Old 05-13-2004, 04:29 AM   #1
arkansasrailroader
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Default Infinity focusing with digital

I used to leave my digital camera's focus set to infinity (Sony Cyber-Shot DSC-V1). While I usually leave my zoom set to the widest angle, I noticed that when I did use the zoom with the focus on infinity that the shots would be out of focust slightly. I turned the auto-focus back on and now the zoomed shots are in sharp focus. Is this a problem with just my Sony or should infinity focus be avoided?

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Old 05-13-2004, 09:10 PM   #2
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Well, not everything is going to be at infinity all the time, and depending on the focal length of the lens in use, the distance at which the lens is considered to be focused at infinity will be different.

In addition, you're giving up a great deal of depth of field by focusing at infinity. If you want to set the focus and shoot, try to find out what the hyperfocal distance of the lens on your camera is at a given aperture and set it there. This is what these journalists do that seemingly blindly aim their cameras while taking pictures. By using wide angle lenses, and stopping down to small apertures, they get an immense amount of depth of field. The markings on interchangable lens barrels (provided they have them) allow for a photographer to quickly determine depth of field and hyperfocal distance at a given aperture by referencing those marks. No marks? Not really a problem as the hyperfocal distance can be calculated. There are numerous calculators for doing that on the net.

I'm probably going to give a crappy definition of what hyperfocal distance is, so I'll just provide a link.

http://dfleming.ameranet.com/hyperfocal.html

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Old 05-13-2004, 09:32 PM   #3
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Great advice and article! Thanks. Carrying out some of that advice ought to be relatively simple.

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Old 05-20-2004, 02:56 PM   #4
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I don't think there is a "universal" answer to this question. It depends on what type of camera you're using. I use a Nikon Coolpix 5700. I found that most trains move faster than the autofocus can react. The result is that the front of the train is usually past before the camera finally decides that the subject is in focus and lets me take the photo. The manual even says that the autofocus is not recommended for fast moving subjects. I leave the focus set on infinity unless I'm taking a close-up photo of a still subject.
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Old 05-31-2004, 03:58 AM   #5
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Default Re: Infinity focusing with digital

It is also possible that infinity is out of focus. I was trying to shoot some airplanes in the air over my house the other day and noticed that infinity was too much focus, and that to get a sharp picture, I had to back off just a bit.

....I noticed that when I did use the zoom with the focus on infinity that the shots would be out of focust slightly....
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Old 10-29-2004, 04:10 AM   #6
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Default Infinity Focus

Does by chance anyone else have a Gateway DC-T50 camera? It seems though, my camera isn't the only one with the similar problem. I tend to get better shots on infinity focus because most of my shots are taken at more than 25 feet, and usualy in motion. With the auto focus on, it can be extremely difficult to get a shot at the "right time". I noticed that the majority of the shots I have taken on both infinity and auto, come out the same. It's unfortunate, that there is only one lens to use, and certain photos that may require a specific lens for the shot is not available. I have tried everything to gain clarity in the background, and it seems impossible. Overall, the general clarity produced with this camera in any distance, sucks. See link. This shot was taken on a tripod, and the train at a standstill. Out of 6 shots, this is the absolute best, altering auto, and infinty focus, and three shutter settings. This particular shot was set on auto, at a range of about 50 yards, F=3.5 speed=25 zoom=80%. It was a rainy day, and the sun was close to set.

http://www.geocities.com/mmetalhhead/bnsf.jpg
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Old 10-29-2004, 02:07 PM   #7
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A Gateway camera?? Is your computer from Nikon?

I'm sure a lot of the simpler digital camera have lens that focus "past" infinity, similar to mirror tele lenses. This takes care of any expansion/contraction due to temperature.

What you will have to do is take a number of pictures of a distant very detailed object (of course, a test pattern of fine parallel lines would be best) with your camera set at very small (reproducable) increments at and just short of the infinity setting.

Very closely look at these images under high magnification to determine which is the sharpest, and use that setting for infinity.

With non-DSLR digital cameras, the size of the CCD imager is very small, thus making the "normal" focal length lens very short. The good thig about this is that the depth of field is very great with these cameras (they make great cameras for shooting models). With bright sun, you should be able to get everything in focus from about 11 feet to infinity. If you are not, make sure you shutter speed is high enough. For a moving train you MUST be able to control the shutter speed. Use the camera in shutter priority mode.

I don't know about Gateway cameras (other than they didn't make it, but bought it from someone else), but some cameras used in auto mode could be shooting pictures at 1/60 of a second ... not gonna stop the train's movement.

I went to the Gateway website, and they do not offer any cameras under their name, only digital cameras from Canon, Nikon, Sony, etc.

Only one camera, the digital rebel, is a DSLR. The others are a great variety of digitals from about $200-900. The cheaper ones you can probably not use in shutter priority mode.
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Old 10-29-2004, 03:46 PM   #8
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Default Re: Infinity Focus

Quote:
Originally Posted by mtrails
Does by chance anyone else have a Gateway DC-T50 camera? It seems though, my camera isn't the only one with the similar problem. I tend to get better shots on infinity focus because most of my shots are taken at more than 25 feet, and usualy in motion. With the auto focus on, it can be extremely difficult to get a shot at the "right time". I noticed that the majority of the shots I have taken on both infinity and auto, come out the same. It's unfortunate, that there is only one lens to use, and certain photos that may require a specific lens for the shot is not available. I have tried everything to gain clarity in the background, and it seems impossible. Overall, the general clarity produced with this camera in any distance, sucks. See link. This shot was taken on a tripod, and the train at a standstill. Out of 6 shots, this is the absolute best, altering auto, and infinty focus, and three shutter settings. This particular shot was set on auto, at a range of about 50 yards, F=3.5 speed=25 zoom=80%. It was a rainy day, and the sun was close to set.

http://www.geocities.com/mmetalhhead/bnsf.jpg
Some cameras in general are poor performers in low light conditions. You may want to read this review about your camera: http://www.steves-digicams.com/2004_reviews/t50.html
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