E-M5 flare problems with Pany 7-14mm

Started Sep 2, 2012 | Discussions thread
Sanpaku
Forum MemberPosts: 62
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Solutions.
In reply to Anders W, Sep 14, 2012

I'm satisfied with the conclusions of this thread:

1) Sensor/rear element reflections occur with the 7-14mm and all m43 bodies due to the close proximity of the lens rear element to the sensor and the concave surface of the lens rear element surface. The 7-14mm rear element is clearly single-coated (note the purple hue of reflections on the element itself). See How lens coating works: http://rick_oleson.tripod.com/index-166.html

2) These reflections are most visible with the O-MD EM-5 body because the Sony sensor has an uncoated or single-coated hot mirror (the colored glass that blocks IR affixed to the sensor) compared to perhaps multicoated Panasonic sourced sensor / hot mirror assemblies in all prior m4/3 bodies.

Therefore, a permanent solution might appear to be to interpose a multicoated surface (which damps all reflections better than a single coated one, which works best around 550nm (green) and less well in the far blue (to 400 nm) or red (towards 700 nm). See the aforementioned link.

That sort of glass is commercially available, and is used in the multi-coated clear lens protector filters. The glass itself is not that expensive, an Hoya 55mm Clear Pro 1 Digital Multi-Coated Glass Filter (with 8 coats) is $17 at B&H.

Alas, that filter is 3mm thick.

On my 7-14mm lens, the circular space behind the rear element isn't cylindrical, its diameter ranges from 18.4 mm (at the rear element) to 20.8 mm at the rear most surface, while its depth is 2.08 mm. Hence 2 mm thick glass with a diameter of 18.4 mm or 1 mm thick glass with a diameter up to 19.6 mm (simple interpolation) might be fitted, and affixed with tape top and bottom (outside the image circle).

If 3mm filter glass is used, then the filter glass would project 1 mm past where the lens ends, and would have the 18.4 mm maximum.

As the m43 format has an image diagonal of 21.63 mm, with any homebrew solution like this the image corners may be lost, but maybe not, as the 7-14mm lens only projects 5 mm inside the 20mm flange to sensor distance of the m43 format.

One could cut 2 such filter glasses out of a 55mm filter. And probably 4 from a 77mm.

How much it would cost to persuade an optical shop to cut a filter glass down to size?

Does anyone here have any glass cutting equipment? I'd be more than happy to obtain and donate a filter or two for the experiment.

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