Barn Door Mount for Camera

[shaneaust]

Hi all:

I've just built a bard door mount for my camera for astrophotography; been having probs with tracking, as I'm doing that by hand. My barn door mount is very similar to the one at: http://www.jlc.net/~force5/Astro/ATM/Barndoor/Construction.html (http://www.jlc.net/~force5/Astro/ATM/Barndoor/Construction.html)
But instead of a stepper motor to move the top board in time to the earyth's movement, I simply turn a screw a certain distance each X minutes.

Question - I have to do 2 things to get the mount set up properly (this is per an article at: http://solar.physics.montana.edu/YPOP/Classroom/Lessons/Sundials/skydome_S.html). First, ensure that the hinge is pointed at the Celestial South Pole; second, ensure that the angle between the top and bottom boards is equal to my latitude here in Australia. Once that's done, so the article would lead me to believe, I'm ready to go.

Okay - but when I turn the screw to keep up with the earth's movement, isnt this throwing my latitude-angle setting out of whack?? I'm at 38° South, so when I turn the screw, the gap is actually decreasing.

Do any of you barn-door experts have any advice as to whether my logic on this is correct?

Thanks!

[Peter Bobroff]

If the top and bottom boards are those joined by the hinge and the hinge is pointing at the celestial pole, I don't think the angle between boards is relevant.

[huckabuck]

hello shaneaust. if i'm not mistaken the article is slightly misleading. you must adjust your altitude UNDER all your tracker. see the unit i use . especially the bottom board. it's basically a barndoor with some mods.

if you point the hinge to the pole you should already have your alt set. you are correct. turning the screw will track in ra. image the whole thing sitting on a wedge or tripod with the angle you need already set.
http://www.iceinspace.com.au/index.php?id=63,373,0,0,1,0

[shaneaust]

Thanks Peter - so, am I correct in assuming that "locating" the celestial pole is just a matter of getting a compass and pointing the hinge due south?? This is really what I need to know.

TIA!

[jjjnettie]

It won't be exactly due south. Depending on your location it will be a few degrees off.
I can't remember off hand where to get this info. But someone will come forward and point you in the right direction. LOLOL Pun not intended.

[Karls48]

You can get Magnetic Declination for you location at http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp

[RAJAH235]

Hi Shane. The hinge points towards the South Celestial pole but see my pic for explanation re; your base board etc.
Having made a Curved Rod Tracker, I made a wedge for my latitude which sits flat on the tripod.
This tilts the base board to the correct angle.
I made another smaller wedge & fitted the ball joint on an extension here. Gives a lot of movement for the camera & assists in getting 'CG/balance' correct. (Second Image).

http://i2.photobucket.com/albums/y7/RAJAH235/IMG0001.jpg

http://i2.photobucket.com/albums/y7/RAJAH235/IMG0004.jpg

To help with finding South Celestial see attached.

HTH. :D L.

[shaneaust]

Thanx, Huck! Your advice and more importantly the pix of your mount, have seemingly fixed my problem! I actually added another "bottom" board on the mount, adjusted the angle to my town's position, then put all the rest of the mount on top of it. I then pointed the hinge axis south and all seems well now. I'll post a pic once I get something recognisable! But I'm not having any probs now with blurring or similar, as I did before.

Thanks again, mate! :thumbsup:

[huckabuck]

glad i could help

[shaneaust]

Tommy:

One more question - looking at Figure 9 on your article on here, did you measure the angle for your altitude using the top of the bottom board to the bottom of the top board?

I measured and set mine using the angle 38 degrees), from the top of the bottom board to the top of the top board...is this correct? Or is your way correct? My boards are ~ 1 inch thick.

[huckabuck]

HEY SHANE, MY WAY IS CORRECT. THE PIVOT POINT IS THE POINT THE TWO BOARDS HAVE IN COMMON, hope THATS CLEAR TO YOU. oppps, sorry for the capitals, i didn't know they were locked. anyway, i am trying to send an attachment to explain better. a picture is worth a thousand words. well my printer is out of ink. so i'll get back to you in a little while

[huckabuck]

hey shane, maybe this will help. as you can see the bottom of the top board and the top of the bottom board are where you set your alt angle. hope this helps.if not then i'll try another approach

[shaneaust]

Tommy, you've explained it fine - have modified my angle calculations accordingly.

Thx

[DobDobDob]

So for an antipodean like me, you mean the inside right :whistle:

[huckabuck]

ummmmm........yes????

looking back, after i got my thinking cap on, assuming the two sides of each board are parrell to theirselves it wouldn't matter where you measure the angle:D

[DobDobDob]

Ain't science grand :P