Possibly chromatic focus error. If they neglected to adjust the infinity focus and the auto-focus algorithm correcting for the difference between average visible light and near IR, which is considerable, then you would obtain a noticeable out of focus result after IR conversion.

With film 35mm cameras when using IR film the focus adjustment with a 50mm lens at infinity meant turning the focus collar 15-20 degrees to obtain correction. If you were lucky with some lenses there would be a red dot on the lens barrel to mark the IR infinity focus position.

the cause is basic, IR wavelength is different from visible light wave length.

I posted a response to your question on the DPreview Nikon Talk forum. I'm wondering if my answer was the solution.

Quote:
I had a Nikon CP8400 converted by LifePixel but the camera returned with autofocus issues.
In regular AF mode it can't focus at the wide end but it does fine at the tele end.
In infinity mode it's actually completely out of focus.
In macro mode AF works fine at both ends.
LifePixel doesn't seem to know what the problem is insisting the camera worked fine after the conversion but nonetheless offering to take it back to try to fix it.
Although the present outcome is a disapointment the camera is still able to perform its intended mission, shoot landscapes.
Before sending it back and taking the risk of things getting worse I'd like to know if anyone has a clue as to what went wrong during the conversion.

Thanks in advance

Robert Trudel

Thank you for your suggestion.
I did try every possible AF settings combinations to no avail.
I was wondering if the previous poster wasn't on to something in regard to the different focus point of IR light ? That would explain my out of focus infinity setting. How is your 8400 when set to infinity ?
I stated that the camera will AF fine in the macro mode meaning it focuses through the entire zoom range both close and far objects just as I would expect the regular AF mode to do. Is the macro mode supposed to behave that way or am I right to suspect the modes might have been "switched" during the conversion ?
In your opinion what would I be risking in keeping the camera the way it is ?
Would I miss the infinity mode ?
What would be the drawbacks of only having the "macro" mode to AF ?

Thank you for your time,

Robert

Have you looked at my gallery. My camera has no trouble focusing at any distance. Life Pixel charges $250 for the 8400 IR conversion. If you can't get it to focus, you should send it back and see if they can get it working.
http://bermangraphics.com/coolpix/8400-infrared-gallery.htm

But like I said in my original reply, I remember having focus problems when I first got the camera back and it went away after I changed the settings.

If you want to call me, I'll compare all my settings with your camera's settings. My contact information is on my web site and you can call me tomorrow.

In my occupation we have a saying that better is the enemy of good.

Even though your right that for the price paid I shouldn't have to put up with a less then perfect result, the camera such as it is seems to be perfectly usable.

The regular AF mode is defective but this appears to be completely compensated by using the AF in Macro mode.
As for the infinity focus mode I think I can live without it since it's mainly useful for low light, low contrast landscape, a situation ill suited for IR photography.

It's obvious that I'm very hesitant in sending the camera back to LifePixel.
If it's good enough as it is why should I pay to ship it over, taking the risk that something might happen along the way, that LifePixel might not be able to fix it or that the repair attempt might make things worse.

The counterpoint to this is that I'm unsure the present problems with the camera are without further consequences or that they might be the harbingers of future major malfunctions.

Right now I'm leaning towards keeping the camera but if you think there are holes in my reasoning you are more than welcome to point them out to me.

Thank you,

Robert Trudel

If I remember correctly, macro is good throughout the entire zoom range. If that's the case ,does the camera focus correctly at all distances if left on macro?

It does so to the point that I'm wondering what's the purpose of having a "regular" AF mode.

Robert Trudel

Quote:
I had a Nikon CP8400 converted by LifePixel but the camera returned with autofocus issues.
In regular AF mode it can't focus at the wide end but it does fine at the tele end.
In infinity mode it's actually completely out of focus.
In macro mode AF works fine at both ends.
LifePixel doesn't seem to know what the problem is insisting the camera worked fine after the conversion but nonetheless offering to take it back to try to fix it.
Although the present outcome is a disapointment the camera is still able to perform its intended mission, shoot landscapes.
Before sending it back and taking the risk of things getting worse I'd like to know if anyone has a clue as to what went wrong during the conversion.

Nothing necessarily went wrong during conversion. Zoom lenses can focus with high accuracy at one end of the range, and be way off at the other. Or at macro vs infinity. I see this all the time; I've tested over 120 lenses for infrared backfocus.

If the camera won't focus at all in some areas, this may be a camera limitation, or it could be, as you suspect, a conversion issue. That would be unusual, but possible.