I've recently started imaging again after a hiatus over the summer (and as a direct consequence we have had almost unending cloud cover). When looking at the flat subs I have taken, i notice that there are now a fair few rectangular "shadows" appearing in the flats. These are new, as they do not show up in the flats I was taking back in the spring. Their appearance coincided with the emergence of a fair number of additional hot and cold columns on the chip (not sure if that is related or relevant at all, just mentioning in case). Any idea what these are and if they should be a source of concern? Uploading an image of a spring flat sub and a fall flat sub to illustrate the phenomenon.
Hi Mark, What's the list of equipment (models, optical parameters) in your optical train? (I should have asked in the frost thread). e.g. Scope -> Focuser/Rotator -> Field flatenner/focal reducer -> AO-X -> Guider -> FW7-STX-> Filters -> STX-16803 There's hints of one of them on the earlier flat. Due to the differences in exposure times and average ADU count, it's not easy to make a good comparison. Based on the size of your dust specs, clean your Halpha filter, and if there is an AO-X or FF/FR, clean that too. I suggest solving your suspected frost problem first, come back to this. If you have MaxIm, you can use Process... Pixel math to subtracted scaled versions to look at the differences.
Frosting is definitely the higher priority issue as it is preventing me from imaging. Equipment is as follows: TOA150 to Nitecrawler focuser to TOA67 flattener, to StarChaser 3 to FW7 Filter Wheel to SBIG 16803. Chroma filters. I should also say that the older flat was taken with the following setup: FSQ106 to Nitecrawler Focuser (a different unit) to StarChaser 3 to FW7 Filter Wheel to SBIG 16803. Chroma filters. So, if the rectangles are appearing in both (I can't see them for sure in the older flat (rescaled older flat attached)), then it is somewhere in the chain of SBIG equipment. They show up in the same place regardless of which filter is being used, so I am guessing not the filters or filter wheel? And I don't see how it could be the star chaser...which leaves the camera. I'm curious as to what these rectangles are, not just their emergence. They show up in the same place regardless of which filter is being used, and are definitionally not dust or debris given their precise rectilinear form . I assume they have to be electronic somehow? But I can find no mention anywhere of those kinds of shapes appearing in a flat?
I have not. Haven't gone near it (incredibly reluctant to touch things in the optical path). It was exposed when I removed the desiccant plug to recharge it, but I didn't touch it then and replaced the camera body immediately. Happy to do so, though, as there do appear to be some streaks somewhere in the path. But the 3 or so rectangles showing are very, very rectangular and at perfect right angles to the frame borders. Given their shape and alignment, doesn't seem likely that they are the result of anything that incidentally contacted the window.
We're looking at extremely low-contrast features here, a fraction of 1%. I think dealing with that sort of thing is what you do flat-fields for.
Completely agree. I imagine these will flat out. However, when I see precise rectangles appear in my flats, it understandably causes me to ask why? I've never seen anything like it and I can't find any reference on any forum to anything like them (not saying there isn't such a reference, just not finding it). That makes me concerned it may indicate there is an emerging problem.
I can't conceive of an electronics issue that could cause anything like that. The effect looks optical to me. I'd just keep an eye on it.
