PRIMER....How I image the ISS (By popular request)

[Vega]

Well ok, I guess I have to reveal my secret formulae for capturing the ISS prime focus style.... I'm afraid it's nothing special or new really but I will outline how I did my last few successful shot's. This guide is only for when using dobsonians...

Equipment Used

Skyliner 250px Dobsonian

Phillips ToUcam Pro II & 1.25" Nosepiece adaptor w/ UV/IR block filter attached

2x Barlow (optional depending on how lucky I feel!)

Phillips V-lounge capture software

Laptop

Preparation

First up, be well prepared, this is something you don't wanna be rushing. As that 17,000mph station screams towards your location it can be on you and gone before you know it. You need to be well up on what time and more importantly, where in the sky the ISS will move at your location. As most of you will already know this can all be obtained from heavens-above.com. I then make sure all the equipment is out, finderscope aligned and ready a good half hour before the pass (if the sky is dark enough to enable me to). Another small thing worth checking is the positioning of your equipment. Check that you can freely move the dob in altitude with webcam attached without hitting any tables/laptops/tangling any wires etc. Easily tested beforehand.

Finderscope Alignment (THE VITAL BIT)

I cannot stress just how important this bit is. The finderscope alignment with the main scope has to be bang on if you want any chance of getting the ISS anywhere near that webcam field of view. I align the finderscope with the main scope as normal using a bright star and aligning with a 25mm eyepiece then with a 6mm for added accuracy. This is then re-tested in the next bit when toucam is turned on. Note: This whole procedure can prove difficult if the impending pass is very early in the evening as you have to wait until you can see at least 1 bright star to align with. Time sometimes is against you.

Focusing the Webcam

If you want to capture nice detail of the station then this also requires extra care and attention. Drop in the toucam (either in the scope eyepiece holder or in the 2x barlow if ur a super confident nutter). Turn on your capture software and move the scope to a brightish star for focusing by watching it on screen. If your using a long focal length scope and/or 2x barlow this can be very difficult as a dobsonian is not tracking the star movement. It's a case of magnification vs ease of use. You have to keep moving the scope to track the star giving you enough time to watch it on the laptop screen. It's best to let the star drift across the screen while you make a focusing adjustment then move the scope a bit and keep repeating until your happy with the focusing (depends how fussy you are). Note: Some people like to use the moon to focus their webcam with because it's a nice large target. This is all good and well but using a star is much more accurate, especially for Newtonion's.

Webcam Settings

Hate to break it to you but there is no secret formula here. shutter speeds and webcam settings will vary from scope to scope. If your using a 10" Newt and Philips Toucam Pro II like me then here's what mine are generally...

-10fps or 20fps (been successful with both and cant go any higher with my laptop/USB capabilities)

-Shutter Speed - 1/2000 - 1/2500 (or 1/1000 with 2x barlow) on overhead passes only

-Gain - just below half way to remove noise

-Brightness - Just above half way to compensate for the above

-Auto White balance

-Hue / Saturation - Halfway

HERE SHE COMES

With everything setup hopefully you've had some spare time to look over everything. Be sure to have the capture software ready whereby all you have to do is click 'OK' to start the video capture. When the ISS is visible low in the West, don't rush to the finderscope to catch some frames. A rising space station is still very far away and would look very small in any frames you've captured. As it's rising move behind your dobsonian in relation to the ISS. Move it in azm so it is pointing right at it. This way you should only need to make very minor future adjustments in azm and do the rest in alt. When the station is about 20 deg up I press the ok button to start video capture. For the next 2 minutes you should be looking at nothing else but the sky and/or the finderscope crosshairs. Don't even think of trying to follow it on screen... it wont be there and you'll waste precious time! You'll have all the time in the world to play back the capture afterwards. I use the 'both eyes open' method with one eye on the spacestation in the sky and the other lining it up with the crosshairs. The rest is plain and simple aiming. Try to keep that bright thing as close to the center of the cross hairs as you can. Try to get ahead of it and let it pass through the crosshairs. If your focusing is good, all you need is one still frame to capture it's detail.

AAAAH ZENITH!

The best time to capture the ISS in video is when it's right overhead because that's when it is closest to you and looks the largest in the camera. But guess what.. this is also the hardest time to keep the ISS in those crosshairs.. . It's the point at which it moves fastest in the sky. Not only that, but at some point your dob will be standing upright and this is your que to swing the the dob around 180 degrees (think of it as a dance ) and follow the ISS in the Eastern sky. Hopefully you have thought about your USB cable length here and the dob can freely move through 180 degrees. This is the last desperate stretch to catch some more precious frames before it shrinks in size slowing down in the sky all the way to the horizon.

AND BREEEATH

Now's the time to stop the capture on the laptop and have a look back through the whole movie to see if there are any bright blips across the screen. If there are... BINGO! . don't take your eyes off the movie because 1 frame with the ISS in it can blip by in the blink of an eye.

GETTING THE PHOTO

I use virtual dub to extract any frames I got and use them as photo's. If you are lucky enough to get loads of frames that have captured the ISS at a similar angle, you can run them through registax to stack them in to an improved image.

Other notable problems that may occur.

-Misting up of finderscope.. I find by the time I'm at the zenith, the heat from my face mists up the finderscope which hides those vital crosshairs. My quick fix at the moment is a hair dryer VERY close by for a very quick blast.

-Cannot see crosshairs.. similar to above but sometimes the sky is too inky dark to see the crosshairs if like me your finderscope is not illuminated. I'm working on a DIY illuminator for this.

-A pass of the ISS that has quite a curve in it's motion is VERY hard to manually track with the dob. Reason being you have no choice but to move it in both axis. Trying to get smooth alt & azm movement in a dob is no easy task. I tend to only attempt serious ISS photography on passes that reach at least 80-85 deg in altitude when it tends to move in a straight line.

I hope this helps some of you, sorry for the waffling but attention to detail makes a lot of difference on this malarkey

Good luck with your ISS capturing!

Matt

[Ant]

Thanks for this Matt. This is now a sticky and all comments (except mine) will be in a defferent thread - so this thread stays nice and tidy!!!

Amt