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In search of a cloudy night project

Dom1961

By Dom1961
in DIY Astronomer

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Dom1961

Dom1961

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I'm 14 years old, can do woodwork, metalwork and electronics, have a 8" dob, and in search of a 'make' project. I want something that I could use with my scope or something that I could Use to mod it. I have access to solder irons, various woodwork and metalwork machinery, 3d printer, laser cutter. Any ideas? Has to be cheap-ish

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RLWP

RLWP

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Ooh, I could model one and 3D print it

You could also save your money and make one out of pieces of tube. They aren't complicated, try some Google searches

Richard

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RLWP

RLWP

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The bit from the sloping face to the inner end of the tube needs to be open. You have shown a small diameter hole

I found this website  useful: http://web.telia.com/~u41105032/kolli/kolli2.htm. If you read through the explanations, you could change your design to make the tube the right length for your focal ratio, include tolerance markers and provide slots for the crosswires of a combination collimator

Richard 

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Dom1961

Dom1961

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The bit from the sloping face to the inner end of the tube needs to be open. You have shown a small diameter hole

I found this website  useful: http://web.telia.com/~u41105032/kolli/kolli2.htm. If you read through the explanations, you could change your design to make the tube the right length for your focal ratio, include tolerance markers and provide slots for the crosswires of a combination collimator

Richard 

Ahh right, i'll sort that out, an auto focused is a great idea, thanks!

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Ajohn

Ajohn

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You could make some eyepieces. Plossl's a pretty easy and can be rather high quality. Only problem with them really is that eye relief is low at very short focal lengths. There is one way of doing that shown here along with a focal length calculator

http://www.astronomyboy.com/eyepieces/index.html

Some suitable lenses are available here

http://www.astromediashop.co.uk/Components.html

Plossl's are just two decent quality achromatic lenses arranged together as shown. You might find other sources of suitable lenses, ebay, google cardboard suppliers etc. Items can be bought from SurplusShed in the USA. No tax providing total value is less than £15. I sometimes ask them to split orders into 2 to get round that. The tax we have to pay is one thing but the charge for collecting it is rather excessive on low value items, it can be over £10.

The longer focal length 50mm lens astromedia sell should make a decent finder.  Also the 40mm. Magnification, just in case you don't know is focal length of objective / focal length of the eyepiece. The exit pupil, the size of the beam out of an eyepiece that needs to go into the eye is diameter of objective / magnification. A limit is usually set at about 6mm for that in dark sites maybe 4 if there is low level light about. In practice there isn't much harm having one that is too big to pass through the eye's pupil because the head can be moved around to take in all of the view. Actually I use one like that on a telescope at times - lots of contrast but I can't take in all of the view in one go.

A small newtonian finder maybe - pass, not sure how well it would work out but they do have suitable mirrors even though the 2ndry would be oblong.

There are other sources of eyepieces. Some loupes use a 3 element lens and are well corrected. That type usually folds out of  a metal cover. Their focal length is 250mm / magnification.

Some eyepiece designs you come up with might have problems near the edge of the field because they need a field stop - a disk with a hole in located on their focal plain.

Astromedia do a number of kits often making things out of cardboard. Could be converted to reprap or even metal. Any parts in them will still be useful in some cases.

Some people have made their own equatorial head. One method is in a recent post on here. Another is to use heavy large pipe and fittings using the sort of pipe that they run around factories and probably some schools too. There are designs about on the web.

If you want to make something the best idea is to try and find some way of making items you want or need.

John

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RLWP

RLWP

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You could make some eyepieces. Plossl's a pretty easy and can be rather high quality. 

<snip>

John

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John, I hadn't thought of doing that. I wonder if you would point out some suitable lens combinations? This could be a good route to increasing my usable eyepiece collection

Perhaps we should spin off a new thread for this

Richard

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Ajohn

Ajohn

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The best option is 2 identical achromat for a plossl. Choose any that according to the calculator give a focal length that interests you. It can take a while to find lenses that are stocked in the UK but it can be done with google and I am not sure what is available. You will probably find that the real optical component suppliers work out too expensive.

As an example astromedia show an 18mm dia lens with a focal length of 26.5mm, according to the calculator that will give a focal length of 15mm. They also show an 18mm dia with focal length of 39.5mm which will give 21mm.  There is also a 26mm dia 99.6mm focal length which should give about 51mm.

IRPoiser on the web sells other sizes but frankly I feel he is too expensive at £15 each really. SurplusShed have all sorts of things kicking around including lens kits for eyepieces. Personally I would stay away from 3 or more element designs unless the lenses come from people like that. It's hard to be sure that they will work just picking lenses at random. There is a much bigger variety of lenses available in the USA cheaply including on their ebay. SurplusShed even sell precision achromats cheaply but providing that they are normal types the ordinary ones should give satisfactory results.

When I was interested in this sort of thing I didn't have a lathe at home so as I had an 8in SCT and wanted a very long focal length eyepiece for it I asked Poiser to make it for me. Focal length something over 3in and a massive exit pupil. I've since found on a much smaller scope that as the mag gets lower and lower a hole may appear in the centre of the view. Not sure why but think it's down to it being a very short scope. In terms of making though I happened on a lens suitable for a rather large finder so at some point will be making an eyepiece to go with it. It will also use a normal diagonal so that it can be used as a guide scope.

John

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Ajohn

Ajohn

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This link should give you some posts to look at and more information on them

http://stargazerslounge.com/index.php?app=core&module=search&section=search&do=search&fromsearch=1

On  the other hand it doesn't seem to have the search terms so - go to search, top right of the page, click the gear symbol, enter barn door in the search term and diy astronomy in the forum section.

John

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