Question About Full Detail (100%) Crop

I have read about using this method to determine sharpness but can't you just set the original to 100% and achieve the same results? I realize that at 100% you will only see a portion of the picture on your screen but you can drag the picture around and see any portion of the shot that you want to view. Maybe I am just misunderstanding what the full detail crop is and how to use it. An explanation would be appreciated. I am a newbie so please try not to use the "big" words or a lot of 3 letter abbreviations.

It's so that you can easily share with others a slice of that full res image, without subjecting us to the download time for a full res image.

Please allow me to add a few additional words to the explanation from John.

For your personal purposes there at your computer, that works quite well. In fact, if you view your original at 200% or even 300% you get an even better idea of whether things are sharp or not.

However, think about our plight here at the receiving end. What we usually get is not the original. All we get is a scaled down picture with only 800 pixels on the long side instead of 3000 or more pixels you have in your original. So, what we can see at 100% is perhaps only 1/4th of the detail that you can see. The objective is to take a small piece of your picture and give it to us at full size, so that you don't break the rules for file size but we get to see the full detail in our little piece of the pie.

Thanks for clearing that up for me. The part I missed was that the crop was for sharing on the forum and not for reviewing my shots at my computer. It makes perfect sense when I know what you are talking about.

When you are viewing your images in an image editing program, I like to keep zoom percentages to some "magic percentages" : 25, 50, 100, 200, 400, 800. This allows the pixels to be rendered at a power of 2 ratio. 100% is obviously 1:1 (well actually it isn't, but I'm going to keep it simple). 25% combines data from 4 pixels and shows it in one. 800% uses 8 pixels to show one pixel. See how these zoom percentages make for nice, easy math for the display? Now here are my other pixel peeping tips. The only reason to view above 100% is to see close up exactly how much haloing sharpening is causing, or how much sharpness your noise removal plug-in is affecting. For final output, I like to get the image to the final print size in pixels (about 240-300 ppi note: see Scottes Cropping Tutorial) and set the view to 50%. Then I slide my chair back about three feet from the monitor and view the image. If it looks good, it is good.