79

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 caused by the four 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): ...


44

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 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 ...


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 ...


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

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

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 ...


25

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 ...


22

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: ...


22

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 f/...


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.


20

This is really simple when you think about it. The additional element changes the focal length of the lens, without changing the apparent size of the aperture. That means that the relative size of the aperture decreases, so the f number does in fact actually change. (If this is unclear to you, see the bit about f numbers in this other answer.) This is also ...


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

The Exif:ApertureValue is stored as an APEX value as mandated by various EXIF standards. The APEX system is a way to calculate exposure and works using base-2 logarithms. The use of base-2 means a rise of one in the value equates to a doubling, which we know as 1 stop; which makes it pretty handy for photographers if they're good with logarithms (which we ...


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

You've hit the diffraction limit. That link has some amazing answers with a lot of detail, so I won't be redundant, but in short, once the aperture gets to be below certain physical size, diffraction causes inevitable blur. For your camera (and any other camera with an APS-C-sized sensor), the limit is a little beyond f/11. The amount of light let in doesn'...


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 ...


19

If you care about image quality then there isn't really a "don't care" aperture any more. With 35mm film the effects of diffraction at f/11 or f/16 weren't readily apparent, however with a high megapixel DSLR diffraction has a measurable effect at apertures as wide as f/5.6! It's worth stating for the record: more megapixels does not make diffraction worse. ...


19

It's widely believed that a lens with a faster aperture will perform better stopped down compared to a slower lens wide open. Whilst this is often the case it's not a hard and fast rule. With DSLRs the lens is wide open until you take the shot (at which point the iris quickly closes). Having a faster lens therefore means you get a brighter viewfinder image. ...


19

The Factors There is an equation, and by convention, it's set up to be really simple. There are basically five factors to consider together: Aperture — the size of the opening which lets light in, Shutter Duration (or shutter speed) — the amount of time the sensor (or film) gets that light, Sensitivity (or ISO, or sometimes "film speed") — how quickly the ...


18

Many many reasons exist to buy lenses slower than f/2.8. Price Size Specialty lenses No need for a wide aperture Versatility Compromise over above factors As you suggested not all types of photography require wide apertures. Landscape photographers oogle over the Canon TS-E 24mm f/3.5 L II Tilt-Shift Lens for example. It is f/3.5, costs around $2,000USD, ...


18

The easiest way to think of this is with an image. When you use a wider lens, you have to be closer to your subject, which emphasizes the distance between the subject and background by making the background smaller. In contrast, if the camera is far away from the subject, you'll have to zoom much farther to get the same size of subject relative to the ...


18

Hitting the DOF preview with a stopped down aperture should make it obvious: what you see can be very dim, dim enough it can be very difficult to compose and focus. That's why cameras have the lens wide open until actually taking a picture, so you can get the brightest image by which to setup your shot.


18

In order to control the aperture from the D3400 with an older 'D' type lens that has an aperture ring, you need to set the lens' aperture ring to the narrowest (highest f-number) and lock it there. If the aperture ring is in any other position, the camera will not operate the lens' aperture properly. Keep in mind that there are a few other considerations ...


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