With some clear weather, but with a waxing moon, I thought that I would play around with some of my NIR (Near Infrared) filters and the new 91FLT rig.  Having just shot (and posted) M101, the Pinwheel galaxy, I thought that I would see if I could tease out some additional information on the structure of this large, face-on galaxy.  I have used my small QH5III462c (NIR)-capable camera with a 950 nm edge filter in the past with a 12 inch reflector.  I thought that I would try it on my new refractor to see if I could see anything interesting.  My experience with that camera and filter was that I could see interesting differences in stars and nebulae.  The most pronounced capability is to very strongly disfavor the signal from bright hot blue stars and strongly favor the signal from colder, redder stars.  Having done some work with it on the Whirlpool, it was clear that I was able to clearly see a different structure to that strikingly blue galaxy.  I thought that M101 would be better because it is much larger in the FOV and more details are seen in RGB and OSC images.  To add to the fun, I also mated an Astronomic Pro Planet 807nm filter with my QHY268c to get an intermediate NIR image to add some complexity to the overall imaging.  

The main (front) image is from my recent OSC RGB "Intergalactic" image.  The mouse over is the full spectrum, RGB false-color image as described below.  In case you are interested, I have also added the bicolor images to compare each wavelength image to the other two.  I also include gray images of the root NIR images and the blue channel image from the OSC. 

For the shortest wavelengths, I selected the blue channel of my recent OSC image as the only visible wavelength of the process.  I decided to try a conventional mapping (Blue -> Red, being short wavelength -> long wavelength), sticking with putting the OSC blue into the blue channel.  The next step up was to map the 807 nm signal to the green channel.  Finally, the 950 nm and higher signal to the red channel.  The Pro Planet 807 nm filter/camera combo likely is pretty restricted to 807 nm and maybe 20-30 nm higher.  The reason is that my OSC 268 camera has poor efficiency at 807 nm (~30%) and only rapidly falls from there.  However, the Bayer filter layer becomes transparent to wavelengths above ~700 nm, so that OSC camera actually becomes a mono camera in that wavelength.  My NIR camera has got much better efficiency at 950 nm and is still significant at 1000 and likely 1100 nm.  So each of the three channels is well separated from each other.  

Having said all that, this is no James Webb telescopic view!  Really, this whole exercise is still under a very restricted band width.  However, it should be noted that the NIR images really do show clearly the abundance of smaller, older and cooler stars where one expects to see them.  One example is the rather smallish bar in this galaxy, which is difficult to see in my OSC RGB image, becomes more evident as the wavelength increases.  I had a hard time even finding anything referring to M101 as a barred spiral online.  However, it is listed as an SAB galaxy which means it does have a mildly barred central bulge. 

The 950 nm image was the most problematic to collect data on and to process.  The sensor is small and everything is extra work to get preprocessing and processing to look decent.  So 950 nm is rather blotchy.  Don't trust those blotches as being any interesting structures.  I do not really see that in the subs, but the registration and integration was very problematic.  

Something to do with OSC cameras and a waxing moon!  Hope you find this interesting!