Why do a majority of still cameras only have one tripod hole?

Previous answers have already suggested acquiring an Arca Swiss style dovetail adapter plate, typically made from aluminum, that is formed with a ridge or lip that mates with the body of the camera for a distance of typically around 2 inches (50-60mm).

This width of engagement of the ridge or lip against the body of the camera, combined with the screw point mounting hole that the adapter plate is affixed to the camera with, serves to eliminate rotation between the camera and the adapter.

Naturally, the adapter must be formed to fit the camera body, so these adapters are specific to the model of camera that you have.

To solve rotation or wiggling between the adapter and the tripod, an Arca Swiss B style dovetail head must be used on the tripod. Here again, the physics that stops wiggling and rotation is that 2 or so inch length of engagement that the machined dovetail plate (mounted on the camera) and receiver (mounted on the tripod) affords.

As you pointed out, a single point is a pivot point. But multiple points in a rigid line, and in the case of this dovetail plate engagement, two rigid lines, cannot rotate. This is why the Arca swiss B style dovetail plate arrangement is so popular among serious photographers.

Arca Swiss is a brand, but like the Xerox brand is to photocopying, or the Google brand is to searching… there are many brands and manufacturers to choose from when it comes to selecting a dovetail plate formed for your particular camera. I personally use the Really Right Stuff brand, but I’m not mentioning this to promote that brand… I merely mention this as a way for you to find a catalog online to visualize the variety of plates and tripod heads that just one US manufacturer makes. There are plenty of other, often cheaper, typically imported brands to choose from as well.

Previous respondents also mentioned L plates in passing, and this deserves more detailed discussion as L plates offer a significant step up advantage over just an adapter plate. A formed L plate, combined with a quick release head on the tripod, can make changing from portrait to landscape mode a snap, while maintaining close to the same framing.

If a traditional screw mount multi axis tripod head is used, and you want to switch from portrait to landscape, a lot more additional adjustments might be necessary to compensate for the change in framing when the camera is “swung down and to the side”.

An L plate, combined with a quick release head, can with some cameras be designed and positioned such that the center axis of the lens remains unchanged when the camera is quick released from its’ horizontal position and remounted in its’ vertical position.

Again, this can be camera and L plate dependent, but it is one of the design goals of quality L plate manufacturers, that is sometimes undermined by data access ports for tethered shooting… which explains why it all depends on the specific model of camera.

Be that as it may, having an L plate adapter is still vastly more utilitarian than just a bottom plate adapter, because the L plate also affords additional attachment points for accessories.

For example, if you want to mount an on camera light, that is off axis from the lens, the hot shoe for the flash generally isn’t strong enough to cantilever a light source off axis while remaining hand held… but an L plate, combined with various brackets attached to the L plate, can hold a light 3 feet up in the air above the camera, or 18 inches off to the side of the camera, if you wanted. The hot shoe would rip out, but the dove tail plates formed as part and parcel to the L plate can tolerate significantly more clamp load and leverage.

So while the foregoing response mainly served to clarify and augment the ideas that you’ve already been given (adapter plate and L plate), I’d like to introduce to you another way to support your camera, especially when using long lenses.

Long focal length lenses often have their own lens foot, and there are dovetail adapter plates that mount to these lens feet as well. As with camera mounting plates, lens mounting plates have an anti rotational feature incorporated as well. For the really long lenses, whose feet have more than one hole, the adapter plate takes advantage of the secondary hole in the lens foot.

But for shorter or more compactly designed (diffractive) long lenses with only one mounting hole in the lens foot, the adapter plate will have a ridge or lip that will engage along the fore or aft width of the lens foot. Some lens feet have curved edges, and in those cases, the adapter plate might have a couple of machined holes with allen head cap screws placed in them, and the round sides of these two cap screws are what engage with the radius edges of the lens foot.

Because there are two screws, there is no pivoting, because two points make a line, and we actually have three points of engagement when we remember that there is still the mounting screw that holds the adapter plate to the lens foot.

So why would you use a lens foot to mount the camera on a tripod rather than screw hole under the camera? For two reasons:

  1. Better weight balance. Good glass is heavy, and the weight of a long lens can easily outweigh a still camera. The lens foot is positioned such that center of gravity can be optimized with the camera clicked into the lens, which provides the optimum balance for not only tripod mounting (reducing inadvertent lens droops and tilts), but also for hand holding.

  2. Instantaneous portrait to landscape orientation changes while maintaining the same lens axis. Since the lens is rotating within the lens collar that incorporates the foot, the camera body is just along for the 90 degree rotational ride, and nothing changes in the central area of the frame. Because the entire rig is supported by the lens foot rather than the camera body.

Lens feet, and their adapter plates, tend to be longer, which provides more opportunity to fine tune weight balance in a dove tail grip system, because you can slide the plate within the receiver fore and aft until the balance is optimal.

All of the foregoing applies to both still photography, and videography using DSLR form factor camera bodies.

When I worked as a photographer (now retired), I mounted the longest dovetail lens feet I could find on my lenses, and mounted more stuff to the unused length, like radio transmitters for remote cameras, light triggers, pistol grips, reflectors, etc.

I think you asked a GREAT question, which is why I took this time to respond. Why don’t manufacturers include anti rotation holes in traditional body style SLR camera bodies. There is no reason why they couldn’t, so any answer to that specific question of “why” would amount to speculation and opinion.

So I endeavored to answer with ways you could solve the problem of “wiggling”, as you described it. And believe me, when mounting remote cameras suspended up in the rafters of an arena with thousands of people below, we don’t want any “wiggling”. I found that the dove tail mounts were secure and confidence inspiring in my set ups, and I think you will too.

authentication – seems like a wide gaping hole in the process for checking integrity of e.g. linux distro releases

Many linux distributions recommend using downloaded signing keys to verify the integrity of downloaded checksums. This seems utterly retarded to me, since the downloaded keys are just as suspect as the downloaded checksums. And checking key fingerprints is exactly the same thing, ie the page with the fingerprints is just another file downloaded by my browser.

Example: https://getfedora.org/en/security/

If I trust the PKI of my browser (assuming https) to authenticate the key or key fingerprints, then I dont need the signing process in the first place. But of course I DONT trust the PKI because the list of root certs distributed with major OS’s is chocked full of very very dodgy CAs.

At minimum, shouldn’t the keys of a new release be signed with the keys of the previous release? That way you can maintain a chain of integrity.

Given that the same process is used for GPG: https://gnupg.org/signature_key.html
I assume I am being a moron and missing something obvious. Can anyone explain?

algorithms – Filling a hole in an image in O(nlogn)

I have a grayscale image (given by a float matrix with values between (0, 1)) with a hole in it (a cluster of pixels/cells with values of -1).


The boundary of the hole as all the cells that are 4-connected to a hole pixel (a pixel with -1 value) (you can read more about pixel connectivity here: https://en.wikipedia.org/wiki/Pixel_connectivity).

I(v) is the color of the pixel v.

I need the fill the hole using this formula:

Denote the boundary with B. So for each u – hole pixel:

I(u) = frac{Sigma_v{_in}_B w(u,v) * I(v))}{Sigma_v{_in}_B w(u,v)}

Where w is some arbitrary weighting function (for example using euclidean distance)

w(v,u) = frac{1}{|| u – v||}

Denote the number of hole pixels with n, the naive solution will be O(n^2), since for each hole pixel, we sum over all boundary pixels (and the upper bound for the amount of boundary pixels is 4n, of course).

I was told a solution could be achieved in O(nlogn), but I couldn’t think of anything even close to that.

I thought of doing some bitwise operations, but I reached a dead end. I also tried reusing computations, but I couldn’t find any.

Moreover, the way I see it, there’s no avoiding calculating w(u,v) for the n^2 pairs of hole/boundary pixels – which is already more than O(nlogn).

What am I missing? Could you point me at the right direction?


The Medicaid Black Hole That Costs Taxpayers Billions – General Forex Questions & Help

Here’s some cheerful news: States and the federal government are doing little to stop a costly form of Medicaid fraud, according to a government report released last week.

Medicaid, the federal-state health insurance program for poor Americans, now covers more than half its members through what’s known as Medicaid managed care. States pay private companies a fixed rate to insure Medicaid patients. It has become more popular in recent years than the traditional “fee for service” arrangement, in which Medicaid programs reimburse doctors and hospitals directly for each service they provide.

Despite the growth of managed care in recent decades, officials responsible for policing Medicaid “did not closely examine Medicaid managed-care payments, but instead primarily focused their program integrity efforts on [fee-for-service] claims,” according to the Government Accountability Office, the investigative arm of Congress. The managed-care programs made up about 27 percent of federal spending on Medicaid, according to the GAO. The nonpartisan investigators interviewed authorities in California, Florida, Maryland, New Jersey, New York, Ohio, and Texas over the past 12 months.


polygon clipping hole concept

I am using @Angus Johnson’s clipper library for finding unions for bunch of shapes. The shapes length & breadth are manhattan – parallel to x & y axis respectively.

After performing union operation I get this result:

4 (IsHole: 1, IsOpen: 0, lvl: 2)

-494940 1088000
-494940 930000
-495940 930000
-495940 1088000

4 (IsHole: 1, IsOpen: 0, lvl: 2)

-494940 1778000
-495940 1778000
-495940 1882000
-494940 1882000

14 (IsHole: 0, IsOpen: 0, lvl: 1)

784060 3140000
784060 1948000
-14940 1948000
-14940 1777000
-15940 1777000
-15940 1907000
-495940 1907000
-495940 1939000
-845940 1939000
-845940 63000
-844940 63000
-844940 0
3584060 0
3584060 3140000

From the link – the holes should be counter-clockwise which is not seen here in the verbose result.

I am using the wrapper from: https://github.com/abetusk/clipcli

What am I understanding wrong ?

dnd 5e – What options are available for a portable hole owner?

The portable hole can be opened by two people, holding it open like a sheet.

No, it can't. the portable hole(DMG, 185) emphatically states:

You can use an action to unfold a portable hole and place it on or against a solid surface, after which the portable hole creates an extra-dimensional hole 10 feet deep.

Only one person can open the portable hole, whoever has it must use his action.

If even the smallest part of the tissue is opened, the portal is opened and the character can enter the extra-dimensional space.

This question also suggests a way to open the hole which is not included in the description. The only RAW way to use the portable hole is for a single character to use his action to unfold it completely.

The portable hole can be projected upwards and unfold on its way downwards, thus opening the gate.

For your last question, please refer to the original quote on the portable hole mechanical in that the article is to be placed on or against a solid surface. Throwing it in the air does not place it on or against a surface. Yeah, it might end up falling and landing on one, but that is not placing it.

dnd 5e – How fast would a floating Tenser disc go down if I pulled it out of a hole covered by a board, and then removed the board so that the disc fell?

It is not clear, as the rules as written (RAW) do not deal with this.

In this situation, a Tenser's floating disc floats above a surface, and the surface suddenly becomes a hole. Unfortunately, the rules provide no indication of exactly what will happen next, as the disc should not be above a hole more than 10 feet deep.

The mechanics of the spell suggest that it was not intended for this scenario, as it "normally floats 3 feet above the ground" and "can move on uneven ground, go up or down stairs , slopes and the like, but it cannot go through an elevation change of 10 feet or more. "

The spell description does not specify a speed for the speed at which the disk moves, horizontally or vertically. The disc itself is a "horizontal force plane", which may or may not mean that the plane is fixed in place.

There are therefore different possible results, depending on the interpretation:

  1. The disc is not stationary and would therefore fall like any other object affected by gravity. It falls until it floats 3 feet above a surface or exceeds the maximum distance of the caster.

  2. The disc is affected by gravity, but "cannot go through a change in elevation of 10 feet or more". If the hole is more than 10 feet deep, the disc stays in place. Otherwise, the disc will fall, as described above.

  3. The disc is a magic force, and therefore gravity does not apply, so it remains hovering.

Ultimately, the DM should decide what is going on.

discrete mathematics – average of the application of the pigeon hole principle

Arrange 0-9 on the circular table
There is a section where the sum of three adjacent numbers must be 14 or more

I know we can solve this problem using the pigeon hole principle

I know the dovecote is number 10
I want to know why we have to add 0 + 1 + .. 9 = 45 x 3 = 135

And divide it by 10 = 13.5

Is this the right way to solve this problem? If yes, I want to know why we have to find the average?

Obtain a clear image for a paper with a 7.62 mm hole located at 50 m

I'm going to assume that you only want to count the holes on a paper target and know their approximate location.

7 mm at 50 meters is 0.008 degrees.

Then we have to make some assumptions about the camera. I will be using my equipment, a Canon 7D, APS-C (1.6 crop sensor), of around 5000 pixels on the long side.

I would like the holes to be around 10 pixels wide, this is an estimate of how important you need the holes in the camera frame.

10 pixels / 5000 pixels = 1/500 of the frame

0.008 degrees * 500 = 4 degree field of view

You can achieve this with a 400mm lens, these are fairly common and a decent good is $ 1,000 to $ 2,000. See this calculator.

Note that your field of vision will be 2.8 x 1.8 meters. It’s probably bigger than your goal. If you want the target to fill the camera frame, the calculation will be different.

Edit: test the image. 3.5 mm hole at 25 meters. I can't easily walk 50 meters.

Canon 7D, zoom 100-400 f5.6 M1 @ 400 mm, f8, remote flash.

enter description of image here

Zoomed to display the actual pixels:

enter description of image here

mp.mathematical physics – Is the Wikipedia representation of the ergosphere of a black Kerr hole a Cassini oval?

Warning: this is a cross article from MSE, where this question was asked on November 4, 2019 and has so far received no positive votes, no comments, and no responses. .

By taking a look at https://en.wikipedia.org/wiki/Rotating_black_hole (revision in progress), I thought that the boundary of the ergosphere appearing in the photo at the beginning of the article considered looks very much to a Cassini oval. Is it really one? If so, how do you prove it?