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ISS Webcam Images from Good Friday

Dave

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jwr

jwr

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Very cool images. May I ask what your technique is? Do you sight up a spot on the predicted path, let the ISS roll through and just shoot video? Or is there some tracking involved?

James.

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Dave

Dave

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Here's how I did it:

I made sure that the 10x50 finder was properly aligned with the main scope and the main scope was well collimated. Webcam was focussed on Polaris using a Bahtinov Mask with a very slow shutter and bright image to see the diffraction spikes. (I could even see the companion when the Bahtinov Mask was removed). I used Polaris as it doesn't move much when focussing as I'm using a manual Dobbo with no tracking.

I removed the Bahtinov Mask and centred the scope on Saturn. I then set the shutter speed at 1/1,500, (It needs to be this fast to freeze the image as the ISS is really travelling some) and adjusted the brightness of the image so Saturn was a little faint in the picture (The ISS is much brighter than Saturn and I made a guess at how much brighter it was). In the evening sky the ISS will be brighter in the East. In the morning sky it will be brighter in the West.

Saturn does move rapidly across the field of view while doing this as a Dobbo is used and keeps having to be re-centred. This can be done in relatively strong twilight, but leave enough time to get this process done properly well before the appearance of the ISS. When you're faffing around and starting to panic the time soon time ticks by. You want to be as relaxed as possible once the ISS appears as you soon won't be.

I used SharpCap to take the AVI and Webcam Control to adjust the exposure. Once ready it was just a case of relaxing and waiting for the ISS make its appearance.

I started the recording when the ISS was high enough. Once I knew the AVI was definitely recording (yes I have spent time tracking the ISS and the AVI hadn't even started recording).

Now for the fun bit.

I positioned the scope just ahead of the moving ISS. Looking through the finder scope, I adjusted the scope to TRY and get it to move right through the cross hairs of the finder. This I hoped would give a flash of the ISS in the view of the webcam as the recording was being made. Once it had moved through, I then repositioned the scope ahead again, repeating this process as it raced across the sky, before stopping the recording. And Boy! does it move fast when you are doing this... Especially if it is almost overhead as it was when I took the images above.

The old adrenaline really starts pumping at the speed you need to track and you soon realise just how rubbish you are at manually tracking this thing as it frustratingly passes well away from the cross hairs far too many times during the process. I do prefer to use this method of moving the scope as you will then only have the movement of the ISS to freeze. If you tried keeping the ISS in the frame all the time you would have the motion of the scope to contend with as well as the movement of the ISS. The field of view of a webcam is very small and even a small movement will blur your image.

Then when the ISS is getting low down or gone into the Earths shadow, stop the recording and start breathing again and let the shaking subside. (This is especially true the first few times you attempt this).

Once the AVI is captured I inspect each frame using Virtual Dub and extract any that are fortunate enough to have the ISS on them. It's not very many out of the many hundred frames, I can tell you.

Don't worry if all you get is a blur. Don't be disheartened, try it again another time. It will work. Each time you try you will notice an improvement in the amount of images captured and the quality of image improving. Like anything, it takes a while to learn what works for you.

I hope this helps. If it has inspired you, go on, have a bash and let us see your images too. But do it quickly, we only have until the 3rd May before apparitions of the ISS stop from the UK until the end of May.

Dave

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