Personally I find this drop-down list (found in the Find Utility Panel) to be extremely hard to use. I'd much rather just type in my file extension, just like you type in what to match. Baring that, an option to sort the list by raw file extension would also be appreciated.
Thanks and keep up your fantastic work on Directory Opus.
You can do this with wildcard matching...
For a single extension type the following in the "Name Matching" field
*.gif
For multiple extensions
*.(jpg|jpeg|bmp|gif|png|tif|tiff|ico)
Reference
http://www.gpsoft.com.au/help/opus12/index.html#!Documents/Pattern_Matching_Syntax.htm
Also, right clicking the search result header (Name, Size, Modified, Attr, etc) will open a context menu clicking "Type" will add that to the search header (at the end) that you can then click to sort by file type. This can also be saved so "Type" will always be displayed in the header in whatever position you want, look into "Folder Formats" and "Folder Options" on how to do that.
Thank you for the suggestions, but these workarounds don't seem much better than just scrolling through the giant list. Wildcard matching doesn't allow me to do any other name matching in addition (at least without using regex or something, which I feel would be kind of unnecessary). Similarly, columns also aren't ideal. Sorting by type forces each filetype section to be further sorted by filename, which can be annoying when I'm running a search inside a large number of subfolders.
File Types are not a 1:1 map to extensions. File Types may include multiple extensions, and can even match on things unrelated to the file name or extension. Typically, the type drop-down is used to restrict matches to files or folders, and the ability to choose other file types is rarely used but sometimes important for special file types.
If you want to search by typing the extension, typing the extension into the Name Matching field is what makes most sense.
If you want to do additional Name Matching checks on top of the extension, you can either combine them into a single wildcard (usually very simple if it's just one wildcard plus the extension), or you can use the Advanced tab to get two separate Name fields to match with.
For example, both of these will get you all .jpg files with "cat" in the name:
Note that neither will find things with a ".jpeg" extension. This is part of what I was talking about with File Types and extensions. The JPEG File Type will typically match both .jpg and .jpeg. (But this is not the only way a file type can differ from a simple extension check or wildcard.)
You could use wildcards like cat.(jpeg|jpg) to match both in this case.
The file type list drop down is still hard to use, as it registers only the first typed letter (e.g. typing "ca" jumps to the first item with "c" in the file name and then to the first item with "a", not to the item with "ca"). I don't know why it behaves like that, as other drop downs on the same box have the easier to use behavior.