Much harder to image than I expected. Though a nearly full moon (77%) and a lot of light polution should have been an indication that it would not be easy: 30s exposures, ISO200, 200mm F/2.8 on Kenko Skymemo
around March 6 2009, 2000h UT, when Lulin was closely passing a magnitude 9.7 star (GSC 1383.160)
The Bahtinov focussing spikes are detected automatically, allowing for a quantification of focus quality (movie):
You can also point your webcam with its original lens to an image of Bahtinov spikes to test:
or test it on a set of three dark artificial lines, by checking the “dark lines ona lighter background” checkbox:
Or even point it at a movie in your browser (from YouTube for example) to see it track focus live:
The Nikon D90 has a very low “dark current”, which makes it better suitable than the previous D70 and D80 for “deep” sky photo’s. Here are some examples:
Core of the the Orion nebula:
4x 30s ISO1600 @F10(?) C8/LXD75 mount, rough polar alignment
Pleiades: (f=200mm f/5.6 ISO200, 4x 180s)
Orion as a whole:
Andromeda nebula:
A Bahtinov mask is a mask on a telescope that produces a line pattern that shows whether you are focussed well, and even shows if you are front or back focussed if not properly focussed. It requires a quite complicated mask, but almost the same effect can be achieved with 2 wires stuck to the aperture:
This results in a line pattern (Bahtinov results in dotted lines of 1st, 2nd etc order diffraction patterns):
But it still tells you where your current focus is (front, back or in focus):
Release 4 of the Virtual Moon Atlas is now available with destriped LOPAM image database:
Just like Registax, but live this time. How does it work?
- acquire images via webcam (I use the Philips Toucam 840k, 640×480 mode).
- center images based on the “center of mass” of the image or register the new image via “phase correlation” to the first in stack
In case of center of mass: set the threshold slider above noise level and the image will be centered on its center of mass. This works for a planet or star image, not for images showing only part of the moon.
- a stack of 16 images is kept, but larger and smaller stacks can be selected
- the sharpness of each incoming image is measured (variance/mean brightness)
- if the “sharpness” exceeds that of any of the images in the stack, the least sharp image is replaced with the new image
- the “live” tab shows the incoming frames, the “stacked” tab shows the average of the images in the stack
As more time passes, hopefully sharper and sharper images will be acquired, resulting in a sharper stacked image.
This software was made on .NET, so you will need the .NET framework as well if not already installed.
Screenshots:
Sunday, December 16th, 22h57 UT, 15.9 arc seconds in size. C8 plus 2x barlow+2.5x powermate. 300 frames out of 1600, moderate to reasonable seeing.
An unexpectedly bright comet, already heading away from the sun close to Mel20 in Perseus:
piggyback on the C8/LXD75
And a bit closer: C8, f/5.6 focal reducer and 2x barlow allowed for prime focus photography (bit awkward, maybe should heve left all the extra glass out but there was little time to try between the clouds passing over head). The comet fully filled the 10 megapixel frame
Actually, first Mars ever: October 7th, 2007, 5h05UT, diameter 10.1 arc seconds, altitude 62 deg, phase 87%.
Animated gif comparing CalSky with the real thing.
Airy disk Wiener deconvolved, 2x drizzle, 32 frames out of 2400 stacked:
Intrigued by wanting to tell time accurately by looking at sun’s position, I built the following after browsing the internet.
If you know all exceptone of these, you can tell the value of the missing one:
- Longitude
-Latitude
- time (Summer or Winter)
- north-south direction
- date
- levelness (spirit level)
Normally you would use it to tell time of course. Brass versions of this apparatus were used to tell time accurately until radio was invented to transmit an accurate time signal to the rest of the world.
