Example. These birth records are indexed:
Now I would like to search the index for children with a certain namen, or e.g. without mother, rather then reading through the whole file.
Is that possible?
Rescued URL: https://www.familysearch.org/ark:/61903/3:1:S3HT-DYS3-918?i=980&cc=2138500&cat=644615. (Don't give links their own line in this Community. It'll mangle them.)
You can search in the specific film/image group. One way to get there is to start at the image viewer page linked above, and click one of the index record links (one of the "piece of paper" icons at the far left on the Image Index tab). On the resulting index detail page (such as https://www.familysearch.org/ark:/61903/1:1:QJDL-HFDQ), expand the Document Information at the left and click either the Digital Folder Number or the Microfilm Number. In this particular case, I recommend using the film number, because the image group number is one of the ones that has had extra stuff added to it, which will likely restrict your results more than desired. (The matching algorithm for the film/DGS field is very simplistic: 00123456_78 matches neither 123456_78 nor 00123456. You can get around this by using wildcards. For example, if you use the DGS link, it'll put 004058887_003_M94S-NJW in the search field; edit it to 004058887* [or *4058887*] to expand your search to everything in the group, instead of limiting it to the few index entries that have exactly the same specifics.)
That wasn't easy but it works! Great answer.
One more thing I would need though, is how to indicate in the search that a field is empty. because then I couls look for "there is no mother". (I tried the checkbox "exact match" leaving the field empty, but that didn't work)
Unfortunately, FS does not have a means of searching for entries where a field is specifically empty. You're not the first to mention this gap; see for example https://community.familysearch.org/en/discussion/comment/533090#Comment_533090.
thank you for your answer. I will do the suggestion, I think it would be quite useful in some cases AND not difficult to implement.