Focus Issues

[Krystal]

Hello,

I have a few questions on focus issues. First I was wondering if someone could give me tips on focusing on subject at night. I just recently started experimenting with night photography, and of course when there is not enough light the auto focus doesn't work, but also hard to see if subject is in focus on manual setting when it is hard to see it.

Also for some reason I'm still having problems with my DOF, and pictures out of focus. I have tried the rules of hyperfocal distance, and even have a card I carry to refer too. When I first started photography I was setting aperatures at f22 and higher, and someone told me that may be why I'm not getting clear pictures due to refraction issues. So I have been trying to keep my aperature closer to F16 and F11. I always use my mirror lock-up for slow shutter speeds, below 60, but sometimes below 30. I do have IS on both my lenses, and sometimes wonder if it makes a vibration to cause my photos to be out of focus. Sometimes my entire picture isn't in focus. I use my timer on the camera wtih slow shutter speeds, along with the mirror lock up.

I would appreciate any tips on these issues as it gets frustrating. Also I do use a tripod most of the time, and these issues happen even with tripod.

Example...My subject is about 30 feet away, and I want everything to be in focus from about10 feet in front of subject to infinity. My focal distance is 70mm, and I'm using a lens that is 28-135mm. Where is my focus point? I have tried everything, and do get a shot that is crisp sometimes. Thank goodness I take a lot of the same shot. The thing is if your subject is already really far away do you just focus on that? Lets say 70ft or farther? Also when using a higher zoom lens with closer shots do you need to have higher aperature settings?

Thanks for any input. Hope this makes sense.

Krystal

[kencaleno]

you should have a light in the viewfinder that shows when focus is spot on-If you are on a tripod turn off IS/VR fuction or lens will try to combat camera shake that doesn't exist,resulting in blurred images. Your focus point for 10 ft to infinity is 20 ft. Below is a chart of hyperfocal distances on 18-55 and 70-300 lenses- (Half the distance from focal point to as far as you can see):

[Krystal]

Thanks, I was wondering about the IS function and the tripod. Wouldn't that be great if it is my problem.

[irieness]

Having a good tripod for your heavy lens is essential. A zoom with a so so tripod might buckle and start to shake with a little wind. You can check if that is an additional cause because kencaleno gave great advice.

[OsmosisStudios]

Your focus POINT is your subject: your depth of field is in the chart Ken has provided.

[kencaleno]

Originally Posted by OsmosisStudios

Your focus POINT is your subject: your depth of field is in the chart Ken has provided.

Your focus point is not your subject-your focus point is the hyperfocal distance,as per chart,for instance you have a person 10 feet away from you,and you want the depth of field to be from just in front of you,to a point in the far distance:
- aperture at F11
- focus at 5 ft
-All will be acceptably sharp from 2feet 6 inches to as far as the eye can see. The chart gives that hyperfocal distance (Focal point) Regards, Ken

[inkista]

Ok, just a tiny detail, but if you're using a DoF chart, make sure that it's one that's calibrated for the sensor size you're using. If you're shooting full frame and the chart is for 35mm film, you're fine. But the numbers will be off if you're using a crop body (this is also why using a DoF scale on the lens to set hyperfocal distance may not work, darnitall). I'd highly recommend grabbing a DoF calculator from dofmaster.com, especially if you habitually carry a handheld PalmOS device or an iPhone.

As for IS and the tripod--it depends on what generation IS you've got. If you're using the 18-55 IS lens, though, it should be ok to leave it on while using a tripod (and for panning); it's a fifth-generation IS lens, while I think it's only the first and second generations that can't detect tripod use.

[kencaleno]

Originally Posted by inkista

Ok, just a tiny detail, but if you're using a DoF chart, make sure that it's one that's calibrated for the sensor size you're using. If you're shooting full frame and the chart is for 35mm film, you're fine. But the numbers will be off if you're using a crop body (this is also why using a DoF scale on the lens to set hyperfocal distance may not work, darnitall). I'd highly recommend grabbing a DoF calculator from dofmaster.com, especially if you habitually carry a handheld PalmOS device or an iPhone.


As for IS and the tripod--it depends on what generation IS you've got. If you're using the 18-55 IS lens, though, it should be ok to leave it on while using a tripod (and for panning); it's a fifth-generation IS lens, while I think it's only the first and second generations that can't detect tripod use.

Chart is one I made for 1.5 crop lenses regards, Ken