Frumious: Explanation of FZ20 vs. FZ30 "ISO discrepancy"

[John_Reed]

First, your FZ20 image: (click to see)
http://www.dcresource.com/forums/attachment.php?attachmentid=5702&d=1128750546
Next, your FZ30 image: (click to see)
http://www.dcresource.com/forums/attachment.php?attachmentid=5703&d=1128750592
Since you set up the conditions for "identical" exposure, with both cameras in P mode, ISO 80, why is the FZ30 photo so much brighter than the FZ20 photo? One natural conclusion might be that at ISO 80, the FZ30 gathers more light than its older brother. But, when I looked at the EXIF data, what really happened is that in P mode, the FZ20 limits the minimum shutter speed to 1/4 second. (Kind of handy, actually, since that's about the lower limit of what I'd hand-hold anyway; my FZ15 had the same limitation) But the FZ30 allows much more creative freedom in P mode, imposing no lower limit on shutter speed (well, maybe it's 8 seconds?). So, your FZ30 photo, shot at 1 second, was properly exposed, your FZ20 photo, shot at 1/4 second, was not. Ergo, no ISO discrepancy.

[frumious]

Thanks John -

I am kind of relieved to learn from you that there is a logical reason for the FZ30's brighter shot at ISO 80 than the FZ20. I was starting to attribute it to Panasonic sorcery. I'll just have to be sure to continue using a tripod for those long shutter shots.

Also, since I am keeping my FZ20 ("loaning" it to my daughter and teaching her how to use it), I deduce from your analysis that I could get the same shot from the FZ20 if I put it on S mode (shutter priority) and set it to shoot at 1 second. (Am I right?)

I am still in the dark about EXIF data: How do you extract the data from an image? Knowing this would save me a lot of writing! :)

[meillana]

if you're using Windows XP, just right click on the image > go to properties > summary > advanced.... to check the EXIF data but not extract it.
to extract the EXIF, i use the Arcsoft Photobase v4 software included in my 20... select View > EXIF File Reader > Export and save it as a txt file using same numeric filenaming convention of the camera. :)

then again, most image host websites offer viewing of the EXIF data straighforwardly

[John_Reed]

Thanks John -

I am kind of relieved to learn from you that there is a logical reason for the FZ30's brighter shot at ISO 80 than the FZ20. I was starting to attribute it to Panasonic sorcery. I'll just have to be sure to continue using a tripod for those long shutter shots.

Also, since I am keeping my FZ20 ("loaning" it to my daughter and teaching her how to use it), I deduce from your analysis that I could get the same shot from the FZ20 if I put it on S mode (shutter priority) and set it to shoot at 1 second. (Am I right?)
Wouldn't be necessarily the same. If you forced the FZ20 to shoot at 1 second for the same scene, since its lens can be 1/2 f-stop faster than that of the FZ30 (f2.8 vs. f3.7 at full zoom, no diff at 1X), the shot may come out brighter, depending on the zoom level of your shots. I think the most honest comparison would be to choose a lighting level, then force the aperture and shutter speed, i.e., in manual exposure (M) mode. So pick a scene that gives a good range of lighting for, say, f4.0, shutterspeed of 1/10 second (or whatever you like within both cameras' ranges), and then see if at the same forced ISO (you can't use auto ISO in M mode anyway), you get the same brightness. If you performed that comparison at different apertures from min to max (though FZ30's min is f11, not f8), that'd be a good comparison, I'd think.
I am still in the dark about EXIF data: How do you extract the data from an image? Knowing this would save me a lot of writing! :)
Read Maillana's excellent post on this topic. EXIF data is embedded in your image files, as I said in my post on this subject in your other thread. If you were using Smugmug, when you upload an image, you can also see the EXIF displayed there, click the following link to see one:
http://john-reed.smugmug.com/photos/newexif.mg?ImageID=39381852

[frumious]

if you're using Windows XP, just right click on the image > go to properties > summary > advanced.... to check the EXIF data but not extract it.
to extract the EXIF, i use the Arcsoft Photobase v4 software included in my 20... select View > EXIF File Reader > Export and save it as a txt file using same numeric filenaming convention of the camera. :)

then again, most image host websites offer viewing of the EXIF data straighforwardly

Thank you Meilana. This is a real big help.