Optics – What is the difference between a pentaprism and a pentamirror?

The basic difference is that a pentaprism is a solid block of glass. That said, it's pretty difficult. It has mirror material on all but two sides, so that the light enters on one side, is reflected on the inside and then exits on the other non-mirrored side. This means that only two air / glass interfaces are involved: one where light enters the prism and one where it leaves the prism. This reduces the loss of light to a minimum.

A penta mirror does pretty much the same thing, but it consists of several separate mirrors, so there is air in the middle instead of a solid glass block. This makes it much easier and less expensive. This also means that there is an air / glass interface for each individual mirror, so that the loss of light increases considerably.

As a result, a penta mirror is used almost exclusively in relatively simple cameras, where reduced cost and weight are more important than a relatively poor view through the viewfinder.

stochastic processes – what is the difference between a logarithmic random walk and a geometric Brownian motion?

I am trying to do some research on modeling asset paths and have difficulty understanding how the stochastic differential equation dS = S (σdX + μdt) is classified.

I know that it's a logarithmic random run and that dX is a stochastic process, but I've also seen that this equation is a Brownian geometric motion. I'm confused here because I don't understand the explicit difference between a logarithmic random run and a geometric Brownian motion, or how this equation can be both!

Any help is greatly appreciated and apologizes if any of the above is wrong :))

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Entity Framework – The difference between ORM and stored procedures

When developing my web application, I was asked the following question: What would be the difference between using EF, ADO.net with Linq, or stored procedures in CRUD methods? Apart from the differences in performance that I would like to test myself, I am curious to see what scenarios people choose from each other. Is it a matter of context or just personal preference?

In addition, after doing some research, I read that some ORMs use stored procedures. It is not entirely clear to me which ones do this and how it works. Is it also better to use an ORM with stored procedures?

Therefore, I ask for help comparing ORM frameworks and stored procedures, both conceptually and in terms of usability.

EDIT: I appreciate any feedback, be it positive or negative. But if you have the time to read and vote on this post, you can also help a newbie with advice on what he did wrong.

Time machine – display the difference between APFS snapshots


APFS is amazing … and annoying about the lack of tools available.

What I'm trying to do is just an equivalent of btrfs send --no-data -p /snapshots/parent /snapshots/child

My investigation

  1. Most Google Fu returns uses of tmutil
    • tmutil is capable listlocalsnapshots /. deletelocalsnapshots /. localsnapshot (create)
    • tmutil compare does not accept 2 snapshots
    • tmutil compare EXISTING_SNAPSHOT Returns cryptically and without papers Must specify a snapshot root when performing a machine comparison.
    • tmutil calculatedrift does not seem to have anything to do with APFS snapshots
    • tmutil includes some undocumented options, but nothing related to snapshots
    • Snapshot created by tmutil hard coded com.apple.TimeMachine.YYYY-MM-DD-HHMMSS.local Name format
  2. diskutil Contains limited support for snapshots

    • diskutil deleteSnapshot works as intended
    • diskutil listSnapshots List snapshots with sizes and some metadata (as opposed to tmutil)
    • No way to take snapshots
  3. Contains kernel fs_snapshot_* System calls

    • The documentation is almost nonexistent, but only one man Page is available
    • All usual operations (fs_snapshot_delete /. fs_snapshot_list /. fs_snapshot_create /. fs_snapshot_mount) are supported
    • GitHub ahl/apfs hosts a small utility that demonstrates the use of syscalls
    • fs_snapshot_list list just com.apple.TimeMachine.* Snapshots
    • All writes (e.g. fs_snapshot_create) ends with the application being killed fs_snapshot_create: Operation not permitted (probably because of the reason documented in the man: "You need an additional claim")
  4. The commercial Carbon Copy Cloner app can edit snapshots

    • For obvious reasons they do not disclose how they do this;)

Help? 😉

Is there a way to get a difference between two snapshots? Is there any documentation on how to manage it?
The only naive approach that cannot be implemented due to the speed is running rsync between r / o mounted snapshots … but that's just stupid.

What is the difference between the Photoshop RGB curve and the Lightroom RGB tone curve?

I am very confused with the following situation. Let's say we have an image with two colors: (RGB 0.60.60) and (RGB 255.0.0).

(RGB 0.60.60) and (RGB 255.0.0)

I noticed that the tone curve works differently in Adobe Lightroom than in Photoshop. What I understood is that Photoshop's RGB curve resets the tonal values ​​of each color channel to the new values ​​determined by the curve. For example, if we make the following change to the curve:

Curve change in Photoshop

The left color, which was now (RGB 0.60.60), is (RGB 0.0.0) because the value 60 has now been reassigned to 0 in both the green and blue channels.
The correct color (pure red (RGB 255.0.0)) has not changed at all since we have not shifted the point of the curve that corresponds to 255.

What confuses me is that something different happens in Lightroom with the same change in tone curve.

Straight curve in Lightroom
Curve change in Lightroom

Now the red color (RGB 255.0.0) has turned to black (0.0.0), but I haven't moved the point that corresponds to 255. I also know that Lightroom uses the ProPhotoRGB color space and not sRGB.
But in general I don't understand exactly what happens when I change the curves and why Photoshop and Lightroom make different changes. I found some other similar questions in Photo.Stackexchange, but they didn't help me.
Can someone please explain to me what exactly happens in detail?

Thank you in advance.

Lens – Is the focal length range the only significant difference between Canon EF-S 18-135 IS and 18-200 IS lenses?

As you have already noticed, they are more similar than different.

One of the most conclusive information for comparing the two can be found in the test of the EF-S 18-135 lens on the digital image:

While the focal length range is shorter than that of the 18-200, the 18-135 is cheaper and has an image quality that is similar or slightly better in sharpness and distortion.

I would look at the ratings of both lenses to find which one suits your style and price range better:

It is unclear why Canon introduced both lenses in 2008/2009. I would guess that the difference in price is the main factor that many people consider. The 18-200 costs around $ 600 and the 18-135 costs around $ 350 – that's quite a difference for most people. I would consider which one fits your budget and buy it accordingly.

This is a direct comparison of the IQ of both lenses at 18 mm wide open: the-digital-picture.com

As others have commented on, other options may be better, e.g. B. the purchase of a 70-200 mm 1: 4 without IS or a 50 mm 1: 1.8. The possibilities are endless, but I will keep this answer and only focus on what you specifically ask.


For me, the 18-135mm is a bit better IQ at a lower price. So if I only looked at these two lenses, I would choose the 18-135mm.

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