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Methods and Equipment

Some basics

I have taken the pictures mainly in my backyard in two kilometers distance from center of small city Kirkkonummi. There is quite much light pollution around. When taking deep sky images, the sky has to be cloudless and there should be no moon. This limits the good deep sky imaging session to about 30 nights per year in Kirkkonummi.

In image below is the equipment. Telescope Celestron 8, Sky Watcher 80/600 ED and the tele zoom lens EF100-400L. Camera Canon Eos 60Da is specially designed for astrophotography. It passes the infra-red light trough to CMOS Sensor. Normal cameras filter away the infra-red light.

Essential thing when photographing stars is that the telescope must follow the rotation of sky with high accuracy. It is essential to make good polar alignment of the tripod before the photographing sessions. Aligning the tripod to North star is not enough, since it is half a degree from the celestial pole. In Celestron CG-5 mount there is a built in alignment process and it takes about 15 minutes to execute it before starting imaging session. In 2019 I bougth new HEQ5 mount which has the capacity to carry the Helios Skyliner 200/1000 telescope which I bougth in 2004.

When taking exposure series for stacking the TC-80N3, timer remote controller, is a good equipment.

The optical combinations which i use are in table below.
Optics Angle in degrees Targets in the sky
Celestron 8 F10 0.5 Distant objects and the Moon and the Sun. With the Sun always a Baader solar filter.
Celestron 8 + focal reducer F6.3 1 Wide dim objects, like galaxy M33.
Helios Skyliner 200/1000 1 Wide dim objects
Celestron 8 F10 + 20mm Ocular 0.2-0.05 Planets.
SkyWatcher 80/600 ED F7.5 3 Wide objects like Andromeda galaxy M31 and Orion M42 ar.
Canon EF100-400L F4.5Ė5.6 telezoom objective 10 - 4 With 400mm zoom and 4 degree view M31 and Horsehead nebula. With 100mm zoom and 10 degree view, large star cluds of Milky Way galaxy.
Canon EF-S 18-135mm f/3.5-5.6 IS objective 74 - 11 Constellations and Milky Way.
Canon EF-S 10-18mm f/4.5-5.6 IS objective Wide angle Constellations, Milky Way, Meteors, Northern ligths.

In Finland in winter there may be minus 10 to 20 degrees cold. This may cause problems to the tracking electronics of telescope. As a solution I have covered the electronics with thin polyester-metal sheets, which reflect 90 percent of heat back. With this system it is possible to have a astrophotography session of 2 hours in minus 20 degrees temperature. Camera shall not be heated. The sensitivity of camera gets better in cooler temperatures.

Auto Guider

In March 2013 I bought the Orion StarShoot auto guider. It is a camera connected to computer and to CG-5 tripod. If the system observes that tracking star moves, it gives commands to tripod to make correcting move. By this system it is possible to make very long exposures. The PHD-Guide software is installed to small laptop Toshiba NB100 ( Intel Atom N270 1.6 GHz, 1GB , USB2, Win XP).

First auto guiding test object was Galaxy Messier 66 in constellation of Leo. Exposures were 5 x 6 minutes. ISO1600. Baader UHC-S filter.

During testing, i captured by luck a supernova in galaxy M65. It exploded 10 days before taking this image.

Autoguide practicing with M51.

More autoguided images taken 6.4.2013. Galaxies M106 ( exposures 5x6 minutes, UHC-S, ISO1600) and M101 (3x6 minutes, UHC-S, ISO1600). Distance to M106 is 25 million light years and to M101 27 million light years.

Year 2014 i got a physical problem in my CG-5 mount causing it to make small jump every minute. That is why you donít see much autoguided images on this web site. I should disassembly the mount and clean it or send it to service.

ISO sensitivity of the camera

In image below i tested the ISO sensitivity of the camera and how it affects the noise patterns in the image. Target was globular cluster M13 in Hercules. From the original 5200 x 3500 pixel image a small area of 350x260 pixels has been chosen to see the noise patterns. Images below in first row are raw images without any modifications. In second row are stacked images. It can be concluded that the noise is smaller with low ISO sensitivity.

Using Deep Sky Stacker(DSS)

I use Deep Sky Stacker(DSS) software to reduce noise from pictures. Noise is caused by heat from camera sensor and from light pollution. This random noise can be reduced when several images are taken of the target and they are compared to each other.

Below is example of effect of using DSS. Target is Andromeda galaxy M31. On left is one original 2 minute exposure with Canon Eos 60Da, with ISO 1600 sensitivity. Telescope was SkyWatcher 80/600 ED. Image on right has 6 original exposures stacked with DSS. After DSS the picture must still be edited e.g. with Photoshop or with Gimp.

The stacking improves the signal-noise relation of the image. And then it is easier to make afterwards image improvements. Stacking method is useful especially for galaxies and nebulae. For planets, sun and moon there is another method implemented for example in Registax software.

Signal-noise relation is improved in relation to square root of the amount of the stacked images. So a stack of 4 images has 2 times better signal-noise relation than a single image. The images have to be taken with same exposure times and ISO sensitivity.

The DSS does not support the RAW format(CR2 files) of Canon Eos 60Da, so I will convert the RAW images to TIFF format with Canon Digital Photo Professional (DPP) software, and then I stack the TIFF images.

Concepts in stacking:
Light frame The original image of the target, galaxy or nebula
Dark frame Image taken with lens cover on, with same ISO sensitivity and exposure time as the light frame. This will contain the noise patterns of the camera sensor and this will be reduced in stacking process from the stack of light frames.
Bias frame Used to remove the noise signal caused by camera reading the sensor. Taken with lens cover on, with shortest possible exposure time, for example 1/8000s. About 10-20 images needed. I do not use this in my astroimages.
Flat frame Used to remove vignetting effect. Taken with putting a white blanket in front of the optics and take images of it in daylight. Optical setup and focusing has to be same as in light frame. I do not use this in my astro images.

When using DSS first time, you first wonder why the result image looks like highly overexposed. This is normal. Same the image and make further adjustments of the brightness and contrast for example in GIMP or photoshop. The image gets then much better.

Registax and Autostakkert for Moon, Sun and Planets

Registax is used to stack images of planets, Moon and the Sun. It calculates a average image from large set of frames, so that the distortion caused by earth atmosphere is reduced.

Latest registax is from year 2011 and it does not support Canon Eos 60Da camera 5184x3456 pixel images and HD video(H.264 MOV). For images the max limit is 4096 pixels, so images has to be adjusted to that size. In Canon Eos 60Da camera the video-mode with 640x480 pixels crop video mode can be selected. A 30-60 seconds video is taken. The resulting mpeg4 video is converted to 640x480 AVI for example with Pinnacle studio software. The AVI vide file is processed with Registax to produce final image.

Below few trials with small stack size.

Closeups of features on the Moon, with video stacking method, using Registax software. The size of each image is 103 arch seconds, which is 183 kilometers on surface of the Moon. I use F10 focus in Celestron 8 telescope, with 20mm ocular. In Canon Eos 60Da camera the video-mode with 640x480 pixels crop video mode was used. A 30-60 seconds video is taken. The resulting mpeg4 video is converted to AVI with Pinnacle studio software. The AVI vide file is processed with Registax to produce final image. With default settings Registax selects about 10 percent best video frames for stacking.

Om March 2020 I learned to use Autostakkert software for stacking images on Moon and planets. Autostackerts gives easily much better results than Registax. Below are few examples of stacking one minute videos of Moon.

Light pollution

Below is a test of light pollution. Same target in urban area and on country side with same camera settings. Difference is huge.

Sky-Watcher Merlin travel tripod

Below is a picture of a compact tripod with sky tracking capability. It is easy to take this system with e.g. when traveling abroad with plane. I used this equipment in a trip to Cran Canaria 2013, to take images if Milky Way galaxy center areas.

I started astrophotography with Canon film camera in 1980s. The telescope was Carl Zeiss Telementor 63/840. Camera with normal objective was mounted on telescope and I used the telescope to make manual tracking of stars, by keeping a bright star in the middle of the view during the exposure. I started the astrophotography again in year 2010 with better equipment.

Link to main page.

Oskillation in HEQ5 tracking , february 2020

It is typical to have all kinds of problems when doing astrophotography. Here is solution to a oskillation problem in R.A axis of HEQ5 mount which was just 6 months old. Apparently in the factory the bolts holding the motor and the gears were not set tigth enough in the factory. They were loose and the gaps between gears had grown too large, causing a large oscillation movement in R.A axis.

In image below rigth, there is 3 gears A, B and C for R.A axis. They are tightened like this:
(1) Loosen the 3 bolts marked with letter T. Push down the metallic plate so that gears B and C are tigthly together. Then tighten the T bolts.
(2) Loosen the 3 bolts marked with letter M. Press at same time the 3 M bolts downwards so that gears A and B are tigthly together. Then tighten the M bolts.

Copyright (c) for pictures, 2012-2019 Harry Rabb. All rights reserved.