[GUB]

I wonder if the OP has a nonstandard filter on the back?

[Bob 256]

One other thought - make sure when you compare the K-1 and your film camera, that comparisons are done at the same aperture. Vignetting is pretty dependent on aperture (generally decreasing with higher f-stop values) and it's possible that the K-1 had a larger aperture than your film camera comparison. Same lens but different apertures can lead to misleading results.

I previously mentioned that wide lenses have a wider light cone but for many modern wide angles, that isn't necessarily true. Newer wide angles use a nearly normal type lens behind a highly negative set of elements so when the light cone leaves the former, the lens can be behaving like a 50mm lens as far as the light cone is concerned. That's one reason to take another look at comparative apertures between different cameras.

[GUB]

One other thought - make sure when you compare the K-1 and your film camera, that comparisons are done at the same aperture. Vignetting is pretty dependent on aperture (generally decreasing with higher f-stop values) and it's possible that the K-1 had a larger aperture than your film camera comparison. Same lens but different apertures can lead to misleading results.

I previously mentioned that wide lenses have a wider light cone but for many modern wide angles, that isn't necessarily true. Newer wide angles use a nearly normal type lens behind a highly negative set of elements so when the light cone leaves the former, the lens can be behaving like a 50mm lens as far as the light cone is concerned. That's one reason to take another look at comparative apertures between different cameras.

Ummm -m42 - aperture adjustment entirely on the lens.

[Lowell Goudge]

For the OP if he wants to really check vignetting, or exposure fall off at the edges, there is a simple test.

Find a spot with a uniformly lit block wall, and take a shot.

Then with a photo editor capable of measuring greyscale within a selection, check the greyscale value in the middle in a small selected area, and a similar size area in the corner.

As many have mentioned, sensors do not have a uniform response at all incident light angles, and there may be exposure fall off at the edges.

Even my K50/1.4 has about 1 stop of exposure fall off on my *istD between center and the corner.

[stemked]

It probably vignettes on film too. What fisheye are you using? From your description (heavy with T-mount), it is not the Zenitar 16/2.8.


Steve

That's a tougher question than you think. It's all in Russian. bevomo (where the 'v' is upside down. Technically it wasn't a T mount, but I was able to thread it on.

---------- Post added 03-24-2021 at 09:35 AM ----------

I wonder if the OP has a nonstandard filter on the back?

No filter on the back (but it did come with options)

[stevebrot]

That's a tougher question than you think. It's all in Russian. bevomo (where the 'v' is upside down. Technically it wasn't a T mount, but I was able to thread it on.

The maker was Belomo in Belarus. They make the Peleng 8mm circular fisheye, but I was not able to find any other fisheyes related to that maker. The Peleng looks like the lens below...


Attribution: By Ashley Pomeroy - Own work, CC BY-SA 4.0, File:Peleng 8mm Fisheye 8225.jpg - Wikimedia Commons

If that is the lens and you have vignette, it might be due to it not being a 180 diagonal fisheye.


Steve

[steephill]

The OP's lens is probably the Peleng 17mm f2.8 fisheye. It doesn't fully cover the full frame sensor apparently - Review of Belomo MC Peleng 17mm f2.8 Fisheye for Full Frames | Feedbacks - Peleng 8mm f/3.5 Circular Fisheye Lens for Canon, Nikon, Olympus which would explain the vignetting.

[stevebrot]

The OP's lens is probably the Peleng 17mm f2.8 fisheye. It doesn't fully cover the full frame sensor apparently - Review of Belomo MC Peleng 17mm f2.8 Fisheye for Full Frames | Feedbacks - Peleng 8mm f/3.5 Circular Fisheye Lens for Canon, Nikon, Olympus which would explain the vignetting.

Cool! I was unaware of this lens and apparently, it is uncommon. Even so, it has its own small group on Flickr and a smattering of reviews on the Web.

Flickr: The Belomo MC Peleng 17mm f2.8 Fisheye Gallery Pool


I read a couple of forum threads and the lack of corner coverage may be a matter of orientation of the lens to the camera at the T-mount.


Steve

[stemked]

The OP's lens is probably the Peleng 17mm f2.8 fisheye. It doesn't fully cover the full frame sensor apparently - Review of Belomo MC Peleng 17mm f2.8 Fisheye for Full Frames | Feedbacks - Peleng 8mm f/3.5 Circular Fisheye Lens for Canon, Nikon, Olympus which would explain the vignetting.

That seems to be the lens. 17mm f2.8 Peleng

[barondla]

That seems to be the lens. 17mm f2.8 Peleng

Many lenses with rear mounted filters require a filter to always be mounted. The filter is one of the optical elements. Doubt it will affect vignetting, but it sure affects sharpness of the Arsat 30 fisheye on my Pentax 645. I remember the Peleng. Always wanted one.
Thanks,
barondla

[photoptimist]

Many lenses with rear mounted filters require a filter to always be mounted. The filter is one of the optical elements. Doubt it will affect vignetting, but it sure affects sharpness of the Arsat 30 fisheye on my Pentax 645. I remember the Peleng. Always wanted one.
Thanks,
barondla

Very true!

Not only would the absence of a required filter cause a loss of sharpness, it might even prevent infinity focus. A curious (and essential) property of light traveling in a dense medium such as glass is that refraction makes the effective distance travelled by the light less than the thickness of the glass.

For purposes of flange focal distances, a 2mm thick rear filter acts like it's only 1.33mm thick (assuming it's ordinary glass with an index of refraction of 1.5). Remove that filter and the point of focus shifts 0.67mm further from the lens which might be too far for the focusing mechanism at infinity.

[barondla]

Very true!

Not only would the absence of a required filter cause a loss of sharpness, it might even prevent infinity focus. A curious (and essential) property of light traveling in a dense medium such as glass is that refraction makes the effective distance travelled by the light less than the thickness of the glass.

For purposes of flange focal distances, a 2mm thick rear filter acts like it's only 1.33mm thick (assuming it's ordinary glass with an index of refraction of 1.5). Remove that filter and the point of focus shifts 0.67mm further from the lens which might be too far for the focusing mechanism at infinity.

Is there a reason to make filters with lower refraction glass?

Thanks,
barondla

[photoptimist]

Is there a reason to make filters with lower refraction glass?

Thanks,
barondla

Alas, the only decently hard/strong materials offered by our universe have high refraction. There are some clever ways to make thin films with an index of refection near that of air (great for making anti-reflective coatings) but I don't think they scale up to make a nice solid disk. And there are some clever ways to make thick disks with an index of refection near that of air (aerogels!) but they are quite fragile.

One can reduce the problem with thinner filters. A gorilla glass filter could be only a fraction of mm thick without being too fragile.

[HomeMadeSin]

The FOVs of the K1 and LX are virtually the same* but the photosensitive surfaces are not. Film and silicon sensors have very different optical properties that affect performance in the corners.

For film, the matte surface of emulsion can readily absorb light coming from all angles.

For digital, the microlens-studded surface of a silicon sensor cannot readily absorb light coming from all angles. The microlenses int he corners are optimized for certain angles that assume the exit pupil of the lens is a certain distance from the film plane. Older ultra-wide angle lenses may have exit pupil distances that are too close to the film plane and that cause vignetting.

*The exception to this occurs when shake reduction, composition adjustment, or astrotracer are used. These features shift the sensor up to 1.5mm in both directions which puts one or two of the sensor corners further into the extremities of the lens's image circle.

P.S. This fact about silicon sensors is one of the reasons that the short mount distance of MILC cameras doesn't really enable lenses as small as proponents of MILC might think. MILC still require retrofocus designs (or heavy vignette correction) with wider lenses.

This is interesting to me. Although I've yet to be fitted for my dunce cap, intuitively what you wrote makes sense. However, I have not been able to find similar information concerning the large diameter/short flange distance of the latest MILC offerings (Nikon for instance, but they are not alone). I was interested in the Z series cameras.

Does this help explain the 645Z appeal/performance with 'old' tech? Because a MF mirrorless (Fuji, H-blad) could be in a similar boat as the new FF ILCs. Of course, I just assumed (due to lack of other sources indicating this) that it is a technicality that doesn't affect the image as much as one might construe.