screen as much as possible by pressing the + button on my camera.
- Turn the focus ring back and fro until I believe it is the right focus. (glad that there were lights on the ship)
- Shoot the fireworks with remote shutter.

When I shoot the moon, I use the same way. But I use the craters on the moon for focus reference.

TCampbell · Oct 26, 2012

Don't auto-focus. Landscapes can work a bit differently.

Landscapes are typically high focal ratio shots with very broad depth of field. Set your camera to f/16. Calculate the hyper-focal distance (lots of websites have calculators. You can download a calculator for your smartphone if you have one -- lots of these are free and there are some paid apps as well) for f/16 and the focal length you're using (wider is better -- it naturally has more DoF). Manually focus the camera to that distance and take the shot.

Note that if there's a breeze, then you're going to get some tree leaf & branch movement and in a 30 second exposure that _will_ show up as motion blur.

Example: Suppose you're using a 20mm focal length. Set your aperture to f/16. The hyper-focal distance for f/16 & 20mm on a Canon APS-C body is 4.38'. Turn off auto-focus, adjust the lens to about 4.38' (4.5' or even 5' is close enough). Meter, dial in the shutter speed, & take the shot.

I used DoFmaster.com to come up with the numbers: Online Depth of Field Calculator

480sparky · Oct 26, 2012

TCampbell said:
........ Turn off auto-focus, adjust the lens to about 4.38' ..........

How does one do that on today's lenses that don't have a focus scale?

Derrel · Oct 26, 2012

Never focus at 4.38 feet for a distance shot. Everything except stuff at about 4 feet to 5 feet will look like crap. Seriously. Hyperfocal distance focusing is not all it is cracked up to be. Theory and practice do not agree many times. This is one of those times.

ronlane · Oct 26, 2012

Thanks for all the help. I will have to get up in the morning and go out and try it again.

TCampbell · Oct 27, 2012

Derrel said:
Never focus at 4.38 feet for a distance shot. Everything except stuff at about 4 feet to 5 feet will look like crap. Seriously. Hyperfocal distance focusing is not all it is cracked up to be. Theory and practice do not agree many times. This is one of those times.

Have more faith in math. When lenses get wide, the DoF can get really deep. I've got a 14mm wide angle that you basically get to dial to 3' and not bother to focus... everything is in focus (including at f/2.8). When I first got that lens, I recall reading a tip that it could be used like that. I seriously questioned the article and wondered "could this really be true?" I had to test it and see for myself. Yep... it's true.

With a reasonably wide focal length (I just picked 20mm as an example) and a high f-stop (f/16) the DoF is really deep.

Here's an example of it:

This is using the EF 14mm f/2.8L at f/9. It's probably focused to about 3'. Look at the blades of grass in the foreground. Look at the tree leaves in the background.

Martha-Mary Chapel by Tim Campbell1, on Flickr