Need an idiots guide to barn door imaging please!

[spaceboy]

Hi All

I have searched the net and found some pretty good how to build a barn door sites but with out sounding too much of a dumbass I have to admit I can't get my head around it. I understand the whole earth rotating, tracking the sky thing but what I don't get is how you set up a barn door accurately enough to get egg free stars. The barn doors I have come across have a polar scope screwed on one end then have the camera mounted on a ball head pointing in a total different direction?? Also why are the threaded bars bent? would this not cause some vibration? and how do you figure out what size gears you need if planning to motorize the barn door and where would you pick some thing like that up from? I have looked on youtube as pictures can speak a thousand words but video says so much more but most of the videos I have found don't really give much insight on how to set them up etc.

Any help would be appreciated please.

[Adamar98]

Hi Spaceboy,

Try these.

http://www.garyseronik.com/?q=node/52

http://www.garyseronik.com/?q=node/184

I followed these instruction to build my first barndoor tracker. You don't need a polar scope. I just lined up the hinges with Polaris.

If you get it right you'll get some good images. Don't expect to get good tracking with anything over a 50mm lens. You'll get exposures of over a minute. Which isn't bad for what they cost to make. Take plenty of pictures then stack them. I think youll be surprised at what you'll get.

Good luck and have fun!

Adam

[spaceboy]

Thanks Adam

I will give the links a good look over and hopefully they do the trick.

When you say nothing over 50mm is that due to the accuracy or the ruggedness of the barn door to support weight?

[Adamar98]

A bit of everything. The wider the f.o.v the easier it is to track. Anything over 50mm and you start to get eggy stars fairly quickly. I'm not saying its not possible to image with more than a 50mm. It just starts to get harder and tends to take the fun out of it.

[Moonshane]

it's comparable to an equatorial platform Nick. the eqp is set up so that the centre of the cone of roation (hinge on the barn door) points at polaris and follows an arc around that centre point. you can point your scope (camera) where you like as it still tracks the rotation of the Earth around Polaris.

[spaceboy]

Thanks guys. I admit to having a tight budget for this one as I'm not too sure how often I'm going to be able to get out to dark skies to actually get to use it. I have picked up some hinges FOC and got myself an EQ1 motor drive off astroboot to use as the power source as I found this a reliable little unit on my EQP. Sorted a polar scope and can knock up a holder for it on the lathe. The wood should come up free at some point but the gears seem to be around the £4-6 mark which was more than I had intended to spend on a piece of plastic. Also any ideas where should I search for the imperial (1/4") bits to mount the ball head? and the thread insert for the threaded bar to run through?

[Adamar98]

I just took the instructions down to my local hardware shop and the fella there sorted it all out for me. Cost me around £15 for the lot (apart from the motor). He even cut the wood for me!

[spaceboy]

Blimey that was a result Adam. I'm gona make a start the weekend so will hopefully have it all up and running for the dark nights closing in. (which I think have already started )

[spaceboy]

Looks like I've fell at the first hurdle I just can't seem to find anywhere cheap for the gears. Any members with suggestions where I could get 64 & 16 tooth spur gears and would be appreciated.

[spaceboy]

Just found this that might be of interest to others who find themselves in the same boat as me http://www.petesastrophotography.com/

[Viewmaster]

A single arm tracker with straight screw drive is 20 arc secs in tracking error after 30 minutes , But a double arm type 4, is within 1 arc sec after 2 hours. So tracking accuracy all depends on the type you build. The smaller type 3 double is within 3 arc secs after 75 minutes. Allthis is assuming that the motor/manual drive is correct, of course. Happy tracking.

[spaceboy]

Thanks everyone for your help but I just don't think I've got the funds to do it and I finally settled with retrofitting the EQ1 drive to fit a surplus EQ3-2 I have. I will post some pics of the drive fitted to the EQ3-2 for those who want a driven mount on a budget as the EQ3-2 drives are £80 and the EQ1 drive can be picked up from astroboot for £16.50 delivered. I will also post some images once I get chance to see if the set up works. I figure it being an EQ mount it can be polar aligned with more accuracy than a barn door and as the EQ1 motors have variable speed controls I should be able to adjust for any errors in tracking??

[spaceboy]

This drive is 9v and runs off 2 x 9v PP3 batteries so I'm guessing it will give me plenty of tracking time before running flat. If it doesn't it will be easy enough to wire a 2.5mm jack and run it of a power tank/ car battery with switched voltage adapter..