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Thread started 23 Apr 2010 (Friday) 11:41
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7D noob question: how to use the microadjustment scale

 
trale
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Apr 23, 2010 11:41 |  #1

I have a 50mm 1.4 that I suspect has a tendency to backfocus, so I'm going to try to MA it. The thing is, should I use negative values or positive values?

Also, what does each increment mean as far the "strength" of the correction? I know it's different depending the max aperture of the lens, so for a F/1.4 how does that translate to real life figures? For example, does each increment represent a correction of 1 inch? etc. How about for my other lens with a max F/2.8?




  
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canonnoob
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Apr 23, 2010 11:45 |  #2

There are two icons.. one that has a mountain, and one that has the camera. The camera is on the left and the Mountains are on the right. If your lens is back-focusing move the dial towards the mountains, if it front-focuses vica-versa.

typically when M/A'ing a lens I go in +/-5 increments until i see a noticeable difference, then after I get it within 5, I will go back and do 1 mark increments until im happy.


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Apr 23, 2010 11:46 |  #3

Positive moves your focus plane backward (front focusing lenses) and negative brings your focus forward (back focusing).

Supposedly, according to Canon each division is equivalent to 1/8 of the depth of field for that lens.


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int2str
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Apr 23, 2010 11:48 |  #4

Look at the adjustment scale on the camera. It shows which way is closer to the camera and which way is furhter away. No need to think of it in positive or negative numbers when you can see the scale.

As far as "strength" goes, there's no real answer to this. It depends on distance to target, aperture etc. The micro adjustment is more of a trial & error thing rather than an absolute science. Just anchor your camera on a tripod, pick a consistant focusing target and adjust & review.




  
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jacuff
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Apr 23, 2010 11:52 |  #5

But if you read the manual you'll see that it mentions
- is Forward and + is Backward. (p211)

Unless there is an errata for the manual (I haven't had to MA any of my lenses, so I haven't messed with it), it would seem looking at the icons would be counter to what the manual mentions.

Thus if your less is back focusing... you want to move it forward, so you want to dial in negative, aka towards the camera..

But to answer your strength question, the manual says the amount of each step will vary depending on the maximum aperture of the lens.


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trale
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Apr 23, 2010 12:04 |  #6

Hi canonnoob and TeamSpeed... it seems your answers contradict each other. =(

canonnoob: "If your lens is back-focusing move the dial towards the mountains" which means setting positive values, or I should be going right on the scale

TeamSpeed: "...negative brings your focus forward (back focusing)." which means I should be going left on the scale.




  
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Apr 23, 2010 12:05 |  #7

Simple to remember: + values means you add distance between you and the focal plane and - means you are shrinking the distance between you and the focal plane.

Ignore the icons or the words, just remember + adds to the gap, - takes away from the gap.


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sandro9mm
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Apr 23, 2010 13:53 |  #8

why don't you shoot all starting from -10 up to +10, and somewhere there you will get your perfect focus. Take test shoots 2 at each and compare. it's that simple...


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Ken ­ Nielsen
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Apr 23, 2010 15:54 |  #9

sandro9mm wrote in post #10052217 (external link)
why don't you shoot all starting from -10 up to +10, and somewhere there you will get your perfect focus. Take test shoots 2 at each and compare. it's that simple...

This is a good plan, but I only shot one for each, tripod mounted with cable release. At 35' away, I shot a target board at 400mm and got what seemed like 1/32nd inch increments or even less - It's very fine and exacting. There was one that was the obvious choice by its sharpness. The camera and lens now perform flawlessly and with spectacular results every time! Very much well worth doing.




  
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7D noob question: how to use the microadjustment scale
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