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ChrisRoss

Purple fringing with Panasonic 8mm f3.5 lens on Olympus body

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Posted (edited)

Hi all,

 this discussion started branching from another thread, so moving to a thread of it's own.   I see soft corners with my Panasonic 8mm f3.5 fisheye on Olympus EM-1 MkII body.    I was referred to this article:  https://alanwatsonforster.org/writing/mft-purple.html   By Interceptor121.  Looking at the first image of the reeftop I can certainly see fringing in the corners, the top corner is a zoomed in view.  I first put it down to the dome.

Looking at the second image of the sea fan, the problem is there but not as bad.  First image the corner in question is closer while I think I'm more square on withe corner at the same distance as centre with the second seafan image.  Should be fixable according  the article with a Wratten 2A gel in the rear holder.  Before I rush out and buy one anyone else have similar experience or actually installed a 2A gel filter?   Gel filters are not the easiest thing to find and are pretty fragile but I believe I can order a 75mm square one for $A85. 

Details are Olympus OM-D EM-1 MkII + Pany 8mm f3.5, Nauticam housing/Zen 100mm dome.  Shooting at f8.   Click on the images to see them bigger.

 

LoLouReeftop_CornerDetail.jpg

LoLouReeftop_CornerDetail2.jpg

Edited by ChrisRoss

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Generally although mft is supposed to be interchangeable some construction issues interfere with performance
I have looked at my images and I can confirm the Panasonic 8mm with 4.33 dome is sharp from f/5.6 and smaller
At f/4 corners are soft however there is no fringing in the images
I am not sure if the zen dome being smaller makes things worse but at f/8 there should not be fringing nor soft corners.
Looking at your images the corners are not soft but there is purple fringing all over.
To exclude the dome I would shoot on land at the same aperture and check


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An update, I did some more digging and opened up the the file in ACR, then used the defringing tool which removed the purple fringe quite well, but the definition in the corners is still not great.  Here's the corner in question with and without defringing:

 

Corner _100%_Not_defringe.JPG

Corner _100%_defringe.JPG

 

I'll try some outdoor shots and try to induce some fringing.

 

Edited by ChrisRoss

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Interesting tread. It is obvious that defringing is not helping to sharpen the photo...

To test the lens over water will be revealing: The purple fringing that is due to UV light should be much smaller UW compared to the surface, since UV is very quickly absorbed by water. An example is the Tokina 10-17mm FE, that shows excessive purple fringing over water, but little UW. See here for overwater test photos with this lens (excessive purple fringing):

https://www.dpreview.com/forums/thread/4267346

https://www.dpreview.com/forums/thread/4299636

I put UW testphotos with MFT Oly somewhere here in WP, but cannot find the link right now (but there are many to find in the Internet).

 

In addition to UV absorption UW, the corner unsharpness should persist over trhe water, in case it is not the dome to blame...

I guess it is the small domeport: the smaller the radius, the smaller and nearer the virtual image is and the more critical is exact focus and also the exact extension...

 

Wolfgang

Edited by Architeuthis
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OK here's some samples from on land, one is a bit of white paper against black BG far corner of frame second is outside tree branches against the sky both have strong purple fringing which is removable with tools in the Raw converter.  You can see in the outdoor corrected file it's not completely gone from the very fine needles.

 

Indoor_Pany8mm.JPG.093e63c8c68701c074a3cdc5595c6ef8.JPGOutdoor_Pany8mm.thumb.JPG.32b7b483cdd61c4018e23caeb6362be3.JPGOutdoor_Pany8mm_corrected.thumb.JPG.bcdbeeebdba4485d6e798aef6de4e224.JPG

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So it seems the dome is having some influence on the very corner of the frame as I noted the first sample (reeftop photo) the corner is very much closer compared to the seafan where the blurring is not so bad.

I'm wondering if it's worth trying out a Wratten 2A or not, seems like this is correctable which the problem solved by the 2A was not and the blurring is likely due to the dome??

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So it seems the dome is having some influence on the very corner of the frame as I noted the first sample (reeftop photo) the corner is very much closer compared to the seafan where the blurring is not so bad.
I'm wondering if it's worth trying out a Wratten 2A or not, seems like this is correctable which the problem solved by the 2A was not and the blurring is likely due to the dome??
Defringing reduces the sharpness of the image in both cases.
It is obvious that the issue in water persists from your shots
The softness of the dome is also a factor but getting a bigger port is more expensive than the filter
I have never seen underwater optics improve over land and purple does penetrate deep in blue water so I would try and kill this issue on land first of course matter of opinions

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