Using a telescope – with Glaucoma

I have no history of glaucoma, none in the family, and was initially, maybe 10 years ago, treated with drops to reduce my eye pressure, picked up in eye tests as being too high. This continued for many years, with more drops, stronger drops, but eventually the field tests showed that I was losing vision in the lower two quadrants of both eyes, initially the left lower quadrant in one, and the right in the other, so I did not lose any overall vision when using both eyes.

I eventually changed hospitals as the specialists in the first were just rubbing their heads, giving more eye drops, and sending me away for another 12 months – they never mentioned Glaucoma: but they lost my notes continually, so started again twice and did not treat the condition seriously. In the second Hospital I was told I had severe open angle Glaucoma, told to advise the DVLA, and take a driving fields test at an opticians – that led to my car driving licence being withdrawn.

The driving field test does not really demonstrate to you how badly your vision is affected. When I can see the effect of the combined blind spots, just under my eye line, it is when talking to someone at normal face to face distance, maybe 2 feet, when if I look into their eyes I can’t see their lips moving: in fact I can’t see their mouth at all. It’s also surprising how a significant part of effective hearing relies on also observing the lip movement.

After 3-4 years at the next Hospital I had moved up the priority list, having been using two different drops to try to reduce the eye pressure – ineffectively. So I reached the end of a waiting list for an operation called a Trabulectomy.

A Trabulectomy

It’s a frightening operation, more from the point of view of your own worries and not for any pain. The eye is immobilised, and anaesthetised, and my surgeon was very skilled. Nevertheless I would have liked some form of tranquiliser into the line they put into a vein in the back of my hand. Maybe I was so paralysed by fear, they thought I was calm. The objective is to put a slit into the eyeball, to allow the internal fluid to drain out through this slit, rather than through the normal route, which has probably furred up. (Maybe we should have bought a better water softener?) From the instrument engineer’s point of view, it’s a drain hole like a safety valve, an over-pressure valve, to let fluid out when the pressure gets too high. Say at over 20mm Mercury, to reduce the normal eye pressure – to the desirable level of 12-15mm Mercury.

The drops used after the operation are of two types: one seems to be an antibiotic, to stop germs getting inside; the other, a corticosteroid, is to ‘stop inflammation and swelling’. This also delays the healing process, so allowing the slit put in the eye to settle down without the edges healing together across the slit, keeping a drain slot open once the eye recovers. So the drop delivery immediately after the operation controls the slot width/gap, and the objective is to make this the right size to suit your condition – – and so it takes some tweaking. Hence the frequent return trips to the specialist to see what is happening.

What happens next?

Now I have one eye operated on, getting better after about three weeks, hopefully the pressure is going to be lower. I am now thinking about the next eye needing the same operation, but next time I’ll ask for something to tranquilise me. It’s a fairly long operation, about half an hour, with them working on the eye and you just lying there, so you can get a bit worried.

After effects are interesting. I’m an optical/telescope/photography guy, with a collection of over 200 telescopes, a few binoculars and other optical things: I’ve always worn glasses and could never bring myself to use contact lenses. I studied physics at University and specialised in wave theory, optics, refraction, etc. So I can see my own blind spots, know that the left eye (yet to be operated on) has a blind spot almost impinging on the centre line, to the right, such that I can check text reading backwards more easily than forwards, etc. Alternatively you can tip your head to the right so the line of text on the PC screen is angled above the line between the eyes.

Apparently the eye has a membrane over the outside surface: when the eye pressure is reduced, maybe this membrane does not shrink, like the outside of the eyeball does. So it is a little loose on the eye. The slot, that somehow in the operation they put in the actual eyeball, leaks fluid out as far as the inside this membrane (which somehow maybe they repair in the operation): it forms in a “bleb”, ie a bubble of fluid, like a lump, on the eye surface, and slowly disperses through the membrane. I think in the operation they inject something to form the basis of the ‘bleb’. Bleb is a real technical term.


But when like me you work on a PC, at night, with light radiated directly into your eye mostly, it appears that the folds or ripples in the surface of this membrane can appear to move across the pupil, and at certain angles the light is refracted into the eye, so you see occasional hair like white lines of light running across the field of vision. This presumably will stabilise/disappear as the membrane does shrink, and the eye diameter stops going up and down with pressure variations. I asked the Consultant about this, and he just commented that I was too observant. Trouble is, understanding what I could see, is what made me interested in optics to start with.

Just a final comment: how do you still use a telescope, with almost total blind spots in the lower two quadrants? I use them on aeroplanes, to see the registrations. These you read by almost taking a snapshot of a good sighting into the brain and processing it. The answer I thought was to use binoculars, but it’s not the same. The answer is that you have to use the top half of the eye view, the top two quadrants, for the snapshot, ie aim the telescope below the target of the registration, or whatever. Thank goodness for autofocus on digital cameras!

The future

If the eye pressure is reduced by the dual Trabulectomy, the damage will be arrested, and I will not lose any further vision. But what has been lost, is lost, as it is caused by pressure damage cutting the optic nerve where it leaves the eye: so until they can get little biotic nerve bridging robots to repair that break (and spinal chord breaks in people who have neck injuries), that area of vision will remain cut off. The technique is being developed, with the research on stem cells etc, but not that fast.

Maybe there will be a follow up blog later. But I have to work out whether this is a post that should be used on the “Insider” process control marketing blog, where I always promote the use of optical techniques for process analysis and control, or this Telescope Collector’s blog! The answer is both….

Update December 2016

The Summer was good, plenty of aeroplanes to spot: a bit frustrated I suppose – by lack of trying to use a telescope, in the fear that it would be bad – I called in at a camera shop and asked if they had any image stabilising binoculars. At least that would overcome the standard binocular jitter, but might help the glaucoma.

Came out with the only one in the shop, just traded in, second hand, Canon 10×30. Absolutely brilliant! Maybe not as high powered as my telescopes, but really stable, a lot more time available to snatch a registration when everything else is right. OK, still not converted, but they are the go to pair for fast spotting of overflying aircraft….

Much to my wife’s displeasure I still buy at least two new scopes a month, the older and more dilapidated the better, cos they are cheaper.

Davis Victorian Scientist’s Optical Set

This was one of the rich Victorian gentleman’s “must have” items!

The first draw in position as part of the telescope!

The first draw in position as part of the telescope!

In those days the landowning aristocracy spent their time “Doing Science”, and the things they needed were a microscope to really understand the small bits of nature, and maybe also a telescope to see the larger animals that moved a bit too fast for them to catch up. So around 1850 the thing to have was a scientific set, which was thankfully provided by the instrument makers of the day – the ones who had identified a good marketing plan anyway.

The complete scientific set, and box

The complete scientific set, and box

This boxed set was made by B. Davis, of 430 Euston Road, London, as is engraved on the first draw of the telescope. The rest of the set, apart from the box, comprises a microscope stand, some specimen slides to look at, plus an eyepiece with a ruby glass lens, to reduce glare, presumably from an arc light focused on the mirror under the slide. There was also a little glass roofed brass sided enclosure, presumably to enclose a fly or bug or something in the right place under the microscope,to be observed in a trapped area.

A flea on one slide

A flea on one slide

There are several pre-prepared glass microscope slides with the set, which look to be French, and that probably means they were added later. They are labelled, as S**d Po* – Grass  (Seed Pod – Grass); Cuticle Onion; Scale – Perch; S**rch – W*ea* (Starch – Wheat?); Seed Carrier – Aster; Sole Scale (also Scaille de Sole). Two others are home-made slides, one is labelled as a “Small spider’s leg”, the other is unidentified, but looks like a flea!

DSCN2543sThe idea behind this scientific set is that the first draw of any telescope, with typically four eyepiece lenses, is actually a microscope: when acting as the first draw of the telescope, it allows the observer to see the small image of the remote object created by the objective lens, positioned just in front of the end of this microscope, but upside down. The eyepiece lenses turn this image the other way up and magnify it.

But when this first draw is used separately, screwed into another holder in a vertical position, it creates a microscope in a frame, that is positioned above a specimen slide to be inspected. By using the same mounting threads, in the microscope frame and the telescope body, it all fits together and has a dual purpose…..

The Maker, B Davis

So this became a great little scientific set to sell to the man with time on his hands, and interest in the developments being made in botany and science and astronomy etc, all at once. The problem really is that these boxes get broken up, and the bits get separated, so it is really good to find a set still with all its components intact. They were manufactured in Victorian times, B Davis was said (in Gloria Clifton’s Directory) to have been an Optician, who attended the London Mechanics Institute from 1830-32, and then lived at 1 Lower Terrace, Lower Road, Islington, London.

DSCN2552xThere are records of an Isaac Davis at Lower Terrace, Lower Road Islington from 1832-38, and then with his brother Marcus here until 1842: they had also traded as Davis 33 New Bond Street from 1820-38. But there are also records that show Lower Road was at times called Essex Street, and could indeed have been renamed as an extension of Euston Road, given that the roads around the newly growing railway stations were probably being developed. Since the Clifton Directory covers only the period to up to 1851, possibly this set was produced by B Davis after that date, when the road name had changed.

The complete boxed set: the box is missing one of the side panels.

The complete boxed set: the box is missing one of the side panels.

Postscript: The Winter 2015 Tesseract catalogue features a combined microscope/telescope set like this, but in better condition, and earlier, made by W&S Jones in maybe 1790. The microscope specimen carrier is better quality, and the whole thing is in better condition. But that one would cost you $9500. Maybe I should rethink the value of this little set too…or clean it up a bit more, restick the box together!

A James Chapman Octagonal Telescope

Early last month I summarised the various octagonal and decagonal telescopes in the collection, then set about updating the overall listing: surprisingly perhaps I found another very old Octagonal scope, and in fact it is one I had been worried about, as I had promised to tell the Ebay vendor about it, when it had been renovated: but it had got misplaced. It was bought from a lady near Bournemouth, in February 2014. The photos here show it has not yet been cleaned up in any way!


The scope is mahogany, planed down to be eight sided, with a single brass draw. This draw is retained within the mahogany barrel, and has three in-line joints: the maker’s name is engraved on the second section of the single draw, which would seem unusual. However there is no way that the first two sections could have been transposed, as the threads are not compatible in any different order.

The maker, James Chapman


The maker’s name engraving reads “Made by JAS CHAPMAN” (with the “S” as a superscript) on the first line, and “St Catherines London” on the second line. James Chapman worked there from 1774 to maybe as late as 1804. Gloria Clifton, in her Directory of British Scientific Instrument Makers, gives James Chapman’s addresses as:

1774-1796: St Catherine’s, Near the Tower, London

1776: Hadley’s Quadrant, opposite the King’s Store House, St Catherine’s, London

1793: 41 St Catherine’s, London

1794: 5 St Catherine’s, London


DSCN2528As can be seen, the only thing missing is the bezel on the eyepiece end of the main barrel, which also means that when in use the brass draw can be out of line with the axis of the barrel and objective, so it needs to be held in the correct position carefully: but then the telescope works very well. Three lenses are present in the single draw, one at each of the splits in the tube, and each lens is held in place with its own internal bezel. The three lenses are equi-spaced, presumably in what Dr Chris Lord would describe as a Schyrlean eyepiece arrangement. The three sections of the draw are effectively keyed by having different screw-threads, so they cannot be attached in the wrong order!

There is no slider to protect the eye lens, but it is well recessed below the bell housing: the telescope can appear to be slightly easier to use without the bell housing in place, which possibly explains why sometimes these pieces are missing.

DSCN2530The magnification is reasonably good, but at times the view can show some chromatic aberration at the edge. This comes from the single lens used as the objective, ie it does not use the Dollond patented dual objective lens. The objective only has a visible used diameter of around 0.6”, in the mount, which is a part of the protective slide assembly at the end of the barrel: the actual barrel is much bigger, about 1.375” across the flats of the octagon – this restriction is presumably deliberate so as not to use much more than the central part of the lens, which can reduce the effects of chromatic aberration. Total length fully open is approximately 23”. There is one orifice restricting the light transmission from the edges of the view, near the final eyepiece lens.

So, having now re-located this telescope it now needs a little careful cleaning! Since the Dollond Patent expired in 1772, it seems likely that this telescope was produced in the early 1770s, since after 1772 the lens doublet became fairly standard with London instrument makers.


Accession Number 194.

Postscript in 2017

I have to say having been struggling all afternoon to get a Ramsden to work properly, picking up this old little telescope was a real pleasure! While the magnification might not be quite as much as the Ramsden, it worked so easily. Then you think it has such a small objective (to reduce the chromatic aberration with one lens in there) but still delivers at least 10x magnification and a good field of view. Plus the definition of the image is brilliant (have I been looking at dodgy digital photos too much?) and with the ease of focusing, this telescope is a little masterpiece. Yet  possibly 240 years old. Plus it focuses down to 12 feet away …..but it does get a bit wobbly without that bezel!

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The old slider design! It is still doing its job, and works quite well even without the bezel.

2020 update:

After polishing  the brass the Chapman telescope looks much more desirable: but the wood seems to look right in its used and battered state. Photos coming below. 

In November 2020, after polishing with tomato ketchup, Brasso and then on a wheel…. the main brass draw area looks good! The barrel remained a problem, and was eventually sanded and re-polished