There are point-and-shoot cameras that offer large range of angle of view. For example, Nikon P900 with 24mm-2000mm.  How such lenses exist only in point-and-shoot and too at a very low price? Why does the same equivalent lenses in SLR cost very high?
This week I've read two news stories about two different camera lenses that can magnify things that are very far away.  The first is the , which is a point-and-shoot camera that costs $600, has an 83x optical superzoom lens ("the same field of view as a 2,000mm lens on a full-frame camera"), and lets you see the craters of the moon.  The second is the , which weighs 36 pounds, costs $180,000, and can take portraits of people a half mile away.  A non-photographer might ask, "Why would somebody spend their life savings on a gigantic telescope of a lens when you could take far away pictures with a handheld camera for 1/300th the price?"  Well, I am basically a non-photographer, and I would like to ask that question. What does the big one give you that the little one doesn't provide? I understand that small changes in lenses can make a big difference in size and price, but this seems to be of a different scale entirely.   What is going on with the optics of the lenses that makes the small one able to be so small and the big one have to be so...big?   I'm trying to get a basic intuition for what makes lenses different, and I realize I don't understand enough about how lenses work to even know how to compare these apples and watermelons.
Multiple returns from a function How can I make a div not larger than its contents? The message that appears in the reputation tab of a user's profile when they gain or lose reputation due votes disappearing when another user is deleted is simply:     user was removed   This message is confusing and unhelpful. Below are comments that demonstrate this confusion, . I don't have any quotes from the users who could not find it and remained confused.  There is , and . However, the message has not been changed.  I know that in the past the developers have been reluctant to direct users to meta in some situations, such as question bans, because it may cause users to post here appropriately. That does not seem to apply to this case. This is not typically a case of ""; most of us have probably seen the message at some point.  Why is this message vague and unlinked? What negative behaviour does this confusion mitigate?       My first interpretation was that I was the user who was removed!        I just simply wished the explanation on the reputation page was better. Seems like I shouldn't have had to come to the meta section to figure this out.        It must be better to show "User  was removed". For a moment I just thought that I was removed :-(        the information should be better. I lost 10 points yesterday by "user removed" and assumed that I was the one being removed, leaving me wondering why and feeling somewhat embarrassed.         The recalc policy is fine. But the red mark and "user was removed" looks cryptic and unnecessarily negative--especially since the only user name mentioned on a profile is one's own. So the natural impulse is to bind "user" to the account you're looking at. (It was jarring to me and I could tell what it meant, but still this could be clearer.) I agree that orange is better than red and ideally all of these things would have hyperlinks to a help page (or at least a meta post) explaining what the deal is.        +1 (to HostileFork) for the idea of linking to an explanation of 'User was removed'. It just took me 10+ minutes to find this particular thread and read through, when I could have simply clicked through! I would also like a little more info on why user was removed (abuse, friend upvotes, rules, etc) , as that could help educate the community as a whole on what behaviors to report.        I could care less about the rep gain or loss, but when you have a loss it is a scary message without context. I honestly thought for a moment that my account had been inhibited in some way. No, it didn't say "Your account was removed." Still, there is that moment of "what did I do wrong?" which seems silly to cause simply by not posting a few extra words. A clearer "A user who voted on your posts was removed along with reputation changes they caused" would have gone a long way to not cause me to question my participation in the review queues as of late.         My problem is that the message "user has been removed" is not a clickable link like the other messages - so I had to search meta to discover this question to find out what it meant. Prove that the projection $p_i$ from the product space $X_I S_i \tau$ into $S_i \tau_i$ is open for each $i \in I$ Full question: A function $f$ from a space $X, \tau$ to a space $Y, \tau'$ is said to be open if $f(V)$ is open in $Y$ whenever $V$ is an open subset of $X$. Prove that the projection $p_i$ from the product space $X_I S_i \tau$ into $S_i \tau_i$ is open for each $i \in I$.  Attempt: Let $S = \Pi_{i \in I} S_i$ be the product space. Then, let $p_i: S, \tau \to S_i, \tau_i$ be the projection $p_i(s) = s_i$ for each $s \in S$. Then, $p_i$ is continuous for all $i \in I$.  Then, if $V_i$ is open in $S_i$, then $p_i^{-1}(V_i) = S$ is one of the open sets in the basis, namely $\{\Pi_I V_i : V_i \text{ open in } S_i \text{ and } V_i = S_i \text{ for all but at most finitely many i}\}$, and we see clearly that $V_i$ fits the criteria for all $i \in I$ because we defined $V_i$ as being open in $S_i$ and $I$ is a finitely countable set, hence there will be at most finitely many $i$ for which $V_i = S_i$.  Thus, the projection $p_i$ is open for each $i \in I$.  I'm not sure if I tackled this correctly and wanted to make sure I was on the right track or got it right. Difference between modelAttribute and commandName attributes in form tag in spring? How do I get help for "echo" or other bash commands? man echo works. but out of curiosity, does echo have something similar to a --help flag/parameter? What is the definition of $2.5!$? (2.5 factorial) I was messing around with my TI-84 Plus Silver Edition calculator and discovered that it will actually give me values when taking the factorial of any number $n/2$ where $n$ is any integer greater than $-2$. Why does this happen? I thought factorials were only defined for positive integers and $0$, so what is my calculator doing to get the answer $3.32335097$ when I enter $2.5!$? Is there actually a definition of $2.5!$ or is my calculator just being weird? How is the factorial function implemented?  I understand the binary implications of $2.5$, so that could possibly have something to do with it. I get a domain error when trying to take the factorial of $-1, 2.3, e$, and any number that is not of the form $n/2$ where $n$ is any integer greater than $-2$. Does timbre consist in pitch and volume? I read that the physical properties of a sound wave correspond to its audible qualities: pitch, volume, and timbre. However, an oscilloscope uses only two-dimensions to accurately depict the physical properties of a wave. Intuitively, pitch and volume seem more basic than timbre does, so I surmise that timbre must consist in those two properties.    Does timbre consist in those two properties? How do two-dimensional waveform diagrams depict three properties of sound waves? How to not count blank pages in frontmatter of two-sided document Possible point location algorithm Bibtex style for "Statistics and Computing" I would like to create a bibtex style which answers the requirements of Statistics and Computing journal. How could I do that? Here is an example of how the bibliography should look like:  Journal article: Hamburger, C.: Quasimonotonicity, regularity and duality for nonlinear systems of partial differential equations. Ann. Mat. Pura Appl. 169, 321–354 (1995) Book: Geddes, K.O., Czapor, S.R., Labahn, G.: Algorithms for Computer Algebra. Kluwer, Boston (1992) Book chapter: Broy, M.: Software engineering — from auxiliary to key technologies. In: Broy, M., Denert, E. (eds.) Software Pioneers, pp. 10–13. Springer, Heidelberg (2002)  In the text, the references should be as follows:  Negotiation research spans many disciplines (Hamburger 1995).  Thank you for your help! Can I reposition AdSense ads with Javascript (for responsive purposes)? I have a responsive blog where ads are displayed in the sidebar. On mobile devices however, the sidebar is pushed to the bottom below the posts.   So what I'd like to do is move the ads from the sidebar and insert them into the post itself on mobile devices   I do this using javascript:  &lt;div id="main"&gt;     &lt;div id="article"&gt;         &lt;div class="post"&gt;             &lt;p class="intro"&gt;&lt;/p&gt;             &lt;p class="text"&gt;&lt;/p&gt;         &lt;/div&gt;     &lt;/div&gt;     &lt;div id="sidebar"&gt;         &lt;div class="adbox-1"&gt;&lt;/div&gt;     &lt;/div&gt;     &lt;/div&gt;  &lt;script&gt;     jQuery(document).ready(function(){          // AD REPOSITION         if ($(window).width() &lt; 769) {             $('.ad-box1').insertAfter($('.intro'));                    }      }); &lt;/script&gt;   The ads are always loaded in the sidebar, but if the screen width is below 768px, they will be moved somewhere else.  I wonder if this would violate AdSense terms of service? How do I detect running processes using a library package? This command is doing the rounds for detecting currently running processes using glibc:  lsof | grep libc | awk '{print $2}' | sort | uniq   I find it intensely annoying, since /libc/ matches not only libc, but on my system:  /lib/x86_64-linux-gnu/libcap.so.2.24 /lib/x86_64-linux-gnu/libcgmanager.so.0.0.0 /lib/x86_64-linux-gnu/libcom_err.so.2.1 /lib/x86_64-linux-gnu/libcrypt-2.19.so /lib/x86_64-linux-gnu/libcrypto.so.1.0.0 /usr/lib/libcamel-1.2.so.45.0.0 /usr/lib/unity-settings-daemon-1.0/libcolor.so /usr/lib/unity-settings-daemon-1.0/libcursor.so /usr/lib/x86_64-linux-gnu/colord-plugins/libcd_plugin_camera.so /usr/lib/x86_64-linux-gnu/colord-plugins/libcd_plugin_scanner.so /usr/lib/x86_64-linux-gnu/gtk-3.0/modules/libcanberra-gtk3-module.so /usr/lib/x86_64-linux-gnu/libcairo-gobject.so.2.11301.0 /usr/lib/x86_64-linux-gnu/libcairo.so.2.11301.0 /usr/lib/x86_64-linux-gnu/libcanberra-0.30/libcanberra-pulse.so /usr/lib/x86_64-linux-gnu/libcanberra-gtk3.so.0.1.9 /usr/lib/x86_64-linux-gnu/libcanberra.so.0.2.5 /usr/lib/x86_64-linux-gnu/libcap-ng.so.0.0.0 /usr/lib/x86_64-linux-gnu/libck-connector.so.0.0.0 /usr/lib/x86_64-linux-gnu/libcolordprivate.so.1.0.23 /usr/lib/x86_64-linux-gnu/libcolord.so.1.0.23 /usr/lib/x86_64-linux-gnu/libcroco-0.6.so.3.0.1 /usr/lib/x86_64-linux-gnu/libcupsmime.so.1 /usr/lib/x86_64-linux-gnu/libcups.so.2 /usr/lib/x86_64-linux-gnu/samba/libcliauth.so.0 /usr/lib/x86_64-linux-gnu/samba/libcli_cldap.so.0 /usr/lib/x86_64-linux-gnu/samba/libcli-ldap-common.so.0 /usr/lib/x86_64-linux-gnu/samba/libcli-nbt.so.0 /usr/lib/x86_64-linux-gnu/samba/libcli_smb_common.so.0 /usr/lib/x86_64-linux-gnu/samba/libcli_spoolss.so.0 /usr/lib/x86_64-linux-gnu/samba/liblibcli_lsa3.so.0 /usr/lib/x86_64-linux-gnu/samba/liblibcli_netlogon3.so.0   I understand that libc is used by pretty much everything, but I'd like to refine this command. Consider its applications for other libraries. How can I do this?  The flaw in this approach, in my opinion, is that the package providing libc may include a whole host of other shared library files (all of which may or may not be covered under the umbrella term that is the library name, like glibc, or libboost-python). Using a word boundary or - to mark the end of libc doesn't really fix this. This may not be a flaw, perhaps, as Braiam points out, since many or all of these .so files may link to a core file in which the flaw resides, as is the case for libc6 on Debian.   If a specific OS/distro is needed, assume Debian Linux.  Also annoying is that this command could be condensed to lsof | awk '/libc/{print $2}' | sort -u. Different results between individual and batch clip of rasters in QGIS? Nikon d5100 producing extremely underexposed images Well, may be this is not really useful, but I've thought if it was possible to put all the document in one long page. I mean, if your document is going to be read in a computer, mix all the pages in a continuous page. If your document has 90 pages (A4), where each one is 21cm by 29.7cm the continuous document should be (more or less) one page which is 21cm by 90 · 29.7 = 2673cm. Is this possible? EDIT: Some things I would like to achieve:  The \newpage, \chapter{}, \part{}, etc. shouldn't go to a new page, they should only add more vertical space. The package pdfpages should add the pages continuously with almost no space between them. The titlepage, in this case, has a different color, so it could go alone in a basic A4 page (just to make things easier).  Question Is this possible? How to make program autostart only in GNOME I use both GNOME and KDE SC. In GNOME, I use Docky but I do not use it with KDE. So, I would like Docky to start up only when I login into GNOME not KDE. In KDE, there is an option to make a program autostart only in KDE. But I cannot find any such option in GNOME.    How can I do this?    Thanks in advance. With variable length instructions how does the computer know the length of the instruction being fetched? Some days I'm working with extremely large Excel files.  They have too many sheets that can't be shown in one sheet tab. (see image)      So, I'm wondering whether or not we can show Excel sheet on more than 1 row. Many tries with Google don't help much.    Many tries but I still can't make Excel show the sheet bar the way I want (≥ 2 rows), so I'm working with some VBA Scripts kopischke suggested.    FYI, right click on |&lt; &lt;&lt; &gt;&gt; &gt;| button on the bottom-right corner show you a list of up to 15 sheets.  For more, click on View more in the list appeared. How to create animated GIF images of a screencast? I've seen animated GIF images of screen casts (like the one below) promoted a few times on this site as a way to improve answers.    What toolchain is being used to create these? Is there a program that does this automagically, or are people taking screencasts, converting them into a series of static frames, and then creating the GIF images?