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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Hi Sergej,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Yet another (very unpleasant) possibility is an intermittent short in the coil of a projector lens. You won’t be able to easily detect this by monitoring the lens current because the lens power supplies are constant current. Instead, check the voltage across the lens coil for intermittent jumps. The magnification change spikes will also be visible on the fluorescent screen.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>I would put my bet on a communication/software issue though because the few spurious images had higher magnification than what was requested. Is the 50kX mag one of the standard mags? In other words, were the spurious images at a different mag from the standard mag range?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>All the best,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Rado<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'> 3dem [mailto:3dem-bounces@ncmir.ucsd.edu] <b>On Behalf Of </b>Subangstrom<br><b>Sent:</b> Tuesday, February 20, 2018 23:29<br><b>To:</b> 3dem@ncmir.ucsd.edu<br><b>Subject:</b> Re: [3dem] Set value and actual magnification differ<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p>Hi Dr. Masich,<o:p></o:p></p><p>There are a few points to make here and two things that could cause magnification problems in general.<o:p></o:p></p><p>Some points:<o:p></o:p></p><p>The magnification you read out in the user interface is the magnification at the "flu screen." The magnification you read out on the user interface when you lift the screen is the magnification at the film plane. The actual magnification (or as we commonly refer to it: pixel size) at the camera plane will depend on the camera's position along the path of the beam. The further along the beam path, the greater the magnification. <o:p></o:p></p><p>It is expected that you will have a higher mag at the camera plane than what is read out on the user interface. From your description however, it sounds like the mag that is read out on the screen is fixed but the effective magnification at the camera plane is changing (from 50kX to some other value). If this is indeed the case, I would check on the following:<o:p></o:p></p><p>The magnification is determined by the excitation values of the projection lenses. For any given magnification, each lens of the projection system should have a specified current flowing through it that would achieve that magnification at the given high tension value. For CM systems, if you open up the service documentation that is delivered with the system, a table of these currents is available for reference. You can open up the "display currents" page on the interface and compare them. For a fully functional system the current values won't be exact, but very close. In my experience, these values are trustworthy. In theory, it is also possible to pull out the lens cable, put a current meter in series, and measure the 'true current' in the event you need to get into deeper troubleshooting.<o:p></o:p></p><p>If the currents are correct sometimes and not other times, then you have a problem to troubleshoot. <o:p></o:p></p><p>The problem can be:<o:p></o:p></p><p>1) The HT circuit- there are several boards that govern the HT and how it ties in to the lenses, any one of them could be defective<o:p></o:p></p><p>2) The lens circuit- there are several boards that amplify the signal and produce the current for each lens, any one of them could be defective<o:p></o:p></p><p>3) Both circuits- this is less likely, but it could be more than one board on each circuit causing this issue; if that were the case I'd expect a more dramatic symptom<o:p></o:p></p><p>I hope this was helpful.<o:p></o:p></p><p>Best,<o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>Mark Ebrahim<br>Subangstrom LLC<o:p></o:p></p><div><p class=MsoNormal>On 2/20/2018 2:04 PM, Sergej Masich wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal><span lang=EN-GB>Dear 3D-EM community,</span><span lang=EN-GB> </span><o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>We have observed a strange phenomenon in our old FEI CM200 microscope. For example, among many images acquired at the set value of 38 kX, there were a few images having actual magnification of 50 kX. The similar behaviour was observed for other magnifications as well. Our very experienced engineer could not explain the discrepancy. Can somebody advise what can have caused the problem?<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Best regards,<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Sergej <o:p></o:p></p><div><div><div><p class=MsoNormal><span style='font-size:9.0pt;font-family:"Helvetica",sans-serif'>=============================<br>Dr. Sergej Masich<br>Dept. of Cell and Molecular Biology<br>Karolinska Institutet<br>171 77 Stockholm, Sweden<br>tel: (+)46 - 8 - 524 873 61<br>mobile: (+)46 - 736 - 833 693<br>e-mail: <a href="mailto:Sergej.Masich@ki.se">Sergej.Masich@ki.se</a><o:p></o:p></span></p></div><div><p class=MsoNormal><o:p> </o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal><br><br><br><o:p></o:p></p><pre>_______________________________________________<o:p></o:p></pre><pre>3dem mailing list<o:p></o:p></pre><pre><a href="mailto:3dem@ncmir.ucsd.edu">3dem@ncmir.ucsd.edu</a><o:p></o:p></pre><pre><a href="https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem">https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem</a><o:p></o:p></pre></blockquote><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>