An entire expedition's photos ruined by a pol filter

Lou Jost · Post by **Lou Jost** » Thu Mar 21, 2019 10:21 am

I've just come back a few days ago from a fantastic five-day trip to a remote area in Ecuador. I found several plant species important to my work, including two recently-described species of magnolia trees. I made lots of automatic focus-bracketed stacks of these plants using my Oly PEN F and 60mm macro lens. I did not have time to run the stacks through Zerene during the trip.

Now that I am back, I find all my stacks are garbage, with weird angular patterns and strong astigmatism in all highlights. It is heartbreaking. What could have gone wrong? I had done this hundreds of times before, with excellent results.

I had a Bower circular polarizer on the lens at almost all times, in case it would be useful. It turns out that this filter is what ruined the stacks. I just ran some test stacks, and there was no problem when the polarizer was removed, or when a different polarizer (B+W) was used, but they were ruined by the Bower polarizer.

Left: 200% no pol, middle 200% Bower pol, right 200% B+W pol:

Scarodactyl · Post by **Scarodactyl** » Thu Mar 21, 2019 11:02 am

I have encountered a similar problem when trying to use camera polarizers with my stereo scope. I wonder why some of them produce such terrible abberations.

Lou Jost · Post by **Lou Jost** » Thu Mar 21, 2019 11:05 am

I wonder why some of them produce such terrible abberations.

I don't understand why this happened either, especially since other brands did not cause this problem.

Antal · Post by **Antal** » Thu Mar 21, 2019 11:50 am

It would be interesting to see a non stacked picture..

rjlittlefield · Post by **rjlittlefield** » Thu Mar 21, 2019 12:24 pm

Lou, do you know if this a previously good filter that went bad? Or was it just bad from the beginning?

If you look at reflections off each face of the bad filter, can you see any sign of ripples?

--Rik

Lou Jost · Post by **Lou Jost** » Thu Mar 21, 2019 12:55 pm

Rik, I don't see any ripples while looking at the reflections on the filter.

Antal, here are 200% crops of two single shots through the polarizer, one focused closer than the slice of best focus, and the other focused farther than the slice of best focus. You can see that the out-of-focus highlights of the two slices form sharp lines, in perpendicular directions from one slice to the other. These streaks, being relatively sharp, appear in the final stack, forming crosses everywhere.

Ichthyophthirius · Post by **Ichthyophthirius** » Thu Mar 21, 2019 1:56 pm

Hi,

I don't know any specifics but I thought it was possible to correct such errors (patterns that are uniform across the whole image) in Fourier space. Have you ever looked into this? Maybe there is a filter availabe for Photoshop or Image J.

Lou Jost · Post by **Lou Jost** » Thu Mar 21, 2019 3:00 pm

Thanks for the suggestion. I do not know of such a filter in Photoshop but will look.

Using DMap with contrast level set at 99.8% gives roughly reasonable results if the pictures don't have to be enlarged much.

ray_parkhurst · Post by **ray_parkhurst** » Thu Mar 21, 2019 7:18 pm

I have not found a filter of any kind that did not degrade IQ, so for studio work I never have a filter installed. For walkaround macro, I use a haze or UV filter only (to protect the lens), never a polarizer, since I've found they all cause degradation.

Lou Jost · Post by **Lou Jost** » Thu Mar 21, 2019 9:01 pm

Ray, the degradation caused by the B+W polarizer is very slight, and the change in light quality can be dramatic, more than enough to make up for the small sharpness loss caused by the filter.

joeD · Post by **joeD** » Wed Mar 27, 2019 10:39 am

Hi Lou , thanks alot, this topic was a real eye opener , i had the same issue with MARUMI EXS52CIR and i thought it was a diffusion problem...lol
may i ask you the model of your b+w polarizer?

thanks again

Lou Jost · Post by **Lou Jost** » Wed Mar 27, 2019 5:39 pm

joeD, the B+W polarizer has the following text inscribed on the front of the ring: "B+W 52 KSM HTC-POL MRC". On the outside of the ring it says "F PRO". "B+W", "MADE IN WEST GERMANY".

By the way, this is what the very distinctive false-detail cross-hatched astigmatism artifacts looked like in my stacks. here shown at 200%. On the real object there are no linear features whatsoever.

Yawns · Post by **Yawns** » Thu Mar 28, 2019 7:03 am

a bit off topic:
but I noticed you complained you did not have time to check your stacks during the trip:

Speaking about PROCESSING TIME.
I found the current version of Helicon is significantly faster than Zerene at processing JPG.
Let’s say Helicon is 3 minutes faster with a particular set of frames.
That’s irrelevant. 3 minutes is nothing, it's not enough to make a coffee….
But, when I come home, after a morning out, and I have 20 bracketed sequences and 2.500 photos to stack… 60 minutes (3*20) is very significant time…
So I bought the most basic and cheap license of Helicon.. 1 year for like 30 USD, if I remember well, only to “quick preview” the stacks.. and I just work with Zerene the sequences who are worthy to turn into final images.

Antonio

Lou Jost · Post by **Lou Jost** » Thu Mar 28, 2019 7:26 am

That's good to know, Antonio. Thanks.

Pau · Post by **Pau** » Thu Mar 28, 2019 11:54 am

Lou,
Do the astigmatism crosses show across all the frame or only at the periphery?

I ask it because I have the same issue with the AZ 100 objectives although only at the periphery. I'm blaming the objectives although now I also can suspect of the EO optical window placed in front of it to compensate spherical aberration (they are designed to see through a quarter wave plate or plain window)