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Can't afford a C14...problem solved.

RAC

By RAC
in Imaging - Planetary

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RAC

RAC

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Last year sometime I decided I wanted a larger planetary scope in particular for when Mars gets big in 2018. There was no way I could have slipped a C14 passed the wife so I looked into making a large reflector of some sort.

There was/is a guy here in NZ selling large plate glass blanks from 12"-33" that were 35mm thick.

Making your own mirror does take alot of time but I knew it would be a good challenge and a great achievement if i could pull it off. The scope would also be a good visual instrument too.

I decided on an 18" f3.3 as that was about the largest size by far I was ever going to get onto the mount and it had to be around f3 to keep the length as short as possible.

There seems to be a common thought that fast mirrors are very hard to make but I would say they are more time consuming than anything.

The scope ended up being 25kg so not too heavy for and 18". I still want to prove the optics a bit more with some better seeing but at this stage I'm happy.

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18inch f3.3 Done! by Raymond Collecutt, on Flickr

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18inch_Surface by Raymond Collecutt, on Flickr

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Planetary imaging 18" f3.3 scope. by Raymond Collecutt, on Flickr

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Saturn test with new 18" scope. by Raymond Collecutt, on Flickr

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RAC

RAC

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I just thought, I bet this would also rule for DSO imaging!

It would need a very good mount for that. Also holding perfect collimation for that kind of work is hard with a large mirror. I have a Paracorr and can confirm the views are awesome with pinpoint stars right to the edge so I'm sure you could do DSO's with the right mount. But at f3.3 I can also confirm that focus shift as temps drop is too much with the alloy truss frame.

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RAC

RAC

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What a monster :)

Any chance of a couple more photos of the OTA from different angles to show it off a bit more?

James

Ok.

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JamesF

JamesF

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It really is a monster! :)

It was hard to get an impression of the scale of it at first, but it looks enormous there.  I'm surprised your mount hasn't run away screaming.

James

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RAC

RAC

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It really is a monster! :)

It was hard to get an impression of the scale of it at first, but it looks enormous there.  I'm surprised your mount hasn't run away screaming.

James

Well I would only call it just adequate. It's not the best but I would rather hurt this mount than my Tak NJP. It's only a few kg's more than a c14 but it's alot bigger.

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Chris

Chris

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It would need a very good mount for that. Also holding perfect collimation for that kind of work is hard with a large mirror. I have a Paracorr and can confirm the views are awesome with pinpoint stars right to the edge so I'm sure you could do DSO's with the right mount. But at f3.3 I can also confirm that focus shift as temps drop is too much with the alloy truss frame.

Good point, I think my mount wold actually fit inside this scope! I guess it would need CF rods instead of ali to keep things thermally stable at that speed, we all know what ali F/4's are like. 

Great that it works so well with the paracorr, it must really knock your socks off visually when it has been freshly collimated. That Saturn pic is superb! :)

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RAC

RAC

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That's very inspirational and a great result on Saturn. How much time did it take you to make the 18" F3 mirror?

About 4 months doing it most nights and all weekend. It would have been an easy 200 hours but alot of that time was due to inexperience with it being my first mirror. There was alot of back tracking when there was no need.

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