Yup, you're absolutely right. But in practice it's easier said than done. Scanners are passé, but they are beneficial in this case to get very precise results from the software.
I personally have my own rig for product photography that allows me to mount any camera perfectly level and perpendicular to the object. If anyone doubts how far out you can be simply by skewing the camera even just a tiny bit, check out this example.
The square paper is EXACTLY 100mm in both dimensions. You can see how far out the top is from the bottom, that's HUGE when it comes to measuring targets and consequently you will have VERY misleading results.
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Trying Ontarget for the first time and having trouble being able to add dialog and also uploading pic with all the neat measuring lines on it. But anyways, was quite interesting.
Target shot at 500m with my Savage/Shilen 260 improved and 140gr Bergers.
Using the ruler pictured - OTO was 2.125" or 1.86" CtC
Using a caliper - OTO was 2.115" or 1.85" CtC
So these are pretty close. There is a bit of error trying to judge the outside of the holes.
Using ontarget with the pic centered as best I could, The program said I was 1.83" or 0.321MOA. This value can vary quite a bit depending on where you put the aiming circle for the hole. Doesn't take much.
With the camera tilted approx 45deg to the left, it measured 1.757" or 0.307MOA (0.073" diff)
With the camera tilted approx 45deg to the right, it measured 2.037" or 0.356MOA (0.208" diff)
It was nice to see that whether using a manual method or getting a 'square' image, the measurement was close enough to be interesting.
Just need to learn how to put in the text (there was no obvious button to activate), save as a jpeg with all the data on it so I can upload to photobucket.
Jerry
I hear what you're saying, but there are exceptions to your generalization. Anyone who posts a measurement in hundredths or even thousandths of an inch is CLEARLY interested in precise measurements. I'm simply trying to illustrate the perils of photograph analysis and offering a couple solutions to provide more accurate results.
I'm critically analytical, don't hate me.
Wow Jerry! I shot a group like that today.... at 200m. I'll work up to 500
Thanks for taking the time to actually test the camera angle thing... as we say in my industry, 1 test is worth 1000 expert opinions.
As for this issue in general, how accurate do your group measurements really need to be? If the "actual" group is 1.105" and you measure it to be 1.120" using a caliper or 1.095 using OnTarget... unless you are competing it shouldn't matter that much. I measure my targets and record them in my shooting book so I can see my progress over time. It's great to look at the numbers over a year or so and see them steadily shrink.
As for what's posted as group sizes on the net, well, kinda like fishing stories on Monday around the water cooler right?
Barry
If I have to photoshop errant shots to make a group look smaller after spending $2K+ on building a rifle then I have bigger issues than how I am measuring my groups.
