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Old Sep 3, 2005, 2:58 PM   #1
dlw
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I'm using a Canon 75-300 is USM on my Rebel XT and when taking shots of objects on a long telephoto, I'd like to try to have everthing in focus as much as possible. I've tryed a lot of settings, experimenting with f stops, etc, but the lens lets you use a very limited range. Any suggestions, other that a new expensive lens? Thanks in advance!
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Old Sep 3, 2005, 8:21 PM   #2
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Here are some options, not all of which should be needed, but every one of which, by itself or in combination, can help:

Use a tripod, increase the f-stop, use depth of field preview, increase the ISO, and use software noise reduction in the post-processing to reduce the effects of the high ISO (e.g. 1600), shoot in bright sunlight, minimize the range of distances in your picture (don't let nearby objects get into your picture as well as very far ones), ignore the blurring of non-critical objects.


Edit: What the heck was "combatination"? - changed to "combination". Must be getting feisty.
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Old Sep 3, 2005, 10:04 PM   #3
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Madwand, thanks for the supply. Will increasing the ISO allow the f stop increase? I think that's what you are saying and I'll try that tomorrow. I'm usually just using 200 ISO and the maximum f stop available then just doesn't seem to help that much.
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Old Sep 3, 2005, 11:04 PM   #4
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Yes, increasing the ISO increases the light sensitivity, so you can increase the f-stop, which reduces the amount of light coming in. You'll get one more f-stop for every doubling of ISO.

Using the sunny-16 rule, you should be able to shoot at f/16, 1/ISO - bumping the ISO to 400, together with IS, should be enough -- shooting at shutter speed 1/400. Of course, thiswould bebetter with a tripod -- you wouldn't have to worry about shake from the speed dropping further, and could go to f/32.

It might be useful to play with an online DoF calculator here.

http://www.dofmaster.com/dofjs.html
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Old Sep 4, 2005, 10:17 AM   #5
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This is making some sense to me, but in searching I found this:
Quote:
sunny 16 rule that we used with film cameras. Set your aperture to f/16 and your shutter speed to what ever ISO speed you have your camera set to. This will give you perfect exposure every time.
OK. It is very bright & sunny out. I'm using a Canon 50MM 1.8 lens. In full auto mode, the camera selects 1/500 @9. If I go to manual mode and select 1/200 @ 16 (iso is 200) the picture is darker than in the auto mode. What is the correlation here?
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Old Sep 4, 2005, 12:46 PM   #6
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1/500 at f/9== 1/640 at f/8 ~ 1/800 at f/8 == 1/400 at f/11 == 1/200 at f/16.

By "==" I mean "is equivalent to".

By "~" I mean "is close to".

The sunny 16 rule is a good one, but of course it's an approximation. But your camera's reading is not necessarilyan exact reading either -- it's an approximation of the appropriate exposure values based on the reflectance of your subject and internal logic.

You camera is suggesting an exposure1/3 of an f-stop brighter than the sunny 16 rule. This is so close that I wouldn'tworry about it (I often use 1/2 stop settings, not 1/3 stop, so this might have rounded been down anyways). I'd fine-tune these things in post-processing anyways, as needed. When shooting, ifin doubt or otherwise, you should look at your histrogram (see elsewhere on how to use it).

If you want that 1/3 stop brightness increase, you can also add it back after raising the aperture. The important thing to realize is that for every shutter speed step increase, you can decrease the f-stop by one step, without affecting the exposure value.

One way for you to control the aperture without having to use the sunny 16 rule is to put the camera on Av mode -- this is Aperture Priority, which means that you set the aperture, and the camera sets the corresponding shutter speed based on its exposure reading (and ISO). Set it to f/16 or f/32, whatever, and observe the shutter speed -- if it's getting slow (roughly slower than 1/focal length- 1/300 for a 300 mm lens (and this is an old rule of thumb, before IS, so may be conservative, but may be not, considering how much we pixel peep and magnify these days)), then either back off on the aperture, or, better, use a tripod.

A tripod is generally better, because it is "rock" steady, not merely steady enough, and it also stabilizes you and lets you be careful about composition, image clutter, etc, and so reduces the chance of you making last second mistakes because you were doing too many things at the same time. Another thing that it's good for is to control flare -- light on the lens -- if your hands are free of the camera, you can both examine the lens to see if any light is falling on it, and also do something to shade it further if needed.

But if you're using the 50mm lens and not the 300mm, then you have a lot less to worry about camera shake because the lower magnification does not magnify camera shake as much.
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Old Sep 4, 2005, 1:33 PM   #7
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You can try Auto Exposure Bracketing (AEB). It's sort of like a tolerance level for light - usually you take one shot and get a certain lighting exposure. What bracketing will do is that instead of one shot you take three. The first shot will be the regular exposure. The second shot is a darker exposure. The third is a lighter exposure. After that, you just pick the one you like and delete the others.

It's in the menu bar. Just select it, and then set your tolerance level (i.e. 1/2 stop, 1 stop, etc.) This means the under and overexposed shots are going to be a 1/2 stop or 1 stop difference. Remember you need to take 3 individual shots of the same thing, so I'd suggest changing to burst mode if you're hand holding the camera. It's a lot quicker and easier that way. Just remember to turn AEB off when you're done (a fast way is just turn off the camera and then turn it on).
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Old Sep 4, 2005, 8:43 PM   #8
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Thanks for all the help, AEB has helped a lot, as have other suggestions. I spent as much time as I could on it today. The wife finally insisted that I do something "useful" so will have to get back to it later. So much to learn, so little time! Thanks again!
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