Inevitably, the Earth's revolving around the Sun and at some point of time, it's a good idea to be prepared for more frequent (L)RGB imaging. While narrow band imaging is really a lot of fun, galaxy season will come sooner than later. Since there hasn't been a streak of clear consecutive nights these recent days, giving me the opportunity to go for another set of SHO data, I chose to play with the broad band gear and be prepared.

I still have my stock Canon EOS250D DSLR around and I was wondering which path I should take: use the DSLR only for the brightest objects (e.g., M31, Plejades) and use my ASI294MM doing LRGB work for all the other stuff OR see how far I can push the unmodded DSLR to be the RGB working horse (and add L from the ASI). 

To send ahead: I'm a Swabian. For those who don't know the cultural impact of this fact: we're excellent machine builders, we invented the motor car and besides all this and most importantly, we are notoriously stingy people. Hence, I'm still not investing in an electronic filter wheel as I just don't want to spend these Euros. I want to stick to my filter drawer and run a single filter through the night. So, unless I want to spend four nights on an LRGB target with the risk of interruption from cloudy nights, I would have to find a way to change filters during the night without the need of getting up and doing it manually.
Therefore, I took a closer look at my DSLR again. Recently, I mostly used it to assess the optical quality of my optics as it would allow to detect color fringes from optical aberrations. Fortunately, my optics are clean in that sense. However, I had noticed some psychedelic color background noise which gave me some concern the DSLR might not be very suitable after all for more serious imaging. An additional common issue is the fact that the sensor isn't cooled which supposedly makes calibration more difficult. Furthermore, the unmodded DSLR is said to be rather insensitive to the wave lengths of Ha and SII. While that's true in a relative sense, it's false in an absolute sense. The camera does still collect Ha data but at a much lower rate than a dedicated mono would do and of course with much less contrast than a mono + NB filter.

Now to the image: it wouldn't be me if I didn't do things that are against mainstream wisdom.
So what did I do:
1. ISO setting: the 250D doesn't have a sensor that uses a high conversion gain which means that the largest dynamic range is likely at lowest ISO. It basically behaves like any other dedicated astro camera in that sense. Hence: maximum dynamic range through lowest ISO.

2. Dark frame subtraction an temperature: Why should we subtract dark frames? To compensate for dark noise patterns as the pixels aren't pair-wise identical. Otherwise the dark current is an offset in the signal.
Hence, I captured a 600s dark frame with the DSLR at room temperature and analyzed spatial variations. The results was that I haven't found anything worth mentioning. There is no star-burst or amp-glow and further more (Canon) DSLRs are actually using technology to reduce overall dark current. 
Long story short: just don't care about Dark frames. Dither sufficiently for the statistics being on signal's side.

3. Low Ha-sensitivity: Well, it is what it is. In the end however, the camera itself using a daylight white balance which will result in a natural color image. Something many people are looking out for. So, nothing to worry about.

4. Moon: Yep. Very annoying when capturing LRGB. However, clouds don't really care about moon phase and neither do I. Last night was clear and so I chose to try to put theory into some practical results. 

The result of this "swimming against the tide" is shown in the image above. Due to the low ISO, I was using 300 second exposures. Sadr is a very bright star but still the only one heavily saturated. I dithered after each frame. The lights were calibrated with bias and flats. The post-processing was done in PI. No extraordinary processing steps. The most notable processing thing is that I've color saturated the reddish nebula regions. The rest if "common" post processing.

After all: I believe the approach is worth it, the stock DSLR capable for galaxy work to come, money saved and mainstream wisdom not the end of knowledge.

Please feel free to share feedback.

CS!

Björn