Posts tagged 'Andromeda'

Observing Report / Lens Test 22nd September 2009 (Big Dubyah)

Posted by on September 23rd 2009 in Astrostuff, Observing Reports, Pics, Shiny new kit

I'd not planned to go out observing, but there was an hour or so of cloudless sky yesterday evening and I had a little time to spare. This was an opportunity to sky-test the Nikon AF-S DX NIKKOR 35mm f/1.8G lens to assess how well it is suited to taking widefield pics of the night sky.

In particular I was looking to see:

  • how much sky would be captured in the frame;
  • if a reasonable focus could be achieved using the camera's auto setting;
  • how quickly the camera sensor would become saturated at f/1.8 and ISO 200;
  • how much vignetting would be caused by using a 52-48mm step-down ring and Light-Pollution filter;
  • how much coma would be present at the edges and corners of the image; and
  • how much star-trailing would be caused when using a static tripod as opposed to using a driven equatorial mount.

The challenges would be to see if I could find a reasonable exposure time, get a small number of images for stacking, and then process-out the vignetting, star-trailing and any light-pollution.

Jupiter was in the southern sky so I pointed the camera at it to get the autofocus set. I then turned off the autofocus and fixed the position of the lens focus ring by the judicious application of duct-tape.

Next, I pointed the camera at the Cassiopeia / M31 Andromeda area and took a few test-frames of various durations. Eventually I settled on an exposure duration of 30 seconds and took 12 pics.

These were stacked in DSS and hurriedly processed in PSCS3, and here's the result:

 

Mouse-over the pic for details, click it for a bigger pic.

 

I have to say that I'm quite impressed with the raw images that this lens produced. Shooting with the aperture wide open captured a lot of light, and for a change I had to tone down the details rather than go through the usual routine of having to drag the details out of the murk. I'm damned if I can find any coma in the raw frames, which means that there'll be no need to crop off any bad areas. The expected vignetting was dealt with in PSCS3, the compensation isn't perfect but to be fair I've only done a quick fix, no doubt I could get it better if necessary. The amount of star-trailing was acceptable, and I'm confident that I could get it processed out if necessary and if I had enough time.

And the framing? I'm happy with it for targets the size of Cassiopeia, but the capture-area might be a tad small for meteor-work. Time will tell - between now and the end of the year there will be plenty of opportunities for snapping a few meteor trails (more on that in another post very soon (but don't hold your breath)).

Andromeda reworked #3

Posted by on October 13th 2008 in Astrostuff, Observing Reports, Pics
Tags: ,

Click on the pic to open up a bigger version in a lightbox thingy, you'll need to wait until the page has finished loading.

I went back to the stacked output from original set of frames and then applied a load of Photoshop Actions from the Astronomy Tools package available from Noel Carboni. It's amazing what detail can be strained out of what seems to be a dull picture. I've probably overcooked it, so this'll be the final edit unless I find more tools to play with:

M31/NGC 224 Andromeda Galaxy, reworked with Noel's Actions

Andromeda reworked #2

Posted by on October 7th 2008 in Observing Reports

Had a more thorough go at processing the original Andromeda frames, having supplemented them with some more taken on Sunday. The field of view has been extended, now there are three galaxies there for your viewing pleasure:

M31/NGC 224 Andromeda Galaxy (centre), M32/NGC 221 Le Gentil (left) and M110/NGC 205 (lower-right).

Andromeda reworked #1

Posted by on September 29th 2008 in Observing Reports
Tags: ,

Had another go at processing the Andromeda frames, here's another version:

 

Andromeda Galaxy (M31).

(Nikon D50 at prime-focus on C8-N, ISO 200, no filters, 22 x 30s colour exposures stacked with DSS, reprocessed in PS CS3)

Observing Report 26th-27th September 2008 (Andromeda)

Posted by on September 28th 2008 in Observing Reports

After what seems to be many weeks of overcast skies, Friday evening was clear enough to get out and test the new focuser setup. After a delayed start due to a mucky secondary mirror, the scope was recollimated and set up in the back yard. I did a few visual checks of random bright stars to confirm that all was OK, then decided that it was time to grab a few images for analysis later.

I slewed the scope around to the faint blur that is the Andromeda Galaxy (Messier 31), then slapped on the D50 for some prime-focus shots. This was to be my first semi-serious foray into taking this sort of shot, and I just wanted to get a few images to stack and play with, nothing too difficult.

Anyway, focusing was a lot better with the new setup. After transferring a few shots from the SD-card to the laptop to confirm image acceptability, I rattled off a series of raw files (NEFs), all at 30s, just to see what could be achieved at such relatively short exposures.

After a quick look around to see a few double-stars, the dreaded dew started to form and it was time to pack away and start photo-processing.

The individual frames didn't seem too bad - focus was just a tad out on the later pics, it looks like there was some minor focus-drift over time. The stars at the corners of the pics are distorted due to coma (typical of Newtonian optics - correctable with optical hardware, at a price) but the central stars are hardly trailed at all, which means that the initial polar-alignment of the mount was either very good, or just plain lucky!

Anyway, I plugged them all into various bits of software and , much later on, it spat out the following pic. There's a definite hint of spiral structure there, and the centre's not burned-out too much due to over-exposure or drastic levels/curves adjustments. Not bad for a first attempt with a basic set of frames, and I reckon I could drag more detail out of the data, given enough time. That said, I'm quite chuffed with it as it is.

Next time I'll go for much longer exposures, and more of them.

 

Andromeda Galaxy (M31).

(Nikon D50 at prime-focus on C8-N, ISO 200, no filters, 22 x 30s colour exposures + 1 dark frame stacked with DSS, processed in PS CS3)

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