Sharpstar 150mm f/2.8 HNT collimation

[Davey-T]

Had this scope for a while and had a couple of stabs at collimating it but noticed that when mounting it and tipping it back and forwards something goes clunk.

Took the mirror cell off today and its the mirror flopping up and down, there is tension on the adjuster springs and locking screw are tight, but I can see the mirror dropping back and forth when tilted.

Should it do this or should I attempt to fix it.

Never collimated a Newt' so no idea if mirror should be this loose, presumably when pointed up at the sky it will stay back.

Dave

 

[GlenM]

To be honest Dave I would be tempted to send it back for a check up.

 

Stay safe,

Glen.

 

[Davey-T]

35 minutes ago, GlenM said:

To be honest Dave I would be tempted to send it back for a check up.

 

Stay safe,

Glen.

 

Doesn't appear to be any way of adjusting it.

Dave

[david_taurus83]

How much does it move? On a newt, its recommended that you should be just able to slip a thin piece of paper between the mirror and the retaining clips so to avoid distorting the mirror. Wouldn't expect ti to be loose however.

[Davey-T]

32 minutes ago, david_taurus83 said:

How much does it move? On a newt, its recommended that you should be just able to slip a thin piece of paper between the mirror and the retaining clips so to avoid distorting the mirror. Wouldn't expect ti to be loose however.

Doesn't appear to have any retaining clips, just seems to be an interference fit in the surrounding metal work, its resting on three small domes underneath then there is a gap of a couple of millimetres or so under the top retaining ring (see pic) which allows the mirror to move up and down.

Dave

 

Edited April 29, 2020 by Davey-T

[Chris]

Can you send these pictures to the vendor Dave, and get their thoughts. Mirror flop can't be part of the design for super fast optics. 

[Davey-T]

24 minutes ago, Lockie said:

Can you send these pictures to the vendor Dave, and get their thoughts. Mirror flop can't be part of the design for super fast optics. 

Got it off FLO Chris but not something they normally deal in.

It appears to be the way it's designed as there are no mirror clips as such so the mirror floats in the cell and the whole cell is adjusted to collimate it.

Haven't got far, still mucking about trying to adjust the secondary which is fiddly, be easier if it was 12" lol.

Dave

 

[Chris]

24 minutes ago, Davey-T said:

Got it off FLO Chris but not something they normally deal in.

It appears to be the way it's designed as there are no mirror clips as such so the mirror floats in the cell and the whole cell is adjusted to collimate it.

Haven't got far, still mucking about trying to adjust the secondary which is fiddly, be easier if it was 12" lol.

Dave

 

I know you can't fasten mirrors too tight else you get astigmatism, pinching and the like, but to have play in there with such fast optics doesn't seem great. It might need a bit of DIY then if there is no way of adjusting to remove flop.

Initial thoughts are to use a few little squares of felt around the out side of the mirror, or if you can remove the primary 3 very small blobs of silicon sealant on the back of the mirror? Not too much as temp differences mean the mirror cell expands at a different rate to the mirror, and if there is too much silicon it distorts the mirror (I found this out the hard way with an f/4 newt!) 

[Davey-T]

24 minutes ago, Lockie said:

Initial thoughts are to use a few little squares of felt around the out side of the mirror, or if you can remove the primary 3 very small blobs of silicon sealant on the back of the mirror? Not too much as temp differences mean the mirror cell expands at a different rate to the mirror, and if there is too much silicon it distorts the mirror (I found this out the hard way with an f/4 newt!) 

They've bought out a bigger 200mm f/3.2 version with a cooling fan, probably the same design as I can see the mirror jamming in that metal frame if it expanded.

Dave

[Chris]

3 minutes ago, Davey-T said:

They've bought out a bigger 200mm f/3.2 version with a cooling fan, probably the same design as I can see the mirror jamming in that metal frame if it expanded.

Dave

You're not selling this design to me Dave lol

Edited April 29, 2020 by Lockie

[Davey-T]

Just now, Lockie said:

You're not selling this design to me Dave lol

Haven't found any proper reviews of it yet but it seemed a good idea at the time, still need to buy a colour CMOS camera and probably one of those Rainbow mounts for a lightweight imaging setup but not until I get some results out of it first.

Dave

[Chris]

Just now, Davey-T said:

Haven't found any proper reviews of it yet but it seemed a good idea at the time, still need to buy a colour CMOS camera and probably one of those Rainbow mounts for a lightweight imaging setup but not until I get some results out of it first.

Dave

That Rainbow mount looks fantastic! At the IAS2019 I saw one throwing an Esprit 120 around like it wasn't there, and the mount didn't even have a counter weight on!

[Davey-T]

10 minutes ago, Lockie said:

That Rainbow mount looks fantastic! At the IAS2019 I saw one throwing an Esprit 120 around like it wasn't there, and the mount didn't even have a counter weight on!

Yes saw that, seems just the thing especially with the mucking about I did getting this balanced in the iEQ45 😁

Dave

[Davey-T]

Still messing around with collimating this thing, it has occurred to me that as the mirror is free to move back and forth perhaps I should be doing it upright rather than horizontal ?

Following the recommended order of aligning secondary and focuser which is fine but the trying to align secondary with primary it looses all alignment with the focuser.

Bought this HG laser with grid attachment for fast scopes but no instructions so no idea what I'm trying to achieve, it is impossible to get the spider pattern central on the grid, does that matter ? I don't know.

Laser spot central on primary spot.

Adjusting the secondary is a pain as there appears to be a thread in the silver disc and a thread in the back of the secondary so these keep locking up when trying to adjust it and rotating the mirror.
The drawing in the manual only seems to indicate one thread

[Davey-T]

More messing about as it's raining see picture, thinking of inserting double side sticky tape between the two bits of secondary mirror to keep them together as one part comes loose from the other really easily, anyone see a problem with that ?
Be easy enough to remove anyway.

Dave

 

[Davey-T]

Read the whole Sharpstar HNT thread on CN , probably a mistake as I now have a list of mod's to perform on it 😂

Dave

[Davey-T]

Still playing with this, got collimation close and thought I'd check it on some real stars so fitted an RDF and it appears whoever drilled the tube for the base did it by eye after a liquid lunch 😂

Dave

[Davey-T]

Still messing around trying to collimate the SharpStar 150HNT.

Lined up secondary and focuser but can't adjust primary to centre it.

If I carry the scope by the handle I can hear the primary mirror flopping back and forth so how can one collimate the thing, various howtos say have it level on a bench but there's no telling how the primary has ended up.

It's sitting on three small domes behind the mirror, visible as rusty looking thing in the video.

Dave

What a faff uploading a YT video is now, haven't done it for years, sure it wasn't that much messing around last time I did it, gave up and got son in law to do it 😂

 

 

Edited June 23, 2020 by Davey-T

[tooth_dr]

That video worked well and showed the problem. How are you supposed to collimate the scope of the mirror flops around?

[Davey-T]

1 hour ago, tooth_dr said:

That video worked well and showed the problem. How are you supposed to collimate the scope of the mirror flops around?

Good question.

Dave

[Davey-T]

Made a disc with a centre hole and when stuck on the end of the scope, the laser pointer shines straight through it, with mirror fitted its a good 10mm off centre and not enough adjustment to centre it probably because it leaning over in the cell.

Dave

 

[Davey-T]

As I couldn't line up focuser and secondary using a collimation cap I tried this method as demonstrated by Dion on Astronomy Shed.

Now find if I rotate the camera in the focuser it gives a completely different picture so no good centring using this method.

The focuser is adjustable so guess I'll take it out and have a look as a guy on CN was having a problem and found a bit of flocking material stuck under the focuser.

Dave

This is with s4condary adjusters backed right off and centre screw tight and it still needs to go further right.

 

a

Edited July 4, 2020 by Davey-T

[Adam J]

It should not be flopping like that, if you are not able to tighten it down then something is wrong. Lots of primary mirrors use several think slivers of cork between the mirror and the older on the read surface to buffer it. If something like that is missing it may explain your issue.

100% call your supplier and stop trying to colimate it there is no point with mirror doing that.

Adam

Edited July 4, 2020 by Adam J

[Davey-T]

12 hours ago, Adam J said:

It should not be flopping like that, if you are not able to tighten it down then something is wrong. Lots of primary mirrors use several think slivers of cork between the mirror and the older on the read surface to buffer it. If something like that is missing it may explain your issue.

100% call your supplier and stop trying to colimate it there is no point with mirror doing that.

Adam

I've stuck some small felt pads in the gap to stop it flopping about.

There doesn't seem to be enough towards spider movement in the secondary adjustment to centre it under the focuser, it says there's 5mm gap in the instructions but I measure it as 6mm.

However nil desperandum got it all in bits now and will reassemble later and have another try, may be able to centre the primary now hopefully as I can centre a bit of white card mounted instead of the mirror.

Dave

[Adam J]

10 hours ago, Davey-T said:

I've stuck some small felt pads in the gap to stop it flopping about.

There doesn't seem to be enough towards spider movement in the secondary adjustment to centre it under the focuser, it says there's 5mm gap in the instructions but I measure it as 6mm.

However nil desperandum got it all in bits now and will reassemble later and have another try, may be able to centre the primary now hopefully as I can centre a bit of white card mounted instead of the mirror.

Dave

Seriously dont mess with it just send it back its not right. You dont pay that much to have to fix it yourself.

Adam