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Old Aug 24, 2003, 8:13 AM   #1
TG
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Default Safe Shutter Speed

With the 10D & 300D having a effective focal length 1.6x do you have to adjust you shutter speed to suit? With film photography a minimum safe hand held shutter speed was 1/focal length. EG 300mm lens (no IS) would be 1/350 sec, with a 10D 300mm would be 480mm so do you have to adjust yor safe shutter speed to 1/500 sec? I do not own a digital SLR and I am looking at getting a 10D or a 300D when I have saved enough cash. I do own a EOS 300V and a PowerShot A70. I have posted this topic on another site and have recived mixed answers.
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Old Aug 24, 2003, 11:33 AM   #2
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IMO I don't think so, but I could be wrong... The 1.6x is internal crop to the camera, and not a multiplier of the focal lenght!

Just think of it this way: if the 300D/10D were a full-frame dSLR the same lens would have filled up the whole film chamber; however the sensor for theses cameras is smaller hence it only captures a smaller area effectively reducing the angle of coverage of the lens -> an effective 1.6x increase in focal lenght. 8)

The real focal lenght of the lens hasn't changed (and so is the focal plane)! ie 1/350 sec in the above example should still apply :? :? :?
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Old Aug 25, 2003, 2:31 PM   #3
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NHL, there is another school of thought on that that says you need to apply crop factor to the old 1/mm rule and use "effective 35mm focal length." Maybe I can make it clear with an example.

Start with a 35mm film camera and 50mm lens. Apply an angular motion to the camera of 68.75 degrees per second. With a 1/60 exposure that makes for 1.145 at the film plane or 1mm of blur with the 50mm focal length. Enlarge that 24x36mm frame to 8x12" and the 1mm blur is now 8.46mm.

Take the same shot with the same lens, same motion and same 1/60 exposure but with a DSLR body with a 1.6 crop factor. You'll get the same 1mm blur at the film plane but since the film plane is smaller it has to be enlarged more to make the 8x12" print so the blur is now 13.46mm. Apply the crop factor to the shutter speed and you'll get an effective blur the same as the 35mm camera.

It makes sense when you put it in terms of digicams with tiny CCDs and ultra small true focal lengths. We still use the effective focal length for safe shutter speeds so there's no free lunch.
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Old Aug 25, 2003, 2:53 PM   #4
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Padeye, this is good...

I'm unsure myself: Let's see if we can reason it out! Let takes a 300mm lens and mounted on the 1Ds, it'll take a full frame. Now let's do the same on the 10D... the image put out by the same lens on the 10D did not change @ the film plane (the peripheral area outside the sensor just got dropped right?).

Any enlarging is only an artifact created by the smaller sensor. This is very much like an image which is cropped and enlarged again (similar to digital zoom), but is done after the smaller image is already captured, ie the 1.6x is after the fact. The movement of the smaller sensor is relatively constant in relation to its larger full-frame cousin... This is why there's a benefit realized in smaller sensor as well since it uses only the best middle part and not the peripheral!

Now if the 1.6x factor applies to the focal lenght (which will affect the speed formula) then the resulting image would have been bigger and would have the same bad parts of the lens in it as well shouldn't it (and the movement amplified as well)? :? The 1.6x is really good for people shooting long (they have their cake and eat it too)... It's the folks @ the wide who'll suffer (one tries a pano and the camera clip off both ends!). It's all the fault of the viewfinder! :lol: :lol: :lol:
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Old Aug 25, 2003, 7:45 PM   #5
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To simplify it think of blur movement as a percentage of the frame size. If the blur displacement is 1mm with a given lens/shutter speed/camera shake condition that's 2.7% of the long dimension of the frame. With a 10D sensor that 1mm is 4.4% of the long dimension.

Looking at it another way the "200mm equivalent" on a dimage 7is really 50.8mm. If you try to shoot at 1/60 hand held you're likely to get motion blur unless you're very steady. You're better off shooting 1/180 or above just as you would with a 200mm lens on a 35mm film camera.

The angle of view is what's important. It is just a lucky coincidence that the 1/mm rule works out for 35mm cameras.

Non-availability of super wides at a reasonable cost has kept me away until now. If I can get the equivalent of my 24mm Nikkor at a reasonable cost I'll make the plunge.
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Old Aug 28, 2003, 11:43 AM   #6
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why bother...and let the shutter speed rules your shooting?...knowing the facts is good, in general you will avoid mistakes. Let the result of the picture decide how do you want to handle your shooting. If DOF is important for your picture, when using long telephoto lens, the only insurance you have is to use the tripod if you don't want to take risk. Apply the shutter speed rule to handheld shooting if you don't have any other choices...cheers
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Old Aug 29, 2003, 4:05 AM   #7
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tuanokc,

My question was specificly about hand held photography and how the 10D/300D effective focal length of 1.6x related to the lens and shutter speed. There are situations when a tripod is not suitable EG when I shoot motorsport (hand held or a monopod) and use a slower shutter speed (1/350 or slower) in order to blur the wheels to give your picture the look of motion.

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Old Sep 15, 2003, 12:55 AM   #8
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The shutter speed has nothing to do with the crop factor. But hand holding with a slow enough shutter speed probably would require a Canon IS lens & they do a wonderful job.
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Old Sep 15, 2003, 4:49 PM   #9
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I'm fascinated by these type of posts. While I have heard of these types of "rules of photography" they seem less important in this day and age where we can take a picture. Look at the results often with 10x zoom to check for focal quality and then adjust the settings on the camera to compensate for the results. These rules were designed before IS lenses, before photoshop, and before we had instant results. I always shoot first and then if the picture has problems I then think of the rules. And I know many of you will say "sometimes you only have one chance for the shot". For me that is rare and any time that is the case I shoot test shots in preparation.

Don't get me wrong. I am an amateur photographer and I've never had any formal training so I can only speek from a practicle position.
I also enjoy learning from many of the photographers on this site. I have learned a lot from all of you.

thanks!
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