Conventional practice and advice is that discussing compensation on the first interview is in bad form and can cost an applicant future interviews.

If you are a hiring manager and make it your practice not to discuss income at all on the first interview or if you are an applicant and plan not to bring up the subject of compensation on the first interview, my experience has been that you are making a mistake.

If a hiring manager makes an offer to a candidate, the hiring manager is now only halfway to making a hire.  For the first time, the applicant has the 100% power over yes or no in the process.  Also, from my experience, if an interview process goes to the point of that an offer is extended and the offer is rejected, it is intuitively obvious why the offer is turned down:  compensation.
Think about it.  The applicant is very likely sold on the company, the people, and the responsibilities.  Why else would the applicant have invested so much time to prepare for the interviews and make the trips to interviews if everything is not positive, and then turn down the offer when it is extended?  The answer is compensation.

Do you need to discuss the details of an offer on a first interview?  I do not think so.

However, I think that both the hiring manager and the applicant need to get some framework around the subject of compensation (salary, bonus, benefits) from both what the hiring company pays and what the applicant is making to know that the two are at least in the same range of expectation.  So save yourself some time.

If you are a hiring manager, save yourself some time and let the applicant know that if he or she is chosen for the role, the person can expect the position to pay approximately a certain amount.