I'm a rising senior and will be applying to PhD programs this fall. I'm wrapping up a research project I was doing this summer at another school (basically an REU-like program) and the school is at the top of my field. I learned so much this summer and was able to accomplish a lot with my project. I was mentored by staff scientists and basically worked with them the entire summer. The PI of the lab is very hands off and hard to pin down. I met with him once in the beginning of the summer and have a meeting with him this week as I finish up. I was planning on asking him to write me a letter of rec then. The staff scientists said that what will probably end up happening is they write it and he'll sign it/co-sign it, but I need to ask him myself. I'm just a bit nervous/paranoid he'll say no so if anyone has any advice/words of encouragement, I'd appreciate it.
I understand that letters should come from people who know you well and I plan on my other two to be from professors that I am close with at my school. Given that I attend a school where there are limited research opportunities, I consider it to be integral that I get a letter out of this experience that speaks to my capabilities as a researcher. Based on the advice from the career office at this visiting school and other lab members, the letter should be coming from the PI/professor. The scientists I work with will contribute to a strong recommendation - they themselves acknowledge that it just wouldn't be as valuable coming from them. I guess my nervousness has to do more with the fact that here with big labs and big name PI's everyone says this situation/procedure is the norm and coming from a smaller school I'm not as used to it.