"Back Focus" Anomalies

I recently purchased an old Nikon D70s, but one with a low shutter count and really in quite good cosmetic shape.

All functions are operative. I made the purchase to have a digital body with which to use my AF prime lenses without

breaking the bank while I search for a current higher end camera.

 

I quickly found, however, that the camera exhibits a much documented & complained about tendency to position the

point of best focus well behind the target focused on. While there are any number of home made remedies and

workarounds to the problem Nikon appears to have remained silent on the issue as I can find nothing on their website

or in Google searches indicating that they addressed the problem. Some owners report sending off their cameras for

re-calibration only to have them returned in substantially the same condition.

 

But while looking into my D70s problems I kept coming across conversations from any number of photography forums

concerning similar issues with all of the DSLR cameras regardless of make. As an example there was this recently

running thread from Photo.net regarding the D7000:

 

http://www.photo.net/nikon-camera-forum/00XnSk?start=0

 

You can type any DSLR camera make & model into the Google search field followed by "back focus problems" and

see the problem for yourself.

 

Two factors here strike me as odd: first, that the manufacturers as well as the professional review community have

seemingly blown everybody off on this issue; and, even more mysterious, there seems to be no effective blow back

from the users community to push the equipment makers in a remedial direction.

 

You might speculate that the complaints indicate a finite and limited number of units that had a problem. I would,

however, suggest that many owners just haven't noticed (if you're using a full frame image and keeping prints under 8

X 10 the focus may seem fine) and the fact that the problem appears across the board in all makes & models seems

to me to indicate a serious defect in AF technology.

 

Have we been so seduced by the digital "WOW" factor in manipulation possibilities that we have abandoned what

was once most sacred in the field: the critically focused image?

 

I would appreciate hearing others' views on this matter while I ponder my recent yearnings to "upgrade" my

equipment. I mean, why spend $3000 or more for bad images when I can get them for a fraction of the price in "entry"

level cameras?

<p>If you can't or do not want to return your camera to the seller for a refund, send it to Nikon with your lens or lenses that exhibit the issue and have them correct it for you.</p>

<p>My 2 cents...<br /> <em>" manufacturers... have seemingly blown everybody off on this issue" </em> Actually, they have responded responsibly by adding AF fine tuning to their cameras.</p>

<p> </p>

<p>I agree - the problem is too widely reported to be fictional. Now that the manufacturers have managed to produce miracle ISO with high MP counts they should turn their attention to improving their autofocus modules.</p>

<p>The problem here is that the OP has an old D70s. If he sends it to Nikon for adjustment, it will not be under any type of warranty and the cost can easily exceed the value for such an old camera.</p>

<p>Personally, I own close to 30 different Nikon lenses and have used and tested various Nikon SLRs. To me, back focus is a rare problem. I bought my F5 in late 1997 and only had back focus issues with it occasionally with my 500mm/f4 AF-S in 2003, 2004 or so. Before that, in the first several years of my ownership of the F5, there was no problem at all. I still own that F5 but haven't used it much since I got the D2X in 2005.</p>

<p>A recent issue is the 85mm/f1.8 AF-S test sample I had on loan from Nikon for a month and half. That lens is perfect on the D300, D700, and D800, but on my D7000, it requies -8 AF fine tune. For a little while I was concerned that I may have damaged my D7000, but then I tested my 50mm/f1.4 AF-S on it @ 1.4 with it razor-thin depth of field, and AF is perfect with that combo. A few days ago I bought my own 85mm/f1.8 AF-S and I am glad that my own lens has perfect AF on the same D7000 I have (I only have one D7000), and I cancelled the AF fine tune on it.</p>

<p>I don't really have a good explanation why one 85mm/f1.8 AF-S has some problems on the D7000 while the other one does not on the same D7000, and both lenses are perfect on several other bodies. So this has to be related to specific body/lens combos. Nikon provides AF fine tune for a reason; I would definitely use that feature on DSLR bodies with that capability; unfortunately the OP's D70s is not one of them.</p>

<p>I remember reading an article on LenRentals (I think) that discussed camera and lens variations. The quick and dirty is that there is an acceptable range of functional variation during manufacture between the same models of cameras and lenses. Sometimes a lens on one end of acceptable finds it's way to a camera on the other (or same) end of acceptable and the results are unacceptable. If you sent the camera or the lens back to be fixed, you would most likely hear that there was nothing wrong - functioning within specifications. As mentioned above, this may be why AF Fine tuning was added to higher end cameras.</p>

<p>Note that it is an old D70. My old faithful D1x still focuses fine, same as Shun's F5, D2x. Those were built much better than a D70</p>

<p>I would check if manual focus is still ok with your D70. The problem may be with the lens too</p>

<p>Backfocus and frontfocus are an inherent shortcoming of phase detect autofocus systems. It is one of the tradeoffs of the autofocus system, and as the owner of a decently performing contrast detect camera, I can tell you that I prefer phase detect for most situations. It is faster, can track motion, etc. Here is the article that Steve mentions:<br>

http://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths<br>

And the update two years later:<br>

http://www.lensrentals.com/blog/2010/03/this-lens-is-soft-and-other-facts<br>

I am in the same camp as Shun: I have not had significant issues with my cameras, and with respect to Nikon DSLRs, I've owned a D40, D80, D90, and D200, and had a decent amount of seat time with a D70, D300, D3100, and D7000. Also, my lenses range from 1980's AF Nikkors to newer AF-S ones, and some Tamron and Sigma AF lenses thrown in as well. I'd guess that, as the second article mentions, there could have been a bad batch of D70's that went out. However, sending it in to Nikon with lenses should fix the issue. There's no blowback because there isn't some autofocus conspiracy; millions of DSLR uses have gear that focuses just fine. If you're working off of a tripod, consider a newer camera with live view. One of my mentors, a landscape photographer, upgraded his D70 to a D3100; the main reason was to get live view to attain critical focus.</p>

<p>Les, it's not a perfect world, so get used to it. Do rally-drivers race cars with automatic gearboxes? No! So why is that? Could it be because automation isn't as good as manual control?<br /> Some things to consider:<br /> All mechanical gearings have a thing called "backlash" where servoed gears either undershoot or overshoot the desired aim point.<br /> Lenses have curvature of field, so what's in focus in the centre of the frame won't be in focus at the edges or corners and vice-versa.<br /> Many lenses also suffer from a shift in focus as they're stopped down.<br /> Wide aperture lenses (>=f/2) nearly all suffer from spherical aberration at full aperture, and this aberration fools both the eye and any automatic focusing system.<br /> Autofocus relies on an <em>absolute</em> accurate registration between the AF sensor and the actual image sensor - something not easily acheived in the real world.</p>

<p>My own opinion is that we should be grateful for those little technical miracles we call DSLRs, rather than moan about their slight shortcomings. As Ariel says, if you want really accurate focus, then do it yourself with Liveview <em>at the taking aperture</em> or just by checking the focus on the viewfinder screen by eye.</p>