Cleaning the 1m Mclellan telescope at the Canterbury University Mt John Observatory

To clean the 1m mirror all of the equipment on the back of the telescope must come off, so in this photo I am positioning the trolley for the HERCULES fibre feed unit

(HERCULES) High Efficiency and Resolution Canterbury University Large Echelle Spectrograph  

Dome floor has been raised and also the trolley top, so now the weight of the Fibre feed unit will be on the trolly, from there I would have unbolted the fibre feed unit from the telescope as well as removed the power supplys

Nigel Frost (Mt John Superintendent) Pam Kilmartin (Mt John Observer) Alan Gilmore (ex Mt John Superintedent) with the 1m mirror cell trolley

On the South side of the dome there is a block of wood to activate a safety pressure switch (this pervents the floor from being raised to high which could result in the floor crashing into the telescope peir) this needs to be removed

Floor max height safety block removed

Alan positioning the counter weight holder bar - when you take all the equipment and the mirror cell off the telescope there is to much weight on the counterweight side, so this bar is placed there for support

Nigel shining a light to help align the counterweight support bar

Counterweight support bar has now been bolted in place

Nigel turns the RA countweight handle to 100 on the measure - this is to make the weight less on the counterweight side

The counterweight bar is in two parts there is a bolt to hold it together - the tread of the bolt needs to be on the north side for the bolt to go through the hole in the floor

On the bottom of the telescope there is a thermometer the cable needs to be unplugged

multi board needs to be removed

Nigel and Alan aligning the mirror cell trolley

Floor being raised as high as we can with care not to crash into the telescope peir

Floor Max height with a slight clearence between the floor and the telescope peir

final adjustment for the alignment of the mirror cell trolley

Mirror cell trolley is jacked up to now take the weight of the mirror cell

There are 4 bolts holding the mirror cell onto the telescope these are now ready to be removed (one on each truss, north, south, east, west)

Each of the 4 bolts has a identical tappered alignment spacer - so you don't have to remember which bolt came out of which side. We remove the east and west bolts first

Nigel removing the south side mirror cell bolt

The mirror cell holder is labelled because you must put it back on the telescope exactly the same way as it came off

The mirror cell has now been removed from the telescope and the floor lowered

The blocks around the edge of the mirror are there to hold the mirror in the same position no matter which way you point in the sky

Looking at the surface of the mirror

Looking at the surface of the mirror

Looking at the surface of the mirror

Looking at the surface of the mirror

On the edge of the mirror there are holders to prevent the mirror from tipping out if the telescope is at a very steep angle

There are 4 of these holders which need to be removed to be able to remove the mirror from the mirror cell holder

With the floor lowered right down the mirror is then moved into the Aluminising room

To remove the mirror from the mirror cell holder the mirror positioning weigths need to be slackened off

The North, South, East, West adjustments can only be made with the mirror cell removed from the telescope (need to remember this when we put the mirror back on the telescope)

Alan and Nigel prepair an attachment to be able to lift the mirror out of the mirror cell holder - the 1m mirror weighs about 265kg

The mirror lifter is carefully lowered though the hole in the primery mirror

The mirror lifter is carefully lowered though the hole in the primery mirror

On the mirror lifter there are 3 swing arms, once in position these can be swung out and locked into place by the locking pins

With the swing arms locked into the out position the mirror can now be lfted out of the mirror cell holder

When lifting the mirror out care needs to be taken that the mirror position weights dont suddenly swing inwards hitting the mirror

Nigel opperates the hoist at Alan and Pam keep check

Pam looking concered as one of the mirror contact points is missing (red point instead of white - this had stuck to the underside of the mirror and was put back in the correct position)

With the mirror lifted out of the mirror cell holder the holder is place back in the dome (so it wont be in the way)

The 1m Primary Mirror with the vacuum tank in the background

Alan prepares the stands, so we can make a table

positioning the stands so to keep balance when we lower the mirror

Mirror washing tub is place on the table - remember to attach the drainage pipe so any chemicals go into the drain

Spacers are added evenly so the mirror can be lowered into the tub but not sitting on the bottom

Mirror being lowered into the tub and balance of the table checked

Once the table, Tub, and spacers are all looking stable the swing arms on the mirror lifter can be put back in

There are two sets of holes in the mirror lifter, one to have the arms locked out and the other to have the arms lock in

Alan takes care for the mirror lifter not to scrape against the mirror

Alan holder the mirror lifter as Nigel unclips it from the hoist - care must be taken as if anything falls it will hit the surface of the mirror

Nigel clips the hoist hook onto the chain to prevent it from falling and so you dont hit your head on it

The mirror is now ready for stage one of cleaning

The mirror lifter

The mirror is rinsed with filtered water

Alan rinsing the mirror with filtered water, taking care that the pipe dosen't touch the surface of the mirror

The mirror is rinsed with filtered water

The mirror is rinsed with filtered water, Nigel is holding the first cleaning solution

Nigel prepairs to poor the first cleaning solution - PhotoFlow

Nigel pouring PhotoFlow over the surface of the mirror

Nigel wiping the surface of the mirror with soft cotton wool the mirror is still wet from the PhotoFlow

Alan rinses the mirror with filtered water

Nigel and Alan wiping the surface of the mirror with soft cotton wool

Pam and Nigel place tissue paper on the mirror

Pam, Nigel, and Alan placing tissues on the mirror

Mirror is completely covered with tissues with care to make sure there were no gaps, the tissue is used to hold the caustic soda on the surface of the mirror

Nigel carefully pouring caustic soda onto the tissue paper - when working with the caustic soda you must wear the protective gloves

Nigel carefully pouring caustic soda onto the tissue paper, it may take a few tries with fresh tissue paper and caustic soda to entirely remove the old aluminium surface

Nigel carefully pouring caustic soda onto the tissue paper

Nigel carefully pouring caustic soda onto the tissue paper - making sure that there is an even coating and not to rip the tissue

Caustic soda has now been poured over the entire surface of the mirror - make sure there is adiquate ventilation as the will be many fumes

Starting to see the old aluminium being disolved by the caustic soda

Caustic soda granules (Sodium hydroxide) - carefully measured to make the correct strength, 80 grams will be mixed with 1000 ml of filtered water

Caustic Soda (Sodium hydroxide) dissolving the surface of the Canterbury University Mt John Observatory 1 meter mirror

The old aluminium mirror surface has now been removed

We now rinse the glass

This rinsing process may take a while as we must remove any trace of the caustic soda

Solutions used in the cleaning process

Umicore substrate cleaning cotton wool

Nigel pouring Nitric acid solution over the glass as Pam and Alan polish with cotton wool

When polishing start in the center and get closer to the edges - care mush be taken not to bring materials back into the center

Nigel rinsing the glass

Nigel preparing to pour Methanol over the glass

Pam, Nigel, and Alan polishing the glass surface

At first the methanol looks as though a rainbow coloured layer has been put on the glass, but as it dries / evaporates while polishing this disappears

For every solution added fresh cotton wool is used as well as a new pair of gloves - care mush be taken not to contaminate the surface of the glass


Alan and Nigel polish the glass surface as Pam looks for any imprefections

Wiping the side of the glass - once you touch the side of the glass you must use fresh cotton wool

Substrate Cleaner number 1 is applied to cotton wool

Substrate Cleaner number 1 is rubbed over the surface of the glass

The entire surface is now covered with substrate cleaner number 1

Pam cleans the subrtrate cleaner from the edge of the glass

Nigel handing out fresh cotton wool

When the substrate cleaner number 1 has dried it is ready to be polished off

Try to keep a fresh part of the cotton wool for polishing - if the cotton wool becomes to dirty change it for a fresh peice

Nigel polishing the glass surface with a clean peice of cotton wool

Glass surface after polishing with number 1 substrate cleaner

Substrate cleaner number 2

Substrate cleaner number 2 is rubbed over the surface of the mirror - do not let this cleaner dry to the surface of the glass

Substrate Cleaner number 2 is polished off the glass surface before it dries

Nigel cleaning the inside edge of the glass

Pam taking care to clean the glass

Nigel porring another dose if Methanol

Polishing the glass and removing anything that the Methanol picked up

Glass inspection

Polishing with a lint free cloth, to remove any fibres left by the cotton wool

Nigel making final polish of glass surface

Glass inspection

Glass inspection

Glass inspection

Lowering the mirror lifter into position

Mirror lifter with the swing arms out

Lifting the 1m glass on of the cleaning tub, with Nigel cleaning the underside of the glass

The bottom side of the 1m glass and looking at the mirror lifter

Mirror holder on the vacuum tank lid

Prepairing the vacuum tank mirror holder

Starting to move the vacuum tank lid in position - when Nigel realises tht we have used the wrong mirror lifter - with the mirror lifter used you are not able to lower the glass onto the vacuum tack holder as both use the center hole

reassemble the stands and table - lower the mirror and remove the mirror lifter

Attaching the second mirror lifter - nervous moment as this is quite heavy and it is directly above the glass (please take care not to drop anything onto the glass)

Second mirror lifter attached, on the left side you can see that one of the hands is tilted out, this is to make it posible to position it over the glass

Lowering the second mirror lifter, taking care not to hit the glass, a few people is recommended so atleast one person can take care of one arm

With the second lifter now in position the left side arm can be locked into the closed position, by moving the locking pin from the first hole to the second hole, take care not to drop the locking pin onto the glass. New person is Byron

Underside of the second mirror lifter

Second mirror lifter and the Vacuum tank lid tipped over ready to be positioned

With the glass lifted right up the vacuum tank lid (tilted over) can be pulled out and positioned under the glass

Glass is now positioned on the vacuum tank lid and Nigel is removing the locking pin to be able to take the second mirror lifter off

Left side hand is being opened out and locked into position

With the left side hand locked outwards the second mirror lifter is now ready to be removed

Care being taken to take the second mirror lifter off

Unclipping the second mirror lifter from the hoist

Clip the hook back onto the chain so it is out of the way - Alan taking away the second mirror lifter and Nigel is putting a holder in place

Nigel tightening the holder to stop the mirror from falling off when the lid is tipped back upright

Glass is now on the vacuum tank lid with the holder in place and ready to be positioned

Vacuum tank lid being tipped upright again

Vacuum tank lid upright and ready to be aligned with the vacuum tank

Glass on the vacuum tank lid

Looking inside the vacuum tank - you can see the tungsten elements on the back of the tank

Tungsten element with aluminium wire - in a vacuum and when heated this aluminium will melt, hopefully into the element, and then vaporise - spreading an even coat of aluminium

There are 6 x 21mm lengths of 1.5mm diameter 100% Aluminium wire per filament, 12 filaments in total. This will make the new mirror coating and be about 1000 Angstroms thick (100 nanometers or 0.000 001 mm)

This was worked out by trials with glass plates and neutral density filters, the 1000 Angstrom coating thickness was recommended so that the coating was not transparent or to thick, this related to a optical density figure of 6. Different thickness coatings were put on various glass plates (using varying Al wire lengths) and compared (looking at the sun) to a combined set of ND filters to give a optical density of 6, when a match was achieved that determined the length of Al wire per filament.

  What is a Nanometer?  

Nigel wiping off dust with a lint free cloth

Alan moving the gas bottle (Nitrogen) in place - we will blow off any final bits of dust using the hose

The Aluminium (plasma discharge) ring is put in place this enables plasma cleaning of the mirror (also called Crooke's Discharge), the discharge removes impurities and contaminants from the surface of the mirror through the use of energetic plasma from a gaseous medium (air, oxygen, argon). The plasma is created by the a high frequency neon transformer (under the cover on the lid of the aluminising tank) and the discharge works at a vacuum pressure of 6 to 7 x 10-4 Torr and we run the discharge for 10 minutes, using dry nitrogen to control the tank pressure within the 6 to 7 x 10-4 Torr range.

Vacuum tank lid closed

The vacuum tank closed with the glass inside - ready to be recoated

Nigel turning on the diffusion pump