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    <title>PFS-JIRA</title>
    <link>https://pfspipe.ipmu.jp/jira</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>8.3.4</version>
        <build-number>803005</build-number>
        <build-date>13-09-2019</build-date>
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<item>
            <title>[INSTRM-73] Absolute exposure time</title>
                <link>https://pfspipe.ipmu.jp/jira/browse/INSTRM-73</link>
                <project id="10300" key="INSTRM">Instrument control development</project>
                    <description>&lt;p&gt;We need to make a philosophical choise about absolute exposure time.&lt;br/&gt;
In operation, we don&apos;t care too much about this, because exposures are much longer.&lt;/p&gt;

&lt;p&gt;However, during our current test, exposure is only few seconds. &lt;br/&gt;
The opening of the shutters last about 0.39s &lt;br/&gt;
The closing of the shutters last about 0.38s&lt;/p&gt;

&lt;p&gt;If we open and close right away, let&apos;s call that a 0 sec exposure, here is what the detector actually see in terms of exposure time:&lt;br/&gt;
 &lt;span class=&quot;image-wrap&quot; style=&quot;&quot;&gt;&lt;a id=&quot;10408_thumb&quot; href=&quot;https://pfspipe.ipmu.jp/jira/secure/attachment/10408/10408_exptime_vertical.png&quot; title=&quot;exptime_vertical.png&quot; file-preview-type=&quot;image&quot; file-preview-id=&quot;10408&quot; file-preview-title=&quot;exptime_vertical.png&quot;&gt;&lt;img src=&quot;https://pfspipe.ipmu.jp/jira/secure/thumbnail/10407/_thumb_10407.png&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/a&gt;&lt;/span&gt; &lt;/p&gt;

&lt;p&gt;What I would propose, it&apos;s to choose the least bad solution :&lt;/p&gt;

&lt;p&gt;exptime = (shutter_opening_time+shutter_closing_time)/2 + time_shutters_fully_open&lt;br/&gt;
for that &quot;0 sec&quot; exposure above it would give a 0.385 absolute exposure time.&lt;/p&gt;

&lt;p&gt;Anyhow, I think that&apos;s important enough so I can&apos;t be the only one to decide.&lt;br/&gt;
The sooner the better.&lt;/p&gt;

&lt;p&gt;Thanks.&lt;/p&gt;</description>
                <environment></environment>
        <key id="11431">INSTRM-73</key>
            <summary>Absolute exposure time</summary>
                <type id="3" iconUrl="https://pfspipe.ipmu.jp/jira/secure/viewavatar?size=xsmall&amp;avatarId=10518&amp;avatarType=issuetype">Task</type>
                                            <priority id="4" iconUrl="https://pfspipe.ipmu.jp/jira/images/icons/priorities/minor.svg">Minor</priority>
                        <status id="10002" iconUrl="https://pfspipe.ipmu.jp/jira/images/icons/statuses/generic.png" description="The issue is resolved, reviewed, and merged">Done</status>
                    <statusCategory id="3" key="done" colorName="green"/>
                                    <resolution id="10000">Done</resolution>
                                        <assignee username="arnaud.lefur">arnaud.lefur</assignee>
                                    <reporter username="arnaud.lefur">arnaud.lefur</reporter>
                        <labels>
                    </labels>
                <created>Wed, 11 Jan 2017 13:53:55 +0000</created>
                <updated>Wed, 31 May 2017 16:43:18 +0000</updated>
                            <resolved>Wed, 31 May 2017 16:43:18 +0000</resolved>
                                                                        <due></due>
                            <votes>0</votes>
                                    <watches>5</watches>
                                                                <comments>
                            <comment id="11743" author="cloomis" created="Wed, 11 Jan 2017 14:46:09 +0000"  >&lt;p&gt;This comment is not intended to help, sorry.  &lt;/p&gt;

&lt;p&gt;Do we know how long calibration exposures will be?&lt;br/&gt;
Which axis is wavelength?&lt;br/&gt;
Have you tested several shutter mechanisms, or just one?&lt;/p&gt;

&lt;p&gt;The choice only really matters at the limit. To the extent that we care, we would want to know the shutter motion time.&lt;/p&gt;</comment>
                            <comment id="11744" author="arnaud.lefur" created="Wed, 11 Jan 2017 15:06:47 +0000"  >&lt;p&gt;The wavelength axis was horizontal. &lt;br/&gt;
If I reorient the graph according to the orientation we currently have (wavelength =&amp;gt; vertical),  it would be like this( not sure about  the top/bottom orientation)&lt;br/&gt;
 &lt;span class=&quot;image-wrap&quot; style=&quot;&quot;&gt;&lt;a id=&quot;10408_thumb&quot; href=&quot;https://pfspipe.ipmu.jp/jira/secure/attachment/10408/10408_exptime_vertical.png&quot; title=&quot;exptime_vertical.png&quot; file-preview-type=&quot;image&quot; file-preview-id=&quot;10408&quot; file-preview-title=&quot;exptime_vertical.png&quot;&gt;&lt;img src=&quot;https://pfspipe.ipmu.jp/jira/secure/thumbnail/10408/_thumb_10408.png&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/a&gt;&lt;/span&gt; &lt;/p&gt;

&lt;p&gt;This graph is totally theorical, it&apos;s only based on shutters opening/closing time I&apos;ve measured.&lt;/p&gt;</comment>
                            <comment id="11745" author="atsushi.shimono" created="Thu, 12 Jan 2017 01:44:36 +0000"  >&lt;p&gt;I put the previous study for normal exposure, which includes&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;shutter cuts in collimated beam, but not directly cuts on focused plane. so difference among pixels are small. (e.g. beam size for one pixel is ~300mm, detector size is ~60mm)&lt;/li&gt;
	&lt;li&gt;shutter moves in horizontal direction, which is wavelength direction&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;so, I think difference on light coming time range from transient period is not large as total shutter moving time, and we can say real exposure time is &apos;commanded&lt;img class=&quot;emoticon&quot; src=&quot;https://pfspipe.ipmu.jp/jira/images/icons/emoticons/help_16.png&quot; height=&quot;16&quot; width=&quot;16&quot; align=&quot;absmiddle&quot; alt=&quot;&quot; border=&quot;0&quot;/&gt; exposure&apos; plus average of shutter open/close transient time.&lt;/p&gt;</comment>
                            <comment id="11746" author="rhl" created="Thu, 12 Jan 2017 06:20:17 +0000"  >&lt;p&gt;As Arnaud says this is probably academic.  However, it would be good to respond to Shimono-san&apos;s comment about the shutter being in a collimated beam.&lt;/p&gt;

&lt;p&gt;The exposure time is probably most important for dark current correction and I hope that there isn&apos;t enough dark current for this to matter.  If this isn&apos;t true we probably have to think about a map for the spatial structure of the exposure time.&lt;/p&gt;

&lt;p&gt;However, I think we need to distinguish a bias (exposure time really == 0) from a 0s exposure, so I think we should go with Arnaud&apos;s proposal (once we&apos;ve sorted out the real effective exposure time).&lt;/p&gt;</comment>
                            <comment id="11940" author="cloomis" created="Wed, 15 Mar 2017 16:48:00 +0000"  >&lt;p&gt;Do you need anything more on this, Arnaud? I assume you are done, but for the record I agree with you and RHL: 0s should be reserved for when &lt;em&gt;no&lt;/em&gt; light is allowed through.&lt;/p&gt;</comment>
                            <comment id="11945" author="arnaud.lefur" created="Thu, 16 Mar 2017 09:49:48 +0000"  >&lt;p&gt;At the end, exposure time is calculated as I proposed :&lt;br/&gt;
&lt;em&gt;exptime = (transientTime)/2 + time_shutters_fully_open&lt;/em&gt; with transientTime = shutter_opening_time+shutter_closing_time&lt;br/&gt;
For each exposure: &lt;b&gt;dateobs, transientTime, exptime&lt;/b&gt;  keywords are generated.&lt;/p&gt;

&lt;p&gt;I&apos;m not sure how we can measure that exptime gradient accurately, it&apos;s true that in our 1 sec flat we do see that fluxes decrease along with wavelength. &lt;br/&gt;
But it&apos;s could be also related to halogen spectrum itself.&lt;/p&gt;</comment>
                            <comment id="12115" author="arnaud.lefur" created="Tue, 25 Apr 2017 16:18:53 +0000"  >&lt;p&gt;For the one channel, I think the solution implemented is consistent. &lt;br/&gt;
An action which we could take internally is to check on Zemax if this gradient is real and to quantify it. &lt;br/&gt;
Kjetil and Sandrine would be a good help to investigate that.&lt;/p&gt;</comment>
                            <comment id="12212" author="cloomis" created="Wed, 31 May 2017 16:43:18 +0000"  >&lt;p&gt;We agreed on the 2017-05-31 ICS/SPS phonecon that the current choice  &amp;#8211; fully_open_time + transit_time/2 &amp;#8211; is what we want..&lt;/p&gt;</comment>
                    </comments>
                    <attachments>
                            <attachment id="10409" name="201505-exposure-time-v2.pptx" size="66736" author="atsushi.shimono" created="Thu, 12 Jan 2017 01:37:27 +0000"/>
                            <attachment id="10407" name="exptime.png" size="12639" author="arnaud.lefur" created="Wed, 11 Jan 2017 13:39:07 +0000"/>
                            <attachment id="10408" name="exptime_vertical.png" size="13375" author="arnaud.lefur" created="Wed, 11 Jan 2017 15:08:04 +0000"/>
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