5D3 + 24-70 f2.8 II + FoCal

[TotoEC]

I have AFMA my 5D3 and 24-70mm f/2.8 using FoCal v1.6. I’m getting variations on the results and wondering if is this normal? I've searched the internet and the FoCal site for comparison but none that I could find except from this forum.

Comments are welcome.

 

[rpt]

I have AFMA my 5D3 and 24-70mm f/2.8 using FoCal v1.6. I’m getting variations on the results and wondering if is this normal? I've searched the internet and the FoCal site for comparison but none that I could find except from this forum.

Comments are welcome.

I had a similar problem some time back and it boiled down to two things:
[list type=decimal]
[*]I had the center mast of the tripod up and that caused some sway. The camera should be absolutely steady.
[*]I was doing it in the morning and the sun was going in and out of the clouds so variable light...
[/list]

Other than that, was your battery completely charged?

 

[Loswr]

If you're getting inconsistent FoCal results, it's almost always due to insufficient light or an unstable support. EV should be 10 or higher.

 

[TotoEC]

I have AFMA my 5D3 and 24-70mm f/2.8 using FoCal v1.6. I’m getting variations on the results and wondering if is this normal? I've searched the internet and the FoCal site for comparison but none that I could find except from this forum.

Comments are welcome.

I had a similar problem some time back and it boiled down to two things:
[list type=decimal]
[*]I had the center mast of the tripod up and that caused some sway. The camera should be absolutely steady.
[*]I was doing it in the morning and the sun was going in and out of the clouds so variable light...
[/list]

Other than that, was your battery completely charged?

Batteries were fully charged. The camera was mounted on a video tripod with fluid head and was weighted further by a 10 lb barbel. The height of the target (bullseye), and the center of the lens were the same. What concerns me is I am not getting a consistent sharpness 'reading'. Shouldn't I get the same resolution 'reading' even if the distance are varried?

@neuroanatomist: I have EV of 11.6

 

[Loswr]

What concerns me is I am not getting a consistent sharpness 'reading'. Shouldn't I get the same resolution 'reading' even if the distance are varried?

No, you shouldn't. If you change the framing, you're changing the size of the target image projected on the sensor. Further away (at same focal length) means smaller target covering fewer pixels on the sensor and thus a lower resolution. When you use a real test chart (ISO 12233 type), you must frame the full target for the resolution values to be accurate (there are framing marks on the chart).

 

[TotoEC]

What concerns me is I am not getting a consistent sharpness 'reading'. Shouldn't I get the same resolution 'reading' even if the distance are varried?

No, you shouldn't. If you change the framing, you're changing the size of the target image projected on the sensor. Further away (at same focal length) means smaller target covering fewer pixels on the sensor and thus a lower resolution. When you use a real test chart (ISO 12233 type), you must frame the full target for the resolution values to be accurate (there are framing marks on the chart).

Thanks a lot neuro! I was suspecting the same but can't quite pin down the reason until you put it together. What a relief! For a second there, I thought I have a bad copy. My salute to you!

 

[Mt Spokane Photography]

There are lots ov variables, distance is one of them, its fine to vary the distance, but expect different results as well.
Notice how little variation there is accross the top of the curve, Just a tiny bit of difference will change things. The good news is that the sharpness doesn't change much from +2 to -2 so the setting is not that critical. Sharpness won't be a issue unless you get well down on the curve.

 

[Funkmobile]

Did you cover over the viewfinder the entire time?

 

[rpt]

Did you cover over the viewfinder the entire time?

Yes, that is the third thing I did when I got consistent results. I forgot about it when I posted earlier...

 

[TotoEC]

Did you cover over the viewfinder the entire time?

Yes, that is the third thing I did when I got consistent results. I forgot about it when I posted earlier...

All the time while the test was conducted, except when acquiring the target after moving from 25x or 50x the focal distance, or when I tested it at 5' and 10' prefered shooting distance for portrait.

 

[rpt]

Did you cover over the viewfinder the entire time?

Yes, that is the third thing I did when I got consistent results. I forgot about it when I posted earlier...

All the time while the test was conducted, except when acquiring the target after moving from 25x or 50x the focal distance, or when I tested it at 5' and 10' prefered shooting distance for portrait.

Ok. So you could try this:
Set the MA values for Wide and Telephoto as suggested by FoCal. Then take a set of pictures each at 24mm, 50mm and 70mm. Each set would consist of two photos. Both taken of the same target at the same distance. One imaged thru the viewfinder and the other imaged with live view. You may change the distance of the target for the three focal lengths. If the pair looks equally in focus, that MA setting is good. If not, it is not. If both extremes are good and the 50 is not I think you should replace the lens. If one of the extremes is good and the other two are bad, you need to run FoCal again and then repeat this test.

My 100-400L is in the shop and when it comes back I am going to run this exact test on it. Hope this helps.