F16 causes dust?!?!

pevelg

pevelg

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I was talking some photos today and noticed what appeared to be sensor dust on my photos. I only use one lens, the 50mm Zeiss ZM Sonnar f1.5. I usually use it wide open. I took several test shots, f16, f5.6, and then f1.5 EDIT: The following photos are upper right corner crops.

F16
5061156854_42cb5f8a4f_b.jpg



F5.6
5061157140_04161d711e_b.jpg


F1.5
5061157466_42eeb84d01_b.jpg


Is this normal of sensor dust or is something else going on?
 
Yep, most dust only show up at smaller apertures. As for cleaning the sensor, I will let people more experienced than me answer that one...

EDIT: A quick google search revels a plausible explanation. With a large aperture, the light reaches a point on a sensor through multiple paths, so only the spot directly under and in contact with the dust is covered, as the light hits that spot from multiple angles. At a small aperture, there are less paths for the light to travel through to get to that same spot on the sensor, so the light hits the dust from a much smaller range of angles, and the dust blocks a lot of this light, casting a shadow of sorts onto the sensor.
 
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I shoot at f16 or 22 towards the sky to check my sensor. It will reveal dust spots. I now have a special magnifier with internal lights for sensor cleaner and it works better for me because I don't have to clean and shoot, I can just keep examining the sensor until clean. I also use the Lens Pen with the articulating end, not the straight one, and it works well.
 
This is even more pronounced when you use a pinhole body cap in place of a glass lens; you'll see every surface defect in the light path to the sensor.

In fact, the pinhole body cap is a good post-sensor-cleaning test.

~Joe
 
Yes, dust will show up at higher f-stops, because the light is more like a point source, and the dust will cast a shadow on the sensor. If you have a low f-stop, the light is coming in from a larger aperture from all directions, so it doesn't cast a shadow on the sensor. (Well, it does, but it's diffused.)

By analogy, think of your shadow on a sunny day, vs an overcast day. It's a similar effect.
 
Also, remember the dust is not actually on the sensor, but on the cover glass. Therefore there is room for the light from the edges of wider apertures to go around and fill in the shadow. This to add to the very good descriptions above and not replace them

Mike
 
sepiareverb said:
Can you see the spots in your largest print size?
Click to expand...

Haven't printed anything yet as my Canon is low on ink...

Thanks everybody for the explanations. Makes a lot more sense to me know. I was afraid something was horribly wrong with my glass or something. I'll look into getting some sensor cleaning stuff.
 
I've seen all the special tools and all the warnings. But I've always just blown the dust out with canned air. I've done this scores of times with my various DSLR's over the years (and I use them heavily as a newspaper shooter) with no ill effects. YMMV, though. I take no responsibility if you trash your camera. ;)
 
pevelg said:
Haven't printed anything yet as my Canon is low on ink...
Click to expand...

I use a big print as the test. If I can't see it on paper why worry? Pixel peeping is fun (for some I guess) but I'm shooting for prints, and if it doesn't appear on the print I don't much care. I've already got dust on the M9 sensor which I can see on the screen when zoomed way in, but they are invisible on the prints, even on 17x22" paper.

One could go this far, but if it is invisible on your normal print size I say ignore it.
 
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Pickett Wilson said:
I've seen all the special tools and all the warnings. But I've always just blown the dust out with canned air. I've done this scores of times with my various DSLR's over the years (and I use them heavily as a newspaper shooter) with no ill effects. YMMV, though. I take no responsibility if you trash your camera. ;)
Click to expand...

I do the same thing. I love the look of horror on the faces of sales reps in camera stores when I tell them that :D
 
Ya mon... agree with Shane.

Don't be using the compressed air to clean sensors.
I've been using the wet method as described (Eclipse fluid w/ pec pads) since I've gone digital with the Canon 10D.

I now use the Visible Dust Arctic Butterfly dry method - seems to work well.

Cheers,
Dave
 
sonofdanang said:
There is some credibility to the rep's concern.

I clean my digital bodies (D3 D3x) about once a week. I use Eclipse swabs and fluid along with a squeeze bulb, a really big one, to provide a blast of air. I don't use cans of compressed air.

I work in fairly hostile environments - sand, salt spray, dust, etc. The bulb-swab-fluid system seems to work rather well.

Careful with the can of air. Condensation due to the refrigeration effect along with other junk (it's not just air in the can - quality varies) can wind up spattered on the sensor/anti-aliasing filter making the situation worse. If you don't believe me fire off that can for a few seconds against a mirror. Have a look at what comes out.

The only time I use compressed air is for blowing dust off negs when I scan or enlarge. And, again, never a can. I have a small electric compressor with filters on the intake and outlet sides of the tank. The compressor is in the basement about 100' of hose away from the studio space. The valve is foot-operated with another 8 or so feet of hose to the nozzle. I run the system at a fairly low pressure to minimize the condensation problem. I've never spattered negs with this system (used, incidentally, in labs all over the world), but I have seen legions of $h1t come out of a can of compressed air. It's best used for blowing leftover lunch out from your keyboard.

Seriously.
Click to expand...

Oh I fully understand the rep's concern. And caution is definitely required. But I've never had a problem when keeping the can upright and blasting a few bursts to "clear the lines" before cleaning a sensor.

Maybe Japanese canned air is better quality than what you get over there .... ;)
 
Also check the back element of the lens for dust. My wife shot a roll with the Nikon F4s and an 85mm lens. The film had similar shadows.

A dirty sensor is likely in any case if you've had the camera for a while and haven't had it cleaned.
 
jonmanjiro said:
Oh I fully understand the rep's concern. And caution is definitely required. But I've never had a problem when keeping the can upright and blasting a few bursts to "clear the lines" before cleaning a sensor.

Maybe Japanese canned air is better quality than what you get over there .... ;)
Click to expand...
Yeah the only thing I ever get out of canned air is air? :confused:
 
pevelg said:
Thinking of getting these:

http://www.bhphotovideo.com/c/product/402856-REG/Visible_Dust_2325429.html
http://www.bhphotovideo.com/c/produ...ust_4139291_1_1_3x_Sensor_Brush_Cleaning.html
http://www.bhphotovideo.com/c/product/435201-REG/Visible_Dust_2863173_Swabs_for_1_3x_Sensor.html

and maybe this? its really expensive... but worth it?
http://www.bhphotovideo.com/c/product/532551-REG/Visible_Dust_3599839.html
Click to expand...


If you have never cleaned the sensor before there are a couple of things to consider. A Rocket Blower (or even compressed air) is good for blowing large dust out of the shutter box, but shooting air at the sensor is just another good way to fill the sensitive parts of the camera up with dust. You have no control over if the dust comes out of the camera, or up into the edges of the sensor ready to drop down again. So you aren't really cleaning anything, just re-distributing the dust. You want the dust OUT of the camera.

Then there is the fact that if the sensor hasn't been cleaned before there could be dust and OIL on it, splattered from the shutter mechanism, and often seen on new cameras. So before touching the sensor with any form of brush (like an Arctic Butterfly) a wet clean is needed.

After a wet clean oil should be gone, and most of the dust. This is a good time to use an Arctic Butterfly brush to lift out any residual specs. Then the job is done.

So its, blow shutter box with Rocket Blower, wet clean sensor with swabs, Actric Butterfly to finish. After that you can usually get away with just using the Arctic Butterfly for regular cleaning, with a wet clean after heavy use or at longer intervals.




Steve
 
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