D90 focus issues?

[gardy]

Looking at the charts, I think this is within specification. Why do I say this??? Because the error at close range appears to be very,very slight back focus. At least at first glance. But...(there's always a but, isn't there?) I think we need to keep in mind that the AF brackets in the viewfinder are quite often NOT EXACTLY in accordance with the EXACT location where the AF system's sensor's actually take their information from...most ultra-critical testing will show that the ****exact*** area that an AF sensor's in-viewfinder scribed marks represents a very good approximation of the actual AF area--but not a totally accurate, ultra-precise indication of where the actual AF data is accepted from. In other words, in plain English, the AF marks in the viewfinder are not 100 percent accurate. In simple terms, the AF areas in the viewfinder are often not quite aligned with the bracket marks. And as a result, in really critical situations, there can easily be slight mis-focusing.

In these test...a 3/8 inch AF error toward back-focusing is pretty good...that could EASILY be attributable to a bracket/AF sensor mis-alignment, that results just from the sheer size of the AF bracket when it subtends a close-range target. At longer ranges, the AF brackets will, naturally, and inevitably, cover a wider and wider area of physical real estate. And as such, it makes it even more difficult to ***precisely*** lay the AF sensor's actual area right onto an ***exact*** target of smaller size. In other words, with say a moderate wide-angle, at 30 feet, the AF bracket might appear to be on a human's arm...buuuuuut...if the actual AF data is collected from say the LEFT EDGE of the outside AF bracket, what you think is the left arm might in actuality be...the house behind, some 10-12 feet back...

Anyway...I'm not saying this is what is going on in your situation, but the discrepancy in the AF bracket areas and where an AF system actually gets its data from is an issue that has been covered at length in many articles. Thom Hogan had some articles and posts years back on diagnosing AF problems, and the above points are ones he has made many times. I am only going in to this at this length because your test chart results make me think that the body is what Nikon would call "within specification" for function. And because you've presented some real,empirical evidence, and it deserves real commentary. From the above sample pics, I think with that lens,at close range, the AF system is doing relatively well.

Thank you tons for all the help and info Derrel. the one thing that concerns me is how the slight back focus can translate at further distances. and the fact that with another camera on the same chart with same lens it was much more like one would expect from doing a test like this, i do realize it it just a simple check and cant be used as hard fact. I do attempt to make sure the entire area of the bracket and sometimes more is covered if possible, which is something I've always done, because well it just makes sense haha. but any how like i had said before i never really noticed a problem with focus inside of about 15 feet ish. i will continue to dig up the internet in search of some answers. in the mean time ill try to get some more hard data in the form of samples. I really do appreciate the help and the time you have given to helping me figure this out. if you have any ideas im all ears!
-tim

 

[JohnYoung]

Not sure if its related but I have recently sent my D90 off for repair as sometimes it would refuse to focus and you could hear the focus churning away in and out without hitting focus. This was only now and again but no good when I am using it for weddings....


I did read online somewhere where you can manually (altering small hex bolt) to adjust focus. Sorry I cannot find where I read it it but it had a diagram etc

 

[gardy]

Not sure if its related but I have recently sent my D90 off for repair as sometimes it would refuse to focus and you could hear the focus churning away in and out without hitting focus. This was only now and again but no good when I am using it for weddings....


I did read online somewhere where you can manually (altering small hex bolt) to adjust focus. Sorry I cannot find where I read it it but it had a diagram etc

i have seen that before, you can use the small 2mm hex bolt closest to the image sensor to adjust the focus, not sure if i want to try it or not, since that bolt is so close to the sensor. i am considering getting a split prism focusing screen like the Katzeye and just use manual focus

 

[gardy]

ok, finally sent it in to Nikon ill post what they find out when i know

 

[gsgary]

Derrel,
thanks for the quick reply, and the link. i have not blown out the AF sensor area specifically but before i cleaned the sensor went through everything i could see without the lens on and blew it out with some rocket air. i will go back in and do so focusing on cleaning the AF sensor area.

Never used canned air you have probably damage something

 

[gardy]

Derrel,
thanks for the quick reply, and the link. i have not blown out the AF sensor area specifically but before i cleaned the sensor went through everything i could see without the lens on and blew it out with some rocket air. i will go back in and do so focusing on cleaning the AF sensor area.

Never used canned air you have probably damage something

it wasn't canned air, it was one of those rocket air blowers

 

[Roger3006]

The same problem manifested itself in my D90. I sent the body to KEH for repair. They could not find anything wrong with it and sent it back to me. It has worked fine ever since. You may try taking the battery our for a day and see what happens. Wish I could be more help.

Roger

 

[gardy]

Hope they do find something wrong, the only thing that would frustrate me more than not having my camera for a month is getting it back when they say nothing wrong lol

 

[gardy]

Update: got the quote from nikon, said that major parts needed replaced but didn't say what.. has anyone had experience with them before, and how long can i expect it will be to get it back once i approve the repairs?

 

[RICH531]

Anyone have any ideas? My D90 Auto Focus only works with 55-200 lens but not AF-S DX NIKKOR 18-105mm f/3.5-5.6G (although I can manual focus which works fine)

Is my 18-105 lens AF hosed?!? - I have already tried cleaning the contacts (don't want to spend too much on it...seems like it costs nearly as much to fix it as it would to replace it!)

 

[gardy]

Anyone have any ideas? My D90 Auto Focus only works with 55-200 lens but not AF-S DX NIKKOR 18-105mm f/3.5-5.6G (although I can manual focus which works fine)

Is my 18-105 lens AF hosed?!? - I have already tried cleaning the contacts (don't want to spend too much on it...seems like it costs nearly as much to fix it as it would to replace it!)

AF switch on the 18-105 set to AF not MF?

 

[JohnYoung]

Well regarding my D90 I was told it was un-repairable. They never said what was wrong but it was under shop warranty and I got my full money back

I now have a D600

 

[teribithia]

Take off the lens. Set the shutter to B, in manual mode, and press the shutter release and HOLD it firmly so the mirror stays in the UP position, then blow out the AF sensor area, which is located at the bottom of the mirror box; you might very well have some fibers caught in there. Seriously.

Here is a link to an excellent article entitled Autofocus Troubleshooting. Autofocus troubleshooting by Thom Hogan

Thanks this always happen to me .