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Old 10-08-2009, 01:41 PM
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RobF (Rob)
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DSLR focus for wide field astrophotography

Hi all

How do people go about ensuring a good focus on their DSLR for widefield work? In my case, I have a Canon 450D (with liveview) I would like to use to try some widefields using the 25-55mm kit lens that it came with. This is widefield milky way stuff I have in mind, so the moon won't be around to tweak focus on.

I imagine I'll just have to snap off short shorts and keep checking them on the larger laptop screen? I don't really want to by an angle finder magnifier for the odd shot I expect to be doing.

Any info appreciated,
Rob
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Old 10-08-2009, 02:29 PM
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deadsimple (Ash)
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I just fire up the EOS utility on my laptop, activate remote liveview, enable 10x magnification (important!), point at a bright star and click the manual focus buttons left and right until I have the smallest circle/dot possible. It's a bit more accurate than adjusting the focus by hand. After that I turn off auto-focus on the lens so that it keeps the setting, then swing the camera around to the ultimate object of interest.

Easier on longer focal lengths, but I'm quite sure I did that at 50mm too.

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Last edited by deadsimple; 10-08-2009 at 08:25 PM. Reason: spelling
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Old 10-08-2009, 02:32 PM
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rogerg (Roger)
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Options I would consider:

1) using live view and getting it as good as you can - I think this is the easy option.

2) using software on a computer which the camera is connected to, taking exposures and looking at the sharpnesss, adjusting focus until optimal.


Option 2 is aided by software which takes a rapid succession of frames showing them to you once they have downloaded and in some cases always zooming in to a star you select. Such software is Images Plus, Nebulosity2, DSLRFocus (if using XP or older OS), MaximDSLR, and there are probably lots more. Google those and you should find download/buy pages.

If I were you, I'd stick to using Live View at 10x magnification (presuming you can do that on the 450D) and save the hassle of a PC.

Roger.
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Old 10-08-2009, 06:40 PM
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RobF (Rob)
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Thanks Ash and Roger. Must confess I haven't spent a lot of time pondering this - thought I go straight to plundering the mass of experience out there

I can't have looked too hard at the EOS PC Liveview program, because I've managed to miss the focus options previously. I'll certainly give that a go. Didn't want to get too deep into software unless necessary.

Roger, I run the scope using EQMOD now, so the PC is always out anyway - just works easier if I'm doing astrophotography at prime focus, which is what's usually happening the majority of nights I'm out. Liveview on the camera or PC works really well for prime focus through the Newt - bright stars give nice diffraction spikes, but I figured I wouldn't have this bonus for widefield through a lens.
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Old 10-08-2009, 06:45 PM
Ian Robinson
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I focus visually and with the lens switched to manual mode (unless it's an adapted Minolta MD lens or Canon FD lens in which case it's manual focus anyway) via the view finder and a rightangle multiplying (non-canon) viewer.
Works for me.

I really can't be bothered using liveview and having to use my lappy outside in the damp night air (killing my night vision BTW).

I adhere to the KISS approach.

Cables connecting the camera to the lappy have caused several people here at IIS dramas (over tensioned accidentially by an very taught cable , stuffing up the USB socket on the camera , and I bet a few near misses when the owners or hangersoners have walked into the cables !!!

The only thing hanging off my camera when I have on my GEM is a TC80n3 chinese clone , chinese clone 3x angle viewer (for those awkward camera angles (always to awkward for me without the angle viewer (which is also rotateable) and the neck strap (and the lens and GEM off cause), I like it that way.
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Old 10-08-2009, 07:45 PM
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tlgerdes (Trevor)
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Hi Rob,

I am with Ash on this, the EOS Utility is great for widefield stuff with the kit canon lens. I run a 1000d like that and have used it from the 18-55 and 55-250mm lens.

Yes, it took me a while to figure out how to use it, but now it is so simple you can get focus in about 1 minute on any bright star.

Dont forget to capture in RAW as well.
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