Sony Nex 5 Auto contrast in M mode = Problematic

[vegetoe01]

First time posting but I've ran into a small problem with my Nex-5 regarding the auto contrast.

Basically; I have both the 16mm and 18mm-55mm lenses.

Now when ever I try to take a photo with the 16mm in a dimly lit room. The auto contrast slams to -2 forcing me to use a longer shutter speed to compensate. This can't be changed in Manual mode, only in P mode which means I can't adjust the other settings. Intelligent Auto mode just changes the contrast to - 2 again....

The dilemma is the fact that the 18mm- 55mm lens does not slam to -2 in a dimly light room. So I can happily take a shot with the 18mm without a problem.

The irony is, the aperture on the 16mm is ofcourse, larger (2.8) when comparable to the 3.5 on the 18mm-55mm lens.

So by default, the 16mm lens should be better, and brighter in darker rooms, but when it comes to practice; it's not!

IS there anyway to change the contrast for M mode?

[Watashiwateshdes]

A lot of this is going to be speculation but feel free to fill in the blanks as you go along.

When you talk about auto contrast (-2), I assume you mean the exposure level where it goes -2...-1...0...1...2

If this is the case, there are going to be a few things you need to consider. First of all, try not to use Auto ISO since that can throw off readings and cause irregularities between lenses or even a slight movement in your frame so try and balance that manually in a test.

Now since you are compariing two different lenses, your readings will be different even though your 16mm is faster in low light.

The camera itself does take note of your lens but the mian thing it is doing is looking at your scene and the amount of light in the frame.

If you have left your metering mode on Multi (Brightness/Colour) then your NEX is taking light readings from the entire frame. Now since the 16mm is wider, in theory there is more darkness in the frame and the light source will appear smaller (not by much) which will drop your shutter speed down.

Then moving onto your 18mm, since there will be less darkness due to that 2mm drop, the shutter speed may bump up.

As a test, I would recommend setting up a table in a dimly lit room.

Set the NEX up to ISO400 (or whatever you wish), take a photo with the 18-55 at f/4.

Once done, set up the 16mm in exactly the same spot (tripod will help) and also set it to f/4 and take a photo. Your shutter speeds should be different.

Do a second shot with your 16mm but move it forward so the framing is the same as your 18mm and the results in shutter speed should be close enough the same.

What you could also try is Spot or Centre modes also to see what differences you get. Spot should give you virtually the same shutter speeds if not faster on the 16mm.

Sorry if it sounds a bit messy but it as best as I could note it down.

Be more than happy if you fed back your results.

[vegetoe01]

Thank you for the reply. I tested out the lens some more with your advice, and I'm starting to think the lens itself is broken. The aperture of the iris will not open wider then what appears to be f8. Maybe even smaller..8

I'm using this as a guide.
http://en.wikipedia.org/wiki/File:Aperture_diagram.svg

I noticed one of the 'fins' which closes the hole, appears to be lower 'shadowed' then the rest. I'm going to assume this might be causing mechanical failure.

Here's a photo of the lens at the widest the aperture will open.

The arrow is pointing at the 'fin' which is visibily lower than the rest. Resulting in the shadow. (it's like this from all viewing angles).

Reckon it's faulty?

Message was edited by: vegetoe01