I. INTRODUCTION Since its invention almost 20 years ago, Scanning Force Microscopy (SFM)[1] has become an extremely powerful tool for a huge variety of nanoscale investigations. With respect to resolution and sensitivity, Dynamic Scanning Force Microscopy (DSFM)[2] seems to be the most promising technique. Even though (true) atomic resolution was first achieved with contact mode in liquid environment[3], now atomic resolution studies are generally performed with DSFM working in UHV environment[4–6]. Recently even sub-atomic resolution has been reported using DSFM [7]. In spite of the impressing advances of SFM and DSFM we believe that the ultimate limit of these techniques is still an open issue. For most applications, the temperature at which quantum limits become relevant, T$_{Q}$ = $_{ℏ}$ω$_{0}$ /k ≃ 1 µK , is well below typical temperature ranges used in SFM. Correspondingly, either thermal vibration of the cantilever[8–11], or fundamental limits of the detection technique used[11– 13] - related to shot noise of the “detection particles” - determine the resolution in SFM and DSFM. In most practical applications, the fundamental limit of SFM and DSFM is set by thermal noise. Thermal noise in an SFM set up is the consequence of the equipartition theorem, which relates the mean energy of the cantilever with the thermal energy kT , where a 2 th is the (mean square) displacement of the cantilever induced by thermal fluctuation, and c is its force constant. For high resolution distance measurements stiff cantilevers[14, 15] should be used ( δz = $^{√}$kT/c , with δz fluctuation of tip-sample distance), while for high resolution force measurements soft cantilevers[16] are needed ( δF$_{th}$ = c · a$_{th}$ = √ c kT ). Although the mean displacement and the mean force fluctuation of the cantilever are im- portant quantities, in many applications they do not directly determine resolution, either because appropriate filtering significantly reduces the measured noise, or because the SFM technique used -as for example DSFM- is not directly limited by the displacement or the force. In typical DSFM applications the cantilever is excited at or near its natural frequency and the variation of its resonant properties -oscillation amplitude, resonance frequency or quality factor - are recorded. For imaging applications in liquids or air usually the oscillation amplitude is used as control parameter that defines constant tip-sample distance and the frequency shift is measured as secondary channel. In UHV applications DSFM operation is 1 2 c a 2 th = 1 2 kT (1) 2