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How do PC power supplies control there fan speed like the corsair RM series? Is there just a basic switch or are thermistors and a digital circuit involved? I've added a thermal switch to 3d printer power supplies before specifically a 'KSD9700 50 degree normally open'. The mod is really easy but involves draining the capacitors for electrical safety. The result of the mod was a perfectly silent printer when printing with a fan occasionally kicking in which is great for my ears and excellent for fan bearings. PS I know talking about modding power supplies isn't ideal and receiving a shock from a charged power supply could be fatal so please dont fill the thread with condescending comments about electrical safety.

First of all, let me start of by saying that this is intended for people who want a quick and dirty guide to knowing what to look for in a lens. Hence a lot of what I write will be oversimplified, because for more details there are many resources out there on the web where people have taken their time and put in a great effort to provide you with all the knowledge you want. Instead of competing with them, I will refer you to their work if you want to know more. I'm here only to give you a head start. Let me start off by saying, whether you're interested in photography, cinematography, or even just recording sound: While having high quality expensive gear would be nice, don't let the lack of having such gear stop you from being creative. Another thing I want to say before I begin: There are many good online resources where you can read or watch well written reviews of camera gear. The people who produce the reviews (hopefully all of them) handle the gear and put them through various tests. So if you're not sure about a camera or a lens, so go look at the various reviews. You can even look at what customers have to say on places like B&H, Adorama, Amazon. But, I also advise you to go to a place like Flickr. They allow you to search for photos based on camera model and perhaps lens model too. Maybe you will need to look for Flickr groups dedicated for a particular camera or lens, or look for keywords and tags. the reason I am telling you to do this is because a majority of the photos on places like Flickr will show real world examples of photos taken with the gear you are interested in acquiring. They are different from looking at test charts or test photos on review websites. Those who review camera gear, such as DxOMark, perform rigorous tests to find the flaws in a camera or lens. Most of those flaws appear in extreme test cases that tend not to reflect real world usage of a camera or lens. For example, the Sony A7sII has a stellar performance when it comes to low light, but think about how often you are going to find the darkest room in the house during a blackout on a moonless pitchblack night to take a portrait of someone. So if you're not sure about what you can achieve with a camera gear that people claim is "shit" and that you need to spend more than you want or currently have, go look on places like Flickr and see the photos others will have captured with said gear. Having good gear helps, but having better skills and experience helps even more. Both photography and cinematography cameras require lenses (a.k.a. glass). So hopefully what I have to say here will be of use to people in either field. I believe two main questions come to mind when people are thinking about buying a lens: What focal length do I need? What is the quality of this lens? Firstly a basic intro into the types of lenses you will find on the market, and explain why they differ in quality. There are two main types of lenses on the market, with some subtypes: Single focal length lenses, people often refer to them as prime lenses, fixed focal length lenses, and sometimes normal lenses Zoom lenses, and with zoom lenses there are two subtypes Constant aperture Variable aperture There is also another category for lenses: Photography lenses Cine lenses Both photography and cine lenses have a mixture of single focal length and zoom lenses. The added benefit of a cine lens include: A wider turn of the rings that control focal length, aperture and focus giving the user a more precise control over manually adjusting the lens. A zoom cine lens will also most likely be a parfocal lens, while it is almost 100% certain that all zoom lenses for photography are varifocal. What this means is that on a parfocal zoom lens, you can focus on your subject at one focal length of the lens and as you zoom in or out the focus doesn't change. On a varifocal lens, zooming in and out on the lens will affect the focus. In cine lenses, there is also something that is called a T-stop. It is similar to a F-stop on a photography lens and at the same time a bit different. The main point of a T-stop is that (primarily) on a zoom lens, at 50mm f/2.8 the light transmitted through the lens is exactly the same as when the lens is set to 25mm f/2.8. With modern lenses with specialized coatings the difference between F-stop and T-stop has become smaller. But in the olden days, light transmitted through 50mm f/2.8 was not always the same as light transmitted through 25mm f/2.8. Because of these design factors, cine lenses have a tendency to be more expensive than photography lenses. Note: Both photography and cine lenses can be mounted on photo and cinematography cameras, as long as the lens mounts are compatible. Now let's talk about lens quality, in order of what I believe is the tendency for quality to go from highest to lowest: Single focal length lenses (for example, a 50mm f/1.4) Pros: They are often the fastest of lenses, in other words they feature the widest aperture/f-stops. They are easy to design and manufacture. So they can be less expensive than comparable zoom lenses. Some can be priced very low and are budget friendly. These types of lenses quite often have the bests quality among any lenses produced because the manufacturer doesn't have to worry about how the quality of the light passing through the glass elements will change if the focal length of a lens changes such as in a zoom lens. Hence the manufacturer can fully concentrate on making sure the lens performs its best at that single focal length. Cons: The only con of this type of lens I would consider is the fact that because it is a single focal length, the lens is not as versatile as a zoom lens that offers a range of focal lengths. Constant aperture zoom lenses (e.g. a 24-70mm f/2.8) Pros: Zoom range and the fact that the aperture stays the same at any focal length. Constant aperture offers a big advantage over zoom lenses with variable apertures, because you can zoom in or out on the lens whilst keeping the same aperture setting and will not have to worry about readjusting shutter speeds, ISO or aperture. The same exposure setting you had for f/2.8 at 24mm will work at f/2.8 for 70mm, within a very tiny and almost negligible margin of error. Those of you who own lightmeters (e.g. the Sekonic 478 or even a lightmeter app on your phone), you know that any value you set for two corners of the exposure triangle it calculates the third corner for you based on the measurement of the light falling on the subject. The three corners of the exposure triangle are Shutter, Aperture and ISO. Focal length is not included. This implies that the lens has the same low light capability throughout the entire zoom range. With variable aperture lenses the exposure value remains near constant only if the aperture used at the widest focal length is equal or smaller than the widest aperture available at the longest focal length. Cons: Can be big and expensive. As aperture is a value derived from the focal length of the lens divided by the diameter of the opening of the iris within the lens, (for example, a lens with an aperture of f/1) for a 50mm lens to have an aperture of f/1 the diameter of the iris has to be 50mm wide. When designing a zoom lens, (for example, a 50-100mm zoom), the manufacturer has to design the body of the lens so that at 50mm focal length the iris can open up to 50mm in diameter but at 100mm focal length it has to be able to open up to 100mm in diameter. This adds to the cost and size of the lens. Variable aperture zoom lens (e.g. 24-85mm f/3.5-5.6) Pros: Zoom range and cheaper and easier to manufacture Can be smaller than a constant aperture zoom and also some very fast single focal length lenses. Cons: Variable aperture, meaning the widest aperture supported by the lens is only available at the wider end of the lens' focal length. At the longer end of the focal length, the widest aperture available is indicated in the description of the lens (i.e. 5.6 in the example above). Of the types of lenses, this type of lens will quite often will be the lowest quality of lenses. When designing a constant aperture zoom lens, because of the investment needed in designing such a lens the manufacturer will also decide to invest in the time and money to keep the quality of the lens above a certain level, because constant aperture zoom lenses are often targeted at professional level of customers. But with a variable aperture zoom lens, manufacturers will and can often skimp out on investing in quality. There is also another factor that determines the quality of a lens, any lens: The manufacturer. The quality control and decision by the manufacturer to invest in the design and production of a lens is another important factor that determines the quality of a lens. It is the same in the manufacturing of any product, as I'm sure most of you will understand as the same kind of factor exists in the manufacturing of computer components. As this video (below) by John Hess of Filmmaker IQ explains, compromises have to be made by the manufacturer when designing a zoom lens so that the quality of the light being transmitted through the lens does not fall below a certain level throughout the change in focal lengths. Trying to make a zoom lens the best quality at one focal length might mean that it performs very badly at another focal length. With a single focal length lens, the manufacturer doesn't have to worry about this issue, hence they can concentrate on keeping the quality of the lens high above a certain level. The longer the zoom range of a zoom lens, the more compromises that might have to be made by the manufacturer. I also recommend watching these two videos below from Filmmaker IQ to know more about lenses and camera sensors: This video below gives you a quick overview of differences between a photography and a cine lens: Before I go onto talking about understanding how to choose a focal length, I want to mention two specialty lenses: Tilt-shift lenses (TS), also referred to as Perspective Control lenses (PC) Lensbaby lenses Both lenses are quite often manual focus only lenses. They tend to be single focal length lenses. So most likely no zoom. Both lenses allow you to change the angle of the focal plane in relation to the sensor plane which can assist in controlling DOF in various ways. Additionally TS lenses tend to have a much wider image circle than regular lenses. There are also lenses that only shift, without the tilt part and vice versa. A Lensbaby lens has only the tilt part, not shift. (Unless Lensbaby has produced other models that I am not familiar with.) There are adapters that can turn your regular lens into a Tilt or Shift or Tilt+Shift lens. TS lenses for DSLRs owe their origin to the design of large format cameras with accordion style bellows. Lensbaby lenses can be used to produce some creative images. Such as creating an effect where the face of your subject is the only thing in focus and everything else is blurred/zoomed effect in a portrait. I recommend you do a Google Image search for photos taken with a Lensbaby to understand what kind of effects they produce. Some accessories for Lensbaby lenses allow for a changing the shape of the bokeh from the regular rounded shape. Of course you can also do this with regular lenses, if you know how. Because TS lenses give you more control over perspective than regular lenses, they are often used for architectural and landscape photography. The Shift aspect of a TS lens can let you take a distortion and parallax free panorama. You can even use the Shift aspect of the lens to mimic a medium format camera. The Tilt aspect of a TS lens lets you create the miniature effect. For example, the opening sequence of Sherlock uses a TS lens. The Tilt and Shift of a TS lens can help you create very deep DOF landscape photos. With regular lenses, to get a deep DOF you need to step down your Aperture/f-stop. But step down too much and the quality of your photo may suffer due to diffraction. With a TS lens by altering the plane of focus a landscape photographer can capture a photo where elements that are close to the camera and far in the distance are both within the acceptable level of sharpness. Some nice links on how to use TS lenses: http://www.oopoomoo.com/tag/how-to-use-tilt-shift-lenses/ http://www.digitalcameraworld.com/2013/10/30/tilt-shift-photography-how-to-use-1-lens-for-6-different-effects/ http://www.northlight-images.co.uk/article_pages/using_tilt.html Focal lengths: what to choose? I generally group lenses into three general groups. Just a warning that I'm a 35mm photography sensor (Full Frame) shooter, so if I do mention field of view or specific focal lengths you will may have to convert the values to what is equivalent for your camera sensor. Do not confuse 35mm FF with Super35mm used in cinematography which is closer to APS-C cropped sensor in photography. Both 35mm FF and Super35 can use the same film stock, however 35mm for photography is the long strip of film held side to side while Super35 is derived from when the film strip is held top down. Wide angles, including ultra wide and fisheye: I generally consider any focal length shorter than 35mm to be wide. Medium angles: between 35mm to 70mm. Telephoto: Everything longer than 70mm, including super telephotos like 400-1200mm lenses which can be very expensive. Of course you are free to group the lenses however you want. When choosing a lens, think about the subject you want to photograph and perhaps how you want to position the subject in relation to the foreground and background. For example: If you are taking a photo of a group of people, they are generally standing side by side and in a close group. For this kind of situation you can decide to use a wide angle lens or a telephoto lens, as long as you can get everyone within the frame. But if you are taking a photo of just a single or person or a couple of people together, (for example with the Grand Canyon or Eiffel Tower close in the immediate background), here are the possible effects using different lenses: Using a wide angle lens so and standing at a sufficient distance far enough so that you capture the people and the grand scale of the Grand Canyon. What can happen is that while the wide angle lens captures the scale of the Grand Canyon the people in your photo might appear small and less significant in the frame. So you step closer so that the people take up a larger portion of the frame, you want to give the people more prominence. The background object will become less prominent. How about using a telephoto? What will happen is you compress the scale and distance of the foreground and background, the far side of the Grand Canyon will seem to be closer than it really is. Another thing is when you're talking a photo of a group of people spread out, using a wide angle can make the group appear dispersed while a telephoto can make the group appear dense. Watch this video by one of the masters of photography: Joe McNally So when you choose the focal length or lens you need for the photo, think about what you want to show to your audience in the photo, or even video. Do you want people to be awed by the magnificent grandeur of the Grand Canyon or make your subjects (the people in the photo) appear larger than life, as if they are explorers who conquered the Grand Canyon? As my guides are intended to give you a quick intro to beginning your understanding of lenses, I will refer you to my other guides which have links to YouTube channels and websites where people have spent their time and effort to providing knowledge in more detail than I could provide in a short topic like this. You can find the links to my other guides in my signature. Think about distortion when you take photos. Ultra wide and fisheye lenses have the tendency to make straight lines appear as curves, especially around the edges of the frame. Because their field of views tend to be very wide, from around 90 degrees and up to 180 degrees. Distortion like pincushion or barrel distortion can be easily corrected in post, software like Lightroom come with profiles for some popular lenses or you can perform a manual correction, with the risk of losing certain portions of the frame. Additionally different focal lengths can change the appearance of your subject, as seen in this animated gif below. You can also see how the relationship changes for foreground and background elements. Keep in mind, in journalism where capturing the reality of the moment is more important than creativity you might want to think about whether you want a distorted image or not. Same thing when you take portraits, full body to head shots. Normally people recommend using focal lengths between 70-135mm for portraiture as this range of focal length tend to have a minimal distortion on your subject's appearance. So far I have talked about photography when discussing lenses. A lot of what I have said can also be applied to video. This video below shows the use of a technique called the Dolly Zoom (sometimes referred to as the Hitchcock Zoom as Alfred Hitchcock used it to create dramatic scenes in some of his movies). Dolly zoom relies on the distortion effect of focal lengths and the change in relationship between foreground and background elements. You can use any lens or focal length for both photography and cinematography, just keep in mind how that lens or focal length affects the image. For example, people often think that a Wide Angle lens is necessary for landscape photos. This is not true, you can also use a telephoto. to be continued...