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Today I took my new 21mm prime lens to my local lake hoping to do some long day time exposure shots using my variable Promaster ND Filter. Now, I needed to use a step up ring as the thread is 49mm and the filter 52mm, no problem, screwed on the step up ring. Next goes on the filter voila, all looks and feels fine.
Everything is going to plan with set up etc, however I noticed that when tweaking the darkness close to max I'm getting (on the viewfinder) a purple cloud/fringing cross like pattern. If taking a photo this is also reproduced.
I recall using my ND filter with another 52mm thread lens (no step up ring required), and i was getting a similar purple effect coming in from the edges also, it never was quite as bad as this however. I surmised that perhaps I was screwing the filter onto the lens poorly, perhaps some light leakage coming in and ruining the filters objective?
Anyway, i took it all apart several times and screwed everything back together, again and again, nothing got rid of this purple cloud coming in whenever I really cranked up the darkness.
It meant that even at f22 iso 100 I could only manage about 3secs exposure, nothing like the 20secs I've managed before (without the step up rings).
What's going on?
I can try and take a picture of the viewfinder and what it's showing later on to help trouble shoot. Is this a common issue? Step up ring naff? Variable ND bad idea? Not sure where to turn next...
Cheers,
Bruce