GracieAllen
Senior Member
Rather than make my other query overly complicated, I'll ask separately...
Sigma 150-600 C on a Nikon D500.
This combination spends the vast majority of it's time at 400mm or longer (90% probably at 600mm). And the focus distance is RARELY closer than 30-40 feet. Not 100% of the time, but things shot at 10 - 30 feet seem sharp and not a problem.
So, if I need to calibrate anything (I have hundreds of disastrous images from an earlier shoot when the bif are very visibly out of focus even when the focus point is right on the bird), I'd say 400 and 600mm at the ~45 feet and infinity distances. I don't see a way to shift the focus distances in the calibration so I presume my choices are 9.2, ~20, ~45 and infinity feet.
First question is HOW do you tell if there is likely a front or back focus issue? I can put a long-ish chart out, mark it where I want to focus, put the camera on the tripod and all that. Focus on the spot and voila... Except even at 600mm and f/6.3 the DOF is at least 6 inches, and I can't see any significant loss of sharpness for at least a foot in either direction... And even then it's so subjective I'm reluctant to shift the focus...
And HOW do people actually do this? For example - 600mm ~45 feet f/6.3. Let's say I want to shoot a series of images from +20 to -5 in 5 step increments. So I'd have to pull the lens off the tripod and body, put it in the dock, go to the calibration, set it at +20, put it all back together and take a picture. Then repeat at +15, +10 +5 0 -5 -10 -15 -20... I figure with my luck it would take a huge amount of time and I'd probably drop the lens at least once! Is this brute force method what people use to do the calibration?
And HOW do you do it at infinity? I'm not sure where this lens hits infinity, but how far do I have to be from the chart (or whatever subject I use) to get a reliable "infinity" test? Again, even at 6.3, at 100 feet the dof is at least 2 FEET, and at 150 feet it's over FOUR feet... How do you even make a guess that there's a problem?
Sigma 150-600 C on a Nikon D500.
This combination spends the vast majority of it's time at 400mm or longer (90% probably at 600mm). And the focus distance is RARELY closer than 30-40 feet. Not 100% of the time, but things shot at 10 - 30 feet seem sharp and not a problem.
So, if I need to calibrate anything (I have hundreds of disastrous images from an earlier shoot when the bif are very visibly out of focus even when the focus point is right on the bird), I'd say 400 and 600mm at the ~45 feet and infinity distances. I don't see a way to shift the focus distances in the calibration so I presume my choices are 9.2, ~20, ~45 and infinity feet.
First question is HOW do you tell if there is likely a front or back focus issue? I can put a long-ish chart out, mark it where I want to focus, put the camera on the tripod and all that. Focus on the spot and voila... Except even at 600mm and f/6.3 the DOF is at least 6 inches, and I can't see any significant loss of sharpness for at least a foot in either direction... And even then it's so subjective I'm reluctant to shift the focus...
And HOW do people actually do this? For example - 600mm ~45 feet f/6.3. Let's say I want to shoot a series of images from +20 to -5 in 5 step increments. So I'd have to pull the lens off the tripod and body, put it in the dock, go to the calibration, set it at +20, put it all back together and take a picture. Then repeat at +15, +10 +5 0 -5 -10 -15 -20... I figure with my luck it would take a huge amount of time and I'd probably drop the lens at least once! Is this brute force method what people use to do the calibration?
And HOW do you do it at infinity? I'm not sure where this lens hits infinity, but how far do I have to be from the chart (or whatever subject I use) to get a reliable "infinity" test? Again, even at 6.3, at 100 feet the dof is at least 2 FEET, and at 150 feet it's over FOUR feet... How do you even make a guess that there's a problem?