7D2 + 100-400 II + 1.4 III MFA

[digital paradise]

I seem to need a lot of MFA with this combo. Before I proceed the 100 and 140mm adjustments are around +3 for both TC on and off. Without the TC I'm at about +4 @400. When I add the TC I need +14 @560.

I came across this article and the author states that TC's are tuned for long primes. Canon does say that the 100-400 is compatible with the TC.

http://www.lensrentals.com/blog/2009/01/teleconverters-101

I don't shoot a lot with my 300L F4 IS anymore but I tried it. No TC = +4. With TC = +5

It is not a problem but I'm just curious what would cause that on a telephoto zoom. There are a few more people out there saying they need these high numbers. +12 was the other highest.

Thanks in advance.

 

[candc]

Its just a matter of + or - tolerances that add or subtract from one another. I haven't been able to figure out any predictable pattern. The same tc added to a lens may cause -afma on one lens and + on another. As ling as you can bet the combo to work right then don't sweat it.

 

[digital paradise]

I'm not concerned. Mostly curious what physical/optical properties would case a need for such a high MFA number.

 

[AlanF]

My two copies with two different 1.4xTCs both have 10 point difference with the TCs added. I recall on looking at Focal 2's comparisons with other users that this large correction is common.

 

[digital paradise]

You have two copies of that lens? I don't recall seeing data on TC's at Focal but I'll look again.

Based on what lens rentals says perhaps a small difference in normal body and lens tolerances can throw a zoom at f8 out a lot. Exponential error. It is really not an error, just normal tolerances that will be exploited in a certain direction. A lens and body both the minus range, a lens and body both in a plus range and both opposite can cause different results how the light waves move trough the TC and lens even when final results being +3 or +14 look good. Just guessing. I'm not an engineer.

I know it surprised me. I ran Focal 5 consecutive times and got +15 three times, a +16 and a +17. It is PD so there will be some variation. My previous first run gave +15 as well. The three 15's showed excellent while the 16 and 17 showed acceptable. G& B showed +15 in the RGB report. I was about ½ the recommended min distance to target. I had to reduce the target size and I entered new value in. I need to read more about changing target sizes and distance.

Next week I'll be at a location where I can be at the correct min distance so we'll see. It is still going to need +14 or more but we'll see what Focal says.

 

[2n10]

Interesting data on the wide variance at telephoto. Mine settled well with my Canon TC but I have seen something similar with another brand TC.

 

[digital paradise]

I would have preferred that that is was not at +15. Closer to 0 would have made me happier but it is what it is. I sure would like to know what causes such big drifts between owners of the same lens which is really why I posted in the first place. Not a lot of info on the interwebs for that specific inquiry.

Good thing I don't use it much. I find I lose too many focusing options with it. Having too much fun with with the cam. Not that I can't nail a BIF but you can crop so much with the 7D2 as I could with my 7D. I use it mostly for stills.

 

[tphillips63]

Just curious, what does it do at +15 vs if it had been say +7? I mean is it going to be sharper the closer it is to 0 or focus faster or both?

 

[digital paradise]

Less sharp at +7 and focusing speed is not noticeably effected.

 

[candc]

Afma is a way to correct for different distances in the light path between the af sensor and the image sensor. Those differences can be from mount variations, mirror alignment etc. Once its zeroed it should perform as well as any other combination regardless of afma value required. Don't think that because a particular lens/tc/camera combo requires afma makes it substandard. Its just a luck of the draw thing.

 

[digital paradise]

Thanks for the info.

 

[digital paradise]

Instead of starting a new thread

Does anyone know how do save the data you enter for a resized printed target? Printed Target Width box is located in Preference's - Tests. When I enter the new value and close the Preference window it resets. At this point I'm wondering if you are just supposed to leave it open during the test?