Micro Four Thirds Focal Reducer Shootout

Started Feb 20, 2014 | Discussions thread
Klarno Veteran Member • Posts: 4,170
Re: Micro Four Thirds Focal Reducer Shootout

Anders W wrote:

Klarno wrote:

MichailK wrote:

So, I want to ask everyone using these adapters if in real life use the results of the second test (Hotspotting) are a deal breaker - we are talking about solid white back illuminating frame and solid black center rectangle which is an extreme case - isn't it? In a "normal" lit scene it should be no real fuss unless nitpicking I suppose but what do you guys using such adapters say?

I've actually observed hot spotting in entire lenses. When I had the Super Takumar 50mm f/1.4, used with a simple adapter (this was on a DSLR and before focal reducers were a thing), upon stopping down it would develop a spot of blue flare in the dead center of the image. This was under normal daylight conditions with subjects of average contrast levels. The more stopped down, the smaller, better-defined and brighter the blue flare was. I felt this problem made the lens unusable for color photography. From what I can see from samples, the blue spot flare on focal reducers that exhibit this problem seems just as bad, if not worse.

I don't think it's that unusual for legacy lenses to display this problem, the reason presumably being that the antireflective coatings on the rear side of the lens elements where never designed to handle a shiny digital sensor. Here's another example with a 50/1.4:


I haven't seen this problem on my singlecoated OM lenses, so it's probably on a lens-by-lens basis. The singlecoatings on the early Takumars from the 1960s don't seem to be very effective. I've even seen horrendous flare magnified off the rear element that seems to show a magnified image of the bayer filter array:

I'd be curious to see if a focal reducer that doesn't suffer inherently from hotspotting could actually mitigate that problem in lenses that by themselves exhibit this kind of flare. I can't test it anymore as I got sold off my Super Takumar (got more for it than what I originally paid, so I'm happy with that tradeoff).

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