[purplepleaser]

Hi,

I just received a new lens today and i thought it was dirty. After checking the 24-105 and 100-400 it seems to be on the sensor.

The spots seem okay at f2.8, f4 etc but when i get to the higher numbers f16, f32 they are clearly there.

So i need to clean the sensor but why does it show better at higher f-numbers.

Sorry if its a dumb question.

Lee

[Markulous]

Originally Posted by purplepleaser

Sorry if its a dumb question

Well, I'm sure it's a DOF thing but I can't for the life of me work out the whys and wherefores!

..... so maybe we're both dumb, Lee!

Which reminds me - I really must clean my sensor - dust "bunnies" now number in the high 10s! Takes me 2 or 3 mins to "clean up" my shots now

[Dave Canon]

Well it is definately true that the dust will show up more at smaller apertures. It is also affected by the distance between the outer filter and the actual sensor. I believe that with a wider aperture the light will come from a wider angle and thus some will get to the pixel which otherwise would not if the light is narrower as for a small aperture. Anyway, I think it is down to the angle of arrival of the light.


A useful way of checking dust is to photograph a sheet of white paper at say f11 then transfer to Photoshop or Eements. Apply auto Levels and you will clearly see all the dust. After cleaning your sensor, you can repeat the test to ensure that the dust has been removed.

[purplepleaser]

Hello

Thanks for the information. I will get a sensor cleaning kit, just have to steady my hands first

Lee

[stepheno]

Nah....don't worry. It's a doddle......................................after the first time

[purplepleaser]

I might try and follow Rob's guide, doesn't seem that scary