Field Test - Purple Fringing of PL25/1.4 on EM1

Started Feb 3, 2015 | Discussions thread
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slartz
slartz OP Senior Member • Posts: 1,583
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

Anders W wrote:

OrdinarilyInordinate wrote:

Would it help to use a step-up ring and a good multi-coated filter, like Hoya UV(0) HMC?

Unfortunately, a Hoya UV(0) or any other ordinary UV or skylight filter won't help at all. You need something significantly stronger. A 2A (Wratten 2A) is the minimum strength I'd expect to have much of an effect. The slightly stronger 2E is likely to work as well but might be slightly overkill.

Regrettably, there seem to be no multi-coated 2As and 2Es on the market. Part of the explanation may be that these filters were originally meant for a very different purpose than the one we now use them (haze reduction in B&W film photography). And since that purpose isn't exactly "hot" these days, we might be grateful that they are available at all.

As to step-up as well as step-down rings, they will work fine as with any filter (as long as you don't step-down so much as to get vignetting).

But one other solution is to use a gel filter affixed by means of thin (not thick) double-sided adhesive tape on the ring surrounding the rearmost element of the lens. That's what I use with my 7-14/4 (where there is also the worse problem of purple flare to be reckoned with) although for that particular lens it is possible to get a special gel filter holder to keep the filter in place as you can see here. Gel filters aren't multi-coated either but their location at the rear might alleviate any problem with flare.

Multicoating is not just about flare - it is also about reflectiveness of the glass - with a non multicoated filter, u have more rays that reflect of the rear element back, then from the front element again and into the sensor with an offset and some color spread (like a prism). it's of course not dominant, but may have some effect on contrast and color. This is of course enhanced greatly with "stray" light (even if not really "flaring").

The latter, of course, is irrelevant with rear element, and I also think there might be less problematic angled rays of light, but most importantly - I think gel filters are just so much better than glass filters in regard to their reflective characteristics, so that they do not need so much coating.

I thought about trying to either adapt that rear holder to the PL25/15 or to tape a filter on the back as some people did, but in all honesty, at least for this lens, this issue is so minor (only at f/1.4, high contrast) that I can really live with it without starting to "patch" the lens. I should get my PL15 next week and will see about that.

BTW - I also tested the Panasonic 35-100/2.8. I don't know if the lens is better designed, or simply because it only opens up to 2.8 - but Icould not really get any serious PF on it. at f/2.8, in the corner, at 1:1, if you REALLY hardpress me, I could find traces of it, but it's so light I would not even bother to postprocess...

 slartz's gear list:slartz's gear list
Olympus E-M1 II Olympus 12-40mm F2.8 Panasonic Leica DG Summilux 15mm F1.7 ASPH Olympus 7-14mm F2.8 Pro Panasonic Leica 100-400mm F4.0-6.3 ASPH +10 more
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