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76

What you're seeing isn't the result of an iris aperture like in a camera. The 4-point diffraction spikes in the telescope are cause by the 4 struts holding the reflector in the mirror telescope. This diagram from the Diffraction spike Wikipedia article shows the diffraction pattern (below) created by the corresponding strut arrangement (above): Comparison ...


69

To increase readability and avoid exceeding the answer length limit, this answer has been split across two posts. General information and APS-C cameras are covered in this post; full-frame and APS-H cameras are covered in a separate post below. TL;DR answer In general, Canon DSLRs require a maximum aperture of at least f/5.6 or wider to autofocus, although ...


44

Angenieux (for one) makes some f/2 zooms. They're used primarily for movie making. The Optimo 17-80, for example, is an f/2 (T2.2) lens, covering, obviously enough, the 17-80mm range. As for why these aren't common, consider that this particular lens weighs 11 pounds and costs about $50,000US. Going even more extreme would be the Optimo 24-290, which is f/...


41

Why the wide aperture blurs the background more Let me start with Wikipedia figure: Above we have a wide open aperture. Only point 2 is in focus. Points 1 and 3 are out of focus. Due to wide aperture, the rays coming from them through different parts of the lens intersect the screen 5 (a film or a digital sensor) in different points. We may also tell that ...


41

I was recently trying to figure this out myself, and found this question. I didn't feel the accepted answer was quite complete, so here's my shot (no pun intended!): The first thing to understand is that the light that reflects off any one point on a surface isn't one beam of light, but many, coming in at many different angles and reflected off at many ...


38

It's worth noting that sensor size plays a huge role in depth of field and behavior of the lens. A smartphone has a tiny camera sensor, often around 25 square mm. This gives the camera a crop factor of about 6. (For the Samsung S9, I'm not sure about the dimensions.) You can calculate the hyperfocal distance (or "depth of field") but you can also get a ...


37

It's likely the sum of a few factors. Firstly, although you state "the same f-stop", it's important to realise that the manufacturer stated focal length and aperture values are often rounded, and not always in the way you'd expect. It might be the case that the Samyang is f/1.45 in reality, not f/1.4. The next factor is vignetting, wide aperture lenses are ...


36

Broadly speaking wide aperture lenses are easier to design the longer the focal length. The reason that you don't see any 400mm f/1.4 lenses is due to manufacturing difficulties, e.g. keeping dispersion low while producing elements of the size required for such apertures. It's worth restating that the designation f/1.4 means that the size of the aperture ...


36

Firstly the iPhone 5 lens has to be f/2.2, due to the small pixel size, the effects of diffraction which start to creep in at f/11 on a DSLR, start to creep in at f/1.45 on a 5.6mm (diagonal) sensor! I though that in order to have a big aperture such as f/2.2 a big amount of light should be able to enter to the sensor and in order to do it, a big lens was ...


34

F-stops are purely geometrical, the ratio of aperture to focal length, regardless of actual light transmitted. But all lenses absorb a part of the light passing through them, and the amount being absorbed varies lens to lens. So, in situations where even the slightest change of lights being transmitted affect the output, i.e cinematography, where many images ...


34

What makes the difference on partially and fully visible moon? In a word: shadows. I cannot understand why the IQ is extremely diminished when doing the same with an almost fully visible moon. The second image does appear to suffer from lower sharpness and overall quality. However, even if the technical image quality factors were equal, most importantly,...


31

Depth of field depends not only on aperture but also on distance to the subject. Depth of field increases as the subject gets farther away. If the wave and boats were all relatively far from the camera, but not terribly far from each other, then it's not surprising that they were all reasonably sharp. You can use DOFMaster to run the numbers yourself. Some ...


27

Assuming this is only on the LCD screen (it is in this case, I can see part of the viewfinder in the top of the photo), then it may be image burn from using the screen to display shooting settings. You could try taking an underexposed photo in manual mode, eg with the lens cap on, and see if you see it on the screen. Does it stay in the same place if you ...


26

An F-stop indicates how much light the lens could theoretically transmit - focal length divided by diameter of aperture. In practice, there are some losses each time a light ray enters or exits a glass surface. In a lens with many elements, these losses may sum into a considerable amount (like 25% loss in some old zoom lenses). This, naturally, affects ...


26

do most photographers avoid using zoom No. If "most photographers" avoided zoom lenses with variable aperture, there'd be fewer zoom lenses with variable aperture on the market. Furthermore, there are plenty of fixed aperture zoom lenses available at a range of focal lengths, so it's safe to say that photographers don't have to avoid zooms just to have ...


25

No - the aperture is set by the physical blades in the lens when you take the photo; a RAW "image" contains the readings from the sensor when the photo was taken, so there's no way you can go back and modify the light which was captured by the sensor. While it's not as obvious, this is equivalent to asking "Can I modify what the camera was pointing at from a ...


25

The blur is caused by the people moving while you were taking the photograph with a slow shutter. Honestly, I think it improves this particular photo a lot: it shows that the people are dancing, rather than just standing in weird positions. If you want to, the only way to avoid it is to use a faster shutter speed. This necessarily involves compromises. If ...


24

This is called the "program line". Imagine a grid labeled aperture in one direction and shutter speed the other way, as in the "exposure rectangle" in the middle of this answer. There are many different combinations which could produce the same exposure, and the program line is literally the line drawn on the graph to represent what a given program actually ...


24

This is normal behavior, caused by: Imperfections of aperture. Usually there are variations from technology process which cause not to have exact size of the hole. On 50mm lens f4 you should have 12.5mm opening, but it can be 12.4mm or 12.6mm Imperfections in shutter speed. The shutter is also mechanical unit and based on some factors as temperature, how ...


23

Aperture limitations are a consequence of the design of phase detect autofocus systems and are not specific to Canon. Phase detect autofocus in SLRs works by directing light to the AF sensor using a second mirror behind the semi-silvered main mirror. The AF sensor uses a pair of lenses to focus light from the subject onto a pair of 1-dimensional sensors, ...


22

Looking at your samples, the answer seems clear to me: that's not grainy, that is, actually, out of focus. Here's a 1:1 crop of your wide-open image: It seems pretty apparent that the wooden sign is sharp but the dog isn't, and the appearance of the blur looks completely in line with what one would expect from out-of-focus blur, not noise or grain. ...


22

One way is to simply use manual focus. Since the landscape is very distant, there is only one thing to focus on once, then you frame and shoot multiple pictures as you like.


21

This is normally referred to as something like "dual control dials", and you're right, it's a very desirable feature. Very few entry-level cameras have this, but it's common on mid-tier "prosumer" DSLRs, and universal on higher-end models. You can find a list of models with this feature on a camera review / database site like Neocamera; try this search: ...


21

There are two hard limits on how fast a lens can be: The first is a thermodynamic limit. If you could make a lens arbitrarily fast, then you could point it to the sun and use it to heat your sensor (not a good idea). If you then get your sensor hotter than the surface of the Sun, you are violating the second law of thermodynamics. This sets a hard limit at ...


20

Sigma 28-300mm F3.5-6.3 DG Macro? You are going to get a $7,000 camera with that piece of glass? Or even any of those Tamron's. I highly doubt anyone in the market for the 1DX even has these in a backup kit. How important is it? Not important at all.


20

There is NO difference at ALL because the physical aperture has not changed. The Fuji Finepix S4000 simulates a small aperture using an ND filter. When you stop-down the ND filter slides into the optical path. The Aperture written in the EXIF data is adjusted to reflect the transmittance of the ND filter, but note that since the size of the opening has not ...


20

The entrance pupil is limited by the diameter of the front element, and that is what usually restricts the maximum aperture of telephoto zoom lenses - not the physical size of the aperture diaphragm. The physical size of the diaphragm is only part of what determines the maximum aperture, expressed as an f-number, of a lens. Magnification between the front ...


20

There are (at least) four ways to do this: Use manual focus: This is (one of the reasons) why good cameras still have that feature. For this specific scene, there are other ways to achieve equivalent results, but there are situations (such as trying to shoot wildlife photos with grass or tree branches in the foreground) where manual focus is pretty much ...


20

If by "landscape" you mean something like this: then the answer is simple: at very large distances, depth of field is extremely large even at large apertures. That is, at any aperture if you focus at infinity, objects 20m, 200m, and 2000m from you will be sharp. However, focal length of the lens also influences depth of field, see answers below. Smaller ...


19

Let's start with lenses at the same location, and then address the moving the longer lens farther away to get the same field of view. Lenses at the same location The 50mm f/1.4 lens has an effective aperture that's twice the diameter, and four times the area, of the 25mm f/1.4 lens. The 50mm will, therefore, collect four times as much light (four times as ...


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