Astronomy – Page 2 – anderswallin.net

Aurora Borealis, Oravais

Some nice northern lights (aurora borealis) appeared just as I was going to pack away by tripod and camera after shooting another fixed-tripod milky-way time-lapse.

So no packing away and instead Aurora Borealis shooting for another three hours. These are 20s exposures through a 17mm/F4 lens on a Canon 500D at iso3200. Fixed tripod.

The time-lapse video is 340 frames shot from around midnight to 3am on Wednesday 28th September 2011 looking north from Oravainen, Finland. As with all photography the camera sees things differently from the eye. The lights look brighter and more yellow on the camera, and the red hues visible on camera are very faint or nonexistent by eye.

Photo equipment was fairly simple: I hung a plastic bag containing stones on the tripod to stabilize it in the wind. Timing and shooting with an intervalometer. Shoe-driers taped to the lens with masking-tape worked as improvised dew-heaters. I'm using a Canon ACK-E5 powersupply so I don't have to change batteries constantly.

Time-lapse movie was compiled by first resizing images (JPEGs straight from the camera, no modifications) with
mogrify -resize 1280 *.JPG
and then compiled into a movie with
mencoder -nosound mf://*.JPG -mf w=1280:h=853:type=jpg:fps=8 -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=2160000:v4mv -o movie.avi

Update: I also had my older 20D camera with me, and a 50/1.4 lens. No tripod, just camera placed on a wooden board pointed towards the sky. No dew problems despite no dew-heater. Here is a time-lapse of ca 400 frames exposed for 3 s. This is much darker than the first video, and doesn't bring out as much red/yellow color. This is probably closer to how it looks to the naked eye.

Fixed-tripod astro time-lapse

Up north away from the ~~civilisation~~ light pollution, it's easy to see the milky way with the naked eye. Here's a short time-lapse of 60s exposures with the camera on a fixed tripod (I didn't drag my tracking-mount with me this time).

Without a dew-heater it didn't take long for the lens to fog up (I didn't bring my dew-heaters either!).

Equatorial wedge – knobs

I turned these knobs from 40mm stock on a manual lathe during the week, and JI cnc-milled them to shape today.

There's still one bit missing from the wedge: the fine-adjustment piece for the azimuth-angle during polar alignment. I'll try to make it on the lathe next, and then everything should be ready for anodizing.

Equatorial wedge – side plates

CNC machined two side-plates for the equatorial wedge today. Next up are some M10 and M6 knobs on the lathe, and the fine-adjustment for azimuth. Then all parts should be polished and anodized.

Equatorial wedge – top plate

This is the top plate of the wedge which will be tilted so that the alt/az mount which is bolted to it has its azimuth axis pointing towards the celestial north pole. The side-plates will have to wait until next weekend.

Equatorial wedge – base plate

I'm building an equatorial wedge which will transform my new alt/az goto-mount into an equatorial mount. This is the first part which attaches to the tripod. Two smaller side plates will be bolted to this plate and support a similarly shaped tilted plate to which the alt/az head attaches. The design is similar to the "mega wedge pro" (how about that for a product name!).

Leo and Mars

Wide-field shot of the area around Leo. The bright dot low and right of center is Mars, and I think next to mars is the open cluster M44 (a.k.a. "the beehive cluster" or "Praesepe"). These pictures really need to be taken on nights without the moon. There's a huge gradient from dark to bright towards the direction of the moon.

I tried to add some lines and text for constellations, but it's fairly difficult because so many stars are showing in the picture:

Ursa Major

3 x 20 min = 60 min exposure of Ursa Major through a 17-40/4L lens at ca 17mm and stopped down to F5.6. There is something funny with the polar-alignment or the guiding which makes the stars in the lower left corner not look good.

M42 Orion Nebula

Canon 500D camera with EF-200/2.8L lens on EQ6 equatorial mount guided by a QHY5 camera and PHDGuiding. Stacked 5 frames in Deep Sky Stacker, total exposure ca 5 minutes. Shot on Sat-Sun night 23-24 Jan 2010 in cool -18 C but calm weather. Would have wanted longer exposures and more frames, but the guiding wasn't working very well, and Orion is pretty low, hiding behind trees from my site. The dark thing on the right is a tree 🙂

Same image but cropped:

A nice improvement over my 2008 December attempt on M42.

Michelson interferometer

Tried this simple Michelson interferometer for measuring the error of a 100mm translation stage yesterday. The interferometer and stage are mounted to the same optical table, but there's still a fair amount of vibration of the measurement corner-cube which causes instability in the signal when the stage is not moving.

Some sample data here: interf_data. One channel is an encoder signal from the motor which should come every 5 um, the other channel is the interferometer output. Analysis will follow...