Anybody know what this is?

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Not sure if this is the right place for this, but can anybody tell me what causes this mark (approx. full size):

spot.jpg


I've cleaned the area about six times and it's still there. It's not apparent below f11, this shot was f22. Could it be a fault on the filter? I know it's not a sensor problem like a hot pixel or a dead pixel, and am worried maybe I damaged the filter when cleaning.

Ta :)
 
You may need a sensor clean!
 
Not dust, just a mark on the filter - I know this because a) I've cleaned it six times and b) it goes away after about f11 ... just looks too regular to be dirt. Dust marks are easily identifiable - they look softer and more even - I know cos I've seen plenty ;)
 
Not dust. I don't want to worry you but...

Looks to me like the mark left by sensor cleaning fluid when too much has been used...
If I'm right then I think the damage is permanent.

At f/22 (far too small an aperture for sharp images BTW) it shows more because of the increased depth of focus. As f/11 is the smallest aperture you should use if you have a cropped frame DSLR it may not cause a problem.
 
dellipher said:
Thats definately a dust bunny.

I'd take it to a professional for a sensor clean, IF you have cleaned it yourself.
Take the filter off and try it again,
Click to expand...

Take the filter off??? I think that's a job for Olympus tech guys not me!

Trust me, dust would have moved by now. ;)
 
Garry Edwards said:
Not dust. I don't want to worry you but...

Looks to me like the mark left by sensor cleaning fluid when too much has been used...
If I'm right then I think the damage is permanent.

At f/22 (far too small an aperture for sharp images BTW) it shows more because of the increased depth of focus. As f/11 is the smallest aperture you should use if you have a cropped frame DSLR it may not cause a problem.
Click to expand...

Thanks for confirming what I didn't want to hear! So why does the lens go to f22? It's supposed to be designed for the sensor - 4/3 system. Is f11 suitable for landscapes?
 
Grave Robber said:
Thanks for confirming what I didn't want to hear! So why does the lens go to f22? It's supposed to be designed for the sensor - 4/3 system. Is f11 suitable for landscapes?
Click to expand...

Why does the lens go to f/22? Good question, just manufacturers trying to have plenty of features to shout about I suppose:'(

I didn't realise you're on 4/3rds, which is even smaller than Canon/Nikon APS-C sensors and my guess is that f/8 is probably as small as you should go.

The reason is diffraction limitation, which causes an overall loss of sharpness at small lens apertures. If you want an explanation of how and why, please look at this non-technical info, which was posted on another site

Diffraction is NOT due to light passing through a hole, but rather to light passing over the sharp edges of a hole.

"Diffraction" itself is related to f/stop or aperture in that the GREATER the f/stop or aperture, the greater the edge surface area over which the light passes, and the GREATER the diffraction. The circumference is all that matters when calculating the potential diffraction.

But few people are concerned about diffraction on it's own. What is important is the amount of diffraction COMPARED to the amount of image forming light.

Diffraction is more prominent at smaller f/stops or apertures NOT because there is more diffraction -- because there isn't, there's LESS diffraction at smaller f/stops / apertures -- but due to the even smaller amount of image forming light getting through. What we observe at decreasing f/stops / apertures is actually an increase in the diffraction to "signal" ratio. That is, as we decrease our f/stop / aperture, even though the total diffraction goes down, at the same time the total amount of image-forming light is going down at an even greater rate at smaller f/stops / apertures. So the ratio between them changes in favor of the diffraction at smaller f/stops / apertures.

In ANY group of common activities, there tends to be abbreviations and resulting jargon -- which is intended to increase the speed and accuracy of communication between initiated members. However, this "coding" actually inhibits accurate communications with the uninitiated and thereby limits the growth and penultimate success of the group. What you have been hearing people say is probably, "... diffraction increases at smaller apertures ..." when what they should have been saying is, "... the total effect of diffraction increases at smaller apertures ..." or, "... diffraction-to-signal ratio increases at smaller apertures ..." That would have been more accurate if more time consuming.
 
i had a spot just like that , i would say
in need of a sensor clean , not cheap but worth while although as you say it only shows up at certain aperture's .
had mine done last year canon 5d cost was around £60 and until i fell confident to have a go myself i`ll take it to an expert .

or you could just clone it out of the photos :shrug:

rog
 
Garry, if that's non-technical I'm a goose ;) Thanks for the info anyway - it seems I have been doing it all wrong for years, because I aim to use all the f numbers right up (or down) to the limits, and f22 seemed like a natural choice for landscapes.

Since your post I've actually found this site: http://www.zenadsl5251.zen.co.uk/photos/doftut.html which amongst other things says this:

The smaller the aperture of the lens, the greater your available DOF. A smaller aperture - a smaller hole in the iris - but a larger number - will increase DOF. For most general purpose shots, apertures in the range f8 - f11 will give the optimal sharpness from the lens with maximum DOF. Unless you're very close to your subject and using a very long focal length, it's unlikely that going much tighter than f11 will offer any significant advantage for most scenes.

Hyperfocal distance is also the point in front of you for the focal length and aperture combination where if you focused at infinity, the near point of acceptable focus would be. So you can see how focusing at that point would give some sharpness in front of it, but also all the way to infinity. You can download various charts and there are many sites that allow you to work out the hyperfocal distance for any particular aperture and focal length combination - and there's a simple formula if you want to work it out yourself: H (in mm) = focal length ² / f stop x CoC (circle of confusion, for the 300D and 350XT, this is 0.019mm).

But my own quick rule of thumb that's easy to remember in the field is 11:30. That's all I need to remember - that at an aperture of f11 and a focal length of 30mm, hyperfocal distance is 11 feet (it's actually a bit more, but the easy to remember version works reliably enough).


So although I don't understand exactly why this is the case, I am pleased I found out. It hardly seems worth cleaning sensors at all, because virtually nothing shows up at f11 or less (or is it 'more'? I always get confused!) and as only about a third of my shots are landscapes, I think really I have nothing to worry about now :)

Thanks again for the help :thumbs:
 
santana007 said:
i had a spot just like that , i would say
in need of a sensor clean , not cheap but worth while although as you say it only shows up at certain aperture's .
had mine done last year canon 5d cost was around £60 and until i fell confident to have a go myself i`ll take it to an expert .

or you could just clone it out of the photos :shrug:

rog
Click to expand...

I'm afraid it may be beyond cleaning, but in the rare cases it might show up (see previous post) I will clone it :)
 
Just to show the difference, this is what actual dust on the sensor would show up as:

dust.jpg


That is a same size crop as the other pic, to give an idea of the difference in size, density and shape. The usual round 'spots' are often not dust, but contaminants like oil and grease, pollen, saliva, soup ... etc etc ... or a mixture of those and smaller dust particles.

;)
 
As that mark is dead central, I'm wondering if it isn't a manufacturing fault that you have not noticed before. There are a lot of noise reduction speckles in that blank image too so another possibility may be the camera noise reduction system creating marks that aren't really there. Assuming this was shot as jpeg it might be worth repeating the test using RAW and not applying any noise processing.

As to f22 and normal use... I'd agree that I rarely use f22 but that said i wouldn't hesitate to use f22 if the situation needed it - like getting a slow shutter for some landscape shots where you want movement in water showing. I certainly do not notice image quality degrading. On my macro lens however I have seen that it performs best at around f11 and softens a small amount at f16 f22 sort of range. So whilst I understand the argument I don't see a noticeable problem with landscape.
 
Ah no maybe people have been mislead - that pic is an actual size crop, not the full image! It's about 1/9 the actual image size, and the mark is lower left corner.
 
How much of a crop is that first shot? IE how big is that blob on a photo? (You say full size, does that mean it is a 100% crop? ("Actual Size" in photoshop) and at what f-stop does it stop appearing? To be honest I would be annoyed but I wouldnt worry about it too much, it will probably easily cloned out of any shots that it would show up in.

Not sure I understand this not using f22 thingy, I use whatever the lens will go to, like Robert says, I think my 10-20 goes upto f32 :) Cant say I have ever noticed any extra softness or problems when closing it down all that way, might have to read up more on that.

P.S I take it you have checked the front and back of the lens for any marks that could cause this?


EDIT - lol ok, answered while I post :p
 
stop down too much and diffractions from the hole creates it's own distortion - Youngs Double Slit experient springs to mind...
 
Diffraction limitation is a law of physics so is constant, but sometimes it does make sense to use apertures that are theoretically too small. Like everything else, we sometimes need to trade off need against perfection.

For example, I had a (very boring) job shooting tiny items at near macro distances and needed to use f/22 to get maximum DOF. I was using a full frame digital and diffraction limitation kicks in after about f/16 but my choice of f/22 was neccesary IMO.

Some people say that they can't see any difference when diffraction limitation rears its ugly head, but this depends on a couple of things - partly on the degree of enlargement and partly on the quality of the lens. Poor lenses that can't produce a sharp image at any aperture may not look any worse with apertures that are too small.

For landscape photography with a small camera though, I can't see the need to use very small apertures in normal situations.
 
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