mgutierrez

Thanks for the reply Han. That's much clearer for me. Regards

Han, thanks for such a nice feature. I have a question. Point #2 requirement states that background value must be higher than pedestal; if not, expose longer. The provided light must be uncalibrated, right? So, given a particular pedestal; how is possible that the corresponding light could have a lower background even with very short exposures since that light has already the pedestal? For example. Let's say my pedestal is 400, as measured from the corresponding dark. The corresponding light should have always a background value higher than 400, since the pedestal is included in the light. Am I missing something? m

https://www.cloudynights.com/topic/864002-siril-tutorials/?p=12498709

I also noticed this. Site is down since a couple of days ago. Any news?

hi all, just a quick update. Switching to Astronomik MaxFR version of OIII filter, has led to a HUGE improvement: 27min of an uncalibrated OIII stack (same object). Left, the maxfr version. Right, the older one. Note the brigther corners on the right image. Watch the corresponding calibrated stacks (on the left the maxfr): The difference is evident. Note, however, that maxfr calibrated stack has still some gradient. But that's a completely different history. I expect that kind of gradient: bad flats (OIII flats are specially tricky), light pollution (OIII filter is more sensitive to lp compared to Ha or SII), etc. I consider that's completely normal. In fact, a standard ABE or DBE gets rid of it completely. Not the same with the other stack. Is a pain to deal with it in post-processing. Well, I just wanted to share with you my findings. m

Thanks Steve. Yes, esprit and the 268. Great combo 😄

yes, sorry, I missed the details (pasted from astrobin): Frames: Astronomik Deep-Sky Blue 36 mm: 15×120″(30′) (gain: 56.00) f/5.5 -5°C bin 1×1 Astronomik Deep-Sky Green 36mm: 15×120″(30′) (gain: 56.00) f/5.5 -5°C bin 1×1 Astronomik Deep-Sky Red 36mm: 15×120″(30′) (gain: 56.00) f/5.5 -5°C bin 1×1 Astronomik L-3 Luminance UV/IR Block 36 mm: 178×60″(2h 58′) (gain: 56.00) f/5.5 -5°C bin 1×1 Integration: 4h 28′ Darks: 50 Flats: 20 Bias: 500

Yes, sure, first image I upload here, not my first image ever 😄 Thanks for the comment

Hi all, This is my first image I upload. One of my favorite targets. Hope you like the rendition.

yep, sure, I got your point, thanks!

yes, I thought about reflections. But this is the second filter I try. I also guess that it should affect to other filters as well; at least not only to OIII. Furthermore, this filters have already a blackening edge. I'm in contact with another user and starting to think that this is the "normal" behaviour of this filter and the trick is to take the proper flats. Honestly, I don't know how a light with white corners can be considered normal, but now I'm considering it.

Thanks for the reply. I also think is not normal. These filters have already blackening edge. Also, this filter was replaced by astronomik because of a similar issue (see 1st post). My guess is that for some reason I cannot understand, I'm meeting the requirements for a perfect storm.

I will summarize the question: do you think is normal to have bright corners instead darker ones in a single light?

absolutely sure steve. I was going, in fact, to upload the non-dark version but I saw some hot pixels and I didn't want you to think I'm a bad boy ;-D

That's it. Well, only calibrated with darks to remove hot pixels (without darks, the result is obviously the same)

I'm having this issue from the beginning. I deal with it with post processing, but I would like to get rid off it. Many times makes the post processing quite difficult. It has nothing to do with the target. Longer exposures makes more evident the issue. In any, case, being well exposed, the final stack will reveal the gradient independently of the individual exposure time.

No. That's the problem. The stack without flats shows lighter corners. Download the file ending in NOFLATS from the dropbox link

forget about the flats. Do you think the "reverse vignetting" on the single light is normal? (the gradient is more prominent in the stack) PS: thanks for pointing out about the stars. Yes, I do use the flattener. I usually have a quite flat field. This time I rotated the cam so I may messed it up; no worries

Hi Steve, Thanks for the reply mate You can find here some files: https://www.dropbox.com/sh/6ajza48ha3vkcpg/AAD-F6PtCeUilew4x189jBPRa?dl=0 There is a single light, the master flat, the non flat calibrated master light and also the calibrated one. The gradient on the single light is not so evident. After stacking, it is revealed completely. I always have some kind of vignetting on all of my lights with different filters. What makes this vignetting special, is that is reversed. That is, corners are lighter, not darker as usual. My flats, as you can see, look like a normal flat: corners are darker. But since the lights have an opposite gradient, what the calibration does is to exaggerate these gradients. I want to focus on the lights. If that gradient is normal, then I would focus on taking proper flats (sky-flats, a different flat panel, etc.). But to me, those gradient present on the single lights should not be there. That's basically my question. m

Hi all, I'm searching someone who shares this setup with me: QHY268M camera, Astronomik OIII 6nm 36mm filter (non-MaxFR) and a Esprit100. I'm experiencing a weird issue that I cannot fix Here is a only dark calibrated master OIII: Note the white gradient towards the corners. My master flat looks like a regular one: darker in the corners and lighter towards the center. But since the gradients are reversed between them, the flat calibrated OIII master is even worse, with more white gradient. My master flat may be bad or not. I don't know and honestly I think it's not important: the white gradient is present on my uncalibrated master, and I think it's not normal (or it is?!) This filter was replaced by astronomik a couple of months ago for a similar issue. Similar, cause the gradient was mostly present on one lateral; my guess is that the other lateral had some spot on the filter. So I think it's not a filter issue. I also swapped the OIII position within the fw, just in case. Same result. Shooting different objects at different altitude and completely different position, makes no difference. What do you think? m PS: sorry if I posted in the wrong forum

that matches very exactly with the stddev practical aproach (to have a stddev > 3xbias_stddev on the background) among other calculations I'm playing with. I was aware I was using ADUs, and noticed as well that converting to e- led to more correct results, but I thought it also should work with ADUs. Clearly is not Thanks a lot for your help and clarifying, Vlaiv. Very useful

Thanks for the prompt reply@vlaiv I need some time to digest your info 😅 and make some tests. Just wanted to clarify your doubts. Read mode is effectively 1. At gain 56 the camera enters high gain mode and read noise decreases drastically, as you can see in the graphs. Furthermore, read noise, gain and other values, have been calculated with basic ccd parameters pixinsight script, and also compared with other colleagues which have characterized the qhy268m. I would trust the results. Regarding the dark noise, yes, I though about it but since this cam has a very low dark noise and the sub is not too long, I ignored it for this example. Maybe I shouldn't do that. I will come back to you with the proposed tests. Thanks a lot for your time

Hi @vlaiv, I'm trying to make the same exercise with one of my lights, just out of curiosity. Let me explain, cause I cannot figure out what's going on. I have a 60sec light (M33): https://www.dropbox.com/s/j9bglelhgmkh4v1/M33_Light_L_60_secs_035.fits?dl=0 And the corresponding bias: https://www.dropbox.com/s/qh0ah4ix1g5shnn/M1_G56_OFF30_Bias_300.fits?dl=0 Note the following parameters: Gain: 0.333 e-/ADU Bias mean value: 486.9 ADU Bias stddev: ~4.9 Read noise: 1.61 e- ---> 1.6 / 0.333 = 4.83 ADU ADC depth: 16bit -> no need to convert from DN to ADU I've read multiple times that a more practical approach to make sure I'm swamping the read noise by x3 (read noise, not LP signal, as you correctly clarified) is to get a clean region of my light, with no stars nor nebulosity (only background) and measure its stddev. I want this stddev to be at least x3 higher than my bias stddev. This makes completely sense to me. But cannot match this approach with yours. I'm doing something wrong. ** editing to complete post. Pressed sent accidentally ** Using ImageJ and defining a clean region, I get a stddev of ~17, which is > 3x bias stdev (4.9 x 3). That means is sufficient swamped. Furthermore, using Rista's formula, I get a very close DN compared with the current DN background of my image using a swamp factor of 10 over the background signal (don't want to extend explanation with this calculations). I assume is right Using the same region, I get a mean of ~565 ADU. Background is, hence, 565-486.9 = ~78. Read noise is 4.83 ADU (I guess I need to use ADUs here...). Then, I need a signal of (4.83*3)^2 = ~209 ADU. 78 / 209 indicates I'm clearly underexposed (~0.37 times). What am I doing wrong here? Why the results are so different. I'm clearly missing something quite trivial here... Thanks

Nice shot Steve! LP does not deteriorate the photo at all. Color and nebolisity process is outstanding. Looking forward to see your progress! m

No worries Dave; thanks for the feedback!