Focal Length

leighroy

leighroy

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Will Thomas
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Ive read a few posts about setting the shutter speed according to your lens' focal length, but not sure how to find out what the actual focal length is.
Any help appreciated
 
The rule of thumb for getting a "sharp" hand held non-wobbly shot is to shoot with the shutter speed set to 1/focal-length.

Focal length is how "long" your lens is. The standard kit lens is a 17-55mm zoom so at the long end 55mm you should shoot with a shutter speed of at least 1/55th (ie 1/60th) of a second.

If you have a 500mm f4 lens then 1/500th is as slow as you should go, hand held with no IS. Of course with one of these beasties you'd be well recommended to use a stonking great tripod and gimbal'd head, so it's not handheld and you can go a lot slower.
 
Focal length is usually printed on the lens - usually around the front element. You should see something like 1:2.8 200mm. This would mean the lens has a max aperture of f2.8 and a focal length of 200mm.
 
oldgit said:
The rule of thumb for getting a "sharp" hand held non-wobbly shot is to shoot with the shutter speed set to 1/focal-length.

Focal length is how "long" your lens is. The standard kit lens is a 17-55mm zoom so at the long end 55mm you should shoot with a shutter speed of at least 1/55th (ie 1/60th) of a second.

If you have a 500mm f4 lens then 1/500th is as slow as you should go, hand held with no IS. Of course with one of these beasties you'd be well recommended to use a stonking great tripod and gimbal'd head, so it's not handheld and you can go a lot slower.
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Keep hearing/reading this advice but then forget. Perhaps this explains my blurry shots.. :bonk:
 
oldgit said:
The rule of thumb for getting a "sharp" hand held non-wobbly shot is to shoot with the shutter speed set to 1/focal-length.

Focal length is how "long" your lens is. The standard kit lens is a 17-55mm zoom so at the long end 55mm you should shoot with a shutter speed of at least 1/55th (ie 1/60th) of a second.

If you have a 500mm f4 lens then 1/500th is as slow as you should go, hand held with no IS. Of course with one of these beasties you'd be well recommended to use a stonking great tripod and gimbal'd head, so it's not handheld and you can go a lot slower.
Click to expand...

Don't forget to add in the 'crop factor' into the equation - A 200mm lens on a 1.6x crop Canon will have the effective focal length of a 320mm lens, therefore you should (as a rule of thumb) select a shutter speed of at least 1/320th of a second...
 
kevin_c said:
Don't forget to add in the 'crop factor' into the equation - A 200mm lens on a 1.6x crop Canon will have the effective focal length of a 320mm lens, therefore you should (as a rule of thumb) select a shutter speed of at least 1/320th of a second...
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I have to disagree, the focal length of a 200 mm lens on a DSLR with a crop sensor is still 200 mm. Its field of view will be the equivalent of a 320 mm lens on a full frame sensor. So the magnifcation will be the same.
 
kevin_c said:
Don't forget to add in the 'crop factor' into the equation - A 200mm lens on a 1.6x crop Canon will have the effective focal length of a 320mm lens, therefore you should (as a rule of thumb) select a shutter speed of at least 1/320th of a second...
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This one gets quoted occasionally Kevin, but it has no credibility for the reasons stated by ThisPhotoGuy. The Rule of Thumb that minimum safe shutter speed = focal length, is one of the nice easier ones for people to remember and this just muddies the waters. ;)
 
The crop factor was introduced early on with the first DSLRs to try explain to a lot of confused togs how the field of view compared to 35mm film as a sort of reference point. It probably causes more confusion than any other single factor, but it seems we're stuck with it now. :D
 
ThisPhotoGuy said:
I have to disagree, the focal length of a 200 mm lens on a DSLR with a crop sensor is still 200 mm. Its field of view will be the equivalent of a 320 mm lens on a full frame sensor. So the magnifcation will be the same.
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CT said:
This one gets quoted occasionally Kevin, but it has no credibility for the reasons stated by ThisPhotoGuy. The Rule of Thumb that minimum safe shutter speed = focal length, is one of the nice easier ones for people to remember and this just muddies the waters. ;)
Click to expand...

This is why I said the 'effective' focal length... I may have worded it badly but yes you are correct the focal length does not change at all, but in my experience, a 200mm focal length on a film body/FF DSLR is easier to hold still than the same lens giving a field of view of a 320mm on a crop digital SLR.
 
... and the 'rule' is always just a guide. If you don't get good shots with 1/length then try 1/length x 1.6, as Kev says, or whatever. We're all different and ability to handhold a shot at longer lengths especially will vary quite a bit.
 
The Rule Of Thumb is indeed just a guide, and we all vary enormously in our abilities to handhold. The Rule Of Thumb provides a guide which is suitable for most people in setting a minimum safe shutter speed, and it's always been the case that it is considered a minimum, and going faster if you can, is even safer. It's also true that some people with practice can achieve shutter speeds much slower than the ROT would suggest - at least on a fair proportion of shots.

This hasn't changed with digital at all, and bringing the crop factor into it just confuses the issue.
 
Isn't the whole point of the rule being to compensate for lens shake / movement.

if you get a blur due to camera shake at 200mm & the FOV is equivalent to 320mm (cropped) are you not getting 1.6 x the shake ??

say the camera lens 'lets in' 10mm of wobble so the sensor 'lets in' 16mm of wobble, shouldn't we ratchet up the shutter by 1.6 to compensate ?
 
Why does the sensor record more wobble than the camera? The same size image is recorded on the sensor regardless of focal length. If the camera moves 1 thou during exposure, the sensor moves the same distance with it.
 
I'd argue that crop factor is important. It's the field of view that's important, because it's the percentage change in the location of the subject within the field of view that would determine motion blur. 1% movement in a tiny tiny frame, when blown up would have similar motion blur to 1% movement in the largest of frames. The field of view of a 100mm lens on 35mm is similar to the field of view of a 150mm lens on an APS-C camera.

It's all academic really. You need a higher shutter speed if the subject is closer than if it's in the distance (1 degree shift at close distances is much larger than at long distances.) You need a lower shutter speed if you have good technique.

I suppose it would be appropriate to post this here.
Good technique means keeping your elbows close by your sides.
Have your right hand on the camera, and the left hand under the lens/body, so it's cradled. You can still roll your finger over the lens to change the focal length/focus.
Roll your shutter finger over the shutter rather than jabbing it.
Slow your breathing. Take a deep breath in, out, in and then on the slow breath out fire the shutter.

It's pretty much the same as principles of marksmanship, if you've ever fired a rifle. Some people (like myself) prefer to catch their breath for half a second just before firing the shutter. This works for me, but I've found that others don't get on with it. Experiment.

The other principle of marksmanship that applies is that the camera/rifle should point naturally in the direction you're shooting. If your back is twisted so you can get the shot, you'll never make a sharp shot as your muscles will be twitching.

Best of luck!
 
The other principle of marksmanship that applies is that the camera/rifle should point naturally in the direction you're shooting
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It would help tremendously

Good one...sorry i saw the funny side.

I guess you mean the photographer should be facing square on to the subject.
 
CT said:
Why does the sensor record more wobble than the camera? The same size image is recorded on the sensor regardless of focal length. If the camera moves 1 thou during exposure, the sensor moves the same distance with it.
Click to expand...

The way I was looking it that if you get the equivalent of FOV/1.6 then the 'apparent' camera shake would be 1.6x greater requiring a higher shutter speed :thinking::shrug:
 
I can see where you're coming from, and on paper, you can argue support for the idea in theory, but it all depends what subjects you're taking anyway. With my bird togging and long lenses, the 40D with it's 1.6X crop gives me a huge advantage, even over full frame sensors with lots of pixels - I need to crop less to get a decent size image of the bird. With other subjects, landscape being a good example, the crop sensor is at the disadvantage, and as has been said every time this argument comes up.... if you carry this to it's logical conclusion, so much depends on the degree of enlargement of the final image/print anyway.

I'll stand by the Rule Of Thumb, as being more than capable of covering all the bases as long as good hand holding technique is used, which is a basic requirement anyway. :)
 
CT said:
I I'll stand by the Rule Of Thumb, as being more than capable of covering all the bases as long as good hand holding technique is used, which is a basic requirement anyway. :)
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What ever shutter speed / technique is used to get good images is (y)


what wiki says (and they're always right ;))

The old rule of thumb that shutter speed should be at least equal to focal length for hand-holding will work equivalently if the actual focal length is multiplied by the FLM first before applying the rule
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I always use a higher speed than required because I seem to vibrate :wacky:



but it keeps the wife happy :naughty:
 
I agree that the crop factor does confuse the h*ll out of some people :) (especially the ones who 'bunked-off' maths lessons on that day :))

If a shutter speed/focal length/fov combo works for a person then great, but if that person then changes from a FF/35mm body to a 1.6/1.5x crop body they may have problems getting shake-free shots at the same focal length/shutter speeds.

Personally I tend to have to nearly double the 'rule of thumb' with long(ish) lenses on my 20D. Not because I drink too much coffee, but because the shutter release on this thing is pretty 'heavy' and the mirror does 'clonk' up and down pretty heavily. This tends to invoke a small amound of shake in my experience.

I came from a 35mm film camera background, and even now when I shoot with my Canon EOS30 or Nikon F100, the shutters/mirrors seem so much smoother and refined, and the magnification is less (no cr*p factor!) I find I can hand-hold at a lower speed.

An interesting discussion though... :)
 
mrgubby said:
What ever shutter speed / technique is used to get good images is (y)


what wiki says (and they're always right ;))



I always use a higher speed than required because I seem to vibrate :wacky:



but it keeps the wife happy :naughty:
Click to expand...
:LOL:


I totally believe everything on that site... :cautious:
 
Well we'll agree to disagree Kev! :wave:

All I'll say is given our climate, if I had to invoke the 1.6 crop factor in determining shutter speed, I wouldn't be able to take a bird shot on lots of days and that's at 800 ISO! I can see why a dodgy shutter button could make things difficult though.
 
CT said:
Well we'll agree to disagree Kev! :wave:

All I'll say is given our climate, if I had to invoke the 1.6 crop factor in determining shutter speed, I wouldn't be able to take a bird shot on lots of days and that's at 800 ISO! I can see why a dodgy shutter button could make things difficult though.
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I don't think it's faulty, it's just not a smooth as my film bodies - Maybe I need to upgrade... :naughty:
 
just to add my 2 penneth - on a crop body the circle of confusion is smaller, so it would seem logical to increase shutter speed since allowable wobble would be similarly reduced IMHO.

Anyway all irrelavent to me as I have continually wobbly hands, I mean properly shaky, 1/2000th regardless for me :eek:
 
I was wondering about that, it's quite a clunk. I wonder if the viewfinders will ever be electronic from the sensor like bridge cameras (but look as good as through the glass).
 
Come on guys...I am as wobbly as wobbly gets from time to time but let us get real here and keep in mind that we are using equipment with limitations and we have (individual) limitations.

90% of us had all these problems (dust, camera shake etc) in the good old film days and chances are we never noticed them because we printed jumbo prints...:bonk:

Now we have digital and we view our piccies at billboard magnifications...:wacky:

Let's take more time to do photography and less time to discuss the useless parts of photography such as pointless technical arguments...
 
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