I searched and couldn't find any topics on the following questions.
I understand the "basic" rule of avoiding camera shake. 1/ (2 times the focal length). Some would argue that; but I don't want to get into that.
My 10D is arriving on Mon the 15th!
How do you account for camera shake with the 1.6x factor of the 10D?
Do you calculate on the 50mm lens that is on the camera or do you calculate on a 80mm; thus accounting for the 1.6x?
--I guess I don't understand the 1.6x. Is the cmos sensor only using part of the lens' optics?
In other words if the cmos was a screen, the lens would be projecting an image bigger than the screen but because of the size of the screen it only picks up part of the projection; thus it is capturing what a 80mm lens would see and not the whole projection of the 50mm lens. This my interpretation of how it works; that it is a crop and not a magnification.
If the above is true, then one should calculate on the 50mm because you are still at that focal length just only seeing part of the image.
Hope this isn't confusing. Or I'm just confusing myself and making this too complicated.
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
I try to double the recommended 1/focal length as shutterspeed, so that it is roughly 1/2xfocal length. My reasoning is this: while the 1.6 crop is actually the equivalant of a smaller section of a 35mm frame, the fact is that the 10D/D30/60 etc frame then gets treated as if it were a full 36x24mm frame, rather than a roughly 22x15mm frame. In other words, you might go for an 8x12 from either frame, which means that the smaller frame is blown up to a greater degree. Therefore, the blur that might be present on the 36x24 frame would be less noticeable than that from the 22x15 frame.
This is also what is "disappointingly soft" about the digital images when new users first look at them at 100% on the monitor. The circles of confusion in the two frames are the same size, but the greater enlargement of the smaller frame when printing the two frames at the same size means that the smaller frame will look softer. Same with the motion blur, so up the shutter speed to compensate.
Also, remember that this rule of thumb says nothing about your camera holding technique, how much coffee you've had, your strength, concentration, etc.
All that taken into consideration, you'd have to pry my Image Stabilization lenses out of my dead hands...they really increase the likelihood of sharper images at a given shutterspeed.
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
I see that there are two layers to your question. I will answer them in a rather ornate way.
First, the matter of the "1.6" factor. You certainly have the basic idea right. I'll unfold it in a bit more detail.
The sensor on a 10D is smaller than the film frame on a full-frame 35 mm still camera. A lens of a certain focal length will take a certain "amount of scene" and make from it a certain sized image at the sensor (or film) plane (bigger than the sensor in all cases - the famous "image circle"). The amount of scene whose image fills the sensor is essentially the "field of view" of the camera. If camera B has a smaller sensor than camera A, then for a certain focal length lens, the amount of the scene captured by the full sensor of camera B will be less than the amount of scene captured by the full sensor of camera A. Thus, for that focal length lens, camera B will have a smaller field of view than camera A.
Unfortunately, since many photographers have spent much of their shooting careers shooting with a full-frame 35 mm camera they have gotten to know what focal length lens will produces what field of view on such a camera - what focal length is best for a certain situation. When they start using "camera B", they want to know, "What focal length lens do I need on my camera B to give me the same field of view as I would have gotten with a 40 mm lens (for example) on my 35 mm camera."
The answer is 40 multiplied by the ratio of the size of his camera B sensor to the size of the film frame of the 35 mm camera - a ration of about 0.63. Thus, a focal length of about 25 mm will do that job for him.
But usually we see this math set up in the opposite direction. We say, "I have a 25 mm lens on my camera B. It will give me the field of view that I would get with what focal length on a 35 mm camera?" Well, to do that, we divide 25 mm by 0.63, and of course get 40 mm. But we usually don't say it that way either. We say, "take the focal length of your lens, 25 mm, and multiply it by 1.6 to get the focal length of the lens which, on a 35 mm camera, would give you the same field of view you have with your lens on your camera B - namely, 40 mm." In this case, we say, for short, that "the 35 mm equivalent focal length of this 25 mm lens, when used on my camera B, is 40 mm."
Now to the shake criterion.
The shake criterion is based on the assumption that the shake we humans give our cameras produces, at peak, a certain rate of change of the aiming angle of the camera (a certain angular velocity). The amount of displacement of the image on the sensor is proportional to the product of that (assumed) peak angular velocity, the exposure time, and the focal length of the lens.
This is why a rule of thumb based on a minimum exposure time inversely proportional to the focal length works.
But the impact of that displacement must be judged by the fraction of the image size that the displacement represents. A displacement of the image by 0.01 mm would be inconsequential on an image 100 mm wide, but quite serious on an image 10 mm wide. (One way to look at this is that the smaller image would be magnified 10 times as much to produce the same size print for comparison, and thus the blurring caused by the displacement would appear 10 times as large.)
So the rule of thumb has "built into it" an assumption about the size of the image - normally, that it will be 36 mm wide (a full-frame 35 mm situation). (We never hear that.)
If we have a sensor whose size is 0.63 that of the 35 mm camera, the impact of the presumed maximum angular velocity of the shake over a certain exposure time would be 1/0.63 (1.6) times as great. (Again, we can just realize that this image will need to be magnified by 1.6 times as much to produce the same size print, thus enlarging the displacement.) Therefore (assuming we believe the rule of thumb is valid in a 35 mm environment), to carry it to our camera B environment we need to use a maximum exposure time that is 0.63 that which would be the recommendation for the 35 mm case.
But of course another way to do this math is to just multiply the focal length by 1.6 before we take its reciprocal to get the maximum exposure time. If our rule in the 35 mm case is to not use a shutter speed faster than 1 divided by the focal length (for example, for a 100 mm lens, 1/100 sec), we now should say that the shutter speed limit would be 1/160 sec.
So, to (finally) answer your queation, yes, it is reasonable, when applying the rule of thumb for minimum shutter speed, to use the "35 mm equivalent" of the focal length of the lens involved.
Best regards,
Doug
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
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I had to read your post slowly, and a couple of times. (No offense)
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Oh, no, I understand. It was a very elaborate explanation, and I knew from your post that you didn't really need that, as it seemed that you were certainly already well on the right track, but that's how I work!
This stuff is fun, isn't it?
Best regards,
Doug
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
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