K2 Summit and K2 Base Direct Detection Camera User's Guide
37
Single particle cryo-EM
Tilt series cryo-
tomography
(exposure/tilt)
Specimen exposure (e
-
/Å^2)
20
0.5
Camera exposure rate
(e
-
/pixel/sec. )
10
10
Nominal
mag (kX)
Physical
pixel size at
specimen (Å)
SR
exposure
time (s)
Counting
exposure
time (s)
SR
exposure
time (s)
Counting
exposure
time (s)
62 0.60 0.7
0.7
49 0.75 1.1
1.1
0.03
0.03
39 0.95 1.8
1.8
0.05
0.05
31 1.2 2.9
2.9
0.07
0.07
25 1.5 4.5
4.5
0.1
0.1
20 1.9 7.1
7.1
0.2
0.2
16 2.4
0.3
0.3
12 3.0
Use K2 base or linear mode
with <1 sec exposure time
0.4
0.4
10 3.8
0.7
0.7
8 4.7
1.1
1.1
6 6.0
1.8
1.8
For linear operation, the dose rate is not tightly specified. That makes it possible to adjust the
exposure rate between the single-particle and the tomography modes. The minimum exposure
rate is dictated by the read noise equivalent dose, which for the Base Linear mode is
approximately 0.1 primary electron equivalents per pixel per second at 300kV (the Summit
camera’s corresponding value in linear mode is about 1.3 electrons/pixel/second). Thus, users
who do not have a processing unit can span the full range of cryo magnification and dose
settings without limitation by read noise.
Switching Between Base and Summit Modes
To switch to Base mode (from Summit mode):
1.
Open the K2 toolbox dialog.
2.
Press the
Switch to Base
button. Follow onscreen instructions.
3.
Check the acquire and view settings, your preferred settings (Dark Subtraction for
instance) may be different between summit and base modes.
4.
Switching between Summit and Base causes a temporary loss of temperature control, so
wait until the temperature is stable at the cold set point before proceeding with imaging.
To switch to Summit mode (from Base mode):
1.
Open the K2 toolbox dialog.
2.
Press the
Switch to Summit
button. Follow onscreen instructions.
