Confused about infinity focus point - EP1 kit zoom

Djarum · Jul 6, 2010

So my gf and I went out to watch the local fireworks show. Of course I brought along my camera and tripod. I don't have a cable release, but I figured I could give enough on the timer delay for some decent shots. Two problems cropped up. The first is unrelated to the camera. A tree was basically in the way. We had no idea where the fireworks were going to be from, so most of my pictures have a tree or cropped top of a tree in them. Location was important, and we though we were in a good one. We had no idea what type of fireworks and the exact spot that they were going to be lit from.

The second issue is focus point. Everything I had read is that setting the focus point ot infinity should be suffecient. Most of the pictures look a tad out of focus, and I noticed maybe why. If I turn the camera off and back on with reset lens set to on, the lens should be set to focus at infinity. But if that were the case, then why can I turn the lens ring toward infinity, and objects within the frame go slightly blurry(and I can here the focus movement in the lens). I guess what I mean is, if I turn the camera on and off with reset lens on, the camera actually has the focus point set to somewhere between rotating the ring all the way left and all the way right. Is this truly infinity?

Secondly, is my assertion correct about fireworks? Should the focus point be set to infinity? Almost toward the end of the show, I manually focused on the fireworks as they were going off, and got two that were slightly sharper than the rest.

photoSmart42 · Jul 6, 2010

One of the problems with electronics lenses lacking focus markings is the uncertainty of what happens to the focus point upon reset. I'm not sure we know exactly what these lenses are supposed to be doing when you reset them.

As for the focus point on fireworks, it depends how close you were, and what aperture setting you had. Most people focus to infinity then back slightly off for these situations. IMO manual focus is the best solution. Also try to have a smaller aperture so you can catch more of the fireworks in your image. A large aperture means shallower DOF, so it may have contributed to your focus issues.

Djarum · Jul 6, 2010

Well, the I keep the reset lens setting to ON, which is supposed to reset the lens to infinity. I'm not sure if its doing that or not.

I kept the aperature at f5.6. with the shutter at shutter speed between 2.5 and 3.2 seconds. I had it at f4, but the whiter fireworks were overexposed. I tried f7.1, and some were too dim with the streaks I liked. It just seemed like a focus issue. I had manual focus on, but I was relying on the camera lens reset, which may not be working right.

squeegee · Jul 6, 2010

I'm not sure if "reset" is "reset to infinity", it might just be reset to some other distance.

Having said that... based on what little I know...

1) for fireworks way out there, yes you will be focused at infinity so the easiest way would be to prefocus on something absurdly far away (then change it to manual focus so it doesn't refocus every time you press the shutter) as I'm guessing it won't focus fast enough when the fireworks go off.

2) I also read that most lenses can focus "past" infinity which is might be what you're talking about. I don't know if these are all true or not but the reasons cited include manufacturing tollerances between every camera, they need to allow it to go just a bit further in case some one elses mount/camera isn't exactly down to the same nano metre as yours. The other reason I've heard of is temperature. Basically you know how metal expands and contracts in heat and cold, (allegedly) this can be significant enough to change the focus, so the lens needs to be able to go beyond infinity because infinity changes depending on the expansion and contraction of the lens materal due to temperature. etc..

of course I maybe all wrong about the above, just stuff I'd previously read online. *shrugs*

Djarum · Jul 6, 2010

According to the manual, it is reset to infinity.

I'm going to do some experimenting to see if this setting actually works or not.

I was pretty close to the fireworks. However, point sources of light do focus differently.

And yes, focal length of simple lenses can change as the glass heats or cools, and I would imagine this to be the same with a kit lens like this.

sparklehorse · Jul 6, 2010

I wouldn't count on the "reset lens" function accurately resetting to infinity. What I did on my E-P1 for fireworks is map auto focus to the AEL/AFL button, then set the camera on manual focus. Once set up on the tripod, I point the camera at a distant building, or anything a couple hundred feet or more away, then hit the AEL/AFL button to force an auto focus. Done. Now I'm focused at infinity and ready for the show. For fireworks I've found a smaller aperture, like f/8 at ISO 100 works well. Typical shutter speeds are going to be 10 sec to maybe 20 sec or more. I'll make test shots before the fireworks start to determine exposure, then keep checking my shots and make adjustments as I work. A good technique is to use a cable release & trip the shutter as soon as you hear the boom of the lift charge. An exposure of 10 seconds or longer should capture the entire flight and blossom of the shell.

Like you I happened to pick a poor spot this year: