Muse Field Of View

[Gano Richardson]

Theconcept of MUSE foresees the splitting of the adaptive optics corrected field of view in 24 sub-fields. Each of these sub-fields is fed into a spectrograph (called Integral Field Unit, IFU). An image slicer in front of each IFU serves as entrance slit, thus producing a spatially resolved spectrum of the full sub-field.

MUSE will use adaptive optics. This image gives an idea of the MUSE field of view in the WFM including one natural guide star (NGS) and the four elongated artifical laser guide stars (LGS), here shown in green (click to enlarge).

The Narrow Field Mode will provide an exquisite spatial resolution (up to 10-30% Strehl ratio in the I-z band) in a smaller field of view. This mode will enable a wide range of scientific applications similar to the HST STIS type science but with an improved spatial resolution and a 2D spatial coverage.

Whilst researching some new tutorial content for this site, I stumbled upon a topic which seems to have a lot of people confused, and I have to be honest that when I began delving deeper into it, initially I just became more and more confused myself.

I realized that in the past I had used the two terms somewhat interchangeably, but I began to wonder if that was incorrect even though I found many other people doing the same thing, such as Bob Atkins, who refers to FOV when defining the equation for it, but labels the resulting graph with AOV.

That actually made a lot of sense to me, but other sources I trust explicitly on such matters, such as the excellent Photography Life website, contradict that statement by saying that whilst AOV and FOV are different things, they are both measured as angles. In their article it states that AOV is a property of the lens and does not change no matter what size of sensor is in the camera, whilst FOV is a function of the lens AND the sensor size. In other words, a full frame lens can have a particular AOV, but when used on a crop sensor camera the actual field of view (FOV) is going to be smaller. Once again, taken in a vacuum, this sounds like a perfectly excellent way to define both terms, but it does contradict other sources and I struggled to find anywhere else that suggested that particular pair of definitions.

I then started to look around to see how camera manufacturers were using the terminology and found that Canon, Nikon and Sony all cite angle of view in their lens specifications on their websites and appear to prefer this terminology over field of view. However, they also include the angle of view for both full frame lenses, and APS-C lenses (see example below), which is contrary to the usually excellently researched content on Photography Life which says that AOV for a lens is constant, and only FOV changes based on sensor size.

The angle of view is the visible extent of the scene captured by the image sensor, stated as an angle. Wide angle of views capture greater areas, small angles smaller areas. Changing the focal length changes the angle of view. The shorter the focal length (e.g. 18 mm), the wider the angle of view and the greater the area captured. The longer the focal length (e.g. 55 mm), the smaller the angle and the larger the subject appears to be.

At this point I was thoroughly puzzled by all of this and all signs were pointing to the fact that the two terms are just so similar to each other that the internet has completely befuddled itself about them. Then I started to notice a third term popping up in some content, such as this article by Edmund Optics which was referring to AFOV, as in angular field of view.

I was thinking the same thing about how binocular manufacturers refer to FOV as a function of distance. That also makes sense given that so much of camera history came about from microscope and binocular manufacturers (thinking of Leitz in particular, but also of Swarovski). I have to imagine that, had some of those mathematics junkies been born a century later, some of them would likely be aerospace engineers as well!

Great article.

Thank you for your explanation obout FOV and AOV.But I have another confusion about FOV. In display industryespecially AR/VR,a key parameter is FOV that is different from what you said. It is showed as an angle,for example,which will be printed on the specification of VR/AR product,such as 210 showed by Sony.Meanwhilethere is another key parameter which is called AOV ( angle of viewof LCD or OLED screen. I just want to know the mathematical relationships between AOV and FOV what I said above. Thanks again!

I also think that people who are going to bother to read this article will have enough common sense to make the switch in width and height if they are calculating this in order to know how much horizontal view they will capture with the camera in the vertical orientation. They just have to follow the diagram.

*AOV and FOV are definitely not the same.

*When a lot of people (including camera manufacturers) speak about AOV they are actually talking about FOV.

*AOV is an inherent characteristic of a particular lens which is not alterable.

*FOV is a property resulted from a combination of the characteristics of a lens and the film/sensor format.

Describing the FOV as angles is the Angular Field of View (AFOV), describing FOV as dimensions (width and height) is the Linear Field of View (LFOV) but adding such esoteric terms to a presentation that is meant to clarify may not be helpful. Bottom-line is when the lens has been focused to infinity the angular FOV equals the AOV just like what occurs with f-stops when we fully open up our aperture.

The AOV does not equal the angle of coverage or image circle. For example, Canon states that all of their 50mm lenses have an AOV (diagonal) of 46, even their TSE-50mm! For the TSE-50mm to accomplish shifts, its angle of coverage has to be significantly larger than 46 probably closer to 64. Because the AOV that manufacturers identify for a lens directly relates to the size of the sensor, using the crop factor works well when determining AOV when working with other sensor sizes.

Does this reduce confusion? A little, for some. But the technical aspects, let alone the terminology, has little to do with the joy of photography and the sense of creativity experienced with a great capture.

From my observation, On a FF Camera sensor, a single digit (say 7 degree or 8 degree) AOV lenses with higher focal length (400 & above) lenses produces exclusively very good sharp subject in IC, leaving rest all elements in OOF. It means FOV is with very shallow DoF with its widest aperture.

Most of the wildlife photographers, do shoot at natural light environment. Therefore, they intend to gather more light to sensor. This action results them to keep lenses operate at its widest aperture of the lens manufacturer and rarely they narrow down if there is very much bright light available at that area/land. So, the FOV does matter a lot as the subject isolation from the background is to be achieved in this kind of photography.

The easiest way I think about the difference (in the most simplest sense) is to photograph a subject matter with a zoom lens with lots of foreground and background showing. If you wanted to fill the subject matter completely in the frame and if you zoom in, that is altering the AOV. If you walk up to the subject matter, keeping the same focal length on the zoom and fill the frame you are changing the FOV. The latter also applies to cropped sensors (sorry Nikon, Et al) and cropping an image.

I am strong believer in learning on different fixed focal lengths lenses as it teaches you the discipline of moving around a subject matter to achieve composition. Even on a photo shoot while using a zoom for speed and convenience, I have to fight the urge to zoom in or out rather than think about a different way to achieve a certain look. Especially in situations where there are back ground distractions or space is tight and you foolish opt for the widest focal length on your zoom.

I have been studying this for a while. I think the important issue is the affect of angle of view in the images. It is very important and often neglected. The angle of view is the reason your portraits of faces at 35mm lens are distorted from the same shot at the same size with an 85mm lens. If you look at a full body portrait on a 35mm lens you will see the too of the shoe is very long. On the 85mm you see more of the front of the shoe. 135mm is my favorite portrait lens because the angle of view give a more realist and flattering reproduction of what I saw when I took the picture.

The angle of view describes the geometry of the lens. Field of view describes the scene on the camera sensor. On a wide Angle lens the angle of view remains the same but your field of view will change as you move closer or farther from the subject. Angle of view also can add unwanted distortion on very wide angle lenses which is why most portrait lenses are traditionally 85-135mm.

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Traditionally astronomical observations in the optical region have been separated into imaging and spectroscopy. The former can cover a wide field of view, but at the cost of a very coarse resolution in the wavelength direction. The latter has tended to either lose spatial resolution - completely in the case of fibre spectrographs, and partially in the case of long-slit spectrographs - or to have only coarse spatial resolving power in the case of recent integral field spectrographs.

MUSE was devised to improve on this situation by providing both high spatial resolution as well as a good spectral coverage. The principal investigator of the instrument is Roland Bacon at the Lyon Centre for Astrophysics Research (CRAL) in charge of a consortium consisting of six major European institutes: CRAL at Lyon Observatory is the PI institute and led the construction of the majority of the instrument. Other involved institutes include the German Institut fr Astrophysik Gttingen (IAG) and the Leibniz Institute for Astrophysics Potsdam (AIP), the Netherlands Research School for Astronomy (NOVA), the Institut de Recherche en Astrophysique et Plantologie (IRAP), France, ETH Zrich, Switzerland as well as the European Southern Observatory (ESO).

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