I recently put together a nice portable astrophotography setup incorporating a new ZWO AM5 mount, a WO RedCat 51 telescope, ASI533MC Pro Camera, an ASI Air Plus.  Here is a picture of that setup:




The entire setup weighs less than 25 lbs including tripod and mount.  I have found it works exceeding well and I have been having just a blast imaging from my back yard in northern area of Phoenix Arizona.  Since I wanted to image in lots of different locations and I wanted this setup to be able to work in a very portable mode, I decided on working mostly with the ZWO OSC ASI533MC camera.  I've found this camera is a great fit for this application as most times when I work portable I will not have days to capture LRGB multi filter setups.  I need to get everything all in one night.  I had already owned two of the four Optolong multi band NB filters so I in setting up this system I purchased the two others so in total I have 4 Optolong NB filters: L-Pro (basically city lights), L-eNhance, L-eXtreme (7nm) & L-Ultimate (3nm) all 2" versions. The end of last week I was looking at the weather forecast for my home and realized I was looking at 4 consecutive nights where the seeing and photographing environment was going to be extremely similar.  I thought this was an excellent opportunity to image a nice object and use a different Optolong NB filter on each night so I could get a qualitative look at the differences between these 4 filters.  I knew, quantitatively, that the higher cost extreme narrow band filters of the eXtreme and Ultimate would have the lowest background noise and enhanced nebulosity at the expense of reduced faint star visibility while the cheaper wider filters of the L-Pro and the L-eNhance would show a wider color range and more faint star fields.  It is one thing to look at graphs and quite another to look at images.  So this was the premise for my project.  For completeness let me review my acquisition results as well as my post processing workflow so others can understand my baseline approach.

Image Acquisition

My location in Phoenix is not center city and typically I have seen, via my SQM meter, I will typically start at a Bortle 7 sky around 9pm on a moonless night and end just into the Bortle 6 range around 4-5am the next morning.  While my setup is on a tripod I did not take it down or move it from night to night so I could keep framing and such as close to similar as possible.  Every night I would redo my PA as well as check my Guide focus and Guide calibration.  My main camera, the 533MC was set to a gain of 101 which just puts it into the low read noise category.  From analysis of my SQM seeing and information on the SharpCap website of ideal sub frame length I decided that all subs were going to be 300" (5 min) and that the number of subs would be limited to 90 which comes to 7.5hours of imaging.  This works well for the window of approx 9pm - 5am.  On these particular days, the moon was still not up and in fact down over the horizon before I started shooting.  I have a new Pegasus Astro Meteo sensor and I recorded my sky SQM readings at the start and end of each imaging session.  I also loaded my PA, RA, DEC, Total error data into a spreadsheet so I could easily see if my imaging was on track from day to day.  My guide camera was a ASI290MM Mini.  It was set to guide using 2sec exposures with a gain of 400.  I was using a dark guide camera library that the new beta ASI Air Plus uses.

Post Processing

I use PixInsight and Photoshop mostly to post process all my DSO images.  I am not an expert using PixInsight but I know enough to get a basic DSO image calibrated, integrated, background noise removed and the color calibrated.  If you are familiar with the Adam Block FastStart Training series, this is basically the workflow that I used.  The only "by hand" thing I did on each processed image is I did use DBE which is a by had operation as opposed to ABE which is an automatic operation.  On finishing assembly and color calibration in PixInsight, each final image was exported as a 16bit TIFF and I would import into Photoshop and all I would do was a quick Levels adjustment later and bring the blacks up to a level of 50 from the preset of 0 which would darken the background.  I use the exact same setting of 50 on each image.

In combining I was interested in seeing two things actually.  I wanted a representative image of each filter but I also was curious as to how stacking the different filters together would work or what my final image might look like.  To this end you will find two quadrant photo sets below.  One shows 4 photos from 4 nights, each of a 90x300" image for just one filter.  The quad is stacked up L-R, T-B in the order of L-Pro, L-eNhance, L-eXtreme, L-Ultimate.  The second quad shows a stacking of first the initial L-Pro and next is one with the L-Pro, L-eNhance followed by L-Pro, L-eNhance, L-eXtreme and finally the L-Pro, L-eNhance, L-eXtreme and L-Ultimate.

In doing all of this I decided on making a 2 day composition of the L-eNhance + L-Ultimate.  I thought this set was the best compromise of darkening the background but giving a nice star field.  I processed this image just a tad more in Photoshop as I reduced the red saturation a bit and added just a little contrast and sharpening.  This is the single image I have posted.

For myself and for others perhaps, I made two quad images for comparison.  The first quad image below shows each image as processed above.  This gives a nice qualitative representation of each of the filters on nights that are as close to each other without setting up 4 separate telescopes on the same night.



The next quad shows what the image looks like when I successively stack in the previous nights images. 



For all of the PixInsight users here is a screenshot of the immediate post integration step of the 4 separate filtered images.  This shows the differences but on tone mapped linear images as opposed to compressed .jpg pictures.



This was fun to do and at least for me, very informative.  Hopefully it may help others.

Clear Skies!