Open Sharpcap on the PC. Plug the camera into the USB port, look for the model in the camera tab and select your camera.
When the camera has been selected, you should be able to see a live image on the screen directly from the camera. If there is no image or it appears too dark, adjust the exposure and the gain sliders on the right until you get a visible picture. At this point you need to ensure that your camera is focused correctly. You should be able to make out the focus point by moving the focusing dial back and forth until you obtain the sharpest point. Use the feather touch dial to find the final focus point and lock into place when you have found it. The last focus point adjustment will require only slight touches to find the ideal spot. The wobbling image from the ‘seeing’ can interfere with the view and it can sometimes be quite challenging to know whether you have found the correct focus point. The way to achieve this is to look at the brief instances of clarity and focus on these. When you find the focus, keep in mind that it could change very slightly during the session as the temperature changes and that you may need to keep adjusting and refocusing during your session.
It may not always be possible to achieve focus in all situations as this depends on your equipment. A common problem with the inability to gain sharp focus is due to the focal point extending too far behind the sensor. In this situation, an extension tube may be required to increase the gap between the camera and the focuser. This additional space directs the focal point correctly towards the sensor.
The image below shows the quality to expect from a typical live view image; you will notice a difference in the field of view using different equipment. The first thing you will see on the live view are some of the finer surface details which will be accompanied by varying amounts of intermittent blurring. The intensity of this blurring varies depending on the atmospheric conditions and this live view image will provide an initial sight of whether the ‘seeing’ is good or bad. The image will be in black and white even though you are using a colour camera. This is normal and the colour can be brought out in post processing if required.
Image viewed through the Skymax Pro180 using ASI224MC camera.
Sharcap – histogram view.
There is another step to complete before you start capturing; you need to ensure that the camera is exposing correctly. Select the histogram view using the icon on the top bar to bring up the histogram. Then adjust the gain and exposure sliders to increase and decrease the exposure/brightness of the image. As the image becomes brighter, the histogram will move to the right and, conversely, lowering the exposure or gain will move the histogram to the left. Aim for about fifty per cent to sixty per cent on the histogram. Any more than this may hinder the post-processing because part of the post-processing involves expanding the histogram in a controlled manner and the fifty-sixty per cent figure leaves room for this part of the process.
The balance between gain and exposure is critical to capturing a high frame rate and obtaining the ideal exposure; a high frame rate allows a quick capture and an excellent chance of cutting through the seeing. To achieve 100 frames per second (fps), the exposure must be no more than 10ms, otherwise you will compromise the capture rate. As increasing the gain produces more noise, you must balance both gain and exposure to obtain an optimum position.
For example, setting a fast exposure will allow more fps to be captured and give you more frames to stack in the final image, however the use of more gain for compensation will generate more noise. On the flip side, setting a slower exposure will result in fewer fps and less gain and, therefore, less noise, but setting the exposure too slow will hinder the positive effect of cutting through the atmospheric distortion and lose resolution.
It is better to compromise the max fps for lower gain and to use an accurately polar-aligned tracking mount. Excellent tracking will keep the Moon static in the viewfinder long enough to capture as many frames as you need. The maximum fps is not as crucial for lunar imaging as the Moon is tidally locked. For planetary imaging it is much more critical as you need to factor in the rotation rate of the planet which makes quick imaging essential. The essential aspect is to concentrate on capturing the correct number of frames for stacking and to spend time setting up your tracking to ensure that you can capture high-resolution frames over an extended period. It is appropriate to obtain a minimum of 5000 frames to ensure that there are enough quality frames for stacking. This usually takes a few minutes. If you find that the Moon drifts out of the field of view during the imaging period, this will be noticeable after stacking the video frames, as visually there will be stacking artefacts and noise in areas of change around the edges of the stacked image.
Finally, select a colour space format. It is preferable to shoot in either the 8- or 16-bit raw modes but ensure that you have plenty of spare hard drive capacity, as each short video can be up to 10GB. If you intend to process the image intensely, it is better to use the 16-bit mode, as the colour depth is so much deeper. This ensures that there is less likely to be any banding or colour distortion on the final image.
The difference in colour depth between 8 bit and 16 bit is quite astounding. The total number of colours for an 8-bit image is 256 shades of red, 256 shades of green and 256 shades of blue resulting in 256x256x256 = 16.78million, whereas a 16-bit image has 65,536 shades of red, 65,536 shades of green and 65,536 shades of blue resulting in a total number of possible colours of 281 trillion!
When you are ready to capture your image, click the Start Capture button and the software will bring up a box in which you either type the number of frames you want to capture or select unlimited and stop the capture in your own time. Click Start.
The software will start capturing frames. You can keep an eye on the total number of frames captured and the number of frames per second displayed in the bottom left-hand corner.
The video capture will stop when it has completed the designated number of frames or if you manually stop the process. The file will automatically save in the Sharpcap captures folder; all the videos from the capture session will be saved in the same folder.
If the computer, which you are using, has inadequate processing power, you may find, when shooting in 16-bit mode, that Sharpcap starts dropping frames. Capturing the 16-bit frames requires intense processing power. Dropping frames is not such an issue if you have accurate tracking, as it will just take a little longer for the total capture. If tracking is not available or not working very well, the 16-bit mode is not the best option, as it is very processor hungry, and you will not have enough frames for your stack. In this situation, a better option would be the 8-bit mode, as it uses less processing power and is unlikely to drop frames.
Another method of increasing the frames per second is to reduce the capture area; you can change this in the settings on the right. The smaller capture area will generally use less processing power as there is less data per frame; resulting in an increase in fps, although the image resolution may be compromised to some extent. Try experimenting with different settings to find an optimum capture profile for your set-up.
How does the image compare with different telescopes?
What image can you expect using the same high frame rate camera with different telescopes?
The following images show a comparison with telescopes of different focal lengths. The first image was taken through a Skywatcher Esprit 80mm refractor (400mm focal length) using a ZWO ASI224MC and you can see that the Moon fits inside the field of view. It is a much broader perspective than the second image taken with the Skymax Pro180. The stacked image resolves surface detail nicely in both pictures and if you compare these images with the DSLR images using the same telescopes, you can see the dramatic difference in FOV and clarity. The benefit of using a high frame rate camera is clear.
The Moon imaged using the ASI224 with the Skymax Pro 180 (2700mm focal length) has unprecedented detail of the lunar surface features. This image shows the Sinus Iridum and Plato region of the Moon. You can see how fine detail has been resolved using this setup.
ASI224MC, Skywatcher Esprit 80ED, stacked image.
ASI224MC, Skymax Pro180, stacked image
Adding a Barlow lens – expanded view.
Inserting a Barlow lens
This image shows how the Barlow lens fits inside the imaging train; the type of Barlow lens shown in the picture is a 2x Televue 1.25”. Insert the Barlow lens into the eyepiece holder between the camera and the telescope. The camera then fits into the other side of the Barlow lens.
When fully assembled and attached to the scope, the focal length of the Skymax Pro180 will be doubled from 2700mm (f/15) to 5400mm (f/30). At this focal ratio every aspect of the imaging becomes more complicated, the focusing becomes more sensitive and very difficult without a micro focuser and the tracking needs to be almost perfect.
The image left shows the magnification gained by adding a 2x Barlow lens to the imaging train; this addition has doubled the focal length and changed the system from f/15 to f/30.
ASI224MC, Skymax pro180 with 2x Barlow lens, stacked image