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Re: [OM] Unintentional Vignetting

Subject: Re: [OM] Unintentional Vignetting
From: Moose <olymoose@xxxxxxxxx>
Date: Wed, 14 Mar 2018 22:25:58 -0700
On 3/14/2018 4:05 PM, John Hudson wrote:
I use the cheapest circular rubber hood with, or without, a step-up ring which generates no vignetting with the fixed focal length lens in question. When used with a zoom lens I ensure that there is no vignetting at the widest angle of zoom.

For example: The Fujifilm 23/1.4 and 56/1.2 lenses are both 62mm filter threads. I use a 62mm to 77mm step up ring to mount a wide angle 77mm rubber hood which generates no vignetting with either lens. The 56mm lens comes with a dedicated circular push and twist on hood which I ignore. The 23mm comes with a dedicated tulip shaped hood which generates  vignetting if the hood is not rotated properly in place. This 23mm vignetting problem is a pain in the donkey. The hood on the 62mm to 77mm step up ring does not work on the Fujifilm 16mm-55mm/ 2.8 zoom [a 77mm thread] at any wider than 23mm. The zoom's dedicated tulip shaped hood has the same vignetting problem as the 23mm when not rotated properly into place.

I do all that stuff, if necessary. But if there is a manufacturer hood, I use that. I even found an original in great shape for the FL 58.1.2. Same basic thing as the original metal, slip-on hoods for the OM 50 mm lenses, but with matte finish base piece, rather than shiny chrome. Came with a heavy duty, stiff leather case with a place to store the push-on lens cap. Of course, this lens was a bit of a big deal at the time it was introduced, "A standard lens for 35mm SLR cameras with the largest aperture in the world when marketed."

Panny includes hoods with lenses. Oly does not, but there are plenty of third party folks who duplicate theirs for fewer $. What I particularly appreciate are those that bayonet on and may be reversed over the lens for storage.

I have a hard time thinking that train window glass per se can generate a vignetting problem. Your thru the window snowscape image shows almost equal lighting degradation at all four corners which tells me that something physical, like a lens hood, prevented all of the necessary light from reaching the camera's sensor.

I am not convinced. First of all, Tina is using the Leica designed hood for the lens. I am of the opinion that they are competent to design a hood that doesn't detract from their lens.

Second. As yet, I don't believe anyone has yet designed a zoom that doesn't have at least a little vignetting, wide open at its widest FL. From one review: "Vignetting was found in raw files at the widest aperture settings with all focal lengths, although it was barely noticeable." so some portion of the vignetting is from the lens. Unfortunately, none of the review sites that measure vignetting have tested this lens, so we have no hard data. I do know that vignetting has been strongest wide open at widest FL in every other test I've read. And that's exactly how it was used for this shot, according to EXIF, 24 mm, f2.8.

Next, I do think " . . . that train window glass per se can generate a vignetting problem.", if it is tinted and relatively thick. I imagine that these windows are actually double glazed, with different types of glass in each pane. A brief search shows that train carriage glass is required to keep flying passengers from going through in a wreck, so needs a combination of strength and resilience. Double glazing is used even where weather isn't severe, to combine characteristics of kinds of glass and to reduce A/C loads. Tinting, of course, also reduces the heat load.

Lets just assume 5 mm glass with a 50% tint. That would be one stop straight through. Tina says she was using the lens in the worst case scenario, right against the glass, so the angle at the corner would be almost 45° and the path through the glass about 7 mm. Combine that with the lens vignetting, and we might be looking at another stop in the corner.

All speculation, as  and we don't know anything about the glass, nor have real vignetting data for the lens. If we had a window from that train, an SL and the 24-90, we could see if stepping back a foot or two reduced vignetting. :-)

Also, as the smudging shows, there's something else going on, as well, which may have a greater effect. If schmutz is being deposited in the corners, which might be expected with windows set in from the carriage surface, as well as in drifts near the corners, that would also cause vignetting.

In any case, I'd be amazed if it was the hood.

Hooded Moose

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What if the Hokey Pokey *IS* what it's all about?
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