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Old Jun 24, 2005, 3:35 PM   #1
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I have been playing around with a couple of f2.8 lenses from sigma and tokina and have found that shots taken at f6-f8 are much more clear.

Sigma ex24-70 f2.8

Tokina 80-200 f2.8

Both lenses new

I have been shootng at a poorly lit gym Competitive cheerleaders doing gymnastic tumble routines.

The lighting made me push the iso to 1600 to get enough shutter speed so not to have blurr the fstop was at 2.8

the pics came out grainy i think i know y duh iso 1600 right?

TV was 1/125-1/250 still getting hair and feet blurring!

Im getting so frustrated!



WHY? Technically speaking? is it me? I dont get it?
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Old Jun 24, 2005, 4:27 PM   #2
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I'm no expert on this, but I have taken a lot of pictures and gymnastic events. most of the time I used a canon 85mm f/1.8, and tried not to go over ISO 400, but depending on where I was at in the gym sometimes had to push it to 800. Even at that I still get some blur sometimes, which I beleive is mostly caused by the poor lighting not letting you get a fast enough shutter speed, more than your ability to take quality pictures. As far as pictures taken at f8, I have heard the f/8 is kind of the sweet spot so to speak with most lenses, don't ask me why though, maybe NHL can answer that one if he decides to chime in here.
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Old Jun 24, 2005, 4:55 PM   #3
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Every lens performs at its best about 2-3 stops down from wide open. For example, the sweet spot for the Sigma 24-70 f2.8 is about f7.1-f8. This is why you see many tests shot at wide open apertures (e.g., f2.8) since this is about as hard as it gets for a given lens. If the lens is good wide open, it only gets better stopped down. Of course, there is a limit to this as once you stop down to "landscape" apertures like f16 and beyond, often the problem of "diffraction" comes into play and IQ begins to spiral downward, including sharpness. Just like your car's fuel mileage: not good at 10 mph and not good at 100mph; best right around 55mph. Lame analogy but gets close to the point. The kit lens is best right around f8.

As of note, many super-wides (e.g., Sigma 12-24)are best right around f14-f16, which is not uncommon for this type of lens.
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Old Jun 24, 2005, 7:08 PM   #4
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Thanks guys just reading this is reassuring I thought i was gonna lose it!
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Old Jul 24, 2005, 8:12 PM   #5
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Some lenses are made to be very sharp at a wide open aperture, such as the EF 500 or EF 600 f/4 lenses. (And they are about $5500 and $6500, respectively.)

With most lenses there is a big difference in sharpness from wide open to stopped down a couple of stops. But there is another factor not mentioned in these posts:

'The depth of field is much shallower at the largest aperture, and increases as the aperture gets smaller. So at f/2.8 on a 200mm lens at a given subject-to-sensor distance, say, 10 ft, if you are shooting somebody's face the eyes might be in sharp focus yet the ears and tip of the nose would appear out of focus, and a background might be a smooth blur. At f/8 or f/11, and the same focal length and distance, not only might the whole head be in focus, but the background might be much less blurred.

So in addition to a lens being sharper when stopped down a couple of stops, the apparent sharpness from increased depth of field would also add to the effect.
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Old Jul 24, 2005, 9:03 PM   #6
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1texan wrote:
Quote:
I have been playing around with a couple of f2.8 lenses from sigma and tokina and have found that shots taken at f6-f8 are much more clear...

WHY? Technically speaking? is it me? I dont get it?
There's also the light that come into play - in a dark gym there's a much lower contrast, try the same lens outside wide opened and you should see a big difference...

The MTF(contrast) of a lens are always plotted wide-opened so you can see how sharp they should be @ those limit when comparing lenses. For example this image was captured wide opened outdoor with a Sigma 120-300 f/2.8 EX:

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Old Jul 26, 2005, 1:10 PM   #7
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Very interesting thread here. Anyone have a table of "sweet spot" f stops for various lenses? I'm particularly looking for info for the following (cuz these are what I have )

Sigma 70-200mm EX HSM f2.8

Tamron 28-75mm Xr Di f2.8

Canon 50mm f1.8 mkII

Canon 75-300mm IS USM f4-5.6
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