Dust explanation required
Discussion
After noticing a couple of major bogey like blobs on some prints from the last outing, I thought I'd do a dust reference shot to see how bad the issue was...
And it scared the bejeezus out of me!!
So, I have a quick blow at it as per the manual, fire off another couple of tests and then I'm about ready to top myself, why o' why couldn't I leave it alone????
Calls to a couple of local stores for a cleaning kit with little success. Oh bugger.
Point the thing out the window for a proper shot to see how noticible it is for real... and can't pick out more than two minor bogeys.
Can someone explain in really easy terms why the dust which I KNOW is there isn't that apparent on real pics?
Was it always there in the miniscule bits with only the big chips making the difference?
Are the test shots just extreme?
And it scared the bejeezus out of me!!
So, I have a quick blow at it as per the manual, fire off another couple of tests and then I'm about ready to top myself, why o' why couldn't I leave it alone????
Calls to a couple of local stores for a cleaning kit with little success. Oh bugger.
Point the thing out the window for a proper shot to see how noticible it is for real... and can't pick out more than two minor bogeys.
Can someone explain in really easy terms why the dust which I KNOW is there isn't that apparent on real pics?
Was it always there in the miniscule bits with only the big chips making the difference?
Are the test shots just extreme?
From my humble experience, dust/crud etc only really shows up against a plain background like sky. Any texture/detail masks it.
I did some tabletop work yesterday against a cream b/g and couldn't understand why there was crud in some shots but not in others. Then I realised it was only noticeable when I was going for max DOF - so - that can't be on the CCD then...
I did some tabletop work yesterday against a cream b/g and couldn't understand why there was crud in some shots but not in others. Then I realised it was only noticeable when I was going for max DOF - so - that can't be on the CCD then...
Lifes a bitch - and a dusty on at that.
When CCD gets bad, I suggest you send the camera off to the experts to clean. If you are really clever you can do this yourself, but I (and many others) just make it worse when we try it ourselves.
Mine goes in for a yearly service and comes back (almost) perfect.
Meantime, I change lenses very rarely and always outside facing the ground!
When CCD gets bad, I suggest you send the camera off to the experts to clean. If you are really clever you can do this yourself, but I (and many others) just make it worse when we try it ourselves.
Mine goes in for a yearly service and comes back (almost) perfect.
Meantime, I change lenses very rarely and always outside facing the ground!
The pieces I read about for test shots all suggested min apperture which would tie in with your findings but why would that make a difference?
Only thing I can think of is that if the light is coming through a very small apperture, it would only be hitting the sensor at particular angles. If you have a large apperture, the light could be coming through at a variety of angles thereby letting light in "behind" the particles lessening the effect???
No doubt someone with more knowledge of physics/optics will be along in a while....
Only thing I can think of is that if the light is coming through a very small apperture, it would only be hitting the sensor at particular angles. If you have a large apperture, the light could be coming through at a variety of angles thereby letting light in "behind" the particles lessening the effect???
No doubt someone with more knowledge of physics/optics will be along in a while....
I've got a lens that could do with a service so i was going to drop them both into the Nikon HQ service centre (which is just down the road) in a couple of weeks but I've maybe just moved that forward...!
Someone did say that they'll do a while you wait for a sensor cleaning but I haven't got round to calling them to find out the truth, anyone on here know..?
Someone did say that they'll do a while you wait for a sensor cleaning but I haven't got round to calling them to find out the truth, anyone on here know..?
I'm no expert, but I'd say there's two factors here.
The first is your brain. If you look at a uniform surface, you expect it to be uniform, so the dust marks stand out. This is the same as seeing equivalently sized specs of dust on the actual reference surface. Obviously if you take the angular size from the focal point of a dust spec in your camera, and an equivalent dust spec on the target, the target dust spec must be much larger to have the same apparent size.
I'd geuss it's also to do with contrast. The dust spec in your camera can only attenuate by a fixed ammount. The more light that enters your camera, the smaller the fixed attenuation is as a proportion of the total ammount of light.
The first is your brain. If you look at a uniform surface, you expect it to be uniform, so the dust marks stand out. This is the same as seeing equivalently sized specs of dust on the actual reference surface. Obviously if you take the angular size from the focal point of a dust spec in your camera, and an equivalent dust spec on the target, the target dust spec must be much larger to have the same apparent size.
I'd geuss it's also to do with contrast. The dust spec in your camera can only attenuate by a fixed ammount. The more light that enters your camera, the smaller the fixed attenuation is as a proportion of the total ammount of light.
You "notice" the first because it's dynamic range is much smaller...
Histogram of first
and now of the second
Now - the eye is a fabulous thing, but when the dynamic range gets larger it "smooths" things out because, unbeknown to you, it actually does the "opposite" of what you did on your camera.
The first was f18, but because the resultant image has such a narrow dynamic range, your brain and eye "expand" it to fit the normal range (if you looked solely at it your pupil would expand), and hence you notice the fact that the splodges are there.
When there is a wider dynamic range (i.e. when you open up the camera's f-stop) your eye will potentially narrow the pupil to get the same "range" on the rear of the eye as in the first.
If you look close (i.e. stare at the screen) you can find quite a few of the splodges in the second.
Brilliant things the eye and brain!
J
Histogram of first
and now of the second
Now - the eye is a fabulous thing, but when the dynamic range gets larger it "smooths" things out because, unbeknown to you, it actually does the "opposite" of what you did on your camera.
The first was f18, but because the resultant image has such a narrow dynamic range, your brain and eye "expand" it to fit the normal range (if you looked solely at it your pupil would expand), and hence you notice the fact that the splodges are there.
When there is a wider dynamic range (i.e. when you open up the camera's f-stop) your eye will potentially narrow the pupil to get the same "range" on the rear of the eye as in the first.
If you look close (i.e. stare at the screen) you can find quite a few of the splodges in the second.
Brilliant things the eye and brain!
J
I WIN!!
From www.photo.net/equipment/digital/sensorcleaning/
Technical note: The dust isn't actually on the sensor surface. It's on the surface of a filter which is in front of the actual sensor itself. This is why dust shows up more at smaller apertures. Since the dust spots are some distance from the actual sensor pixels, a wide aperture lets in light which can "go around" the dust spot. It's a bit like using a large softbox for lighting. Shadows (and what shows up in the image is the shadow of the dust spot) are light and soft. At small apertures it's like using a small pinpoint spotlight and shadows are dark and hard edged. The following images show dust spots as f22 and f11. They have been GREATLY processed to show the dust spots as clearly as possible. On the straight images the spots are totally invisible at f11 and only very faintly visible at f22
From www.photo.net/equipment/digital/sensorcleaning/
Technical note: The dust isn't actually on the sensor surface. It's on the surface of a filter which is in front of the actual sensor itself. This is why dust shows up more at smaller apertures. Since the dust spots are some distance from the actual sensor pixels, a wide aperture lets in light which can "go around" the dust spot. It's a bit like using a large softbox for lighting. Shadows (and what shows up in the image is the shadow of the dust spot) are light and soft. At small apertures it's like using a small pinpoint spotlight and shadows are dark and hard edged. The following images show dust spots as f22 and f11. They have been GREATLY processed to show the dust spots as clearly as possible. On the straight images the spots are totally invisible at f11 and only very faintly visible at f22
More on the dust thing....
After much reading (and being quoted 80 quid+ for a clean by Grays of Westminster with a turnaround of 2-3 weeks) I bravely/stupidly/rashly decided to have a go myself...
I thought I'd have a go at the "Pixel Sweeper" method...
Browsing at the art shop got me a ProArte Sterling 201 Short Flat (did you know they use squirrel hair for some paint brushes???)...
A quick trip to Maplin got me a large tin of Aero duster and we're ready to go...
Following all the instructions about washing, rinsing, drying, spraying and trialing I actually got to trying it out on the camera this afternoon.
And it worked a treat! I'm very happy with it, all my little bogeys are gone, even at f29 and I only have three largish ones which disappear at about f18. I reckon these must be pollen or bigger particulates that have a more robust hold on the glass, they can be dealt with professionaly when I get round to it.
If I was to do anything different, I'd buy a sligtly smaller brush, the one I got was a fraction to large for a single sideways swipe and I had to do two vertical instead. Brush was a size 8.
I'm not recommending this method, just telling my story... I tried it at my own risk, if you try it and it doesn't go so well, don't blame me!!!
After much reading (and being quoted 80 quid+ for a clean by Grays of Westminster with a turnaround of 2-3 weeks) I bravely/stupidly/rashly decided to have a go myself...
I thought I'd have a go at the "Pixel Sweeper" method...
Browsing at the art shop got me a ProArte Sterling 201 Short Flat (did you know they use squirrel hair for some paint brushes???)...
A quick trip to Maplin got me a large tin of Aero duster and we're ready to go...
Following all the instructions about washing, rinsing, drying, spraying and trialing I actually got to trying it out on the camera this afternoon.
And it worked a treat! I'm very happy with it, all my little bogeys are gone, even at f29 and I only have three largish ones which disappear at about f18. I reckon these must be pollen or bigger particulates that have a more robust hold on the glass, they can be dealt with professionaly when I get round to it.
If I was to do anything different, I'd buy a sligtly smaller brush, the one I got was a fraction to large for a single sideways swipe and I had to do two vertical instead. Brush was a size 8.
I'm not recommending this method, just telling my story... I tried it at my own risk, if you try it and it doesn't go so well, don't blame me!!!
HankScorpio said:
even at f29
What have you got that goes down to F29?
I didn't think anything I use goes down past F4, well I rarely turn the dial past there
, 'til I looked and saw I had an old Tamron that starts at F5.6. Anyway, I'm sure all my lenses go only to F16 or 22 at the outside...
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