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#1 labmand

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Posted 10 May 2013 - 12:05 PM

Hi, Double star observing is new to me and came across
this Binstar program but other then the info on the Budget
Astronomer web site have not been able to find much info on
it. Does anyone here know if this program would be helpfull
in finding PA and sep values? Also if anyone is using this
software with avi files from other camera's other then a webcam. If not BinStar then what is
best to use without a GEM with motor drives to find pa/sep.
Thanks for any help

#2 StarDusty

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Posted 10 May 2013 - 03:32 PM

When I started measuring doubles with a webcam, I did used BiStar successfully for a while. You should look into REDUC. I have switched over to using REDUC instead of BiStar.



Without a mount that tracks you will have a tough time. I did a few with a tracking platform.

The following link is to my website that has some information about software used for double star measurement using a webcam or other avi capture type camera.

http://www.clearskyo...ory/22-doubl...

Two of the three articles listed may be of interest to you.

#3 labmand

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Posted 10 May 2013 - 08:39 PM

Thankyou Allen, I will check into reduc, I have a Nexstar 6se mount, not on a wedge at this time, Is it a problem using this non GEM for the video method, looks like tracking
is off during vidio capture, so it seams it should work.
I have a chdk moded Cannon powershot that I want to try shooting some AVI's with, I have a eyepiece attached, it's lightweight and I don't need to have a laptop crashing or
locking up spoiling the party. Do you think it will work?
Too cloudy tonight to try.
Thanks for all the info and the links, very helpfull.

#4 StarDusty

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Posted 11 May 2013 - 08:05 AM

I looked up what "chdk moded" was. It is worth a try.
Shooting through an eyepiece is tricky too. I have done a few images, but mostly on bright objects like the moon.

Field rotation while shooting is an issue, but if you use just a portion of the video, maybe only 100 frames, it may not distort the Separation and PA measurements too much?

You will need to record at least two videos of the subject double. One with the mount tracking and a second "drift" video with the mount off or stopped. REDUC uses the drift video to determine West and from that the PA angle in the non-drift video. You also need to know the image scale your optical system to use REDUC. [Bistar uses the drift video to determine this, however REDUC does not.]

You can determine the image scale of your optical system by shooting a double of known Separation using the Calibration routine in REDUC to back calculate your image scale. Once you have this, write it down, it will not change if you use the same optical system each time. If you change the eyepiece or add a barlow, that will change the image scale and you need to recalibrate.

All of this will be a little off because you are using a Alt Az mount. I have not looked at how much the field rotation might affect you measurements. I think it will vary depending on the Declination of the subject double.

#5 labmand

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Posted 11 May 2013 - 10:11 AM

Good points Allen,
If the mount is off when video is captured why does it
matter the type mount, that is if Binstar can calc. sep.
or if I find out this value with Redux etc. When the AVI is
shot, what frame rate should be used 10fps? Prob depends on
star magnitude, or can 1 frame per second manual (timer) be shot and avi made from the idividual frames so fainter stars can be captured?
Thanks again for the help, clouds may clear tonight so I
can give it a try.

#6 StarDusty

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Posted 11 May 2013 - 01:57 PM

If you use Bistar, a stopped Alt Az will work.

The same is not true for REDUC because REDUC needs two avi's. One with the mount stopped and the other with it tracking.

During time between recording the first and second videos the earth has rotated a little and there will be some rotation of the sky field as recorded using an Alt Az mount. Maybe if you make a note of time difference between the first and second video recordings, you can correct the PA REDUC calculates by the amount the earth turned between the two videos?

If your camera is not sensitive enough and you need long exposures, like 1 frame per second, to capture both stars of the double, then you will be getting star trail images, not stars. You may need to find a few doubles where both stars a relatively bright so you can image at 10 frames per second. You might be able to make 5 frames per second work.








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