[watsisname]

Heh, I've only ever worked with alt-az mounts and to be honest the thought of doing a polar alignment kind of scared the crap out of me.  Your post makes it much less intimidating than I'd thought it would be.

My understanding is that polar alignment is wonderful for doing long-exposure astrophotography, because the drive of an alt-az mount has to move in separate steps vertically and horizontally in order to track the target across the sky.  This causes a small amount of image blurring.  As you mention, a polar mount only has to move along one axis to track a target, so with a smooth drive there should be almost no blurring whatsoever.

[Herra Tohtori]

Equatorial mount is just like a simple dobson type alt-az mount, it's just that the azimuth axis is aligned with Earth's rotational axis.

The blurring in long exposures with azimuthal mount is because the image rotates slightly in the view (even if it is mechanized and tracks the object automatically). In equatorial mount, you basically just rotate the telescope about the axis that points to Polaris (well, not exactly to Polaris but approximately).

I've been thinking about hooking my camera (somehow) to one eyepiece of a 15x70 binoculars and see if I can bring it to focus somehow, then use the other side as a viewfinder. I likely won't invest in any equipment with tracking mounts, though that would be seriously awesome to try sometime.

[Herra Tohtori]

Here's something interesting....




You can just faintly see some diagonal dark belt formations. I would disregard them entirely, but they happen to align exactly to the reference:



A significantly more exposed (and brightened) shot reveals all four Galilei's Moons:



This time, my equipment consisted of Helios 15x70 binoculars, on a shaky tripod, with the Canon PowerShot SX130IS McGyver mounted on the eye piece with liberal use of cardboard tube and tape.

[watsisname]

Yep, I'd say those are definitely the equatorial bands.  Awesome job!

I wonder, how rapidly can you snap pictures with that setup?  If you can take 'em at a steady clip then maybe you could try stacking them to improve the quality.

[Herra Tohtori]

I tried that but there were a lot of problems with chromatic aberration and tripod stability. I used ten second self trigger and the vibration only barely settled down in that time and none of the rest of the frames had any detail whatsoever...

[watsisname]

Had a nice clear (and COLD) night here, but the seeing was too poor to make any planetary shots.  So I took out the new camera for a quick low-light test instead.  The subject?  The Orion Nebula (M42) and surrounding area.



This was a 15 second exposure using a Canon PowerShot ELPH 300HS with tripod, brightness/contrast adjusted in GIMP.  The nebula is the pinkish-colored area.  Some star trailing is also slightly apparent.  Overall I'm fairly pleased with the result -- despite heavy light pollution, the star and nebula colors show up nicely, and some stars too faint to be seen with the unaided eye from this area are visible as well.

[Scourge of Ages]

With that little camera you got that? Awesome. I wish I was somewhere with less light pollution, and without needing to get up at 2:00 and drive out to the desert or something.

[Herra Tohtori]

Six exposures, taken through some hazy cloud.

I need to do this again some clear night...

[watsisname]

Tonight I enjoyed mostly clear skies and 3/5 seeing, so I finally managed to go out and photograph Mars.


Equipment:  Meade 8" SCT with LPI camera.
~160x magnification, best 100 of 276 frames combined in Registax.  The north polar icecap is visible as the white area at top.


I tried again with a 3x magnifier (~500x magnification total) and 220 of 565 frames, but the either the seeing isn't good enough and/or my focus wasn't perfect, so there's not really any improvement in detail.

Mars info at time of shots:
Distance:  0.984AU (Very close to the average Earth-Sun distance)
Angular Size:  9.51"
Phase Angle:  32°
Currently approaching Earth at ~15km/s and 'growing' ~0.1" per day.  Closest approach is on March 4.

[Nuke]

Had a nice clear (and COLD) night here, but the seeing was too poor to make any planetary shots.  So I took out the new camera for a quick low-light test instead.  The subject?  The Orion Nebula (M42) and surrounding area.



This was a 15 second exposure using a Canon PowerShot ELPH 300HS with tripod, brightness/contrast adjusted in GIMP.  The nebula is the pinkish-colored area.  Some star trailing is also slightly apparent.  Overall I'm fairly pleased with the result -- despite heavy light pollution, the star and nebula colors show up nicely, and some stars too faint to be seen with the unaided eye from this area are visible as well.

why does that look like a black metal album cover?

[watsisname]

why does that look like a black metal album cover?

lol



Getting slightly better with Mars.

[watsisname]

Held camera up to eyepiece, pressed button.  Got this:



Amazingly this was taken from indoors, through a window -- the glass didn't distort the image anywhere near as much as I'd expected.  Scope is a Meade 60mm zoom spotting scope on tripod, at around 40x IIRC.  ISO speed was 800.

[Herra Tohtori]

Here's an interesting trick that can be used to reduce chromatic aberration and noise, but it also means you need to use greyscale.

Basically, the CCD grid in cameras is built like this:

████████████████████████████████
████████████████████████████████
████████████████████████████████
████████████████████████████████
████████████████████████████████
████████████████████████████████
████████████████████████████████
████████████████████████████████
████████████████████████████████
████████████████████████████████
████████████████████████████████
████████████████████████████████


So, each pixel consists of two green subpixels, one red subpixel, and one blue subpixel. The raw information from these subpixels is then mixed into RGB values for each pixel:

████
████

Now, because there is essentially twice as much green subpixel detectors in the camera, and each pixel's green value is interpolated from the data from two detectors instead of one, the amount of noise on green channel is actually less than the noise in red or blue channels.

If you have a camera that can output RAW images, you could extract only the green channel from them, and use that as a greyscale image.


This is especially handy if you are looking at objects that are already pretty much monochrome (such as the Moon) or if you are looking at low intensity objects and want to stack the images, while minimizing the noise.

This is, incidentally, the reason why practically all scientific astrophotography is actually done with monochrome CCD cameras, with wide wavelength response, and the colours are produced from multiple exposures through multiple filters.


As an added benefit, because of the narrower wavelength range you have from using only the green channel, it should also somewhat reduce colour aberration both from atmospheric refraction and the optics used. Especially with camera optics not designed for astrophotography, you can sometimes get quite a lot of chromatic aberration on the edges of the field of view, especially when using wide field of view. Reducing aperture size of course also reduces chromatic aberration, but also reduces the total amount of light that gets to the sensor.

[Mika]

First time we had -15 degrees on this January, and clear skies. I decided to take my 40D and tripod for a spin, and went to shoot photos instead of drinking heavily and partying all night on Saturday evening. Sometimes man has to make sacrifices... the trip took me something like 4 hours, and the front element of the lens was completely frozen. That didn't stop me from taking pictures anyhow, so the only way to stop me was for the battery to run off. In the meantime, I captured Orion above the surfer's tower stairs.



I also managed to get Plejades, but more of that later.

[watsisname]

Nice picture!  Very crisp stars, and lots of them.  How long was the exposure?

[newman]

Since he didn't use a polar aligned, tracking eq mount that can't have been a long exposure. Judging by the short trail lengths on the stars themselves I'd say no more that 15-16 seconds max. I'll be interested to know how much did I miss for here

[Mika]

The image is taken with Canon 40D at ISO800, lens is EF 28/1.8. The actual aperture was F/3.5, and the exposure time was 8 seconds. Luckily almost all short prime lenses achieve rather good drawing capability around F/4.0 if the maximum aperture is somewhere around F/2. The field of view presents the view of what a 44.8 mm focal length lens would see on 35 mm film camera.

I took the image as JPEG and did no dark frame subtraction. It's basically what the camera saw, no additional photoshopping or image processing done. I'm surprised how well the stars remained star like given that the front lens was almost completely covered with a thin layer of ice...

[Mika]

Pleiads and the surfer's tower. Otherwise the same settings as before, but now with 15 second exposure time.

This photo was taken about 5 km from the center of the city, and at the shore of the sea. I'm actually surprised of how the city lights improve the picture in the first case.

[Mika]

Hmmm, now that I think of it, I could (possibly) try it out with the equal aperture 70-200 zoom, fixing the lens to 200 millimeters. That should give me ~5.7 times more magnification compared to the 28 millimeter lens.

The star trails and their apparent motion is probably 5.7 times worse as well. I would need to use 5.7 times shorter exposure time. Damn, I'm running out of ISO! Or, wait, from 800 to 1600 means a factor of 2, and from 1600 to 3200 is another factor of two. If only it weren't for the fact that ISO3200 is hopeless for low light photography...

[watsisname]

Away from home and stuck in bad weather for a while, so to pass some time I decided I'd go through my lunar images and start labeling the features (I've had this weird desire to learn them for a while...)  Haven't got much worthy of sharing at the moment, except this one which I thought captured some interesting stuff:


*Original

Here we've got one of the larger craters, Copernicus, along with the Apennine mountain range that borders Mare Imbrium.  Some of those mountains are over 15,000 feet tall!  And I totally wasn't expecting this, but this frame also contains the landing site for one of the Apollo missions (15).  I'll try to get a sharper / more magnified view of that region (apparently there's a nice Rille there that's too small to be seen in this image) when I have the chance -- hopefully around the next 1st quarter moon if the weather cooperates.