Made my barn door tracker, but...

It was forecast to be clear tonight and there seems to be some cloud. It was drizzle a bit earlier.

Anyway, from the quick session that I did, I could not find Polaris due to cloud. I did a guess as to where it could be. Anyway, I noticed that on 20 second exposure at 55mm, I get the stars to go round in almost a circle. Could that be due to not quite aiming the hinges at Polaris? I have noticed quite a bit of shaking when I increase the focal length.

If you are getting a nice circle then I suggest polar aligment could well be the cause. Love to see a picture of the mount and the results

Thanks Martyn. I will try and see whether I can actually see Polaris instead of having a chunk of cloud in that direction all night! I just noticed this amazing barn door tracker on a different forum, so I will try and implement some of the things he has done.

http://stargazersloung​e.com …st-barn-door-tracker.html

I need to get a ball head thingy from Bernie & Quasimodo. It is forecast to be clear tonight again, let's see just how accurate it is. If it works well, then I will do a write up on how it is made. I hope to post up photos after taking my lights and darks.

Please do Naddie. I have always been interested in these mounts, but never completed mine.... Maybe I should!

naddieuk wrote in post #12947348
It was forecast to be clear tonight and there seems to be some cloud. It was drizzle a bit earlier.

Anyway, from the quick session that I did, I could not find Polaris due to cloud. I did a guess as to where it could be. Anyway, I noticed that on 20 second exposure at 55mm, I get the stars to go round in almost a circle. Could that be due to not quite aiming the hinges at Polaris? I have noticed quite a bit of shaking when I increase the focal length.

Are you saying that each individual star makes a small circle, on a 20 second exposure? That would lead me to think of camera shake, and the tripod/mount setup is not sturdy enough.

Maybe best to just post the result in question, then we can see exactly what the problem is

Hi everyone,

Sorry, I have been rather busy in the daytimes for the past few days. Anyway, I finally had time to switch on the desktop and plug the camera in to download the images.

This is the barn door tracker that the family made. We used laminate flooring for a few reasons. It is smooth, therefore there should be less chance of friction, the other reason is that it is not heavy.

The bolt is an M10 hex bolt from B&Q, I used the formula in this page to place the bolt, which I worked out to be about 41cms: http://www.mikeoates.o​rg/mas/projects/scotch​/ The disc is from the underside of a CD-ROM packet and is slightly thicker than a few CDs. I bought the ball head specifically from that infamous jungle. It's a Joby one.

We could not make the tilted version, as we did not know how to make it tilt and at what angle. The mount was screwed onto the tripod using two screws and a drill. As for the tripod, this is one that I bought about 5 years ago from E-Bay for about a tenner. The next post will hopefully show the photos.

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41 cms? My calculation from that page for M10 (1.25mm pitch) work out at 286mm at one turn in 60 secs, or 343mm if your M10 has a 1.5mm pitch?

Got these from L = (pitch * 1436) / (2 * pi)

This is one of the images that I took, it is the best one out of all the others. When looking at 100% crop, each one looks like baby Saturns. There is too much shake in each photo. Did I mention that there is a lot of light pollution here? I have a feeling that the tripod is not able to hold up the mount.

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martyn_bannister wrote in post #12956538
41 cms? My calculation from that page for M10 (1.25mm pitch) work out at 286mm at one turn in 60 secs, or 343mm if your M10 has a 1.5mm pitch?

Got these from L = (pitch * 1436) / (2 * pi)

From that page, I got L = (x*60/50*1436)/(2*pi)

where x = pitch.

I counted that there were 150mm for 100 turns.

(1.5*60/50*1436)/2/pi = 411.4mm ~41.1cms

EDIT
-----

I just noticed what I have done wrong! You are correct, I was in a rush and assumed that the equation I had up there was the one to use! Aaargghh!!!!

You can buy Light Pollution filters which clip into your DSLR.

Seems like trailing with the stars on the left, but not on the right, so might well be polar alignment problem.

martyn_bannister wrote in post #12956682
You can buy Light Pollution filters which clip into your DSLR.

Seems like trailing with the stars on the left, but not on the right, so might well be polar alignment problem.

They only work with EF lenses, not EF-S. I usually do the light pollution removal in Iris after I have stacked them. However, I think the main problem is stability, and I cannot afford to buy any new items.

I will try to improve my polar alignment. I am having to do the photos through the window.

naddieuk wrote in post #12956662
From that page, I got L = (x*60/50*1436)/(2*pi)

where x = pitch.

I counted that there were 150mm for 100 turns.

(1.5*60/50*1436)/2/pi = 411.4mm ~41.1cms

EDIT
-----

I just noticed what I have done wrong! You are correct, I was in a rush and assumed that the equation I had up there was the one to use! Aaargghh!!!!

No, I think you are OK. It just means that you have to turn your rotor once every 50 secs, rather than once every 60 secs like I calculated. This is just tiresome, but it means that you can still use your device without re-siting the hinge.

I have been busy for the past week, so I had no time to adjust the barn door tracker. Last night it was clear, so I decided to have a go at using it.

The first photo is without the tracker, the second is with. I have managed to get large stars that look out of focus, is that due to misalignment? I am hoping to try and get the tracker a bit more steady on the tripod. This is somewhere around Ursa Major and the Bode's Nebulae are supposed to be slightly lower right.

Thanks.

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Looking good Naddie. Focus is a pain. I like to try and use a lens where the infinity stop is adjusted correctly and then stop down a couple. Polar misalignment usually shows up (I am told!) by central stars being round, with those on the edges of the shot being slightly trailed.