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Archive 2015 · Dot Tune Middle of a Zoom Range

  
 
msalvetti
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p.1 #1 · p.1 #1 · Dot Tune Middle of a Zoom Range


I haven't seen this discussed before, so I'm probably overthinking things.

On my 7DII, I can MA for the wide and tele ends of the zoom range. Should I set both the wide and the tele ends at the same MA value as I Dot Tune? If I don't, won't the value on the tele end influence the result? How does the camera know which MA adjustment to use while I'm Dot Tuning?

Probably easier to explain with an example. At 70mm, my Dot Tune range is +12 and -5. While zeroing in on these values, I had the tele MA value at 0. If I had the tele value set at something other than zero, would it have affected the MA result at 70?

What if I want to check the MA mid-range, at 135mm? Normally the camera would interpolate an MA value for that focal length using the MA results at 70 and 200. Using Dot Tune at 135mm, I got +6 and -11. I thought I better set both the wide and tele values at the same number as I Dot Tuned to make sure no interpolation was occurring. Was that the correct approach?

Thanks,

Mark




Oct 31, 2015 at 02:44 PM
charlyw
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p.1 #2 · p.1 #2 · Dot Tune Middle of a Zoom Range


I think not. Simply perform a tuning cycle at the wide end (it will not be influenced by the tele setting) and then perform one at the long end (which will not be influenced by the wide angle setting)... Then the interpolation of the intermediate values should be correct too.


Oct 31, 2015 at 03:22 PM
msalvetti
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p.1 #3 · p.1 #3 · Dot Tune Middle of a Zoom Range


Thanks. That assumes that the MA adjustment is linear across the range, but I'm not sure it is, and that's why I want to check MA in the middle.

I didn't think I'd have time to test this (I always seem to start MA as I'm losing light), but I just finished adjusting the 70-200 again.

When adjusting MA at the wide end, it doesn't matter what the tele setting is, and vice versa. I'm sure this is because the camera recognizes which end of the zoom range is being adjusted, and it ignores the opposite setting.

But in the middle, it's a different story. Here are my latest results with my 70-200:

At 70mm: +1 and -13, midpoint = -6
At 200mm: +3 and -14, midpoint = -5.5

That looks fantastic, except at 135mm I have +8 and -9, midpoint 0. I achieved these numbers setting both the wide and tele settings to the same value. At +8, if I set the Tele value at a much larger number (say +20), then +8 no longer achieved focus. I suspect the camera was averaging +8 and +20 and getting +14, which doesn't work. If I went the other direction with the tele setting I was able to still achieve focus as long as the average between the wide and tele settings was between +8 and -9.

Now I have to figure out what MA settings to plug into the camera for the 70-200. Seems like whatever values I use, I'll be quite a ways off somewhere. If I force MA to be sharp at 135 (by using +6 on the wide end), I'll be way off below 135mm.

I will probably just use -6 at the wide and tele ends and see how the lens performs in real life. I'm also not sure why the results are so much different than the last time I adjusted this lens.

Mark



Oct 31, 2015 at 04:37 PM
schlotz
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p.1 #4 · p.1 #4 · Dot Tune Middle of a Zoom Range


Hmm... each of the settings 70 & @200 I believe should have been derived from a base point, that is with NO AFMA set in the camera, i.e. set to 0. The 135mm should also be established without any AFMA set in the camera. If you do this, then what are the results?

Matt



Nov 01, 2015 at 07:53 AM
Ian.Dobinson
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p.1 #5 · p.1 #5 · Dot Tune Middle of a Zoom Range


with the latest version of MA (i.e. the ones with wide and tele settings) you need to do both . the system then adjusts as the focal length changes . if your settings are close or the same for either end then the change from 1 offset to the other is either very small or non existent .

if as you say your settings change that much in the middle of the focal range and then drift back at the other end then I don't think the system is going to compensate for the focal length your at .

in that case its either going to need a trip to canon or you may have to do a complete chart of MA settings and ride with a default all-round setting (same MA for both ends as your results are pretty dam close) that you would change when you are working at different focal lengths .
something like settings for 70 -100 - 135 -175 -200mm

By the way I know the dot tune system is pretty good (i have used t myself) but it may be worth trying a different method as well to make sure your getting the correct or at least very close results .

you can also use a tethered method using the canon software .

set the camera to 0 ma and then get it to focus (not live view) . the in the canon there'd software you can adjust focus using the <<< << < > >> >> buttons on screen . a single hit on the < or > is a 1 MA point either way .




Nov 01, 2015 at 09:56 AM
charlyw
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p.1 #6 · p.1 #6 · Dot Tune Middle of a Zoom Range


msalvetti wrote:
But in the middle, it's a different story. Here are my latest results with my 70-200:

At 70mm: +1 and -13, midpoint = -6
At 200mm: +3 and -14, midpoint = -5.5

That looks fantastic, except at 135mm I have +8 and -9, midpoint 0.

So with the two settings you got for the short and long end your mid range experiment confirmed that you achieved a good calibration. If I misunderstood you then your lens is inconsistent and a case for a trip to the service centre (which it would be for me anyway even if the result were consistent at -6)...



Nov 01, 2015 at 10:28 AM
msalvetti
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p.1 #7 · p.1 #7 · Dot Tune Middle of a Zoom Range


Matt, I'm not sure what you are asking. At 135mm I tried setting both wide and tele at zero, and then only adjusting one of them. These results are different than if I adjust both together, but I didn't write them down.

Ian, I agree. The plan was just to adjust each end. That's the only advice given in the camera manual. This is my first camera that allowed two MA settings. With my 7D and 1DMkIV I would check MA at various focal lengths, and then select either the average or a number within the focal length range I used the most. From that experience, I knew it was possible that MA was not consistent across the zoom range. My 100-400 has been pretty consistent from 200-400 (linear), but at 100 it tails off. However, my 70-200II has always been very consistent throughout the range, so I am suspicious of that 135mm result. Your suggestion that I use another method is a good one. I also have FoCal, and I've never attempted using the Canon software either. I may also try checking the MA values again with the lens on my MkIV and see if I get similar results.

Charlyw, yes, if in fact the middle of the zoom range is that far off, I may decide to send it to CPS.

Thanks everyone,

Mark



Nov 01, 2015 at 10:51 AM
schlotz
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p.1 #8 · p.1 #8 · Dot Tune Middle of a Zoom Range


Mark,

I'm trying to determine specifically how you went about the afma. Did you do it for the wide, determine the number then make sure no afma was plugged into the camera prior to determining the long afma? i.e make sure there is no wide afma in the camera when you do the long afma, same the other way. If not, what you got might not be accurate. Same thing with the lens at 135, determining its afma should be done prior to setting any afma in the camera. Now if that is how you did it then a trip to cops might be in order.

If everything is done correctly one should expect the 135 figure to be near or between that of the 70 and 200.

Matt



Nov 01, 2015 at 04:01 PM
msalvetti
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p.1 #9 · p.1 #9 · Dot Tune Middle of a Zoom Range


Thanks Matt. So you're saying that if the lens already had MA settings saved (mine did), I should have reset them to zero before trying to MA the lens again?

I didn't do that - I just went back in and re-established MA settings at the wide and tele end. I guess I assumed when I entered the "adjust by lens" menu, the camera would ignore any previous MA settings that were saved for that lens. Maybe not.

I'll need to experiment some more, but I won't have daylight to do it in until next weekend. I haven't shot with my 7DII very much. My first MA settings for this lens were 4 at 70mm and -8 at 200mm. I shot an event recently and I wasn't happy with the sharpness at 200mm. Today I shot some test charts with MA turned off, and the lens sharpness decreased as I zoomed out. I always thought this lens was plenty sharp on the 7D and 1DMkIV with minimal MA.

I shot a hockey game this afternoon with the lens - I will hopefully have time to look at some of those images later tonight or tomorrow.

Mark



Nov 01, 2015 at 10:03 PM
jcolwell
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p.1 #10 · p.1 #10 · Dot Tune Middle of a Zoom Range


So, if you set the AFMA values at both wide and long ends to be the correction value that's needed for 135mm, then are you better off on average? At least, you'll be right at 135mm.


Nov 01, 2015 at 11:31 PM
RustyBug
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p.1 #11 · p.1 #11 · Dot Tune Middle of a Zoom Range


I've not used AFMA on any body yet ... but have wondered about such things.

Is it possible to set your wide end at say 90, and your long end at 180 (or maybe 100 & 150 or other FL's of choice) @ just a tad "in" from the ends to "smooth" things out across the range? Or does the AFMA only function to be set at the end points?

The "why" would you being to the OP's point at more accuracy / less interpolation for your midrange (or other "sweet spot" in your shooting), at the minor expense to the end points? Or does the "how" restrict you from doing so at end points only (regardless of the rationale for / against the "why") ?



Nov 02, 2015 at 09:02 AM
Ian.Dobinson
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p.1 #12 · p.1 #12 · Dot Tune Middle of a Zoom Range


RustyBug wrote:
I've not used AFMA on any body yet ... but have wondered about such things.

Is it possible to set your wide end at say 90, and your long end at 180 (or maybe 100 & 150 or other FL's of choice) @ just a tad "in" from the ends to "smooth" things out across the range? Or does the AFMA only function to be set at the end points?

The "why" would you being to the OP's point at more accuracy / less interpolation for your midrange (or other "sweet spot" in your shooting), at the minor expense to the end
...Show more


Rusty , I think with the dual system your supposed to do either end and not the points in between .
From what I gather the system is supposed to adjust by a different offset at other focal lengths . i.e. (slightly over simplified) if wide = 0 and tele = +13 then the offset would change by 1 for each 10mm difference in focal length .
But I doubt its a simple as that . I bet there is a weighting toward the tele end due to the thinner DOF needing a more accurate MA . and also I doubt you will see many lenses that have that big a spread over the zoom range .

what It can't do is adjust by less than 1 ma point . so if you wide and tele ends are only 1 point apart then the shift will come in at some point in the zoom range (my guess would be between 1/2 and 3/4 distance)

what this assumes is the lens only changes that set difference and doesn't have a completely different setting in the middle (like the OP's supposedly has) .
in this case then as I suggested above its probably better to MA at that mid point and then set both the wide and tele points the same .



Nov 02, 2015 at 09:57 AM





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