dust spots on stacks

In spite of my new Rocket blower's best efforts, although a single image appears spot-free,
when amassed together in a 25 image stack, they all gang up together in some amazing arrangements that appear all too readily in the final stack-image.

What sort of shot can I take to show all the spots on a single (printed) image, to indicate their position on the sensor?

Thanks in anticipation,

Roger.

Are you seeing dust spots or hot pixels in your stack worms?

Steve

Bright blue uniform sky. Stop down to f22.

Fire

Just remembered. Both my K20D and K3 have a 'dust alert' function which involves pointing the camera (with lens) at a bright, white wall or similar then pressing the shutter button. The result is an image on the rear screen showing the position of each speck of dust as it appears when you look at the sensor. You can't print it or save it permanently, but I've occasionally found it useful for tracking down a recalcitrant speck of dust. Have you tried with your camera (whatever it is)?

Steve

Here's one with several (groups) in the b/g




Dust or hot pixels (the latter of which I know absolutely zilch!)?

Thanks for your time & help.

Roger.

Thanks, Steve.
I don't think K5 as "dust alert".

R
Just looked, Spanner page 4.
D/A is there, but not high lighted for use!!!

Was that function really an extra, all those years ago..............?

R.

here's a "better"(!) one.




R.

On the rare occasions I do stacks I hand prepare all the frames beforehand to avoid this problem (or am I being over finicky?). I know where the 'permanent' dust bunnies are.

I see your problem - can't miss it with those examples!

It's hard to tell whether they are due to dust or a pixel problem. My dust tends to be bigger blobs! Strange that dust alert is greyed out, particularly as the earlier K20D has it. Perhaps it's the lens. The K20D manual doesn't say what type of lens to use apart from setting to A position when the lens has an aperture ring. The K3 manual explicitly says that the lens must be a "DA, DA L, FA J lens or a D FA, FA or F lens that has an A position, and set the aperture ring to the A position". So the dust alert function won't be available if one of your pre-A lenses is attached.

However, it's possible that some might be due to dead pixels. Pixel mapping (in the spanner menu) claims to correct an image for defective pixels - permanently dead or permantly stuck on - presumably by interpolating from adjacent pixels. It won't deal with hot pixels, though, which are pixels that become temporarily stuck on due to long exposure or lots of shorter exposures in quick succession (stacking!). They revert to normal when the sensor is no longer in use. Hot pixels appear as coloured spots (the RBG colour of the pixel).

All this reminds me that I always intend to check for dust and do pixel mapping before starting a stack but always forget to do it. Note to self - do it, you know it makes sense!

Steve

And by way of illustration, here's a crop from one of my stacks. The dark, thicker streaks on the left are due to dust on the sensor (they are sometimes much bigger... ). The lines of coloured dots are pixels that are stuck on for whatever reason.




Steve

Dust on the sensor tends to be OOF ,these are in focus like a stuck pixel

I wondered if it is a dead pixel moving around due to lens breathing while refocussing the stack.



John

Yes, this combined with software trying to align images in the stack is definitely the cause of each cluster. The giveaway is that many clusters have the same basic pattern with clusters that are closest looking the most similar.

Steve