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14

What is the purpose ... for the existing convention? Math. It's because in many equations regarding simple optics, the ratio N = ƒ/D (where N is the ƒ-number, and D is the lens (or more often precisely, entrance pupil) diameter) pops up a lot, or the use of the ratio simplifies the expression or understanding of the expression. Example 1: The hyperfocal ...


6

Note whether there are any symptoms that indicate the elements may be out of order, flipped, or misaligned. There are other reasons lenses may not focus as expected that aren't related to elements being misplaced. Focus may need to be calibrated. The lens may be soft wide open. Draw the lens diagram, as you have it. This can serve as a reference if you ...


5

A similar aperture numbering system called the U.S. system (Uniform System) was used by the first Kodak cameras (until around 1920s). That system originated in England (1880s). Not 1, 2, 3, 4, but those stops were numbered 1, 2, 4, 8, etc, starting from todays f/4 equivalence. It was more useful than 1, 2, 3, 4 because it represented exposure increase ...


4

It certainly depends on whether or not your lens manufacturer supports this officially or has planned for people using it. Some mechanisms won’t be pushable, which means you might break them when attempting to do this. You could always send a mail to the specific lens manufacturer and ask them about it. I would not recommend doing it for any lens that’s ...


4

It takes a LOT of damage from scratches or fairly sizeable obstructions before they become noticeable! These photos from Roger Cicala's blog entry at lensrentals.com illustrate just how far a lens can be damaged or obstructed with very little impact on image quality. Although it is true that the coatings on the surfaces of lens elements that face other lens ...


4

This question is five years old but I do have the correct answer. The original Canon EF 80-200mm f/4.5-5.6 did not have a provision to mount a lens hood so there is no designated lens hood for it. One solution is to use a generic 52mm screw in lens hood. A better solution is to use the Canon 62-L adapter which normally comes with the Canon ES-62 hood ...


3

I do something similar with my Sigma 100-400 zoom, it is normally a manual ring zoom but it's slow to operate that way in some cases, so I sometimes use it as a push-pull zoom when tracking fast moving subjects. What makes me think that it won't suffer from this is that it extends by itself fairly quickly when pointed downwards, and folds when pointed ...


3

Indeed I didn't see but one is C and the other is CS so that's why the extension tube of 5mm was working. One of your cameras is C-mount with 17.526mm registration distance, the other is CS-mount at 12.526mm. There is a 5mm difference in the registration distance of those two mounts. You need a 5mm extension tube to use your C-mount lens having a ...


2

Well to answer you Michael C, in owning about 400 lenses, knowing what company made a particular lens should have 'everything' to do with how said lens will be used photographically. Your comments seem to indicate a belief that all lenses make images the look the same. However, since every lens ever made has it's own unique look, I can't understand why a ...


2

It seems that the camera will be in a (fairly) fixed position, while the item you're photographing will always be the surface of a cylinder. The "distortion" in this case is not caused by the lens, but by the shape of the cylinder. The way scanners handle this problem is to scan a single pixel strip that runs the length of the cylinder. This would require ...


2

I suppose the least lens-distorted rectangular part of a shot is defined by the focal length of lens I'm using, but I'd like to know which part it is exactly, or at least how to calculate that part. I think you really need to start here: What is the difference between perspective distortion and barrel or pincushion distortion? ... because there are ...


2

The control ring is a third ring on the lens in addition to the zoom and focus rings (of course primes lack the zoom ring so they have only two rings: focus and control). The control ring typically has clicked positions, so it adjusts some camera parameter in steps. As a cost reduction measure, the RF 24-240mm superzoom lens has focus and control ring ...


2

I own the Canon 100mmf/2.8L macro, and I bought the 65mm MP-E, but sent it back after a couple of weeks. I love my 100mm macro, but personally, I found the MP-E was too difficult for practical use: there is no focus ring... you focus by moving the camera. This means a tripod and a focusing rail at a minimum. More gear than I was willing to carry for what I ...


2

I agree with user86418's assessment that Jerry Coffin's answer has this backward, though he in turn seems to have conflated numerical aperture with ƒ/number. Quoting outdoorphotographer.com In a variable-aperture zoom ... elements in front of and behind the diaphragm move (and the diaphragm itself moves), so the entrance pupil doesn’t vary in ...


2

To answer your question directly, there isn't a photographic reason why it would be shifted from the optical axis, other than packaging, electronics, weight placement, or other industrial design compromises that are specific to that camera or model line. But to fix the issue so that the optical axis intersects the axis of panoramic rotation, the easiest ...


2

This is possibly to achieve the most natural balance on a tripod(*). If you are using a ball head, to have the center of gravity over the head reduces the strain, and a small tripod, this also reduces the changes of the tripod tipping over. Of course the balance along the lens axis may be harder to achieve, but even then you have one single axis to consider ...


1

The tripod mount on the Canon G11 is located adjacent to the battery door for convenience and structural stability. I examined seven compact cameras (chosen for ease of access). Five of them have the tripod mount adjacent to the battery door. All of them have screws located near the mount. I examined three mirrorless cameras (also chosen for ease of access)....


1

For rectilinear lenses, the field of view is a simple similar-triangles geometry problem: The ratio of the distance to the subject a over the horizontal field of view b at the subject distance, is equal to the ratio of the focal length ƒ to the image sensor width w: ƒ/w = a/b Thus, ƒ = (w a) / b You didn't state any assumption explicitly, but I get the ...


1

https://en.wikipedia.org/wiki/Image_sensor_format#Table_of_sensor_formats_and_sizes offers a chart to determine approximate sensor size from the "1/x inch" descriptions. It may not be precisely exact, since a few sensors might all use the same description. Should be ballpark, close enough. Crop Factor is (43.266 / that diagonal) The 43.266 mm is the 35 ...


1

It's not very safe. The gears form a kind of a worm gear and you're putting the mechanism under much more stress when you push on the lens tube. This particular lens does not have tight tolerances to begin with and has some play in the mechanism, so it might not cause too much damage, but in the end, it will damage the lens. You will get wobble towards the ...


1

There is another option for extreme macro: the Laowa 25mm f/2.8 2.5-5x. I got this because I wasn't satisfied with the quality of the Raynox, and my Nikon camera is not compatible with the MP-E 65mm. It has comparable image quality to the Canon, and the depth of field is slightly better thanks to its shorter focal length. It is possible to handhold stacks at ...


1

My experience is about the same as Seamus, although I still have my MP-E 65mm. I haven't used the Raynox diopter, so I can't compare. It is unlikely that you will find someone who has used both. The working distance of the MP-E 65mm is very short, many subjects will not tolerate a lens this close. DOF is very narrow, to be expected at high magnification. ...


1

Observations: You are summing the values of each pixel, but your exposureAdjust() function assumes that after conditioning, each pixel will be in the range [0, 1). This is not correct. Assume a pixel's value in each of the 3 input images is, say, 50% full-scale (thus, 213 = 8192). Summing that three times yields 3 * 8192 = 24,576. Then the result after ...


1

In the overall scheme of Canon's EF lens system, any of the EF-S 55-250mm variants are pretty light. The STM version only weighs about 375 grams, and all of that weight is at less than 120mm from the lens flange when the lens is stored at its shortest length. Your camera only weighs around 532 grams. The same EF mount is designed to support cameras that ...


1

Your EF-S 55-250mm weighs about twice as much as your EF-S 18-55mm. When compared to most other lenses, it is still a very light lens, and there is NO WAY it will damage your camera. Store it any position you find most convenient. For me, the most convenient method is lens down in the camera bag. With the bag open I can grab the camera with one hand and be ...


1

The Canon EF-S 55-250mm f/4-5.6 IS STM is a light-weight lens made mostly of plastic. There should be no harm to your camera from the weight if you store it with the lens facing upwards. However, the LCD may be scratched if you happen to rest it on any grit. There is risk of scratching the lens if you place it face down in the bag without a lens cap. The ...


1

Fungal growth is less common in recent lenses mainly because the glue used to hold some lens groups together is no longer an organic compound made from the sap of the Canadian Balsam Pine, as it was for many years. Fungi need three things to grow: Moisture Organic material for nourishment Protection from UV rays


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