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Andi Turner
Yellow Main Sequence
Joined: 27 Oct 2008
Posts: 325
Location: Leek / Staffordshire
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 Posted: Mon Feb 01, 2010 6:15 pm Post subject: Manual DSLR Focussing? |
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I realise that this is a time consuming and laborious activity but I just wondered if anyone had any pearls of wisdom on manually focussing lenses for astrophotography.
I realise that there are programmes which can do this for you, but the whole reason for my set up is that it doesn't need any computer control. I quite literally hate cables!
A bahtinov mask on my ED80 means I can be focussed in minutes, is there anything which would come close for my lenses or am I doomed to an eternity of focussing a fraction at a time and zooming in on my picture, another fraction, another zoom and so on, and so on, and so on....
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Skywatcher SKP2001 (DIY Dob mount)
Pentax 75 SDHF
Astrotrac
Canon 20D (modded) 24mm f2.8; 200L f2.8
Bresser 10x50 Binoculars
http://www.flickr.com/photos/30536520@N02/ |
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Dangerous_Dave
Supernova
Joined: 03 May 2007
Posts: 7292
Location: Consett
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| Posted: Mon Feb 01, 2010 6:45 pm Post subject: Re: Manual DSLR Focussing? |
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| Andi Turner wrote: |
| am I doomed to an eternity of focussing a fraction at a time and zooming in on my picture, another fraction, another zoom and so on, and so on, and so on.... |
Yes 
But once you've got the focus position, you can mark it with masking tape, take a photo of it with your phone or write something meaningful in a log book which makes it easier to focus next time out.
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EQ6 Pro, Vixen GP, Astrotrac TT320X-AG, WO Megrez 90, WO Megrez 72, SXV-H9, various fisheye, apo and medium format lenses, SPC900NC, DMK21AU04, Lidl+Pulsar bins
Dave's pics |
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geppetto
Black Hole
Joined: 27 Dec 2007
Posts: 11201
Location: Bolsover Derbyshire
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| Posted: Mon Feb 01, 2010 6:46 pm Post subject: |
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I used a right angle x2 viewfinder magnifier for a year or more
and got true focus 99% of the time tweaking on a bright star...
Since then, I've got a Canon with live view which is an absolute god send
and is 100% reliable.....
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Regards
Philip
Dollhouse and miniatures web site
http://www.pctee.co.uk
200mm F5 Newt : WO 66mm Petzval frac : HEQ5 mount : Mono SPC900NC SC1.5 : Canon 1000D DSLR astro modded : 12" F5.3 ATM truss DOB : 102mm ST102 F5 achro frac
Skywatcher 150PL 6" F8 Newt :ED80 PRO gold tube : WO Binoviewer : Atik 16ic mono : Skywatcher 150P DS : free bus pass : B&Q over 60's discount card |
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starrybird
Red Dwarf
Joined: 13 Sep 2009
Posts: 20
Location: London
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| Posted: Sat Feb 06, 2010 11:10 pm Post subject: |
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Whats your setup? If you're using a DSLR you can take a test shot and then use the preview mode to zoom in and tweek your focus. Dslr wins over film 'cause you can preview and tweek. Assuming DSLR, manual focus, test shot, preview, zoom in, refine.
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ETX105
TV Pronto
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Andi Turner
Yellow Main Sequence
Joined: 27 Oct 2008
Posts: 325
Location: Leek / Staffordshire
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| Posted: Sat Feb 06, 2010 11:33 pm Post subject: |
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Cheers all.
I've actually made a Bahtinov Mask for my lens now and it seems to work effectively. I suppose the only issue is that I need a different one for each aperture setting, but this is no real hardship bearing in mind that only a couple of speeds are used with each lens.
It suprised me that it worked actually as I'd heard negative reviews on using them with camera lenses. You live and learn...
_________________
Skywatcher SKP2001 (DIY Dob mount)
Pentax 75 SDHF
Astrotrac
Canon 20D (modded) 24mm f2.8; 200L f2.8
Bresser 10x50 Binoculars
http://www.flickr.com/photos/30536520@N02/ |
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Lester
Yellow Main Sequence
Joined: 20 Apr 2009
Posts: 603
Location: South Australia
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| Posted: Sun Feb 07, 2010 4:55 am Post subject: |
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Hi, I use the Live view function on my cameras with a magnifying glass as well to get precise focus.
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Scopes=Meade 14" LX200, Takahashi FS102, Takahashi Astrograph 160mm f3.3, Losmandy Titan mount, Canon 40D Astro, 20Da, DFK21af04 modified. |
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Dangerous_Dave
Supernova
Joined: 03 May 2007
Posts: 7292
Location: Consett
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| Posted: Sun Feb 07, 2010 5:25 pm Post subject: |
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| Andi Turner wrote: |
Cheers all.
I've actually made a Bahtinov Mask for my lens now and it seems to work effectively. I suppose the only issue is that I need a different one for each aperture setting, but this is no real hardship bearing in mind that only a couple of speeds are used with each lens.
It suprised me that it worked actually as I'd heard negative reviews on using them with camera lenses. You live and learn... |
I think the problem is a Bahtinov mask dramatically limits the amount of light transmitted and DSLR lenses tend to be ~ 2" aperture or less to start with, and can have six or seven elements which also limit light transmission. I presume your Canon 200 has a good aperture on it? Good to hear that it works, I might give this a try with the Leitz, although I suspect that has a lower aperture than your Canon.
_________________
EQ6 Pro, Vixen GP, Astrotrac TT320X-AG, WO Megrez 90, WO Megrez 72, SXV-H9, various fisheye, apo and medium format lenses, SPC900NC, DMK21AU04, Lidl+Pulsar bins
Dave's pics |
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Big Dipper
Ole Slap'ead!
Joined: 15 Sep 2006
Posts: 13694
Location: Oxford
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| Posted: Sun Feb 07, 2010 6:38 pm Post subject: |
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| Andi Turner wrote: |
It suprised me that it worked actually as I'd heard negative reviews on using them with camera lenses. You live and learn... |
Including a thumbs down from the Bahtinov manufacturer/retailer when I enquired about masks for camera lenses (see here - eighth post down. I spent a long time trying to get the best focus that I could with each of the lenses & then marked the point on each lens with a very fine red metallic pen & also held it in place with some blutack. Yes, I know that the exact point of focus can slightly alter due to the effect of differing temperatures and using filters etc. - but 'near as dammit' does find for my standards!
Glad that the mask has (hopefully) been a success for you Andi. 
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Remember: - If all else fails, read the instruction manual!  
Andy
Skype: bigdipperandy
Equipment: AstroTrac camera platform, modified Canon 350D DSLR, Tasco 10X50 binoculars, 35mm SLR + various lenses
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Andi Turner
Yellow Main Sequence
Joined: 27 Oct 2008
Posts: 325
Location: Leek / Staffordshire
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| Posted: Sun Feb 07, 2010 7:19 pm Post subject: |
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Yeah, it worked really well. The aperture for the lens is about 72mm (f2.8 200mm). I think I've deleted the focussing shots, but they were the typical diffraction spikes you would expect and 'in and out' focus was shown through the central spike moving up and down, if you know what I mean i.e. you could tell which way to focus, which you can't do easily with the shoot-preview-zoom-adjust method. I was focussed well (in my opinion) in a couple of minutes and that was with a bit of a botch job cardboard mask, I'll now make a neat one from the cover of a plastic folder or a beer can
It was a relief!
_________________
Skywatcher SKP2001 (DIY Dob mount)
Pentax 75 SDHF
Astrotrac
Canon 20D (modded) 24mm f2.8; 200L f2.8
Bresser 10x50 Binoculars
http://www.flickr.com/photos/30536520@N02/ |
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Big Dipper
Ole Slap'ead!
Joined: 15 Sep 2006
Posts: 13694
Location: Oxford
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| Posted: Sun Feb 07, 2010 9:02 pm Post subject: |
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I'd be tempted to use the beer can Andi, as you now have the perfect excuse for emptying it beforehand! 
In fact in case you end up with a botched job several times over, best to get a few six-packs in to be on the safe side (though you may be wise to leave any fine focusing til the following day)!
_________________
Remember: - If all else fails, read the instruction manual!
Andy
Skype: bigdipperandy
Equipment: AstroTrac camera platform, modified Canon 350D DSLR, Tasco 10X50 binoculars, 35mm SLR + various lenses
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Dangerous_Dave
Supernova
Joined: 03 May 2007
Posts: 7292
Location: Consett
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| Posted: Sun Feb 07, 2010 9:33 pm Post subject: |
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72mm is a good size aperture for a DSLR lens. My Leitz 180mm is only 53mm. In fact I use a Bahtinov mask with a Megrez 72 and it works well.
_________________
EQ6 Pro, Vixen GP, Astrotrac TT320X-AG, WO Megrez 90, WO Megrez 72, SXV-H9, various fisheye, apo and medium format lenses, SPC900NC, DMK21AU04, Lidl+Pulsar bins
Dave's pics |
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