GH1 Brand New 20mm is darker that 14-45 in low light ???

[ChipThome]

OK, scratching my head over this one. Today I got my brand new 20mm and tonight went to shoot an image of my living room with indoor lighting. This is what I got, several times and the camera always says I am at f1.7



It seems pretty dark to me so I then grab my used 14-45. I had that set to 14mm and the camera always said I was at f3.5. This is what I got from that lens.



OK, so I am thinking I have something seriously screwed up in my camera settings, so in P mode I went and hit Reset for both options. I was always under the assumption that doing this brought me back to factory settings. I squeezed off a couple more images in IA, same thing, f1.7 is dark. Then I tried it in P mode and set ISO to 400 for each. Same thing, the f3.5 is brighter than the f1.7.

I take the lens off and examine it. The aperture appears to be open as wide as the rear lens element. I even checked to see if maybe there was an protective film I was supposed to remove first, and couldn't find any.

So what do you think ??? Operator error or do I have a junk lens ???

 

[Trucci]

Check your shutter speed. The way the auto settings work on each lens may be different.

 

[Dazza]

The framing is different in each shot, therefore the camera will be calculating exposure differently.

I'm sure if you set the 14-45mm to 20mm to achieve the same framing and have the ISO set to the same value the pictures will be the same brightness.

If you really want to prove your 20mm is actually "brighter" then goto manual settings set the ISO and the shutter speed the same, and have the 14-45mm set to f3.5 and the 20mm set to f1.7, it will be heaps brighter guaranteed

 

[DrDave]

You should be in manual mode, then set all your parameters individually. The relative brightness is just the exposure, but other factors will affect the apparent brightness as well, just as the the dynamic range boosters and the "curves" like standard, smooth, dynamic, etc. If you are worried about about your lens, just shoot a resolution chart or a brick wall. I am 99.9 percent sure you have one of the best lenses ever made. If there is an issue with the lens, the automatic exposure is only a test of the camera, not the lens.

 

[ChipThome]

One day later now.

I just shot a couple of images of the room with only the lights from the rest of house to light it, not those in the room. Now the lens is coming through like a real f1.7 and I am seeing light in the image that I don't see with my eyes.

Phhhhheeeeewwwwwww !!!!

So now my fear of a junk lens is dashed. Thanks for the input, I wil start trying out these suggestions.

 

[hsitz]

I just shot a couple of images of the room with only the lights from the rest of house to light it, not those in the room. Now the lens is coming through like a real f1.7 and I am seeing light in the image that I don't see with my eyes.

The fact that you see light in the image that you don't see with your eyes is not directly related to fstop. You could take a picture in near blackness with an f16 aperture that appears bright as day -- IF shutter speed is slow enough, say 1 hour.

Just to clarify what some others have alluded to: the relative brightness or darkness of your picture is not directly related to fstop. It's directly related to your "exposure", and "exposure" is a combination of (1) aperture, (2) shutter speed, and (3) iso. For example, you could take an F8 picture and end up with an overexposed/way-too-light picture -- if your shutter speed is set way too slow. Likewise you can take an F1.0 picture and end up with something that's underexposed and dark -- if the shutter speed is too fast, which means not enough light was let into lens given the fstop and iso.

In other words, the fact that your lens may have given you some dark and/or underexposed pictures at f1.7 has nothing to do with it not being a "true f1.7". It has to do with the shutter speed the camera was using.

One main difference of, e.g., f1.0 over f8.0, is that, all other things being equal, a picture taken at f8.0 that needs 1 second for proper exposure (meaning any movement will be blurred) would have the same exposure in 1/60 of a second at f1.0. (The other main difference is depth of field.) That f1.0 picture would end up dark and underexposed at a 1/120 second shutter speed. In that case the f8.0 picture w/ 1sec shutter speed would be "lighter" than the under-exposed f1.0 picture, but only because it was taken with a shutter speed appropriate for its particular fstop and iso settings.