Talk:Resolution: Difference between revisions

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==Confusion of high and low resolution==

High resolution is characterized by being able to distinguish smaller features, so there is an inverse relationship between the quality of a structure and the length scale given for the resolution. For example, a 1.0 Angstrom structure resolves finer detail than a 4.0 Angstrom structure, so the 1.0 Angstrom structure is said to have higher resolution than the 4.0 Angstrom structure.

==Resolution of a reflection and resolution of a diffraction data set===

Each diffraction spot (i.e. reflection) in a diffraction pattern has a nominal resolution. The higher the diffraction angle (i.e. further from the center of the diffraction image (where the incoming X-ray beam would hit), the higher the resolution. In a diffraction experiment, the goal is to collect as many reflections as possible. However, reflections of high resolution are more difficult to measure because their intensity drops with resolution. In a diffraction image, you will see high intensity spots near the center, and more and more faded spots as you move away from the center. The overall resolution of a diffraction data set refers to the resolution range of reflections measured. For example, "data was collected from 20.0 Angstroms to 2.3 Angstroms with an overall completeness of 96.5%" means that most reflections in this range were collected, and the data set would be described as "2.3 A resolution" data set, referring to the high resolution limit of the data collection.

==Resolution and Disorder ==

The resolution of a diffraction pattern depends on how ordered the crystal is. If it is highly ordered (atoms are in defined positions throughout the crystal and over time), the crystal will diffract to high resolution. The more disorder there is (atoms moving over time, or the content of one unit cell different from the next), the lower the resolution of the diffraction image because the intensity of spots drops with increasing disorder. In order to still be able to measure these weak reflections, it is sometimes possible to increase the intensity of the X-rays used in the experiment, increase the exposure time or sensitivity of the detector or increase the size of the crystals.

==Resolution and diffraction data quality==

A well diffracting crystal will yield a high resolution diffraction data. The higher the resolution, the more reflections in the data set. The number of reflections increases with the inverse cube of the resolution, so a 1.0 Angstrom data set has '''eight''' times the number of reflections than a 2.0 Angstrom data set. If you compare a given reflection measured on a well diffracting crystal to one measured on a poorly diffracting crystal, the former will be measured with higher precision (lower error).

==Resolution and structure quality==

The higher the resolution of the diffraction data, the more measurements are present to base the model on. Also, an increase in resolution means that low resolution reflections were measure with less error than in a corresponding lower quality diffraction data set. As a consequence, the model can be built with less systematic error (such as missing or misplaced atoms) and with less average coordinate error. The coordinate error (how different two models would be based on the same crystals, but independent measurement, model building and refinement) correlates with resolution, but is of a different order of magnitude. It is also influenced by completeness of the data (higher is better), the free R-factor of the refinement (lower is better), and the completeness of the model (higher is better). A typical crystallographic model based on 2.0 Angstrom data has a coordinate error of around 0.2 Angstrom. (http://www.ccp4.ac.uk/newsletters/newsletter33/murshudov.html)

==Resolution and B-factors==

Disorder of a crystal is reflected in lower resolution of the diffraction data. Disorder in the coordinates based on that data can be modeled by introducing B-factors for each atom.

--[[User:Karsten Theis|Karsten Theis]] 19:12, 15 May 2014 (IDT)

Proposed revision for the beginning of this article, after discussion with Keiichi Namba. Comments welcome!

Talk:Resolution: Difference between revisions

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+==Confusion of high and low resolution==
+High resolution is characterized by being able to distinguish smaller features, so there is an inverse relationship between the quality of a structure and the length scale given for the resolution. For example, a 1.0 Angstrom structure resolves finer detail than a 4.0 Angstrom structure, so the 1.0 Angstrom structure is said to have higher resolution than the 4.0 Angstrom structure.
+==Resolution of a reflection and resolution of a diffraction data set===
+Each diffraction spot (i.e. reflection) in a diffraction pattern has a nominal resolution. The higher the diffraction angle (i.e. further from the center of the diffraction image (where the incoming X-ray beam would hit), the higher the resolution. In a diffraction experiment, the goal is to collect as many reflections as possible. However, reflections of high resolution are more difficult to measure because their intensity drops with resolution. In a diffraction image, you will see high intensity spots near the center, and more and more faded spots as you move away from the center. The overall resolution of a diffraction data set refers to the resolution range of reflections measured. For example, "data was collected from 20.0 Angstroms to 2.3 Angstroms with an overall completeness of 96.5%" means that most reflections in this range were collected, and the data set would be described as "2.3 A resolution" data set, referring to the high resolution limit of the data collection.
+==Resolution and Disorder ==
+The resolution of a diffraction pattern depends on how ordered the crystal is. If it is highly ordered (atoms are in defined positions throughout the crystal and over time), the crystal will diffract to high resolution. The more disorder there is (atoms moving over time, or the content of one unit cell different from the next), the lower the resolution of the diffraction image because the intensity of spots drops with increasing disorder. In order to still be able to measure these weak reflections, it is sometimes possible to increase the intensity of the X-rays used in the experiment, increase the exposure time or sensitivity of the detector or increase the size of the crystals.
+==Resolution and diffraction data quality==
+A well diffracting crystal will yield a high resolution diffraction data. The higher the resolution, the more reflections in the data set. The number of reflections increases with the inverse cube of the resolution, so a 1.0 Angstrom data set has '''eight''' times the number of reflections than a 2.0 Angstrom data set. If you compare a given reflection measured on a well diffracting crystal to one measured on a poorly diffracting crystal, the former will be measured with higher precision (lower error).
+==Resolution and structure quality==
+The higher the resolution of the diffraction data, the more measurements are present to base the model on. Also, an increase in resolution means that low resolution reflections were measure with less error than in a corresponding lower quality diffraction data set. As a consequence, the model can be built with less systematic error (such as missing or misplaced atoms) and with less average coordinate error. The coordinate error (how different two models would be based on the same crystals, but independent measurement, model building and refinement) correlates with resolution, but is of a different order of magnitude. It is also influenced by completeness of the data (higher is better), the free R-factor of the refinement (lower is better), and the completeness of the model (higher is better). A typical crystallographic model based on 2.0 Angstrom data has a coordinate error of around 0.2 Angstrom. (http://www.ccp4.ac.uk/newsletters/newsletter33/murshudov.html)
+==Resolution and B-factors==
+Disorder of a crystal is reflected in lower resolution of the diffraction data. Disorder in the coordinates based on that data can be modeled by introducing B-factors for each atom.
+--[[User:Karsten Theis|Karsten Theis]] 19:12, 15 May 2014 (IDT)
 Proposed revision for the beginning of this article, after discussion with Keiichi Namba. Comments welcome!