Dear all
A Quandry.
My D70 is not the cleanest of beasts after the IR conversion, I got some dirt of the sensor itself and had it professionally cleaned.
Last week I noticed it was getting dirty again, and cleaned it.
I was happy with the results, but noticed that the dirt comes and goes with F value.
I converted the camera to IR so that I could use all the functionality of the SLR.
I know with the IR conversion its advised to short at f8 or more to compensate for the different wavelengths.

So here are three images, f3.5, f11 and f22
F3.5 looks okay


F11 looks okay


f22 dust bunnies are here


From this I would continue to shoot at f11 and not worry.
I am not sure more money thrown after cleaning this (I've used a Giotto and swabs already) is worth it.

OR (Big OR)

Am I hamstringing myself and should be striving to use smaller apertures for IR

Looking forward to experience/advice from the illustrious group here
Many thanks in advance

The problem with high F numbers (small apertures) is that because of the greater DOF, the sensor can record every fleck of dust that is on the lens - filter - floating in the air ! As well as IR work, this is a common problem with high F number macro work too.

If there are no signs of some of the spots at larger apertures, then those spots are unlikely to actually be on the sensor itself.
With high F numbers and DOF, it's vital to ensure that all lens sufaces and filters are totally dust free, and try to work in clean air conditions, such as soon after rainfall.

Hope this helps.

Just a couple spots there Simon. Try to shoot and larger F-stops and use the healing tool when needed.