Mirror clips on OO UK scopes

[osbourne one-nil]

Long story short - I dropped a screwdiver down the tube and it chipped the mirror. I used CN to ask what damage I might have caused mainly so no one here would find out; imagine how embarrassing that would be. 

Anyway, the consensus is that the damage to the image from the chip will be negligible, but the degradation to the image from the mirror clips will be quite significant. Any views on this? I'd be surprised if Orion went to all that effort to make nice mirrors only to spoil them with the mirror cell. 

 

Sometimes I wish I'd just bought a Skywatcher!

[Doc]

They are rather large, I would say they could be at least half of the size. As for the chip I agree it's negligible you won't notice it at all.

[John]

The clips on my OO 12" are a similar design but around 50% smaller than yours I reckon.

Agree about the chip mark though - it won't make any difference visually.

[osbourne one-nil]

Thanks - I think the clips are part of a one-piece mirror cell looking at the OO website - http://www.orionoptics.co.uk/ACCESSORIES/mirrorcells.html so I don't fancy tinkering. What would the actual difference be at the eyepiece?

This scope is becoming a bit of a trial; the secondary it came with was very small (25mm) as it was intended for planetary use, so I got a 35mm secondary from OO. That has an M6 bolt fitting whereas the previous one had an M4, so I had to drill out the middle of the spider to accommodate the larger bolt, which then meant I couldn't reach the adjustment screws for the secondary. I then spent a whole evening getting the secondary back in the right place....views lloked great when I did get to look through it through and I really do love the difirraction spikes the spider gives on bright stars, but man, it's been hard work so far. 

I've got some socket-head cap bolts coming which should make things a lot easier. 

[John]

My cell is the older type (see below) but the clips look similar to yours - they are not 1 piece though, the steel piece (with the felt backing) is screwed onto the end of each of the mirror support struts with mine:

 

 

[osbourne one-nil]

That's how I remember my previous OO scopes being. I'll take it out later and have a look. I might put touch up the chip with a bit of silver paint too. I used to polish my childhood telescope's lenses with Pledge, so I wouldn't put it past me. 

[NGC 1502]

Sorry to hear about the screwdriver accident, a bit of a pain, but as noted, it won’t make a scrap of difference to the viewing.

However, those mirror clips are way too large. I’m a compulsive tinkerer, and while my OO 10” mirrors were away for a recoat several years ago, I reduced the size of the oversized clips. I like OO Newtonian scopes in general, but sometimes wonder about some of the features. The aluminium trim at the front end of the tube has an opening only fractionally larger than the primary mirror. If you read up on construction of truss tube Dobs, the upper tube section is always larger than the primary by some margin. I reduced the width of the trim on mine, therefore increasing the size of the opening to almost the diameter of the tube.

Ed.

[Bukko]

I have the newer type of cell, as per OO site, but do not think they are as big... But mine is also a 12" so I am guessing the OP is much smaller.. 8" or so? This would make is seem bigger than it actually is.

Were you happy until the screwdriver incident with the optical performance?

If so, I would not be over troubled about this.

And I agree that the chip will not make a lot of difference.

HTH.

Gordon.

[osbourne one-nil]

It's a 6" so I reckon they're using the same sized clips on all their mirrors?

I hadn't had a chance to look through it before the incident, but I've looked through it since and all was well. The image was dark, but then I noticed it was very hazy, so that probably had more to do with it than the mirror clips! 

I'm not one to tinker really, but I suppose over the long summer nights I could trim them down a bit. 

[osbourne one-nil]

12 minutes ago, NGC 1502 said:

Sorry to hear about the screwdriver accident, a bit of a pain, but as noted, it won’t make a scrap of difference to the viewing.

However, those mirror clips are way too large. I’m a compulsive tinkerer, and while my OO 10” mirrors were away for a recoat several years ago, I reduced the size of the oversized clips. I like OO Newtonian scopes in general, but sometimes wonder about some of the features. The aluminium trim at the front end of the tube has an opening only fractionally larger than the primary mirror. If you read up on construction of truss tube Dobs, the upper tube section is always larger than the primary by some margin. I reduced the width of the trim on mine, therefore increasing the size of the opening to almost the diameter of the tube.

Ed.

I actually measured the opening the other day I was constructing a template drawing in CAD to make sure the secondary holder was central, and you're right...the tube opening is exactly 150mm (the tube itself is 165mm). Logic suggests that's ok as long as everything is aligned though....to me anyway. 

[Peter Drew]

I join the consensus that the clips are unnecessarily large and that the screwdriver scratch will be of no performance consequence. However, leave the scratch as it is or paint it out with matt black if you must, silver paint will cause unwanted scatter. 

[jkwhinfrey]

I think you’re probably right about the same size clips on everything, perhaps on the principle that if it’s big enough to hold the largest mirrors it’ll work fine on small ones... It’s a good thing they aren’t making professional observatory mirrors or your clips would meet in the middle! 

[osbourne one-nil]

I'm equally glad I didn't go for their 1" Newtonian either, although at least the mirror would have been protected from the screwdriver. 

[Astrobits]

4 hours ago, osbourne one-nil said:

I actually measured the opening the other day I was constructing a template drawing in CAD to make sure the secondary holder was central, and you're right...the tube opening is exactly 150mm (the tube itself is 165mm). Logic suggests that's ok as long as everything is aligned though....to me anyway. 

That is too small an opening for the end of the tube. As soon as you view off axis objects in your field of view then you get vignetting. Even 165mm is a bit too small for a 150mm mirror. That's why all telescope openings are typically about 25mm or more larger than the mirror, or should be.

nigel

[osbourne one-nil]

Hmmmmm, I'm going to remeasure when I get home. I must be wrong as I'd be surprised if a company sent out stuff that fails basic physics. 

EDIT: Their website states the tube diameter as 167mm so I wasn't far off for that dimension. 

[John]

17 minutes ago, Astrobits said:

That is too small an opening for the end of the tube. As soon as you view off axis objects in your field of view then you get vignetting. Even 165mm is a bit too small for a 150mm mirror. That's why all telescope openings are typically about 25mm or more larger than the mirror, or should be.

nigel

That raises an interesting issue about Orion Optics optical tubes which has been discussed before here but not for a long while and not, as far as I recall, with any definite resolution. OO use a top end tube ring which does reduce the aperture of the tube. Their tubes are already narrower than the chinese equivalents by 10mm or so. On my OO the top aperture is 308mm and the primary is a 300mm F/5.3. Is the top aperture impeding the performance of the primary and, if so, by how much ?

I don't know the answer but maybe someone else does ?

I ought to add that this top tube ring design is a feature on all the VX / SPX / Europa models that I've owned / seen.

 

[osbourne one-nil]

Is it structural? I suspect it is, because when I took the bottom equivalent piece off to remove the primary cell, the tube seemed to relax a bit. 

[jetstream]

Maybe they hope that those clips and small tube ring covers up that mirror edge?

[osbourne one-nil]

My poor mirror!

[John]

17 minutes ago, osbourne one-nil said:

Is it structural? I suspect it is, because when I took the bottom equivalent piece off to remove the primary cell, the tube seemed to relax a bit. 

Yes - it's an aluminum tube so the tube rings plus the end rings help it keep it's shape roughly round. I say rougly because mine has a distinct flat section where the seam is. It does the job though.

There might be something in what Jetstream / Gerry says - the outer edges of the primary are where figuring errors are going to be greatest

If it reduces the effective aperture of the primary then I think OO should be up front about it though.

[jetstream]

11 minutes ago, osbourne one-nil said:

My poor mirror!

I'm half joking, the real issue with the clips is stray light. If you can see them as shiny pointing a flashlight in there or if they glow when a flash shot picture is taken you should paint them flat black. I would also flock the tube and paint the secondary edge.

Can you send a picture of your focuser? I own 2 VX's.

[osbourne one-nil]

Definitely agree about the flocking (if I keep it - I just don't know if we can make it work as there's a trust issue) and painting them flat black is a good idea too. 

I'll grab a photo of the focuser when I get home. I might even show you my heath-robinson attempt at the adjustment bolts!

[Moonshane]

I chopped the clips down on my old 6" f11 and I seem to recall it did make a difference to scatter.

I have not even thought about the clips on my latest one although that has the improved CNC cell.

Looking at these pics they may be as bad

http://www.orionoptics.co.uk/ACCESSORIES/mirrorcells.html

 

[Timebandit]

 

 

 

 

The top ring IMO is a strength piece. Obviously the OO tube is a rolled aluminium. So its place it is most likely to deform is at the ends. These L type  circle rings will provide a lot of extra strength at the ends of the tubes.

Also the ends of the tubes are likely to be sharp being thin type sheet metal. These rings also reduce any possible chance of a cut due to contact with the thin gauge material when moving or lifting the scope

A lesson to be learnt here for others to help to stop damage to another mirror. Lie the scope on its side if working on it with a screwdriver ect. If it falls it will hit the side of the tube , rather than straight down onto the mirror. Also tie a short piece of string to the tool on one end, and to your wrist at the other. If you drop the tool it will not drop down the tube and hit your precious mirror 

Hope this helps

 

 

[osbourne one-nil]

Back in the 70s I remember asking an elderly acquaintance why he didn't wear a seat-belt. He replied because he drove really carefully so what was the point? It's all his fault.