More aperture is better. I’ve started to build a 240 mm Newtonian with some mirror blanks from Tammilasi and knowledgeable help and grinding materials from Teknofokus.
The first task was to grind the 240 mm diameter (40 mm thick) borosilicate mirror blanks flat on each side. This took around 1.5 hours per side using 60-grit silicon carbide and grinding against a flat steel plate.
I got an OD=5 solar filter for my 80 mm refractor and took a first look at the sun this afternoon. Two sunspots are clearly visible. The large spot at 3 o’clock is dirt on the camera sensor. The apparent rotation period is supposed to be around 28 days, so by taking a picture each day it should be possible to make a time-lapse movie.
To really see structure in the sun requires a very narrow (~0.7 Ã…ngström) bandpass filter centered around the H-alpha emission line at 656.28 nm. Unfortunately these range from expensive to very expensive…
A little left of Regulus and where Saturn is right now in Leo there’s a group of three Messier objects: Two spiral galaxies M95 (magnitude 11.4), and M96 (magnitude 10.1), and an elliptical galaxy M105 (magnitude 10.2).
This is a stack of around ten 8 s exposures through an EF 70-200/4L set to 200mm and full aperture. Resolving details from the galaxies will require a longer focal length and much longer total exposure time. Focus is pretty good, and stars appear as points even in the corners - but the image shows severe vignetting. I need to learn how to use flat-frames to correct for that.
For those of you that don’t spot the galaxies immediately from the pic above :), below I’ve indicated their positions:
Around 10 images of Saturn stacked with registax. 102mm refractor (f=1000 mm) with a 2x and a 3x barlow stacked between camera and prime focus. This time through the 90-deg diagonal, so it looks flipped up/down compared to the picture a few days ago.
It’s been cloudy almost every night for about three weeks now, but finally today a half-decent sky-watching night. The moon is full, so my moon pictures were predictably quite bland. I tried to search for some messier objects, but with a poor finder-scope and 25mm being the widest eyepiece that didn’t work out too well (even with Stellarium on the laptop right beside me…). Here’s the best of around 10 shots of Saturn.
102mm refractor, f=1000mm (~F/10), 2x Barlow, Canon 20D, 1/3 s exposure at ISO100
The big picture shows a normal photo through an f=1000mm F/9.8 telescope with a Canon 20D. The field of view should be around 1° 17‘ 20″ according to this FOV calculator. The small frame is taken with an additional 2x Barlow lens between prime focus and the camera sensor. It ends up magnifying the image around 2.7- to 2.9-fold. I guess this could be tuned a little each way by inserting the Barlow differently in the focuser or with a T-ring standoff between the camera and the Barlow.
Something to try on the moon or bright planets once the skies are clear again…
30s exposure at ISO400 of the Pleiades. Again some light clouds rolling in around 22:30 preventing further photos…
Had hoped to shoot the Pleiades with some longer exposures today, but clouds rolling in prevented that. So some snapshots at ISO100 and 1/4s of Saturn instead. These are 100% crops, so maybe I need to get an adapter for eyepiece-photography for shooting planets at higher magnification?
The clouds caused this round halo-effect around the moon. By 23:00 it was impossible to shoot stars.
Pooling our hardware resources together in the lab, we now have a 102 mm F/9.8 (f=1000 mm) refractor on an EQ6 equatorial mount and either a Canon 20D or a Canon 400D to shoot with. When one camera is coupled to the scope the other one can simultaneously take a wide-field photo. Did not bother with polar-aligning the mount today, so just looked visually at the moon, mars (it happened to be close to the moon), and M42. The moon is so bright no tracking is really needed.
Here is the moon through a 102mm F/9.8 (f=1000mm) refractor with a Canon 400D at prime focus, set to ISO400 and 1/160s. Around 21:40 local time on Friday 15 Feb 2008.
Astrophotography in Finland is a cold hobby, I was somewhat unprepared for the weather so around 60 min in -7 C was enough for me…
I’ve made a first attempt at pointing my camera towards the night sky. Achieving good results is not an easy task - some people spend considerable amounts of time and money on the hobby of astrophotography ! (and the results are breathtaking)
Just a fun thing to do for me - for now… (they call it ‘aperture fever’ when you get hooked!)
Having read a little bit about wide-field astrophotography I experimented quite freely with different iso settings, exposure times, focusing etc. Out of about 70 pics, these are the better ones.
All of these are with my Canon 20D, shot from a stationary tripod with a cable release.
The moon shot at 200mm with a 70-200/F4L, stopped down to F22, shutter 1/160s and iso800. A ca 180% crop. I had the camera on program-mode, but it would probably have made sense not to stop down as much. The light-meter in the camera really does a bad job of metering in this kind of a shot. The only way to get the exposure right is to take lots of pictures with different shutter times. I really need to get that EF-mount adapter for the 500mm mirror tele-objective to get some nicer moon shots !
Ursa Major, partly hiding behind the trees. With 17-40/F4L at around 17mm, 10s exposure at F4 and iso1600. Click on the image for a full-screen version.
Polaris in the middle. 17mm/F4, 30s exposure at iso800. Click image for a full-screen pic.
Next I suppose I will have to learn about dark-frame substraction, “barn-door” tracking mounts, stacking multiple exposures, etc. Anyone interested should check out Canon_DSLR_Digital_Astro and digital_astro, but beware of the message volume, up to 1000 per month !
The only problem with this hobby in Finland is that it’s only dark enough during the winter - and on clear winter nights it tends to be really cold. (think remote-controlled “go-to” mount and laptop-operated camera from the livingroom sofa…)
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