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How'd you figure out about this ratio thing? Is it made up or is there someplace online that gives info about the best ratios for different emission nebulae? Gross estimate from my tests with the same nebula (OIII/Ha ratio) and the results from this one for SII. And no, it is just for this one but in general you wouldn't go too wrong with the other emission nebulae using the same proportion. |
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Ok a couple of fits are posted in the link. It looks like I have an even number of each of SHO files. About 100x5minutes for each. On a tangent... Let's say I dithered every frame. (I think I did, or every second frame). How does doubling my number of actual exposures differ from say simply making a second copy of all my data, then adding that to the integration? Given 100 frames, how much difference is more exposures going to make? Won't the light pollution simply be additive like the nebula is? |
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Sean Mc: Makes no difference, there is no actual data added. Might as well add 10x is still the same SNR. If properly calibrated additional exposures will always add signal and thus improve the SNR because the background mean value is always removed from the stack (but not so its noise which decrease with the square root of the number of exposures) while the mean value of the signal is always added. |
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Sean Mc: As I suspected the fault with the gradients lies in the flats that are, I shan't stress strongly enough, very very wrong (especially the SII one which bears no relationship with any possible flat profile). As interim measure, before you find what is wrong with them (when and how you take them would be the main questions) you'll be better served in the interim to redo everything without using these flats (none, not even Ha) and use Graxpert for final flattening. I'm sure the final stack would look much better. |
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| Haha oh boy... Do you have a suggestion for taking flats with the 294mm pro? I'll restack without them and see how it goes. |
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| Sky flats. Better still dusk flats, just before sunset pointing at the zenith (and not tracking), start with SII then Ha and finally OIII. 20 each. 1/3 of the histogram at most. |
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This to show what is happening. Top (left OIII/right SII) are the original lights. Bottom the same files once flattened (divided) by their respective master flat frames. Can you spot the difference? |
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ea the flat field error is strong, which probably robs the Oiii frame from signal. Here is my quick processing of it in the FORAXX palette utility. Graxpert for each channel BXT Autostretch NoiseX StarX Histogram transformation, to bring the blackpoint to barely from clipping the data. ForaxxPalette utility I then used the Ha frame to create a mask and use curves to improve contrast and saturation I use an Ha frame as an L channel because it was by far the cleanest frame. Typically I like to combine the channels for an L sometimes, but in this case the Ha frame preserves far more details. Further curves Rescreen foraxx stars.  |
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Sean Mc:andrea tasselli: Some years ago, there was a thread on CN that eventually revealed that the ASI294 uses a Sony sensor package that doesn't allow the sensor to be most effectively cooled, which gives rise to many of the problems calibrating this camera. I don't recall exactly when the thread was started, and the search there sucks...but...that is potentially part of the problem. |
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I think my bin2 master dark is messed up too! I uploaded it to the folder. Does it look right? A dark shouldn't have a gradient/ vignette right? |
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Sean Mc: If your ASI294 has the cooling issues, then, its possible. This camera is known for cooling issues, gradient issues, interference issues with filters, and there are even some theories about dark pattern "lock in" among other things. I have not been able to find the thread on CN where a lot of the issues were investigated, and I think some potential procedures to minimize them discussed. I would search CN threads related to ASI294 cooling, dark calibration issues, etc. These problems are pretty well known for this camera. |
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Sean Mc: That's right. If there is any then you have a light leak problem (which may tie with the issue with flats). It should look something like this:  |
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I have checked and there is definitely a light leak when taking darks.  |
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| Well… lots of work for me to do. Next up - collimating my edge 8 :/ |
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I posted 3 new masters. Calibrated with new darks. Unfortunately the original flats were calibrated with probably wrong dark flats and there’s no way to fix that now. still…. HUGE difference. It’s amazing the effect that messed up calibration frames can have. thx all for the help! |
