My Barn Door Mount Project (with photos)

[gazza666]

Jut been doing a bit of reading and it seems that you have to align your scope to the hinge the scope must be parallel to the hinge axis then point at polaris but over a bit LOL

the way you have done it is not 100% right you have sighted you hinge at a distant star then moved your scope to that point so the hinge and scope are not parallel but will be very close

depends on how acurate you want to be

as I have mentioned I have seen some scopes in the middle of the barn door but they are still aligned to the hinge axis first ,they dont have to be by the hinge

if you had a scope in the middle of your barn door and aligned the hinge by eye to polaris then moved the scope to that point you can see that would be more out of alighnment that your setup

[Doc]

Thats maybe why it was never really accurate, I thought it was always the play in the hinge but who knows.

[gazza666]

Some adjustment of the direction of the scope is needed so that it can be aligned with the hinge. The alignment can then be made by clamping the lower board and viewing a small very distant object. The object is first centred on the cross hair or reticle by moving the boards together with the top board in the down position. Then when the top board is hinged upwards the object should remain centred in the cross hair. If it moves the scope position should be adjusted left/right, or up/down, until the movement during this test is eliminated

this is what I have read so you cant be far away

[glowjet]

It is the same principle as your finder on your scope, you first need to align your hinge center on a very distant object or the pole star, laying a straw or something similar along the line of the hinge will do, or if your design allows, a removable hinge bolt so you can sight through the center hole, so long as your finder scope, fixed on the camera board, is mounted near the hinge, and centered on the same target, the angle of error between the hinge center axis and finder scopes optical axis is so small as to make little difference in tracking error, HTH.

John.

[julian_1234]

It is the same principle as your finder on your scope, you first need to align your hinge center on a very distant object or the pole star, laying a straw or something similar along the line of the hinge will do, or if your design allows, a removable hinge bolt so you can sight through the center hole, so long as your finder scope, fixed on the camera board, is mounted near the hinge, and centered on the same target, the angle of error between the hinge center axis and finder scopes optical axis is so small as to make little difference in tracking error, HTH.

John.

I know it's an old thread, but I've got the "urge" to try to make a barndoor.

Just wondering about the mounting of the finderscope. Surely if you're looking at a star that is several light years away then the angle would be the same at the hinge as it would be at the tip of the barndoor .... even if the barndoor piece was several feet long.

Or am I missing something ?

Julian.

[haitch]

I know it's an old thread, but I've got the "urge" to try to make a barndoor.

Just wondering about the mounting of the finderscope. Surely if you're looking at a star that is several light years away then the angle would be the same at the hinge as it would be at the tip of the barndoor .... even if the barndoor piece was several feet long.

Or am I missing something ?

Julian.

As I understand, so long as it is parallel to the hinge, it's fine.

[Reginald]

Very good suggestion, pictures are very beautiful.

[Polar Bear]

How did I miss this, another great barn door project, thanks for sharing.

Paul

[JimStan]

A little common sense here. It is quite doubtful that you are going to mount more than about a 300mm lens and DSLR on such a device, so polar aligning is a real uncompicated process !

I published a chart on this forum, showing the amount of time that can elapse before stars start to showing trails. If your barn-door is just roughly polar aligned, and the tracking error does not exceed that amount of time as shown in that chart, you probably will see nearly pin-point stars.

In other words, if you tracked a point in the sky for 30 minutes, and the TOTAL elapsed error was less than 30 seconds ( for a 50 mm lens, that would be about right ) you would probably not see trailed star images.

I would be very interested to see if anybody is successfully driving their tracker with an electric motor, and if the driving circuitry is electronic ( stepper style )

You might even show up as an article in "The Observer" !

Clear Skies, Jim S.

[todd8137]

hi all could some one build me one ,my diy skills are not this good ? pm if any can ,pref with a motor drive ect

thanks

[NickK]

I think vibration would be a problem.

You're turning by hand through a hard piece of metal. I think having a flexible solution could help reduce the transfer of vibrations.

An alternative would be to use the flex stuff that has a coil of wire inside a hard plastic outer. the inner can turn but also move back'n'forth so a movement lock would be needed.

You can then run a motor on the ground with a rubber band absorbing vibration when it turns the wheel. The rotation is transferred through the flex pipe to the worm used to open/close the barn door.

[Gina]

I think if you're using a rubber band you won't also need a flex tube. I've often used rubber bands to drive things and found one or two problems. The ordinary office sort are very elastic and if there's any stiction the movement at the destination can be jerky. Also, ordinary bands have a fairly short life when used like this - I guess they don't like the continual flexing. Changing to a special purpose drive band and pulleys solved the problems. Still some "springiness" in the rubber band but not excessive. The one I have to turn our CCTV yard camera has been fine for well over a year now.