Roger Samworth

Window-sill Trapezium dehaloed

As I have previously posted, I have been trawling through my archive looking for likely candidates for the “dehalo” processing i came up with to get rid of those irritating dark haloes around bright objects the PD camera sometimes produces. (I think it is probably an artifact of the PD’s compression/noise reduction algorithms). Again, I’ve already posted some of these. M42 seems particularly to benefit from this:

Digital Astronomy – things to do when it is cloudy!


However, I found this one too, that I was particularly taken by. Here is the original and the dehaloed version.

It is quite simple and quick to do in GIMP and I’ll post the method if anyone is interested, but I suspect it is just my kit and methodology that creates the issue. “Proper” imagers don’t seem to get the problem!


Weird eclipse!

Spaceweather says

“A REALLY WEIRD SOLAR ECLIPSE: Earlier today, NASA’s Solar Dynamics Observatory (SDO) observed an eclipse of the sun–a strange kind of eclipse that you can only see while orbiting Earth. The black disk of the New Moon passed in front of the sun, reversed course, and did it again:

During the eclipse, which lasted just over 4 hours, as much as 82% of the sun was covered. Technically, that makes it an annular solar eclipse, not total. At maximum, an annulus or “ring of fire” completely surrounded the Moon.

The strange “double-dip” motion of the Moon across the sun is a result of orbital mechanics. Both SDO and the Moon are orbiting Earth, but at different speeds. SDO’s velocity of ~3 km/s is faster than the Moon’s velocity of 1 km/s. SDO thus overtakes the Moon first in one direction, then the other, during the long eclipse.”


You can see it here too:

Video electronic eyepiece again

Here are another couple of snapshots from the video electronic eyepiece screen, (see this time the M41 cluster as well as M42. It is quite difficult to get a decent snapshot with a camera due to it being tricky to get the exposure right.  I have also found that for visual observing in the dark, it is best to turn down the brightness and contrast as far as it will go on the monitor.

It is probably worth-while comparing these with the processed images from from a few minutes exposure with EXACTLY the same kit (plus a PC, of course) from EXACTLY the same location. (the window-sill). Both methods have their place, of course! Perhaps unsurprisingly, the clusters come out best.


By the way, given some recent discussions, the M42 image is a composite of 4 exposures

DSOs 27-28/02/2019

It was such a nice night, at least for starters last night that I was tempted away from the window-sill!

First, M46 in Puppis, an open cluster that also seems to contain a planetary nebula, NGC2438. It isn’t in the cluster, in fact, it is just a line of sight effect. Since I couldn’t get the whole of M46 in field, to set the scene, the first image below is from the window-sill telescope from last year, followed by last night’s images:

Here is an enlarged and further processed version of the planetary nebula.

Then on to two little known open clusters in Gemini, NGC2129 and IC2157

Then some quite tricky galaxies in Coma Berenices, NGC4274 and NGC4559 (C36).

Finally, another pair of tricky galaxies in Virgo, the “Siamese Twins” NGC4567 and NGC4568

Video electronic eyepiece/image intensifier

Imaging is imaging, usually with a computer to process said images later.

Visual observing is when you look through an eyepiece and get an “instant” view.

As soon as you start to use electronic assistance such as an image intensifier the distinction between these two gets a bit blurred.

The PD camera produces a video output that you can feed directly into a video monitor and get an “instant” or “near instant” view, depending on what integration time you use. No computer is needed.

So here is a slant on that theme. I purchased a 5″ video monitor for the princely sum of £16.99. It runs off 5V, so I also purchased a 12V-5V converter for another couple of pounds. I then coupled it to the PD camera like this:


Here are a couple of snapshots of the “instant” result of the Orion nebula using the window-sill 80mm refractor. The first one is as it comes, the second with a UHC filter.


Not a patch on proper imaging, of course, but interesting!

I could easily see the Flame nebula like this, and I fancied I could (maybe) also see the Horsehead – – -! (From the window-sill, of course!)