attempting to MFA 7D, but having difficulty interpreting inconsistent results

Started Jul 7, 2011 | Discussions
photoweasel
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attempting to MFA 7D, but having difficulty interpreting inconsistent results
Jul 7, 2011

I am attempting to use a Lens Align to MFA a Canon 7D with a few lenses and am having difficulty interpreting the seemingly inconsistent results. I'm not sure where in my process the trouble lies, but the AF variance seems too wide to adjust for. I've tried multiple times and several ways (different distances, lighting, racking/not racking focus in-between shots, multiple lenses etc.) and even when simply taking successive shots (without racking the focus in-between) the results still seem to vary too widely to use MFA - one shot back-focusing towards one end (on the LA scale) and another taken two seconds later front-focusing towards the other. Attached are two 100% crops of shots taken with a 70-300L @300 from 24' feet (jpeg, spot AF on the target center, one-shot, spot metering, IS off) simply by pressing the remote release halfway to engage the focusing mechanism, pausing, taking the picture, and repeating the same process again. I did this for 64 shots with four different MFA adjustments (incl. 0) and cannot seem to find any setting that yields more consistently in-focus shots.

I know the target isn't exactly parallel but it is close, and that this is about half the Canon-recommended distance, but still seems like a reasonably 'real-world' test. Could one of these be causing the AF inconsistency, or is this level of AF variance normal? Thanks for any suggestions.

photoweasel
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Re: attempting to MFA 7D, but having difficulty interpreting inconsistent results
In reply to photoweasel, Jul 7, 2011

I'm not sure how I did this as they were uploaded separately and each reflect the correct file names, but the images in my post appear to be identical rather than as they do on my computer. Here is a screen snapshot of the same two images side-by-side to illustrate the AF variance I am trying to figure out:

Thanks in advance for any suggestions.

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akin_t
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Re: attempting to MFA 7D, but having difficulty interpreting inconsistent results
In reply to photoweasel, Jul 7, 2011

Lol, you have a lot of time on your hands.

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Sailor Blue
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Re: attempting to MFA 7D, but having difficulty interpreting inconsistent results
In reply to photoweasel, Jul 8, 2011

If you are serious about microfocus adjustment then follow the procedure given in this link. It was developed by and for bird photographers and is far better than the Lens Align method.

http://www.stanford.edu/~ahazeghi/Photos/MA-web/

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andy792
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Re: attempting to MFA 7D, but having difficulty interpreting inconsistent results
In reply to Sailor Blue, Jul 8, 2011

I've been playing with MFA of my 7D for different lenses and found one interesting thing. Let's say you use one the charts with a black horizontal line as the focus point (e.x. http://www.focustestchart.com/chart.html ). Do you think that focusing above the line will not work for the single-point AF? Wrong! Depending on your paper micro-structure it may focus perfectly. When you focus exactly on the line, it may focus somewhere within the bounds of the focus square, not necessarily in the center. I guess, it may cause some focus deviation.

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Jerry-astro
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+1 to this suggestion
In reply to Sailor Blue, Jul 8, 2011

This is a much more reliable method to set MFA. Try it first before you reach any conclusions about the consistently of your camera or lens' focus. BTW, you can use the mirror that comes with that kit to ensure that your camera is completely perpendicular to your target. Also, find a target with more detail if you can. It really helps in getting that last point or two correct when going thru the process.

Sailor Blue wrote:

If you are serious about microfocus adjustment then follow the procedure given in this link. It was developed by and for bird photographers and is far better than the Lens Align method.

http://www.stanford.edu/~ahazeghi/Photos/MA-web/

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birdbrain
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+2 for this suggestion!
In reply to Sailor Blue, Jul 8, 2011

Sailor Blue wrote:

If you are serious about microfocus adjustment then follow the procedure given in this link. It was developed by and for bird photographers and is far better than the Lens Align method.

http://www.stanford.edu/~ahazeghi/Photos/MA-web/

I had a Canon 100-400 which was a bit lacklustre, after getting a 7D and analysing my images I could see that the 100-400 was front focussing. So I used the above method and quickly established the 100-400 needed +6 AF MA. I went on to check my lens collection, 10-22, 15-85, 100 L Macro and 500 f4 and all these checked out OK.

Here is an example of the problem, you will notice that the barbs in front of the bird are sharper than the bird itself even though the AF was on the bird.

So out with a trusty bank note mounted on a board and set at about my normal subject shooting distance. This is an actual pixel crop having applied +6 MA.

Which then gives me results like this, with lots of feather detail.

So many thanks to Arash Hazeghi!

The first shot was taken using a EOS 300D, I also used a 450D with similar results. I then got a 7D and was able to carry out AF MA, and when I got a second 7D that also needed +6. So the lens is definitely out I also checked it at 100,200,300 and 400 and found it was fine. So it was a 'global' focusing error it would seem.
--
Phil

I wondered why the ball kept getting bigger, then it hit me.

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Zee Char
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Re: attempting to MFA 7D, but having difficulty interpreting inconsistent results
In reply to photoweasel, Jul 8, 2011

If you are getting inconsistent back/front focusing no method on the planet will help you. Stop driving yourself nuts and send it to Canon.

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Severian The Lame
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Re: attempting to MFA 7D, but having difficulty interpreting inconsistent results
In reply to Zee Char, Jul 8, 2011

Here's my method: http://forums.dpreview.com/forums/readflat.asp?forum=1029&message=35880088

Beyond that, I can't add much other than to note that Canon recommends a minimum of 50' at 300mm FL (that's 50 x FL rounded up to the nearest foot).

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Zee Char
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Re: attempting to MFA 7D, but having difficulty interpreting inconsistent results
In reply to Sailor Blue, Jul 8, 2011

Sailor Blue wrote:

If you are serious about microfocus adjustment then follow the procedure given in this link. It was developed by and for bird photographers and is far better than the Lens Align method.

http://www.stanford.edu/~ahazeghi/Photos/MA-web/

When you read the whole thread on that bird site one thing comes up. First off this method does not show you how much you are front or back focusing. Not sure if this was mentioned in that article since it has been a while since I read it but I know that Canon recommends that the target be perfectly parallel to the plane of the sensor. Without a method you are taking your best guess.

I recently blew the dust off my lens align because something did not seem right with my 300L F4 IS. It showed it needed a -15 so it is at Canon right now.

I picked up a Canon 50 1.4 yesterday. It appears to be front focusing so I dusted off the lens align again. I used both the birding method combined with the lens align. I taped a piece of a fake dollar bill around the centre hole of the lens align and used the bird method. I clicked forward and backward and it looked like it needed a -1.

However when I took an image and viewed it on my monitor it was clearly front focusing according to the ruler. I had to go to - 8 to centre it.

I repeated the test using the birding method and if I went 2 clicks + or - the focus started to be off. I repeated the test using the lens align again and it showed it needed a -8.

I then took the bill and scotch tape off to see if that had an effect. The bill must be about .003 to .004 and with the tape not sure how thick that is and if it could be throwing off the tests. There is enough information on the lens align to to use the bird method. Same results.

I repeated this 4 times with the same results.

I use the bird method combined with the lens align to ensure the target is parallel to the target. Even though I am not a big fan of MFA I use it to help me decide how well my lens is performing. If it is off it goes to Canon.

The place has 2 more 50's. Gonna exchange it today. If I can't get a good copy it is off to Canon.

It si small and light so the cost should be minimal.

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Jerry-astro
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Sorry... confused
In reply to Zee Char, Jul 8, 2011

Zee--

I really don't understand how these two tests can or even should be used together. The amount of front or back focus measured by the test contained in the link below is an exact function of how many + or - clicks it takes from your default (0) setting to achieve proper focus. It's an iterative process you use until you get the target in perfect focus. The number of clicks away from zero will become your MFA value. The slanted ruler that accompanies the target is basically superfluous and adds no value, and yes, it could throw off the ruler if it isn't perfectly aligned with the surface of the target.

All you need is a single target located at the recommended distance of at least 50x your FL. You can still use the Lens Align mirror to ensure that it's perpendicular to your camera. From my own experience, you're probably a bit better off with a somewhat larger and much more detailed target than the one that is provided with the lens align kit (which I also own but never use any more). I've never had any issues with this method and without question get much better MFA accuracy using it vs. Lens Align, but that is my own experience. Obviously YMMV.

BTW, if I ended up investing the time to do this and still got inconsistent results, my lens would end up going straight back to Canon as well. Same goes for anything more than minor differences in MFA across a zoom's FL range. Some people can live with manually changing MFA settings depending on their FL setting. Not me. That's a problem that Canon needs to address IMHO.

Zee Char wrote:

Sailor Blue wrote:

If you are serious about microfocus adjustment then follow the procedure given in this link. It was developed by and for bird photographers and is far better than the Lens Align method.

http://www.stanford.edu/~ahazeghi/Photos/MA-web/

When you read the whole thread on that bird site one thing comes up. First off this method does not show you how much you are front or back focusing. Not sure if this was mentioned in that article since it has been a while since I read it but I know that Canon recommends that the target be perfectly parallel to the plane of the sensor. Without a method you are taking your best guess.

I recently blew the dust off my lens align because something did not seem right with my 300L F4 IS. It showed it needed a -15 so it is at Canon right now.

I picked up a Canon 50 1.4 yesterday. It appears to be front focusing so I dusted off the lens align again. I used both the birding method combined with the lens align. I taped a piece of a fake dollar bill around the centre hole of the lens align and used the bird method. I clicked forward and backward and it looked like it needed a -1.

However when I took an image and viewed it on my monitor it was clearly front focusing according to the ruler. I had to go to - 8 to centre it.

I repeated the test using the birding method and if I went 2 clicks + or - the focus started to be off. I repeated the test using the lens align again and it showed it needed a -8.

I then took the bill and scotch tape off to see if that had an effect. The bill must be about .003 to .004 and with the tape not sure how thick that is and if it could be throwing off the tests. There is enough information on the lens align to to use the bird method. Same results.

I repeated this 4 times with the same results.

I use the bird method combined with the lens align to ensure the target is parallel to the target. Even though I am not a big fan of MFA I use it to help me decide how well my lens is performing. If it is off it goes to Canon.

The place has 2 more 50's. Gonna exchange it today. If I can't get a good copy it is off to Canon.

It si small and light so the cost should be minimal.

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jpr2
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re: +3 for Arash Hazeghi! (n/t)
In reply to birdbrain, Jul 8, 2011

jpr2

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Zee Char
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Re: Sorry... confused
In reply to Jerry-astro, Jul 8, 2011

Thanks for responding. You stated 50x the focal length (which is what Canon recommends) but the birding procedure states 20X? I have also read 25X and using the lenses minimal focusing distance. So what you are saying the the ruler with the lens align adds no value? That is interesting. I thought the whole point of lens align was the ruler. OK so I agree perhaps I should not use both. It was just a reference. The bird one that tells me -1 and the lens align that tells me - 8.

I exchanged that 50 and took a few shots and they looked great. Then I realized I had it - 8. I put it to back to zero and it looked as bad as the first one. Lens has been shipped to NJ.

Last conversation I had with Canon they told me MFA is a quick fix and if you are using it the lens should go to Canon. I know there are 3rd party lenses and people do not want to send their gear in and that is great. All the best. I fully respect that. I have had different results at different focal lengths with primes.

Until Canon comes out with concrete procedure and not Chuck's where at the end he states if you can do better go for it I'm going to continue using Canon. They serviced my 24 -105 recently and it is spot on now.

Jerry-astro wrote:
Zee--

I really don't understand how these two tests can or even should be used together. The amount of front or back focus measured by the test contained in the link below is an exact function of how many + or - clicks it takes from your default (0) setting to achieve proper focus. It's an iterative process you use until you get the target in perfect focus. The number of clicks away from zero will become your MFA value. The slanted ruler that accompanies the target is basically superfluous and adds no value, and yes, it could throw off the ruler if it isn't perfectly aligned with the surface of the target.

All you need is a single target located at the recommended distance of at least 50x your FL. You can still use the Lens Align mirror to ensure that it's perpendicular to your camera. From my own experience, you're probably a bit better off with a somewhat larger and much more detailed target than the one that is provided with the lens align kit (which I also own but never use any more). I've never had any issues with this method and without question get much better MFA accuracy using it vs. Lens Align, but that is my own experience. Obviously YMMV.

BTW, if I ended up investing the time to do this and still got inconsistent results, my lens would end up going straight back to Canon as well. Same goes for anything more than minor differences in MFA across a zoom's FL range. Some people can live with manually changing MFA settings depending on their FL setting. Not me. That's a problem that Canon needs to address IMHO.

Zee Char wrote:

Sailor Blue wrote:

If you are serious about microfocus adjustment then follow the procedure given in this link. It was developed by and for bird photographers and is far better than the Lens Align method.

http://www.stanford.edu/~ahazeghi/Photos/MA-web/

When you read the whole thread on that bird site one thing comes up. First off this method does not show you how much you are front or back focusing. Not sure if this was mentioned in that article since it has been a while since I read it but I know that Canon recommends that the target be perfectly parallel to the plane of the sensor. Without a method you are taking your best guess.

I recently blew the dust off my lens align because something did not seem right with my 300L F4 IS. It showed it needed a -15 so it is at Canon right now.

I picked up a Canon 50 1.4 yesterday. It appears to be front focusing so I dusted off the lens align again. I used both the birding method combined with the lens align. I taped a piece of a fake dollar bill around the centre hole of the lens align and used the bird method. I clicked forward and backward and it looked like it needed a -1.

However when I took an image and viewed it on my monitor it was clearly front focusing according to the ruler. I had to go to - 8 to centre it.

I repeated the test using the birding method and if I went 2 clicks + or - the focus started to be off. I repeated the test using the lens align again and it showed it needed a -8.

I then took the bill and scotch tape off to see if that had an effect. The bill must be about .003 to .004 and with the tape not sure how thick that is and if it could be throwing off the tests. There is enough information on the lens align to to use the bird method. Same results.

I repeated this 4 times with the same results.

I use the bird method combined with the lens align to ensure the target is parallel to the target. Even though I am not a big fan of MFA I use it to help me decide how well my lens is performing. If it is off it goes to Canon.

The place has 2 more 50's. Gonna exchange it today. If I can't get a good copy it is off to Canon.

It si small and light so the cost should be minimal.

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akin_t
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re: +3 for Arash Hazeghi! (n/t)
In reply to jpr2, Jul 8, 2011

Why +3 ... Why not +4?

jpr2 wrote:

jpr2

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Jerry-astro
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Zee...
In reply to Zee Char, Jul 8, 2011

Zee--

I usually try a few different variants both with FL (for a zoom) and distance. 50x is a guideline, not gospel BTW. If there's much of any focus variance across different FLs and/or distance, it's a good sign that it's time for a trip to Canon. Fortunately, the major offender in my lens inventory (the 100-400 at +12) seems to work pretty consistently both at different distances and FL's with the MFA adjustment. And, it's pretty well razor sharp now, so the test does work.

The reason for not bothering with the angled chart is the fact that the birding procedure uses a tethered and magnified view of your target to zero in on focus. That's what you're really trying to accomplish here, so if you can get a razor sharp image of your target consistently, then you getting the focus performance you want. The angled view adds no value at that point.

The only other reason I hesitate to send my lens to Canon is the fact that MFA issues are often related to tolerance issues both in the camera and the lens. So, ideally, sending both in together makes the most sense. My fear (rational or otherwise) is that any adjustments they make in the camera would also throw off my other lenses. I have zero interest in sending in my whole kit to Canon.

Again, YMMV, and if what you're doing works well, then by all means stick with it. I've had good luck with MFA and that procedure in particular, so simply wanted to share that here. Thanks for clarifying your earlier point.

Zee Char wrote:

Thanks for responding. You stated 50x the focal length (which is what Canon recommends) but the birding procedure states 20X? I have also read 25X and using the lenses minimal focusing distance. So what you are saying the the ruler with the lens align adds no value? That is interesting. I thought the whole point of lens align was the ruler. OK so I agree perhaps I should not use both. It was just a reference. The bird one that tells me -1 and the lens align that tells me - 8.

I exchanged that 50 and took a few shots and they looked great. Then I realized I had it - 8. I put it to back to zero and it looked as bad as the first one. Lens has been shipped to NJ.

Last conversation I had with Canon they told me MFA is a quick fix and if you are using it the lens should go to Canon. I know there are 3rd party lenses and people do not want to send their gear in and that is great. All the best. I fully respect that. I have had different results at different focal lengths with primes.

Until Canon comes out with concrete procedure and not Chuck's where at the end he states if you can do better go for it I'm going to continue using Canon. They serviced my 24 -105 recently and it is spot on now.

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andy792
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It all depends on the test object you focus on
In reply to Jerry-astro, Jul 8, 2011

This is my own experience of MFA on different lenses - Canon, Tamron and Sigma. First, I tried following the classic method of focusing on various angled charts to see the dof shift relative to the central focus point. I was also getting quite inconsistent results for the same shots across all lenses. The variation was about 3-4 adjustment notches, while the overall pattern clearly indicated front focusing for all lenses.

Another point. Sometimes, an adjustment of 2-3 points didn't lead to any noticeable results on the picture. So, I realized that the problem could be with the testing chart itself. I was using the single-point AF pointing to the horizontal line on the chart. Moving the focus point above or below the line, i.e. on the white chart area also resulted in instant focusing on that area. Perhaps a high resolution lens (aka my 100mm f/2.8L) can capture tiny paper structures enough for focusing.

After all, I replaced testing charts by this house model (2x3 inches):

Focusing on any elements of that model returned the same focal shift numbers, very consistent. I use the same procedure as described in
http://www.stanford.edu/~ahazeghi/Photos/MA-web/

This method works better for me than a chart-based adjustment. All my lenses show front focusing and adjusted for +6 to +7. It looks as the 7D body drift.

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Eugene Powers
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50x is for a different method of MFA .......
In reply to Zee Char, Jul 9, 2011

If you use 400mm lens for example you would have to be (60 feet) 20 meters away so DOF will not cover the ruler on Lens Align.
I think 50x rule was suggested for screen moire method.

I use "Can I see blur on both sides of the ruler method" so anywhere between MFD and 20 feet at the most.
--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Quote by Lee Jay

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andy792
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Re: 50x is for a different method of MFA .......
In reply to Eugene Powers, Jul 9, 2011

Eugene Powers wrote:

If you use 400mm lens for example you would have to be (60 feet) 20 meters away so DOF will not cover the ruler on Lens Align.
I think 50x rule was suggested for screen moire method.

I use "Can I see blur on both sides of the ruler method" so anywhere between MFD and 20 feet at the most.

Totally agree. I use the closest distance and max aperture for MFA to create the shortest dof possible.

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shutterbug nut
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Re: attempting to MFA 7D, but having difficulty interpreting inconsistent results
In reply to photoweasel, Jul 9, 2011

I'm not sure this will help but possibly try using the lens align at just past the MFD. I just adjusted one lens of mine this way and had consistant results. It seems there is less variance when the lens is closer to the target maybe.

At least Romy does it this way but with a dollar bill instead of the lens align. After looking at some of his results I would be very hesitant to doubt his method.

http://forums.dpreview.com/forums/readflat.aspforum=1029&message=36488647&changemode=1

I'll copy and paste the part I'm referring to...

liquidstone wrote:
snip

MFA does take a whole afternoon in the garage, plus tons of field tests to confirm correctness. The reward though is pinpoint focus accuracy which the gear can deliver if we do our job behind the VF.

I have the following MFA "workflow" for my birding primes.

1. Shoot wide open at just past the MFD for least DOF. I tried 50xFL, but AF errors can be masked by the deep DOF, making precise adjustments very tough.

2. I shoot a detailed 2D object (currency bill) with almost no thickness. This will make each shot either in focus or not in focus, no gray areas masked by deep DOF. I make sure of course that the bill is as close to parallel to the sensor plane as possible.

3. I take many shots using contrast detect AF in LV, plus many more using MF. I select the sharpest of these and consider this as my reference shot. I usually shoot in jpeg with sharpness turned high to make review of detail on the camera's LCD (at max. zoom) easier.

4. I then shoot the target at 0 MFA, then + 15 and - 15. These shots are compared to the reference shot. I adjust the MFA to converge on matching the shaprness of the reference shot. In all test shots, good long lens technique is practiced to minimize shake (MLU and/or LV shooting, remote switch, IS off, no wind, etc.).

5. I repeat No. 2 - 4 with a TC attached.

6. I shoot various targets outside my garage at varying distances to confirm correctness of MFA. Field use of the gear as MFA'ed will further confirm correctness of the adjustments.

-- hide signature --

Romy

Regards,

Roger

photoweasel wrote:

I am attempting to use a Lens Align to MFA a Canon 7D with a few lenses and am having difficulty interpreting the seemingly inconsistent results. I'm not sure where in my process the trouble lies, but the AF variance seems too wide to adjust for. I've tried multiple times and several ways (different distances, lighting, racking/not racking focus in-between shots, multiple lenses etc.) and even when simply taking successive shots (without racking the focus in-between) the results still seem to vary too widely to use MFA - one shot back-focusing towards one end (on the LA scale) and another taken two seconds later front-focusing towards the other. Attached are two 100% crops of shots taken with a 70-300L @300 from 24' feet (jpeg, spot AF on the target center, one-shot, spot metering, IS off) simply by pressing the remote release halfway to engage the focusing mechanism, pausing, taking the picture, and repeating the same process again. I did this for 64 shots with four different MFA adjustments (incl. 0) and cannot seem to find any setting that yields more consistently in-focus shots.

I know the target isn't exactly parallel but it is close, and that this is about half the Canon-recommended distance, but still seems like a reasonably 'real-world' test. Could one of these be causing the AF inconsistency, or is this level of AF variance normal? Thanks for any suggestions.

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Severian The Lame
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Re: 50x is for a different method of MFA .......
In reply to Eugene Powers, Jul 9, 2011

Eugene Powers wrote:

If you use 400mm lens for example you would have to be (60 feet) 20 meters away so DOF will not cover the ruler on Lens Align.
I think 50x rule was suggested for screen moire method.

I use "Can I see blur on both sides of the ruler method" so anywhere between MFD and 20 feet at the most.
--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Quote by Lee Jay

LensAlign says 20X FL minimum: http://www.whibalhost.com/lensalign/what-is-lensalign.html

But Canon (via Chuck Westfall) says 50X FL minimum: http://www.pixel-shooter.com/forum/showthread.php?t=21099
Who do you believe? Anyway, whatever works for you.

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