[tonibosss]

Greetings everyone!
Recently I've bought a K-30 and I started noticing purple lines around the image.
Its noticeable on transitions between black and whites and I am not sure if it's the lense that's causing the problem or is it something else. Could it be that the UV light is interfering with sensor?
Two more issues:

1. Sometimes colors appear to be purple instead of black, and there isnt any possible way of changing that but in post.

2. Images tend to be underexposed, I've read topics and concluded that the aperture motor works fine, so its either faulty device or something else I'm missing out.

Currently I am using SMC Pentax-DA 50mm F1.8 and i dont have any filter on.

Will post more images soon.

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[stevebrot]

I suspect this to be longitudinal chromatic aberration, also sometimes called "bokeh" fringing. It occurs as a thin fringe around slightly out-of-focus objects. There is also an outside possibility that the appearance was made more prominent by part of the post-processing.


Steve

[clackers]

Hi Toni,

This is common in high contrast situations (the colour is green in front of the focal point, purple behind) and is worsened by wide apertures.

I fix these in Lightroom as part of my normal postprocessing ... I push the slider up to 4 or 5 and that usually does the job.

[tonibosss]

Here are some more examples..

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[tonibosss]

@clackers Thanks for the advice! Works good

[Alex645]

The purple fringing is called chromatic aberration. It commonly occurs on the edges of high contrast subjects and backgrounds. Some lenses have very little CA while other have a lot.

You may want to run tests with your SMC Pentax-DA 50mm f/1.8 of similar shots but at a range of apertures. You may find that at a certain f/stop, the CA is minimized or at another it is very pronounced.

There are many post processing software options to help reduce or eliminate CA (I use Lightroom or Photoshop). FWIW the Pentax DA 50mm f/1.8 is known to have very little CA relative to most other Pentax lenses, so I'm a bit surprised by your images.

Camera Lens Database - DxOMark

[08amczb]

I think your DA50 is faulty, a lens element alignment may help in the service.
And yes it's looks like longitudinal CA, but it's stronger than normal at F3.2 or even at F1.8.

[victormeldrew]

That CA is pretty catastrophic. That lens has issues.

[tonibosss]

Guess I'll just keep shooting and solve the issue in post since the repair is probably too much to be worth.

---------- Post added 05-30-18 at 10:00 AM ----------

Btw. when I bought the camera I had to take it to repair shop to get the CMOS aligned properly, since the picture was way blurry due to either this glass which came with the camera or the sensor being moved slightly by someone who has opened the camera before..

Guess I'll find out when i buy another lens. First in line is 18-55 kit.

[stevebrot]

I think your DA50 is faulty, a lens element alignment may help in the service.
And yes it's looks like longitudinal CA, but it's stronger than normal at F3.2 or even at F1.8.

I was able to reproduce the fairly alarming purple fringing (PF) in the last image (f/3.2) posted with my copy of the DA 50/1.8 using a standard technique to exacerbate purple fringing.* Klaus at Optical Limits (formerly Photozone) noted significant LoCA in his test sample down to f/4. Unfortunately, he did not subject the DA 50/1.8 to his PF torture test for that review. I was able to reproduce the reddish fringe in the first two images with mild backfocus and two stops overexposure.

I consider both aberrations to be within the normal behavior for the lens with neither being a particular issue in normal shooting. There may be a problem with the OP's lens, though it is hard to say without having the lens in hand.


Steve

* By "purple fringing" (PF), I am referring to the classic digital capture aberration that is apparently related to LoCA. PF has a characteristic "bloom" appearance and may be present even with sharply focused subject elements. To reproduce, I found some bare branchlets on a bright cloudy day and over-exposed two stops. The intent is to clip whites adjacent to dark boundary.

[DeadJohn]

The samples are a mix of full images (downscaled for posting) and 1:1 zoomed-in crops, correct? Zooming in on a photo will exaggerate purple fringing (PF). PF is generally strongest in out-of-focus and high-contrast areas. The underside of branches against a bright white cloud are a common culprit. Black and white graph paper can work as an indoor simulation.

For testing, take multiple photos of a high contrast scene in one stop aperture increments (1.8, skip 2.0 because it's close enough to 1.8, 2.8, 4, 5.6, 8, 11). Use a tripod and manual focus for consistency. You should see decreasing purple fringing as you stop the lens down.

This review reports minimal fringing. Your lens definitely seems worse. Pentax smc DA 50 mm f/1.8 review - Chromatic and spherical aberration - LensTip.com

[nocturnal]

Hi I've had a K30 since 2012/2013 and a great camera it is!

I started off with legacy lenses and the kit lens, basically budget options. I remember hating seeing purple fringing, I had a Kiron 70-200 f4 zoom which was a horrendous purple fringer.

Anyhow many years on I have a few top-end lenses (SMC F*300 f4.5, DA HD 15 f4 Ltd, DA HD 20-40 f2.8-f4 Ltd, SMC DA40 f2. Ltd) and purple fringing is a distant memory with these lenses.

Back in 2012 I could only dream of buying these but eventually I got them, 3 out of 4 were previously owned but optically as good as new due to their build quality.

[tonibosss]

@DeadJohn
Images are in full size( downscaled ) and I'd say for the first ones about 90% zoom in. I have few more samples of the window image where PF is not so expressed.