Using non IS canon Lenses

Iron Flatline · Jan 22, 2007

Big Mike said:
Lets think about it in terms of the size of the movement. Lets say that the camera/lens shakes 1/16" during exposure. That is a small fraction, compared to the size of a 2.5x2.5 negative...but it's comparatively a much bigger movement to a APS-C sensor. So would that movement cause more of an effect on the smaller surface? Does that argument have any validity?

No, lemme see if I can explain that.

Let's say the camera shake is a pencil mark on a piece of paper. In this case the pencil mark will still be a quarter inch long, regardless of whether the piece of paper 8.5x11 inches big, or 13x19 inches.

It is not comparatively a much bigger movement - it is the exact same movement!

In the case of camera shake, the piece of film or sensor at the end has no meaning to what is happening to the light on the way into and through the camera - just how big an area of the whole image is ultimately recorded.

Big Mike · Jan 22, 2007

I think I see what you are saying...but let me try this...

The pencil mark is 1/4" long...and we photograph it with a MF camera..and a APS-C DSLR...with the appropriate focal lengths. The pencil mark on the piece of film may be 1/32"...but on the smaller sensor the mark would be smaller...say 1/128" (I'm just using numbers here, not calculating).

So although the mark is the same size...it's a different size on different film or sensor sizes.

So the same camera shake will move the 1/32" mark...say 1/128" on the film...and it will move the 1/128" mark, 1/128" on the sensor.
So the mark on the sensor has been moved/blurred an amount equal to it's length...while the mark on the film has only been moved 1/4 the distance of it's length. Would that not make the mark on the film...appear to be less blurry?

:scratch:

Iron Flatline · Jan 23, 2007

You got it, BUT you made a false assumption. You used the phrase appropriate focal lengths. It is THE SAME focal length, all you're changing is the size of the sensor. The lens remains the same, the amount of light remains the same, the distance from subject to lens to sensor remains the same... all that changes is the sensor size.

Heck, you could have a sensor the size of a laptop screen, and one the size of a business card. Now shine a fat beam from a flashlight at them through your reading glasses. The light passing through your glasses is still going through the same amount of glass, just onto differently-sized surfaces.

It's the same thing, just the light spot on the business card may be going beyond the card's edges. It's cropping the captured data.

Big Mike · Jan 23, 2007

Ya...I guess my logic was a little faulty...I was already assuming my rule of different focal length rules for different sensor/film sizes...:scratch:

I guess I could do some real world tests...but I probably won't. Someone must have tested this somewhere.

Orgnoi1 · Jan 23, 2007

Its really pretty easy... crop is NOT magnification whatsoever right? Well lets do this without a camera... make a circle with your thumbs and pointer fingers... so its about a 4" diameter... and move it around at arms length... not make that smaller..say touching the pointer finger and thumb only on the same hand... hold that out arms length... the amount of movement does not change the amount of shake does it? The length of distance between the sensor (film plane) and the end piece of glass does not change because the sensor is smaller... the only thing that happens is the edges are missing (cropped)... so your movement is your movement is your movement...

Iron Flatline · Jan 24, 2007

Mike, what you're thinking about is this: if you photograph something and shake while doing it, the movement is the same amount, regardless of sensor size. HOWEVER: if you print both of those out on a 5x7 card, the image shot with a smaller sensor will show a bigger movement. That might be the confusion.

Big Mike · Jan 24, 2007

Ya, that's exactly what I was getting at. The smaller sensors/film need more enlargement to get to the final output...so therefore the the blur/movement is also enlarged.

So if our final goal is a 5x7 printed image, with either camera...wouldn't you want to (or need to) use a faster shutter speed with the smaller sensor?

Orgnoi1 · Jan 24, 2007

That would really depend on what you are trying to get out of the image... if you have two cameras say for argument sake the Canon 30D and 1D Mark II... one is 1.6x crop... the other 1.3x crop... if you were taking only a small portion of the image that both sensors can see (say a small 100% crop) then there would be no need in shutter speed differences... the only reason you would possibly... and I use that term loosely because honestly I am not sure I believe you need anything faster period... is if you are using those same two images without cropping them... you would have to blow up the 1.6x crop further so you would be inducing blur because you are stretching the image slightly more... but shutter speed isnt necessarily the cause... or the fix there...