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BWBlackett

Dobsonian on a wedge

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Help! Am I being stupid :x or am I right in thinking that if I put my Dob on a wedge with the same angle as my latitude I can use it for basic imaging by using the Az rotation of the base to follow my target e.g. Saturn :saturn: ?

Brian. :)

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You need to rotate the wedge itself and therefore the OTA above it. The base itself will be flat on the ground and its axis of rotation will be at about 35 degrees south of where you need it. The path the scope would take would start at one point on the horizon then appear to dip southwards in a curve then rise again towards the western horizon relative to the stars. In effect your axis of rotation will be rotating your scope around the zenith.

The axis of rotation has to be at 50 odd degrees (depending on your exact latitude) so if you can rotate the wedge you'll be fine.

James

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Assuming the wedge is under the dob's base, won't it have to made at an angle of 90 minus the viewer's latitude?

Mike

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Of course, if the wedge is under the base then you'll be fine. For some reason (lack of sleep?) I assumed that the wedge was above the base... :? :?

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Had a fleeting thought about this myself once and did a scribble.

If you look at it, there are lots of problems with balance and such

as the OTA arcs over.

wedge.jpg

A motorised platform is the way to go but is expensive and difficult

to DIY.

Better bet is to mount the OTA on an EQ mount for astro photography.

Having said that you can do luner and planet photography through your DOB.

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Had a few thoughts on this myself, dismissed it as a difficult one, due to balance and keeping the tube on the mount.

Solution that I have been researching, is the Fork Mount, with the tube bearing held captive, and needing a fairly heavy base / secure anchor to the ground, even for a 8" dob.

Still looking for / at ideas.

naz

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Here are a few easy options to equatorialize your Dob. OTA's.

None are difficult to construct, and all materials are easily obtainable. It just requires the will.

Images are courtest of NE Howards "Handbook for Telescope Making"

Hope they help someone.

Ron. :)

image.jpg

image.jpg

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A "Dob OTA" is a Newtonian reflector. "Dob" refers to the Alt./Az mount popularized, but not invented, by John Dobson in the '60's. If you put it on an equatorial mount, it's still a Newt, but loses the Dob. I built a simple English Yoke mount, (Barkis' middle illustration) in about an hour and a half. Not great, but it worked.

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If money is no factor.... an EQ6 PRO and some fat tube rings will sort ya ! :wink:

Vega

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I'm tempted by the middle image, the yoke mount, but how do you turn the thing to face where you want it to without messing up the polar alignment?

Up and down is easy, but what about aiming it on the azimuth plane?

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I may get shot down in flames here (so whats new you ask) but wouldn`t it be possible to mototise the dob and use a guide cam and computer control to guide it?

(hastily ducking back below the parapet)

mike

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The OTA is pivoted a la Dobsonian in the rectangular frame. The frame is itself pivoted at both ends. The frame axis is aimed at Polaris so that the tube pivots in the Dec. axis and the frame is the RA axis.

Kaptain Klevtsov

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I understand the mount now, thanks KK!

That joke mount is nice, but is basically what I already got unless there is an easy way to motorize it for tracking. I'm actually thinking I could probably knock together the "german mounting" but I have questions.

1. Does the axis going from lower left to higher right point at polaris?

2. Does the tube on that axis allow the T joint to rotate?

3. Can it be easily motorized?

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Jakey - Ive looked into that idea, the electronics / mathematics goes over my head.

I've got serious thoughts of creating a German Mount that I could perhaps leave outside if I could make it weatherproof. Is this a good mount short of getting an EQ?

It will probably replace my dob mount (which I will keep), but will use the dob base for storing the OTA and maybe for 'grab n go' moments.

If I decided to build one, could y'all give me help with it?

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