Micro calibration and TCs

[KIPAX]

This subject was touched upon some time ago. However more people now have the ability to do there own lens calibration so am gonna ask..

If you calibrate a 300/400 lens or suimmilar. Then add a 1.4tc or a x2TC should you have to recalibrate or should it work exactly the same? Or indeedy? Have you found the need to recalibrate and if so by how much per TC?

 

[seriousrikk]

From my understanding of how TC's work you should not need to recalibrate as they don't actually change the focus point. All should be the same

 

[markrichardson]

According to Canon you'll need to calibrate again - the camera will store the calibration separately with and without the TC. (There'd be no reason to do that if there was no need for a second calibration)

 

[seriousrikk]

Good point Mark, thinking about it my 50D does recognise the 1.4x when it is attached so it woul dmake sense that if you saved info for the lens you would need to save it again for lens & tc.

Although the amount of adjustment required should be the same.

 

[KIPAX]

According to Canon you'll need to calibrate again - the camera will store the calibration separately with and without the TC. (There'd be no reason to do that if there was no need for a second calibration)

This is what made me think because it does come up as a seperate item with a TC on

But wouldnt there be a mathamatical formula? ie if you already calibrated a 300 lens at +8 then add 1.4 focul lenght then ?? thats the point my head falls off

 

[KIPAX]

Although the amount of adjustment required should be the same.

Is this a written in stone absoloute fact? or?

 

[admirable]

They do need calibrated separtately and the lens + TC should be treated as a separate calibration alongside the lens without the TC.

There is no magic formula so get the tripod out and get to work!

 

[KIPAX]

They do need calibrated separtately and the lens + TC should be treated as a separate calibration alongside the lens without the TC.

There is no magic formula so get the tripod out and get to work!

We are still getting different answers.. Your now saying a different calibration and someone elsee saying same calibration...

We need a difinitive answer... Maybe time to ask canon ... haha only kidding.. they wont know

 

[admirable]

trust me

 

[KIPAX]

trust me

Thats what canon said when they sold me the mkIII

seriosuly thouhg.. there surely has to be a formula if your adding an exact focul length.. unless i completely missunderstand how calibration works

 

[Canon Bob]

trust me

I do

... there surely has to be a formula if your adding an exact focal length..

A Micro Adjust value of 1 equates to 1/8 of the depth of focus (front or back, but not both added) at the maximum aperture of the lens/combination installed (maximum aperture is always used to focus).
The maximum aperture is reduced by the T/C so this means that the unit value of MA has changed when using a T/C.... but any inherent calibration error in the lens is still there.
MA will also correct for any angular mispositioning in the body's secondary mirror assembly...hence, the same value is not always mapped when a lens moves from body to body.

If the T/C is so perfect that it doesn't affect focus then it is theoretically possible to calculate the "new" value by working out the new depth of focus and modifying the value ascertained from the naked lens. In practice, you'd have done the calibration "normally" long before you'd have rammed your sliderule up the dog's jacksy in manic frustration.

HTH

Bob