Lacerta Flatfield Box in lightweight design with neutral white LED light - dimmable
A Flatfield Box (FFB) is ised for creating Flats which are needed for exact calibration of astro images. With them, vignetting (darker edges) and also shadows of dust particles in the image (called donuts) can be removed. That is not only necessary for aesthetics, but only a perfectly "flat" image can be processed in a way that weak signals become visible. The contrast can be increased more, the background does not become blotchy and weakest extensions of the object become visible.
Use of the Flatfield Box:
With this flatfield box, so-called FLATs can be created. These flatfield exposures capture vignetting and "donuts" which are caused by dust particles on sensor, filter or corrector. They can be seen as unaesthetic dark rings or areas in the image.
In the course of image processing, these distracting phenomena are subtracted from the image. Almost all image processing software offers the possibility of subtracting a flat.
The result is a perfectly smoothed image. The contrast can be increased considerably more to show finest details of the objekt, and the background stays evenly smooth.
The advantages of the Lacerta FFB plus LED flatfield boxes: The LED flatfield generators deliver a very colour-neutral light, so the colour channels are evenly strongly saturated. This is the ideal base for a successful flat even with narrowband filter, with DSLR or with color astro cameras. The illumination of the LED Flatfield Box is extremly uniform, even better than with the EL films, which still have a weak variation over the surface (banding). Unlike the EL film, the LEDs do not flicker with the line frequency, allowing significantly shorter exposure times like 1/500 seconds. The LEDs can be controlled in the brightness. With this, for example cameras with mechanical shutters can be used which need a somewhat longer exposure time for a correct flat. A flat with an exposure time which is too short would be flawed by the shutter. We recommend a minimum exposure time of 2 seconds per flat.More information about the DIMMER30KHZ which is included in the scope of delivery.
|Plastics for low weight
|Dimensions flat field box:
|212 x 212 x 60 mm
12 V cable with cigarette lighter plug
How do I get a good flat field image?A good flat compensates for edge shading (vignetting), but also for darkening caused by dust on the filter, sensor or corrector. The background becomes even, the contrast can be raised further to make finer details visible in faint nebulae. The following basic settings should be noted: The ISO or gain setting must be the same as for the lights, i.e. the actual astrophotography. Telescope, camera and accessories, such as filters, off-axis guider etc., must be the same as for the actual exposure, also the position of the focuser should be unchanged. The exposure time should be so short that nothing is "burned out", i.e. overexposed. Only in this way can the flat unfold its full effect. We recommend an exposure of 30-50%. The flat should not be burned out, but it should also not have any unexposed areas.
How do I find the right exposure time with the shooting software, for example Maxim DL?
The ADU value (Analog Digital Units) helps here. Every capture program shows this value when you move the mouse over the image. In the center of the image, where the illumination is highest, the ADU value is highest. The longer you expose, the higher this value becomes. If the ADU value is higher than the maximum value of the camera, the image is overexposed. A camera with 16 bits has a max. ADU value of 65536, one with 14 bits has 16384, one with 12 bits only 4096.
The exposure time of the flat should be so short that in the middle of the flat the ADU value is at most 50% of the maximum value of the camera. Then the flat looks well exposed. We recommend to take at least 10 flats per exposure and to process them to a "master flat".
If the flatfield box is too bright, that means it always produces overexposed images, then a white paper, which is fixed in the flatfield box, helps. This will dim the light and allow for slightly longer exposure times.