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Imaging Saturn with a DSLR


A320Flyer
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Guys,

I am looking for some feedback/help on imaging Saturn with a DSLR.

I had a first go last night where I took 110 exposures (ISO 400 @ 0.4 sec) and then stacked them to produce a final image. I have attached a sample single frame and the final stacked composite. As you can see, the stacked image is a lot smoother but there is no more detail.

My setup was a SW 150P Newtonian with a Canon DSLR attached so as to image through an eypiece. The canon was connected to a standard t-ring which was, in turn, connected to a 1.25" extender slid directly into the 1.25" EP holder; on the end of the extender (inside the EP holder) was a 1.25" LPR filter. Inside the 1.25" extender was my SW 10mm EP with the SW 2x Barlow lense attached directly to the EP.

I focussed on a bright star (Arturus) using LiveView at 10x magnification then slewed to Saturn. I then took a succession of 110 frames and saved them direcly to the harddrive as colour JPEG's. I sellected a small subframe around the planet to speed up the dowload time to the harddrive.

There could be a number of issues that has resulted in my lack of success - optical path, exposure, seeing (it wasn't great last night), resolution etc.

If anyone has any comments, feedback or advice that might help me, then that would be most welcome.

Thanks

Bill

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DSLR are just not good for planetary imaging. You need a lot of sharp frames captured in a short period of time at very short exposures. DSLR can't do that (except maybe some that would record an AVI).

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Thanks for your response. This resolution issue is something I dont fully understand. How can a 1.3Mp webcam produce higher resolution images than a 10Mp DSLR? Does the webcam have an in-built zoome facility? How do you get such close-up images?

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As you can see on your image - a big part of the frame is empty. Smal sensors are faster as there is smaller frame to send. Even 330kpix frame in webcams and dedicated planetary cameras are enough to catch whole planet.

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Are you saying that the planet would almost fill the frame of a small sensor without the need to add EP projection, Barlows etc, ie Prime Focus? In other words, the small sensor images a much smaller area of sky but at a reduced resolution to a DSLR? so that the resultant image appears much bigger?

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Planets aren't big enough. I have 11" scope and even at scope max resolution around f/20 (I'm using around f/25) Saturn easily fits on a small frame. If you would have a very big scope like 1000/17000 on Pic du Midi then you would need a bit bigger sensor (around 1/2"), but still far from APS-C size in DSLR.

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Thanks, for chipping in.

I must be missing something. If the chip is 4.6mm x 3.97mm (692 x 504 pixels) that equates to something like 150 pixels per mm. So, if Saturn occupies about 0.2mm, that equates to about 30 pixels. From the webcam pictures I have seen, there is a fair amount of detail. How do you get that detail into 30 pixels?

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I have already taken the plunge and ordered the webcam bundle from Morgans.

Can you do EP projection by adding an EP+Barlow into the optics? Whould this increase the size considerably? Does the webcam software have exposure control? and does it have a LiveView? so that you can see your video feed and adjust as necessary?

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Bill,

When imaging Saturn with a DSLR you're going to want to try and push the shutter speed upwards.

Using ISO 1600 produces brighter images and / or allows for a faster shutter speed but you will get some additional graininess although with image stacking that tends to reduce a little in the processing.

I'm starting to think it's better to trade off some light in favour of a sharper image as stacking many bright blurred images still tends to yield a blurred final result whereas darker but sharper captures more detail when stacked.

This also means shooting in RAW rather than JPG as the lossy compression of JPG will produce false data and increased blur when stacking. With small images this is going to be much more pronounced on the final result.

Also, looking at your stacked example.. Did you run the deconvolution process on the stacked image to tease out the detail?

Alan

Edited by blackparticle
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Alan,

It didn't occur to me to shoot in RAW as I thought the subject would be bright enough. I will try your suggestion and increase shutter speed and see what happens. I will also try the deconvolution process on my existing image to see what that produces.

Thanks for that.

Bill

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What camera do you use?

If you're able to record in crop mode, then all hope is not lost :)

Here's what i've been able to get with the canon 550d and explorer 200 PDS (1000mm) under rather rought seeing conditions.

Not the best of course, but hey, a good start at least ^^

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Edited by Jannis
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De-convolution is essential to remove the blur from the stack. It's worth doing a search relating to the process for astro images and also wavelet shaping as well if your software has this function.

So far I've done stacks of approx 100, 250 and 500 images.. Needless to say the stack of 500 produced the best result so far. That was 2 x 4Gb memory cards filled with RAW images of 1/20s at ISO 1600. In practice it's quite a task to do this manually (even with remote shutter release).

While I think frame per frame the DSLR is giving a better result, it seems the webcams are ultimately producing the better planetary results for sheer number of frames captured.

I think it took me about 30 minutes to take 250 shots the other night. If you compare that to 30 minutes of AVI footage at 30 fps.. that's a staggering 54000 images from which to work from.

I'm going to give Saturn one more go on the DSLR, see if I can hit the 1000 frames mark and try for something like 1/45s at ISO 800 although I'll have to find some dark skies for those settings using a 9mm eyepiece.

That should at least give me some practice for Jupiter ! :D

Edited by blackparticle
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Yes, the more frames, the better, BUT:

you're forgetting something very important. even if you can take thousands of pics over a long time, it won't be better then a revorded movie. The reason is simple: the planet rotates so fast that recording for even more then 2 min will cause an unclear picture at high magnification. However, if surface details isn't in focuse, then yes, it will work with many still pics.

In the case here, if still pics are ony option on camera, i strongly recommend to buy a webcam instead, they can do wonders for almost no cost.

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Yes, I think the webcam route is the way forward. I have ordered the webcam bundle from Morgans and will let you know how I get on. I hope it arrives soon. Thanks for all your help, guys.

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..the planet rotates so fast that recording for even more then 2 min will cause an unclear picture at high magnification.

Yeah, I realised this after seeing a sequence of shots from Jupiter staggered by 30 mins to highlight the speed of rotation. As both planets only take 10 - 11 hrs to rotate, spending a couple of hours taking shots is only going to produce an image with defined outlines of weather bands albeit with no actual detail inside the bands.

I have to say it, the more I look and learn, the more I realise that the universe has been so cleverly organised to test our ingenuity. :D

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I use a Canon 550D DSLR with a specially threaded 2x barlow lens that attaches to my T-ring. I use the "zoom" function to select a 640x480 block of pixels from the total 3456x5184 pixels on my sensor. That effectively magnifies Saturn by 7 times. Then I record the .avi file at 30 frames per second and process through Registax. This is the result:

SaturnwithDSLRand2xbarlow-1-1.jpg

?action=view&current=SaturnwithDSLRand2xbarlow-1.jpg

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There's nothing wrong with using a DSLR to capture planets, but you need to capture at the pixel level. If you're using a Canon DSLR with liveview then I recommend you use eos_movrec to capture the pixels.

Here's an example of saturn, 5/13/2011, captured with a Canon T2i and eos_movrec, using a 8" newtonian and eyepiece projection.

Doug

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