33

The D750 is a full frame camera, while the 18-200 lens is made for DX cameras, which have a smaller sensor. So the lens can't project a big enough image onto the sensor to cover the entire sensor, which is why you see the dark circles. The reason your other lenses don't exhibit the problem is that they are likely all FX (full frame) lenses. The reason it ...


31

Your camera is almost certainly applying lens correction for geometric distortion to the JPEG images. This results in the edges of the widest angle images being cropped slightly to correct the barrel distortion most zoom lenses demonstrate at the wide end. The 8.8-175mm (24-480mm FF equivalent) wide focal length ratio zoom lens of your Panasonic FZ2000 ...


14

This is field curvature. Simple lenses naturally project a curved field, not a flat one to match film or digital sensors. Modern lenses attempt to correct for this, but many older designs do not. In fact, it's sometimes called the "Petzval effect" after a classic design famous for this look. Interestingly, just this week Sony showed prototypes of a curved ...


13

Those have completely different impact. Vignetting Vignetting is a darkening of the corners or edges which depends on aperture and focal-length. In order to correct this in software, pixels around the edge must be gradually lightened in proportion to the light fall off: Slight vignetting is hard to notice unless the background is known to be uniform. Thus,...


13

There are three major considerations that make lenses with less distortion, vignetting, or any other "correctable" aberrations more desirable for many photographers than correcting later in post. Time constraints. While it is true that you can use postprocessing applications to correct for distortion, vignetting, and other aberrations, doing so ...


13

From the "Recommended For" tab of the Tamron web page for that lens: Tamron Di-II lenses are engineered expressly for digital SLR cameras with image sensors commonly referred to as APS-C, measuring approximately 24mm x 16mm. This means the image circle is sized for the smaller APS-C sensor, and is too small for a full-frame camera like the 6D. This is ...


8

Sensor based vignetting is a real problem for cameras with a large sensor and short flange distance (distance from mount to sensor). This is simply due to the oblique angles of incidence of light hitting the edges of the sensor, which isn't really flat like a piece of film, but contains a stack of objects starting with UV/IR/AA filters, followed by ...


7

Two techniques: The old technique (Gimp or Photoshop) Duplicate your image Set the top layer to Grain extract Apply a Gaussian blur to the top layer, enough to make vignetting disappear, but before halos appear around bright objects. The result will have a mostly gray background so use Curves or else to restore the blackpoint and add a bit of contrast. A ...


6

Many modern digital cameras are designed with the expectation that lens compromises will be... de-compromised... in RAW processing. That appears to be the case here. The preview image is based on the JPEG rendering, which includes this processing. The RAW file, however, does not. The amount of apparent vignetting will not be dependent on the scene, but on ...


5

Any wide angle lens will have problems with multiple filters, simply because the edge of the filters will start to encroach on the corners of the image formed.


5

This could be due to either the angular dependence of image pixels or the design (level of offsetting) in the microlenses. If you imagine an image pixel as a bucket with the light sensitive part in the bottom, light coming from directly above will hit the bottom with no problems. However the more oblique the angle of light the less will hit the bottom as it ...


5

As you know, a polarizing filter darkens the blue sky and this causes clouds to stand out in bold relief. The polarizing filter will increase the vividness (color saturation) of a vista without changing the overall color balance. Additionally the polarizing filter is able to cut through haze -- thus they are a valued asset for aerial photography and ...


5

Stopping down the aperture (using a larger f-number) will have a two-fold effect. The FOV of the lens is narrowed slightly by stopping down. For example, on your 14mm lens, going from f/4 to f/8 would narrow the physical aperture from 3.5 to 1.75mm which would in turn reduce the diameter of the FOV by 1.75mm in a lens with rectilinear projection (slight more ...


4

Vignetting depends highly on both aperture and focused distance. For example, see http://www.dpreview.com/lensreviews/nikon_35_1p8g_n15/3 which has an example on how wildly the vignetting varies by shooting a 35mm f1.8 for cropped sensors on a full frame at different focus and apertures. So, not only you should worry about apertures, but also the focused ...


4

In all cameras lens design affects lens vignetting. The lens has an 'image circle' which is designed to match the size of the film/sensor (which is why on FX cameras DX lenses vignette a lot). For digital cameras there is an additional source of vignetting called pixel vignetting. In short, the individual pixels of the sensor physically sit at the bottom ...


4

Having had similar problems with an enlarger light source, I made a correcting mask. In the dark, I affixed a sheet of black & white film and diffuser so that the light would play on this material. The film material has a low ISO. I turned on the lamp for as short a duration as I could. I developed the film in a very dilute developer. The resulting ...


4

To build on the other answers, this is indeed caused by a lens with undercorrected petzval. It is also vignetted, but more in one plane than the other. Here you can see a ray intercept plot for a large format tessar lens, these are also known as RIM plots or H'-TanU' Curves. On a RIM plot of the line is clipped, it indicates vignetting. You will notice ...


4

The size of the image circle depends on the lens. Specialty lenses like some fish-eye lenses aside, lenses are constructed in such away that the image circle covers the whole sensor/film area. So there is no such black area, but this is one aspect why ultra-wide lenses are difficult to design and expensive. The only circumstance where you may see such a ...


4

That lens is designed to be used for APS-C sized sensors with the Canon EF-S mount. It projects a smaller image circle than is needed to cover the larger full frame sensor of your 6D. Most third party APS-C lenses do not include the additional tab that prevents them from being mounted on a FF Canon camera that uses the EF mount. That is why you can even ...


4

Don't use 18-200 3.5-5.6 ED VRII on D750. That's DX (small) lens on FX(big) camera, the result is heavy vignetting, as you describe. Or the camera switching into FX crop mode. It's pretty much "a waste of full-frame camera", as you'd get better results when using much cheaper DX body. Get a 28-300mm f/3.5-5.6 VR instead. This is the closest FX equivalent of ...


4

The EOS 80D has a sensor measuring 22.3 × 14.9 mm. The lens, at 10mm, on this sensor, takes in a 96° horizontal angle of view. A step-down ring going from a filter diameter of 82mm to 67mm is quite a jump, and, with such a wide angle of view, is going to result in severe, objectionable vignetting.


4

Radial Falloff What you are seeing is known as radial falloff. The coloration is a result of the green-magenta compensation common to most color correction schemes in RGGB (bayer) sensors. Basically, the amount of light lost as you move to the edges of the frame is normal and more green is lost because there is more green sensitivity. Flat Field Correction ...


4

This isn't unusual. Remember that you're looking through the lens at its maximum aperture, and light falloff (aka optical vignetting) is at its worst at maximum aperture. (Physical vignetting is where the corners of the image are being physically blocked by the lens design, filters, hoods, or the like, but that's not the problem that you are experiencing.) ...


3

The first two look like typical light falloff at the corners that is normal for telephoto shots taken with a wide open aperture. Even though the aperture is f/6.3, that is as wide as that lens goes. With the darker the sky the falloff will be more noticeable due to the way light curves and gamma are applied to the linear data coming off the sensor. In the ...


3

In general terms, as you ask, well... there is no general answer to this at all. It entirely depends on the lens design, the sensor size, and, possibly, on obstructions mounted to the front of the lens like lens hoods and filters. For example, my phone has a 3.8mm focal length, and shows no sign of darkening in the corners. However, the Canon 1200mm lens — ...


3

You'll only see that kind of vignetting in two cases: If you're using a circular fisheye, where the lens is designed to have an image circle small enough to fall completely inside the frame borders. You're using a lens that was designed for a smaller format on a larger one (i.e., most typically, an APS-C ultrawide zoom lens on a full-frame sensor). Because ...


3

Use an overcast sky + put a semi-transparent textile or paper on the lens, covering the front completely. Basically the latter will be so off focus, it will work as a low pass filter, blurring everything, including the textile or paper texture. Just make sure what you use to cover the lens is pure white. Tissue-paper is a very good candidate. Use RAW for ...


3

Here are some ideas you can try... Use a Fresnel Lens at the light source to distribute light more evenly. This may already be built into the microscope. Use a convex-plano lens at the sensor. This will affect magnification, sharpness, and focus. Use flat-field correction software. This is a digital version of the film technique @AlanMarcus describes.


3

Vignetting in telephoto lenses is due to the entirety of the entrance pupil not being visible from certain angles. The entrance pupil is the image of the aperture stop as seen from the front of the lens. Detach the lens and look through it at a bright light. You should be able to see the circular wide open aperture. Now look at it from the side and you'll ...


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