Reluctance to use the AF fine tune feature in my D7000

[bill_brooks]

<p>Am I being naive or stubborn in not wanting to "succumb" to assigning AF fine tune numbers to any of my lenses? I understand that even with the superb tolerance levels of Nikon engineering, we still need to allow for the possibility of needing AF-FT, and that it's not a "bad thing" per se, but still...<br>

My primary gear: D7000, using 24-70 and 70-200 VRII lenses a lot, and also 10-24, all Nikkor. (And man, do I love all 3 of 'em.)<br>

I suspect that I will need to fine tune my newest lens, the 70-200 VRII for a bit of back focusing, but need to follow Thom Hogan's instructions with focus chart to the "T" this weekend to ascertain. Also trying to figure how to use Live View as he mentions in his manual for comparison shots also but not "getting it" yet.<br>

Just curious what frequency of AF fine tuning lenses for the D7000 is going on out there among the Nikon people on the forum... especially would love to hear from you Shun, if you see this, as you have offered much useful insight on the D7000.</p>

[anura1]

<p>Here is a good article on the same subject. <a href="http://www.focustestchart.com/chart.html">http://www.focustestchart.com/chart.html</a> . I have a nikon D7000 as well and I used this featuer with my 35mm 1.8 AF-S lens but normaly AF fine tune is not recomend for zoom lenses. I would like to see others input as well as I am not sure how it going to effect zoom lens if we do use the AF-FT for zooms.</p>

[ShunCheung]

<p>Bill, do you sometimes override the camera's metering, e.g. with exposure compensation?</p>

<p>AF fine tune is similar to exposure compensation but for focusing. In particular, with older equipment, they may need some adjustment.</p>

[bill_brooks]

<p>Shun, I do sometimes use exp. comp and understand the comparison. I do not have a problem with making the adjustments for my lens(es). My main curiosity is how much it happens with the D7000 and the new G series lenses, especially the zooms such as my 70-200 VRII.<br>

Anura makes a good point about the variable zoom lenses. Seeing as I can only Fine Tune for one focal length on a given zoom lens, maybe I'm better not adjusting the AF-FT function on those lenses and just focus manually whenever possible?</p>

[joseph_wisniewski]

<p>AF fine tuning is physics. Lenses have a characteristic called "spherical aberration" that causes the focal plane to shift between large apertures like f1.8 and small ones like f5.6.</p>

<p>The AF sensors, the focus screen, and (if you've installed one, or if you're using an older camera) the split image "focus aid" all see about a 10 degree cone of light, or f5.6. So, at wider apertures, there's a focus shift. The AF fine tune lets you compensate for this, so you're spot on at wide apertures, and still good at smaller apertures.</p>

[richardsnow]

<p>The reason you get "AF Fine Tune" these days is not because of spherical aberration. Additionally, the focal plane does not "shift" when when you use large apertures. The depth of field at larger apertures is shallower. For those of us that shoot at larger apertures, front and back focus is more apparent because the DOF can become so shallow that the focal plane being even millimeters off can be noticed.</p>

<p>AF Fine tune was added to cameras because Nikon's cameras and lenses are built to certain tolerances. Sometimes, when a lens at one end of the tolerance range is attached to a camera at the other end of the tolerance range, you get very noticeable focusing issues. Confused? Here's an example:</p>

<p>Your Nikon D7000 has a focus tolerance range of -3 to +3 with 0 being perfect.<br>

Your 70-200mm has the same focus tolerance range of -3 to +3 with 0 being perfect.</p>

<p>If both the D7000 and 70-200mm are off by the same amount, (lets both are -2), then you will not have any focusing issues. Additionally, if they are off by only fractions, you will likely never see any focusing issues.</p>

<p>However, sometimes you get a camera that is off by -1 and a lens that is off by +1...this would likely be noticeable at large apertures, but may disappear by the time you get to f/4 or f/5.6 due to larger DOF at smaller apertures. (In other words, you'd never know with a kit lens).</p>

<p>What used to be done before AF Fine tune?<br>

You could ,(and AFAIK still can), send your entire kit to Nikon to be tuned and written to the camera's software by Nikon's engineers. This was time consuming and costly. Usually only people that relied on their camera equipment to pay their bills would choose this option, but as consumer DSLRs became more affordable and the general public has started to shoot with more expensive lenses, Nikon needed a solution.</p>

<p>This solution if AF fine tune. consumers and pros alike can now tune their personal lenses to their specific camera body.</p>

<p>Hope this helps you understand why AF Fine tune is available<br>

RS</p>

 

[samuel_lipoff]

<p>Ummm . . . actually Joseph is, as usual, entirely correct. Actually the focal plane does shift as you change apertures, and this due precisely to spherical aberration. This is called focus shift. The phase-detect AF systems in SLRs look through exit pupils at about the f/5.6 region of most lenses, and so lenses that exhibit sigignicant focus shift between this region and wider apertures are difficult for the AF system to focus. AF fine tune can help correct that defocus due to focus shift at wide apertures. If the lens is actually set to f/5.6, it is likely that the increased DOF will cover any focus shift induced defocusing anyway, even after an AF Fine Tune value is set.</p>

<p>To the OP, there is no reason why you shouldn't use AF Fine Tune. There's nothing wrong with using it, and nothing special about this adjustment compared with any other adjustment in your camera. However, if you don't know what you're doing, you can make every image you take worse. Read tutorials on-line, understand what it does (simply applying a constant offset to whatever value the phase detect AF suggests) and consider getting a product like LensAlign to help you.</p>

<p>I don't own a D7000, but I have borrowed a friend's several times, and found that I had to dial in -17 for both my 28mm f/1.4 and 85mm f/1.4 AF-D lenses. Neither requires any AF Fine Tuning on my D700. This is just one anecdote, however, and says nothing about what you should expect.</p>

[ilkka_nissila]

<p>Well, I doubt it's a question of simply correcting for focus shift due to spherical aberration. I have a D3 which requires a fine tune of -14 when using the 200/2. My D700, which has the same focus system, requires -5 with that same lens. Neither camera requires any fine tune with the 70-200II when the same aperture (f/2.8) is used in comparisons between the zoom and the 200mm prime. So, it's an interaction effect.</p>

<p>Incidentally, both cameras require -3 units on the rightmost AF point vs. the center one, whereas the left side is +3 (compared to center). And when I turn the camera upside down, this discrepancy between different sensors appears to disappear. I would suspect it's a question of alignment of the sensor, AF sensor, camera and lens mount, and the sub-mirror under the main mirror. Clearly, if it were an effect due to spherical aberration, both cameras would see a similar effect in terms of overall focus fine tune value for the center sensor, but they don't.</p>

<p>Incidentally, my D7000 focuses both lenses without a bias, but when tracking moving subjects the focus is a lot more often incorrect than when using the FX cameras.</p>

[johnwingfield]

<p>For my D7000 I used it and have my 35mm and 50mm both at +10. My 85mm and 18-105mm are both at 0 and appear spot on. Its so simple to do the tuning and it meant I have sharp pictures from all lenses and no need to send anything away for service. Now when I get an unsharp picture, I know exactly who to blame :-)</p>

[elliot1]

<p>Ummm.... Actually, I don't know if Joseph is correct or not as I an not an engineer, but, I agree fully with Richard. I had three D200s at one point and my 17-55mm focused perfectly on two of them and front focused on the third. I had to send the camera and lens in to have the problem resolved. Perhaps they are both right?</p>

<p><em>"if you don't know what you're doing, you can make every image you take worse"</em> Does anyone really find the AF Fine Tune feature difficult to use?</p>

[bill_brooks]

<p>Elliot, to answer your last question, *yes*, in the framework that I first posted, that of a serious amateur like me who is typically much more hesitant (yes, timid!) to mess with original engineered settings, especially given that, as Richard notes, prosumer camera bodies have just recently included the AF-FT feature. That's why I was curious about frequency of use for this feature, which appears to be high.<br>

With thanks for these great responses and info, I am now ready to charge boldly ahead and Fine Tune away to a fair-thee-well!</p>