Reciprocal rule for focal length?

Rovers_Andy

Rovers_Andy

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A quick question, the rule about keeping shutter speed at least the reciprocal of focal length e.g 1/400th for 400mm.

Does this apply the same for full frame and crop bodies :bonk:
 
I try to exclude the crop from the initial maths, then add it .

That makes no sense at all does it?.........:lol:

Example:

300 F2.8 on my D700, i keep at 1/300 or more. Same lens on my 1.5 crop D300 and I try to keep it over 450,does that make sense?


:thinking:
 
Rovers_Andy said:
A quick question, the rule about keeping shutter speed at least the reciprocal of focal length e.g 1/400th for 400mm.

Does this apply the same for full frame and crop bodies :bonk:
Click to expand...

Its only a guide, just cut down on the coffee you'll be fine :D
 
yeah :) thats what i thought. so for the 400 on the MKIII i'd need to keep it at 1/520 :thinking:

i did some test shots on monday night during the footy and at 1/640th they're sharp drop it to 1/500th and its hit and miss 1/400th and they're soft. Could be dodgy technique though :lol:


Ta for the reply


Martyn... said:
Its only a guide, just cut down on the coffee you'll be fine :D
Click to expand...

don't drink coffee :razz: :lol:
 
Rovers_Andy said:
A quick question, the rule about keeping shutter speed at least the reciprocal of focal length e.g 1/400th for 400mm.

Does this apply the same for full frame and crop bodies :bonk:
Click to expand...

You need to apply the crop factor as a multiplier in the same way as you do for the effective focal length calculations.

So a 200mm lens on a 1.6x crop becomes a 320mm equivalent which requires a 1/320s shutter speed to handhold.

Thing is these are all estimates anyway and if you're particularly steady handed then you can normally push the rule a little, eg 1/40 rather than 1/60 is still ok. Because of this you can make the maths a little easier by assuming a 1.5x multiple if you like - it's only a guide after all.
 
Cheers Pete :), i do have IS but for the football i don't use it as IMHO it slows the AF too much
 
Rovers_Andy said:
Cheers Pete :), i do have IS but for the football i don't use it as IMHO it slows the AF too much
Click to expand...

Fair enough! From what I hear it's not much good if the subject's moving anyway!

That's interesting about the AF speed - I'm looking at buying my first IS lens and hadn't considered AF speed, cheers.
 
Rovers_Andy said:
:naughty:

I do use it for wildlife stuff occasionally, and the odd time ive tried shooting handheld with the 400:nuts:
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Yeah, I saw that pitiful effort............:lol:

I think I`m off out and about on Monday Andy,will phone and confirm at the weekend.
 
^yeah your end picture is cropped so 'zoomed in' 1.5x so any blur, although the same amount is now 1.5x bigger on the end picture so more noticeable. well that how I think of it.
 
I always look at as the FOV has been changed by x1.6 so the bluro-factor has increased by x1.6 :)
 
I've actually been rethinking my earlier post since as ever with this crop factor discussion you have to remember that it's really only the field-of-view that's changing and the multiplication effect is when that image is scaled back to the same size as you'd have got from a full-frame sensor.

So given that the lens length hasn't changed, only the field-of-view produced with it; why can't you get away with the original formula?

b****r. :thinking:
 
IMHO, the crop factor has nothing whatsoever to do with the rule of thumb. You don't actually alter the lens's focal length, just the proportion of it that is recorded on a (smaller) sensor.
George

So 1/300 on a 300mm lens is just that, never mind the sensor size.
 
Since the rule of thumb only really applies to 35mm, you DO have to take any crop factor into account. However, rather than rely on the rule of thumb, get out there with your camera and your lenses in a variety of conditions and see what shutter speeds you can handhold without too much camera shake.

andrewc, cropped 35mm has existed for some time - http://en.wikipedia.org/wiki/Half-frame_camera
 
incapete said:
it's really only the field-of-view that's changing and the multiplication effect is when that image is scaled back to the same size as you'd have got from a full-frame sensor.

So given that the lens length hasn't changed, only the field-of-view produced with it; why can't you get away with the original formula?

b****r. :thinking:
Click to expand...

I'm with inkypete on this one :thumbs:
 
Nod, I assume by 35mm you mean full frame?? I'm sorry, and perhaps someone will convince me otherwise, but if you take the argument that crop factor does affect the reciprocal rough guide (and it's only that) if you had a sensor that only covered for example one tenth of an equivalent full frame, then the shutter speed should be 10x that for the same lens on a full frame????...sorry can't agree with that argument!!
 
I've never really bothered too much about the crop factor in the rule of reciprocity, and I haven't run into many problems, but I'm curious. How much of this is due to technical reasons, and how much of it was originally governed by the difficulty of hand holding long, heavy, lenses?
 
mrgubby said:
I always look at as the FOV has been changed by x1.6 so the bluro-factor has increased by x1.6 :)
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Spot on :thumbs:

This has nothing to do with pixel density or other issues of focal length being 'different' on DX/FX - it's only a guide to stopping apparent blur caused by camera shake

On an FX you may get away with 1/50th on a 50mm lens IF you also have good camera technique too, but if the lens was a 75mm you'd obviously expect to have to increase the min shutter speed too. DX gives you a similar effect to using longer lenses, hence you need to also increase your shutter speed due to magnifying your bluro-factor ;)

If using a FX 200mm, but you put a 2x converter on it, would you really stick with 1/200th as the lens itself is still a 200mm??? Or would you go for 1/400th now - and if you would go for 1/400th how is this any different really to using a DX???

But please guys also remember that the reciprocal is at best a guide, and it's also a MINIMUM guide, ideally you always want to be much faster even if it means raising your ISO :)

DD
 
By 35mm, I mean FF as applied to DSLRs, yes.

Try this on for size. The actual focal length on my 'phone's camera is 5.2mm; I really don't think I could hand hold it at 1/5th. My compact's zoom is from 6.2mm - 18.6mm (35mm - 105mm 35mm equivalent focal length) again, guess which shutter speeds are more appropriate. Equally, I have an 8mm fisheye and a 12-24 UWA but even on 35mm film and FF digital, I try to stay faster than 1/30th if not 1/60th.

As I've already said, it's a rule of thumb, not a hard and fast rule, it depends on the individual, the lens, the conditions and many other things so get out there and see what YOU can do with YOUR kit.
 
DiddyDave said:
Spot on :thumbs:

This has nothing to do with pixel density or other issues of focal length being 'different' on DX/FX - it's only a guide to stopping apparent blur caused by camera shake

On an FX you may get away with 1/50th on a 50mm lens IF you also have good camera technique too, but if the lens was a 75mm you'd obviously expect to have to increase the min shutter speed too. DX gives you a similar effect to using longer lenses, hence you need to also increase your shutter speed due to magnifying your bluro-factor ;)

If using a FX 200mm, but you put a 2x converter on it, would you really stick with 1/200th as the lens itself is still a 200mm??? Or would you go for 1/400th now - and if you would go for 1/400th how is this any different really to using a DX???

But please guys also remember that the reciprocal is at best a guide, and it's also a MINIMUM guide, ideally you always want to be much faster even if it means raising your ISO :)

DD
Click to expand...

Putting a 2x converter is affecting the optics and giving you a 400mm lens whatever body it goes on, so you'd have to alter the rule of thumb appropriately, ie make it 1/400 rather than 1/200 ( ignoring for the moment IS or equivalent). The crop factor doesn't alter the focal length of the lens, just alters the area of that lens you are using.

Also the rule's use is really for telephoto lenses, and has many caveats.
 
But it isn't actually related to the focal length of the lens. It's just convenient that for 35mm film, it works quite well.

If you have an image that is a 1.6x crop of a 35mm frame (either by cropping or by using a cropping sensor) and you want to enlarge the image to the same size print then you are applying an additional 1.6x magnification to the output of the crop. Therefore crop factor does make a difference.

And in fact, so does pixel resolution if you want to use all that data. So, for a sharp 100% view on my 18Mpx 7D, it is more demanding of good technique and the "guideline" needs to be used more cautiously than on a 6Mpx 10D. Now, if both outputs are to be printed at 12x8" (6Mpx at 300dpi) then it doesn't matter but if you are hoping the new super resolution camera will give more detail, then you will need a faster shutter.
 
DiddyDave said:
Spot on :thumbs:

This has nothing to do with pixel density or other issues of focal length being 'different' on DX/FX - it's only a guide to stopping apparent blur caused by camera shake

On an FX you may get away with 1/50th on a 50mm lens IF you also have good camera technique too, but if the lens was a 75mm you'd obviously expect to have to increase the min shutter speed too. DX gives you a similar effect to using longer lenses, hence you need to also increase your shutter speed due to magnifying your bluro-factor ;)

If using a FX 200mm, but you put a 2x converter on it, would you really stick with 1/200th as the lens itself is still a 200mm??? Or would you go for 1/400th now - and if you would go for 1/400th how is this any different really to using a DX???

But please guys also remember that the reciprocal is at best a guide, and it's also a MINIMUM guide, ideally you always want to be much faster even if it means raising your ISO :)

DD
Click to expand...


Cheers DD :D

explained it nicely
 
The reason why you multiply the focal length by crop factor is because ultimately you are enlarging the portion that you see by 1.5x times, so blur is magnified 1.5x. The 50mm focal length is still 50mm regardless of the camera you put it on, but with crop bodies, the central portion (i.e. DX/APS-C bit) is now enlarged to fill the entire frame, rather than taking up the centre section. You could use the original rule of thumb IF you resized the picture so it was smaller...but then you'd be throwing away megapixels. Technically if you had a high enough megapixel count on your sensor you could get away with ridiculously blurry shots (assuming they were equally blurred in all directions) and just resize the picture really small to get sharp shots!
 
grumpybadger said:
But it isn't actually related to the focal length of the lens. It's just convenient that for 35mm film, it works quite well.

If you have an image that is a 1.6x crop of a 35mm frame (either by cropping or by using a cropping sensor) and you want to enlarge the image to the same size print then you are applying an additional 1.6x magnification to the output of the crop. Therefore crop factor does make a difference.

And in fact, so does pixel resolution if you want to use all that data. So, for a sharp 100% view on my 18Mpx 7D, it is more demanding of good technique and the "guideline" needs to be used more cautiously than on a 6Mpx 10D. Now, if both outputs are to be printed at 12x8" (6Mpx at 300dpi) then it doesn't matter but if you are hoping the new super resolution camera will give more detail, then you will need a faster shutter.
Click to expand...

:agree: but couldn't be bothered to type it all :lol:
 
Rovers_Andy said:
Cheers Pete :), i do have IS but for the football i don't use it as IMHO it slows the AF too much
Click to expand...

IS and AF are completely unrelated functions. If the IS is on and activated by first press on the shutter release (and held on in this way) then AF speed is unaffected.

andrewc said:
would you have to do it with 'cropped' 35mm film? (My new invention)
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Yes. Grumpy Badger explained it very well.

andrewc said:
Is it to do with pixel density?
Click to expand...

No, but the 'rule' is about magnification (not focal length) and the latest cameras with very high pixel density, and therefore equally high resolution potential, really need the rule to be increased.

The rule is about reducing camera shake to an acceptable level, not eliminating it completely. If your degree of 'acceptable' sharpness is increased to a new level, then the rule needs to be tightened up accordingly. With cameras like the Canon 7D, I would add another stop. IS is beneficial here as the whole sharpness threshold is raised and it helps enormously if you want to get the best from these cameras.
 
HoppyUK said:
IS and AF are completely unrelated functions. If the IS is on and activated by first press on the shutter release (and held on in this way) then AF speed is unaffected.
Click to expand...

Does it not take time to 'settle' though? This is no good for sports as you often lock AF and snap in a fraction of a second! The general rule for sports is not to use IS.
 
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