Thin behind lens clear filter in Sony/Minolta reflex lenses

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Chris Malcolm
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Thin behind lens clear filter in Sony/Minolta reflex lenses
3 weeks ago

The last member of this range of Minolta reflex lenses, and the only one to be continued by Sony, was the recently discontinued 500mm reflex. These lenses are of fixed aperture, f/8 in the case of the 500mm. They have a behind the lens slot into which ND filters of various strengths can be fitted, ND4 In the case of the Sony 500mm. Plus a clear filter to fill the slot when none is used.

The official advice (e.g. in the lens manual) is that the clear filter is important for the proper operation of the lens. But these filters often get lost and are very hard to obtain. What difference could a clear thin glass plate behind the lens possibly make? Buyers of second hand hand lenses missing the clear filter are often advised that it really makes no visible difference, and if the clear filter is missing just to cover the empty slot in the lens barrel for its insertion with black tape.

But these recent discussions of the effects on lens IQ and performance of the various widths of the filter stack on the front face of the sensor suggest that it might make a difference. Perhaps those who have claimed a missing clear filter on the 500mm reflex makes no difference simply haven't known what to look for.

I'm sure I'm not alone among owners of the 500mm reflex who have the clear filter in being interested to look for the difference. So what effects should I look for?

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Chris Malcolm

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Sony Alpha DSLR-A550 Sony SLT-A77 Sony 50mm F1.4 Sony DT 18-250mm F3.5-6.3 Sony 500mm F8 Reflex +7 more
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