Micro 4/3 My "definitive" post on the Panasonic 7-14mm "Purple Blob" Problem

[entropic remnants]

I posted this as a reply in another thread but I'll post it here as well. I'm sure this will continue to be debated -- but I've solved it to my satisfaction and decided the 7-14mm will usually be on my G5 body and not my E-M5. Image samples follow below.

Here are the comparison shots I did last night. A few observations:

• I made these shots from more or less the same spot, at more or less the same angle but they aren't exact as I was working hand held and took the images at different times. I more or less matched the image color and so forth but I did minimal processing.
• I did this in several places in the mill and got the same result every time.
• The problem will only occur with bright light sources quite a few stops above the average scene level -- like the sun or in this case the very bright overhead lights. Although bright, the space is big and the overall scene light level is low. Perfect to reproduce this.
• You can readily see that the reflections are of the light pattern on the roof. There are multiple ones from different distances or the "ping ponging" of the light in the lens that results in different blobs but in the same patterns.
• Clearly, these are typical sensor/lens reflections. The 7-14mm has no filter on it so we can't blame that.
• Not only are the G5's reflections neutral in color, they are also much dimmer indicating a lesser reflection.
• The E-M5's sensor somehow reflects a narrower color band, but reflects a LOT of it.
• The 7-14mm optics sit closer to the sensor than any other lens I own. I wish I'd checked the Olympus 9-18mm before I sold it. I had this problem for sure with it, but less than I do with the 7-14mmm.

So, I'll repeat that I think this problem is the "perfect storm" of lens and sensor design interacting poorly.

Here's the images, first the full size and the image with the E-M5 is first, the G5 second and the difference is quite dramatic.

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Now here's 100% crops from the images in the critical areas.

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This problem is real, but requires certain conditions to excite. However, this is a very common condition in the urbex I do in poorly lit buildings with windows and holes in the wall leading to bright daylight. I will be doing my urbex shooting with the 7-14mm on the Panasonic G5 body and I'm perfectly comfortable with that.

I would not recommend the 7-14mm for anyone with an E-M5, E-PM2, or E-PL5 who does shooting in these conditions therefore.

 

[Yeats]

I don't own any of this stuff, but I think it's very useful information and research, John.

 

[entropic remnants]

Actually, member kwalsh over on MU-43 pointed out that somebody went way further with this than I have -- really scientifically in fact. I had posted this same thread over there and this was his reply. I knew my post was really a definitive statement of the problem and not the solution and I deliberately quoted "definitive" in my title to soften it a bit.

They traced it to problem with reflection of near-UV light and a difference in the way the Oly sensor handles UV/IR filtering. Here's his post in its entirety:

This was explored in great detail over in DPR by AndersW. The cause is near UV reflections that pass on to the E-M5 sensor but not most other m43 sensors. The solution is to affix a particular UV filter to the rear of the 7-14. Then you can use it on the E-M5 without any purple blobs showing up.

As already described, this has nothing at all to do with software corrections or CA or anything else to the effect. It is purely an optical coatings issue with the 7-14 that is only made obvious on the E-M5 with its slightly wider band UV/IR cut filter.

Here's the thread on DPR showing what the issue is and how to fix it:

The flare from the 7-14 on my E-M5 is no longer purple: Micro Four Thirds Talk Forum: Digital Photography Review

But, I won't be modifying my lens. I'll just use it on the G5. Most of the work I do with it will be tripod based anyway so the stabilizer of the E-M5 really doesn't figure into it.

 

[Azon]

Thanks John,
It's good to know before final decision and as always your posts are interesting and informative.

 

[kyteflyer]

I think there are just too many forums... John, I don't think your G5 has a sub 1" sensor, does it? Confused about where to post? I get that way too, sometimes. Right now, tossing up where to put a couple of shots taken with my FZ100. In this forum? In an image forum? In Chris's thread about superzooms? arghhhh

 

[entropic remnants]

I think there are just too many forums... John, I don't think your G5 has a sub 1" sensor, does it? Confused about where to post? I get that way too, sometimes. Right now, tossing up where to put a couple of shots taken with my FZ100. In this forum? In an image forum? In Chris's thread about superzooms? arghhhh

DOH!!!! Thanks for pointing that out.

I worked an overnight (I shot these late at night) when I'm normally all weekdays and posted this with about 4 hours sleep. I goofed for sure on where I put it and I invite mods to move it as appropriate and sorry for the inconvenience!

 

[kyteflyer]

DOH!!!! Thanks for pointing that out.

I worked an overnight (I shot these late at night) when I'm normally all weekdays and posted this with about 4 hours sleep. I goofed for sure on where I put it and I invite mods to move it as appropriate and sorry for the inconvenience!

Nobody gets really upset about it but sometimes I think people don't notice when they do things like this. I don't! And I get the 4 hour thing. I've been running on 4 for weeks. Its bad. And I dont even work anymore.