"One over focal length" rule, what iso?

[hhyndman]

So...
I recently got a canon 75-300 lens, and took it on a trip to the zoo (nothing moving too fast). I was kinda setting the shutter speed to 1 over the focal length, with mixed results.

I had the iso set to 100 for mist of the pictures, would the rule work better if I was using 400?

Or do I just need to find a wall to lean against ?

[roanjohn]

most definitely..............use high ISO to get your shutter speed up. The faster the better - especially at 300 mm. I would probably use ISO 800 on some cases.

Ro1

[CyberDyneSystems]

...but only push up the ISO to get the faster shutter speed,. if you allready have a fast shutter at 100 or 200 ISO bumping the ISO up will make things grainy :)

For a 300mm you would be looking for 1/400 - 1/500 sec shutter hand held. (because of the focal lenght multiplier..)

So try to keep a fast shutter,. if the available light won't let you go to 1/500,. boost the ISO untill it does..

[RichardtheSane]

I would have said that usinf the 1/(focal lengh) would give exactly the same results at ISO 100 as it would at 400.

At ISO 100 a shutter speed of 1/350th of a second would give the same camera shake as if it was ISO 400. Do you shoot in AV mode or TV mode

If you are looking to increase your shutter speed, and go faster than 1/(focal lengh) then upping ISO is the best way to go.

What sort of mixed results are you getting? It has been difficult to advise as we don't know this...

[CyberDyneSystems]

You said it better Richard.. The point is to push the iso IF you can't get enough light to get the shutter speed you are looking for...

You can increase shutter speed by opening the aperture farther,. or by increasing ISO.

Can you check the EXIF data to see what shutter speed you were actually taking photos at?

[hhyndman]

I would have said that usinf the 1/(focal lengh) would give exactly the same results at ISO 100 as it would at 400.

At ISO 100 a shutter speed of 1/350th of a second would give the same camera shake as if it was ISO 400. Do you shoot in AV mode or TV mode

(I was shooting Tv)

When I think about it, of course you're right. If i'm setting the shutter speed based on the focal length, it doesn't won't matter what the iso is, the shutter speed is the shutter speed and that's why i'm getting camera shake.

I was looking for a way of judging what shutter speed to set for a given focal length to minmise shake, and that must depend on focal length (I should be able to use a higher shutter speed with a higher iso).

So, I guess the question is what is the rule?

1 / (shutter speed x (iso/100)) :?:

[robertwgross]

The rule is that you probably do not want to shoot (handheld) with a shutter speed slower than the reciprocal of the lens focal length. In the case of a typical digital camera (with 1.6 factor), then use the effective focal length and take the reciprocal. It has nothing to do with the ISO.

This is just a rule of thumb for how fast the shutter must fly for you to avoid blur in the image due to camera shake.

Now, if you can lean against a wall, you can shoot slower than this and get away with it. If you've been practicing for a long time, you can shoot slower than this by using body techniques, like holding your breath, careful squeeze of the shutter button, posture, etc.

---Bob Gross---

[hhyndman]

By George I think I've got it

:oops:

Thanks all.