Need help for inconsistent lens sharpness.

[Turbonetics]

i was setting my Canon 100-400mm lens sharpness to suit my camera in the micro-adjustment function at 400mm end.
and i focus on different item at different distance.
most of the time it performs best at around +15.
however,there was an instance that 0 is sharper than the +15.

anybody can explain why is this so?

 

[Octarine]

Something to read:
LensRentals.com - Notes on Lens and Camera Variation
LensRentals.com - The Limits of Variation
Drop the idea that your camera and lens will perform each AF operation in exactly the same way. You actually figured it already with your setup

 

[Octarine]

Something to read:
LensRentals.com - Notes on Lens and Camera Variation
LensRentals.com - The Limits of Variation
Drop the idea that your camera and lens will perform each AF operation in exactly the same way. You actually figured it already with your setup

 

[Turbonetics]

Something to read:
LensRentals.com - Notes on Lens and Camera Variation
LensRentals.com - The Limits of Variation
Drop the idea that your camera and lens will perform each AF operation in exactly the same way. You actually figured it already with your setup

Hmm..interesting articles which i had always suspected that AF is not always accurate and lens/body performance differs accordingly.
so how should i adjust the camera to get the best result from the lens?
if i choose either 0 or +15, they will be either sharp or soft and vice versa.quite noticeable difference.

 

[Kenneth67C]

Hmm..interesting articles which i had always suspected that AF is not always accurate and lens/body performance differs accordingly.
so how should i adjust the camera to get the best result from the lens?
if i choose either 0 or +15, they will be either sharp or soft and vice versa.quite noticeable difference.

Did you use a tripod for your test and switch off IS?

 

[Turbonetics]

Did you use a tripod for your test and switch off IS?

yes.definitely.

 

[Kenneth67C]

You mention there is an instance when its not sharp.
Exactly under what conditions is this the case?
Can you post both pics here?

 

[daredevil123]

Please also note that when testing AF, you need to do it in good light. And that means no florescent lights also. If have to test in less than stella light, use a flash when testing.

 

[Turbonetics]

You mention there is an instance when its not sharp.
Exactly under what conditions is this the case?
Can you post both pics here?

i set up everything inside my house with minimal wind.basically i used AF to lock focus then switch to MF and 10X live view to make sure things ain't too shaky before i snapped.
it was bright daylight.
i shot at the bus service board opposite my flat,flat unit number opposite my block(about 200M) car number plate parked opposite my block and block number opposite my block.
i already deleted all the photos as i roughly know how my lens and camera performs then.
all the shots are sharp at +15 except for the block number which is sharp at 0.
all shots are across the road being the bus stop service board the nearest and the unit number the furthest.
and also did a couple of shots to verify for all scenarios.

 

[daredevil123]

i shot at the bus service board opposite my flat,flat unit number opposite my block(about 200M) car number plate parked opposite my block and block number opposite my block.

That is not how you tune AF. Use a focus test chart.

Read the instructions in this site:
http://regex.info/blog/photo-tech/focus-chart

 

[Turbonetics]

That is not how you tune AF. Use a focus test chart.

Read the instructions in this site:
Jeffrey Friedl's Blog » Jeffrey’s Autofocus Test Chart

last time i had printed out the same chart to do it for my standard zoom lens and i wasn't really good at it.
i will read up this article to extract the correct ways to do it again.
thanks.

 

[daredevil123]

last time i had printed out the same chart to do it for my standard zoom lens and i wasn't really good at it.
i will read up this article to extract the correct ways to do it again.
thanks.

remember to use a tripod. And if light is not good, use a flash.

 

[Turbonetics]

remember to use a tripod. And if light is not good, use a flash.

sure,i will use tripod especially for such telephoto lens.
for the flash do u mean speedlites or flashlight shining on the chart?

 

[daredevil123]

sure,i will use tripod especially for such telephoto lens.
for the flash do u mean speedlites or flashlight shining on the chart?

speedlite will do.