Crop sensor question

Hello all,
First of all, I want to thank all for your postings. As a returning-to-photography hobbyist your posts have helped me invaluably.
Now, here is my newbie question: If I am shooting with a crop sensor camera (60D) does that mean that the rule/suggestion that one should try not to shoot at a shutter speed slower than the focal length of the lens apply? For example, If I am shooting with a 50 mm lens, then my shutter speed should not be less than 1/60, or should I take the 1.6 crop-which would make my lens the equivalent of an 80 mm lens- factor into consideration?
Thanks again for all of your help and good shooting.

First of all - the rule is very general.

It was from the film era, and a general rule for getting good pictures in reasonably sized prints.

If you magnify the image, then suddenly any camera shake will also be magnified.
And your 1.6x smaller sensor will repsrent a 1.6x larger magnification of the print.

An issue here is that the sensor pixels are very small - and that old rule is not intended to get photos sharp down to the individual sensor pixels.

So as a general rule, you should get a shorter shutter time than that rule suggests.

Next thing is that if you shoot static objects, then some people have problems with camera shake and always needs shorter shutter times. And some people are walking tripods - let's not joke about that third leg - and can get away with much longer shutter times.

The thing you should consider is that at the time of the shoot, you might not know if you would later want to make a big print of that photo. So it's often good to err on the safe side unless you specifically shoot moving subjects and requires motion blur.

You should really determine what YOU need for a minimum shutter speed because everybody's ability to hold a camera steady varies.

To specifically answer your question, assuming that the 1/focal length rule-of-thumb for 35mm film cameras works for the "average" photographer, the equivalent rule-of-thumb for APS-C format cameras would be 1/(focal length * 1.6).

Crop or full frame, my own personal rule is not to shoot at a shutter speed of less than TWICE the focal length, so if I'm at 400mm, I try not to shoot handheld at less than 1/800s.

And thats the point, don't follow "rules" blindly. Figure out what works for you.

8x10 (or 12) was the standard then. It is also the standard to which DoF charts apply. Today everybody zooms to 100%, looks at the equivalent of a 40x60 print and then runs to POTN to cry about their lack of sharpness (or noise).

SkipD wrote in post #14454301
To specifically answer your question, assuming that the 1/focal length rule-of-thumb for 35mm film cameras works for the "average" photographer, the equivalent rule-of-thumb for APS-C format cameras would be 1/(focal length * 1.6).

Why should that be? A 50 mm is a 50 mm - independent how much of the picture is captured by the sensor. It is still the same 'magnification' of a movement. So why should crop sensor cameras be more sensitive then FF? I don't get it.

drmaxx wrote in post #14454425
Why should that be? A 50 mm is a 50 mm - independent how much of the picture is captured by the sensor. It is still the same 'magnification' of a movement. So why should crop sensor cameras be more sensitive then FF? I don't get it.

Because 50mm isn't 50mm in terms of what the camera sees; it depends on what actually falls on the sensor. Try it with a point and shoot; the average one has something like a 6x crop relative to full frame. However, if you've got a P&S cam zoomed out to a 30mm focal length (180mm full frame equivalent) and try to take a shot at 1/30 second, you're going to get a shaky image because the sensor will capture the same field of view as a full frame camera would capture with a 180mm lens, and the rule of thumb suggests you'll need 1/180 for that image to be steady.

This is a film era rule of thumb.

As pointed out above, there is the crop 'Focal length equivalent' consideration, the IS consideration and the operator 'steady hands' consideration.

From my personal experience, I can shoot at say 100 mm focal length:

At 1/25 maybe 1 in 5 photos is a keeper

At 1/50 maybe 2/5

At 1/100 4/5 or more, but they will be some that are definitely fuzzy.

At 1/200 nearly all are keepers (unless I sneezed...).

Results are better with the 70-200 than the 18-200

Lowner wrote in post #14454304
Crop or full frame, my own personal rule is not to shoot at a shutter speed of less than TWICE the focal length, so if I'm at 400mm, I try not to shoot handheld at less than 1/800s.

And thats the point, don't follow "rules" blindly. Figure out what works for you.

And at the same time, I've gotten very good results at half the focal length. I have one shot at 30mm and 1/13 second because there wasn't really any choice to get the image. My 17-55 was wide open at f2.8 with ISO 3200 on a T1i, braced my elbows on a table and took the shot. It worked. I even have a handheld 1/2 second exposure that I took in Italy (night shot of the Duomo in Florence) a few years ago. It won't take a great deal of enlargement but for a 4 x 6 print to hang with a grouping it looks marvelous.

So there are no really hard and fast rules, just recommendations. You have to experiment and find out where your personal comfort zone is, as well as consider the use to which the print will be put.

brokensocial wrote in post #14454505
However, if you've got a P&S cam zoomed out to a 30mm focal length (180mm full frame equivalent) and try to take a shot at 1/30 second, you're going to get a shaky image because the sensor will capture the same field of view as a full frame camera would capture with a 180mm lens, and the rule of thumb suggests you'll need 1/180 for that image to be steady.

I still don't get it. If I take a picture with an FF camera and just crop it - then it has no influence on the sensitivity of the lens for movements. Isn't a crop sensor just exactly that: A crop? But no change in optical behaviour?

A 30 mm P&S might have the same frame as a 180mm lens on a FF. But isn't is still a 30mm optical lens with the same optical behaviour? With a 180mm lens you would stand way farther back to frame the same picture then with a 30 mm P&S lense - therefore you won't have the same optical behaviour.

I might just be too dumb - but in my view a 50 mm should always show the same optical behaviour -- independent of the crop I choose to convert into a picture.

Preeb wrote in post #14454645
And at the same time, I've gotten very good results at half the focal length. I have one shot at 30mm and 1/13 second because there wasn't really any choice to get the image. My 17-55 was wide open at f2.8 with ISO 3200 on a T1i, braced my elbows on a table and took the shot. It worked. I even have a handheld 1/2 second exposure that I took in Italy (night shot of the Duomo in Florence) a few years ago. It won't take a great deal of enlargement but for a 4 x 6 print to hang with a grouping it looks marvelous.

So there are no really hard and fast rules, just recommendations. You have to experiment and find out where your personal comfort zone is, as well as consider the use to which the print will be put.

Agreed.

drmaxx wrote in post #14454654
I might just be too dumb - but in my view a 50 mm should always show the same optical behaviour -- independent of the crop I choose to convert into a picture.

It's the amount of magnification that exposes the real sharpness in an image, at small sizes you can get away with it, but at A3+ and bigger, be sure that all the errors begin to show. So back in the "good old days" when a 10 x 8 was considered a good size, this rule worked, but now we all print at A3 or more the rule needs tweaking.

Keep in mind as well that IS can sometimes permit you to break the rules.

drmaxx wrote in post #14454654
I still don't get it. If I take a picture with an FF camera and just crop it - then it has no influence on the sensitivity of the lens for movements. Isn't a crop sensor just exactly that: A crop? But no change in optical behaviour?

A 30 mm P&S might have the same frame as a 180mm lens on a FF. But isn't is still a 30mm optical lens with the same optical behaviour? With a 180mm lens you would stand way farther back to frame the same picture then with a 30 mm P&S lense - therefore you won't have the same optical behaviour.

I might just be too dumb - but in my view a 50 mm should always show the same optical behaviour -- independent of the crop I choose to convert into a picture.

As we said before, it is a rule of thumb and mainly for film. It applies as is for the 24X36 mm film frame probably for an 8X10.

There is always SOME vibration while the shutter moves. The rule of thumb says you will not see it in the film frame.

Now you are taking an area roughly half the size of the film frame (for the APS-C sensor) and magifying to the same size 8X10. Obviously, you would expect to see more motion blur.

drmaxx wrote in post #14454654
I might just be too dumb - but in my view a 50 mm should always show the same optical behaviour -- independent of the crop I choose to convert into a picture.

You are correct - the lens does not know what sensor it is focused on and the image it projects is unchanged.

However, in order to see the image, you need to display or print it. This involves enlarging it from its original (optical) size to final (physical) size. If you compare equal sized prints, then the image from a smaller sensor has to be enlarged more and so any blur is enlarged along with the image. Camera shake, (visibility of) diffraction and DoF are all affected by this difference.