Why are these images different?

Well there's just four seconds between the shots, the light doesn't appear to have changed. Speed, aperture and ISO are identical. I too could only suggest that the lens has failed close the aperture fully for the second exposure.

John

I'll try using a different lens for a while and see if I still get the same problem. Thanks everyone for taking the time to offer me some help.
Regards
Fran

Were these shot as jpegs? If so, perhaps it could be something to do with the image processor in the camera? If it was on spot metering, the image processor may have tried to adjust the shots assuming that you were exposing for the centre of the frame, and then adjusted the exposure over the whole image to compensate.

Yes, they were shot as jpegs. I also had Auto EV compensation set, but since I was in Green mode none of the Custom settings were within my control. The next 2 shots after the ones shown were also over exposed and then the third was OK, so I'm verging towards the lens aperture not closing correctly theory. I'm going to do some more shooting today in Green mode with a different lens to see if it happens again.

I hope you can continue to give me the benefit of your advice. I took lots of pictures this morning using my 35mm lens and everything seemed OK. I then came home and took some using the 18-135mm lens. Things seem to be OK at the 135mm end of the lens but I'm getting some odd behavious at the 18mm end. The camera was in green mode for all of the following pictures and apart from pressing the shutter (handheld) I did nothing else.
In the first set of images below I moved the focus point from the dark open top half of the caravan door to the white bottom half on every alternate shot. The results don't appear to be consistent with this change.
In the second set of images I kept focus on the dark top half of the door. There are still discrepancies.


Images with change of focus:
[IMG]http://i1134.photobucket.com/albums/m616/Frankie174/CaravanScreenDump1.jpg[/IMG]
Images with no change of focus:
[IMG]http://i1134.photobucket.com/albums/m616/Frankie174/CaravanScreenDump2.jpg[/IMG]

Help please, is it the camera, the lens or me? Is there anything else I can do to try to work it out?

Is the metering still set to spot metering? I would suggest trying different metering and trying the same experiment. If that makes no difference, I would then try shooting another series of shots in manual mode, in Jpeg and then in RAW, and using the aperture and shutter speed settings that gave you a correct exposure using the green mode. Make sure the camera is actually setting the chosen aperture correctly on each shot.

If the problem happens with Jpegs and not in RAW, this would indicate a fault with the camera. If the same results(ie differing exposures) appear with both RAW and Jpeg, it must be the lens that is causing the problem. If both RAW and Jpeg are OK in manual, then it could be the metering in the camera that is at fault.

Edited for (hopefully) clarity.

Thanks Jonathan, No to your question. I changed the metering switch to multi-segment yesterday evening. I've lost the light from that particular location so I'll have another go tomorrow. I've also got a 50-200mm lens so I'll have a go with that too.

I would check the lens is firmly clicked into place and also wipe the contacts on lens and lens mount with a soft dry cloth.

It may be that sometimes the lens is not stopping down properly, possibly because of contaminated contacts.

Thanks John, I'll try that too.

Good idea to try that first...also put the mode dial in Av, select various apertures at the 135mm end and make sure it's showing the aperture setting on the screen. If it just shows a line then the camera is not setting the aperture, which if your other lenses work means the lens is faulty.

Don't forget the camera has an optical stop down preview. Work that a few times to see if the aperture is closing as it should on the camera.

John

I wonder why, when you have such a sophisticated camera, you choose to use the 'green' mode? In that mode, it's little more than a point 'n shoot camera. Try a different exposure mode for a while, starting with Av mode. Set your white balance to daylight, ISO to 100/200 for daylight shots, and go from there.

Turn off auto Ev Comp, turn off auto ISO.

In green mode there are too many variables that can change.

This can happen if the lighting was fluorescent tubes etc. as the colour temperature and intensity of the light is constantly changing.

Mannesty, I was using Green mode because I was getting the problem in other modes and since I'm new to DLSRs and not knowing what I was doing wrong, I decided to try leaving it up to the camera - I think I was trying to eliminate "user error".

So far this morning I have tried the following:
1. Cleaned contacts with a soft cloth. There were a number of very small black particles around the rim perhaps paint or metal shavings. Removed these with cloth but made no difference.
2. Checked Av settings on screen at 135mm end of lens- all displayed OK.
3. Took jpeg shots in Manual mode, F11,ISO100,1/125 sec 18mm (the settings that gave good results in Green mode). First shot OK, subsequent shots over exposed.
4. Repeated manual mode shots in Raw. After a few I could see from the screen that they were over-exposing so on a whim I pressed the green button. The Aperture value changed to F10 and the shutter speed to 1/500 sec and subsequent 7 shots (all I took) were fine. I seem to have found a work-around, even if I haven’t a clue what’s going on.

I’ll keep investigating. If I look on the bright side, this is certainly helping me find my way around the camera.

Thanks for all your help and suggestions I will certainly follow them all through.

Is it possible you have set auto-bracketing ot exposure compensation without remembering to switch back?

To be sure, reset to factory defaults and see if that solves the problem.