Problems MFA 7D?

I wanted to MFA my 70-300 F4-5.6 L IS USM. -really to see if it could be improved.
I put the chart on the floor, measure out so it was taken at 45 degrees, placed on a tripod and took this photo [In fact three all very similar]. The lens was set at 70mm and came up with an f4 exposure.

I was expecting to see the typical scenario where one of the lines was sharp and determining if it was front or back focusing. As I'd seen on my Sony A77 [which backfocused say 1mm.]

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Make another test shot and make sure you've removed any filter from the lens. Check the front and back lens elements to make sure they are clean. Leave the IS off and use the timer to release your shutter. If you can get a remote release that would even be better. Then post another sample.

You can look at the variables yourself and see how it affects depth of field which needs to be taken into account when testing a lens for focus issues. Some specs for the lens you mention include the minimum focus distance of roughly 47 inches. That means if you are at 47 inches subject distance anything nearer than that will likely be out of focus just because of lens capabilities. Points further away will be in focus subject to the depth of field and the lens setting variables (zoom and aperture).

That lens has variable f-stop capabilities at various focal lengths. They are approximately as shown below:

70-103mm = f/4.0
104-154mm = f/4.5
155-228mm = f/5.0
229-300mm = f/5.6

There is a depth of field calculator at http://www.dofmaster.c​om/dofjs.html that should help you in the future. Based on the calculator at 70mm zoom, f4 and 6 foot subject distance the near limit of depth of field is 5.84 feet and far limit is 6.17 feet. The difference of 0.33 foot, or slightly less than 4 inches is your total depth of field. So if you had a perfect lens and focused on the heavy line in the test chart, the line should be in perfect focus, points closer than 5.84 feet will be out of focus to varying degrees and points further than 6.17 will also be out of focus, again to varying degrees.

OK, take the lens out to 300mm, f5.6 and 6 foot subject distance. The near limit is 5.99 feet and far limit is 6.01 feet for a total of 0.02 feet or 1/4 inch! As you can readily see you have very little leeway for error! If you are wondering why I ran those numbers at f5.6 and the previous case at f4 it is because at 300mm the lens is only capable of f5.6.

A: You can only MFA at a given focal length...so pick the one you're most likely to be shooting at

B: When doing this type of a test, you need a flat plane to focus on, with the angled ruler off to the side, like the LensCal, or one of our members has created a printable chart that is similar...hopefully he'll chime in here, since I can't recall who it is off the top of my head...

The reason for this is that when the camera attempts to focus, it picks a spot under the active AF point, but it can be ANYWHERE under or just slightly outside of the box displayed in your viewfinder. If you've placed your target at a 45 degree angle, then you have no idea just WHERE it focused, to determine whether or not the focus is actually off. If your target is square to the camera, then you're focusing on a defined plane, which then makes your measurements on the focus scale meaningful.

John from PA wrote in post #14660546
You can look at the variables yourself and see how it affects depth of field which needs to be taken into account when testing a lens for focus issues. Some specs for the lens you mention include the minimum focus distance of roughly 47 inches. That means if you are at 47 inches subject distance anything nearer than that will likely be out of focus just because of lens capabilities. Points further away will be in focus subject to the depth of field and the lens setting variables (zoom and aperture).

That lens has variable f-stop capabilities at various focal lengths. They are approximately as shown below:

70-103mm = f/4.0
104-154mm = f/4.5
155-228mm = f/5.0
229-300mm = f/5.6

There is a depth of field calculator at http://www.dofmaster.c​om/dofjs.html that should help you in the future. Based on the calculator at 70mm zoom, f4 and 6 foot subject distance the near limit of depth of field is 5.84 feet and far limit is 6.17 feet. The difference of 0.33 foot, or slightly less than 4 inches is your total depth of field. So if you had a perfect lens and focused on the heavy line in the test chart, the line should be in perfect focus, points closer than 5.84 feet will be out of focus to varying degrees and points further than 6.17 will also be out of focus, again to varying degrees.

OK, take the lens out to 300mm, f5.6 and 6 foot subject distance. The near limit is 5.99 feet and far limit is 6.01 feet for a total of 0.02 feet or 1/4 inch! As you can readily see you have very little leeway for error! If you are wondering why I ran those numbers at f5.6 and the previous case at f4 it is because at 300mm the lens is only capable of f5.6.

Thanks I think I hit the problem - when I did the Sony A77 I just hand held it at say 3 meters.
Stupid me in order to get 45 degrees and use a tripod - I stupidly just measured the height of the camera and marked out the same distance to achieve 45 deg. So I guess I might have been under the min focus distance, which per the manual is 1.2m ( I assume at 70mm it doesn't say).
Nope just checked the tripod is 1.2m high so the distance would be just over 1.2 unless my measurement was wrong.

John from PA wrote in post #14659499
Make another test shot and make sure you've removed any filter from the lens. Check the front and back lens elements to make sure they are clean. Leave the IS off and use the timer to release your shutter. If you can get a remote release that would even be better. Then post another sample.

Thanks I ordered a RC06 remote shutter release should be here on Wednesday. I 'll re do it then.

Snydremark wrote in post #14660645
A: You can only MFA at a given focal length...so pick the one you're most likely to be shooting at

B: When doing this type of a test, you need a flat plane to focus on, with the angled ruler off to the side, like the LensCal, or one of our members has created a printable chart that is similar...hopefully he'll chime in here, since I can't recall who it is off the top of my head...

The reason for this is that when the camera attempts to focus, it picks a spot under the active AF point, but it can be ANYWHERE under or just slightly outside of the box displayed in your viewfinder. If you've placed your target at a 45 degree angle, then you have no idea just WHERE it focused, to determine whether or not the focus is actually off. If your target is square to the camera, then you're focusing on a defined plane, which then makes your measurements on the focus scale meaningful.

This was the bit I was unsure of - I chose Spot focus but the spot is so big you don't know where it really is focusing. i.e I could think it backfocusing 5 mm but if that was where it was aiming then it's right on the money. I guess the vertical plane solves that.

Submariner wrote in post #14661440
This was the bit I was unsure of - I chose Spot focus but the spot is so big you don't know where it really is focusing. i.e I could think it backfocusing 5 mm but if that was where it was aiming then it's right on the money. I guess the vertical plane solves that.

Yup! And I also forgot to say that the recommended distance, from Canon, for doing MFA is 50x the focal length that you're attempting to MFA. This will also keep you from running into any issues with minimum focus distance, etc.

I ended up doing mine with a flat target - something like ...

http://jmloptical.com …gets%20figure%2​0q2new.jpg

Get the proper distance away from the target (50x focal length), put on a decent tripod, turn off IS, use timer function and perhaps mirror lock up. Make sure to use a fast shutter speed and always use wide open aperture. In my case I set my 70-300L to 200mm and took a few shots at each MFA from -20 to +20 and picked the setting with the sharpest results. The LensAlign should also work (and be a bit more efficient), but you don't have to have one.

Snydremark wrote in post #14660645
B: When doing this type of a test, you need a flat plane to focus on, with the angled ruler off to the side, like the LensCal, or one of our members has created a printable chart that is similar...hopefully he'll chime in here, since I can't recall who it is off the top of my head...

It's Teamspeed who has the downloadable chart

The "TeamSpeed" Chart, available at https://photography-on-the.net/forum/showthre​ad.php?t=750736 is primarily for setting up MFA on a lens/body combination.

In this instance the OP isn't getting anything clear when using the Tim Jackson Chart focus chart, so there must be some other underlying problem. Although originally done for testing the Nikon D70, is well recognized as a perfectly good chart for detecting front/back focus issues but not necessarily for doing MFA.

Submariner, one other thing you should do when taking the image from a tripod, lock up the mirror to make sure the mirror slap isn't introducing any tripod movement