Whilst still relatively quiet, the Sun showed some impressive new active regions last week, apparently associated with quite large flares. Here are my white light images of the newer regions.
First, AR1745:
AR1746:
And AR1748, just after passing around the limb:
I read on the BBC News website yesterday that Adobe was moving to subscription-based charges for its software and “Creative Cloud” (whatever that means). If you’re in the UK though, it seems like you get stitched up on the pricing compared with the US.
From their website for the US “complete” individual subscription the price is $49.99 per month — about £32.50 at today’s exchange rate. For a UK user the price is £46.88 per month.
On an annual basis that’s about £390 for the US, or £562.56 for the UK, a difference of £172.56. Obviously it costs far more to get those electrons over the Atlantic to UK users than within the USA.
Oh, I forgot. There’s that massive 20GB of storage, too. I can generate more data than that in a single night. What a gimmick.
I can’t work out whether Adobe just think their UK customer base is stupid, or if they just fancy trying to rip us off. Well, Adobe, you’ll be getting no more of my cash. I’d rather donate some money to the GIMP project and use that than help fill the coffers of a company that shows such disrespect for its own customers. Time to get your head out of the Creative Cloud.
I was experimenting with shutter speeds and ISO settings whilst imaging the Moon with my DSLR the other night and when I got down to a shutter speed of 1/250th of a second starting seeing a problem where the top of the frame had a “ghost” image whereas the bottom of the frame was fine. Here’s a crop of the bottom part of one frame:
And here’s the top of the same frame:
I have frames taken at 1/500th and 1/1000th that don’t show this problem at all.
It’s been suggested to me that it might be caused by the vibration of the mirror moving, so I shall configure APT to pause after moving the mirror and see what happens.
Now the weather looks like it’s about to turn I can collect together the images of Saturn from the last five nights. Sadly it’s a demonstration of ever degrading seeing. Perhaps we need a bit of wind and rain to clear the air and I shouldn’t be disappointed that we’ve lost the clear skies for a while.
Anyhow, here they are, from the 29th April to the 3rd May…
Last week someone asked about a guide to stacking planetary images using AutoStakkert!2 (hereinafter known as AS!2) and I said I’d write something up. A few days later than I imagined, I’ve got around to it. This isn’t meant to be an exhaustive explanation of how to go about stacking planetary images. It’s more of a place to start from. I’ve ignored many of the options that you can get by without at first and glossed over a few things that you can pick up once you get into the swing of processing.
The sample I’m using is one of my own, taken using a 127 Mak on an EQ3-2 with the dual-motor add-on. I used a 2x barlow with my ASI120MC camera to capture about 3000 frames over five minutes which is well within the limits imposed by Saturn’s rotation. As long as you have an AVI file saved using a sensible (ie. non-lossy) codec however, you should be fine and the processing will be pretty much the same. It is possible to use sequences of single images, too. I’ve just never tried that for planetary imaging.
The first thing I do is preprocess the AVI using PIPP. This isn’t strictly necessary, but because the tracking on my mount isn’t that great I can’t capture data from just a small area of the camera sensor and there’s usually a fair bit of empty space around the image. PIPP allows me to crop this off and recentres the image to make the stacking faster and easier. I just load the AVI and check the “Planetary” option to set appropriate defaults:
Then I set the output frame size. As you can see above I had a 640×480 frame in the AVI. In the Processing Options tab I set the output size to be 250×250:
Unless you know why you want to change them, I’d leave all the other options along for now. Hit “Test Options” to get a window to show what the output should look like:
There’s clearly going to be enough room around the image, so I’m happy with that. If you’ve chosen too small a size you can go back and change it. This also gives an idea of the quality of my input data. Once everything looks right, go to the “Do Processing” tab and click “Start Processing”. This may take a while…
Once that’s done you’re finished with PIPP. It saves its output in a new folder beneath the one you loaded the AVI from. The location is given in the output in the window on the right.
Now start AS!2.
Click “1) Open” and open the AVI file written by PIPP. It will display the first frame in a new window:
Click “2) Analyze” and AS!2 will scan the images to decide how good they are, producing a graph in the first window:
The grey lines are the quality of each frame in order. The green one is the quality level with the frames re-ordered by quality. At this point you can decide how many frames to stack in the “Stack Options” box at the top right. With this sort of graph I’d probably leave it somewhere near 50%. If you have lots of poor frames or lots of very good frames you might adjust that to try to use as many good frames as possible whilst avoiding the bad ones. Leave the other options for the time being.
Now go back to the other window with the capture frame displayed. You need to set the number and size of the boxes used for stacking. There’s a lot said about box sizes and placement, but to get started and for an image of this sort of size I’d choose a box size of 25 and let it place the boxes automatically by clicking “Place APs in Grid”. It may be possible to do a better job than this, but you can always come back for a reprocess on those rare cloudy nights.
Then go back to the first window and click “3) Stack”. AS!2 will spend a while processing and eventually tell you it has done 100%:
In the folder where PIPP placed the AVI file there should now be a new TIFF file with a name starting “AS…”. That’s your stacked image, and you’re done with AS!2.
The final stage I do with Registax v6. I click “select” and load the TIFF file. You’ll see Registax drops you straight into the wavelets section
The first thing I do is sort the wavelets out. This is a reasonable image for me, so I got really quite aggressive with the wavelets:
If you look at the image now you’ll see that there’s a slight red/yellow tinge to the front of the rings, and they’re slightly blue at the back. It’s hard to see, but it is there. Many planetary images will be like this if they’ve been captured in colour. In fact it’s quite rare in my experience for it not to be present. It’s due to the atmosphere diffracting the different colours of light by different amounts, shifting blue and red away from each other. Fortunately Registax has a tool to help with this. Click on “RGB Align” in the Functions section. A dialogue box will appear with a green box over the image. Stretch the green box until it surrounds the image with some to spare and then hit the “Estimate” button.
Registax may not get this perfectly right and it may be necessary to tweak the colour shifts manually. See what you think when it’s done. You’ll also find that some of the sharpness may have disappeared from your image. Don’t worry about that for the moment.
Registax has lots of other things you might play with in the Functions section, but for this image I’m mostly happy as it is. It may be worth looking at the Histogram graph and stretching the histogram if the dynamic range of the image is fairly compressed. Hit “Do All” which should apply all the transforms to your image and return the sharpness from the wavelets and then save the finished image:
If you have GIMP, Photoshop or some other image manipulation package you can now do your final tweaks.
After two and a half years and having finally managed to locate M83 I’m pleased to say I’ve finally found every Messier object. I started with an ST80 and have gradually moved up through an ST102 and ST120 to my current 10″ dob, though I’ve seen every one with the 120 or smaller at some point. M83 is a challenge even from my relatively southerly location in the UK as it barely makes nine degrees above the horizon at best so finding it wasn’t exactly the most stunning event, but it will go on my list of “things to look for when on holiday further south”.
I intend to revisit all the Messier objects with the 10″ dob now, but it’s time to find some other targets too, I think.
After a late start, Saturn being past opposition already, I finally managed to capture my first images of the season two nights ago. Mostly I’m still using the same kit that I’ve always used for planetary imaging — a 127 Mak on an EQ3-2 mount, but now I’m using the ASI120MC camera rather than my trusty SPC900. Here’s the result. I think it’s the best Saturn image I’ve ever captured, so I’m rather pleased.
I said recently that I’d try to write something up about the way I do full disc lunar imaging with my DSLR, so here it is. This isn’t the only way to do it. It’s possibly not even the best way to do it. But it’s the way I do it.
First a bit about kit. I’m currently using a Canon 450D connected to a laptop via the USB connector and running AstroPhotography Tool (APT) to control it. Given a programmable remote it’s entirely possible that the laptop would be unnecessary. I have the camera connected directly to the visual back of a Skywatcher 127 Mak using a T-ring (no diagonal). The 1500mm focal length of the Mak gives me an image that fills the frame of the 450D just about perfectly. Unless you have a full-frame camera or a focal reducer you’d probably not want to go beyond this focal length. If you use a shorter focal length them the image size on the sensor will reduce proportionally. That is, using a scope with a 750mm focal length you’ll get an image that about half covers the frame height of a 1.6x crop sensor DSLR. I’ve modified my 127 Mak to fit a Skywatcher motorised focuser with a 5:1 drive reduction which means I can tweak the focus in tiny amounts whilst sitting at the laptop.
The telescope sits on my EQ3-2 with the after-market dual axis motor kit fitted. If you’re using a short focal length then you might get away with an alt-az mount, but at the focal length of the Mak my experience is that poor tracking fouls up the stacking process.
There’s no reason not to use another type of DSLR if it there’s a way to get it to take the required images in the first place. In any case what’s required is a good number of RAW images taken in quick succession.
I start by getting the scope lined up fairly centrally on the Moon visually and worry about getting the focus right with the camera later because I can use the Live View in APT to focus. Working without a laptop or with a non Canon camera it may be easier to focus on a bright star using a Bahtinov or Y mask first, then move to the Moon without touching the focus.
With APT started up and the camera connected I enable live view and centre the image using the motor controls, turning down the default Live View ISO And shutter speed settings if required to give a clear but not overly bright image. If the image is a long way out of focus I first get reasonably close based on the image I can see. I then find a good group of craters near on the terminator, click on them to move the 5x magnification box and go to 5x magnification. In anything but absolutely stunning seeing the Moon may appear to ripple and drift in and out of focus. Running the focuser in and out I try to find a point where the focus is similarly bad either side of focus, then home in on where “perfect” ought to be. Occasional moments of good seeing allow this to be fine tuned until I have things the best I can. If the seeing is near perfect I might then repeat the process at 10x magnification though I usually find it doesn’t help matters that much.
With Live View now turned off I start a plan configured in APT to take 120 frames of 1/1000th second at ISO800 with a three second delay between each. Depending on your telescope it may be that you need to change those figures. I like to keep the exposure time high to “beat” the seeing which mandates a high ISO rating to get bright enough images. Given a smaller image that may not be required. Images are stored on the PC in RAW mode. Using a programmable remote it’s possible to do the same. Given a frame with plenty of space around the Moon image I’d just leave it to run, but because there are only a few tens of pixels top and bottom of my images I keep an eye on the images as they come off the camera and tweak the tracking accordingly until the run is complete.
That’s the easy part done, but the rest can at least be done in the warm.
Once the images are on the PC my first step is to convert them to monochrome TIFF files, crop them down and centre the image in the frame using PIPP. The latest versions of PIPP can take RAW files from a wide range of cameras and convert them to TIFF which Registax can read happily. First I load them into PIPP and select the “Solar/Lunar Full Disc” option, ignoring any message it gives me about join and batch mode:
In the “Processing Options” tab, I make sure “Enable Cropping” is selected and change the crop height and width to suit my image. In this example because part of the Moon is dark I also use the “X Offset” to shift the image to the right of the frame a little. Finally I make sure “Convert Colour to Monochrome” and “Enable Histogram Stretch” are checked. It is possible to create colour images of the Moon, but that’s for another time.
Under the “Quality Options” tab I make sure “Enable Quality Estimation” and “Reorder Frames In Quality Order” boxes are checked and that’s pretty much it. Clicking the “Test Options” button confirms that the output will look as I expect:
And then it’s just a question of doing the processing, which may take a few minutes:
PIPP creates a new folder beneath the one from which the images were loaded containing its output TIFF files.
That’s it for PIPP. Just for interest, here’s a single frame from the output of PIPP:
Now the images are converted to TIFF Registax v6 can be used to stack them. Start it up and using the “Select” tab, load the images in all in one go. If there are images affected by cloud they’ll have been renamed to come last in the list. Ones that are obviously dark or that have dark areas due to clouds, aeroplanes or local wildlife should just be ignored. For this set I took the best 100 from my original 120 frames. Should Registax offer to stretch the intensity levels, choose “No”.
The first step is to scan through the frames you have captured and find a high quality one. To do this I uncheck the “Show Full Image” box and use the scroll bars so I can see the same area of craters that I used for focusing, though any area near the terminator would probably work just as well. Either the “Goto Frame” box or the scroll bar just above it can then be used to step through the images to find a good one. It’s hard to say exactly what constitutes “good”, but I usually compare features such as the definition of the craters and their shape. Experience really helps here, so the more often you do it the better you get at it. Here’s the frame I chose for this stack:
Next I click “Set Alignpoints”. Registax will usually come back with 1799 for my images which is far too many. I lower to 200 or 300 at the most in the “Number of Alignpoints” box and click “Align”. Now may be a good time to go and make a cup of tea.
One the alignment is done its time to decide how many frames are going to be stacked. I do this using the “Limit Setup” box. Ideally I want the lowest quality frame to be no lower than 95%, so I select that in the relevant box. The legend underneath the image then shows which frame is being displayed and how many out of the full set will be stacked. In this case 95% gave me 83 out of 100, so I tried 96% which gave me 55/100. That’s a fair place to start. I checked 97% which gave me 29/100 which I think is rarely enough, so 96% was where I stopped and clicked “Limit”:
After being transferred to the “Stack” tab you’ll see an image with the align points shown and often little green lines showing the movement between frames. Ideally those should be as short as possible. I just select “Stack” here.
Once the stacking is complete it can be worth saving the image (as a TIFF) to allow it to be tinkered with later. Then it’s on to the “Wavelet” tab and the black magic starts.
Unless I want to rotate or flip the image, wavelets is all I touch here. For the Moon I have a default set using just layers 1, 2 and 3 that I load which are very aggressive and then I tend to back them off until I’m happy with the overall image. For speed Registax only shows you a small part of the image with the transform applied, but clicking elsewhere will move the effect around. Unclick “Show Full Image” to see what it looks like in detail. If the image starts to look speckled then it’s overcooked and the sliders need backing off. The point at which the image starts to look unnatural and is probably overdone is often down to personal taste. “Do All” applies the transform to the entire image.
I usually save the image as a TIFF and reduce the size for display on websites using Photoshop, but the resize could also be done in Registax. Here’s my final image from this stack:
I was asked about how much difference stacking planetary images made recently and whilst they’re not particularly brilliant images I pulled out a few from a recent capture run to demonstrate. These are all from a single capture run with my 127 Mak and ASI120MC.
First a single frame unprocessed other than to crop down the frame size:
Obviously the image is very noisy and there’s not a huge amount of visible detail other than the two equatorial belts.
Next, the same capture run (around 5,000 frames) with 50% stacked in AutoStakkert!2:
Much of the noise has now been removed and there’s better definition to the belts. In fact it’s possible to see more detail because of the lack of noise and then refer back to the first image to find that same detail amongst the noise.
Finally, because the noise is now much reduced we can transform the image using wavelets in Registax:
This has brought out a huge amount more detail that certainly wasn’t discernable in either of the previous two images, but without the initial stacking there’s no way this would have been possible.
A montage of my next set of images of Jupiter. I’m starting to feel better about these though they’re still not without problems. I have the gain fairly high to help with the colour, but that seems to result in some “bleeding” into surrounding pixels which has led to a clear “rind” artefact on the western limb. Realistically though I think this is pretty much the last of Jupiter for this year. It’s now way past the meridian by the time we get full darkness and has a significantly smaller angular size than when it was at opposition in December.
