Is there something wrong with my lens or camera metering?

[weishengg]

hi all,

i need some technical help with regards to lens/camera metering.
My test equipment here is a Sony Alpha A100 (with firmware v1.4), a KM 50mm f/1.4 and a CZ16-80mm.

Here are the first set of photos with my 50mm lens mounted, no filter mounted.
All taken in aperture priority mode, iso400, DRO disabled, matrix metering, centre-spot autofocus, WB 6000K, no flash fired. Picture is 10mpx high quality jpeg straight off camera with no processing, only resizing for web. Handheld, SSS on.


shutter: 1/125s
aperture: f/2.0


shutter: 1/60s
aperture: f/2.8


shutter: 1/30s
aperture: f/4.0


shutter: 1/15s
aperture: f/5.6


shutter: 1/8s
aperture: f/8.0

[weishengg]

Here's another set of photos, taken using my CZ16-80mm lens, set at 50mm, again no filter mounted.
All taken in aperture priority mode, iso800, DRO disabled, matrix metering, centre-spot autofocus, WB 6000K, no flash fired. Picture is 10mpx high quality jpeg straight off camera with no processing, only resizing for web. Handheld, SSS on.


shutter: 1/80s
aperture: f/4.5


shutter: 1/40s
aperture: f/6.3


shutter: 1/20s
aperture: f/9.0


shutter: 1/10s
aperture: f/13.0


Can someone enlighten me if i'm missing something here?

I found the metering with the KM50mm lens a bit odd. By right the exposure values for the scene is constant, just playing around with stopping up/down the shutter speeds and apertures. Aperture increase 1 stop, shutter speed decrease 1 stop.

But why does the "brightness" of the picture taken with the KM50mm look so different, even though the same exposure value is used?


Some advice needed,
Thanks!
weisheng

[desaintlights]

you will only be able to see the different if you cheat the camera a bit.... that is to say that you keep your aperture setting (for example set it to f/4) and shoot at different shutter speed.....

try and then u'll get the answer.... this is probably the toughest time you have to go through with shutter/aperture.... good thing, you are on the right track. we all came through the same path and it's the only path....

good luck bro...

[creampuff]

Well the first set of photos with the KM50 look like a progression from underexposure to overexposure at identical EV. Given that the images look OK with the CZ16-80, I would hazard a guess that you have a problem with the KM50 lens. The aperture blades could be "sticky", ie. not stopping down correctly. Time to get it serviced.

[Drudkh]

did u set on bracket?

[stjustin]

Originally Posted by Drudkh did u set on bracket?

yea mabe u bracket it hence it took diff exposures

[Agetan]

Just make sure your 50mm lens don't have the sticky blade. Take the lens out, use a pen to move the lever at the back of the lens and see how fast the blade spring back. If it return slowly, then it has some problem with the lens.

The first series seems to me that the aperture blade is sluggish or stuck.

Hart

[Exposure]

Originally Posted by Agetan Just make sure your 50mm lens don't have the sticky blade. Take the lens out, use a pen to move the lever at the back of the lens and see how fast the blade spring back. If it return slowly, then it has some problem with the lens. The first series seems to me that the aperture blade is sluggish or stuck. Hart

this is an advice from a professional.

[Rashkae]

Take a look at the DOF/bokeh from the 50mm set. It's identical in all pics. This indicates that the aperture is not stepping down at all. Also, try pushing the DOF preview button to see if it's stopping down.

[weishengg]

Originally Posted by desaintlights you will only be able to see the different if you cheat the camera a bit.... that is to say that you keep your aperture setting (for example set it to f/4) and shoot at different shutter speed..... try and then u'll get the answer.... this is probably the toughest time you have to go through with shutter/aperture.... good thing, you are on the right track. we all came through the same path and it's the only path.... good luck bro...

hi bro, i don't quite get what you mean about seeing the difference by "cheating" the camera. care to elaborate? sorry

Originally Posted by Drudkh did u set on bracket?

nope, wasn't on bracket. i shot it on single shot drive mode.

Originally Posted by Agetan Just make sure your 50mm lens don't have the sticky blade. Take the lens out, use a pen to move the lever at the back of the lens and see how fast the blade spring back. If it return slowly, then it has some problem with the lens. The first series seems to me that the aperture blade is sluggish or stuck. Hart

Great! I'll go test out this later. Thanks for the advice
Are the technicians at SSC capable of solving this problem effortlessly?

Originally Posted by Rashkae Take a look at the DOF/bokeh from the 50mm set. It's identical in all pics. This indicates that the aperture is not stepping down at all. Also, try pushing the DOF preview button to see if it's stopping down.

wow bro, you're really observant with the DOF
i think its a problem with the aperture blades too, but can only check it out later as the lens is not with me now.


Thanks to all your advices !