![]() ![]() All being well you should end up with a result frame with a median value of close to 0.1 (using the normalised real range in the statistics tool). To do this properly you'd probably want to use an expression like : (A + 0.1) - B so that noise doesn't end up clipping loads of pixels to negative values that are then truncated to zero. Verify this by subtracting "B" from "A" using PixelMath in PixInsight or something similar. If they're markedly different then you either have a problem with the light source (flickering at a high frequency that is sufficient to create different brightness levels from frame to frame and may appear as a gradient), or perhaps the camera/electronics but seems less likely. They should be pretty much the same give or take a few ADU or tens of ADU. Compare the median ADU values of "A" and "B". You may have done this already, but the first thing I'd try taking a flat (call it "A"), taking a second flat (call it "B") then physically rotating the panel 90 degrees and taking another one (call it "C"). Thanks for the information. However that's not my problem then as my exposure is less than 1 sec. The idea is that once the exposure is long enough, so the ratio of flat exposure time to unwanted exposure time during progressive read-out is sufficient to reduce the gradient to a negligible percentage of the median brightness. You probably wouldn't be able to dim the panel enough for LRGB filters, but possibly for narrowband., so you might need to use some material over the panel to reduce output, e.g. The solution is to either set the brightness of your flat light source and/or higher gain to achieve a short exposure less than the cut-off (no gradient) or do the opposite and use a dim source / lower gain to achieve a much longer exposure. For lights with relatively little signal, this does not matter much, but for flats where there is a bright light source you can end up with a gradient of maybe 5% from top to bottom of the flat if the exposure is longer than the cut-off. Shorter exposures below these limits effectively stop the exposure at read-out, but longer exposures read out progressively which means that pixels at the top of the sensor are exposed longer than those at the bottom. Apparently this is to reduce the noise in longer exposure images but ZWO never really explained how or why. With the older versions of the 1600 there is a change in readout modes for exposures longer than 2 seconds (if using USB3) or longer than 5 seconds (if using USB2). the newer "Pro" version has onboard RAM to overcome these issues as it speeds up the readout greatly. I can only speak for the earlier versions of the 1600, i.e. Do you know what exposure is needed to avoid the gradients? Nice writeup, you mention that the ASI1600MM-C give gradients on longer exposure flats, that's exactly the problem I've trying to solve for weeks since mounting a EL flat panel on the wall of my new observatory. Used it this week and results are as good as using my DIY manual diffuser and cloudy sky method, with less risk of floating away in a garden under 2 inches of water!Īnyway, full write up with shopping list, photos and diagrams is available here: This is ideal for my ASI 1600MM-C (not Pro), since longer exposures use a readout mode that creates gradients in your flats. At full brightness I can do flats for LRGB filters in a couple of hundredths of a second, and about half a second for narrowband filters. It is now mounted on my observatory wall and I just have to park the scope and SGPro can take care of the flats for me for a fraction of the cost of the cheapest automated flat panel. I hacked out the original controller and hooked everything up to a 5V Arduino Nano clone (£5) and a MOSFET (£2) and used some Alnitak emulation code written by one of the SGPro developers. The light seems very uniform and I didn't need to add any futher diffusing or similar elements to make it usable. ![]() The one I got has two strips of 30 white LEDs along the long edges - internally it has a reflecting layer, a clear acrylic sheet which the LEDs shine in to and then a diffusing layer sandwiched on top. The key difference seems to be that many of these tracing panels have a grid of LEDs close behind a diffuser panel which creates dark and light spots, or the are edge-illuminated from one side only. Surprisingly the first one I bought turned out to be a real winner - A4 sized, USB power, 60 LEDs and dimmable for £15. Total cost was less than £25 - I used one of those LED tracing panels that you can find all over Amazon and eBay. I've finally managed to get round to building a remote control flat panel (suitable for use in SGPro and any other software that supports Alnitak Panels). ![]()
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