Here’s another image of Comet 41P/Tuttle-Giacobini-Kresak taken from a Bortle red zone location which is in the middle of a larger city. No filters and a stock camera on a F/5.6, 480mm focal length telescope were used.
I was able to shoot 2 minute exposures at ISO 400 before it maxed out the light pollution (LP.) This is the StarFreeze version of the data. I have lots more data, too. There is another set of 40x120sec shots and some 90 sec, ISO 400 sub-images I did early on when the comet was lower in the sky and deeper in the LP muck.
For now, this doesn’t look too bad to my eye, considering the conditions. I would estimate the coma is twice the size we see here from a dark-sky location. I’m glad the sky was nearly transparent this night. It made processing easier.
On the night following the encounter between M108, Comet 41P and the Owl Nebula, the comet was still in the field of view of my setup, so I went back for seconds. I just couldn’t pass up the opportunity to shoot a comet conjunction again!
I went with 3 minutes sub-images at ISO 200, since the 1 minute ISO 800 subs were too cooked by the LP for my taste. Unfortunately, the sky was not as transparent as the previous night and that half-stop of underexposure was needed to get around that. The trade-off was I didn’t get as much of the comet’s coma. Oh, well.
Also, at that exposure length, the comet’s pseudo-nucleus trailed a bit, since it is moving with respect to the Earth and stars and slowly picking up speed as time goes on, to boot. It was not enough to notice if I carefully over-exposed it a bit in processing to make it fatter, luckily. Check the star streaks version, which I did not overexpose, and you can see how far the comet moved in 3 minutes:
A Televue TV-85 w/0.8x focal reducer/field flattener, a Canon T3, my laptop running EQMOD, driving my Atlas EQ-G mount and PHD2 Guiding with an Orion StarShoot guider/Orion Ultra-Mini guidescope was some of the equipment used.
It is not uncommon for comets to pass near famous Messier objects or NGC catalog objects and put on a good show. This comet encounter is special in that there are two famous objects that the comet is having a conjunction with. One is a relatively bright galaxy called M108. The other is the Owl Nebula, one of the better planetary nebulae in the skies.
I shot this with the Canon T3 and Televue TV-85 combo. I used one minute sub-images at ISO 800 and that was about max for the skies I was under. I’m sure people with darker skies got better results. However, I think being able to pull anything out of the skies at this location is great. LP was bad and I had terrible gradients to deal with in post-processing, but I managed. 🙂
I also did a quick star-streaks version that seems to show a longer tail. Not sure, since there were some dust doughnuts left over from an apparently bad batch of flats I used and I had to clone them out. These aberrations were in the tail area, so it could be some remnant of that.
One thing I’ve found out with using electronically assisted methods to view dim objects in bad LP conditions is this: Live stacking generally improves things, but only at first. If you want something as dim as Comet 41P to show any more than just the inner coma, you have to stack with lots more subs using more advanced stacking methods than just average and additive.
So, I shot 103 subs-images, along with 30 darks and about 30 bias images for this object. I brought them into IRIS and used only the first 60 because that is all I could get to align. The usual methods of aligning based on the drift per hour in x and y coordinates doesn’t work if the sub-images are not timestamped. This is another deficiency in the low-end capture and stacking program, RisingSky (ToupSky.) Not sure if SharpCap has the same issues.
Anyway, at least I was able to obtain a basic image and considering the conditions, it is not too bad. Compare this to my previous effort with the Aptina AR0130 sensor. This would probably work lots better at a dark sky site. But, I don’t know if I would waste time on shooting with the RT224 when I could use the Canon T3, which is more sensitive when it comes to comets and captures a much larger field of view.
The target of choice, if it is available, is always M42 when you have some new astrophotography gear to try. I went after it as my first object of the night for this session. I missed it the previous night which was first light for the new RisingTech Sony IMX224 camera because my mount was being a pain when trying to get it aligned and pointing accurately.
This was captured in the RisingTech (RT) version of ToupSky, the software that comes with all ToupTek cameras. RT has it re-branded and calls it RisingSky. lol. I installed it, even though I already had ToupSky installed.
One thing it has that the regular download of ToupSky doesn’t have is Live Stack. It is similar to what SharpCap does and the main reason why I was using that program instead of ToupSky when I imaged with the ToupTek Aptina AR0130 camera.
It does a decent job of stacking when the stars are bright, not so decent when they are dim. About the same as SharpCap. That’s why others are using AstroToaster to live stack, since it uses DeepSkyStacker as its backend, which is more powerful than the ToupTek offering and has better calibration support.
My only gripe about RisingSky is the TIFF save and export supports only 8-bit, and I used that instead of FITS when I saved. My bad for not checking first. The post processing would have went better if I had 16-bit to start with. Live and learn, as they say.
The next night after the above image was taken, I tested the camera shooting with a 0.8X focal reducer for F/5.6. It definitely made a difference in the speed and I got more nebula with less exposure time. Plus, the field of view was wider:
The F/5.6 setup is also better since the camera is screwed onto the focal reducer with a T to C adapter. At F/7, I had to use an 2 inch extension with a regular eyepiece holder and leave it and the camera hanging out of the focuser a ways to even reach focus. So, there is less chance of misalignment or something slipping out of place with the reducer and T to C adapter.
In addition to M42, I also got some time on M41, which is an open cluster in the constellation Canis Major, next door to Orion. Open clusters are too easy with this setup. I can’t wait to try it on some globular clusters!
Images of Comets, Nebulae, Galaxies and Star Clusters