Surplus Shed

[Keltik]

Found this via a post in Cloudy Nights astro forums, and decided it will be the basis for a new telescope. Steep learning curve ahead!
The Surplus Shed website seems to have a lot of very interesting stuff, and priced very reasonably.
127mm objective . (http://www.surplusshed.com/pages/item/l3968.html)

[ZeroID]

Lot of people on Cloudy NIghts are using that objective. You might want to check what they are up to.

[Poita]

Might be worth using for a PST mod for solar.

[mill]

I use that one in a Saxon tube and it is a great lens for the price.

[pmrid]

Bear in mind that it's an achromat, not an APO so CA will be an issue to some degree and at F5.5 you'll want to look at coma correction too.
Peter

[Saturnine]

Have been buying lots of objectives and other bits and pieces from Surplus Shed for many years and have no complaints, can recommend them. My most recent was an 127 x 1200 earlier this year and completed the scope a few months ago and it performs very well . The 127 x 700 lens will make a fine low power scope but an Minus Violet Filter will be usefull in keeping down C.A. to tolerable levels.
Check the Cloudy Nights Refractor Forums and the Yahoo Refractor Makers Forum for more info and feedback on these lens.

Jeff

[Saturnine]

I should also mention that these lens are popular in the USA and are often out of stock so you 'll need to check the site frequently for their availibility and jump in quickly.

Jeff

[mill]

That is why i use a -V filter and will do mono imaging with refocusing between filters, this way it will perform quite well.
Also mine is a F9 so it is very forgiving with coma.
Surplus shed sells two focal length lenses, F5.5 and F9.

[Keltik]

Thanks for the useful info, guys. With regard to coma correction, at what stage in the image train should a correcting lens go? and do -V filters affect the image overall in other ways, such as brightness reduction?

[Keltik]

Actually, solar was at the front of my mind for this project. So, given that we're not dealing with punctate light-sources, and that solar filtration is going to have some effect on the colour balance of the image, would coma correction and chromatic aberration still be enough of an issue to warrant making plans for them? I'm not going to entertain using the scope for night photography, but I may attempt capturing some solar imagery at some stage if the scope works well enough.

[Poita]

You are effectively looking at mono light for solar, so I don't think CA will be an issue really.

[Merlin66]

You could use a single element objective for Ha solar imaging/ observing!!
The narrow bandwidth (<1A) doesn't show any chromatic aberration.
I have a write up on modifying a PST to a larger aperture....just drop me a PM with an email address and I'll send a copy.

[Poita]

So you would really get no benefit between an Acro and an APO for a PST mod?

[Merlin66]

None whatsoever!
One of the best mods I've done used a 90mm Meade starter refractor...

[rainwatcher]

At that price would it not form the basis for making a good guidescope ?. I am finding it difficult to find a good guidescope at a price i can afford maybe i should make one.

[Keltik]

It's arrived! very nice-looking lens, but the proof of the pudding, as they say..... I must say I am really looking forward to the challenge of building my first refractor.

[koputai]

Keep us informed please Trev, I have one of these lens sets and will be building around it one day......

Cheers,
Jason.

[Keltik]

Update: first attempts to plan the scope around a section of 150mm pvc stormwater pipe have resulted in the realisation that there isn't going to be a nice-looking cheap way to make this scope. For one thing, stock PVC pipe isn't quite circular; it's also a bugger to work, resulting in all sorts of confetti, and worse still, it's very prone to static electicity effects...a dust-magnet substance.
So I'm on the web and looking for something a bit special. CST Express (http://www.cstexpress.com/) seem to offer tube in the dimensions I need...but it seems pricey at $467 a metre.
Next line of inquiry is to a Chinese company called Zibo Langda (http://langdicfrp2009.en.made-in-china.com/product/sMfmJDXHCehK/China-Carbon-Fiber-Telescope-Tube.html). I'll let you know what they say......

[Saturnine]

Hi Keltik

Try One Steel Aluminium for aluminium tubing up to 200mm dia. they have 127mm x 1.6 wall thickness in 6 metre lengths, may be able to buy it in shorter pieces. They stock tube suitable for scope making in 3", 4",5" & 6" diameters and more. Could also try Capral, who also stock aluminium tube in many sizes, probably from the same manufacturer.
I've made several scopes using plastic storm water tubing and once the tube is painted, have had no problem with static , if having trouble with the swarth from cutting and drilling plastic tubing, sticking to the tube because of static elec. wipe with a damp rag, that will help reduce static build up .
Good luck with the project, scope making is rewarding and fun, once your finished, which is hard to stop when you realise how easy it becomes with the experience of that first one under the belt.

Jeff ;)

[Poita]

How do you go about mounting the lens so that it is perfectly 'square' to the tube?

[Merlin66]

You can use a laser collimator to get the focuser square to the optical axis, then a bright LED torch and Cheshire eyepiece to check the collimation of the objective. A two stage process.

[Saturnine]

[If you cut and/or machine the end of the tube square and it's the correct diameter to fit inside the lens cell, it should butt up against the back of the inner ring that the lens itself sits against on the other side, therefore being reasonably square to the optical axis. Then, as Merlin said, you can use an laser colimator to fine tune the alignment of the lens cell and the focuser.

Jeff

QUOTE=Poita;811164]How do you go about mounting the lens so that it is perfectly 'square' to the tube?[/QUOTE]

[Poita]

Vey interesting.
I may make it a school holiday project with my daughter over easter, it would be a lot of fun and a good learning experience for us both.

Let me know how yours goes!

[Keltik]

Thanks Jeff, I might follow up that info. The various queries about carbon fibre tube led to the realisation that the tube would be four times more expensive than the lens :eyepop:...back to square one as they say.
My trick for cutting any tubing perfectly square to its long axis is to wrap heavy drawing paper round it and tape the edges together so that they are perfectly aligned ( ie the edges running around the tube where they overlap and you can line them up.) Then slide the paper to the point where you want to cut, use a marker pen to run a line along the edge of the paper, and you have a nice line around your tube. The rest depends on how steady you are with a jigsaw ( or fretsaw if you want to get really fine).

[Poita]

How much coma do you reckon it will exhibit?

[Keltik]

Hopefully, minimal or even none if the lens is good. CloudyNights (http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3374710/Main/3368939) has an interesting discussion on the need (or lack of) for coma correctors in a refractor.

[Merlin66]

You can still get some Chromatic Coma in refractors.