I have written a short guide to starting up with this camera containing my insights from over a years use. I have attached it as a text file. All I can say is this workflow works for me and also give solutions to common problems I have encountered. My apologies, all the calibration and processing tips are using Pixinsight. I have put links to useful tutorials and on line resources.
It is an excellent value camera but sometimes can cause frustration in new users. Hence the guide. This is not an ultimate guide so contribute on this thread if you have found problems but have found interesting workarounds.
This camera is my 1st CMOS style camera and it has been very challenging for me.
I have caught a number of recommendations for the camera which I have been following, but I can't say that I've been successful with the settings yet.
I've followed the recommendation that Spartacus has suggested in regards to 120 Gain and 30 Offset.
I've also heard different things about shooting Flats. One is that it is recommended to get at least 3 second frames with the Flats. With the Flats it is recommended to get the same exposure length and settings for Dark Flats instead of Bias Frames. I've heard that the preferred Median ADU would be a little above 30,000. These Flats don't have to match the Gain and Offset that the Light and Dark frames are.
I'm struggling with a number of the settings with this camera however such as;
1) My flats with the Median ADU of 35,000 have a red cast to them. The red value ADU's are typically 10,000 higher than the Median value.
2) I can see where the Red and Blue white balance is adjustable in the INDI Control Panel, but adjusting these values doesn't seem to lower the ADU for red in relation to the other 2 colors.
3) Is there a way of holding the cooler temperature to maintain a minimum temperature value?
What software are you using to process your images? If it is Pixinsight my guide covers most of the issues.
I usually use 25,000 ADU for my flats. I use a flat panel with a number of sheets of white paper to reduce the brightness to achieve an exposure time of around 3-4 sec. I also use a flat dark series taken at the same exposure as the flats to calibrate the flat (again this is in the guide). As the flats are always taken on the same session as the lights I never change the gain or offset (120 and 30 respectively). The white balance should be left at 50 for each setting in the indi gui panel.
The longer exposure is needed as the sensor response is far from linear at very short exposures.
You say that your flats have a red cast. This is a bit confusing as flats should not have any colour as you do not debayer the image. You just do a simple integration to create the master flat but do not do any other processing. If you view the resulting masterflat after stretching it should be easy to see variations in uniformity which relate to dust and errors in the light path which your processing will calibrate out of the light frames.
All the calibration of light frames using flats and darks are done before debayering the lights. Debayering is not done on flats or darks.
Let us know if this helps and let us know what processing software you are using. I only have experience with Pixinsight but there are other here that use other processing software.
Hi Paul, here are some practical experience notes:
1) I am using GAIN 120 and OFFSET 8, so the default values. I don't see any benefit in using higher OFFSET.
2) I am taking sky-flats, with typical exposure time 1-2 seconds. These sky-flats I calibrate with darks with same exposure time. I am also using flat tool in Ekos, my setting is 32000 +- 2000 ADU (histogram peak is in the middle).
3) I have set the white balance to 50 for both colors.
4) About the temperature, if |i understand it correctly, you want to maintain the temperature as low as possible? If yes, this not a good approach, as you need to have the same temperature for all you lights and their darks; flats and their darks respectively. I am using -10°C as target temperature for all my exposures and it is working well.
I am using Astro Pixel Processor for my stacking and Star Tools for the Post Processing.
My biggest struggle is with Flats, if not for this I think I might be getting somewhere.
With my flats I try to be somewhere between 25,000 to 35,000 with the Median ADU. I purchased a light box to aid in tweaking the numbers. I know that the combination of longer flats and dark flats should yield better results; for this reason I've not really adopted sky flats as the dusk sky can rapidly change with ADU. It has been a challenge in getting the flats to stay in an acceptable range. Normally the issue happens to be that the light from the light box raises the ADU too high even though it is on the lowest setting. I have been playing around with white T-shirts and acrylic additive to the light box to tone it down a little. From there I have tried a grey T-shirt, which brought the ADU too low. From there I experimented with lighter shades of grey T'shirts which I had mixed results.
Recently I tried using an UHC filter that I happened to have. Now that I think about it, this may have been causing the red cast that I talked about. I don't know if I ever got a good flat with this. The red levels were 10,000 above the blue and green. It's a shame that I couldn't get this to work as it really picked up the Veil Nebula well.
Yesterday I tried out the 50 White Balance that I was glad to find suggested here.
Unfortunately in looking over these flats they were truly flat. I think with the red value so much higher than the other levels it must just be messed up.
By any chance would anyone know the trick towards getting good flats with UHC or other prominent red filters?
This evening I received a cheap UV/IR filter which I immediately tried out. I tried a 5 second image. I was elated to see that red, blue and green ADU numbers were very tight and a very good vignetting and dust mote image preview showed up. This is within the light range of the light box towards the low side.
I'm hoping to apply this to an imaging session this evening.
Thanks for your help! I'll feedback whether the UV/IR filter finally achieves what I've been after.
I use a DIY electroluminescent panel and needed to use 6 sheets of white paper to reduce the levels to allow for a exposure of 3 secs approx. Any filters that you use in taking your lights should be used in the flats. As an example I tend to use a ZWO duo narrowband filter as I am in an inner city location.
All my darks and flats and flat darks are taken with 120 gain, 30 offset and 50/50 balance which are my default values for all my light frames. I seem to recall major problems when I used darks with different offset values to the lights. This did cause a red cast that I could not process out so I keep everything standard now and have not had any issues since.
I tried to use APP a year back and could not get it to work satisfactorily and if I recall I did have issues with the flats. In the end I gave up trying to get it to work as I already was using Pixinsight and had spent some time getting over the steep learning curve of this software. I just did not have the time to invest in APP.
I have never needed to examine the individual colour balance of flats as all the calibration is done before debayering and it never seemed important. The resulting images after calibration and integration of light frames always have a prominent red cast but this is easily fixed in histogram transformation. You can check this by doing an auto stretch using unlinked RGB channels.
Have you tried processing your lights without using flats and do they look OK?
Hopefully someone using APP and familiar with how it works can help.
I found the tutorial by "Bulrichi" that I have referenced in the guide a great help in understanding the camera and how calibration works. However I had to read it a few times to really understand it fully.
Hi Paul, I hope this will help you:
1) You cannot use different filter setting for taking lights and flats. This will result in a different "light profile", for example the UHC filter will cut some part of the light spectrum and resulting flat cannot be used for calibration of lights, that are taken without such filter.
2) Taking sky flats in Ekos is really easy. You just sset target ADU with some +- variance and the software will do all work automatically. You just need to take exposures during dawn or dusk, on the opposite site where is sun. And the sky needs to be clear, without clouds. You can start with exposures 10 - 20 minutes after sun is under horizont. If exposures are short, you will skip and wait few more minutes and repeat this steps until you get exposures in range you want, e.g.: 1-3 seconds. Once ADU are not in the specified range, ekos will automatically calculate new exposure time. And this will repeat until you get enough exposures. I am taking 12-20 exposures.
I hope I wrote it understandable
I am making sure that my image train is the same every time that I start an imaging session. If I take UHC Flats and Dark Flats I follow this with UHC Lights and Darks.
Thank you for your description on how you take Sky Flats. This certainly is a viable and simple option. Personally I chose getting a light box as I was aiming for longer flat exposures which I have heard from some that this camera prefers. At the time I tried Sky Flats I had a 10 second download delay (now this is 2 seconds with PowerLine adapter) with Ekos between 5 second Sky Flats. By the time the images were completed the ADU variance due to the darkening sky was over 10,000. Of course a light box carry's it's own set of challenges, such as adding on T-shirts to deaden the light over longer exposures.
The main thing is to stick with what works for you.
I haven't considered using stacked paper for flats. That will be another idea to try should my grey T-shirt and Light Box method fail.
I have attempted stacking my data without flats once. What I discovered was that there was a lot of vignetting, otherwise the image was fairly clean looking.
I did give a once over on what Bulrichi wrote. Even though I don't use PixInsight he had a lot of helpful information. I am still kind of fuzzy on a lot of the terminology but this article helps.
This evening I took some Flats using my UHC-2 filter. I think the captured image might help in conveying what to me poses a problem. This of course is what shows up while in Ekos Capture mode. I'm assuming that the frame is stretched in the FITS viewer. It does look totally different upon import on my MacBook Pro. (The image is quite flat when imported)
This shows how inflated the Red values can be.
Since there is such a variance with the ADU values I am wondering whether this would be considered a good flat frame? If not how would my capture technique need to differ to get this to a better result?
Sorry for invading your tutorial sticky thread. I am hoping that in getting an understanding of what constitutes a good restricted band flat image that it might be helpful to others with this camera.
I think that you are viewing your flats in the fits viewer in a stretched and automatically debayered form. If you open up "configure KStars" and open the "fits viewer" tab. There are a number of options. It is likely that you have auto debayer ticked. Uncheck this and you should be able to view the flats in mono, just auto stretched. This will give a better idea of what they look like. Remember that the flats are never used in a debayered form so the red cast is irrelevant. Just stacked into a master in undebayered form. Your vignetting will be dealt with in the calibration of the lights with the flats (and darks).
The fits viewer just views the images but does not change them so you don't need to worry that there is a problem. You can still use the flats that you have taken. I have never examined any of my images using the autodebayer in fits viewer as I find that it is not as helpful as a mono image in determining contrast and exposure.
All my final calibrated and integrated lights have a prominent red cast but this can be dealt with in histogram transformation. As I said, a quick way of fixing this in the final image is doing an autostretch using unlinked RGB channels. This largely removes much of the redness.
You may be able to attract more help in relation to the use of APP with this camera if you were to start a new thread with the specific problem in the heading. Using the sticky does not really address your specific problem. It may be worth posting a final image pointing out the issues you are concerned about.
I just can't help much with APP and how it handles calibration etc. Happy to advise about KStars related issues though.