Guide Camera Resolution in PHD?

[willuk2010]

Hey,

I don't really understand this binning yet.. but i have a question

When i set up my ASI120MM for guiding in PHD, and i select the ASI120mm, it gives me the resolution options, (640x480, etc, etc)..

I read that the first 640x480 resolution ( as 2 are displayed), in the selection is 2x2 binning (is that the right terminology?)

Question is, what do i select as a resolution for my guide camera in PHD? my imaging camera at the moment is a Canon 1D Mark IV.

Many thanks!

Will

[AstroAdam]

Doesn't 640x480 2x2 binned effectively make the sensor more sensitive, but with an effective lower resolution?  

So, it would potentially give you more guide stars, but at a lower effective resolution.  So... the big question would then be the difference in focal length between your main and guide scopes.  The bigger the difference, then potentially the more resolution you need (I think?).

Correct me if I'm wrong those that know more...!

[willuk2010]

Cheers AstroAdam.

Anyone else got anything to add or help with this subject? Or any suggested reading?

Thanks

Will

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[glowingturnip]

not familiar with your camera, but on both my webcams, I get choices something like 640x480 which is unbinned full frame, 320x240 which is binned fullframe, and something like 365x260 (can't remember the exact numbers) which is unbinned but just the central part of the frame.

I would say that so long as you can see the guide star then:

- full frame, so the guide star can't wander off (my phd throws a paddy occasionally and loses the guide star, so i have to reset it - I view it as 'natural dithering')

- unbinned - phd can guide to sub-pixel accuracy based on the c.o.g of the star, so binning will only throw away accuracy - speed of data capture and s/n are not really issues here

just my humble...

[willuk2010]

Thanks for that glowing turnip! I shall just have to have a play and see what the results are with guiding... I still don't fully understand it, and probably won't see what the differences and effects are of selecting the different resolutions until I experiment!

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[Starflyer]

If you can find a guide star without too much bother then don't bin, you want the highest resolution (within reason) for guiding.  Only bin if sensitivity is an issue with your guide camera and you struggle to find a star.

[Christopher Davenport]

+1 on not binning and using gain instead.

2x2 Binning effectively doubles your pixel size (surface area per pixel)  and thus it halves your resolution.

I use a finderguider (50mm) and I can always find a star with my gain increased. I have never had to bin.

Although I am still new to the game, so maybe I will need to sometime soon and then I will eat my words.

Just thought about it abit, I can only see the need for binning if you are using high focal length and OAG and your star choices are really dim even on max gain.

(But of cause, I stand to be corrected by somebody on here with a bit more experience.)