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Category: Pre-purchase Questions
What's the difference between SE and PE Grade?
Posted on Apr 25, 2011, 12:37 am Author: Jen Winter
 

SE Grade stands for Standard Edition Grade.
PE Grade stands for Professional Edition Grade.
This grade is a classification of the homogeniety of the etalon crystal within the DayStar Filter. 

The SE grade filters are accurate enough to maintain transmission within the 0.81Å wide Hydrogen Alpha line. 
We will also remember that the sun experiences wing shift from the leading edge to the following edge.   This wing shift represents approximately 0.5Å in red and 0.5Å in blue wing.  A filter with a +/- 0.25Å wing shift will always transmit Hydrogen Alpha light when tuned properly.   A visual-only observer might never notice or recognize the difference between an SE grade and PE grade filter. 

In the past, the prior owner, Del Woods used the term "ATM" or "UNI" to describe the difference because ATM units were sold to Amateur customers and the UNI grade were sold to Universities.

At the heart of the DayStar narrow bandpass filter is an Etalon.   This is a crystal made of Mica, mined from the ground, sorted for clarity, cleaved by hand into a thin wafer.  It is then sorted again for homogeniety and coated with our proprietary coatings to produce the narrow bandpass performance of a Fabry Perot Etalon.   Because the wafer on which the coatings lies is an actual cleaved crystal, mined from the ground, each crystal will maintain microscopic variations from crystal to crystal.

While mica crystal is flat to the molecular level, the matrix of the crystal growth still has variation due to the abundance percentages of the various elements within that crystal.  Therefore, across the aperture of the etalon crystal, we see some etalons which are more uniform in their behavior than others.  

So a uniform etalon crystal of PE grade will transmit  an even Central Wavelength accurate to the following specification: 

"The mean peak wavelength of all 12 mm. dia. areas shall be within ± 0.05 ångström of the full aperture wavelength measurement.

An SE grade filter will transmit with a similar accuracy of ± 0.25 ångström over the similar area.

PE grade uniformity of this scale is necessary for Universities and research groups who will perform quantitative scientific measurements of the sun and it's chromosphere, where variations in wavelength will affect their resulting data.  

We have also recently found that PE grade uniformity in FWHM (bandpass) across the aperture of the filter will affect density variations in photographic applications.   For example, areas with sharp changes between 0.4Å and 0.45Å can result from  crystal growth changes of direction and create a "sheer line".   This is different than a steppe between layers of the mica.  A steppe causes an immediate 10Å jump in CWL.    Photographic applications are more sensitive to SE grade filters with FWHM sheer or inhomogeniety.  Some very serious photographers who want the absolute highest imaging quality will consider the PE grade for their imaging appli cations.

Why don't we just manufacture all etalons to the PE Grade?   
In order to understand PE grade, one must first appreciate the issue of scale in an etalon crystal. 
We know that 1 nanometer is 1/billionth of a meter.
1Å is 0.1 nanometer.
So the accuracy of the of ± 0.05 ångström uniformity of the transmission of the PE grade filter equals 5/1,000,000,000,000 of a meter.  This is 5 millionth's of the thickness of a human hair.

We are proud to offer SE grade filters to the non-research based astronomy market for high quality, reasonably priced solar observing.  SE grade etalons are available in Quantum SE, ION and Ca II H line filters and SolaREDi telescopes.

Certain applications like Helium D3 line require PE grade in order to assure isolation of very narrow emission lines.
We also manufacture our Ca II K line filters in PE grade.  K-line is a research specific  line.


Tagged Keywords: SE, PE, uniformity, bandpass, homogeniety, CWL, FWHM, Å

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