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#61
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Bart |
#62
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Hello,
As this is my first post here, first I would like to thank you all for this really interesting (geeky ?) thread. I am a French 1D Mark III owner (got it one week ago) and naturally as I have started to digg into the camera features, I became interested in micro-adjustments. So far I have tried inanimate objects targets, paper focus targets (flat and 45°) and now Bart's LCD moiré target. But no luck. Whatever I do, I get really inconsistent results. I have tried to micro-adjust (@ full zoom, wide open) my Canon 17-40L, Canon 100 macro 2,8 and Sigma EX DG 70-200 2,8 and while I think I get a fair enough result at say +5 if I just try again and shoot some more tests say -10 I see no real difference with the previous +5 tests. I am probably missing something but I really don't get it. So far the LCD moiré method seduces me most (probably because of the geek in me) but I get no better results. Here is how I shoot : Mark III on tripod (old but fair enough Gitzo Gilux with Manfrotto ball head), mirror blocked, 2s timer shot, One shot drive, C.FnIII-8-0 and target displayed on my iMac screen (I tried with a secondary display and laptop screen as well). So any clue or help on my micro-adjustment quest would be greatly appreciated Thanks, Nicolas P.S.: please excuse my French (or at least typos and grammar mistakes from a French English language lover but forever learner) |
#63
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Don't worry, sicnce the beginning I do my best to teach all these English mother tongue guys to understand me, and that's a challenge! LoL! BTW, welcome on board OPF, we're not so many French around here, but quite a lot of very active European guys (though some are still in vacation). Back to the topic, I'm sure that Bart (a Duch fellow BTW) will answer you much more accurately. But your settings seems strange to me. To set easily my 1DS3, I used a tripod, 100 ISO, ƒ2.8 (max anyway) longer lens if a zoom lens, and afair a speed around 1/60s With these settings I could have consistent results… |
#64
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Well, no actually :) that was just a bad humour attempt ^^
Glad to see French people here ! |
#65
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No answer so may be this was really bad humour ?
Seriously, I have tried again and again I have bad results. I just feel dumb now. |
#66
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Please don't feel like that, there really is no need for it. I am certain that Bart has been occupied with the thing we call "life" and was unable to reply. He'll probably come back to you soon. Your humour was spot on, BTW. Cheers, |
#67
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Thanks for your kind words Cem,
I don't feel bad, just dumb as I said. ;) You are right I may be somehow impatient. |
#68
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Hi Nicolas
As I have no idea what info is missing to you, I tried to summarize Bart's suggestions I have kept the # of each post so you may go back there to read the context… Hope it helps (and maybe some oher OPFers too!) Bart's posts below: #3 Quote:
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First Second |
#69
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Thanks for taking the time to assemble all this. I read the thread from top to bottom, but you are right I have to try again and follow scrupulously Bart's directions. I'll let everyone know how it goes.
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#70
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Sorry that I didn't respond earlier. I did read this post, but I was not entirely clear on what exactly you meant by "inconsistent results". Then I got occupied with other pressing matters, and it slipped my attention. So, back to the issue, what's inconsistent? Can't you achieve an optimal adjustment setting, or do you still get front/back focus after settling on a certain setting? Quote:
Bart |
#71
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That is what I don't understand. Hopes this is a better explanation as I realize it is probably as hard to understand as it is to explain... Thanks, Nicolas |
#72
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The first thing you should notice is that the AF will focus on increasingly more distant positions on the focus ring. If it doesn't then the microadjustments are not functioning. Secondly, when you make actual shots at f/2.8 on a tripod, e.g. close-ups of a newspaper at a 45 degree angle, you should see a shift of the AF focus plane. Do note that an angled surface is less useful for a calibration itself, but it could be used as a test of actual performance. However, there can be shifts of the focus plane that are due to the nature of the subject, not the adjustment alone. There should however be a trend as you make more tests at various adjustment settings. Bart |
#73
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This is very clear, thanks for all this ! I HAVE to try on a paper sheet to really check focal plane evolution. This is just so obvious... It is a bit late tonight so I will have to wait a few days before I try again as I won't have access to my camera.
To answer about the target I used,, well I used both your target target and the circles one and also paper targets like these : 1 - 2 but always flat and parallel to focusplane. Whatever I will find, I will report results here. May I post pictures to illustrate here (linked from say Flickr at medium size) ? Cheers Nicolas |
#74
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Bart |
#75
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OK so I tested with my 100 /2,8 macro. First with the LCD moiré target and then checking results with a printed text sheet @ 45 degrees from focus plane. I think I got it right this time. I miss time to post a full walk through today but I surely will.
Here are the neutral and the best setting I ended with (100% crop but still large so big files, be advised): Target on LCD @ +0 focus is on the word "subject" @ +0 Target on LCD @ +2 focus is on the word "subject" @ +2 I would say that this macro lens makes it way easier to see the moiré. I only took a few shots with my Sigma 70-200/2,8 and with this one it is really much harder to get a good feeling. I'll report on it here too anyway. Just have to take time. |
#76
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Hi again ,
please tell me again how to find out if a lens is back focusing of front focusing , the basics thanks |
#77
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Just Auto-focus on the target, enter Life View, and then observe which direction you need to turn the focus ring to improve focus (increase aliasing). If you need to focus closer, you're backfocused, if you need to focus farther, ... Bart |
#78
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Gee thanks that makes a lot of sense now that you made me think about it , thank you ery much !!!
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#79
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Dear Bart,
thanks ever so much for this technique. I had a quick play with it and it is so much more convenient than using focus charts. Here are two questions: 1. Some AF systems apparently are influenced by the colour temperature of the target. A lens backfocusing under tungsten light, can be just fine in daylight. If the colour temperature of the target display used isn't sufficiently close to daylight, this may affect the accuracy of daylight focusing. Have you validated your calibrations with focus chart tests under daylight conditions? 2. My camera doesn't have live view, so I tried to spot the moire pattern through the viewfinder. It works, the moire can clearly be observed (I'm assuming the second "grid" is the structure on the focusing screen), but it is difficult to tell when the moire is at its maximum. I therefore slightly tilted the target screen, so that when I focus, the moire pattern will wander up and down the screen as I adjust. Pointing the lens at the centre spot of the test pattern, I know that I have achieved optimal focus when the moire pattern is centred around the centre spot. Do you think that is a admissable variation of your test? I have yet to confirm my calibrations with daylight focus chart test, but didn't want to wait to thank you for your great work and get your feedback on my comments. |
#80
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#81
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Bart already responded to my posting, but his response and my response to it got lost in a recent system problem. Responding to my mentioning of colour temperature influencing the AF system, Bart said some lenses have different focal lengths depending on the colour temperature. I was wondering whether prism-based AF systems may also be upset by a colour temperature which deviates considerably from daylight. While it is possible to calibrate screens to 6500K, many screens may not necessarily be calibrated. Also, an LCD display will always use three (RGB) components in a mix to recreate a certain stimulus in the retina. A single wavelength, say corresponding to yellow, will be emulated by a mixture of a two wavelengths, corresponding to red and green. I'm not saying this makes the test invalid, but it is food for thought. The AF system may, or may not, be fooled by the specific colour recreation process of screens. |
#82
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I'm currently trying to calibrate a Canon EF 135mm f/2.0 L lens, which exhibits clearly visible CA when used wide open. I need to do some more testing, but I think I'm experiencing an AF position shift as the light changes from daylight to Tungsten (maybe in the order of 0.5% of the actual focus distance, which is very noticable at f/2.0 and that is also used to AF). I can only see that in practical AF verification after AF microadjustment, as my calibrated LCD screens have a constant 6500K color temperature. This also raises a question about the spectral response of the AF sensor. Quote:
Bart |
#83
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I have to thank Bart for the target and explaining how to use it in an easy to understand way. I also have to thank Nicolas for directing me to this great thread.
I adjusted almost all of my lenses. I haven't done my 70-200 2.8 IS or the 500 yet. Most were 1 to 3 +/-. One was I think was + or - 6. Then I got a big surprise, I set up my 85/1.8 that I have never got decent pictures from on the 20D/40D and now the 5DMII. I went to - 20 and it would need from a guess about -23 to get it perfect. Right now it is pretty darn sharp but I know it needs a little more. I guess it needs a trip to canon. The lenses that I always thought were good only needed +/- 1 to 3 and now are even better. I'm a happy camper. Thanks, Thanks, Thanks.
__________________
Somehow the more that I learn, the less I find that I know. Ron |
#84
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I'm glad to have been of service. Don't forget to also test the final settings at the actual shooting distances you use most. Depending on how the lens is calibrated internally, there may be a difference between close focusing and distant focusing. Also, because a lens needs a microfocus adjust on one body, it doesn't mean that it requires the same or any on a different body. It's the combination that may need tweaking. Bart |
#85
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Bart and Ron
Although it's absolutely the case that a lens may need different adjustments on different bodies I had a similar experience when I set mine up. All bar one of my lenses required no adjustment, but my 85 1.8 has a 5 adjustment on the 1Ds3. That was the lens that I found consistently slightly disappointing on the 5D - not awful, but not what I expected. Correctly adjusted it's exactly as I thought it should be. Mike |
#86
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Well, I really hate to admit it but I messed up with the 85/1.8. I tried it and it was off quite a bit. When I tried it first I was stopped way down and it seemed pretty good. I tried it wide open and it was worse than before. I set up this morning as far away from the computer as I could get in the room and it became so much easier. Plus 5 and its right on the money. It was very difficult to tell if +5 or +4 was best but I think +5 was slightly better. First time with the micro-adjust but I can't believe how far off I was. I didn't realize how critical distance is.
I tried the 70-200 2.8 IS but can't get back far enough in this room to do anything. I'll set a lap-top up on the kitchen table and give it a go.
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Somehow the more that I learn, the less I find that I know. Ron |
#87
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Hi Ron,
That's why I suggest people to do some more verification tests at common shooting distances. That may be hard to do with an LCD screen at larger distances. The reason behind it is that the internal calibration settings for a lens may result in a different offset at different distances. Zoom lenses even add another variable, focal lengths. The situation even becomes more critical with wide aperture lenses. On the one side, they allow to pin-point the focal plane offset more accurately, on the other side they introduce residual lens aberrations like spherical aberration. One of the most notorious lenses is the 50mm f/1.2, because it's widest aperture is quite a bit wider than the focus system's, which seems to be based on an f/2.8 aperture. Yet, autofocus is based on the widest aperture that a lens provides. When I look at the Chromatic Aberrations of my 85mm f/1.2 and 135mm f/2.0 lenses wide open, I wonder which wavelengths affect the AF sensor most (the green or the magenta OOF areas, or the in-focus average). The CA is quite noticable on high contrast edges, but it's everywhere else as well. Any discrepancy between short and long focussing distances will aggravate the situation. In theory, the official calibration at a (Canon) service centre should include all the variables, but I have my doubts about the actual accuray of their procedures. Therefore it's a good thing we have at least some control over the final offset parameter. Bart |
#88
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I have used this method to set up my 24-70L on my 1Ds Mk3. It is a big improvement to the usual 45 degree chart I have been using. I went out and took some very ordinary pics to see if there was a difference in real terms after setting up my lens with this method and there was. Brilliant. For the record, when I used the 45 degree method, I had my adjustment set to -2. Using this method, my adjustment is now +5. Thanks so much for posting this.
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#89
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Thank you for the feedback. It kind of demonstrates that calibration based on a tilted surface can give sub-optimal results. When my AF Microadjustment target is not parallel to the sensor plane, it shows as a difference in the moiré amplitude across the image. I try to align my LCD and camera with a mirror (center the lens reflection in the viewfinder). However, the moiré method is so sensitive that even then it is hard to get things perfectly squared, but at least the target will give a signal. At some distance it gradually becomes less critical for calibration, and it's easier to stay within the narrow DOF of a wide open lens. Bart |
#90
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Bart,
Can you perhaps consider editing / supplementing the first posting with the various recommendations and tips that have come up in the forum since your excellent first port over a year ago ? I have now got lost as to what is true best practise using your LCD chart... |
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