6 ms·

Indeed, I ran into this today. Took the following photograph with a 28mm (wide angle) lens on a Pentax K-x DSLR (crop sensor, so 42mm equivalent) + a polarizing

Indeed, I ran into this today. Took the following photograph with a 28mm (wide angle) lens on a Pentax K-x DSLR (crop sensor, so 42mm equivalent) + a polarizing filter, stopped down to f/22: http://i.imgur.com/Wu7HTpo.jpg http://i.imgur.com/Wu7HTpo.jpg If you look at the bottom right, you'll notice a lot of crap. It's all just dust from the filter. It's fixable in Lightroom but it's a huge pain, as I need to manually remove each speck. These dust specks did not appear when the lens was stopped to f/8-ish. Regardless, in response to OP, I've seen some really nice photos taken with really beat-up lenses. But if you push the bounds at all and start to photograph more challenging material exposure-wise, I imagine it'll get bad real fast.

dietrichepp 12y ago
The reason why this is happening is because your entrance pupil is small (1.3mm) and close to the dust. The crop factor is what makes things bad here: higher crop factors means that for a given field of view, the dust is closer (because the lens is thinner) and the aperture is smaller relative to the dust. Paradoxically, the dust is actually less problematic for more challenging exposures. You may wish to use a wider aperture, on a 28mm lens and with modern sensors, f/22 is likely to show blurring from diffraction through the small aperture. The Airy disk will have a diameter of 30 µm, but the pixel pitch on a K-x is around 5.5 µm... which means that you have a ~6 pixel wide blur applied to your image before you even press the shutter! But the good news is that the depth of field on a camera with a crop factor is deeper for the same field of view and aperture.
- Nav_Panel 12y ago
  >But the good news is that the depth of field on a camera with a crop factor is deeper for the same field of view and aperture. To be completely honest, that's the bad news and the reason why I miss my film SLR so much after I switched over to digital. I absolutely adored my 50mm normal lens's nice thin depth of field, and I miss having that on the smaller format sensor. >f/22 is likely to show blurring from diffraction through the small aperture I'm gonna have to learn about these concepts -- I'd heard that diffraction causes decreased sharpness when stopped down but I didn't know it was a significant issue in modern lenses. I do know that I get significant chromatic aberration on my 28mm, but I always figured it was due to its retrofocal design. Do you have any reading recommendations?
  - dietrichepp 12y ago
    > Do you have any reading recommendations? Not really. I remember using a table which gave you the optimum aperture for maximum sharpness, based on the distance that the lens moved when focusing between the front and back of the subject. That kind of thing is only really useful for MF and larger, and I only used it for things like landscapes where sharper was always better. The problem with small formats is that it's hard to know how far the lens is moving, so you can't really use this technique. In the most general terms, opening your lens all the way gives you aberrations, closing it all the way gives you diffraction, so you'll typically shoot in the middle unless you have a reason to do otherwise. For a rule of thumb, take the apertures you use for 35mm and adjust them by the crop factor. So if you liked to shoot everything at f/8 with 35mm (a common choice), then lean towards f/5.6 with your 1.5x crop digital. Conversely, if you start lugging around a 6x7cm camera, you'll use f/16 as your default. Yes, for really small cameras, this means really big apertures. The iPhone 4S always shoots at f/2.4, for example.
bitL 12y ago
I am getting similar specks from the dust on the sensor, not so much on the lens on a D7000.

dietrichepp 12y ago

The reason why this is happening is because your entrance pupil is small (1.3mm) and close to the dust. The crop factor is what makes things bad here: higher crop factors means that for a given field of view, the dust is closer (because the lens is thinner) and the aperture is smaller relative to the dust. Paradoxically, the dust is actually less problematic for more challenging exposures. You may wish to use a wider aperture, on a 28mm lens and with modern sensors, f/22 is likely to show blurring from diffraction through the small aperture. The Airy disk will have a diameter of 30 µm, but the pixel pitch on a K-x is around 5.5 µm... which means that you have a ~6 pixel wide blur applied to your image before you even press the shutter! But the good news is that the depth of field on a camera with a crop factor is deeper for the same field of view and aperture.

Nav_Panel 12y ago
>But the good news is that the depth of field on a camera with a crop factor is deeper for the same field of view and aperture. To be completely honest, that's the bad news and the reason why I miss my film SLR so much after I switched over to digital. I absolutely adored my 50mm normal lens's nice thin depth of field, and I miss having that on the smaller format sensor. >f/22 is likely to show blurring from diffraction through the small aperture I'm gonna have to learn about these concepts -- I'd heard that diffraction causes decreased sharpness when stopped down but I didn't know it was a significant issue in modern lenses. I do know that I get significant chromatic aberration on my 28mm, but I always figured it was due to its retrofocal design. Do you have any reading recommendations?
- dietrichepp 12y ago
  > Do you have any reading recommendations? Not really. I remember using a table which gave you the optimum aperture for maximum sharpness, based on the distance that the lens moved when focusing between the front and back of the subject. That kind of thing is only really useful for MF and larger, and I only used it for things like landscapes where sharper was always better. The problem with small formats is that it's hard to know how far the lens is moving, so you can't really use this technique. In the most general terms, opening your lens all the way gives you aberrations, closing it all the way gives you diffraction, so you'll typically shoot in the middle unless you have a reason to do otherwise. For a rule of thumb, take the apertures you use for 35mm and adjust them by the crop factor. So if you liked to shoot everything at f/8 with 35mm (a common choice), then lean towards f/5.6 with your 1.5x crop digital. Conversely, if you start lugging around a 6x7cm camera, you'll use f/16 as your default. Yes, for really small cameras, this means really big apertures. The iPhone 4S always shoots at f/2.4, for example.

bitL 12y ago

I am getting similar specks from the dust on the sensor, not so much on the lens on a D7000.