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Lens related over exposure


digicammad 17 22.0k 39 United Kingdom
25 Sep 2016 6:22PM
I have an interesting, if somewhat frustrating, problem I'm hoping some of the brilliant minds on here can help with.

I have a Nikon D7000 with which I normally use a Nikkor 18-200 (walkabout). Recently I started using the Nikkor 18-105 which actually came with the camera. This lens had previously been loaned to my wife to use with a D300 and worked perfectly.

I have been noticing that all of my images were half a stop over exposed and was concerned that perhaps the metering was faulty, then I realised that it had only happened since I started using the 18-105. I took 2 identical shots, 1 with each lens and sure enough the image shot with the 18-105 was half a stop brighter than the 18-200, which I consider to be perfectly exposed.

I've never experienced lens related metering problems before and wonder if anybody can help explain them?

Cheers

Ian
4k78l 4 278 1 New Caledonia
25 Sep 2016 6:32PM
You cannot just directly compare two lenses, even if they're from the same brand and has the same aperture data. You can dig deeper into the technical stuff, or just accept that two lenses may act differently and just shoot accordingly to what lens you are using.
Here is some quick info if you are interested: https://www.youtube.com/watch?v=IsWGkUT5A_Y
digicammad 17 22.0k 39 United Kingdom
25 Sep 2016 10:04PM
I understand that different lenses behave differently but I've never actually had a lens cause a camera to over expose before.
Chris_L 6 5.5k United Kingdom
25 Sep 2016 10:07PM
I know to expect different exposures when comparing lens A at 1/100th second, ISO 200, f5.6 versus lens B at the same settings (when in manual mode). Some designs transmit more light than others. I think there's a T* rating for actual light transmission.

If you were in manual mode that would explain it.

It doesn't explain why in an auto or semi-auto mode the camera gets it wrong, if that's what you've found.

Camera measures light and calculates ideal exposure so is the lens actually faulty and setting too wide an aperture than what it reports?

Quote:never actually had a lens cause a camera to over expose

Is it the lens that's overexposing?

Test shooting wide open. It can't overexpose that kind of shot on its own.
digicammad 17 22.0k 39 United Kingdom
25 Sep 2016 10:10PM
I also understand that I can use the lens perfectly well if I just dial in -0.5ev, I was just asking if anybody could explain it.
digicammad 17 22.0k 39 United Kingdom
25 Sep 2016 10:13PM
Thanks Chris I'll try that. I shoot in aperture priority normally, not manual. That's why I was surprised to see a difference.

With the different characteristics of 2 lenses I wouldn't be surprised to end up with 2 different shutter speeds, but the different exposure is also visible in the histogram.
4k78l 4 278 1 New Caledonia
26 Sep 2016 3:06AM
I had to underexpose all my shots 1-2 F-stops when I owned a Canon 60D. I got used to it pretty soon.

Anyhow, you would have to write down all settings, and all info on the lenses, what focal length etc(and post the shots themselves) to let us see if there might be an obvious reason.
LenShepherd 12 4.2k United Kingdom
26 Sep 2016 7:30AM
Most Nikon lenses use aperture stop down levers on the back to which the camera connects when taking a picture.
The levers cover nearly 3 stops in 1mm lever travel. If the levers get slightly bent the lens stops down by the wrong amount.
Another possible cause is you are taking a different type of subject with different characterises to which matrix metering applies a different exposure value.
It is easy enough to apply a general exposure fine tune in Nikon menus or to individual images.
Half a stop would not concern me. The 1-2 stops on the Canon implies something needed a repair.
digicammad 17 22.0k 39 United Kingdom
26 Sep 2016 8:45AM
The 2 test shots were taken less than a minute apart. Both at 18mm and f8, with identical framing.

Now that I know it is a characteristic of the lens and not a metering fault I'm not concerned, just curious. In over 40 years of using slr cameras with various lenses I've never experienced such differences before.

Ian
Big Bri 19 16.6k United Kingdom
26 Sep 2016 8:46AM
Did it
a) cause the camera to meter 1/2 a stop down, or
b) use the same settings on the camera but produce a different result ?

Either way, one would expect the metering system to deal with the amount of light landing on it, which would be the same when taking the photo as it was when metering.

The only thing I can think of is that with the (cheaper?) lens there is some vignetting which is fooling the metering system, or that when the diaphragm stops down, that it is slightly smaller than it should be (because of course you are metering wide open)

Try spot metering and see if it makes a difference.
Try it and the long and short ends of the zoom and see if that makes a difference.
Try it wide open and stopped down.

Chris_L 6 5.5k United Kingdom
26 Sep 2016 9:32AM
It's an interesting puzzle. You have to test it wide open. That will rule out the aperture being opened wider than it's supposed to be. If it exposes correctly wide open and only over-exposes when it's suppose to be using a smaller aperture then it's the lens' aperture mechanism. Or the vignette-influenced metering. Or something else to do with the camera. Or lens. Or your house. Or because it's September.

Or see below...
Big Bri 19 16.6k United Kingdom
26 Sep 2016 9:50AM
(Or it could be his eyesight - he is getting on a bit Wink )
rambler Plus
12 1.0k 17 England
26 Sep 2016 10:43AM
It could be the design of the aperture mechanism being different in each lens.

Ken
EddieAC Plus
15 2.9k 2 United Kingdom
26 Sep 2016 3:04PM
Is your lens being affected by a sticky aperture? Will the lens overexpose by the same amount at f/22 as f/3.5?

I use this lens on my D7000 and have no exposure problems.
digicammad 17 22.0k 39 United Kingdom
26 Sep 2016 7:51PM
Thanks everybody. I'll do some more tests using your suggestions and update here. Don't think I'll go to Specsavers though. Tongue

Ian

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