Canon EOS-300D+Sigma 105mm F2.8 DG Macro

[CDM]

Last weekends went to a pear farm. It's the right time of the pear flower. Played around with the Rebel+Sigma macro. That's a sunny day with strong seasonal wind. Any shutter speed below 1/200s would have high chance to fail. Here are some results.

The first 3 photos are of the same spot with different F stops and shutter speeds combinations (by using aperture priority mode). Can see how the tip of the pear tree on the right background varied with the aperture (the larger F stops the more obvious of the tip of the tree. One thing confusing me is if you inspect carefully on top left corner of the #2 & #3 photos, there are some few mm sized "dirts" which seems to be more clear for larger F stops. I've inspected the CMOS sensor and both side of the lens all of those are very clean. What's wrong with it?

http://www.worldisround.com/hosted/9/157/342.jpg
ISO: 100
F: 4.5
Shutter speed: 1/1600 s
Distance: 13~14"
Click here to view the larger version of the photo. (http://www.worldisround.com/hosted/9/157/342_o.jpg)

http://www.worldisround.com/hosted/9/157/343.jpg
ISO: 100
F: 13
Shutter speed: 1/200 s
Distance: 13~14"
Click here to view the larger version of the photo. (http://www.worldisround.com/hosted/9/157/343_o.jpg)

http://www.worldisround.com/hosted/9/157/344.jpg
ISO: 400
F: 20
Shutter speed: 1/320 s
Distance: 13~14"
Click here to view the larger version of the photo. (http://www.worldisround.com/hosted/9/157/344_o.jpg)

Some more shots:
http://www.worldisround.com/hosted/9/157/345.jpg
ISO: 400
F: 7.1
Shutter speed: 1/2000 s
Distance: 13~14"
Click here to view the larger version of the photo. (http://www.worldisround.com/hosted/9/157/345_o.jpg)

http://www.worldisround.com/hosted/9/157/139.jpg
ISO: 100
F: 2.8
Shutter speed: 1/3200 s
Distance: 13~14"
Click here to view the larger version of the photo. (http://www.worldisround.com/hosted/9/157/139_o.jpg)

[benny]

A good practical example of depth of field here.

As for the specs, check the rear lens element of your lens. You might see something if you put it against bright light.

Cheers,

[CDM]

Thanks benny. Hehe, I infact checked the lens under room light, will go check under strong light later.

[JerseyJay]

CDM,

Thanks for DOF explanation. Well done.

As for as the "dirty" spots, it is time to clean your CCD/CMOS sensor.

Look here:
- http://www.pbase.com/copperhill/ccd_cleaning
- http://www.cleaningdigitalcameras.com/index.html

[benny]

If the spots were on the sensor, it should be apparent in all 3 shots. I suspect it's on the rear of the lens.

Cheers,

[JerseyJay]

If the spots were on the sensor, it should be apparent in all 3 shots. I suspect it's on the rear of the lens.

Cheers,
DOF is related to the "spots". You might be able to see them at X DOF but not at Y DOF. I went through hundreds of pictures thinking that "spot problem" was resolved. When I changed DOF, they re appeared.

I could see them on 2 pictures but I'm not positive about the first one.

[CDM]

I took the lens off and exposed a while. There was no specs anywhere. And, there do have some dirts on the rear lens. I'll try to clean it and try some shots later. Thanks for the help.

[hir0]

try duplicating this with another lens.

[CDM]

Errmm... why I didn't think of that. Thanks hir0. I'll try the 18-50 mm lens later to verify.