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Ptarmigan
Carpal Tunnel
Reged: 09/23/04
Posts: 1874
Loc: Arctic
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I am interested in building a barndoor tracker. I did some research on barn door trackers and notice there multiple variants of them. One is the double-arm drive.
http://hometown.aol.com/davetrott/page17.htm
http://education.jlab.org/tracker/
Here is a single arm barn door tracker.
http://www.jlc.net/~force5/Astro/ATM/Barndoor/barndoor.html
What is the difference and advantage and disadvantage?
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Ptarmigans=Cute and Cuddly
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 12065
Loc: Rockford Illinois
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The double arm (or Tangent Arm Mounts) are supposed to be accurate to about 45 minutes when aligned properly, but they take some precise measurements to make them. I actually have a type-4 (Trott) in the basement I tried making years back (Same article you link to). It's STILL not completed!
A normal barn-door has issues beyond about only 4 or 5 minutes, because as the threaded rod gets longer, the angle is increasing slower. People have overcome this by making a CURVED bolt tracker. Same concept as the standard barn-door, but the rod is curved to the radius of the tracker. Now, as you turn the nut on the rod, it lifts the arm at the same rate, throughout it's travel.
So for making a barn-door, the best (and EASIEST) route would be the curved bolt tracker. 
There was a great article on them in an issue of (I believe) S&T a while back.
Do a search in this forum (and the DSLR forum) for "curved bolt", and you'll even find a nice build here.
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Neo... (Jeff)
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10" LX200-GPS/SMT UHTC "Draco"
 Rockford, Il.
NeoDinian's Eye on the Sky!
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huckabuck
sage
Reged: 02/18/07
Posts: 267
Loc: statesboro, ga
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the write-up jeff is refering to was written by member extrodinar Clownfish(Peter kennett) in the film astrophotography forum. it's under the sticky best of film astrophotography - start here about 2/3's of the way down
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 12065
Loc: Rockford Illinois
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Thats the one.
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Neo... (Jeff)
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10" LX200-GPS/SMT UHTC "Draco"
Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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s58y
Post Laureate
Reged: 12/12/04
Posts: 4850
Loc: Eastern NY
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With DSLRs (or CCD cameras), I wonder how important being able to go for 5 or 10 minutes is? When I was using a barndoor (waiting for the G-11 to ship), I had enough problems getting good tracking with a 300mm lens for 2 minutes, so I just used an extra-large single-arm tracker. With DSLRs, isn't it easier to stack a bunch of short 2-minute subs? I did shoot at f/2.8 so 2 minutes was a reasonable subexposure length given the level of light pollution.
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Hutech 30D, SBIG ST-402 autoguider
SV80S, SV66 guidescope
AP900, G-11, Barndoor tracker
http://www.pbase.com/s58y
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Patrick
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Reged: 05/16/03
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Loc: Franklin, Ohio
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Quote:
With DSLRs, isn't it easier to stack a bunch of short 2-minute subs?
Yep! You can collect an amazing amount of light in 1 or 2 minutes at f2.8. 
Patrick
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 12065
Loc: Rockford Illinois
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If you have superb dark skies, why not take advantage of them.
Of course, with average skies, yeah, stacking multiple subs is best.
But either way, the curved bolt tracker is still simple to make.
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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Ptarmigan
Carpal Tunnel
Reged: 09/23/04
Posts: 1874
Loc: Arctic
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Quote:
With DSLRs (or CCD cameras), I wonder how important being able to go for 5 or 10 minutes is? When I was using a barndoor (waiting for the G-11 to ship), I had enough problems getting good tracking with a 300mm lens for 2 minutes, so I just used an extra-large single-arm tracker. With DSLRs, isn't it easier to stack a bunch of short 2-minute subs? I did shoot at f/2.8 so 2 minutes was a reasonable subexposure length given the level of light pollution.
I read in Terrence Dickinson's The Backyard Astronomer's Guide latest edition that you can get deep exposures in 15 minutes with a DSLR, compared to film in 80 minutes. You can get more stars in a shorter time with a DSLR than film camera. 2 minutes with a DSLR camera will record more than film. I don't see why it would not hurt to stack a bunch of 2 minute exposures. In my opinion with a DSLR or CCD camera, I think 5 minute should be good. With darker skies, even better.
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Ptarmigans=Cute and Cuddly
Edited by Ptarmigan (08/02/08 09:23 PM)
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Adrena1in
sage
Reged: 09/02/07
Posts: 275
Loc: Hampshire, UK
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Don't forget though, you might be able to go nicely to 2-minutes with a single-arm Barn Door Tracker, but between each shot you're still going to need to reset the arm and adjust the whole rig, ready for the next shot.
I was considering making one for myself, just for a bit of fun, and when I'm away from a power-source for my EQ-5 mount. I'd rather go with a two-arm setup at first I think, or a whole new mechanism which I've just thought of...
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Phenix 102mm f/5.9, Phenix 127mm f/9.5 and Orion ST80 f/5 refractors on EQ5 with GOTOStar
Phillips SPC900NC, Meade DSI-C, Canon EOS 450D with 18-55mm IS, 28-105mm and 75-300mm plus 2x TC
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lukasik
scholastic sledgehammer
Reged: 10/11/05
Posts: 875
Loc: Lawrenceville, Georgia
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As Jeff said above, a curved rod tracker is pretty easy to make, and can work pretty well. So far I've managed 3 minute widefield exposures with no trailing. I can track for over an hour without re-setting.
Regards,
Bob
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 12065
Loc: Rockford Illinois
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And as long as your nut (On the bolt) is not permanently attached to the motor, resetting takes very little time... I can spin a nut on a bolt real fast...
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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Ptarmigan
Carpal Tunnel
Reged: 09/23/04
Posts: 1874
Loc: Arctic
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Quote:
Don't forget though, you might be able to go nicely to 2-minutes with a single-arm Barn Door Tracker, but between each shot you're still going to need to reset the arm and adjust the whole rig, ready for the next shot.
I was considering making one for myself, just for a bit of fun, and when I'm away from a power-source for my EQ-5 mount. I'd rather go with a two-arm setup at first I think, or a whole new mechanism which I've just thought of...
I want to motorize, not turn it manually because I might be doing some starwatching also.  I just don't want to turn it manually and somehow forget about it by mistake. Also, I have a zoom lens that can go up to 300 mm. S58y used telephoto lens with a barndoor tracker and came out well in just 2 minutes. He did take a bunch and stacked them with great results.
Edited by Ptarmigan (08/05/08 04:17 PM)
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s58y
Post Laureate
Reged: 12/12/04
Posts: 4850
Loc: Eastern NY
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Quote:
Also, I have a zoom lens that can go up to 300 mm. S58y used telephoto lens with a barndoor tracker and came out well in just 2 minutes.
I'd definitely recommend a motorized barndoor.
I tried a hand-powered barndoor at 200mm, but at that focal length, I got only about 10% yield, without big tracking problems. At 300mm, I think you'd have to keep turning the handwheel every couple of seconds (or even faster) for good tracking.
Also, it's best to be nowhere near the camera when shooting, to avoid shaking the whole setup (I was shooting from a deck, sometimes). In the winter, it's best to stand inside during each 2-minute (or so) subexposure, and go out only to reset the mount. In my case, I could do two 2-minute subs before resetting the barndoor once every 4 minutes or so.
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Hutech 30D, SBIG ST-402 autoguider
SV80S, SV66 guidescope
AP900, G-11, Barndoor tracker
http://www.pbase.com/s58y
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