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QHY EZCap Tutorial

PostPosted: Thu Mar 01, 2012 11:05 pm
by Zakalwe
Right, ladies and gents, this is a very, very basic tutorial on how I use EZCap, the supplied software that comes with QHY’s 8L camera. A few of you are starting to use this camera, and the supplied software might be the first exposure that you have to the wonderful world f cooled CCD cameras (it was for me!). EZCap comes with no instructions or help file, and although it is pretty straightforward once you get your head around it, it can be a bit intimidating.

I thought of scribbling this down as I have been using the camera for a while now, and have learned a few tips and tricks which you might want to use. It is not intended to be a “master class” nor am I the font of all knowledge. Rather this is how I use the software. Oh, and I am NOT doing a video…I wouldn’t inflict my ugly mug on all you good people! ;)

There are some other bits of software that you might want to get, including Deep Sky Stacker (for stacking the resulting images) and FITS Liberator (a freebie download, which allows you to view the .FITS files that the camera produces).

This tutorial will show you the workstream that I use. Again, there will almost certainly be other and perhaps better ways of doing thing, but this is how I do it. If you have a better/faster/sexier way of doing it, then please feel free to share it or ignore this post. If this tutorial helps you, then brilliant (your messages of thanks are gratefully received. Especially if written on £20 notes and posted to the usual address)

First things first, connect your camera up. You must use the correct sequence as you can damage the electronics in the camera if you don’t follow this. Connect the USB lead to the camera and connect it to the PC. Then connect the 9 pin DIN lead to the camera. This lead has a ferrite core (a black cylinder) at one end. This end plugs into the DC-201 control unit. Finally, plug in the 12v cable to the DC-201. When powering down the camera, you should use the same sequence in reverse.
Now start up EZCap. Go to the Camera area of the file menu and select QHY8L.


The next thing I do is to open the Temp. Control section (under Camera Setup) and switch the TEC (the camera cooler off). I do this as it tends to start cooling the camera too soon, which can lead to overcooling the sensor.
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A Word About Cooling
This (and other astro cameras) use a device called a Peltier device to provide Thermo Electric Cooling (TEC). This clever bit of kit is a sandwich of material, that when connected to a suitable electric current draws heat from one side and pushes it to the other side. This is then used to cool the imaging sensor. The colder the sensor, then the less electronic noise that it generates. This is a Good Thing in imaging. The cooling system on the QHY8L is known as Setpoint Cooling, which means that you set the level of cooling and the electronics maintains the sensor at that temperature. The QHY8L can cool the sensor down to about 35 degrees below ambient. When selecting a temperature, chose one that allows you to always achieve it. I personally use -25, but I have had the sensor as low as -45.
Being able to set the cooling means that you can also create a “bank” of dark files. If you have imaged with a DSLR, then you will know that you must take the darks at the same temperature as the light files. This is a pain, as the temperature drops during the night, and you lose imaging time taking darks. With Setpoint cooling, you can fire the camera up at any time of the day or night, and create a library of darks of commonly used exposure length. These same darks can be used over and over again. Having said that, these cameras really are noise-free. I can get good results with mine without using any darks easily up to 300 second exposures.
Right, back to the tutorial. The cooling system on the QHY camera can take a little time to stabilise, which is why I turn it off until I am ready for it. You can see here that I have set it at 0 degrees, but the system has overshot the mark to about -8, then overcompensated to +4. It will settle down, it just takes a few minutes to do so.
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The manual that comes with the camera (written in best Chinglish) recommends cooling in stages to prevent thermal shock to the big sensor. The same when you are wrapping up for the night….reduce the cooling in stages. Always allow the temperature to stabilise on your requested setting before starting imaging, otherwise the temperature that the lights are taken at might vary, which would mean that your darks will over or under compensate for sensor noise. The cooling system allows you to have no cooling (TEC Off), to manually control the cooling (the miss-spelled “Manuel” setting) or to allow the system to control the cooling (Auto Control). If you go for Manual, then you can set the amount of power going to the Peltier by using the slider on the left hand side of the cooler window. Selecting Auto Control, you just use the slider on the right hand side to set the desired level of cooling and the system does everything else.
Another thing that I have noticed, is that the system needs to stabilise on a temperature before starting to take lights. If you start taking lights when the cooling system is driving the temperatures down, then it seems to drastically overshoot the mark. This is another good reason for taking a little time to allow the cooler to settle and stabilise on the required temperature first.


Condensation and Sensor Icing
Cold things cause condensation. Really cold things can freeze. The sensor chamber on these cameras can be dried using a supplied dessicant tube. However, if there is a tiny bit of moisture in the chamber, this can cause ice to form on the sensor surface. This is not good, as you will get horrible gradients in your images. A tip I use, is to set the temperature at 0 degrees, and then go to the Preview window in the software, set the exposure at 1MS and then hit Live.
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This runs the sensor hard, which warms it up. Any moisture that might be in the sensor chamber will then condense on the Peltier cold finger, not the sensor. I’ll let this run for 4-5 minutes, then set the cooling at -10, run Preview again, then -20, the -25 (my desired setting). This means that I have no ice forming on the sensor at all. This has an added benefit as the Live setting displays a constantly updated view of what the camera is seeing, which allows me to get the mount aligned and my subject framed.
On very humid nights, especially if you are using a filter wheel, you might get condensation on the chamber window. QHY increased the chamber window thickness to 3mm to help prevent this, but in very humid conditions you still might get dewing. I wrap a 2” EP dewstrip around the extension tubes that separate my camera from the field flattener and give it a tiny bit of heat to prevent dewing. I believe that QHY also offer a small window heater which does the same job.
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Focusing
EZCap contains a full FWHM focusing tool, which allows you to get you focusing spot on. FWHM stands for Full Width at Half Maximum. This is the width of the star image at half the peak value of the star, a common measure of focus, seeing, and resolution. Ideally the minimum value is achieved for best focus. Once your camera is at the correct temperature, slew to a star. In the Preview tab (on the left-hand side of the application) click on Preview. This will expose an image and download it into the EZCap application. Then click on a star that you are going to use for focusing. EZCap will place a red box around that star.
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Now click on the Focusing tab. Click the Live button, which will then show a real time zoomed view of the area that you selected earlier. This will show you the selected star at the top of the window, and the FWHM reading at the bottom. Simply put, a smaller FWHM number means tighter focus. Tweak your telescopes focuser to get this value as small as you can get it. Don’t use the brightest star in the sky (about 2nd or 3rd magnitude), and aim to get the FWHM figure into single figures. Once you have done this, then you know that your focus is as good as it can be.
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To be continued...


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Re: QHY EZCap Tutorial

PostPosted: Sun Mar 04, 2012 7:22 pm
by Zakalwe
Part 2

Right, lets recap where we are up to. At this point you should now be able to Chill the sensor, and Focus the scope
Chill: reduce the temperature gradually, and run the camera in Live (under the Preview tab) to keep the chip from any chance of icing.
Focus: Select your star by clicking on it’s image in the Preview tab. Then go to Focus, hit Live and teak the telescope’s focuser to get the lowest FWHM number.

In this section I am going to talk about alignment, framing your target, getting an initial exposure to gauge sub length, setting up a schedule of exposures and setting up Deep Sky Stacker correctly to stack your results.
To help with the mount alignment, EZcap includes a reticule to help you centre your chosen alignment star. If you have ever used Al’s Reticule, then this is similar. Go to the Preview tab again, and hit Live. This will give you a constantly updated image on screen. The exposure (in milliseconds) is set by the slider on this tab. Now click on the Cross button. This will place a Cross on the image, which you can use to centre the star in the FOV. Once you have the star centred you can then command your planetarium software to synch to that star. The Preview tab also has an option to superimpose a grid pattern which can help you to repeat the framing of a subject if you are capturing data in different sessions.
A note about the Live button and the Preview button. As mentioned above, Live gives you constantly updated image on screen. Preview takes a single exposure and displays it onscreen. The image is not updated or downloaded onto the PC.
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Once you are happy with your framing you are now ready to start getting some data. Click on the Capture tab to open the main window in EZCap

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The Capture window allows you to set the exposure by moving the slider. If you right-click on the slider a pop-up will open which allows to select from a list of exposure lengths. You can also swap between milliseconds and seconds by clicking the button just above the slider. Below the exposure area are two bar graphs. The upper one shows the progress of the current exposure, the lower one is activated when the camera is sending the exposure back to the PC. Below these is the histogram. If you are not used to CCD cameras you might be wondering how to set the White Balance. Because the camera downloads .FITS files, there is no WB setting. This is all altered in post-processing.
In this section, you can set the binning modes. The QHY8L camera supports 2x2 and 4x4 binning modes only. However, these output grey-scale images only, so they are only really useful for focusing and framing. There is also a high Speed download button which is used only (as far as I know) when getting an image on-screen.
You will also use the Planner tool in this section to schedule your exposures. Go to the main menu, select Planner and this window opens:
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The Planner allows you to create an exposure schedule, with multiple exposure lengths. Place a tickmark in the leftmost check-box to make that line active. Leave the Binning mode on 1. Under ExpTime you input your desired exposure length in seconds. Or alternatively, right-click and you get a list of pre-set exposure times, from which you can select your desired length:
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You set the number of exposure under Repeat. The ColourWheel section is not used if you are using the QHY8L, as it is a One-Shot-Colour camera.
If you want to set another schedule for exposures of different lengths, then you make another line active by ticking the tickbox on the next line. You might, for instance, want to set up 300 second exposures for the nebulosity of M42, and a set of 30 second exposures for the core.
Click on the Folder button to set the download folder for the resulting images. Below this, you have an area to name your images. You can either free type into the field or used the keypad below to input the name.
The Start button does what it says. The Force Stop button will cancel the current and subsequent exposure and download the partial sub to the download folder. Below this are checkboxes for Dark and flat frames. If yo tick one of these, the resulting image name will be prefixed with “Dark” or “Flat”.
Many people new to dedicated CCD camera have asked how to gauge the correct exposure length. Cooled CCD cameras are much more sensitive that DSLR cameras and it is easy to burn out the highlights, or loose the star colour. The way I gauge the correct length is to go to the Capture tab, set an estimated exposure length. When you have set your exposure, make sure that the High Speed Readout is not checked, and then hit Capture. This will expose the camera and display the results on the main part of the screen. The image is not saved top to the PC. You can then check for burnt out highlights, correct exposure and so on. I have not found any way to display the whole image without scrolling around the screen which makes this a bit awkward, so I use now download an image and test it in a program called FITS Liberator. Open the Planner as described above, and set an exposure plan with a single sub length. Once the image has downloaded, got to the download folder and click on the .FITS file, which should launch FITS Liberator.

Re: QHY EZCap Tutorial

PostPosted: Sun Mar 04, 2012 7:50 pm
by Zakalwe
Part 3


FITS Liberator allows you to view the FITS file, stretch it, check for over-exposure and save it as a variety of images. Really, all I am going to use it for is to check for over-exposure and to convert the FITS file into a TIFF.

When FITS Liberator opens, you may see your image onscreen. If it is viewable, it will appear in greyscale as it is not de-Bayered.

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If you cannot see anything, you will need to perform a stretch of the data.

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Click on the Stretch Function and select ArcSinH(x), which will perform a stretch of the data. You should now see something in the preview window.

Below the preview window is a histogram, where you can move the Black and White levels.

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The bit that you are interested in is contained within the Image Statistics section:

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This shows the values of the pixels contained in the image. Bear in mind that a single pixel can have a value from 0, meaning that no light has been captured to 65535 (2 to the 16th power, including zero) meaning that the pixel is fully saturated. Once a pixel on the CCD reaches 65535, it is fully saturated, and will only show pure white. The Image Statistics section will show the minimum value for pixels in the image and the maximum. You should really try to avoid the image going to 65535 as you have over-exposed some areas (normally the stars, so you will have lost the star colour.
If you want to open the file in Photoshop, then click on the Save File button on the right hand side and save the file as a TIFF. The resulting TIFF file will be in grey-scale as it still has not been de-Bayered. This is useful to perform an initial stretch in Photoshop to see what data you have captured.
Once you are happy with your exposure length, go back to EZcap, open the planner and set your desired exposure length and number, click on Start and away you go.



A Note On Deep Sky Stacker

If you are using DSS to stack your resulting images, then you might find that your images have a strange grid pattern visible. This is the Bayer matrix, and you have to tell DSS the correct type to use. Go to the Options section and select Raw/FITS DDP Settings. Click the FITS Files tab in the resulting window and click on the drop-down at Camera. Select Generic GBRG” which then tells DSS the correct de-Bayering mode.

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