I have some crystals with iodinated RNAs that I hope to collect some data from during my beam time on Friday, June 7th. What wavelength would you recommend for SAD data collection? Also, I have read that halogenated RNAs are light-sensitive. Are there specific precautions I can take at the beamline to minimize their light exposure? Do you have more suggestions/recommendations for data collection strategies for these crystals to maximize diffraction and anomalous signal and minimize chances of de-iodination? On Jun 4, 201, James Holton wrote: You want to collect at 7235 eV (1.71367 A wavelength). That is where the detector calibration is best. Be sure to use "inverse beam" with a "wedge size" of one image (usually 1 degree). For brominated RNA, the worst decay rate I am aware of is about a 1 MGy half-life, and you can expect about 10 kGy/s at 7235 eV on 8.3.1, so you will probably have about 100s of shutter-open time before half your iodine has popped off. So, for a 100-image dataset that means not more than a 1 second exposure time. I recommend doing a full 360 (180 degrees in inverse beam) with 0.2 second exposures, and then move the detector in a bit (just enough to move your spots onto new pixels) and then do another 360 with 1 second exposures, then again with 4 seconds, 16 seconds, etc. Do this until the crystal is dead. With luck, you will either get good anomalous signal before the iodine pops off, or you will be able to do "RIP" by treating your early data as a "derivative" and your later data as the "native". You will have to play around with how to merge the data after you get home. We do have a foil cover for the hutch door window that George can install for you. The only other significant light source in the hutch is the backlight for the microscope. I'm afraid there is not a lot you can do about this light since you need it to center your crystal. I'd say just try leaving it off as often as possible and be quick about your centering. Perhaps try turning down the light and letting the camera gain try to compensate. Unfortunately, there is no good "assay" I'm aware of for telling when an iodine has popped off. You may want to do some little preliminary experiments with gel shifts or mass spec to see how much visible light your iodinated RNA can take?