f/32 Black Specks, f5.6 None...

ZWolfe21 · May 9, 2009

I do not doubt this has been asked before but in my attempt to search the forums it proved fruitless. Anyway, i'm stumped, and slightly irritated. I noticed today on one of my shots black specs in my photos, shot at f/32.

So I promptly grabbed my camera and brightened up the lights and shot two shots on a white wall. at f/5.6 I saw no specs at all. on f/32... I could see them on the LCD screen... Dirty objective lens? (It is a zoom lens).

Quantaray AF LD 70-300 Zoom Lens.

I cleaned the front of the lens but I thought these particals wouldn't be in the focus plane? I've been told that there is dust on the inside of the lens, and that just about all lenses will gather dust in the lens as you work the zoom in and out. Any help here?

Or is this perhaps the cost of cheap lenses.

Samanax · May 9, 2009

The specs are probably from dust on your image sensor, not from dust on the lens.

Read this.

ZWolfe21 · May 9, 2009

I had thought of that but the battery isn't at max charge and the camera won't allow me to go into cleaning mode otherwise or i'd had tried to clean it before posting but I was fit to be tied and rushing at work and wanted an answer, will deffinently read this. Thanks alot for the prompt reply.

Dwig · May 9, 2009

Its not dust at the focal plane. Dust there would yield virtually identical shadows (dark spots) at all apertures. What you are seeing is almost certainly dust on the anti-aliasing filter, which also serves as an IR cutoff filter, that is mounted just in front of the sensor. This filter's front surface is subject to dust and is enough forward of the actual focal plane, where the photosites in the senor are, to yield the pattern you describe. The f/stop at which they appear will vary with the lens design and focal length, but with any one lens they will show distinctly at small apertures and become softer blurs at wider ones, often enough softer that they become undetectable.

Dust on lens surfaces will never show as distinct spots in the image. The particles are too close the the lens center to ever come enough into focus to form an image. In very rare cases, generally extremely wide angle lenses focused extremely close, dirt can become visible at very small apertures when its large enough. Something fine enough to be classed as dust, though, won't.

ZWolfe21 · May 9, 2009

It had me going there for a moment, now at least I know its something I can clean! Now i'm calm... Again, thanks for the prompt, (and in depth) reply. as soon as this battery charges, I read sam's link and my owners manual again to make sure I don't screw anything up i'm going to get on this.

Josh66 · May 9, 2009

Get yourself a sensor cleaning kit. It should be in every (digital) camera bag.

There are a ton out there. I use the Copper Hill kit. Just google "copper hill sensor cleaning" or just "sensor cleaning", you'll get a ton of results.

ZWolfe21 · May 9, 2009

OK, after doing some reading, charging the battery, putting the camera in cleaning mode and using a bit of canned air (VERY carefully I might add and only in short bursts). My sensor is almost spotless.

However seeing as a few sposts do remain, I did some research into cleaning kits and as fate would have it the cleaning solution in Copperhill's kit happens to be recommended by Sony... and the methods must be almost standard so its on order. Thanks again for everyones help here!

Overread · May 10, 2009

NO!!
ok take the canned air - get some black fabric and spray the air onto it - you will see loads of little white fleks - those are bits of chemicals used to help keep the air compressed - and your going ot use that to clean a sensor of dust? no no no

Get yourself something like a Giottos Rocket Blower and use that instead. Take some time over it (I like to mount the camera on a tripod so that my arm does not get tired holding it up) and make sure that its pointing downwards (the lens opening that is) an pause every so often when blowing so that the dust can fall out of the camera.
If anything remains after using the blower then you have to use a contact cleaning method - there are loads of guides on the net and loads of cheap kits on amazon (and some expensive ones like the arctic butterfly) so run a google search for some ideas (its all I would do now since I don't have a contact cleaning kit - just a little blower)