Barn Door Tracker

[JemC]

Hi all

Totally new to astronomy of any kind, and not sure if this is in the right thread?

I am planning on buying my first scope in the very near future, in fact LeeWilky (member) pointed me in the direction of FLO to a setup they have. and will probably go for that but not quite made my mind up yet, anyway in the mean time I have been seeing something called a barn door tracker while I have been researching and making Google work overtime, so with me also being into photography and having quite a bit of kit lying around I have convinced myself that I am going to attempt   to make one of these and give it a try with my Canon Eos 450d

If anyone has any tips on building one of these they could pass on I would appreciate it as I am not the best at DIY, I think my main concern more than anything will be getting the correct bend in the threaded rod, does anyone now how I determine how much bend to put in it in layman's terms please

Thanks

JemC

[Langy]

Just did a bit of googling on this myself and found the link below.

I think that this may help what you are looking for.

Depending on what scope you are getting, if it has a MD and on a EQ mount you could stick the camera on the mount. I piggy back mine on top of the scope.

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

[JemC]

Hi

Thanks for the link,

If I go for the scope LeeWilky kindly informed me about that FLO are selling it will be Sky watcher Explorer 200P EQ-5, which judging by some of the pictures Lee has done with this scope it's quite capable of doing what I hope to achieve,

Piggy backing the camera on the scope is not something I had thought of, told you I was new to this....how would I go about that, is there some kind of bracket I would need?

Thanks

JemC

[Langy]

If you look at their image you will notice there is a camera mount (just like a tripod mount) on the rear tube ring. On my cheap Astromaster 130EQ that can be put on either ring. Mine is sat on the front ring.

I bought the cheap MD for my mount and get reasonable tracking, not brilliant by what some guys get on here but it certainly is better than just sticking it on a tripod.

http://www.firstlightoptics.com/reflectors/skywatcher-explorer-200p-eq5.html

[JemC]

Note to oneself.....pay more attention, reading through the description it does say direct SLR connection, guess that will save me trying to make barn door tracker...phew!!

JemC

[niccodeamus]

re. the curve on the thread, the radius of the curve is the distance that you have the thread from the hinge.  

What I learned, in a nutshell, is that precision equals time.  the more precise your measurements and build accuracy, the longer exposure you get with your camera.  Normally you have the rule of 600,  your maximum exposure time  in seconds is 600/focal length of the lens..  if your tracker halves the earths rotation effect, you should double the exposure time.  i.e., it doesn't need to be very accurate to get a big result, especially at wide angles.

i made mine out of bits of lego and managed to get a passable shot of M82 and its super nova

[JemC]

Hi Nebula

thanks for the reply, the penny drops

did you make yours with a motor or was it a manual one...if motor what kind/type/size did you use

Thanks

JemC

[Langy]

i made mine out of bits of lego and managed to get a passable shot of M82 and its super nova

Wow show some pics of that in lego please, would be very interesting to see.

[JemC]

why did I call you nebula, I really do need to pay attention...sorry about that niccodeamus...

[niccodeamus]

Ok.

here we are

Now, I make no claims about the accuracy, beauty, or anything else about my little barn door.  I mashed it together in an hour from bits and pieces and a tape measure because i had an urgent need to try and image the supernova in M82 last month, and at the time was not to be beaten by trivia such as not having a telescope or a tracking device.

the motor is removed from an old central heating valve.  It turns slowly, 5 times a minute, if i remember.  so the thing to calculate is how many times a minute (or fractions thereof) you need your thread to turn.  the number of times you need your thread to turn is related to the thread pitch or , in english,  how much lift you get from a turn of the thread, and the distance the thread is from the hinge.

your variables, therefore, are your gears that you can find or get hold of, that you  turn into the rotation of the nut on the thread, and the distance of the thread from the hinge.  

if you have found some sites describing the calculations, they will be useful because you need to manage what you make to get the rotation about the hinge axis as close as you can be bothered with to the rotation of the earth.  this is the important number.  

on mine, for arguments sake, the motor turned 5 times a minute, i geared it to once every, say, 90 seconds, this meant that my 1mm thread pitch needed to be 115mm from the hinge.  for goodness sake don't use these numbers, they are grasped approximately from a poor memory.  the proper numbers are readily available and my point is, you don't need to be rigid with motor rotation or thread or distance so long as the end result rotation at the hinge is as near as you can be bothered with.

not show in the images, but i blutak onto the hinge  a little scope i try and use as a polar scope

improvements that it needs are some sort of bearer to run the thread through, and basically keeping the thread still.  I badly skipped on this, i flops all over the place, the hinge is floppy, the gears could also have bearers of some sort, perhaps a battery powered motor....you could go on and on.

If i had enough gumption, I would go and buy a few parts and a stepper motor ( i don't know what one is!) and try and harness a raspberry Pi to manage the motor speed (but i don't know what a raspberry pi is either, nor how to program one).  so, fundamental gumption shortages are holding me back.

the result?

taken on a full frame dslr with a fast 135mm lens.  ordinarily i would expect a 4 second max exposure time at this focal length (600/135).  the lego barn door gets me 30 seconds if nothing slips in the mechanism.  This is a single frame 30 second shot of orion.  I haven't tried bulb mode.  it may be good for longer at 135.  it isn't well enough made to stand the weight of a 70-200mm lens and track for better than 20 seconds.

[niccodeamus]

and a small stack (six frames?) of andromeda

[todd8137]

Cool images mine cost about two quid to make but this one looks like the pro job great one

Pat

[smudgeball]

Hi

This is mine

Which is completely manual and gave me this

25 second exposure @1600 ISO with 200mm f4.6 lens

I made up a document on how to make mine

It's got a few "auction" links on it for parts, so not sure if I'm allowed to publish?

If you want a copy, you could perhaps PM me ?

Regards

Neil

[happy-kat]

I have a question, I have found a guide to follow, two actually, and the rod is straight but rests on the underside of the top wood piece so as you crank the spindle and raise the top wood by being pushed up by the rod with captive nut which essentially slides along the underside as it raises.

This looks feasible to me in that I don't have to make a curved rod as the design does not need it.

As any one tried a design like that please?

[niccodeamus]

if it catches, just bend the rod.  mine is a 6mm rod, it bends quite easily, or cut a slot for it to travel in

[Chris Rowland]

I've made the simple straight drive rod manually driven and it was fine for 10 minute exposures.  It was some while ago, IIRC I was using a 135mm lens with a 35mm film camera.

I think a lot of barn door trackers are rather over-engineered, Once you get beyond 10 minutes other things get in the way. such as polar align.  It should be easier with a modern DSLR because you can collect and stack multiple exposures.

Chris

[happy-kat]

So far I have bought the camera ball head mount bit, the other bits I hope to get at my fave old style hardware store.

[Langy]

It may be something to have a go at in the future, but for now I think I will piggy back the scope.

As to getting 10 minute exposures it must be some very accurate tracking. According to the 600 rule I can do 1.3 seconds with a 300mm lens. I've just managed to get 20 seconds on top of the scope. The MD and polar alignment obviously were slightly out as the trailing was starting to show. On an 18mm lens that would go up to 20 seconds unguided and at the same ratio of what I've just had would be just over 5 minutes.

I'd guess that polar aligning a barn door properly would not be that easy compared to lining up a scope.

[happy-kat]

This was the design I had book marked to try, and the second link gave me the wedge info.

http://www.philharrington.net/scotch.htm

http://astunit.com/atm.php?topic=handscotch

[Ags]

^^^ good references.

For polar aligning, I will try a simple RDF. It can be aligned with the hinge by angling the board through 90° while pointed at a distant object. My AZ3 mount should allow good precision with its slow motion controls.