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<p>Hi All,<br>

I read a lot about how it’s necessary to micro adjust new lens purchases due to back or front focus issues and I’m wondering why today’s lenses require this effort. When I got started in the film days (my first camera was a Nikon FTn), all you had to do was turn the focus ring until the subject looked sharp. I don’t recall any mention of a manual lens’ inability to give consistent focus results in any of the popular and modern photography magazines.<br>

So why is this happening today? Is it a quality control problem? Is autofocus technology simply not up to the task? Let’s say I had an autofocus lens that had to be micro adjusted because of a back focus issue. If I deactivated AF and manually focused it until the image looked sharp, would there not be a back focus issue? Or would I still have to manually compensate by not focusing exactly on the subject?<br>

You’d think that camera manufacturers would come up with a solution in which a lens could automatically micro adjust itself on all bodies at all distances/focal lengths/conditions. <br>

Comments from the experts are greatly appreciated.</p>

 

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<p>It is partly because the high resolution of today's sensors and low noise allows you to see clearly what exactly is in focus, whereas with film the quality was lower so it was difficult to tell. Also the manual focusing operation using the optical viewfinder was of limited precision and people's expectations were lower as a result; almost in focus was regarded a pretty good result. In reality the focusing screen and mirror could be misaligned (after period of use and maybe also some abuse) as they can today (in DSLRs) and sometimes they were adjusted to improve focusing accuracy. However, the expectations were much lower then than they are today, and it was regarded normal to use a fast lens and stop down two stops to get the subject acceptably within the depth of field.</p>

<p>Automated methods for focus fine tuning have been developed but there are still some issues. There is also inherent randomness in the focus operation.</p>

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<p>My opinion only and certainly not an expert. First, realize that it isn't <em>necessary</em> to adjust new lens purchases, <em>unless</em> they exhibit inaccurate focus tendancies; most lenses on most cameras don't. Today's (digital) bodies' sensors, as a result of highly sophisticated designs to achieve excellent <em>overall</em> performance across a broad range of characteristics, are much more dependent on increasingly smaller manufacturing tolerances and adjustments, than those we saw with film bodies. In the "good old days" excellent was good enough....unless you were producing commercial quality enlargements, you didn't need micro-adjustments to your gear. Today, we look at our results most often, not as medium sized prints, but at the pixel level, and indeed can discern when things aren't perfect. AF usually does a good job, and if you study the nuances of how software and AF points determine focus (horizontal, vertical, diagonal, contrast detection, face detection, etc) you can see that getting it perfect for all situations probably isn't economically feasible...it is much better to incorporate an adjustment feature for folks or equipment which needs it. Assuming your focus screen is properly aligned, your mirror is properly aligned, and your eyesight is compensated for....manually focusing a lens on a current DSLR body works fine - regardless of what issues there are with AF.</p>
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<p>Agree with Stephen. It should not be necessary and in general, so far, I have not found it to be so for the lenses I have and have used (which is a fair number). But I think the manufacturers give it because it is easier to tell people to go and adjust it themselves than for them to be constantly engaged in "repairs" themselves, often when there is nothing wrong and it is due to user error.</p>
Robin Smith
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"My opinion only and certainly not an expert. First, realize that it isn't necessary to adjust new lens purchases, unless they

exhibit inaccurate focus tendancies; most lenses on most cameras don't. "

 

That's certainly true. The reason it's needed - and if you were a very critical photographer it's always been needed, even

on purely manual slr cameras - is that both cameras and lenses, while being very precise machines, have manufacturing

tolerances and need to be calibrated or tuned to each other. It's the same reason scopes need to adjusted to the rifle

they are being used on.

 

What you are doing is adjusting the autofocus computer to the characteristics of the lens.

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<p>Does anyone know how these micro adjustments are made on a lens? Say a Canon EF lens, for example. Is the micro adjustment a mechanical process or electronic?</p>

<p>I'm asking because one of me EF telephoto zooms, which used to focus on the money, now is off just enough to render photos unacceptably soft, to me at least. If I were to take it to a repair facility, I'm thinking I need to bring both the camera and the lens, correct? But what if I decide to use this lens on another camera? Will it still operate correctly?</p>

 

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<p>Autofocus has progressed beyond the early days of contrast sensing, which is slow and prone to hunting. Phase detection senses both the amount and direction of the needed correction, then instructs the focus motor accordingly. In the rudimentary sense, it's like shooting a basket - once you let go of the ball, you've exercised all the control you have. A technical term for this is "feed forward" control, where you make your best guess based on knowledge of the process. When it works, focus is achieved much more quickly than with feedback control. There is still the possibility of corrective action, a succession of jumps, but there is a dead band in which no further action is taken - focus is locked in.</p>

<p>In micro control, you tune the "best guess" to be closer to the mark. You also have the option of manual control once auto focus decides it's done enough (or you override auto control).</p>

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<p>I have found micro fine-tuning to be very helpful on some cameras and lenses and completely unnecessary on others.</p>

<p>If you'd like to try it, mount your camera on a solid tripod and shoot repeated frames at a stationary, planar subject (like a page from a magazine taped to a wall).</p>

<p>Make sure that your camera is NOT in Live View mode, or it will be using contrast detection autofocus. Micro fine tuning has no effect on contrast detection autofocus.</p>

<p>Go to the AF fine tuning menu on your camera and take three shots each at -20, -15, -10, -5, 0, 5, 10, 15, and 20. Be sure to use a cable release and, if your camera features it, mirror lockup.</p>

<p>Put the fine tuning setting back to 0. Load the images onto your computer and review them carefully. I recommend that you use the software that came with the camera so you have access to all of the fine tuning information in the application.</p>

<p>If the sharpest images are at 0, fine tuning isn't necessary. If the sharpest images are elsewhere on the spectrum, repeat the exercise and take multiple shots at every setting in that range, not just incrementing by fives.</p>

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<p>There are two practical alternatives to micro tuning - live view and f/8. This assumes, of course, that auto focus is locking on the point you wish, rather than the easiest one for the camera to "see."</p>

<p>I was frustrated yesterday when my only auto-focus lens for a Sony A7 refused to "see" the leafing twig I wished rather than the cluttered background. You get spoiled with manual focus in a camera, like the Sony A7, which makes it so easy and precise. I eventually prevailed by overriding AF and turning the fly-by-wire focusing ring one or two complete revolutions. It's somewhat easier when I attach a Nikon AF lens (non-AF on the Sony), with a 45 degree stop-to-stop rotation. It helps to sand my finger tips like Willie Horton (the safe cracker).</p>

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<p>Thanks for the response, Ellis. My EOS DSLR is a lowly 10.1mp XS -- it was the base model in 2008. So it has no fine-tuning settings in the menu. It's semi-retired now, but still, as long in the tooth as it has become, it does a decent job, so I'd like to see things working properly again.</p>

<p>I guess I need to put the camera through its paces with a variety of my EF lenses, and not just the one where the problem is most noticed. For all I know, it might be back-focusing or something with all my lenses. One thing I have noticed, and I guess I've been chalking it up to my imagination, but maybe I shouldn't -- if I take pix with either an accessory flash or the built-in flash, the images seem to be sharper. Maybe the AF sensor for the flash is working better than the main AF sensor(s)?</p>

<p> </p>

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Flash gives a very short burst of light and freezes the movement of the subject relative to the camera effectively,

especially if it is the only or dominant source of light. You may be using a too long exposure time if you get blur due to the

subject movement or camera shake when you're not using flash.

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Hi Michael,

 

Michael Tapes once told me that he developed his original LensAlign target so he could show Canon repair techs

examples of the degree to which his various lenses were either front or back focusing on his cameras. I believe he told

me he did this back around '08 or so.

 

My recollection is that user access to the autofocus fine tune adjust programming first showed up on the Nikon D3 which

was launched in August 2007, but I could be wrong.

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<p>One easy way to tell is there is anything wrong is to manually focus on an object in Live View with 10X mag, switch off Live View and then press AF (without moving the camera of course). If the focus shifts on the lens then this suggests that either you are not very good at focusing manually (sometimes it is not so easy), or the lens needs adjustment. Another thing to consider is focus variability. The lens may not focus on <em>exactly</em> the same point using AF when repeatedly focusing on the same thing. There is nothing much you can do about this, and this usually mimics the eye which may not always pick the same point of focus each time either. Frankly, I have never needed found my lenses to be significantly off, so I often wonder why other people have such problems. Some microadjusting methods just breed paranoia. LensAlign in particular, I thought an entirely useless system - good if you have an optical bench, but hopeless otherwise.</p>
Robin Smith
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