How does Sigma 17-50mm f/2.8 EX DC OS perform? Can I see some pictures?

Started Dec 11, 2010 | Discussions thread
MAC Forum Pro • Posts: 13,572
Re: I'll try one more time


sigh..I tried.

To end my side of this -- I provided a real output example -- 8x10 Prints. Not pixel peeping on screen where people get confused on what the output on print will be.

I provided advise if the shooter is using a 7d and 50mm that they use at least ss 1/80 or greater handheld to ensure no handshake for AN 8x10 PRINT.

I provided advise if the shooter in the same position photographing the same subject is using a 5di and 50 mm that they use at least ss 1/50 or greater handheld to ensure no handshake for AN 8x10 PRINT where the subject statue is SMALLER in the SAME 5di 8 x10 PRINT.

These are real life examples --versus pixel peepin screen examples that you are discussing

Stay REAL LIFE output Keith -- for once this is not math

CoC is about DOF -- not camera shake. Both sensors will shake the same amount -- in total sensor shake and thus total image shake (it's ONE entire image shake -- not down to the pixel shake--which is meaningless) to create one entire 8x10 - image -- not about one pixel shake. You can't move pixels around in space. It is about the overall sensor shake and creating ONE 8x10 PRINT. Think -- IMAGE LEVEL -- not PIXEL LEVEL.

It doesn't matter the pixel density on the two sensors -- what matters is the crop factor -- the magnification -- both producing the 8x10 print from the same position with the same lens.

Respond to me if you want - but stay with the Real life output of 8x10 - normal size prints -- and not pixel peeping. With the example I presented -- it is as simple as HIGHER ss is needed because you are magnifying by a factor of 1.6 what can be ACTUALLY SEEN in the 8 x10 REAL LIFE EXAMPLE

Keith Z Leonard wrote:

Mac, I don't know what you are trying to prove, I've already stated that the image is under greater magnification when viewed as you are suggesting. We agree there. The geometric relationship between the incoming light and the sensor elements however does not change between the two sensor sizes, as you can see in my horribly drawn diagram, so when "pixel peeping" the image is in fact not under greater magnification. So if you judge your images at 100% you would not see greater shake issues.

Now yes, if you blow up the crop to be the size of the full frame image, you are under greater magnification, there is no doubt. Hand shake though has EVERYTHING to do with pixel density as higher pixel density creates a larger circle of confusion in pixel space, therefore mushing together more pixels during exposure, so when viewed at 100% your contrast between pixels will be lessened. The shake remains the same (well, it's variable based upon you, not the number of pixels in your sensor), but the movement of that shake across xxx pixels changes.

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