exposure control with grey card

[andreacioci]

Thanks everyone for the advice but the solution seems to be far.

This time I haven't used the tripod and shooting at 1/5s one pic is a little blurred but it shouldnt influence the gray card values too much.

Again... the values that I read on rawdigger are:

G=436 with the zoom at the long end
G=634 with the wide angle.

The light condition is absolutely the same for both pics.
Regarding the exposure we are about 1/2EV from the 0EV. I noticed the 0EV value is different in the 2 images.
What can I do????

 

[Ysarex]

Thanks everyone for the advice but the solution seems to be far.

This time I haven't used the tripod and shooting at 1/5s one pic is a little blurred but it shouldnt influence the gray card values too much.

Again... the values that I read on rawdigger are:

G=436 with the zoom at the long end
G=634 with the wide angle.

The light condition is absolutely the same for both pics.
Regarding the exposure we are about 1/2EV from the 0EV. I noticed the 0EV value is different in the 2 images.
What can I do????

That's too much of a discrepancy -- your exposure has to be changing.

Camera is set to full manual where you select both shutter speed and f/stop.
ISO is NOT on auto and you've set the ISO (to the camera base ISO ideally).
Zoom at long end (grey card fills frame) and you meter from the grey card.
Set a mid f/stop like 5.6 or 8 and adjust the shutter speed to zero the meter.
Take the photo.
With no change in ISO, shutter speed or f/stop you zoom out and take second photo -- you do not re-meter the second photo.

Here's screen shots of my two test frames in RawDigger.

Joe

 

[Infidel]

Thanks everyone for the advice but the solution seems to be far.

This time I haven't used the tripod and shooting at 1/5s one pic is a little blurred but it shouldnt influence the gray card values too much.

Again... the values that I read on rawdigger are:

G=436 with the zoom at the long end
G=634 with the wide angle.

The light condition is absolutely the same for both pics.
Regarding the exposure we are about 1/2EV from the 0EV. I noticed the 0EV value is different in the 2 images.
What can I do????

Please post image files with exif intact.

 

[andreacioci]

Guys,
here is the snapshots of RawDigger. The second shot is not at completely wide angle to not have the gray card too small.



1/50s f5.6 ISO200 - R=307, G=500, B=300



1/50s f5.6 ISO200 - R=226, G=365, B=221

 

[Ysarex]

You clearly have two different exposures there. I would think the suspect variable is the lens f/stop. ISO and shutter speed are very unlikely to be changing between the two exposures. You're using a variable aperture zoom of nominal quality and from the manufacturer's point of view a discrepancy of this degree is going to be completely smoothed over by software so what's the big deal anyway. It falls into their acceptable tolerance range. Get a Nikon lens with a gold ring around the front and you'll probably see less of a difference.

Try the test at a smaller f/stop like f/8 or f/11 and odds are the discrepancy will be less. But I'd say you're looking at a real hardware/physical difference in your lens that you can't alter. I wouldn't let it bother you too much. It is a zoom lens after all.

Here's some perspective: Go back 30 years and I was doing this for a living and I owned probably 25 lenses at least -- not one zoom. Either my standards for IQ wouldn't let me use a zoom or I couldn't afford one that I thought I would use. Times have changed and now 90% of what I shoot is done with zoom lenses. They have gotten much better, but at the same time software does allow us to compensate for their weaknesses and so the convenience the zoom affords is finally tipping the scale. But they are still zoom lenses and compared with prime lenses they're going to exhibit real faults:

1. Distortion.
2. Uneven exposure (vignette).
3. Chromatic Aberration.
4. Loss of definition at the edges.
5. Increased IQ variability over the f/stop range.
6. F/stop variability.

Joe