# Tag Info

6

There's a reason no one makes even a 24-200mm FF lens. Several, in fact. The main one is that not many photographers who know what they are doing would ever consider buying such a lens for a FF camera, particularly for one with as high resolution as most FF cameras offer in 2021. To get anywhere approaching a constant, usable aperture the lens would be very ...

5

I am assuming that if I use a shutter of a smaller diameter than the lens, the properties of the lens will change (for example, it will become less fast), because of the smaller aperture ring behind it? That is not necessarily the case. The physical size of the aperture is (almost?) never the same size as the objective lens element; because its physical ...

5

When using an EF-S lens on any of the current EOS R series of cameras, only the center 22.5 x 15 millimeters or so will be used to contribute to the image. This is because EF-S lenses only project an image circle large enough for a sensor with a diagonal of around 27mm. That's a linear reduction by a factor of 1.6 from the dimensions of a 36 x 24 millimeter ...

3

Well, the subject area you indicate does look like you may have photographed it through glass (from inside a room to outside). But that aside, most of the "frosted glass" look you see here is noise reduction/interpolation. Sensors in phones are small and comparatively noisy (particularly in limited light) but the processing power in phones makes ...

3

f/4.5 doesn't mean that the hole in the iris is physically 1/4.5 times the focal length. It means that the size of the image of the hole, as viewed from the front of the lens through the lens elements in front of it, is 1/4.5 times the focal length. The image of the hole is the entrance pupil. If you can, look at the image of the hole from the front as you ...

3

Angle of view is determined by (real) focal length and sensor/film size. That's your starting point. AoV=2*arctan(d/2f) where: AoV is the Angle of View d is the size of the sensor/film in the direction measured f is focal length (in the same units as d) For a circular hood you would use the diagonal measure of the sensor/film For a "petal" hood ...

3

After returning that lens and buying the new one, I can conclude with confidence that the first lens was definitely defective. This new lens is not perfect either, but it performs much better. You can see those ghosting flares are going up and a bit to left, but the effect is less noticeable. The focus on both images is the best I could get - at infinity. ...

3

Why do mirrors give less sharpness, gamut, and contrast than lenses? Mirror lenses can be made more cheaply, because the number of surfaces are smaller and typically thinner than in refracting lenses. This results in a "race to the bottom," where lens manufacturers start doing all sorts of things to make their inexpensive design even cheaper. You ...

3

I am looking for such lenses as well. In general putting the aperture at the front or outside is avoided because not good; best is to put the aperture more or less in the center of the objective. With the aperture in front you'll have more aberrations and/or need bigger and more expensive design. Only in two cases the front aperture design is used: if the ...

2

In the "ideal" pinhole camera (pinhole infinitely small), everything is always in focus, because point source of light in the universe outside the camera, the pinhole and the corresponding image point on the film/sensor/back are colinear. In other words there is a single path for light rays between the source and the image, so there is no need for ...

2

"because if the focal point, the point as I understand it to be where all the light converges, was on the film plane, an image wouldn't be rendered, it would just be an indistinguishable point of light." This understanding is incorrect... at all points on an objective lens exists all of the light required to form an mage (a portion of the total). ...

2

Short lenses are often "retro-focus", meaning that their focus node (which your diagram shows) is designed to be well behind the actual lens body, to allow room for a mirror to rise. In a similar manner, the word "telephoto" means that lens design puts that node in front of the lens (specifically to make the lens body be shorter than its ...

2

Since lenses work based on the difference of index of refraction across the interface as well as the curvature of the lens surface (the more the difference in I.R., the more the light rays are bent) putting a higher I.R material between the rear element and the sensor would reduce the effectiveness of the lens. You could incorporate that into the design of ...

2

No. Putting aside the engineering issues with designing a zoom for such a large range, I'd like to put forth a frame challenge: What do you think you want a 2600mm lens for? DSLR lenses of longer than 400mm are generally regarded as "exotic" because of their limited utility. Lenses up to 800mm or so are attractive for wildlife photography, airshows,...

2

A hat is the stylish photographer’s traditional front of lens shutter (and lens shade) though a press fit lens cap with a handhold in the center provides better control. Of course low sensitivity film/sensor and narrow apertures are needed when photographing in bright light due to the slow shutter speed. Packard shutters are a pneumatic alternative that can ...

2

I swapped the EF-S mount on the 10-18mm STM for a metal EF mount from Ebay. It took 5 minutes to unscrew the plastic EF-S and screw on the EF metal mount. You can then use it on the 6D, 6Dii, and 5Div - everything works with no crop. The image circle covers a FF sensor from 12mm-18mm, with good coverage for video from 14-18mm. I've read that the Tamron ...

2

There are two different variables in play here: focusing distance and object distance. Chromatic aberration correction is with some priority employed to stop colored fringes to appear when focusing on infinity: when everything is in the "default" out-of-focus situation, colorful fringes are really undesirable. A similar reverse "default"...

1

The job of the lens is to project an image of the outside world on the surface of film or digital sensor. To do this job, light rays from the subject traverse the lens and the shape of the lens surfaces and the density of the lens alter their travel path. In other words, the lens acts a light wave guide. The focal length is a measure of the distance, lens to ...

1

If all of the magnification takes place between the front of the lens and the physical aperture when you zoom, then the entrance pupil, which is the effective aperture that is actually used to calculate f-number, also grows by the same ratio as the focal length. As you zoom to longer focal lengths the size of the aperture as it appears through the front of ...

1

As you know, the focal ratio (f-number) is calculated by dividing the working focal length by the working iris diameter. Therefore, these fundamental values are intertwined as to their influence on image brightness (exposure settings). The bottom line, as you zoom, image brightness rises an falls significantly. In fact, double or halving the focal length ...

1

I will make a bunch of assumptions along the way along the lines of my comment. If I guess wrong, I hope you can adapt the calculation. Let us assume the camera is pivoted to the left so the 4m you want to see is equally split across the centerline of the frame. I will also assume the 4m is across the middle of the frame vertically. If the height of the ...

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I believe I now see the confusion (sorry, slow on the uptake). Most lens and imaging diagrams do indeed give the impression that all the light comes to a point at the focus point, it's even in the name. However that's not what is actually happening. The smallest point of light is actually an image, not a point. The focal length of a lens refers to the fixed ...

1

The focal length of a lens is a measurement taken when the lens is imaging a far distance object like a star. If the lens structure is a single symmetrical (convex – convex) then this measurement is taken from the center of the lens to the focused image. A distant object is at an infinite distance when its light rays arrive at the camera lens as a bundle of ...

1

Don't confuse formulas meant to be used with refractive optics (i.e., lenses) with projection mapping functions (such as the pinhole projection model). That is, the Wikipedia formula you found has nothing to do with your question. The thin lens formula only applies for refractive lenses, such as glass elements that bend light. The thin lens formula is really ...

1

It's all about etendue. The maximum amount of light available for an exposure is determined by the system etendue, which defines how spread out the light is. Etendue is defined by the angular extent (apparent/relative size) of the source/subject as seen by the objective element. And it is simultaneously/equally the angular extent of the objective element as ...

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Bit of a zombie thread but in case anyone else is looking here ... The Yashica Mat has a 4 element taking lens. The rear two elements are cemented together. They screw out quite easily from the back (provided you have a lens spanner). The front two elements are not cemented together and have an air gap that means fungus can grow in between. Once you screw ...

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