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Neil Wyatt28/12/2015 18:10:00
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Quite by chance I came across this article in a 1965 issue of Model Engineer. It didn't show up in my index searches when we were debating astronomical issues!

Apologies for the low resolution.

moore1.jpg

moore2.jpg

Ajohnw28/12/2015 19:38:23
3631 forum posts
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Maybe the were seeing if there was any interest in telescope making. It was thriving in that period and for many years after. Not so now really but people do make bits and pieces for them as you know Neil.

I seeded an odd idea on that forum. Why stick a counterweight on the end of a long shaky pole and hang a newtonian on the other end when the weight could go on the end of the telescope making it easy to fork mount. I'll bet there will be no takers and me, well lots to do. The LX90 reminded me just how stable fork mounts are for very little weight really.

John

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john carruthers29/12/2015 09:11:58
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The Victorians worked out decent scope mounts. 'Keep the weight between the bearings' and you won't go far wrong.
Just been helping sort out the dec drive on the 28" at Greenwich, a rigid yoke on substantial piers.

I also saw PM's heavy mount when it went to AWR for a refit. It never came off the pallet, too heavy to move manually.

Edited By john carruthers on 29/12/2015 09:13:58

Ajohnw29/12/2015 10:15:16
3631 forum posts
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I haven't done any sums but bought a 6" newtonian, used of course. An xmas present to myself. I'm hoping to use it "hand held" on star fields. It weighs about 4 1/2 kg and the balance point is well up the tube. I haven't owned one of these for a long time and all have been bigger. On a German mount I balanced it with 4.7kg weight as that is what the mount came with.

Then it struck me what would happen if I put that weight at the bottom of the tube and where the centre of mass would be in relationship to the bearings in a fork mount. I'd guess a 2kg weight would do really.

The German mount I used has a very light weight head. 4.7kg so with that head, standard weight and scope the total weight is circa 14kg that could be reduced to 12 by changing the weight to say 2kg but as that would be further out on the shaft the degree of shake would probably be similar.

The entire weight of the 8" LX90 with it's fork mount is circa 15kg. No problem at all focusing it by hand with a 3mm eyepiece in it, a bit short of 700x. Can't say the same about the Newtonian, shake, F5 with a 2x barlow and the same eyepiece. That gives about 500x. It was just about possible to focus it cleanly.

There are some interesting fork mounted scope designs around here - from when people used thick mirrors. The site needs a browser that can translate

**LINK**

It would be pretty easy to do better these days.

John

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Neil Wyatt29/12/2015 10:55:07
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You probably have a good point ether.

The GEQ is good because they are compact can easily be adjusted for most latitudes.

If you have a permanent observatory, a big solid polar-aligned shaft (an car half shaft on good bearings would be ideal) with a hefty fork mount on the end would be simpler and you could make it totally rigid.

Neil

Ajohnw29/12/2015 14:05:39
3631 forum posts
160 photos

The equatorial platform for the sct's is simple to use as well Neil.The one I have used on a 10 SCT is just 2 shaped aluminium plates that are hinged with the usual scale. I'd say around 1/2" thick and they are normally kept on the tripod. Meade had the bright idea of using a nut that contained a compass and level as a nut to fix it on with.

Polar alignment is different as there is no polar scope but it can be done in other ways. Meade did a finder with a polar reticule in it. The other way is to use star drift. For visual use I used to swing the whole lot about initially and then use the adjusters. It was more than good enough for planetary use and didn't take long. It's also possible to keep switching between 2 stars centring them with the adjusters. Getting it exact isn't quick with any type of portable mount.

The biggest pain with all of them is levelling the platform the head sits on especially on a tripod. I feel it would be fairly easy to make a levelling platform using 3 pairs of spherical rod ends with opposite hand threads. That way the tripod legs could be used for a coarse setting.

I still have a vixen pier. My impression is that these are more rigid than a similar weight tripod. Levelling is also easier on hard surfaces as they sit on screw jacks. Never done it but it would be easy to add some locations for the jack screws to sit on in the garden and also locate the head in the mount. That way once set up it could be simply plonked down and used.

Must admit I am not really interested in long exposure photography. I came across some one on cambridge in colour that uses a dslr and shorter exposures. He gets good results so I will be trying that. There are indications that a go to alt az mount might be track well enough if set up carefully. The exposure time that could be used was read on the web though - Always a dubious source of info.

My first bought scope was an 8" Celestron SCT. I've always regretting selling it as they are so easy to move around and use. A 10" isn't so much fun. I also have a now very elderly Meade 5" F9 APO. It's on a Meade GEQ that Astrophysics used to buy off Meade and rebadge and tweak. It's joy to use even with the tripod legs fully extended. Contrast wise it matches maybe beats an 8" sct but it's far more of a handful. It costed me all of circa £250 some time before apo's became really popular. I often wish I had bought a full set of Takahashi eyepieces then as well. Their prices rocketed not long after. I tried to get some discount on a full set off the dealer and he wouldn't offer me any so gave it a miss. A lot of the price hike was profit. I found a Mewlon for sale in France for a lot less than UK prices but the dealer wasn't allowed to sell it out of France. I'm more educated these days - wouldn't want one any way. Dall Kirkams have more problems than SCT and focal reducer correctors can be bought for those a well.

John

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Edited By John W1 on 29/12/2015 14:07:36

Edited By John W1 on 29/12/2015 14:08:17

Bob Mc30/12/2015 16:42:29
229 forum posts
48 photos

dsc_0323.jpgHi Neil & all.....

am at present re-building a 6 inch reflecting binocular telescope... awaiting mirrors coming back from re-silvering.. hope you like pics...

dsc_0324.jpg

Neil Wyatt30/12/2015 16:49:29
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Now that is impressive. Apparently it should give your the performance of a ~8-9" scope as well as more comfortable viewing.

Bob Mc30/12/2015 21:38:23
229 forum posts
48 photos

The binocular telescope was originally made by a member of the Manchester Astronomical Society, it has lain neglected in a garage for some years and the mirrors were in dire need of re-silvering, the inter pupil distance mechanism was also badly made and I re-made it all using perspex. I am told by the company who have done the mirrors that their tests showed that they are identical in focal length and accurate to 1/8th wave...I have been told that the views of the moon are particularly good and seems like you are hovering over the surface...

I will let you know...!

pic of inter pupil mechanism.

dsc_0328.jpg

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