Hi, I have an AC4040. I also use ACP. When using ACP, observing scripts allow for selection of the readout mode, High or HSP, etc. I've run into a minor issue when using an ACP web browser to allow uninformed and inexperienced students to acquire single images of an object with auto calibration. When using ACP's single image interface, it appears to be defaulting to HSP. Since for this type of outreach imaging we are only doing 30, 60 or 90 second exposures unguided, I'd rather use High and use a dark frame library for autocalibration done with High readout mode. I may be able to redo the underlying ACP single image script to force High to fix this, but if I cannot, it occurred to me that a simple fix might be to go into the AC4040 advanced settings and change the minimum subexposure that HSP uses to 90 seconds. If I understand what HSP is doing (I may not!), I believe that will effectively cause the HSP images to be 30, 60 or 90 second High exposures so my equivalent 30, 60, 90 High darks will work. Of course, if the exposures go over 90 seconds, then this won't work, but we won't be doing that for this type of image acquisition. Am I correct or are there other things that would make an HSP dark with 90 sec sub setting not work as a dark for a 90 sec High light frame? Thanks Mark
I am going to do an experiment tonight testing this, I'll post the results. Mostly just intellectual curiosity about what is going on under the hood with HSP.
Hi, for those interested, I created a 90 second HSP dark master with 90 sec minimum subexposure and a High dark master with 90 sec exposures, and then used each of the masters to calibrate a single 90 second High light frame. I've examined the two results closely, super stretched, and I see essentially zero difference in noise, quality, etc. Using pixel math, if I subtract one from the other I get a very low signal residual image, with no pattern. If I reverse the order of subtraction, I get a slightly different low signal level result, but also no pattern. I'd expect something to show up in the pixel math test, since the two master dark frames were created from 10 different subs each and of course will have some variation due to the universe we inhabit. An interesting experiment to me, probably super obvious that this would be the result to those who know what is going on under the hood with HSP. By the way, FWIW Bob Denny directed me to the right spot to change the simple image setting to High, in a pretty obvious spot that I missed, so this isn't necessary anymore. This has helped me better understand HSP in general. Best, Mark
High Gain Stack Pro (HSP as you call it) is designed to stack up to 16 sub-exposures, based on the configured sub-exposure time (15s is reasonable, depending on the sensor, and your tolerance for logic glow, you can go longer). It literally just divides up a longer master exposure into the subs and co-adds them in-camera. No magic.
Hi Colin, I understand how H'G'SP works in general, and have been using it that way for a while. I'm generally using 30 sec subs for longish SHO exposures. I was just curious if it literally was High mode individual subs under the hood, to the extent that you can do what I did with respect to darks if you are inclined to (I wouldn't routinely do that, since there would be no reason to, but I had an edge case that it would work for, now not needed). Mark
By the way, in my defense of the shorthand HSP, in MaximDL, the readout modes are referred to in the pull-down menus as: "High StackPro", High, etc. Your HGSP made me wonder if my recall was faulty.
HSP is just fine by me. HSP darks are built the same way - individual subs co-added. As an aside, a CCD cheat that does NOT work on the CMOS is "scaling darks". Some folks would take a 60s dark on a CCD, and then scale it up to match a longer exposure. eg. 600s exposure. That does not work on CMOS APS sensors, as there is more than just dark current at work in them; the pixels are active, and then there is logic glow.
Since the flats are used to divide into the light images, I think the impact of the "flat-darks" isn't going to be significant between two short exposures. Am still learning what's possible and what the limitations are.
