#, like 1:2.8 or 1:1.4. Some lenses give a range, like 1:3.5-5.6 — this means that over the zoom range of the lens, the maximum aperture changes. (It doesn't give the minimum aperture. See this for more if you're curious.)

The F 2.6 is the f-stop, "speed" or how light sensitive the lens is. A lower number means more light can hit the sensor. A lower number also means you can easier get the background out of focus.

F:

F:2.6 is a ratio. In math, a ratio is written using the : (colon symbol). A ratio is used to show the relationship between two numbers. As an example – in your class there are 12 boys and 14 girls. To compare we can write this as 12:14. In optical jargon, F stands for “focal ratio”. This value compares the focal length to its diameter. We know the focal length is 3.8mm. We know the focal ratio is 2.6. Now we can calculate the diameter. It is 3.8 ÷ 2.6 = 1.46mm. We can’t reap much from the diameter be we can gain much from the focal ratio which is 2.6.

The optical detection is one of the sensing techniques most used in the biological field since it allows to make non-invasive analysis with high resolution and great versatility. With the aim to get an "all-in-one" self device, this type of detection has been recently tried to be implemented within Lab-On-a-Chip (LOC) microfluidic samples in order to reduce coupling losses and improve the S/N compared with the use of external sources. Taking advantage of their small size these devices show the peculiarity to integrate internally the operation of various laboratory macro instruments that allow to investigate phenomena at the microscopic level with high sensitivity. This thesis has been focused on the design and implementation of a coherent light source integrated microfluidic platform, as it is the first step to achieve this type of detection all-in-one. As road maps design was chosen to implement a dye laser with optical resonator Fabry-Perot combining the Femtosecond Laser Irradiation Followed by Chemical Etching and Inkjet Printing manufacturing techniques. The activity has been mainly carried out in the laboratories of CNST Italian Institute of Technology in Milan and has covered all the aspects of the manufacture of microfluidic chip, including the optimization of the process of realization of the semi-transparent metal mirrors within the substrate. This was made possible by using of inks based on organic metal complexes of silver printed directly inside the chip, achieving a great flexibility in reflectivity (10-100%). The chip, entirely buried on fused silica substrate, is composed of a microchannel where the active material flows, two empty “basins” as the seat of the metallic mirrors and, finally, one optical fiber that collect the emitted light. The optical characterization of the device, carried out in the labs of the Polytechnic University of Marche, allowed us to demonstrate the correct lasing operation using rhodamine 6G as dye. A good spectral quality with a full wave half maximum ~3 nm and lasing threshold of few hundred µJ/mm^2 has been the best performance, consistent with the best results reported in literature for this type of configuration.

#mm (in this case f=3.8mm) gives the focal length of the lens. In combination with the sensor size, this determines the field of view for the lens. See What is focal length and how does it affect my photos? for details on focal length. This is also often just written as

The focal length is the most important fact about a lens. It reveals the properties of the lens such as how big images of objects will be and as well as the angular field of view. In other words, does the lens operate as a wide-angle, or telephoto, or does it deliver a “normal” view of the world. These are significant facts because if we fit a lens with a focal length about equal the corner-to-corner measure of the image sensor, the view resulting will be “normal”. Meaning the view matches what we see with our own eyes. If we mount a shorter lens, the view delivered will be “wide-angle”. If we mount a longer lens, the view will be magnified (telephoto).

#mm, like 50mm or 35mm. A range here (like 24-70mm) indicates a zoom lens. Note that even if the lens is marketed using "35mm equivalent" terminology, lenses are almost always labeled with their true focal length.

# (in this case F:2.6) gives the maximum "focal ratio" or aperture stop for the lens. A lower number means more light-gathering ability. Read What is aperture, and how does it affect my photographs? for more on this. You will also commonly see this written on a lens as 1:

By convention we write focal ratio as f/2.6. This value compares the bigness of the image projected by this lens to other lenses. The focal ratio (f-number) is universal in that any lens, regardless of focal length or working diameter, will project an image that is reasonably the same as to brightness as any other lens set to the same focal ratio. Photographers place great value on the f-number setting of a lens. Such a system allows them to set their cameras so the exposure used will yield a satisfactory image i.e. not too dark / not to light. The f-number has many other uses. You would do well if you read up on camera lenses, particularly on focal length and f-number settings.

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f=

F:2.6 f=3.8mm engravings on the lens -- what they mean. The camera lens is a copycat of the human eye. It gathers light rays stemming from object. As these rays traverse the lens their path is changed. The lens causes these rays to travel taking on a converging path. Now they project an image of the outside world onto the surface a digital image senor (or film) located inside the the rear of the camera. The shape of the lens regulates the distance lens to projected image. We call this distance the “focal length”. This lens has a focal length of 3.8mm (about 1/7 of an inch) about the height of three stacked pennies.

In this case 3.8 mm needs to be multiplied with the crop factor of the sensor if you want to get the "35 mm equivalent". After googling I see that the 35mm equivalent is a 37 mm lens.

Also note that the camera only has digital zoom. The result will be, let's just say, not what you hoped for if you use the digital zoom. My advice is to look for something with optical zoom. It's a massive difference. Even a used old camera is probably better, if you ever need the zoom. If you never ever need the zoom than this is probably fine.

It seems their marketing department needs to learn how the focal length works, since this diagram shows a longer focal length as wider. That is backwards.

On this particular lens rim is written "F:2.6 f=3.8mm". What does it mean? Focal point 3.8 mm and aperture 1/2.6 of the focal point ???

The f=3.8 mm is the focal length of the lens. This is the number that describes if it's a wide angle lens (like a GoPro) or a telephoto lens (like sports and wildlife photographers use).

La detection ottica è una delle tecniche di sensing più utilizzate nel campo biologico in quanto permette di fare analisi non invasive con elevata risoluzione e grande versatilità. Di recente si è cercato di implementare questo tipo di detection all’interno di dispositivi microfluidici detti Lab-On-a-Chip (LOC) per ridurre le perdite di accoppiamento e migliorare il S/N rispetto all’uso di sorgenti esterne con lo scopo di ottenere un dispositivo “all-in-one” autonomo. Questi sono dispositivi racchiudono al proprio interno funzionalità di diversi strumenti di laboratorio e permettono date le loro dimensioni ridotte di indagare fenomeni a livello microscopico con elevata sensibilità. Questo lavoro di tesi è stato focalizzato sulla progettazione e realizzazione di una sorgente di luce coerente integrata sulla piattaforma microfluidica primo passo per realizzare questo tipo di detection all-in-one. È stato deciso di implementare un dye laser con risonatore ottico di tipo Fabry-Perot mediante la combinazione delle tecniche di fabbricazione Femtosecond Laser Irradiation followed by Chemical Etching e Inkjet Printing. L’attività, svolta principalmente nei laboratori del CNST dell’Istituto Italiano di Tecnologia di Milano, si è occupata di tutti gli aspetti della fabbricazione del chip microfluidico, compresa l’ottimizzazione del processo di realizzazione degli specchi metallici semitrasparenti all’interno del substrato. Ciò è stato reso possibile grazie alla stampa nel bulk del chip di inchiostri a base di complessi metallo organici d’argento, ottenendo un ottima flessibilità nella riflettività ottenibile (10-100%). Abbiamo quindi realizzato su un substrato di fused silica un canale in cui fare fluire il materiale attivo affiancato da due tasche in cui realizzare gli specchi metallici e infine gli accessi in cui alloggiare le fibre ottiche che raccolgono la luce emessa. La parte di test e caratterizzazione, svolta in collaborazione con l’Università Politecnica delle Marche, ha permesso di dimostrare il corretto funzionamento di lasing utilizzando come colorante la rodamina 6G, ottenendo nel migliore dei casi una qualità spettrale con un full width at half maximum ~3 nm.