Hi,Martin. Congratulations! Your work won the Greenwich astronomical photography competition. Could you introduce yourself for everyone?
Hi,I'm Martin Lewis,a planetary imager living north of London in the UK. As well as planetary imaging I love building telescopes and other astronomical equipment. I also enjoy sketching and observing deep sky objects.
We are very curious that what is Greenwich astrophotography competition? And what will I get if win in the competition?
The Insight Investment Astronomy Photographer of the Year is the largest astrophotography competition in the world with over 4000 entries this year from Europe, US, China and many other countries. The competition is judged by a panel of astronomy experts and artists and there are 10 categories ranging from Our Sun to People and Space. I was fortunate enough to win the first and second place in the Comets, Planets and Asteroids category. The overall winner gets £10,000!
《The Insight Investment Astronomy Photographer of the Year》是全球最盛大的天文摄影比赛，每年会有来自欧洲，美国，中国还有其他国家的共计超过4000多名摄影师参赛。比赛名次由天文专家和艺术家组成的评审团评出，共有10个类别，从”我们的太阳”到”人与太空”。 我很幸运，在彗星、行星和小行星类别中分别获得了第一和第二名。如果能获得大赛的总冠军，会有10000欧元的奖金!
Here are my winning entries, all images taken with ZWO cameras.
'Grace of Venus' 《优雅的金星》
'Parade of the Planets'《太阳系全家福》
When did you start like astronomy? And when did you have your first telescope? What’s the feeling in first observing?
I have been observing for nearly 50 years now. I got my first telescope when I was about 9 years old and I still have it. It was a small wobbly refractor with a very cheap 50mm lens but with that telescope I saw a tiny, and I thought perfect, Saturn, with the rings wide open. I was hooked on astronomy from that point onwards!
I started planetary imaging in 2005 using my home-built 222mm Dobsonian reflector which at that time was unguided. I let Jupiter drift through the field and recorded several drift videos with a Philips Toucam webcam.
I then combined them in Registax to create this first image.
Later that year I built an equatorial tracking platform to improve my imaging of Mars, which was at opposition in Winter 2005/2006. For many years I used my 222mm Dob. for planetary imaging- learning many techniques and improving my methods.
You can see the improvement I made over the years in the following two images taken with exactly the same telescope but 7 years apart.
In 2013 I decided to try planetary imaging with my much larger home-built 444mm Dobsonian telescope which I named 'Fossil Light'. Up until then I had only used as this as visual instrument. I made an electric focuser for it and it worked out really well on the same equatorial platform that I originally built for the 222mm telescope. The extra aperture this bigger scope has given me has allowed me to push on even further with my planetary imaging as the image below shows from 2017.
You are very familiar with Newtonian telescope, do you have any ideas about how to adjust optics axis and what kind of calibrator is necessary?
I have aligned all my optics mechanically to be centralised as part of the design. I store my collapsed telescope in my garage then build it up every night which takes 15-20mins. Because of this the collimation changes each time by a small amount and so I collimate my Newtonian with a sighting tube and Cheshire eyepiece which takes no more than 2mins making slight adjustments to secondary then primary. I much prefer this method to laser collimators. SCTs are much harder to collimate and simple tools don't exist so with those designs you have to collimate on stars using the star test. The simplicity of collimating Newtonians is a significant advantage of this type of telescope.
Dobson telescope has field rotation problem in shooting, so is that a big problem for planetary imaging?
Autostakkert! does have a field rotation feature which might be useful for longer recordings but I've not used it. For me field rotation is not a problem as the equatorial platform eliminates the issue and keeps things simple.
There are a few planetary imagers with big Dobsonian Newtonians on equatorial platforms such as the author of Autostakkert!, Emil Kraaikamp. I hope more people will try it as the method allows you to image with big apertures without spending a fortune. One key issue with this arrangment, however, is that the platform motor must be low vibration. I use a vinyl record turntable synchronous motor which is driven at 100VAC instead of 240VAC and this is mounted on a vibration absorbing plate.
为数不多的拍摄者给巨大的道布森牛反安装赤道式平台，比如Autostakkert软件的作者 Emil Kraaikamp。我希望更多的人能够尝试大口径道布森牛反和赤道式平台，因为这类望远镜相对便宜。有个关键问题，就是这种跟踪平台用的电机必须是震动非常小的。我使用的是唱片转盘的同步电机，它的工作电压是100V而不是240V，我把它安装在一个减震板上面。
What are the advantages of Newtonian in planetary imaging? A lot of people use a SCT.
I mentioned earlier about collimation but there are several other advantages with using a Newtonian for planetary imaging. A Newtonian generally has a smaller secondary size compared to an SCT helping improve image quality.
I use them because they are low cost- especially if you make them yourself. Another advantage of a Newtonian over an SCT is that there are no UV absorbing AR coatings in the telescope which helps with Venus imaging in the UV.
Which ASI camera is your favorite? And why are you choose it?
All my ZWO cameras are great but the one I have been using the most recently is the ASI290MM for IR imaging of Neptune, Mercury and Mars. I love the low read noise and fast speed. If you were to take all my cameras away except one I would keep the ASI224MC as it is so versatile, sensitive and low read noise. Also the ASI224MC is a colour camera and I love the ZWO colour cameras. I have been doing all my colour imaging for the last few years using colour cameras rather than from RGB mono imaging. I experimented many times in the past comparing one-shot colour to RGB mono imaging and I almost always got better results in real world situations with the colour camera.
Is planetary imaging is your favorite? What setup do you use currently? Could share a picture of your setup?
Planetary imaging is definitely my favourite type of astro imaging. My current set up is my 444mm Dobsonian on my equatorial platform. I use a home-built combined ADC + filter block + APM barlow. The barlow can be 2.7x or 6.25x depending if I use one or two barlow elements and this gives f12 or f28 making it really flexible. I do IR or UV imaging with mono cameras but always use a colour camera for colour images rather than doing RGB imaging with a mono camera.
444mm Dobsonian 'Fossil Light' on equatorial platform ready for darkness.
在赤道式平台上静待夜晚来临的444mm 道布森“Fossil Light”。
Optical imaging set-up; combined ADC, filter block and barlow.
What is the hardest part in planetary imaging? And how to get rid of it?
Wow that's a tough question! Success in planetary imaging is all about attention to detail at all the stages, start to end. If you have quality optics of a decent aperture that is correctly set up, collimated and cooled, combined with a good camera, then if you are lucky, and the seeing is good, you will get good data in you videos. Those videos then need to be correctly processed to maximise the potential of the data and there is a lot of experience in that. The process can fail at any of the links in the chain so it is important to see the imaging process as a whole and not neglect any one part of that chain.
To pull out detail in Venus images you need to image in ultraviolet light and I use a special Venus UV filter to achieve this. The best detail is visible when the air is very transparent but it also needs to be steady which is a rare combination unfortunately.
ADCs are wonderful devices to help with planetary imaging especially for Northern Hemisphere imagers who have to suffer with low altitude planets for the next few years. They are particularly important to get the best out of colour cameras which have wider bandwidth in the individual R, G and B colours than mono cameras used with dedicated colour filters.
I also use my ASI cameras at the heart of an AllSky camera I built. This gives great time-lapse videos of the slow turning night sky. Again the big chipped ASI174s work well here. You can see my time lapse videos here.
I love the tremendous range of great value cameras that ZWO sell and they have done really well in quickly bringing the latest chips to the market for astro imagers. They understand what imagers need with cameras and what aspects are important. For planetary imagers those important characteristics are sensitivity, speed and read noise.