THE STORY: Veil Nebula and Planewave CDK14 – it can be so easy
The "Veil Nebula" NGC 6960 is a remnant of a supernova explosion that occurred 8000 to 10,000 years ago. With a length of over one degree it is huge - and the Cygnus loop, to which the Veil Nebula belongs, is even larger at around 2°! For this picture, images from two nights were combined, whereby subframes with seeing values worse than 2.05" FWHM were not used.
Now, I have to admit my preference for long focal lengths right at the beginning. As far as conditions allow, I want to get details out of the pictures - and since I have a location that often has good to very good seeing, I can live out this fondness. Friends of mine could measure the seeing and confirm that it is often better than expected! But: as long as it is not measured, you do not know.
This is another reason why I am a fan of the C14 EdgeHD. In the course of two years and many clear nights I have optimized my workflow to such an extent that many of my pictures were taken with this instrument at almost four meters of focal length (or 2737 mm with the 0.7x Reducer) – see my Facebook channel.
So why now a Planewave CDK14? Thanks to Johannes Baader, I was able to to test this instrument, because my images with the C14 EdgeHD had been convincing. Such a focal length needs to be mastered, just unbox and start imaging normally doesn't work. Besides, I always wanted to experience an absolute high-end performance – preferably "out of the box", but this is beyond my budget. Would there be such a learning curve with the borrowed Planewave CDK14 Astrograph?
Since I have a good understanding of my 10Micron GM 2000 HPS Mount, a resolution of 0.39" per pixel is not a "big thing". I can expose without problems up to 900 seconds with this resolution. To have a comparison with my older pictures, I decided to use the proven Nikon D810A camera. The 36,3MP (4,8µ pixel) and full frame would be a big thing.
At f/7.2, the CDK 14 has got a focal length of 2563 mm, so I quickly realized I would be shooting 480 seconds at ISO800. This combination of exposure time and ISO is perfect for a typical summer in Austria, where I planned my first shots.
So lets get the telescope ready for use. Amateur astronomers have a rather high pain threshold. Something is always missing, and the fact that the same name can mean completely different threads is nothing new. If you have been at this field for a longer time, you know that hardly anything works "out of the box", even if you have been advised in detail by your dealer and all parts are there. But what belongs where, and what settings have to be made? At which set screw do I have to turn, and does a part introduce unwanted bending because it is not stiff enough? So what would I expect from a professional system that offers even more degrees of freedom?
So let's take a look at the PlaneWave CDK14: unpacking and attaching all the parts was well thought out and well prepared. The EFA-Kit (the Motor Focuser or Electronical Focuser Assembly) was already installed, I just had to attach the control unit. The reduction to the M68 system was also quickly attached, so that even heavy accessories cannot tilt – no undersized mechanics that twist or tilt under their own weight. I calculated the M68 adapter for the ideal camera distance in such a way that the extension for the Nikon only had to be 9 mm long. For my other cameras, the FLI ML16200 and CFW 2-7, no more than 3.5 mm are necessary.
I mounted the Delta-T-Heater on the opposite side, so that I achieved a good balance in the DEC axis. This small box does what a long dew cap would otherwise do: It reliably controls the integrated exchange protection system of main and secondary mirror and adjusts their temperature according to the environment. So much for cooling-down times and dew-covered optics! After a quick cabling of EFA and Delta-T, I could already start – without additional reducers, field flatteners or coma correctors, and without readjusting the optics! I attached the spandex light shroud for the bars with the tension cables (seam) exactly on top in the middle of the optics. Additionally, I had attached a 1 kg sliding weight to the upper 3" rail, so I could work with the 10Micron as usual without guiding, perfectly as I'm used to.
All that remains is to press the shutter release button. And now I don't have anything else left to write, I can only say: It's extremely fun to take pictures with the CDK14. The Veil Nebula NGC 6960 was the second object which I shot with the CDK. With the Nikon D810A I achieved 0.39" resolution per pixel, which worked very well unguided. All optics and accessories work perfectly, the stability is top notch.
This way I got enough subframes in three nights, which I merged to one picture. But enough written, I think the picture answers all questions! What is noticeable: At 480 seconds exposure time and ISO 800 there are no reflections at all, although the star has 4.2mag! A superfine image over the whole field, without color fringes. The D810A with 36.3MP and 4.8µ small pixels with full format had set standards at the time of its introduction. And the GM 2000 HPS ran with the 22kg tube like only a 10Micron does - 480s at 0.39" resolution, again and again and again.
With the Planewave CDK14 it was so impressively easy that I had to spontaneously send a message to my astronomy colleagues during the night - with the words "THIS IS CRAZY"! Why? Well, you can see for yourself what I immediately got out of the CDK 14 - what more could you want? Is it even possible to get more out of it?
March 2020, Christoph Kaltseis
THE EQUIPMENT: Perfectly matched
The combination of large aperture and long focal length is ideal for bringing out all details of the object. For this to succeed, everything must work together perfectly – no part must give way. That's why this combination has delivered a quite impressive result already in the first night: The picture of the Veil Nebula was taken without a need to optimize the setup. The Nikon D810A was used to compare the results with an older telescope setup - with a cooled astro camera even more would be possible.
PlaneWave CDK 14 Astrograph f/7,2
Planewave's 14" (356 mm) Dall Kirkham Cassegrain contains a fixed optical correction unit that provides the telescope with a completely flat field of view of 70 mm diameter without coma or astigmatism across the entire field of view at a focal length of 2563 mm. The Hedrick focuser, the EFA motorized focuser and the Delta-T-Heater are available as options. The quartz mirror (fused silica) avoids the temperature instability of crystalline quartz.
10 Micron GM 2000 HPS II – Ultraport
The GM 2000 mount with a weight of 33 kg carries up to 50 kg payload – photographically! The Ultraport version can be disassembled into two parts for easy transport. The axis encoders and the toothed belt drive track even long exposed shots without autoguider, only based on an exact pointing model – and that with an accuracy of approx. 1"/15 minutes (peak-to-peak).
NIKON D810A with Baader M68-System
Tilt is the enemy of every successful astrophoto. The CDK 14 therefore focuses on the large M68 connection system that keeps all accessories firmly in place. This is equally important for a relatively light DSLR like the Nikon D810A, which reveals every flaw with its high resolution and full format sensor, as it is for a heavy CCD camera with filter wheel. The Baader M68 telecompendium allows the adaptation of any accessory.
About the author: Christoph Kaltseis
Christoph is not only an Adobe Photoshop specialist and as Nikon Professional touring for Nikon, but also an experienced astrophotographer. He is one of the founders of the Central European DeepSky Imaging Conference (www.cedic.at), which is held every two years in Linz since 2009.
In addition to his various projects, Christoph has developed an innovative image sharpening process called APF-R (Absolute Point of Focus)in recent years. The procedure is not always the same, but is adapted to the combination of lens and camera. Therefore, a flexible method was necessary to achieve the desired results.
In his career as an astrophotographer Christoph has also created several APODs (NASA Astronomy Picture of the Day), e.g. the APF-R-processed image of the M33 Galaxy or the Heart of the Orion Nebula (M42).