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Gaining Focus - Upgrade, mod, or replace?

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Have you ever paused, and wondered...
How would I cut plastic tubing, if I ever needed to?

If so, you probably dismissed the train of thought, assuming that at some point in your life, you would discover the answer to this conundrum.

The wait is over...   :angel8:

Cutting the 'Lens Mount Assembly' Components

Two items required cutting:

  • Grease tub base - removal
  • Lens holder adapter - shortening

Grease tub base - removal

First step was to mark out the circle to be cut, using a drawing compass.

The base already had a centre punch hole.
Rotating the work piece is easiest, when possible.

Sharpen and strop (to scalpel grade), a small kitchen knife.

The grease tub plastic is very soft.
You cannot simply push the knife through, because once started, it would slice through the plastic like butter.
... running away at a tangent from your circular guideline.

Instead, take your time, and just penetrate the plastic (on the line) with the tip of the blade.


Using that point as the fulcrum ... arc the knife, forward and backwards, following the line on the forward movement.
This 'arcing' of the knife will cause it to cut through the plastic in a controlled manner.

Keep repeating this rocking movement, and work your way around the circle.
Of course, you are going to fail ... it's cuting sooo easy ... whoops!

However, if you are following the procedure, the fail will be inconsequential.
... simply pick up your line, and keep going.

In less than five minutes, the job will be done.

Here it is, with lens, offered into the lens holder adapter.
It fits !  😅


What I would say, when cutting into a radius
... I would recommend cutting to a slightly larger diameter - say 91 mm for 90 mm required.

No matter, I can tidy this; but that task will take far longer than simply cutting it right in the first place  😉

Problems ... or are they?

My goodness, the lens is a tight press fit.
This is due to the grease tub slightly narrowing towards the radius - it's a manufacturing thing.

The plastic diameter is ultimately enlarged - it stretches.
Same goes for the whisky cylinder, when pressed in.

Actually, once the lenses are in place, they will be going nowhere.
There would be no need for the whisky cylinder to lock the lenses in place.
However, that cylinder is still needed, to provide a base for flocking.

The grease tub can't be flocked, as the lenses would not go in.
The only part of the grease tub that requires flocking, is the radius area.

The white plastic around the lens edges will be masked by blacking the lens edges.

Assembly will involve warming the grease tub, to aid insertion of the components.

Final adjustment of the lenses to achieve perpendicular, will have to be done by simply applying pressure to the high side.
... they may anyway be forced to assume a perpendicular position.

Cutting the lens holder adapter

As with the soft plastic base removal...
This task also requires a specific procedure, if the cut is to be perfectly square.

In order to measure where to cut the adapter, the lens mount was assembled
... and why not? ... I placed the assembly onto the 100 mm scope tube.

hahaha ... an early morale booster, seeing how everything is coming together  😀


From the image, you can see that I would drop the vernier depth guage from the top of the adapter, to the top of the lens holder.

Upon disassembly, the cap thread depth was measured, and together, I had the cutting dimension.

Marking off, was achieved by setting the vernier guage to the amount of tube to be removed.
The top vernier jaw was placed on the top face of the adapter, and the lower jaw tip was pressed into the the tube plastic.
The adapter was then rotated, and steadily a line was scribed around the adapter tube wall.

Now the cutting.

You can't simply cut through with a full size hacksaw (in truth).
It is possible ... I could probably do it; but it's not the method.
Think about it...
Just supporting it is a nightmare.
... as would the cutting, because you can't see both sides of the tube
... the tube walls would begin to flop around
... the hacksaw blade would walk; and you'd be left crying, thinking of what might have been  🙁

No; the way to cut such a tube, is to use a junior hacksaw.

Supporting the adapter on sand (and holding it with your left hand) would be ideal for the beginner.
I just held it on my table, and managed the rocking (as the blade cut).

The objective is to gradually cut a slot, all around the tube.
... until the slot begins to break through the tube wall.

Tip ... a worn hacksaw blade really helps.
Even hard plastic is soft to a hacksaw blade, and new teeth will grab.

The worn 'middle two-thirds' can be used to graze out the initial slot (rotating the tube inch by inch).

Once a guide slot has been created, continue cutting, but push the blade further forward.
The worn blade rides in the guide slot, and the unused part of the blade feeds perfectly into the tube wall - without grabbing.

Continue in this fashion, regularly cleaning the blade - otherwise, the plastic swarf binds the blade.

Part way through, this is what it should look like:


At some point, the blade will begin to break through, and possibly grab.
... rotate the piece, to find sections that need further cutting.

Looking on the inside of the tube, you will see if the cut is almost through the entire circumference.

You can take the sharp knife that was used earlier, and either seperate the pieces, or cut enough to allow the hacksaw well into the tube.
... a few strokes, and it's in two pieces.

Place a large sheet of emery, at least 150 x 150, on a flat table, and rotate the cut face on the emery, with light pressure
... until satisfied 😀

Finish off, with folded ultra-fine grit paper, pulling the tube edges outwards, to remove plastic strings.

The end result should look like the piece has been cut on a lathe:


Lens Mount Assembly - 1st View (in the nude)


To me, this is looking great
... but I can understand why, to the casual observer, it looks naff ... the gaudy red lens cap doesn't help.
Though let's face it ... very few of us look good in the nude...

Dressed, and a bit of lippy, and she is gonna be a stunner  😁


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Stainless Steel Adapter Cut

The 'exhaust tailpipe tip' arrived today - 63 mm - 102 mm adapter.

Looked nice, as an exhaust tailpipe tip, but the welding wasn't perfect.
... however, just good enough for my purposes (thankfully).

60 mm Tube Connecter

The first problem was that the OD 63 mm, turned out to be 67 mm.
This meant an ID of 65 mm.
Not great at all, as I have 3 mm to make up  🙁

The options are: Fibreglass sheet, or tin can wall.

It made me research steel tubing.
63.5 OD - 60 ID is a standard size, only it is not stocked locally - so I scrapped that idea.

I resolved to await the laser calibrator.

100 mm Tube Connecter

It wasn't cylindrical - the weld and seam had pulled it oval.

I wasn't worried, as the vice could sort that
... but the first task was to cut off the rolled end.

Placing it on a marble table; with an appropriate tin can, to hold the marker
... the piece was rotated, and marked off.

Unlike the plastic tube; this piece could be held in a vice, and a new blade was installed in the hacksaw.
As with the plastic tube, a guide slot was first cut.

Breaking through, is best achieved by cutting the nearest side of the tube - avoiding the far side.
This allows the teeth to cut into the circumference, rather than meeting the steel wall edge.
The piece is gradually rotated and cut, until the pieces separate.

The dangerous steel strings, and sharp edges, were removed, before cleaning the face on a flat square of emery.
It was then taken to a circular form, by squeezing the high points in a vice.

It wouldn't slide over the 100 mm tube ... but it was almost there.

The inside was cleaned up with a small grinding wheel, and the edges were chamfered - as were the plastic tube edges.
... and this time, it could just slide on (press fit).


Here is the finished adapter :


The image seems to show the 100 mm section to be tapered, but it's not.

Weight = 286 g
Lens mount assembly, currently = 700 g
100 mm PVC tube = 1070 g per metre.

Consequently, the scope front end is likely to top out around 1.3 Kg

Rebalancing of the scope, will be required  🌝

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New Arrivals (and a surprise)!

Laser Collimator
Datyson 90 Degree Diagonal Zenith Prism
Celestron Omni Plossl 2x Barlow
Celestron Omni Plossl 12mm & 4mm Eyepieces

Plus, I was gifted a :
Celestron Plossl 6.3mm Coated Eyepiece


Now that's what I call "a good packing material" 😁

The external cardboard box was sound
Inside, each component was individually very well boxed.

The Laser Collimator and 2" adapter, has a strong storage box ... the components supported in a velvet type injection mould.
Very good.

Note: The Laser requires a CR2032 3V button battery (which I had in stock) 😉

While the simple Plossl appears to be well made - blackened and coated...
The Omni series has a real quality feel to them - a step above the basic Plossl..
They may not be comparable to some of the high end eyepieces, but for what they are, they are well made (from a visual perspective).

Of course, the proof of the pudding...

Plossl vs Omni Plossl vs starter Kellner

I think that it is upon me to carry out, and record, some comparison tests.
Having checked out YouTube, there is a lack of comparison records at this 'initial upgrade' level.

Thankfully, the scope can still be reassembled in it's 60mm format.

A test such as this, will then provide a baseline of optical clarity; from the true starter scope ... through stages, upwards to a 'pro' 😎  90/f1000 refractor scope.

The Test
I envisage using some wind turbines that I know are 10Km distant, and viewable from my location.

A planetary, or celestial test is unlikely to be feesible
... having to manage multiple lens changes within both the scope, and the camera, whilst chasing objects that require focussing
... all that, in the dark.

Er ... No!
A static object, with the scope locked down ... will enable genuine comparisons to be made.

My starter Kellners are : 4, 9, 12.5, 20

This will allow direct comparison with the Omni 4mm and Omni 12mm (close enough).
However, I will take images through each of the lenses, including the Barlow modded magnifications.

This will provide a direct comparison between a Barlow 6mm and a Plossl 6.3mm
It will also be interesting to see a Barlow image at 2mm and 3.15mm.

Once the new scope has been finalised; the test can be repeated.

My goodness ... the results had better be a major improvement 😅


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Collimating a Refractor Teslescope (using a Laser)

The laser collimator is primarily designed for use with reflector scopes.
However, when assembling tubes, it was clearly going to be indispensible.

My basic plan was to use it to centre the objective lens to the eyepiece
... and see what else fell out in the wash.

I first carried out some freehand testing, pointing the laser beam through a lens.
This was very useful, as I discovered that when the lens wasn't square; two additional 'planetary' dots became visible.

Flushed with this important discovery, the scope was reassembled.

The immediate concern was the oversize internal diameter of the focus tube eyepiece mount.
It has a finger screw clamp, but this would push the eyepiece to one side.

I carefully applied plastic electrical tape, to the tube interior.
By, a stroke of good luck, this produced the perfect ID.
(I'm of a mind to lock these strips in place, with a laquer, so perfect are they)

The next concern has been long obvious to me...

The focus tube assembly is held in the scope tube, by just 3 screws (passing throught the steel into the pastic mount).


It simply isn't enough ... a total of 6 screws are required.

Similarly, the objective lens mount ... though that will be anyway ditched
... but it only has 2 fixing screws.


Note: They are tapered screws, so if malfitted, there can be no adjustment.
However, I pressed ahead.


The laser provides 7 settings.
1,2,3,4 is a circular beam of rising power.
5,6,7 is a short 'bar' (or slot) beam, also rising in power.

With the collimator in the focus tube, I managed to centre the focus assembly to the objective lens.

Here the photon beam can be seen impacting the len surfaces:


... and here it is centred against a paper screen:


What I hadn't realised, was that the beam would also be reflected back down the scope, directly onto the collimator target area:


Above, the bar can be seen to be almost directly over the centre hole (through which passes the laser beam)
... but also present were two planetary dots of light.

As you can imagine ... I was more than a little impressed by this laser collimator.

Next, I wanted to see what would happen, when the Barlow 2x was fitted, and within it the laser:


On close inspection, the bulk of the light is focussed plum center, though there is a light glare in the top left quadrant.

At this moment in time, I don't know enough to precisely understand what is happening.

Obviously there has been a focal length change; but...
This was not a strict test ... things were touched and changed (to see the effect)
... and the Barlow is an utterly perfect fit in the focus tube (penetrating deeply).

Reflections from a successful test...

Reflector scopes regularly decollimate.
For this reason, they can be easily adjusted back into shape, by the supplied adjustment screw system (and a laser).

Refractor scopes, traditionally have no such adjustment.
From this, I sense that maladjustment of the lenses may be better tolerated (tell me if I'm wrong).

Either way, it is only logical to assume that a well collimated refractor scope will provide superior performance, to one that isn't.

Because of this, I may need to create an adjustment system for this scope.
... a system that enables screw centering adjustment, prior to clamping, and permanently fixing.

Something to think about, whilst I bask in the warm glow of 'knowing that collimation will be achieved'  🌝


Edited by Fo_Cuss

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Onwards and upwards!

A centre spotted paper target over the front of the objective - the laser spot should hit centre......

I also use a Cheshire collimating tool - illuminate the side and look at the reflection doughnuts at the objective. Ideally they should be uniform and concentric.

That's as good as things need to be.

Suiter's "Star testing Astronomical Telescopes", p122


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Thanks for those welcome words of encouragement,and advice, Merlin :)

However, it has come to pass, that the fundamental errors in the lens industry must be addressed.
From an Engineers perspective; sadly, this is an all too normal event
Take an object, and berate the design team (head of design), for not fixing a fundamental problem ... that is easily fixable.

In this instance, one of the deeply fundamental issues is concentricity.
It is at the heart of lens design
... particularly where lenses are joined together, such as an eyepiece to a telescope, or an eyepiece to a Barlow.

There are two ways to deal with this issue to gain accurate concentricity:

  • The expensive, difficult (silly) method
  • The low cost, simple (sensible) method

Guess what the lens industry chose?
They chose to use 'sliding fit' OD/ID interfaces - the expensive, difficult (silly) method.

This method can work, only that the manufacturing tolerances must be very tight
... in the region of 0.02mm of clearance.

This is not feesible for an aftermarket industry of interconnecting lenses.

The solution chosen, was to simply increase the tolerances
IE. Make the female element large, and the male element small.

From a production perspective, this is an inexpensive solution, as there is hardly any scrap.
Only that, from a user perspective, the male element just flops around
... and over a distance of 700 - 1000mm, the two ends are not concentric to each other.

This is exactly what we don't want, when building a telescope.

The Easy Solution

Use tapers!

Tapers are cones - male and female.
They self align perfectly.
They also possess self-locking characteristics
... yet with a twist can be easily unlocked, given they are finished similarly to as they are now finished.

Further; and most importantly ... they can be introduced into a market of sloppy, sliding fit lenses.
(if either element lacks a taper, the interface becomes the sliding fit).

Further, and also of critical importance ... dimensional accuracy is not required.
The machining angle must be set, but this is anyway programmed, or copied from a pattern.
Dimensional accuracy is a function of 'cutting' (less or more), and dimensional control.

For joining lenses ... taper dimension control is irrelevant
... if the taper is a little forward, or back; it makes no difference, because the scope must anyway be refocussed after a lens change
... and even broad tolerances would produce imperceptible differences in this area.
(unlike sloppy sliding fits, that produce wild concentricity errors)

What? ...
You are thinking that a taper sounds to be difficult to make?

Er... No.
Take a look at the Celestron Barlow 2x.
Check out the two, non-functional, external tapers.

Now look closer, at the vertical middle of the lens.
A taper almost meets the
sliding fit cylinder, but stands proud, and presents a shoulder.


What if that taper was fully machined to the edge of the top element of the lens?
What if the scope focus tube had a corresponding taper?

What if the ID of the Barlow was chamfered, and each lens?

... They would all automatically locate centrally.

If this taper was a little more shallow ... perhaps in the 5 degree range, it would become sufficiently self locking, without difficulty in breaking the lock.
Potentially removing the need for finger screw clamps ... that require drilling, tapping, and producing a knurl-ended screw.

Why is life like this (you may be asking)?
Or specifically ... why didn't the superior system evolve out of the inferior system, when it could do so without negative impact?

Hmmm ... it's complicated.
Back in the 70's I designed a superior stock control system for a major multi-national engineering company.
It was never implemented ... because it highlighted how crap the current system was, therefore highlighting how crap the factory manager was.
Therefore, the improved system was never put forward for approval.

It was one of those early lessons in how life is ... and nothing has changed.
If anything (certainly) we have gone backwards.

Yes, there are other reasons ... incompetence, unwillingness to rock the boat
... or maintaining bad systems, in order to enhance the differentiation between good systems.

Either way...
You can appreciate that my beautifully made lenses, suffer the sliding fit problem.

My electrical tape (in the focus tube) solved the issue with the primary interface.
It's perfect.
The laser can be inserted, rotated, and it stays on point.


Insert the Barlow, and it's female interface is too sloppy.
The laser is off point.


This means that the lenses inserted into the Barlow will also be off point.

What to do?

The Barlow ID = 31.9mm
Laser & eyepiece OD = 31.6mm

Hahaha ... the laser and eyepieces, rattle around in the cavernous Barlow aperture 😁

The correct solution is to reduce the Barlow ID.

I could increase the OD of the other components, but that would mean for every lens in the future.
The way forward, is to add material to the internal face of the Barlow cylinder.

I'm going to investigate this ... but what a waste of time.
I don't mind messing around with sewage, and automotive components, to get them to fit
... but messing around with lenses is sad.

Now, if only I had a lathe....  🌝

Edited by Fo_Cuss

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Being a manufacturing/ production engineer for fifty years, I appreciate your frustrations.....

BUT you're currently playing with, I think we agree, a scope from the bottom end of the market.

There are thousands of amateurs using refractors/ reflectors which although not perfect are capable of performing to their needs.

I do have one serious area of "complaint" - the "safety recess" found on eyepieces/ accessories was invented by the Devil - and should be banned.



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Ken, I know, that you know, that I know that 😀

My point was not relating to peoples perception of need; as that changes with education.
For the most part; belief in what is, is no different to 'ignorance is bliss'.
(Buy the lens, pop it in ... it's great)  👍

My main point, was that the humble taper, in a production context, provides a low cost solution for 'low end scopes'.

One off, on a lathe, it is much more complex to produce ... but not for a production engineer ... it's simply a taper rather than a shoulder.
(and in this context, only the angle is important ... not the depth ... so easy peasy)

Also Ken, surely I am worth forgiving?
It was a rant, based upon the truth of the situation.

In my book ... these truths are worth spreading, because everything is being dumbed down
... even engineering education
(and I know, because I have a son that is going through it)  🙁

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Increasing The Barlow ID

I need to make up 0.3mm
This means adding 0.15mm to the sidewalls.

A two part liquid epoxy offered a potential solution, but I was concerned with getting an even thickness.
Instead, I decided, rightly or wrongly, to proceed with spray paint.

The top of the Barlow unscrews ... it is just a hollow shell.
A tapered grinding tool fitted the threaded end ... very convenient with an attached shaft, for inserting into a hand held drill.

The grinding tool was taped to the top element of the Barlow
... and the assembly was placed in the drill chuck.

0.15mm is quite a gap to fill, and anyway a good key is required.
Hence, I decided to lay down a primer base - typical automotive paint.

After experimenting ... the best method is to trigger the drill slowly, and in very short bursts, spray centrally into the Barlow shell.

There is no throughput, so it is the worst spraying scenario possible.
However, by spraying into the middle of the cylinder, the air/paint jet fans out to the sides, and then returns up the sides of the cylinder, and out (towards you).

Here's what the setup looks like, after two coats of primer.
 😢 my lovely Barlow Lens 😢


I'll probably apply around 6 coats; leave it to dry, and then bake it, before measuring.
(I will clean it up before baking)

My intention is to apply a layer of barbeque paint, and then lacquer ... which can be baked to a hard finish.
Hopefully capable of withstanding the insertion of eyepieces 🙏


Edited by Fo_Cuss

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Increasing The Barlow ID - Base & Clear Coat

Having left the primered Barlow cylinder curing overnight
... it was externally cleaned with acetone dampened cloth.
(thankfully the acetone did not damage the lens lettering)

The piece was then baked for 10 minutes at 80°C then 30 minutes at 180°C

After cooling, the surface was rubbed with a fine abrasive paper
... this to enable a mechanical bond with the base coat.

A superior mount to the drill, was made, using a nut and bolt and some large washers.
A larger nut was used within the large washer, to keep the bolt close to the centre, in order to make finding concentricity easier.

The matt black was then applied - 3 coats - each coat blasted with a hair dryer for a minute or so, before the next coat.
This seemed to be fine.



The clear coat was applied directly after the final black coat had been dried for a minute (till it had turned matt).

The same procedure of spraying and drying was used, in order to rapidly build a layer of lacquer, without runs.
Again, this seemed to work.

Baking - the temperature was set to 180°C
This was a mistake.
The solvents bubbled out.


The initial removal of the solvents should have taken place at a much lower temperature
... perhaps slowly bringing the temperature up to 50° and leaving it there for 15 minutes, then another 15 minutes at 80°
... before hitting the baking temperature of 160°C (rather than 180°).

Or, just warm it with a hairdryer, and leave it overnight (as done with the primer), before baking.

I was basing my information on car spray curing, however, the car industry likely use '2 part' lacquer.
The lacquer that I was using was normal spray can type, and full of solvents.

Never mind ... it is a learning process.
For those wishing to enhance their Barlow lens, these mistakes can be avoided.

The good news is...
The eyepiece no longer fits.
So the process can build the required thickness.

The slightly overcured lacquer can now be rubbed down.

I will likely use a half-round file (or something similar), to support the abrasive paper.
Rotating the piece in the drill, should then enable rapid polishing.

A hole will need drilling in each removable eyepiece cylinder, to allow the air to escape, when fitting the eyepiece in the Barlow.
If this wasn't done, the eyepiece would become a compression piston.

These are the next tasks.... 🌝


Edited by Fo_Cuss

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Increasing The Barlow ID - Finished pre-tidying

This mod was a nightmare!
It has succeeded; but it is not ideal, AND it needs tidying.

The task will always carry difficulty ... but, with a better method, it could have been easier.

Introducing The Method

The Barlow lens cylinder (separable from it's lens), which holds the eyepiece ... is too large in diameter.
To reduce the diameter ... material must be added to the internal surface.

The difficulty, is in adding the material uniformly, in a manner that is readily available.

Spray paint, is readily available.
However, spray paint is difficult to apply in a small diameter cylinder...

The Method

The first, and most critical task, is to create a mount, that can rotate the cylinder perfectly concentric, in a drill.
If the cylinder does not rotate perfectly central to it's axis ... the applied spray paint, will 'puddle' to one side, to balance the centrifugal force.
IE. The paint layer will not be evenly spread.

All time necessary, should be taken, to achieve a perfect spinning cylinder, in the drill.
If this is achieved, the task will be 'one hundred fold' easier.

The paint layers can be sprayed, and centrifugal force will spread the paint evenly.
Note: Lighter coats are less problematic.

Tape will need to be applied, and removed before each bake.

Use a scalpel, or sharp knife, to make an opening for the clamp screw.
This to prevent the threads from being filled.

Two coats is sufficient.
Even when baked hard, the primer is much softer than lacquer.

It can be heated between coats, with a hair dryer, and left overnight, before baking.
It may be possible to speed the process, by warming the piece to 50°C for 15 minutes, and 80°C for a further 15 minutes
... then baking for 30 minutes at 180°C

Base Coat
Typically a matt black - these are extremely thin coats.
Three coats will be likely sufficient.

In the automotive industry, the base coat is cured with the clear coat.
However, in this instance, with the matt finish presenting an excellent surface for clear coat bonding
... The base coat can be baked.
Due to it's thinness, ten minutes at 50° & 80° should be sufficient, before baking at 180°C for 30 minutes.

Clear Coat
Apply two coats, and bake.
Either leave overnight first, or gradually burn off the solvent, as per the primer.
Baking at 160°C for 30 minutes, should be sufficient.

Offer the eyepiece to the Barlow cylinder, and decide if another lacquer coat is required.
Depending upon the play ... but in principal ... proceed with one additional coat at a time, as lacquer goes on thick.

If the final coat was just too much...
Use abrasive paper, supported by a pencil or half-round file, to reduce the diameter.

If the mount was concentric, this surface cleaning should be straightforward.

Final Considerations
This task should not be undertaken lightly, and not rushed.
Having said that ... the goal of self-centering lenses can be achieved.
Thus, improving the focus, and image sharpness, when using a Barlow lens.
... to what degree of improvement, is not clear at this moment.

What we do know is that, with a sloppy eyepiece inteface, the test laser beam was nowhere near central.

How did it go for me?

Bloody terrible 🙁😁

The die was cast, when the first mount was not concentric.
This produced an oval diameter from one side.
However, it is not possible to know which side, until the primer is revealed, when using emery cloth.

Oh ... it was the other side 😀

Also, I had applied too many coats of primer, compared to lacquer.
The project was falling apart, and all that I could do was go with the flow 😉

The saving grace, was that : deeper into the cylinder, the paint had gone on more evenly
(this is what 'phew' means)

After hand relieving high spots, and uncovering vast swathes of primer...
I was able to rotate the piece in the drill again, and (with repeated testing), ease the eyepiece into the Barlow cylinder
... until it was finally a snug fit.

No need for drilling the eyepieces ... the air can escape, if the eyepiece is steadily inserted.

I know that I can add a thin coat of matt black, to make the Barlow look nice again (and clean up the outside edge face).
However, I figured that it would be best if you saw the Barlow cylinder 'warts and all', prior to tidying.


With the outer edge face, taken back to aluminium, and a thin coat of matt black, to cover the primer
... nobody would know the grief that this has caused me 😁

I reassembled the Barlow lens, and checked it with the laser.

I found that there is a position (Celestron text to the top) where the laser seats perfectly (or as near as damn it).
Good enough; and far better than it was.

Here's how it tested:


The above test saw the laser being used on position 4.
In the Barlow, this produces the circle of light that you see.

You can just make out the centre hole ... the optical effect rings are fairly concenric to that hole.

I believe that the setup can be improved, by carefully rebuilding the lenses (they were rush assembled).
However, the main point is that the Barlow can now be used with confidence.

What a job!
Thank goodness it is over (or almost).

I'll tidy it up, reassemble the doublet objective lens
... and then try and grab some benchmark images for the 60/f700 scope, and the various eyepieces.

Just need clear skies now 🌝


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Increasing The Barlow ID - Examination

The surface was given another coat of matt black.
This proved to be very useful.

The eyepiece would no longer enter fully, and all the contact areas (surface to eyepiece) gleamed.
Using a wide-angle lens, these markings were captured.

First note the shiny ring towards the bottom of the cylinder.
... visible evidence that the paint, at the bottom, had centrifuged evenly.

Not all the rubbed areas have shown up on the image, but some solid black regions can be seen:


I have decided to spray some paint into a small container, and attempt to build the low areas by hand.
The entire surface doesn't need to rub, but a little more support is preferable.

This got me thinking...
Perhaps the centrifuge can be done away with.

A thin sponge pad, glued to something like an iced lolly stick, carrying a small quantity of paint, evenly spread over the sponge
... the paint could be easily wiped around the surface.

A drill mount would still be required, for the abrasive work, however perfect concentricity to the drill is less relevant to this task
... the abrasive would only see a rotating cylinder.

Hahaha ... the method continues to evolve.
If I was doing this again, I guess that I would apply the coating layers by hand.

... but that is just a guess, for the moment.
I'll have a better idea, after I have tried the detailed 'filling'....  🌝



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Increasing The Barlow ID - Fine Tuning

Cutting to the quick ... the paint brush 'filling' worked.

I first planned how to do it - holding the cylinder to a light
... and located a small, fine, artists paint brush - which was trimmed with scissors.
Paint was sprayed into a small, flatish, glass candle well.

The paint appeared to be slightly thick, and probably could have done with one, or two drops of acetone (no more).
However, I figured that I should 'go for it', as there was only one way to find out.

The paint was quickly applied to the low points ... it was getting thicker by the second.
The last application was 'the last application'.
For other uses, it was still usable, but it was getting thicker as the solvents evaporated.

It went in the oven to 95° and ten minutes later, to 160° for around twenty minutes.

It bit me!

Wanting to get on, I grabbed it with a beer cloth (instead of leaving it to cool down).
It was good that I did; because I discovered that the paint was in fact soft when hot ... it hadn't cured.
Inadvertently, I had caught some of the paint with the cloth, and it had simply rubbed off.

Well ... you learn something every day.
I've sprayed a large number of items over the years, and always assumed that baking would leave the paint hard (even at high temp).
Maybe it does, with other paint, but this was a high temp BBQ paint - clearly designed to withstand far higher temperatures than the primer.

Yes ... another lesson learned!

No matter; I let it cool (and then it hardened up).
Allowing me to give it a slight cut with fine carborundum paper ... just to remover the matt peaks.
(I cut a 10mm wide strip from a leather belt, to evenly support the paper)

I also took a few microns of paint from the lower area where the eyepiece struggled to enter.

Yes ... I could immediately feel that the extra support had improved the action of inserting the eyepiece.
... it rode home, on a cushion of air.

There was still some sticking.
The hot-spots were taken down individually, and a few more microns removed from lower down.

I finished it off with talcum powder, and the 12mm eyepiece.
This did it ... probably 1 micron; and after cleaning off, all the eyepieces enter on a cushion of air.
Effectively, the limit before an 'interference fit' 😎

No photos ... you need to see it on a video (when I produce it), showing the eyepieces sliding home.

It wasn't over
The laser was not fully penetrating.
It does not have a fine machined finish, and it had a paint finish that was slightly mottled.

I took 1000 grit paper; and with the leather support, I cut a 10mm band, removing the paint peaks.
... and the sharp end edge was removed.

That was it.
The full kit could enter the Barlow, without a hint of play.
The 'sliding fit' assembly method, had finally been taken to its ultimate conclusion  👍

Laser Test

It works.
I took it out, and reinserted it a few times, to establish confidence.

I tried to gently force it off centre.
This can be done.
Not by much, but it can be done,

However, by following a procedure; letting the components find their way; the centre can be maintained.

What hope, a normal setup has?

All that effort ... was it worth it?
I would say 100% yes.

The standard Barlow was miles out, over 700mm.
At 1000mm, the laser point would likely not even hit the lens.

Could this be why astronomers complain about the drop in image quality (when using a Barlow)?
I do understand the mod it makes to the focal length, but perhaps this is only half the tale.

Shame that I do not have any benchmark images for the Barlow (pre-mod).
Anyway, we will see what we see.
I have a Plossl 6.3, and an Omni Plossl 12.
The 2x 12 v 6.3 will have to do, to determine the viability of the Barlow.

Next up, we will reflect upon what we have learned.
I know that this has been a continual process (as it should be)
... but it's only when a project has been completed, that the lessons are fully appreciated, and taken en board 😉





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Increasing The Barlow ID - Reflections

There have been two trains of thought:

  • The concept
  • The method - how to better repeat this task

The Concept
In principal, a lens system will produce better images, if each of the lenses is aligned.
An eyepiece lens, might have a number of component lenses ... each perfectly aligned.
That is, until a Barlow lens is added to the eyepiece.

By reducing the sliding fit between the eyepiece(s) to almost zero, the Barlow can become 'one' with the eyepiece lens system
... enabling laser collimation with the objective lens, to create a single lens system.

In fact, if using an erecting prism, it doesn't end there.
However, the concept is clear, and valid.

The Method
The ideal method has not been proven.

However it is done; material must be evenly added to the internal diameter of the Barlow cylinder.
If the surface has already been painted, I would forgo primer and base coat, and directly apply lacquer
... it goes on quite thick, and can be easily baked hard.

Applying thin layers with a fine artists paint brush, is likely to be less problematic to using centrifugal force.
The key will be to apply  just enough to cover the surface without runs.
Finish by dragging the brush outwards towards you, so that the lacquer grain is perpendicular to the circumference.
This will enable easy and controlled removal of the peaks.

A mounting bracket to a drill, will be required, involving a screw, nut, and various washers.

200, 500, 1000 grit paper should be sufficient.
Cut a 10mm strip of belt leather, to support the rubbing paper.
This will be strong enough to apply pressure over the length of the cylinder, whilst forming well to the shape.

Having a very small, kitchen work top oven, will be ideal for baking the laquer finish - from a time and cost perspective.
Raise the temperature in stages, to first eveporate off the solvents, before taking the temperature to 160°C  for 30 minutes.
Let the piece cool to room temperature, before working the lacquer.

Whatever happens, you will succeed.
The only question is, how long it takes?
In my estimation, the above method will prove to be much quicker than all the steps that I was forced to take.

Once completed, the lower portion of the cylinder (beneath the penetration point of the eyepiece) can be blacked.





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Preparation for Benchmark Testing

90° Erecting Prism
The entry to the focus tube, and the aperture for eyepieces ... both were sloppy.

The male entry tube - I first tried electrical tape, but it was too much.
I resorted to aluminium tape.
It's not ideal, due to it being soft, and has potential to tear
... but it fitted perfectly, so good enough for the time being.

The female eyepiece connector was sloppy, and of course, the prism is akin to bingo balls in a lottery.
(The first 'light entry' error, is doubled at the first bounce)

Within the play ... at 90° angle, the eyepiece (and camera) tilt backwards.
The light could be going anywhere.

I tested with the laser; hoping for a lucky break
... and got it!

Yes; all that slop allowed the centres to align; or at least come very close
... the laser point was (horizontally) only 3mm off
... vertically, it was cock on.

Probably, a small piece of electrical tape will be enough to achieve guidance
... but as it stands, it's not too shabby :)

Camera Mount
The camera is an LG4 mobile phone.

Using a spare skin, I had hot glued a plastic cylinder, cut from an aerosol spray can top
... this for the original kellner type lenses.

The annoying problem was that the OD of the Omni Plossl's was larger
... so the first mod had to come off, and I needed to find a 34mm ID replacement tube.

The top of a water softener bottle was almost dimensionally correct, but it needed the support of a sink drainage tube.
When cut to size, the two together, glued to the phone skin; provide a perfect interface for connecting to the telescope.
It is definitely not pretty; rather it is function over form.
... but if a press fit connection for a camera is required ... this is as good as it gets (and far and away superior to the available mobile phone mounts).


The eyepiece is pressed into the connector, and the assembly is mounted to the scope.
No messing around - it is perfect alignment every time.

Next to the phone skin, is the 'tape modded' prism.

Benchmark Planning

Including the original kellner type eyepieces
... grab images for the eyepiece range (at 10Km).
Repeat with prism.
Repeat with Barlow.
Repeat with Barlow & prism.

Grab an image straight down the scope (sans eyepiece).

Obviously it is a shame that we don't have a full range of shots from the scope, precollimation & firming up.
Never mind ... I do have a couple of shots to compare with.

Primarily, this will benchmark the 60/f700 setup.
It will allow us to judge the 90/f1000 effectively, and the eyepiece improvement over the original kellner type lenses  🌝

Edited by Fo_Cuss

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Benchmark Testing - The Event


Benchmarking is no different to going camping.
Ideally, all material preparations should be completed, the day before the event.

This was to be completed today, with a view to testing tomorrow.
Only that today turned out to be a very nice day, with visibility calculated at 40Km
... while tomorrow indicates rain.

Knowing this, the Pixies got to work, applying particles to the Kellner lenses; forcing each to be cleaned.
The test schedule was not printed on windproof card ... and not even on paper.
The camping table needed setting up and cleaning - so it stayed at home.

Really; having a table, with all the lenses laid out in known positions, would be the way to do it
... particulary with the number of tests required.

Instead, the lenses in their cases were placed in container, which was placed in a rigidish supermarket shopping bag.
It was fine enough, but a touch messy.

Overall, it would have been better to have got the testing underway an hour earlier
... but it could have been much worse.
The sky was mostly clear, and the winter sun was low in the sky, at 14:30hr when the first image was taken.

The Testing

I quickly discovered that the scope needed to be in the shade (to enable 'image viewing').
Thankfully, the Berlingo is tall enough for the winter sun.

Initially, there was no wind, though it arrived soon enough.
For all the 'damping work' done ... it must still be improved.
Either that, or a Bridlington type wind-breaker must be constructed (I think I have one somewhere).
... actually, a tall top-sheet tent  would be great

Focussing was okay at low maginfications ... 4mm was difficult ... 2mm was virtually impossible.
In fact, focussing with the Barlow was generally more difficult, due to the extra weight and length.
(I'm thinking about a gas strut, say, from a hatchback door)

But the Barlow testing was carried out when wind gusts were more prevelant, so it was a double whammy against me.

The 'camera mount tube' needs to be longer, to provide better support for the weight of the phone
... the eyepiece had to be too close to the camera lens.
(Thankfully, the hot glue system allows for easy mods, simply by using a hair-dryer on it)

Recording the results

The main bugbear is the inability to easily record which image was taken by which lens setup
... and it's not like there was just one image per lens.
I was using a 'hand clap', but add in some wind rafals and the damned camera is snapping away happily on its own 😀

What I did, was to switch to video between major changes, to verbally record what I was testing.
If I hadn't done this, the results would be meaningless.
Having said that ... the images now need to be sorted, so we will see how rigorous I was with my book keeping.

Overall, as with the preparation (of course the two are linked), the benchmarking could have been better
... but it could have been much worse.

It definitely needs a table, with the lenses laid out in order, a card printed schedule, and a pen, to note the exact time against each lens change.

If all is well organised; one man can do it.
However, a two man team would be ideal - one on the table and record keeping, the other on the telescope.

It wasn't to be.
Though, the testing wasn't by any means, a disaster.
Hahaha ... well ... I guess that we are about to find out  🌝

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