I’m starting to get used to this narrowband imaging. I’m finding it a lot more fun and generally speaking the image data appears to be cleaner. This is in part down to my not having to fight light pollution. This is because using a narrowband filter, even a dual bandpass one such as the ZWO Duo Narrowband Filter, only allows through specific wavelengths of light, in this case the hydrogen alpha and oxygen wavelengths, almost totally ignoring anything else including, to an extent, the washout from the moon. That said, this particular filter still has a bandpass of 15nm, which is wider than the dedicated 12nm or even 6nm filters, that are mainly used with mono cameras. However, the beauty of these wider bandpass filters is that they’re designed to be used with one shot colour (OSC) cameras, and are a relatively inexpensive way of introducing oneself to the universe of narrowband imaging. The downside, at least to this particular filter, is that it only allows through the Ha and Oiii wavelengths, and not the sulphur, so you’re somewhat restricted in the “palette” you can use. Of course you can do an HaRGB, which is where you use the hydrogen alpha data to enhance the RGB and bring out more of say an emission nebula detail. Or you could use the HOO palette, which is where you would use the hydrogen for the red channel and Oiii for the green and blue channels.
My first session on the Pacman Nebula, NGC 281, this season resulted in a total of 69 minutes of usable data. For the limited amount of time on target, the result isn’t too bad, and far surpasses my previous attempts at it that contained more time. Further aquisition time will only add to the detail in the nebula, and also help to bring out more of the Oiii.
The second session was a bit impromptu. The forecast was dire, however, going into the early evening it was crystal clear so I took the chance and set up at home despite being exhausted. The satellite data showed incoming cloud but taking a rough estimate based on speed and direction of travel, I could probably manage a couple of hours imaging at a push. As it was I got in over 3 hours, although only kept 67 minutes of usable data. To be fair I lost about half an hour as I’d altered my gain settings in the imaging plan but forgotten to change it back. I could’ve carried on but I’ve found that the 270 gain and 340 offset works well with the camera, so I ditched the half an hour I’d obtained. So far I have 139 minutes of duo narrowband data which I’ve stacked and given a quick and dirty process.
The third session on this was meant to start earlier than it did. As is typical these days, the forecast was wrong, and so I spent the first part of the evening keeping a close eye on the satellite data and didn’t actually start any imaging until gone half past midnight. Even then I still had a lot of passing cloud, although the satellite was still insisting it was clearing from the north east. There were some okay frames coming through and it was easy enough to make out the nebulosity on a single 60 second frame, even with the moon now out at 68% and not that far away. This is where the virtues of narrowband imaging come into play in that I was seeing zero effects from our nearest neighbour.
Guiding was rocky to say the least! And Cassiopeia was so close to zenith that I figured I’d probably only have an hour or so before needing to check the proximity of the scope to the tripod legs. So I set my alarm for an hour and decided to get my head down for the duration.
Unfortunately I committed a rookie error and forgot to take flat frames before rotating the camera in the OTA prior to doing a manual meridian flip. And out of the three hours I captured, due to cloud and tracking errors, there was only 45 minutes of usable data. Which brings it up to 3 hrs and 1 minute so far. Still have another clear night on the forecast so fingers crossed there.
The fourth session had gone a lot more smoothly (I thought.) Having left everything setup from the previous night, and fine tuned the polar alignment, getting everything going was simple. As soon as it was dark, I started the imaging run. I set my alarm for 1am and grabbed a few hours sleep. Right now I’m tired right through to my core, and next week’s holiday with Amanda in Pembrokeshire is something I’m looking forward to. This is beyond your usual “I need a holiday” throwaway comment. My soul is exhausted and it needs to recharge out in nature. Keep an eye open for that post!
The fourth session, which garnered me five further hours of imaging, was a total disaster. What I thought was just some minor washout from the moon turned out to be high level thin cloud, that was just thick enough to turn the final stacked image into a complete mess! So, at the moment, we’re at 3 hours of total time on target, across 3 separate nights, even though I’ve spent a total of over 15 hours actually imaging. This is what I get most frustrated about. The time that gets wasted. With the bigger mount, that 15 hours of imaging would probably equate to maybe 12-13 hours of usable data, and the image below would look a lot more defined.
I managed to grab a short extra session after a two hour run on the Double Cluster in Perseus, although I fell asleep before the meridian flip and woke up just after 4am to a scope collision with the tripod. Can’t test that yet, but I may just give it a strip, clean and regrease anyway as I haven’t done that since I bought it a few years ago. Also had an idea on why guiding is struggling and it may well be down to my calibration data in PHD2, so I’ve replaced the darks and bad pixel map library.
But I’ve managed to obtain a further 45 minutes so I’m at just over 4 hours total now. We’ve had some lovely weather the past few days but I’ve been shooting widefield whilst away on holiday with Amanda in Pembrokeshire. Last night looks like the last clear one for at least a week, so for now I’m going to leave you with 4hrs 7mins on the Pacman Nebula in HOO.
I’m going to leave this one here for this season now and move onto other targets as we’re coming into autumn. Thanks for reading, and clear skies all.
AstroHeart UK Photography 