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Ambermile

By Ambermile
in DIY Astronomer

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Ambermile

Ambermile

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Hi all

Some of you may know already but I decided a while ago to build a refactor. I had a choice of three objectives - being an APM 102mm triplet, a William Optics 80mm doublet and a Skywatcher 120mm doublet. None are apo although the APM is close and the WO is designated semi-apo. After a bit of soulsearching I decided to go with the 102mm as really I want an imaging scope - which precludes the 120 (CA) and as big as possible (which precluded the WO).

Anyway, to cut a long story short I got myself a Baader Planetarium rotating focuser and a *very* sexy carbon fibre tube and set to work this morning on the beast. So far so good, I will need to sort a dewshield later but here's what I got so far, as it were...

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Ambermile

Ambermile

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Looking good now. Got a little colour (only have Saturn to look at) at 100x but it sort of "tunes out" on focus. Handy because when the colour goes it's in focus! Dropped a WO VR-1 in and took it up to 200x but seeing is terrible, Saturn too low still. More colour but impressive all the same. I may hold onto this scope for a while! Will wait for the Moon and maybe even drop the SC3 in and see what I can see later but not getting serious with cameras tonight - I've not been well you know :tongue9:

May post some pics of the finished beastie later too.

Arthur

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Ambermile

Ambermile

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M42 awesome, M31/M110 also. Even managed M78 :shock: (sorry Caz) M45 very pretty at 20x or so, as was the Beehive and Christmas tree. Found the Rosette but could only see stars 8) Forgotten what fun a mount and a scope with no electricity/drive/camera/goto can be... May forget the SC3 and just poke the D70 in for the Moon.

Arthur

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Ambermile

Ambermile

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Hi Caz

Making the refractor is rather easy but you have to remember it's the sort of thing I do for a living :lol: In this case I had to make a few calculations (FL for the objective plus the use of the scope plus the focser travel), cut the tubing, make a couple of aluminium adapters (one for each end) and fit them together. Thankfully the math was valid and it all worked as planned!

Arthur

PS - M78. Right, if I can find it with a 102mm refractor (which is F5-ish) then you should have no probs with the newt. Using a 26mm ep I had Alnitak at three o clock on the edge of the field. Moving only the way the axes let you, move Alnitak to the left, then down the same (ie. one FOV) and there it is. With the newt these may be opposite as there's no diagonal, but it's there. Faint, but there.

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Ambermile

Ambermile

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Ah - well it is simple you know. Just the FL of the scope minus the length of the focuser minus the focus travel (and a bit in this case for no need of 2" diagonal) and what you are left with is the length of the tube itself.

Oh yes, of course...peice of cake.... :? :scratch: :(

No really. FL of the triplet is 500mm. Focuser is 130mm closed. 370mm so far. I wanted a 1.25" diagonal to come to focus - another 60mm so 310mm so far. Then a bit for focus movement, another 10mm. So, my tube was cut to 300mm. Cell added, focuser added. All OK! If you look at the last pic of the scope on the mount you will see that the focuser is extended about 10 mm from the focus-right-in. Not bad... :lol: It really isn't rocket science !!

Arthur

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Ambermile

Ambermile

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That penny just ain't dropping Arthur.... :? but I admire your perseverance.... :lol:

OK - last try. A lens (any positive lens) comes to focus at a given point? So if your lens comes to focus at 500mm (the focal length, or FL) then you have to arrange for your eyepiece or camera to be 500mm from the lens so it is in the focal plane. OK so far? When making an OTA you have to make sure that your focuser assembly can pass the camera/ep through this focal plane to allow it to reach focus. Hence the sums - you add all the bits together and hopefully they equal the focal length of the objective and you are a happy bunny :(

Arthur

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MartinB

MartinB

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Its very hard to concentrate when you have a 3 yr old crumbling birthday cake all over her and the floor... :?

:lol::(:p Even harder to carefully fix a lens in place. Sounds like a great project Caz. If I tried I just know my pride and joy would probably turn out looking like a banana.

Build Your Own Telescope - Richard Berry

Martin

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Ambermile

Ambermile

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OK - this is getting silly. An hour to set up the new scope and the FD for guiding, and had the Rini still on the Artemis. OK, try it anyway. M42 (where else) nice FOV, Running man and everything. Couple of focus frames and get set. Oh. Fluffy stuff. Cycle a few 30 sec 2x2 binned - still fluffy stuff. One frame has *three* satellite trails in perfect formation! (I saved that one). Eventually give up waiting and decide to take out the Rini. No clouds. Get new 2" adapter, screw in, refocus just in time for the fluffy bits again. Never mind - M46 is rising methinks - should be below the cloud line. Off I go. In the middle of the plum tree. Doesn't mater though 'cos the clouds moved down anyway. Of course, I'm getting used to it now :insects1:

Will wait it out for another half hour then I'm packing it in for the night.

Arthur

PS - for those visually-minded amongst us, get a peek at M46 if you can. A very nice cluster (extra-galactic I believe...) that has a cute little planetary nebula top left of the globule as it were. Nothing to do with M46, in fact I think the nebula is maybe half the distance from us as M46 is but it looks real nice visually. It's not going to get more than about 30 degrees though so if you're southerly-challenged you could have a spot of bother.

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Ambermile

Ambermile

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OK - that M42 with the satellite trails. Looks like they're hunting in packs now :lol:

Thats a fantastic image, how many images do you see that you have satellite trails.... :shock: :(

Not many Caz 'cos we usually ditch them from the processing. If you want satellite trails say so! Not a night goes by (especially at f/3 and a big chip) that at least *one* frame gets little stripes over it.

arthur

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