After I bought Sigma 150-600mm f5-6.3 Contemporary DG OS HSM Lens I ran some tests. This test was to see the difference in focal length compared to a crop sensor lens vs this full frame lens on a same Crop Sensor body.     Since it's a full frame lens - it s/b equal to 240-960 MM on a Canon Crop Sensor. However when I did the side by side comparison of Canon EF-S55-250mm vs Sigma 150-250mm C, I found that they have identically same field of view and the composition fills up the same too.  I was expecting Sigma to be closer to subject than Canon 55-250mm at the same focal length (150 at sigma, 146 at Canon) . Applying the crop factor of 1.6, Sigma should have given me a field of view of 240mm however it does not.  Please take a moment and look at the video here, I've done side by side comparison.
I have a Canon 7D, which has a crop factor of 1.6x.  When using a Canon EF-S lens I get the focal length stated on the lens, when using a Canon EF lens I get the focal length times 1.6 when used on the APS-C body. At least that's what I thought.  I just compared two lenses:   Canon EF-S 15-85mm f3.5-5.6 Canon EF 70-200mm f4   .  The top photo is shot with the 15-85, the bottom photo with the 70-200 - both lenses are set to 70mm. Now why do they look the same?  I thought I would get 112-320mm (70mm*1.6 crop factor). What did I misunderstand about the crop factor calculation? Lightroom also displays the photos as having "70mm" and not 112mm.
How can I find more music similar to the ones I like? Difference between Hashing a Password and Encrypting it A "failed to fetch" error occurs when apt-get update is run. How do I fix this? Under , is $\exists x(x=a)$ true in every interpretation in first order logic (FOL) with equality? If so, could $\exists x(x=a)$ be considered a tautology? This question was motivated by  which was closed for lacking clarity. Here I have attempted to add that clarity myself so that the same question can be useful to others who are wondering a similar thing. This is a self answer question. Can toddlers be taught to safely navigate stairs? Are there other schools for witches and wizards in the rest of the world? In the books they only speak of 3 schools, but what about Asian or American people?  And even more, were they affected by the events happening in Europe? Ubuntu 18.04 No WiFi adapter found [Dell Inspiron 3542.] Is it bad to defrag a ssd? Or just pointless? I've read on some websites that it's bad to defrag an ssd. But I'm reading on this website now and one person was like "You didnt do any harm its just not necessary to defrag it." I feel like that's wrong since every other website I've read says it will damage the ssd. is $y = \sqrt{x^2 + 1}− x$ a injective (one-to-one) function? I have a function  $y = \sqrt{x^2 + 1}− x$ and I need to prove if it's a Injective function (one-to-one).  The function f is injective if and only if for all a and b in A, if f(a) = f(b), then a = b  $\sqrt{a^2 + 1} − a = \sqrt{b^2 + 1} − b$  $\sqrt{a^2 + 1} + b = \sqrt{b^2 + 1} + a$  $(\sqrt{a^2 + 1} + b)^2 = (\sqrt{b^2 + 1} + a)^2$  $a^2 + 1 + b^2 + 2b\sqrt{a^2 + 1} = b^2 + 1 + a^2 + 2a\sqrt{b^2 + 1}$  $2b\sqrt{a^2 + 1} = 2a\sqrt{b^2 + 1}$  $b\sqrt{a^2 + 1} = a\sqrt{b^2 + 1}$  $(b\sqrt{a^2 + 1})^2 = (a\sqrt{b^2 + 1})^2$  $b^2(a^2 + 1) = a^2(b^2 + 1)$  $b^2a^2 + b^2 = a^2b^2 + a^2$  $b^2 = a^2$  $\sqrt{b^2} = \sqrt{a^2}$  $b = \pm a$  then the function is not injective because $b$ in not equal to $a$, but using online  the function is injective. My server is constantly being attacked I am fairly new to the system administration world. I've been working on an application recently and when I check my application server logs, I constantly get various IP addresses trying to ssh into my server by brute force. Here is an example of my server log:   Feb 14 04:07:20 foodwiz3 sshd[1264]: error: Could not load host key: /etc/ssh/ssh_host_ed25519_key Feb 14 04:07:21 foodwiz3 sshd[1264]: reverse mapping checking getaddrinfo for coenamor.columbiansabbatical.com [23.249.167.223] failed - POSSIBLE BREAK-IN ATTEMPT! Feb 14 04:07:21 foodwiz3 sshd[1264]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=23.249.167.223  user=root Feb 14 04:07:23 foodwiz3 sshd[1264]: Failed password for root from 23.249.167.223 port 32997 ssh2 Feb 14 04:07:23 foodwiz3 sshd[1264]: Received disconnect from 23.249.167.223: 11: Bye Bye [preauth] Feb 14 04:13:04 foodwiz3 sshd[1289]: error: Could not load host key: /etc/ssh/ssh_host_ed25519_key Feb 14 04:13:05 foodwiz3 sshd[1289]: reverse mapping checking getaddrinfo for coenamor.columbiansabbatical.com [23.249.167.223] failed - POSSIBLE BREAK-IN ATTEMPT! Feb 14 04:13:05 foodwiz3 sshd[1289]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=23.249.167.223  user=root Feb 14 04:13:07 foodwiz3 sshd[1289]: Failed password for root from 23.249.167.223 port 41562 ssh2   Is this something that is fairly normal, or should I be worried/doing something about it? How to find all the available tools in mac terminal? I am trying to setup a bunch of development projects in my Mac. I have to run various tools like python, ruby, scala, groovy etc.  To see if a tool is available I use options like   ruby --version.    Instead I would like to see all the list of tools available in Mac terminal via a single command. What is the command/options for it? How to extract code of .apk file which is not working? Given two separate annulus with centers $[C_1,C_2]$ and their corresponding radii being $[R_1,r_1]$ and $[R_2,r_2]$ respectively, larger radius being $R$. There are methods to look at whether they are overlapping or not. If they overlap how to find the overlapping area. Is there any close form expression for it?  equation of first annulus   $r_1^2&lt;(x-x_{c1})^2 + (y-y_{c1})^2 &lt;R_1^2$   equation of second annulus  $r_2^2&lt;(x-x_{c2})^2 + (y-y_{c2})^2 &lt;R_2^2$  If there are three circles overlapping, we get overlapping area as solution to set of 4 in-equations by least squares approach(Though we don't end up getting total area but, area within tangents of circles ). Lubuntu 16.10: How to make login through greeter without typing password work How is hotness score calculated at larger sites? To start with, I am aware that hot questions from larger sites are somehow "penalized" and :     This is designed to ensure that a single site doesn't dominate the list, and that users see a good sampling of questions that are likely to interest them throughout the network...   I would like to understand how is hotness score really calculated at these sites. The reason why I ask is that per my observations, this seems to be quite different than is documented in the . Specifically, I would like to understand the difference in the impact of answer(s) score and aging factor.  Regarding impact of answers score, my observations of hot questions from smaller sites appear to be in agreement with known formula: (MIN(AnswerCount, 10) * QScore) / 5 + AnswerScore. For example, a question with low score (+1, +2) can get into hot list if it has got answer(s) with sufficiently high score.  At larger sites, this doesn't seem to be the case. Say, it looks like Stack Overflow questions just don't enter hot list until they reach certain score (+6,+7), no matter how many answers are there and how high is their score.  Does system simply totally ignore answers until question reaches certain score?  Another thing I noticed is that questions seem to age away from the hot list 2-3 times faster than ones from smaller sites (having comparable question and answers scores). Granted, this is harder to track and I am not yet sure if I figured that correctly. Do larger sites questions age away faster than those from smaller sites?    For those interested, here is a (partial) list of example questions I studied before asking this: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , .  Although above examples are only from Stack Overflow, my question isn't (I only used it as an example of a large site in my studies). I would like to understand if hot questions from other larger sites are handled in a similar way. Java, pointer like way to program this I ran into something a couple of weeks ago that I'd never seen before: A filesystem (ext3 I believe) installed to a storage device without a partition. In essence /dev/sdb was the entire filesystem. I know many filesystems can be extended into empty space, so doing this allows extending without dealing with LVM or some other kind of volume manager, but are there any other advantages for setting up storage this way?  The specific case I saw was as the ephemeral data volume for a number crunching server, the boot and root volumes were traditional partitions on a different storage device entirely. - Why on the first page Google says there are thousands of results but on the last page there are less than a hundred? How to find the working folder of a servlet based application in order to load resources Chain wire methods together in Lightning Web Components According to the documentation  in order to retrieve a list of picklist values for an object we need to pass in a Record Type Id which can be retrieved using the getObjectInfo method.   The issue is that these are both wire functions and I cannot figure out how to chain these methods.  If I try code like the following:  getObjectInfo({ objectApiName: ACCOUNT_OBJECT })             .then(result =&gt; {                 return getPicklistValues({recordTypeId: result.defaultRecordTypeId, fieldApiName: TYPE_FIELD});             })             .then(result =&gt; {                 this.picklistValues = result.data             })             .catch(error =&gt; {                 this.error = error;             });   I get an error      render threw an error in 'c:getpicklistexample' [Imperative use is not   supported. Use @wire(getObjectInfo).]   If I try something like   @track rtId;      @wire(getObjectInfo, { objectApiName: ACCOUNT_OBJECT })     handleResult({error, data}) {         if(data) {             this.rtId = data.defaultRecordTypeId;         }     }      @wire(getPicklistValues, {recordTypeId: this.rtId,fieldApiName: TYPE_FIELD})     picklistValues;   Then it throws an internal server error. Anybody have an idea as to how I could retrieve the record type Id and then call to get the pick list values like the documentation suggests?  FYI my imports are:  import { LightningElement, wire, track } from 'lwc'; import { getPicklistValues, getObjectInfo } from 'lightning/uiObjectInfoApi'; import TYPE_FIELD from '@salesforce/schema/Account.Type'; import ACCOUNT_OBJECT from '@salesforce/schema/Account';