How do I calibrate a lens if I am experiencing problems with lens cast?

QUESTION

How do I calibrate a lens if I am experiencing problems with lens cast?

ANSWER

Lens cast is the result of the sensor being exposed to light from a very sharp angle. This usually occurs as a green cast in one corner of the image, stretching into a magenta cast in the opposite corner. Capture One LCC (Lens Cast Calibration) tool can correct towards uniform light (to correct for lens vignetting) as well as dust.

1. Place the LCC plate as close to the front of the lens as possible. It is imperative that no light passes through the lens prior to passing through the LCC plate first.

To ensure the correct exposure, it may be necessary to increase your exposure time or put more light directly on the plate in dark conditions or setups. The placement of the source of light does not matter as the LCC plate will diffuse the light evenly.

2. Select the thumbnail of the captured image in Capture One and open the Lens tool tab (or create an LCC floating tool via Window -> Create Floating Tool -> LCC).

3. Select the LCC menu and click Create LCC. A dialog will appear. It will provide the options to include dust correction as well as Wide Angle Lens with Movements correction. The latter is designed to correct specific banding at the extreme edge of the image circle on the high-resolution digital backs.

The progress bar will appear and then the thumbnail will have an LCC label at the top.

4. Select the LCC-labelled image as well as any image you'd like to correct. Right-click on any image and select Apply LCC to apply those corrections to all the images. The same adjustment necessary to shift the LCC plate to neutral will be applied to these images as well.

Note that the LCC tool now shows which LCC file is applied to the selected variant. It also offers the option to disable Color Cast, Dust Removal, and Uniform Light. Each of these options has a slider bar which allows controlling the intensity of the correction.

It is very important to note that Lens Cast shows the relationship between the lens plane and sensor plane. If there is any change made (technical camera movements, swings, changes in lenses, etc), the LCC will be incorrect. It is highly recommended to capture the LCC plate shots while in the field or take the copious notes on movements.

LCC correction files are stored within the CaptureOne/Settings100 folder if you are working in a session. If you are in a catalog, the LCC information is saved into the catalog itself. If you pack or export a file as an EIP, the LCC adjustment information is included in the EIP as well.

An LCC file is restricted for use only with the serial number of the individual back.  Since sensors are unique and the camera calibration files that our R&D team develops for each sensor are unique as well, the LCC files can only be used with raw files from that same specific camera.