John, the physical (??) image produced at the back of the camera isn't enlarged by the crop factor, infact it isn't changed at all from one you'd get at the same focal lengths with 35mm. You're simply looking at less of the lens circle than you are with 35mm. Any movement induced by shake at 300mm will be the same on 35mm as it is on digital.

Since we're looking at a smaller portion of the resultant image, it's important that it's sharp, there's no point effectively enlarging something that isn't, but if I took the effective crop into consideration when taking photos I'd get a hell of a lot of frozen propellor blades taking ground to air shots at 1/640.

Yes I agree with you about the frozen prop. blades but my point about enlarging blur (due to camera shake) is, I believe still valid. To illustrate my point imagine a sensor measureing 1 mm x 1.5 mm and try blowing that up to A4. Blur due to camera shake would be magnified enormously.

John

John, I think the blur you're referring to in your example (and in the way you've interpreted camera shake) is wholly a factor of resolution rather than cancelling the effects of movement.

Wheeler, you have raised some doubts in my mind. I need to think about it. I will be back, eventually!

John, as I said earlier, I'll happily be proved wrong, it's just that I've not found this to be the case in practice. I regularly get away (only a fool tries to kid people that a hefty dollop of luck's not involved) with shutter speeds considerably lower than the 1/FL guidance suggests. If the crop factor really did come into play in this calculation then luck would be playing an even bigger part.

Not really, it's just that some people are much better at hand-holding than others.

Hello Wheelr, as promised I am back. This is how I see it although, like you, I stand to be corrected.

Suppose you take two pictures with the same focal length and from the same spot, one on 35 mm film, the other on a digital camera with a sensor measuring 15 mm x 22.5 mm. Providing that the same level of camera shake is common to both shots then the blur on both images will be identical. To obtain a 10 in x 8 in print the film image would need to be enlarged 8 times. However, the digital image would need to be enlarged about 12 times and the blur would, be magnifide 50 % more. Hence the need for a faster shutter speed to reduce the blur. There may be an exception to this which I have yet to think through. If when taking the digital picture you moved further away from the subject so that the field of view was the same in both cases, then the final blur on the print would be the same in both cases (Ithink) and there would be no need to increase shutter speed. The answer to the question thus depends on your standpoint (ha ha). I would be interested in your comments.

By the way I think it would need a hell of a lot of camera shake to equate to the blur produced by a revolving propeller blade.

John

I'll agree with that John, so I also agree with Duncans initial statement.

Ever one to chuck a rock into the pool, I think sensor resolution will also have an impact. ie D2Hs 4mp and D2X 12mp on the same sensor size.

Don

Duncan very informative and extremely well written.....Alex

I found these two pictures whilst having a tidy up. Thought they did a reasonable job of explaining the different effects of slow and fast shutter speeds. Fast shutter on the left, slow shutter on the right.

Duncan