Yet another Telescope question

[thommo10]

Hi all

I have a 150mm f/6 Newt which is quite old now image quality is still good on DSO's although I have nothing to compare it with apart from my ETX 125 which is great on solar system object's now i've got it sorted, and ok on DSO's owing to the long focal Lenght. I was thinking of getting a SW102 startravel synscan to replace my 150mm would the image quality be any different. what I mean by image quality is detail I could see through it.

[brianb]

I was thinking of getting a SW102 startravel synscan to replace my 150mm would the image quality be any different. what I mean by image quality is detail I could see through it.

Your 150mm will be masses better.

It's 50% bigger which means much fainter objects visible (0.9 mags) and better resolution. And the Startravel, being short focus, has lots of chromatic aberration, which your Newt is completely free of.

Get your 150mm re-aluminized if it needs it, and spend the money on a decent eyepiece or two.

[E621Keith]

I agree with brianb. The Startravel will be dimmer and suffer will from chromatic aberration. It will be cheaper getting your 150mm serviced.

[thommo10]

Thanks Guy's unfortunatly I don't think I can get it aluminised because the mirror is fixed pemanently to the back of the scope, it is a Astro Systems scope manufactured back in the eighties it was supposed to keep the scope collimated but it looks ok, the only movement I have is the secondry mirror. I think I will take your advice and get some decent ep's

[E621Keith]

If the secondary is moving around, is it possible the spider was corroded. Replacing it shouldn't be too expensive.

[thommo10]

Sorry. what I meant was the only way I can collomate it is to move the secondry mirror and spider, there is no adjustment for the main mirror.

[NGC 1502]

it is a Astro Systems scope manufactured back in the eighties

Your Astro Systems is a true quality classic, very well worth

restoring. I had a 8.5" Astro Systems once, and the primary

mirror was glued to felt (looked like thick green material, like

on a snooker table) and the felt was glued to the aluminium

cell. It was difficult to remove the mirror for re-coating, but

worth it. The secondary was siliconed to the single stalk

mount, I cut it off.

The alt-az pillar mount was totally bomb proof. I always regreted

selling that scope, superb quality, with a David Hinds mirror. I think

mirrors from other makers were also used, but always top notch.

Once correctly assembled, the collimation stays fixed.

Best regards, Ed.

[thommo10]

Thats exactly the same as my 150mm, I've got mine mounted on a Vixen SP mount and a solid non adjustable tripod, how did you manage to get the mirror off and how did you stick it back on and re-collomate it.

[NGC 1502]

Hi Keith' date=' it's a while back, but from memory :-

After removing the cell from the tube (there were tiny screws

through the end of the tube into the cell) I started by clearing

the bench in my shed and covering it with some old bedsheets

to make a softer surface to work on. I used a new stanley blade

first, to work all around the edge of the mirror where it was

attached to the cell by the felt. This got the edge of the mirror

free about 1" all around. I then used a much longer sharp craft

knife, and gradually worked my way further into the gap.

This took quite a while, and I worked slowly, over several sessions.

If you try this please be very careful, wear thick gloves.

As worked my way into the gap, I placed thin wooden wedges,

to slightly open the gap and allow access further in. I did not

hammer in the wedges, just finger pressure. Gradually I won, and

the mirror was free. It took a while to clean the old felt and glue

from the back of the mirror and the cell.

After re-coating, I decided to remount the mirror in more conventional

fashion. I made three aluminium 'L' brackets, fixed to

the back of the mirror plate, extending up the side of the mirror,

but without any mirror clips over the face of the mirror. I used

aquarium silicon adhesive, three blobs on the mirror back, and three

between the mirror edge and the side supports.

Collimation - I modified the original cell with three double coiled

spring washers (correct name 'thackeray washer') and fitted nylock

nuts externally for collimation. I also siliconed the secondary to the

original single stalk mount. I collimated that by trial and error. That

took a while, I recall having to put shims between the stalk and the

tube.

However, once collimated, it never shifted, even when transported.

If you need clarification, please ask. ( It will be 24 hrs before I'm back online )

That scope is now at Fieldview Astronomy B&B in Norfolk.

Best regards, Ed.

[Peter Drew]

The Astrosystems mirrors were glued with Evistick Time Bond impact adhesive. First, a disc of felt was glued to the back plate, when cured the mirror was similarly glued to the felt. The mirror could be removed by introducing white spirit into the felt and letting it soak in for a while. If this original procedure is repeated, the telescope primary will not need collimating.

[thommo10]

Thanks Ed & Peter, I will take your advice Ed, and restore it, but I'm sorry I can not visualize how you altered the primary mirror cell, I understand about the clips but not about where the washers and nylock nuts are fitted, the three small screws go into the side of the OTA and screw into the mirror cell.

[NGC 1502]

Hi Keith. The closest I can find to the mirror cell on my Astrosystems scope after

modification is this A Simple Double-Plate Mirror Cell for Your Reflector | Gary Seronik.com

Instead of the plywood discs in the link, perhaps you can visualise thin aluminium

ones. The three side brackets to hold the mirror are very similar, with no clips over

the mirror surface, just aquarium silicon. The double coil spring washers (you could

use short standard coil springs) go between the two plates, over the three collimation

bolts, the nylock nuts fitted onto the three bolts externally below the

lower plate. The whole cell & mirror was refitted to the original tube with tiny screws

that passed through the tube into the lower aluminium plate.

Hope all this makes sense ! As I said, I regretted selling the scope.

Peter Drews suggestion to use white spirit to disolve the glue is a much simpler

idea than mine, wish I'd known about that at the time !!

Please feel free to ask further, best regards, Ed.

Edit : The cell in that link differs from mine in that the spring washers go between

the two plates, there is no centre bolt, the nylock nuts are in place of the wing nuts.

[thommo10]

Hi Ed, That's great, yes I see now how you did it, Many thanks, I will be starting the restoration soon (probably may/june) after I have completed my observatory/shed.

Thanks again.

[NGC 1502]

Good luck Keith ! Perhaps you could let us all know how the restoration goes ?

Best regards, Ed.

[thommo10]

Will do ED. and thanks again for the info. BTW the only decent ep's I have are a WO 12.5 planetary a 26mm meade plossl that came with my ETX and a 32mm Kellner, what other ep,s would you suggest that I could possibly use in both scope's.

Kind Regards, Keith