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the 1/focal length rule

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Thread started 21 Nov 2004 (Sunday) 21:51   
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sharky
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This is something which is probably pretty obvious, but I seem to like asking obvious questions. On digital bodies, the 1.6x crop factor makes a 200mm lens an "effective" 320mm, so what does that do to the 1/focal length rule? Would 1/250th still be adequate, or would you need to use higher shutter speeds?

I'm assuming the former because the focal length really hasn't changed, but I've noticed that a lot of shots taken at 200mm with the 10D don't seem as steady as with my old film body.

Post #1, Nov 21, 2004 21:51:53




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slin100
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The rule of thumb should be refactored to take into account the effective focal length. So, a 200mm lens should used with a shutter speed no less than 1/320. Of course, this is merely a rule of thumb. YMMV.

Post #2, Nov 21, 2004 22:01:21


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Chazs
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In my SLR days 20 years ago I used the 1/(2FL) rule, but I just posted a photo taken with a 200mm at 1/250 hand-held. It would have been nice to get to 1/500, or 1/300; I just had to hold me breath better.

My dad has always been able to and-hold a 50mm to 1/4s. and on a good day to 1/2s. Guess I drink too much coffee. :oops:

If you are used to the 1/FL rule with a standard SLR, you should be okay with a 1/(1.6FL) on a DSLR. Me, I'm not usually comfortable until at least 1/(2.5FL). Next lens I get may be an IS type.

Post #3, Nov 21, 2004 22:38:46




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sharky
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Might return to IS!

I actually sold a 28-135IS to buy the 70-200L, and while I like a lot of things about the L, I never realised how reliant I'd become on IS.

Post #4, Nov 21, 2004 22:49:57




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Steven ­ M. ­ Anthony
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The 1.6 crop factor associated with many digital cameras does NOT change the effective focal length of a lens. It does NOT make a 200mm lens a 320mm lens. If it did, any time you wanted a 1,000mm lens, all you would have to do is put duct tape over most of your sensor and a thrifty-50 would be magically converted into a 1,000 mm prime!

The 1.6 crop factor is not magic. It is simply a crop factor--a crop factor relative to the content that would be contained on a full frame of 35mm film.

Here's an example: Close one eye and look at something across the room. Go ahead, I'll wait... Okay, now roll the fingers of one hand up so your finger tips touch the palm of your hand. Now hold your hand up to your opened eye and look through the little tunnel in your hand at the same object across the room. Did the effective focal length of your eye change? No. Did the object across the room look closer the second time you looked at it? No. All that happened by looking through the tunnel in your hand was that you reduced (i.e., cropped) your field of view.

That's how the 1.6 crop factor works. If you put the same lens on a film camera, everything will look as far away as it did through the digital camera--but on the film camera, there would be more content in the viewfinder (above, below, to the left and to the right of what shows up in the viewfinder of the digital camera).

Post #5, Nov 21, 2004 23:12:56


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Olegis
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The magnification of the lens does not change on 1.6 crop body, but the shake is more evident because the frame contains smaller portion of the original picture - that's why you should use the 1/1.6*focal length rule.

Post #6, Nov 22, 2004 02:22:08


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dhbailey
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The lens relative to the sensor doesn't change -- if you have a 200mm lens on a 35mm body you would shoot as close to 1/200th as possible. If you crop that picture down to represent the same angle of view that the 1.6 crop factor of a digital body gives you, you won't see any more shake than on the image as a whole.

But actually, all this is academic -- before anybody gets to a critical shoot where they don't want to blow any pictures, a wise person would test things out for themselves rather than rely on any "rule of thumb." Try the rules-of-thumb out and decide what works for you.

As for what Chazs says about his dad, does that mean that we ALL should be able to shoot at 1/4 and expect steady pictures? I don't think so, but I do envy all the great shots his dad must have gotten that I've had to forego or have ruined by trying to shoot that slowly handheld. So his dad's rule of thumb would be "anything you can shoot at 1/4second, go for it." I don't think that applies to many photographers I know of.

So take your camera and lenses out to a place where you can get good light, clear objects to focus on, and try that 200mm lens at all the shutter speeds you want. You'll find out what YOUR rule of thumb is. You might find that you need to do 1/fl + 1 (one speed setting faster than 1/fl) or even +2 or +3. You might find you can do 1/fl -1 or -2 or -3. Only you will be able to decide appropriately.

Whenever I see those banks of professional photographers at sporting events I sometimes wonder how many "rules of thumb" they are using in their shooting. Probably none at all -- in a professional situation you have to depend on what you KNOW will work, not somebody else's "rule of thumb."

Rules of thumb are great starting points from which to begin to test your own individual abilities.

But it is sad to hear somebody say, about a ruined picture, "but I did what they said I should!"

Post #7, Nov 22, 2004 05:12:26


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Andy_T
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Common sense tells me that the 1.6 crop factor should be taken into account.

Why? Because when your hands shake, the picture moves up and down (let's assume linear shake, for the sake of the agreement).

In the picture you want to print, the movement will be visible if it exceeds a certain amount ... and the further distant your subject is, the bigger the movement due to shake will be.

As is true with the question whether a 50 mm is a good 'portrait' lens on a DSLR .... the focal length does not change with the crop factor ... However, the FOV changes and so maybe the distance to your motive might change. And this will influence both distortion and shake.

Best regards,
Andy

PS: What about a practical example. My G2 actually has a 7 - 21 mm lens (it has a 5x crop factor). I haven't succeeded very well to hand-hold pictures at full tele with 1/20 shutter time.

Post #8, Nov 22, 2004 05:33:34


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chris.bailey
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The 1/FL rule of thumb is less reliable with digital than film as the important thing is the size of the sensor sites. As sensor site size decreases with increased resolution for a fixed sensor size the more sensors are available to resolve the shake so on a 1DS MkII you would need a much higher speed to prevent visible evidence of camera shake than you would with a 10D. To go to extremes if you had a camera with a 100 pixel resolution, though the image would be low in detail, there is little chance that camera shake would change the detail being resolved by any of those 100 sites. There is an article on the Canon website somewhere that goes in to a lot of detail on this but then makes some pretty unbelievable claims about the associated benefits of IS. If I can find it again I will post up the link.

I prefer to not use a tripod in the studio but have found that with the 1dMkII I am having to so to achieve improved results over the 10D. Outside I aim for 1/2 x FL wherever possible and up the ISO if needs be. IS does help, particularly on the 100-400 but I treat this as a last resort rather than relying on it.

Post #9, Nov 22, 2004 07:59:26




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CyberDyneSystems
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dhbailey wrote:
The lens relative to the sensor doesn't change -- if you have a 200mm lens on a 35mm body you would shoot as close to 1/200th as possible. If you crop that picture down to represent the same angle of view that the 1.6 crop factor of a digital body gives you, you won't see any more shake than on the image as a whole.

I disagree here,

If I am shooting film with a lens that I find too short for the tak and KNOW I will be cropping.. I also know that the cropped area will thus be enlarged when I print.. further drawing attention to any defects/camera shake than if I printed without enlarging.


In this case I would certainly try to get more that 1/200th for a 200mm lens.

Thus.. as the 1.6 "X-Factor" is all about cropping and then enlarging at the print end of the post processs.. the same idea would apply.

Post #10, Nov 22, 2004 08:22:27


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Steven ­ M. ­ Anthony
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yes--the factor applies to printing, but not the actual amount of "shake" contained in the image. The 1/f rule wouldn't hold up for film if you were going to make a 8 foot by 12 foot print, either...

Post #11, Nov 22, 2004 08:40:40


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DaveG
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Steven M. Anthony wrote:
The 1.6 crop factor associated with many digital cameras does NOT change the effective focal length of a lens. It does NOT make a 200mm lens a 320mm lens. If it did, any time you wanted a 1,000mm lens, all you would have to do is put duct tape over most of your sensor and a thrifty-50 would be magically converted into a 1,000 mm prime!

The 1.6 crop factor is not magic. It is simply a crop factor--a crop factor relative to the content that would be contained on a full frame of 35mm film.

Here's an example: Close one eye and look at something across the room. Go ahead, I'll wait... Okay, now roll the fingers of one hand up so your finger tips touch the palm of your hand. Now hold your hand up to your opened eye and look through the little tunnel in your hand at the same object across the room. Did the effective focal length of your eye change? No. Did the object across the room look closer the second time you looked at it? No. All that happened by looking through the tunnel in your hand was that you reduced (i.e., cropped) your field of view.

That's how the 1.6 crop factor works. If you put the same lens on a film camera, everything will look as far away as it did through the digital camera--but on the film camera, there would be more content in the viewfinder (above, below, to the left and to the right of what shows up in the viewfinder of the digital camera).

You have to ask yourself under what conditions does this rule work? Part of it must be the size of reproduction you are planning, and I'd say that an 8x10 print should be the minimal acceptable print size.

If you took an image with a 100 mm lens (on full frame 35mm) then the suggested "lowest" shutterspeed would be 1/125 or thereabouts, and most of the time will make an acceptable 8X10 print. If you cropped this image to give you the equivilent crop as a 1000 mm lens and made an 8x10 print, then you would find that it was very unsharp (excluding any grain implications), and now unacceptable.

If you leave the grain/noise out of the equation then the softness with a lens cropped to give you a 1000 mm "look" will be EXACTLY the same as if you used a 1000 mm lens.

It's not only the lens that's at issue here, it's the end use as well.

If you used a 300 mm lens and only made contact sheet sized prints then you could hand hold it down to 1/15 second mostly because you couldn't see the softness. With digital, and the 1.6 conversion you have to take the converted focal length into account because you are basically enlarging the image while maintaining the same size print.

After all this is said an done just remember that: a) the 1/focal length is a minimal not optimal standard; b) it is part of some guy's manhood to brag about how low they can handhold a camera, c) it's not true, their stuff sucks but they don't see it, & d) there are no contests for how slow you can handhold a camera, only for good images; so get over it.

Post #12, Nov 22, 2004 08:41:48


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Steven ­ M. ­ Anthony
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David G.: See my post above yours... plus, don't forget the artistic intent behind the image. The 1,000mm crop of a handheld shot might be exactly what the artist was going for...!

All kidding aside, the point I was making is that the amount of softness in an image due to camera shake is not magnified by the crop factor--because the crop factor does not change the focal length of the lens.

And the 1/f rule is a rule of thumb. Use it or don't. And go easy on those who are proud of how steady their hands are. We are all proud of some aspects of ourselves. I'm not sure how you can claim that their stuff sucks as a general rule. H.C-B. didn't use a tripod, and I think his stuff is generally considered pretty good...

Post #13, Nov 22, 2004 08:58:23


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Steven M. Anthony wrote:
yes--the factor applies to printing, but not the actual amount of "shake" contained in the image. The 1/f rule wouldn't hold up for film if you were going to make a 8 foot by 12 foot print, either...

Yes.. I agree here 100% :wink:

The only "magnification" that results from a "Crop factor" occurs at the printing end.

If you printed all your 10D images on paper that was 40% (or is it 60% ?) smaller than standard print sizes.. there would be no "magnification" at all relative to "full frame" there would only be the crop/loss of angle of view.


Hehe heheh

Here we go again :lol: :lol:

-=CROP FACTOR=- 10,000 posts on the X-Factor <== CLICK ME :)

Post #14, Nov 22, 2004 09:08:55


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Scottes
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Does it really matter if the 1.6 factors in? If *you* can shoot steady then shoot at *your* shutter speed. If someone else is shakey then they should shoot at *their* shutter speed.

You should take some test shots. Whether you start at 1/focal or 1/focal * 1.6 doesn't matter, because the goal is going to be to find what shutter speed YOU can use.

And then learn some techniques on steadying, and practice them. Soon you'll be better.

This has nothing to do with 35mm or 1.6 crop factors. It only depends on the shooter.

Post #15, Nov 22, 2004 09:29:09


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