What you need and getting set up
The first thing to do is to make sure that you have an up-to-date version of SharpCap from https://downloads.sharpcap.co.uk . You need at least version 4.1.12925 to get all the features used here, and at the time of writing, you need to download and install that version (or a later one) manually rather than relying on auto-update.
I'm not going to cover the basics of planetary imaging - choice of telescope, finding the planet, focus, etc - there are plenty of guides elsewhere for that, instead I will concentrate on the setup of SharpCap Planetary live stacking to get good results and animations. I will make some suggestions on camera settings however that help keep things running smoothly...
- If possible, use a camera with a larger sensor than a typical guiding/planetary camera - ideally the timelapse will run without intervention for an hour or more, and if there are any tracking errors, SharpCap can automatically handle them using the camera ROI on a larger sensor camera
- Use the camera in 8 bit mode (RAW8 or MONO8) and set an ROI to show the planet a decent size in the image - a 640x480 ROI was used in the example above. Using an ROI should allow the camera to hit high frame rates, even on larger sensor cameras
- For Jupiter, I have been using an exposure of typically 10 to 15ms, allowing a frame rate of 60-90 fps. The short exposures will help freeze the seeing effectively
- Once you have set an exposure, use the gain control to adjust the image brightness so that the brightest parts of the image are at about 80% on the histogram
- If you have colour balance adjustments for your camera, they are best left set to the 'neutral' values (50/50 for ZWO cameras). Don't worry if this shows an odd colour image in the individual frames - that can easily be fixed in planetary live stacking
Once you have the camera settings adjusted, the planet in view and have achieved good focus, activate Planetary Live Stacking - you can do that from the 'Tools' menu or using the little 'Jupiter' button to the right of the traditional deep sky live stacking button.
The first thing to configure is to check that the alignment and stabilization options are set up correctly for capturing a planet.
- Set the stabilization mode to Planet/Full Disk
- Set the stacking mode to single point (you might want to try multi-point later, especially if you have a high magnification view, but single point will be good enough for now)
- Set the option to track the planet with camera ROI - SharpCap will automatically adjust the position of the ROI if the planet drifts
- Set the option to re-align colour channels (unless you are using an ADC - with an ADC this shouldn't be necessary).
At this point, you should see an image of the planet that is stable and less noisy than the individual frames, but will still be blurry and may have an odd colour, perhaps a bit like this...
Adjust colours and sharpening
The next stage is to have a first go at fixing the colour and brightness and sharpening the image. Return to the 'Sharpening and Adjustments' tab. If you have made adjustments to the settings here before, it might be a good idea to use the 'Reset All' buttons to reset the sharpening and colour adjustments. The next steps are
- Use the 'Auto Adjust Brightness/Colour' button to set some reasonable values to correct the colour balance and the brightness of the image. These can be fine tuned later.
- Start sharpening the image using Level 1 through Level 4 wavelets. Level 1 gives control over sharpening of fine details, through to level 4 which works on larger features in the image. I tend to start with level 1 and work up to level 4, turning each up in turn until it is obviously too much sharpening (makes the image look bad), then turning it down a bit before moving on to the next. You will probably find level 1 or 2 need to be the highest with a little of level 3 and very little level 4 sharpening.
- Adjust the saturation slider to give a richness of colour that suits your tastes
- A little 'Fine' sharpening may help - alternatively you can use more 'Fine' sharpening and less 'Level 1'
- If you see a bright ring around the edge of the planet, turn up the 'De-Ring' slider to help reduce it. If you turn it up too far then you will see that the edges of the planet stop being sharpened, so turn it down again
Activate filtering and set optimal stack length
The next stage is to think about whether to use frame filtering (only include the best frames in the stack) and to also adjust the stack length if required.
Frame filtering can be easily activated on the 'Frame Filtering' tab, and you can adjust what percentage of frames are accepted into the stack. Because SharpCap works in real time rather than stacking an already existing video file, it can't look at every frame and work out exactly which are the best 50 or 25% of frames. Instead, SharpCap estimates what quality level corresponds to the best 50 or 25% of frames based on a history of recent frames. You can adjust the length of the history in use, and a value that is between 1 and 2 times the target stack length seems to work well. You can actually get good final images without filtering the frames, particularly if the seeing is fairly consistent.
Setting the optimal value for the target stack length requires a bit of thought...
The most obvious result of changing the stack length is that it will change the amount of noise remaining in the stacked image (more frames means less noise). Since sharpening tends to boost noise, if you struggle to get detail in the image without also bringing up unacceptable amounts of noise, try setting a longer stack length.
On the other hand, for a fast changing target like Jupiter (fast rotation), setting the stack length to be too long can lead to smearing due to rotation happening during the time over which images are stacked. To avoid this, you'd typically want the total time range of frames being used for the stack at any one point to cover under 3 minutes of elapsed time. Because of the way the 'live' stacking has to work is slightly different from traditional stacking, there is a contribution to the image from frames going back further than the 'target stack length', although the contribution from older frames is smaller. A good rule of thumb would be that the target stack length should not be much higher than the number of frames added to the stack in 60s - so, with a camera FPS of 70fps and a filtering option of 50% used, about 35fps would get added to the stack on average, giving a target stack length of up to 2100 frames or so to be reasonable.
At this point, fine-tuning of any settings that have previously be set is a good idea - for instance if you have increased the stack length to 2000 frames from 1000, you might find you can increase the sharpening a little without noise being a problem. Once you are happy with your settings, it is time to configure the timelapse...
Starting a timelapse
The key things to do when configuring the timelapse are
- Set the output for the timelapse to be either AVI or SER format - these allow the creation of the secondary animated GIF version of the timelapse that is more social media friendly. AVI can play in almost any media player while SER can be 16 bit and contain frame timestamps, but requires a specialised player like SERPlayer
- Set a timelapse interval - how often should a frame be saved. Once every 5 seconds will save 720 frames per hour for Jupiter, which is probably more than sufficient - once every 10 or 15 would be fine if you are planning 2 hours or more.
- Set the option to stabilize brightness - this will help compensate for brightness changes caused by passing thin cloud
- Set the option to create an animated GIF version and (if preferred) to create a forward/reverse playing animated GIF. This animated GIF version is created after the timelapse is completed (when 'Stop Timelapse' is pressed) and will have a play duration of about 5s for a 'forward only' and about 8s for 'forward/reverse'
- Press the 'Start Timelapse' button
Keeping an eye on your timelapse
In practice, it's worth keeping an eye on things - for instance...
- If you have significant drift you might find that the ROI movement runs out of adjustment with the ROI hitting one side or other of the full image sensor area - if this happens make fairly slow mount movements to pull the planet back towards the sensor center - as long as the movements aren't too rapid (maybe 8x sidereal speed), the ROI should track the movement of the planet caused and any poor quality frames should be excluded by the filtering
- If you have an EQ mount, it might reach the meridian and stop tracking
- Conditions might change - if they improve you may be able to increase the amount of sharpening being used
One last thing to note is that when you have a set of planetary stacking setting that work nicely for you, you can save them for later re-use - go to the 'Save/Load Settings' tab and choose to save the settings into one of the pre-defined slots. You will also find the value of these settings in the 'CaptureSettings.txt' files saved alongside the timelapse saved video.
Other things...
Some other things you might find useful:
- If you change target or framing or make large changes to the settings, it may be worth using the 'Reset Stack' button to clear the data in the stack and start over
- Don't forget that you can save snapshot images of the planetary stacking processed image using the 'Save to PNG' and 'Save to TIFF' buttons.
- You can perform normal video captures while planetary live stacking is active - indeed while a timelapse is running. Just press the 'Start Capture' or 'Quick Capture' buttons as usual. This lets you capture SER files (perhaps when the seeing is best) for later traditional processing
- Once you have your planetary stacking settings sorted, you can try fine tuning focus using the planetary stacking as a guide - reduce the target stack length to maybe 200 frames so that the image will adjust quickly to changes in focus, then watch the quality of the image and the 'Display Frame Contrast' value as you try different focus positions
cheers,
Robin
The silliest things can catch us out. 