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

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.

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


Sent from my iPhone using Tapatalk

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:

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

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

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.

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??

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??

It is expensive living in Australia (but worth it if you can get in the water these days). 100 mm square Wratten 2A filters are about $30 US. I haven't tried one for defringeing but we use one occasionally for some fluorescence filtering work in the lab.

Bill

On 5/3/2020 at 3:49 AM, bvanant said:

It is expensive living in Australia (but worth it if you can get in the water these days). 100 mm square Wratten 2A filters are about $30 US. I haven't tried one for defringeing but we use one occasionally for some fluorescence filtering work in the lab.

Bill

The problem is that hardly anyone uses Wratten filters these days, the one I was looking at would be shipped in from overseas.    Cameras used to be really pricey but with new retailers on the scene they now pretty much match US prices these days but uncommon accessories remain pricey unfortunately.

I planned to buy the Lumix 8mm for an Olympus OMD E-M5 MkIII, but looks like the problem with "Purple Fringing" is real:

Purple fringing with Panasonic lenses on Olympus bodies
https://www.dpreview.com/forums/post/61956064

And not only "Purple Fringing" is the problem:

Olympus and Panasonic compatibility. 9 Issues when mixing Olympus & Panasonic bodies & lenses
https://www.apotelyt.com/photo-lens/mft-compatibility

The purple fringing does occur on certain models, this link explains the purple flare issue quite well:

https://alanwatsonforster.org/writing/mft-purple.html

There is a purple flare problem that is not correctable with the defringing tool in Raw converters, while the fringing in my examples is correctable to some extent and they don't list the Pany 8mm as one of the lenses displaying this problem.   The problem may be due to the dome in my case and appears to be purple fringing.

Having said that though I would still buy the olympus lens if I was doing it again. 

It is a pity to hear that you are not satisfied with your fisheye setup, Chris, since these setups belong normaly to the best and sharpest WA solutions...

I have few comments:

#1.: As far as I can judge from here, I do not find that the extreme corners in your example images extremely unsharp. Maybe it is not such a big problem - when I look at the corner sharpness of my Panasonic rectilinear WA at 7mm (with Zen DP170 and 60mm extension), THIS is what I would call really bad corners...

#2.: It may well be an issue of dome port radius (you are using the DP100 with r= 5 cm).

The smaller the radius, the smaller and closer the virtual image is and the more criticial the correct positioning of the lens via the extension becomes. I was considering the DP100 also, but was unable to find a version/extension that would perfectly fit my, admittetly, exotic fisheye solution (Canon 8-15mm and Tokina 10-17mm via Metabones 1x adapter on EM1II). So I went for the (larger) Nauticam 140 (r= 7 cm), where the correct combination for extensions exist.

Here a real life indication for importance of dome radius: When I use both Canon 8-15mm or Tokina 10-17 mm with the Zen DP170 (r= 11 cm), I find IQ at least as good as with the smaller Nauticam 140 (Also the Zuiko 8mm gave perfect IQ with the DP170, but I cannot compare to Nauticam 140, since I never used this combination). This is contradicting the theory, since the DP170 is not a real fisheye domeport (full hemisphere) and correct positioning of the lens is impossible. It seems, however, that the larger radius by far outcompensates the error in lens positioning - indicating how important the radius is...

#3.: In case you go for another lens, as you indicate above, I recommend you also have a close look at Canon 8-15 mm or Tokina 10 - 17mm (with 1x Metabones adapter and Nauticam 34.7mm extension). IQ with Canon is at least as good as with the Zuiko 8 mm and I personally cannot see that the Tokina 10-17mm performs worse in practice (this is a big surprise since over the water the Tokina is garbish). The pleasure to have the opportunity to zoom out during the dive is just indispensable, I never was using my beloved Zuiko 8mm again after haveing the zoom fisheyes...

(And, finally, maybe another lens will be a disappointment, when expecting substantial improvement in IQ with the same dome. Improvements in IQ may just occur by chance, because the extension fits 1 or 2 mm better the new lens)

Wolfgang

It's not to say I am unsatisfied - more that with 20:20 hindsight I would have done something different - the little Pany fisheye is so compact with the little Zen dome.

I think also if I were to change I would look at the 8-15mm lens - the chance to zoom in somewhat while on a wide angle reef dive for interesting fish etc would be quite welcome.   Quite a pricey option in comparison to the m43 fisheyes though.

Just a question though on the 8-15 plus speed booster - the Nauticam chart says take the 34.7mm adapter and use the recommended ports for Canon N120.  So the 8-15 has 30mm extension and you use the adapter plus 30mm extension.  The Zen chart recommends the N100- dome for the 8-15 with no extension.  What stops you using the 8-15 with the zen dome and no extension on the N85-N120 adapter? 

The Metabones adapter should be 24.75mm thick so it looks like the 34.7 mm N85-N120adapter is 10mm longer than it needs to be already so the 8-15 should sit 10mm further back in the port compared to what it does on the Zen 100mm dome on a Canon body/housing.  I assume I'm missing something there.

3 hours ago, ChrisRoss said:

Just a question though on the 8-15 plus speed booster - the Nauticam chart says take the 34.7mm adapter and use the recommended ports for Canon N120.  So the 8-15 has 30mm extension and you use the adapter plus 30mm extension.  The Zen chart recommends the N100- dome for the 8-15 with no extension.  What stops you using the 8-15 with the zen dome and no extension on the N85-N120 adapter? 

The Metabones adapter should be 24.75mm thick so it looks like the 34.7 mm N85-N120adapter is 10mm longer than it needs to be already so the 8-15 should sit 10mm further back in the port compared to what it does on the Zen 100mm dome on a Canon body/housing.  I assume I'm missing something there.

#1.: Regarding the Nauticam 34.7mm N85-N120 adapter: It is designed to work with the 0.71x Metabones speedbooster (MFT to Canon EF). Camera plus speedbooster is constructed to give the same distance of N120 flange to the sensor than with a Canon body (without the adapter) - this is the construction principle of Nauticam and the reason why the length is 34.7mm (24.75mm obviously would be too short, I do not think that the engineers missed 10mm, but did not search for the 10mm by myself (a good pet may be that the Canon bodies (especially those with mirror) are 10mm longer, so th esensor sits more behind)). Regarding the (N120) extension, one proceeds then via the Canon EF charts of Nauticam or Zen, what the right extension for a selected lens/port combination would be, just like for a Canon camera in Nauticam housing. Accordingly, the ports have to be the N120 versions, preferentially without any in-built extension (I think the confusion comes, because of these built-in extensions).

Tokina 10 - 17 mm works excellent with the 0.71x speedbooster (little vignetting at 10 mm (i.e.: 7.1 mm), but starting from approx 11 mm (i.e. approx 8 mm) no more vignetting). The situation with Canon 8 - 15 mm is different, as the focal reduction leads to heavy vignetting, a waste of the shorter focal length range and hence to a restricted range at the upper end. Therefore the Metabones (glassless) 1x adapter is the adapter of choice. @8mm one has approx. 180 diagonal angle of view (AOV), just like with the regular MFT fisheyes. 15 mm provide an AOV of approx. 85 degree, similar to rectilinear 12mm (but without the fisheye look). BTW, also the Tokina 10 - 17 mm performs very well with the 1x adapter, allowing even closer to zoom in, when required (74 degree AOV, similar to 14mm rectilinear WA).

The problem arises as the 1x adapter is 5.6 mm longer than the 0.71x speedbooster. Hence one has to choose accordingly longer extensions and also modify the zoomgear with an extension collar (I have the 3D print files for both Canon and Tokina, even the versions for use with Kenko 1.4x teleconverter. I shared them already here, but just cannot find the link right now).

#2.: Extensions: Here are the extensions that I use with both domeports (the green are the ones I use regularily; NA stands for "not available"). They come very close to the recommended ones (see above at #1):

You are right when you say this all costs a lot of money, but who said ever that making photos UW is a cheap hobby? 

All the best, Wolfgang

P.S.: Is it possible for you to go under the water in Sidney? Here in Austria, we can only dream now about our next encounter with the sea, at most I can go diving in the near-by gravel ponds what is not a good substitute, more a "Dive Emergency Descent"

https://interceptor121.com/panasonic-gh5/fisheye-zoom-rig/

Wolfgang provided all details. You can also use an acrylic port with the same lens that cuts down some costs and takes away some sharpness

Re purple fringing I would also check another program that is not lightroom to process the raw as I can see adobe is not as fine tuned as others

12 hours ago, Architeuthis said:

#1.: Regarding the Nauticam 34.7mm N85-N120 adapter: It is designed to work with the 0.71x Metabones speedbooster (MFT to Canon EF). Camera plus speedbooster is constructed to give the same distance of N120 flange to the sensor than with a Canon body (without the adapter) - this is the construction principle of Nauticam and the reason why the length is 34.7mm (24.75mm obviously would be too short, I do not think that the engineers missed 10mm, but did not search for the 10mm by myself (a good pet may be that the Canon bodies (especially those with mirror) are 10mm longer, so th esensor sits more behind)). Regarding the (N120) extension, one proceeds then via the Canon EF charts of Nauticam or Zen, what the right extension for a selected lens/port combination would be, just like for a Canon camera in Nauticam housing. Accordingly, the ports have to be the N120 versions, preferentially without any in-built extension (I think the confusion comes, because of these built-in extensions).

Tokina 10 - 17 mm works excellent with the 0.71x speedbooster (little vignetting at 10 mm (i.e.: 7.1 mm), but starting from approx 11 mm (i.e. approx 8 mm) no more vignetting). The situation with Canon 8 - 15 mm is different, as the focal reduction leads to heavy vignetting, a waste of the shorter focal length range and hence to a restricted range at the upper end. Therefore the Metabones (glassless) 1x adapter is the adapter of choice. @8mm one has approx. 180 diagonal angle of view (AOV), just like with the regular MFT fisheyes. 15 mm provide an AOV of approx. 85 degree, similar to rectilinear 12mm (but without the fisheye look). BTW, also the Tokina 10 - 17 mm performs very well with the 1x adapter, allowing even closer to zoom in, when required (74 degree AOV, similar to 14mm rectilinear WA).

The problem arises as the 1x adapter is 5.6 mm longer than the 0.71x speedbooster. Hence one has to choose accordingly longer extensions and also modify the zoomgear with an extension collar (I have the 3D print files for both Canon and Tokina, even the versions for use with Kenko 1.4x teleconverter. I shared them already here, but just cannot find the link right now).

#2.: Extensions: Here are the extensions that I use with both domeports (the green are the ones I use regularily; NA stands for "not available"). They come very close to the recommended ones (see above at #1):

 

You are right when you say this all costs a lot of money, but who said ever that making photos UW is a cheap hobby? 

 

All the best, Wolfgang

 

P.S.: Is it possible for you to go under the water in Sidney? Here in Austria, we can only dream now about our next encounter with the sea, at most I can go diving in the near-by gravel ponds what is not a good substitute, more a "Dive Emergency Descent"

Thanks Wolfgang,

on the 24.75mm that is the difference in flange back distance between m43 and EOS so should be the added length due to the 1x metabones adapter. 

My logic is looking at the charts the Zen chart lists the DP-100CR port bare for both the the Canon and Nikon zoom fisheyes.  Nauticam  has a 20mm extension for Nikon  and the Canon a 30mm extension with the 140mm dome port.  Logically you should be able to attach the Zen 100mm port to the 34.7 mm N85-N120 if you wanted to use that port with the Canon 8-15mm.  If you look at photos of the Zen N120 DP100 port it looks to have some extension built in.  https://reefphoto.com/products/zen-dp-100-n120cr-4-inch-glass-dome-port-for-canon-8-15-nikon-8-15-nauticam-removable-shade As the Canon has more extension than Nikon for Nauticam and the same extension with Zen it looks as if the Canon could cope with the extra extension provided by the adapter.

On the diving question Sydney has some of the best shore diving of any capital city in the world - all rocky reefs in and around the entrance to various bays and harbours and off-shore as well.  Dive shops are providing modified service for tank renatls and air fills - but no boats running.  Diving is classed as exercise and you are currently allowed to meet up with one person to dive - with social distancing.   So yes we can dive.

It pays to be careful though - I know Australia has the spread quite well controlled, but you do not want Covid as a diver.  Reports are emerging of divers who had Covid, recovered but have on-going lung damage, which will impact their ability to dive - no idea how long the damage will last as yet.

Chris: If you are still interested in some Wratten Filter material I can dig some out of our lab and send you a 2 or 3 inch square.

Bill

1 hour ago, bvanant said:

Chris: If you are still interested in some Wratten Filter material I can dig some out of our lab and send you a 2 or 3 inch square.

 

Bill

 

Thanks Bill, it would be great to try it out to see if I get an improvement.