Metering difference for lenses

I was playing around with my 18-55 kit lens and the 50/1.8, and a 20mm extension tube today. In Av mode with evaluative metering, the camera was underexposing a full stop with 50 compred to the the 18-55. I shot the following images in RAW and exported straight from Lightroom as resized jpegs - no exposure adjustments. The 18-15 was at 42mm, but everything else was the same.

Can anyone explain why I would get this kind of difference?


50mm f/16 5sec

were you focusing on the same place? because metering will be different depending on the kind of metering you're using and the general lighting around the area.

would probably have been better if both lenses were at 50mm

Maybe it is too early or I am having a "senior moment", but isn't your exposure for the 50 mm only half of the exposure you gave to the image with the zoom? 5 sec. vs 10 sec. ?

ralff wrote in post #12010470
Maybe it is too early or I am having a "senior moment", but isn't your exposure for the 50 mm only half of the exposure you gave to the image with the zoom? 5 sec. vs 10 sec. ?

Well, it sure is early, but you certainly have a point..

ralff wrote in post #12010470
Maybe it is too early or I am having a "senior moment", but isn't your exposure for the 50 mm only half of the exposure you gave to the image with the zoom? 5 sec. vs 10 sec. ?

That's the point he's asking about....why would one lens cause the camera to choose an exposure that is a full stop different when the photo is nearly the same.

To the OP, was this just a one time thing or were you able to replicate it on a consistent basis? I don't care for evaluative metering myself for this very reason....it can do a decent job most times but it rarely nails the exposure exactly as I want. In the brighter exposure, there is slightly more black near the bottom of the photo, this could've prompted the camera to choose a slower shutter speed....that's my guess

ralff wrote in post #12010470
Maybe it is too early or I am having a "senior moment", but isn't your exposure for the 50 mm only half of the exposure you gave to the image with the zoom? 5 sec. vs 10 sec. ?

Yes it is, but that is the point of the question!

Why the same camera, for the same aperture (f/16), same ISO (100) and roughly the same focal length, camera meters differently, and suggests different shutter speeds.

Other than different focusing point being (auto)selected in Evaluative metering mode, I don't see the explanation.
Unfortunately, information about active focusing point was stripped from both images, so it's hard to say with certainty.

Is this an issue with ext. tube communication? Maybe one combo sees it and the other not?

Thanks for the replies.

I was manually focusing using live view, and the camera was on a tripod, so the distance from the sensor to the subject didn't change. There might have been a tiny sideways movement in the framing as I changed lenses.

I also used the same tube with each lens, so I don't think it's a communication issue.

I experimented some more this morning with the same setup. Took six shots with the following results:

All shots a f/16

50/1.8, pattern metering, 8.0 sec
kit lens @55mm, pattern, 8.0 sec
kit lens @43mm, pattern, 6.0 sec

50/1.8, spot metering, 10.0 sec
kit lens @44mm, spot, 20.0 sec
kit lens @55mm, spot, 25.0 sec

I'm thinking it has something to do with the sensor heating up and responding differently to the maximum apertures of the two lenses. The large expanse of white flower probably has something to do with it as well.

Can you just shoot white wall with both lenses?

No extension tubes, no live view.
Use the tripod, same ISO, same aperture, EC 0, center the needle.
One shot with each lens i Manual mode, Spot metering, then one shot with each lens in Av, Evaluative but make sure to use center focusing point.
Shoot .JPG, use the same Picture Style for all shots.
Do not process pictures at all, just resize them to forum standards, so we can see EXIF and active focusing points.