Well I wouldn't describe it as too dark, but it is a darker exposure than the wall pic. Only you can know the lighting at the time you pressed the shutter. It looks to me as if it was shot on a very cloudy, gloomy day. At least, that's what it portrays to me.

For instance, without adjusting my monitor (which is calibrated with a Spyder 2) I can not see any detail inside the top of the main arch. It's all black.

Once again, your histogram is your best friend here. Analyse it and interpret what the camera captured, then compare that with what you see on screen.

Mike,

Your reading of the histogram is correct, nothing is too black, nothing is too white, and nothing is clipped.

This confirms what I said above, and George has reiterated, there is nothing wrong with the image in that it is not overexposed.

The differences between your Sigma and the Pentax 28mm are acceptible in my opinion. The histograms from both lenses are bound to be slightly different as are the rendered images.

As George says, check out your monitor or view the test images on a different one, it all looks fine to me.

Regards,

Mike,

The above statements are contradictory.

The histogram represents black level on the left and white level on the right. The bit in between represents all the colours between black and white.

The height of the histogram shows each colours saturation and ranges from 0% at the bottom to 100% at the top.

If you have a curve which reaches the top (100%), it shows that the sensor cannot capture any more of that particular colour. In other words it's clipped.

If you have a flat topped curve and it is at the topmost (100%) part of the histogram, you have overexposure. If the curve is flat topped but it doesn't reach the 100% mark anywhere along its length, no problem.

Does the histogram for that pic confirm your suspicion that it is overexposed.

To me, the white in the brickwork doesn't look blown out, and the inside of the broken iron pipe looks black enough.

WD40 is designed to get into joints etc. where other lubricants can't reach. A drop on a tissue is all that is needed to effectively clean a lens mount without any harm coming to the mount, lens, or camera.

As for carburretor cleaner, check it's active components thoroughly. If it contains solvents, it could damage the SMC coating.

Glad your mostly sorted anyway.

Close the iris down to it's smallest aperture and check that there is no evidence of oil on the blades (check both sides).
If you suspect lens surface contamination, clean it with lens cleaning tissues or cloth, slightly wetted with lens cleaning fluid. If you suspect the grease is on the inside you'll need to get it serviced unless you have the tools to disassemble it. You also have to ask yourself where di the grease come from?
Your metering could be to blame, try the full pattern metering mode (usually the green one).
As far as cleaning contacts goes, clean the whole of the mating surface of the lens mount. You'll clean all of the contacts then. A very small amount of WD40 or similar lubricant is what I use, but it must be a type that dries, and of a non-solvent type.
Personally, I would never fit an unknown lens to any of my camera bodies without first cleaning at least the contact surface.

On my K10D, a Giottos Rocket Blower is good enough for 'normal' dust where the DR system fails to remove it. For really stubborn dirt I use an Arctic Butterfly from Visible Dust. I haven't had to use the Butterfly much.

My *istD needs a wet system, Eclipse fluid (or straight methanol) to clean it thoroughly, but staining can be difficult to avoid.

The K10D has a special coating over the sensor cover and an equally special cleaner may be required which is version 2 of Eclipse fluid. I've never needed to use a wet system on my K10D . . . so far.

That Cosina 100mm Macro lens of yours looks a gem. Shame the cat is not in focus, it looks like the focus point is a little forward of the cat's location. Maybe lift the foreground shadows a bit in the last one.

What a waste, coating cornish pasties with gold glitter. It's been years since I had a real pastie. Thanks for the memories, now, what's for lunch I wonder?

It'd be great if it was updated every time a lens status changes from 'future' to 'current' as has the DA 18-250mm.