Thursday, 20 February 2020

Optical Instruments and Their Makers


It’s been a while since I’ve updated you on my work in progress, so here goes: It’s non-fiction, and the title is Brass & Glass: Optical Instruments and Their Makers.

The inspiration for the book came from my interests in stargazing, photography, microscopy and bird-watching. These involve using telescopes, microscopes, binoculars and cameras, and soon I began to take an interest in classic and vintage optical instruments. I found the lack of reference material frustrating - I would see an interesting looking vintage telescope at auction, but to find out more about the maker I would have to buy extraordinarily expensive reference books, many of which are out of print. Further, the information I sought was frequently scattered around multiple sources, and time-consuming to collate. I wanted an affordable, simple, encyclopaedic reference in which I could find the name of the maker or optical instrument and a concise, but informative article about them. This book is my attempt to remedy that gap in the literature.

It’s up to over 1700 entries now, and I’m working with several subject-matter experts to get critique feedback on the content. That will lead to a new raft of updates and additions then, when that’s complete, hopefully it’ll be close to being ready for publication.

Watch this space...

Thursday, 13 February 2020

Using Crossed Polarising Filters on a Conventional Microscope

A short while ago I posted an article about sugar crystals imaged in a microscope with crossed polarising filters. I promised to show the setup I used to achieve this, so here we are.


What you see here is a Charles Baker microscope with a Cooke microscope lamp providing Köhler Illumination. (The link is to my previous article explaining Köhler Illumination). I've implemented the crossed polarisation very simply.

I have a small polarising sheet that I have cut into two two-inch squares.
I use one of the squares in a filter slot in the microscope light.
And I place the other over the microscope slide, but under the objective lens. This sheet of polarising filter I rotate, while viewing through the microscope, until I see the best contrast.
And the result... I get to see these wonderfully colourful renditions of the crystalline structure of the sugar (see my earlier post).


A microscope used with crossed polarising filters is sometimes referred to as a polariscope.

Polariscope

In general, a polariscope is an optical inspection device used to detect internal stresses in glass and other transparent materials such as plastics, synthetic resins, crystalline materials, etc. A polariscope is composed chiefly of a light source and two crossed polarised lenses. Material to be examined is placed between the two polariscope lenses and viewed through the lens opposite the light source lens. It is commonly used in detecting the optical properties of gemstones.

All content and images © Tony Benson


Monday, 3 February 2020

Köhler Illumination


Köhler Illumination is a form of microscope sample illumination, invented by August Köhler, (see below), that provides even light across the field of view, and a light cone that matches the numerical aperture of the objective lens. It is suitable for either viewing or photography. It normally consists of a collector lens near the light source, together with a field iris, and a sub-stage condenser with a condenser iris. The focus of both the collector and condenser lenses is adjustable, as is the aperture of each of the irises.

The Cooke microscope light you see here has both an adjustable collector lens (the big lever pointing straight up), and an adjustable field iris (the small lever you see further to the right). You can click on the image to see it enlarged.

It also has a knob to adjust how bright the light is, and slots where filters can be inserted. This particular model of light is designed by Cooke to be used with a Cooke microscope, but it can easily be used with any conventional microscope.

The microscope I've shown in the picture above is by Charles Baker. It has a sub-stage condenser and iris, and a sub-stage mirror. The mirror has a plane face and a curved face. The plane face of the mirror is used in conjunction with Köhler Illumination, since the focusing of the illuminating light is achieved by the collector lens and the sub-stage condenser.



Using Köhler Illumination

The collector lens is focused to form an image of the light source in the plane of the sub-stage condenser iris. The condenser lens is focused to form an image of the field iris in the sample plane. The two irises are adjusted to provide the required light cone. Thus, when the sample is in focus the image of the light source is completely de-focused, resulting in even illumination.

Some microscopes have built-in Köhler illumination. In this case, the principle is the same, but the practicalities of the adjustments may be different.

August Köhler

August Köhler, (1866-1948), was a German scientist who made several innovations in microscopy. He is best known for his invention of Köhler Illumination in 1893. In 1900 he began to work for Carl Zeiss, where he continued to work until 1945, three years before his death.

All content and images © Tony Benson


Thursday, 5 December 2019

Sugar Crystals Viewed in Polarised Light

Nature produces some amazing and beautiful sights. We only have to watch the well-produced nature programmes to see this. Sometimes, however, we need optical instruments to help us see these wonders. 


In this case I've used a microscope to look at simple sugar crystals. The field of view is about 1.05mm by 1.59mm, and the sugar is viewed through crossed polarising filters.


I prepared the microscope slide for this rather simply. It is certainly not elegant, nor is it in any way a professional looking slide - but it works. I dissolved sugar in water until no more would dissolve. I then dripped a small amount onto the slide and waited for it to dry. I built up a rectangular trough around it using some of my wife's nail varnish, and the last coat I used to build up the trough also cemented the cover-slip into place. Simple.




I will do a another post to show the equipment setup I used for this but, in brief, it was a vintage Charles Baker microscope, with Köhler Illumination using a Cooke microscope light and two polarising filters.



For now I just wanted to share the pictures with you in the hope you will enjoy viewing them.

All content and photos © copyright Tony Benson

Wednesday, 27 November 2019

A Walk Around Maidstone – Rootes and the Mill Pond



I recently took a stroll around Maidstone, looking for some of the old bits that had not been bulldozed in the name of progress. I found myself looking at the old Rootes showroom, now earmarked for redevelopment into yet more housing. I first knew Maidstone when my family moved to a nearby village at the beginning of the 1960s, and I well remember Rootes Group and their showroom here by the River Len.

The Rootes motor business dates back to 1897 in Maidstone, and in 1913 the founder’s son, William, formed his own independent motor sales company in Hawkhurst, also repairing and making parts for aircraft engines. William bought his father’s Maidstone business in 1917, later expanding nationally to encompass the motor manufacturers Hillman, Humber, Singer, Sunbeam, Talbot, Commer and Karrier, as well as the Maidstone motor manufacturer Tillings-Stevens. It was here in Maidstone that the showroom, photographed above, was built for Rootes by the architectural firm Howard and Souster in 1937/8.

The building overlooks the mill pond on the river Len, once serving the Corn Mill at its downstream end where the modern road bridge is built over the top of a mediaeval mulit-span bridge on Mill Street. Here you see the bridge pictured from the west where the mediaeval stone arches can still be seen under the modern cantilevered road bridge. When I took this photograph there was a pied wagtail flying in and out of the dark tunnels under the arches.

Turning my back on the Mill Street bridge I get this view of the river Len flowing towards the Medway.

Crossing into the gardens of the Archbishop’s Palace, I see the river Len again, further downstream, now only metres away from where it joins the Medway.

Content and images © copyright Tony Benson

Friday, 4 May 2018

Available Now - Galactic Alliance: Betrayal

Today is the big day! Galactic Alliance: Betrayal is now available on Kindle and ePub from your favourite online bookstore.

The Galactic Alliance has brought advanced technology and trade to Earth. The governments of Earth see them as a friend – why invest in global defences when we have the Galactic Alliance as an ally?

Daniel thinks they're wrong. Nobody, not even Ruth, believes him when he stumbles upon a Galactic Alliance plot to take over Earth and subject humanity to brutal, dehumanising slavery.

Separated from Ruth by Vorth astro-pirates, Daniel is torn between trying to warn sceptical Earth governments and finding Ruth. The astro-pirates, meanwhile, discover that Ruth is not the pushover they expect her to be.

Pursued across the galaxy by hostile aliens, Daniel confronts the Galactic Alliance, plunging himself and Ruth into the heart of the biggest conflict in Earth’s history.


In our galaxy of alien worlds and species it is not always easy to tell right from wrong, or good from bad. Taking on the seemingly invincible might of the Galactic Alliance is more than any sane person would consider, yet it is necessary. If they have their way, human life on Earth will be reduced to a subclass of slaves to a brutal alien species.

This is a story of astro-pirates, love, treachery and fear. You will visit worlds you have never seen before, and meet aliens, good and bad, who all have a part to play in the battle for freedom.

Monday, 16 April 2018

Cover Reveal - Galactic Alliance: Betrayal

Here it is - the cover for my forthcoming book, Galactic Alliance: Betrayal. In my last post I promised I'd show you the cover, so without further ado:


The Galactic Alliance has brought advanced technology and trade to Earth. The governments of Earth see them as a friend – why invest in global defences when we have the Galactic Alliance as an ally?

Daniel thinks they're wrong. Nobody, not even Ruth, believes him when he stumbles upon a Galactic Alliance plot to take over Earth and subject humanity to brutal, dehumanising slavery.

Separated from Ruth by Vorth astro-pirates, Daniel is torn between trying to warn sceptical Earth governments and finding Ruth. The astro-pirates, meanwhile, discover that Ruth is not the pushover they expect her to be.

Pursued across the galaxy by hostile aliens, Daniel confronts the Galactic Alliance, plunging himself and Ruth into the heart of the biggest conflict in Earth’s history.

The release date will be Friday 4th May, and it will be available on Kindle and ePub. You will be able to get the ePub from all the usual sellers, including Nook, Kobo and others.