70D - MFA for Dummies for 70-300L

Started Mar 16, 2014 | Discussions thread
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Myer Senior Member • Posts: 2,787
70D - MFA for Dummies for 70-300L

The lens I'm referring to is a 70-300L. I don't have a tripod mount for this lens so putting it solidly on a tripod is not really an option.

How much good is this?

I have 3 marking pens that stand easily on end. They have the product name in very sharp print on the side.

I'd like to stand them up on a table about a foot and a half apart going from me away and off to a very slight angle. I will sit on a chair and be about 25ft from the table and hand-hold the camera.

I will shoot in manual mode with the ISO at 200 or 400 (depending upon the amount of light), aperture at f5.6 (wide open) and shutter speed somewhere between 1/500 and 1/1000 sec  depending upon how bright it is. Focal length full-tele at 300mm.

I did this a couple of days ago and had no problem focusing on the middle marker (using single point center). When I zoomed in the middle marker name appears sharp. I downloaded the files to my computer and zoomed in and the middle marker appears sharp.

The problem is with the closest and farthest markers. It appears that wide open at f5.6 the farthest marker is quite a bit sharper than the closest marker. I did a previous MFA (hand held) and ended up with the tele end at -3. That's where I started this latest test.

I moved up to -5, -6 and then -10. In all cases the middle marker is sharp and the farthest marker is sharper than the closest.

I'm wondering how much of an adjustment each step makes?

I was hoping that I would either end up with all three markers sharp with the middle being the sharpest. Or, at the least, the middle marker sharp and the farthest and closest approximately the same sharpness (or lack of sharpness).

Is this such a flawed approach that it has no value?

Or, am I doing something wrong?

Or, should I go back, start over, increase the negative value in increments of -2 and go beyond -10?

Canon EOS 70D
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