Good product, quick delivery
The item works well and in my view should be included with the flat field foil. The foil as is was to bright to take flats that were long enough to prevent shutter shadow on my Atik 383 ccd used on my SV80S refractor. Once installed in the foil the RGB flats were excellent but the NB filters Ha, OIII and SII were extremely long, 480 seconds for an SII flat field. I had to remove the filter and use white sheets of paper in front of the foil and no filter for Ha, OIII and SII flats. RGB flats were achieved by keeping the ND filter in front of the flat field foil and white sheets of paper. It took some engineering but I was able to produce good flats for all my filters. The foil does generate a superb flat field that is even across the entire field. If you have a fast system be aware of some issues using this product but the resulting flats are excellent.