Pentax K-3 II Wrong Av time and too bright photos.

Hello,

I'm newbie here.

I have a Pentax K-3 II with Sigma Art Lens F1.8 18-35mm.

If I shoot photos on Av Mode, then I see too bright photos - example here (exported from raw with standard params):


I need to set -1 EV always to shoot photo with proper light. Why it happens?

Additional question - Why I see purple glow at top of trees always? "remove CA" in lightroom only fixes it a little bit. I need to remove saturation in purple colour. It doesnt happen on other cameras.

Thanks for answers and help.

looks perfectly exposed to me. What did the histogram show ?

Purple fringing , especially at the extremes is usually the fault of the lens rather than the camera. Wider apertures show it worse. You should be able to remove that easily in PP

Thank you.

Different abberation than purple I can remove in lightroom and other apps like luminar/aurora.

But always when I shoot the photo of trees I see the same too much gain of purple.
Also on another lenses.

Here is histogram:



Why for example Sigma 17-70 has better photo times on better iso than my sigma art, and more darker photos (closer to reality than my photos - too brighten). I've read Sigma Art Static F1.8 18-35mm is the best lens for dark photos with fastest times without tripod. But in reality that lens is worst than cheaper 17-70 f2.8.

Your histogram is heavily to the right, which might indicate a bit of over exposure. Certainly I think your sample image could be a little darker.

I would suggest using centre weighted metering and making sure that the exposure compensation is set o -0.3EV or -0.7EV.

As regards CA, branches against bright sky are a demanding test for a lens. If you shoot JPEG and make sure CA correction is switched on in the menu that should take care of it.

My K3ii also tends to produce over light images so it's always on -0.3EV.

Welcome Pawel.

With your version of LR, are you on the 'Basic' tab in the 'Lens Correction' panel during your attempts to remove purple fringing, or on the 'Colour' tab?
The latter gives you a few more options and control, including for PF...

With plenty of glare in a scene like this, I would be shooting at the lowest ISO possible, too.

Some lenses produce exposures that are too bright while other lenses don't. My Pentax A 28mm f/2.8 and Sigma 17-50mm f/2.8 both produce images that are too bright, so I usually have to dial in negative exposure comp to get a more even exposure. Purple fringing is due to the lens, not the camera so if you want to keep that lens then your options are to stop down to minimise PF or remove it in post.

Some lenses have very low levels of PF, so if it's something that you really dislike and a lot of your images are taken in a situation that produces it (branches against a bright sky, for instance) then you might want to look at getting a different lens.

The purple fringing is usually the lens. If you have access to a K20D camera you could see if it's any better with that. I always found it better than the K-5 for that reason. I've never used a K-3 so I don't know how that compares.

I don't like the idea of removing purple fringing because whenever I've tried it it's messed up other colours such as dark blue and removed the tints from car windscreens.

The exposure does look too light. -0.7 would be acceptable if it works.

Edit: Just looked at a photo where I removed purple fringing and a blue car has been turned into a grey one Plus the blues look very dull.
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The lens will be wide open for exposure reading until the moment you press the shutter and the aperture closes down to your setting in time for your exposure. I don’t know about the construction of the Sigma lens but I have a Pentax 100mm macro which often over-exposes because it is too slow in closing down the aperture. This is done by a lever on the lens mount which if I flick it I can see that it doesn’t go back quickly - could your lens have something similar? I get over this by repeatedly flicking the lever before using the lens, haven’t tried with a 2 sec delay but that might work.

Just tried the 2 sec delay stopped down and that improves the exposure considerably. Only thing is in timer mode the shake resistance is turned off.

Re the exposure issue, do you have another lens such as the normal 18-55 kit lens you could try or borrow? If that exposes fine then clearly he problem lies with that Sigma you have.

As above, this is very often the lens, rather than the camera. Areas of extreme dark to light boundaries are most prone, so hence you usually see this on trees in images such as the one shown. The degree of purple fringing does changes somewhat based on aperture, so around f8 is often at it's lowest, vs more extreme when fully open.

What metering mode do you have set?
ie single point spot, centre weighted, full auto etc?

Spot metering can lead to extreme metering, depending on what the spot falls upon.