shutter speed and focal length multiplication?

Mark G

Mark G

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Hi all,
A common way of working out what shutter speed to use as a lower is to use the focal length.
So 50mm is a 50th of a second and 200mm is 200th's of a second right?

So for this to work on a digital body with a cropped sensor do we have to take into account. The for the focal length multiplication?
So 50mm = 75mm so is it a 75th of a second
200mm = 300mm = 300th's and so on...?

Don't know if I've explained my question very well. Hopefully you'll understand.
 
No, since the focal length isn't affected, just the field of view is cropped.

ETA: The crop factor doesn't magnify in any way, so its not affecting the focal length, so the speed is the same, whether the lens is on a full or cropped camera.

Unnki.jpg
 
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You also need to remember it's a rule not a law. How slow you can hand hold a shutter speed depends on you, the weight of the camera and lens, weather condions such as wind as well as the focal length. You need to experiment to find out what your limits are .
 
VirtualAdept said:
No, since the focal length isn't affected, just the field of view is cropped.

ETA: The crop factor doesn't magnify in any way, so its not affecting the focal length, so the speed is the same, whether the lens is on a full or cropped camera.

<snip>
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Completely wrong I'm afraid.

The focal length must be multiplied by the crop factor, and the OP is correct.

For the theory to work, the focal length is not the deciding factor - the important thing is magnification, and that's what affects camera shake.

It just so happens that when using a full frame camera, the numbers for focal length and the minimum shutter speed coincide. But they don't for any other format, so must be adjusted accordingly.

Top take an extreme, a compact with a 100mm lens cannot be hand-held at 1/100sec, because the magnifcation is equivalent to a lens of 500mm (crop factor roughly 5x). So in that case you should shoot at 1/500sec as a mimimum.
 
HoppyUK said:
Completely wrong I'm afraid.

The focal length must be multiplied by the crop factor, and the OP is correct.

For the theory to work, the focal length is not the deciding factor - the important thing is magnification, and that's what affects camera shake.
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Now, I'm not being argumentative for the sake of it, I'm trying to understand better :)

I was under the impression that the crop factor doesn't magnify anything, just cuts down the field of view.
 
VirtualAdept said:
Now, I'm not being argumentative for the sake of it, I'm trying to understand better :)

I was under the impression that the crop factor doesn't magnify anything, just cuts down the field of view.
Click to expand...

It cuts down the field of view, so the image is more greatly magnified in the final output.
 
I'm of the opinion that the handheld shutter speed is mainly down to focal length, pixel size and technique rather than form factor.

The smaller the pixels the more likely you will see camera shake.
 
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Its very easy to see the effect of crop if you have live view that can be magnified.
Use a zoom lens , and zoom so that the hand held image looks sort of stable, then use the live view to zoom the image simulating a crop, the slight jitter you had before is now amplified in the view. This is what happens with the crop, you are basically looking at a smaller portion of the image magnified in the view.

So the recommendation of speed for focal length should take in the crop factor.

but for some one like me, whose hands are as steady as a jelly in an earthquake:lol:, i would increase speed by another 50% if I can. but thats just me.
 
I must admit, I'm a bit perplexed by the this one. The D700 has a crop mode which effectively crops the image down to a dx size before it's even reached the computer. It seems counter intuitive to think that I might need to increase shutter speed in that scenario but not if I'd take the same image full frame and then cropped it afterwards. Or maybe any cropped image should have a higher shutter speed regardless of when/how it is going to be cropped?
 
Mark G said:
I had a feeling that there may be mixed opinions on this one.

My technique is decent enough, but I do 'sometimes' get shake and wondered if I'm shooting too slowly.
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If you sometimes get shake then i'd suggest that you do need to shoot at a faster shutter speed regardless of what focal length you are using. As has been mentioned before these are guidelines and not hard and fast rules.

Experiment with differing shutter speeds to see what your capabilities (in terms of camera shake) are.
 
gad-westy said:
I must admit, I'm a bit perplexed by the this one. The D700 has a crop mode which effectively crops the image down to a dx size before it's even reached the computer. It seems counter intuitive to think that I might need to increase shutter speed in that scenario but not if I'd take the same image full frame and then cropped it afterwards. Or maybe any cropped image should have a higher shutter speed regardless of when/how it is going to be cropped?
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yes .. my bad :thumbsdown: when you look at it that way it shouldn't make any difference.
But you just have to try it and see, in my case I have to increase bacause im so shakey:(

I would have also thought that sensor density would start to have an effect here for the pixel peepers, on a smaller sensor the shake would cross a smaller number of pixels ( if you see what i mean ), amd produce less of an effect, as it shoots up and pixels get smaller, the dither will ( should) start to effect more pixels.:thinking:
 
gad-westy said:
I must admit, I'm a bit perplexed by the this one. The D700 has a crop mode which effectively crops the image down to a dx size before it's even reached the computer. It seems counter intuitive to think that I might need to increase shutter speed in that scenario but not if I'd take the same image full frame and then cropped it afterwards. Or maybe any cropped image should have a higher shutter speed regardless of when/how it is going to be cropped?
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You're falling into the trap of assuming that it's focal length that is the deciding factor, when actually it's magnification. Of course focal length is a big contributor to that, and a very handy short-hand reference, but crop factor is just as important.

So, whether you shoot on a crop format camera or shoot on full frame and crop the image later in post processing, the shutter speed should be increased accordingly*.

The live view test mentioned above is a good one. Use it in full scene view and the image looks nice and steady, but zoom in on the LCD and it will dance about alarmingly. Interesting to see the effect of image stabilisation on/off at the same time.

Some other good comments here too. It is only a rough guide, and some people are steadier than others. It also depends how you're holding the camera, nice and steady leaning against a wall or down on one kneee struggling to get the right shot. Most people can't meet the 'rule' when shooting in live view either, which is fundamentally less stable.

And the comment about high pixel counts is relevant too. The new Nikon D800 with 36mp is a case in point and Nikon goes to some lengths to describe the techniques needed to realise that level of detail. They include using only the best lenses, at apertures below the diffraction threshold, high shutter speeds with image stabilisation on, or tripod with mirror-lock up.

* For the same reason, depth of field is also changed when you crop an image, or shoot on a different format camera.
 
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ah hell... I'll get it right some day.
My humble apologies to the OP for giving erronious information.
 
HoppyUK said:
* For the same reason, depth of field is also changed when you crop an image, or shoot on a different format camera.
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This view will never ever ever make sense to me. I do see why you say it but I just can't and never ever will agree with you :D The DoF/camera shake remain exactly the same and all you can do by cropping or magnifying or reducing it or viewing it from nearer or further away is make it more or less obvious but look closely and think about what you're seeing and you should see that it's.... the same, unless you go to an extreme such as printing your image the size of a postage stamp to completely hide the issue or the size of a house to make it blindingly obvious.

Back to the OP. The obvious thing to do is to shoot some test shots and see what you're happy with. For 50mm I'd be happy at 1/100 sec, sort of happy at 1/80, complaining a little but hopeful at 1/50 and resigned to a possible reject at 1/30 and lower. I'd take the focal length and add at least another 1/2 again, whenever possible.
 
woof woof said:
This view will never ever ever make sense to me. I do see why you say it but I just can't and never ever will agree with you :D The DoF/camera shake remain exactly the same and all you can do by cropping or magnifying or reducing it or viewing it from nearer or further away is make it more or less obvious but look closely and think about what you're seeing and you should see that it's.... the same, unless you go to an extreme such as printing your image the size of a postage stamp to completely hide the issue or the size of a house to make it blindingly obvious.

Back to the OP. The obvious thing to do is to shoot some test shots and see what you're happy with. For 50mm I'd be happy at 1/100 sec, sort of happy at 1/80, complaining a little but hopeful at 1/50 and resigned to a possible reject at 1/30 and lower. I'd take the focal length and add at least another 1/2 again, whenever possible.
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Alan, you are a master of contradiction. (And for the benefit of the jury, Alan has previous on this topic.)

First you say you disagree with me, and then you go on to say exactly what I've been saying.

If you can't see that, then all is lost.
 
HoppyUK said:
Alan, you are a master of contradiction. (And for the benefit of the jury, Alan has previous on this topic.)

First you say you disagree with me, and then you go on to say exactly what I've been saying.

If you can't see that, then all is lost.
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It's the way you tell 'em. IMVHO you tend to make statements that aren't strictly accurate unless you make more assumptions and do other additional things but rather than argue point by point out of politeness to you I'll just say why I don't like the smaller sensor = larger DoF and cropping changes everything view (and the reliance on numbers assigned after a whoile load of assumptions have been made by someone else) and then we can both go on viewing this topic in whatever way works for each of us.

Lets assume that I have a 5D and a G1. x1 and x2 crop. Lets assume that the CoC for the 5D is 0.03 and for the G1 0.015. Lets assume that the G1 has a different CoC because images need to be magnified more to produce the same sized image and has enough resolution to accomplish this, and lets also assume that both do and are capable of producing perfectly good prints from passport size to A3.

I know that to get EFOV of FF 50mm I'll need to use 25mm on the G1 and I also know that to get EDoF to FF f2 I'll need to use a wider aperture on the G1 but I also believe that if I shoot two shots with the same 50mm at f2 on each from the same distance I'll see the same G1 image within the 5D image. I also know that I can get the same DoF from the G1 and 25mm as FF and 50mm by using a wider aperture or reducing the camera to subject distance, if not quite the same "look." I personally feel that what matters most is aperture, camera to subject distance and focal length.

In these circumstances I personally think that aperture, camera to subject distance and focal length (although that's a bit of an illusion) are far more important than worrying about how many times each image has to be magnified and the effect this will have on DoF because all that has already been thought of so I can print anything from passport to A3.

"Smaller sensor = bigger DoF" is something that I find misleading. The math will prove it but the differences in CoC, with the resolution in place, and magnification, when kept to a reasonable print size of passport to A3, become pretty much insignificant to me when balanced against the reality of selecting an aperture, zoom length and shooting distance.

Just for fun... (and BTW, my wallpaper isn't dirty. Nothing is visible by eye so the yellowing in some shots must be a WB issue or maybe the wallpaper is picking up the colour of the wood.) These are all whole images, no cropping, and all taken from roughly, give or take an inch or so, the same distance.

FF, 50mm f2.
50-f2c.jpg


MFT f0.95(x2 crop.) Near enough the same image.
25-095c.jpg


FF, 20mm f2.
20-f2-5Dc.jpg


MFT (x2 crop.) f2. Look within the FF image and you'll see almost this exact image.
20-f2-GF1c.jpg


There's no way on Earth to get Kenny in the DoF other than to print the image so small it'll be meaningless and there's no way to get Stan out of the DoF other than to print him the size of a house and claim he was never in it.

It's not wirth worrying about. That's all I've ever meant :D
 
PS. Crops...

50-f2c1.jpg
50-f2c2.jpg


No change :)

I hope the OP found all that "interesting."
:D
 
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wait... But you.. What?

You're comparing the MFT at f/0.95 to the FF at f/2, getting near identical images, then saying this supports that sensor size DOESNT change DoF?!!
 
woof woof said:
No change :)
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I disagree. If I take the web sized images and brush a colour onto everything I would consider in focus, then do the same for the crops, I'll be brushing less on the crops.

Of course the change isnt as extreme as selecting a different aperture, but it's very definitely visible to me. Certainly impacts my macro shooting, where I could call a whole subject in focus at web size but you can easily see it is not viewed larger.
 
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Back to it, i was taught 1 stop above yhe focal length, and crop factor does not change things as only field of view is reduced and the image is not magified any further
 
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