The 0.9-meter telescope is a Cassegrain telescope mounted on an off-axis asymmetrical mounting and used on the east side of the pier. This telescope is at present only used for direct imaging with a dedicated 2048x2046 CCD detector. A CCD-based autoguider, which looks at a small off-axis field, is permanently installed. From Feb 1 2003 the 0.9-m is one of the CTIO small telescopes being operated by the SMARTS Consortium.
Classical observing only. Historically, there has also been service observing, but this is not available due to financial constraints.
Since 2000, the 0.9-m has been equipped with a dedicated 2048x2046 Tek2K CCD detector. Please refer to the Tek2K instrument page [2] for CCD characteristics.
The standard filter size for the 0.9m CFCCD is 3x3 inch. The filters are mounted in two filter wheels which each can hold up to 8 filters. Usually, 2 positions in each wheel are taken up by a color balance filter (for dome flats) and the "clear" position. We also have a single wheel which can hold up to five 4x4 inch filters. This filter wheel can be installed in place of one of the 8-position wheels.
See the Filter list [3] for more information on the available filters.
For projects that require accurate timing information, here is a quick overview on how the time ends up in the image headers:
There are two different header entries relating to time, UT and UTSHUT. UT is read from the TCS. While there is a GPS receiver that displays accurate Universal Time in each telescope's console room, this information is currently not communicated to the TCS automatically, but instead has to be manually entered at the beginning of each night. The absolute accuracy is therefore at best ~1 sec. In addition, the TCS clock often drifts by a considerable amount during the night and is therefore not reliable for both absolute and relative timing.
UTSHUT is taken from the ARCON controller's clock, which is synchronized against the SUN data acquisition computer's clock every time ARCON is started up. After that it runs on the controller's internal clock. The UTSHUT timestamp is the time when the shutter opens and should provide the most accurate timing information currently available. The SUN computer's clock is synchronized with the time reported by the US Naval Observatory and other internet sites (the details of this process are given here). Occasionally, e.g. after a power outage or network problems, this synchronization process fails and it is important to check the accuracy of the SUN clock at various times during a run by visually comparing it to the GPS time display.
To check for the correct UT time on the web, try this link to the USNO Master Clock [4] .
0.9m Observers in SERVICE MODE
0.9m Observers in USER MODE
| Contents | ||
| 1. | Contact People | |
| 2. | Scheduling | |
| 3. | Instrumentation | |
| 4. | Known issues at the 0.9-m | |
| 5. | Planning Observations | |
| 6. | What you need to do now |
Hello, SMARTS, Chilean, and NOAO users!
If you have recently been awarded time on the 0.9-m, you will soon be contacted by 0.9-m coordinator Adric Riedel with detailed instructions on how to proceed. Here, we describe the preparation process (in fact, is almost verbatim from the e-mail you will receive) to ensure you obtain the best possible data for your project. If you are preparing a proposal for the 0.9-m, this website provides information that will best inform you of the capabilities and limitations of the two observing modes (user and service). In either case, this website will hopefully help with your preparations.
The responsible authorities for the SMARTS 0.9m are:
riedel
chara [dot] gsu [dot] edu (subject: SMARTS%200.9m%20Correspondence) (Mr. Adric Riedel) (GSU), SMARTS Fellow for the 0.9m.
thenrychara [dot] gsu [dot] edu (subject: SMARTS%200.9m%20Correspondence) (Dr. Todd Henry) (GSU), SMARTS 0.9m Coordinator.
jsubasavagectio [dot] noao [dot] edu?subject=SMARTS%20General%20Correspondence">
Dr. John Subasavage [12] (CTIO), SMARTS Telescope Fellow at CTIO
charles [dot] bailynyale [dot] edu (subject: SMARTS%20General%20Correspondence) (Dr. Charles Bailyn) (Yale), Director of the SMARTS Consortium.
Questions about 0.9m operations should be directed to Mr. Riedel and Dr. Henry; GSU has been using the 0.9m since 1999 and has been coordinating the 0.9m since the beginning of SMARTS in 2003.
Time on the SMARTS 0.9m is a mix of classical observing and service observing, divided into (generally) alternating seven night blocks the CTIO staff call 'turnos'. Within each 'turno', time is assigned by the night (or half-night, but not less). As such, we cannot guarantee weather conditions.
The observing schedule for the 0.9-m is posted (and updated) here [1]:
Under the 'TIMES' link for your night, you will also find a listing of precisely what hours you have been given. This will aid in planning your programs.
Unless you wish to keep your program completely confidential, this is also where it will be posted for the service observers to see.
Three weeks before your scheduled observations' turno, you will be contacted by Adric Riedel, who will send you a template to use to plan your program. Reminders will be sent two weeks before, and 10 days before, as needed. IF YOU DO NOT RESPOND WITH AN OBSERVING LIST BY 7 DAYS BEFORE YOUR TURNO BEGINS, YOU WILL FORFEIT YOUR TIME.
You will also need to fill out the instrument form at
http://www.ctio.noao.edu/forms/supportforms/ccd_direct.php [13]
(using 0.9M+Tek 2048 CCD) to confirm your time and request the filters you will need. This is critical for the 0.9m in order to be sure that your desired filters are available.
After your observations are complete, Mr. Riedel will contact you again with the night reports from your scheduled nights and instructions on how to download the data from GSU's FTP server. Data will be held there for 30 days as bzip2-compressed fits files plus a text file with brief header information.
Pictures of the instrument can be found here [14]
The SMARTS 0.9m is a 36-inch (91-cm) Boller & Chivens telescope, built in 1965 and currently operated by the SMARTS Consortium for NOAO.
The only available instrument on the 0.9m is a Tektronix 2048x2046 CCD with 65K pixel depth and a FOV of 13.69' on the sky, with a pixel scale of 0.401"/pix (not 0.396"/pix as listed on the CTIO page below). This arrangement has lasted for more than 10 years, and has been incredibly stable, both photometrically and astrometrically.
More detailed information about the following points may be found here [2]:
The Tektronix CCD can be run in a number of modes:
FULL chip (13.6'), ONE amp readout (3 min readout)
FULL chip (13.6'), QUAD amp readout (0.8 min readout)
Central QUARter (6.8'), ONE amp readout (0.8 min readout)
Central QUARter (6.8'), QUAD amp readout (0.3 min readout)
Quad-readout frames will need to be processed with a tool like IRAF's quadproc, as each of the amplifiers has its own bias level. In single-amp mode, the lower left (ll) amplifier is usually used.
There are also three available gain settings:
1: (unavailable, failed in March 2009)
2: Read Noise ~ 1.6 ADU = 3.9 e-
3: Read Noise ~ 1.8 ADU = 3.2 e-
4: Read Noise ~ 2.6 ADU = 2.7 e-
Finally, the 0.9m accepts two filter wheels. There are two sizes available, 8-slot wheels for 3"x3" filters, and 5-slot wheels for 4"x4" filters.
CTIO has a large assortment of filters available for use, listed here [15] (many linked to their filter traces):
CTIO also has some old 2"x2" filters useable in the 0.9m, listed here:
http://www.ctio.noao.edu/instruments/filters/index.html [16]
Their use is not recommended --- many of them are seriously degraded and all of them vignette on the 0.9m in FULL chip mode.
Please make your filter request as specific as possible when you fill out the instrument form. These filters are shared between telescopes so CTIO staff will need time to make sure the right ones are available for the 0.9m on your nights.
http://www.ctio.noao.edu/forms/supportforms/ccd_direct.php [13]
The most common filters in use at the 0.9m are:
* The Tektronix UBVRI 3"x3" filter set (roughly Johnson/Kron-Cousins), which is almost always comprised of the Tek #2 UBRI filters and the Tek #1 V filter. Filter traces for all three Tek filter sets are available at
http://www.chara.gsu.edu/~thenry/SMARTS/smarts.0.9m.filters.pdf [17]
* An SDSS ugriz 4"x4" filter set (Sloan filters, not to be confused with our Thuan-Gunn griz set) Details about the common filters (e.g. exposure time estimates) are available here:
http://www.chara.gsu.edu/~thenry/SMARTS/smarts.0.9m.filters.text [18]
HEADERS --- there is a known issue with the headers. The "new" TCS installed in 2005 does not properly communicate with the ARCON data acquisition computer, and as such several header keywords have meaningless values. We are continuing to work on this long-term problem, but do not yet have a solution. For details, see
http://www.chara.gsu.edu/~thenry/SMARTS/smarts.0.9m.tcs [19]
PHANTOM OF THE 0.9M --- occasionally, the dome will spin 360 degrees seemingly without cause. Many tests have been done to determine the cause, and no convincing gotcha has been found.
POINTING --- pointing is typically good to 20 arcseconds, which means it is reliable enough that you should be able to use the J2000 coordinates of your intended field. However, we HIGHLY recommend that you provide an electronic finder (with orientation and scale labels!)
on a working website for every target.
BAD COLUMNS --- Like many CCDS, the Tek 2k CCD on the 0.9m has bad columns. These can be avoided. Otherwise, a bad pixel mask [20] (unbinned - simply rename to exclude '.txt') can be used to interpolate across the columns.
A sample observation list template (ASCII format) can be found here [7]. YOU MUST USE THE TEMPLATE FOR YOUR OBSERVATIONS. You will be contacted by the 0.9m coordinator with a template appropriate for the current observing semester. The closer you adhere to the format, the smoother your observations will go.
A few tips and requests, because we at the 0.9m like to under-promise and over-deliver:
* No non-sidereal programs in service mode. The timing and instrument changes make this better suited to user mode.
* No polarimetry programs in service mode. As this is a non-standard instrument setup for the 0.9m, it is better handled as user time.
* Assume you are proposing for automated observing. None of us are familiar with your program, so everything you need must be spelled out.
* You may only have TWO possible programs (photometric, nonphotometric backup) per night, and each must be entirely self-contained. A single program that can be done in either case (ignoring standard star observations if non-photometric, for example) is also fine.
* Assume your program will be set in stone once started. We do not have the facility to change target lists for night #2 based on what was observed on night #1.
* Assume the observer is going to go straight down your list as the night progresses. Use the priority system to make sure the observer knows which targets can be skipped if time is short.
* For best results when requesting absolute photometry, use an airmass calculator (such as
http://www.briancasey.org/artifacts/astro/airmass.cgi [21])
to determine the exact times (UT) you want your standards observed, and list each visit as a separate observation.
* The weather at CTIO is worst in winter. Programs scheduled for December or January (Chilean summer) can likely expect to get more than 70% photometric nights, but the odds of photometric weather in August are low.
* Plan for overhead, as detailed for service mode at:
http://www.chara.gsu.edu/~thenry/SMARTS/smarts.overheads [22]
* Keep it simple. Our observers are Chilean CTIO employees. They are not scientists, nor is English their first language, and Mr. Riedel does not want to reword parts of your program to make it clearer for them.
The following requests work well:
* integrating for a certain amount of time
* integrating to X number of peak counts on a target object (marked on a finder)
* dithering between observations (this goes for sky flats as well)
* moving the target off the center of a quad-readout frame
* explicit timing of observations (put UT times in the notes)
* listing objects, such as standard stars, multiple times if you want them observed at different airmasses
* "use ND filter if (object) saturates in less than X seconds"
* "observations may begin in twilight"
* observing a target continuously for an entire night/ until UT time X
Anticipate an email from Mr. Riedel, perhaps begin compiling the necessary information as outlined in this page, and promptly respond with the requested information. You will then be placed on the "confirmed" list for observations in the upcoming semester.
----------------------------------------------------------------------
If there are any further questions about anything in this email, feel free to contact Mr. Riedel or Dr. Henry.
Clear Skies,
Adric Riedel
SMARTS Fellow
Graduate Student, Georgia State University
Dr. Todd J. Henry
Director, RECONS
Professor of Astronomy, Georgia State University
The following is a checklist for you to work through in order to have your service observations made successfully.
You must have your observing templates sent to riedelchara [dot] gsu [dot] edu (subject: SMARTS%200.9m%20Correspondence) (Adric Riedel), GSU SMARTS Fellow, 7 days before your turno stars, OR YOUR TIME WILL BE FORFEITED --- NO EXCEPTIONS.
Notifications and example templates will be sent to you on the following schedule:
21 days before your turno starts --- INITIAL CONTACT
14 days before your turno starts --- REMINDER 1
10 days before your turno starts --- REMINDER 2
7 days before your turno starts --- *** HARD DEADLINE ***
You must fill out a CTIO instrument form at
http://www.ctio.noao.edu/forms/supportforms/visitor_support.html [23]
You should send this in at least TWO WEEKS before the first night of your turno. This allows us to catch any problems, such as whether or not your requested filters are scheduled for a user at another telescope.
For data acquired via service mode, the GSU 0.9m SMARTS Fellow (as of JUL 2009, Adric Riedel) will ftp the data back to a staging area at GSU. You will be given instructions on how to retrieve your data shortly after the observations are taken.
YOU WILL HAVE 30 DAYS TO RETRIEVE YOUR DATA, IF YOU WAIT LONGER THAN THAT, YOU DO SO AT YOUR OWN PERIL
********** WARNING **********
PREPARING YOUR TEMPLATE TAKES FAR MORE WORK THAN YOU PROBABLY ANTICIPATE, SO START EARLY!
Once your observing template has been examined (and likely revised) by the GSU SMARTS Team, you can check it on the nightly schedule website at:
http://www.chara.gsu.edu/~thenry/SMARTS/scheduleYYYYA.htm [25], or
http://www.chara.gsu.edu/~thenry/SMARTS/scheduleYYYYB.htm [26]
There are two sets of times listed below, LIGHTNING and HUMAN. The LIGHTNING case assumes that everything goes absolutely perfectly, with observer reaction time an absolute minimum. This does not occur in real life. The HUMAN overhead is the one that should be adopted for all service observing programs.
| LIGHTNING | HUMAN | ||
| Slew/Target Acquisition | 3 min | 5 min (variable) | |
| Change Directory/File Name | 1 min | 1 min | |
| Change Chip Setup | 1 min | 2 min | |
| Change Tracking (non-sidereal) | 1 min | 2 min | |
| Focus Frame | 3 min | 6 min | |
| Chip Readout | |||
| Full Chip/Four Amps | 0.8 min | 0.8 min | |
| Full Chip/One Amp | 3 min | 3 min | |
| Quarter Chip/Four Amps | 0.3 min | 0.3 min | |
| Quarter Chip/One Amp | 0.8 min | 0.8 min | |
You have a short service program that is inserted into a longer program scheduled for the same night. You want to use a different chip setup, non-sidereal tracking, and a single 300 second integration. The required time is:
| Slew/Target Acqusition | 5 min |
| Change Directory/File Name | 1 min |
| Change Chip Setup | 2 min |
| Change Tracking (non-sidereal) | 2 min |
| Focus Frame | 6 min |
| Chip Readout = Full Chip/Four Amps | 0.8 min |
| Integration Time | 5 min |
| Change Directory/File Name BACK | 1 min |
| Change Chip Setup BACK | 2 min |
| Change Tracking (non-sidereal) BACK | 0 min (flip switch) |
| Total Time for Observation | 24.8 min |
This document outlines the duties of proposers who have user time on
the CTIO 0.9m. This includes both NOAO and SMARTS users who are going
to CTIO to take their own observations. It is the observer's
responsibility to carefully consider all relevant information at the
Georgia State University (GSU) SMARTS website at
http://www.chara.gsu.edu/~thenry/SMARTS [27]
For us to understand what observing modes are most popular on the 0.9m, you may be contacted by members of the GSU SMARTS team to find out the following information:
General travel information can be found at the fundamental site
http://www.ctio.noao.edu/diroff/obser_trav.htm [28]
If someone from your team will be traveling to CTIO, fill out the travel form for CTIO at
http://www.ctio.noao.edu/travel/itinerary.php [29] (or, http://www.ctio.noao.edu/forms/ [30] and click on Travel Plans)
In the "Proposal Number" please write SMARTS.
You can arrange to be met at the La Serena airport by a cab that will take you directly to the AURA offices (and your dorm). If you arrive on time, you should be met after claiming your bags. Otherwise, you may need to catch your own taxi from the airport to AURA/CTIO in "Colino el Pino". You will need to pay in pesos, so make sure you have some. To return to the airport after your run, ask the folks in Reception to arrange for a taxi from the La Serena motel, or just go directly to the airport from the mountain --- ask the carryall driver to drop you off at the airport.
Pay your bill at the ROB (Round Office Building) on the mountain. Credit cards are preferred (but note that many credit cards charge an extra handling fee for foreign charges.)
*** If in dire need of travel assistance only, as a last resort contact xherrerosctio [dot] noao [dot] edu (subject: Observer%20Travel%20Assistance) (Ximena Herreros).
You must fill out an instrument form at
http://www.ctio.noao.edu/forms/supportforms/visitor_support.html [23]
You should send this in at least TWO WEEKS before the first night of your observing run. This allows us to catch any problems, such as whether or not your requested filters are scheduled for a user at another telescope.
You should familiarize yourself with operations at the 0.9m. The link entitled "Observing Hints for the 0.9m" will give you some information about how to use the 0.9m. This link is the one just below the link that got you to the page you are reading now. It can also be found at:
http://www.chara.gsu.edu/~thenry/SMARTS/smarts.observing.YYYY.MMDD [31]
Tek2K is a 2K optical CCD imager that provides a 13.6 arcminute field of view with 0.4 arcsecond pixels when installed on the 0.9-m telescope.
| Detector Parameters (f/13.5) | |
| Pixels | 2048x2046 |
| Pixel Scale | 0.401"/pixel |
| Field Size | 13.6'x13.6' |
The observer can control and change several CCD parameters. These are: the CCD readout format, the binning, and the gain. To reduce the readout time, the CCD can be read out through multiple amplifiers (DUAL or QUAD mode). A single region-of-interest (ROI) can be read out, positioned at an arbitrary place on the CCD. Observers should think carefully whether they need all the field (if not, read a ROI) or the resolution (if not, bin 2x2). Even though the CCDs with QUAD readout have short read times by big-CCD standards, substantial gains in efficiency are possible by reducing the format.
| ***Table of gain values*** | ||||
| Index | Read Noise | 1/Gain | Read Noise | Quad Read |
| LL LR UL UR | LL LR UL UR | LL LR UL UR | Time | |
| (ADU) | (e-/ADU) | (e-) | (sec) | |
| 1: | 1.1 1.2 1.1 1.2 | 5.1 4.8 5.5 4.5 | 5.6 5.8 6.0 5.5 | 25 |
| 2: | 1.5 1.6 1.5 1.6 | 2.6 2.5 2.7 2.5 | 3.9 3.9 4.0 3.9 | 32 |
| 3: | 1.7 1.9 1.8 1.9 | 1.8 1.7 1.8 1.5 | 3.1 3.3 3.2 2.8 | 39 |
| 4: | 2.6 2.6 2.5 2.6 | 1.0 1.0 1.1 1.0 | 2.6 2.6 2.8 2.6 | 53 |
*NOTE: A power outage that occurred on 07 March 2009 caused gain values to spike when the CCD is operated with gain index #1. As such, the full well of the CCD is reached before digital saturation at ~ 44,000 ADU. Non-linearity is likely a problem below this value. We currently do not support this index setting for service observing and strongly recommend that visiting observers select another gain index. For the remaining 3 index values, digital saturation of 65,535 (ADU) is reached before full-well capacity. Read times are quoted for full frame quad readout with no binning. Linearity: gain increases by <0.3% over signal range. Patterns have been minimized for full frame readout at gain 1 (prior to power outage) and will be more apparent though still a minor source of noise at higher gains or when regions of interest and/or binning are used.
A raw quad-amplifier picture looks a little unusual. Each quadrant has a slightly different electrical offset (ie overscan level), and the four overscan segments are in the center of the picture. The real time display automatically removes the overscan and applies an offset to each quadrant to normalize the DC level. In addition, the real time display colors any saturated (ie 65535) pixel in red.
QUAD CCD pictures have to be trimmed and overscan-subtracted in a separate pre-processing IRAF task called quadproc (in the quad package). Note that even after the pictures are trimmed and overscan subtracted the sky levels in each quadrant will not be identical (unless the sky level is zero). This is because each of the four CCD amplifiers has a slightly different gain. After the trimming and overscan correction with quadproc, the images can be processed (bias subtraction, flatfielding) in the standard manner.
Please refer to the CFCCD User Manual.
Important Tip:
The data acquisition computer (ctioa4) occasionally has trouble handling simultaneous processes, resulting in ARCON crashing. It is recommended that you do not do anything (display another image, reduce data, write tapes, etc.) that uses ctioa4's CPU or accesses ctioa4's disks from another computer while an image is reading out. It is perfectly safe to do these things while the image is EXPOSING. If you want to work on your data, it is best to imcopy the raw images over to ctio36 (but not during image readout!) and do all the work there.
A night assistant is not regularly provided on the 0.9-meter telescope. A TCS software manual is available in the control room.
Domeflat exposure times (gain option #2) to reach a level of about 25,000 ADU.
| Filter |
Exp Time (sec) |
| B | 180 |
| V | 100 |
| R | 110 |
| I | 120 |
 [32] |
A sample "master" Bias frame (quad readout) after overscan correction and trimming with quadproc (click on the image for an expanded view). The frame was created by averaging 20 individual frames (rejection option "minmax"). |
 [33] |
A sample "master" Flatfield frame (quad readout, V filter) after overscan correction and trimming with quadproc (click on the image for an expanded view). The frame was created by median combining 10 individual frames (rejection option "avsigclip"). |
When using multiple-amplifier readout, signal from one amplifier can "leak" into the signal of another. Crosstalk is an additive effect and is proportional to the signal strength in a given amplifier. In the sample frame shown below, this effect shows up as negative (white) images of bright stars in the lower left and upper right quadrants. The white images in the upper right quadrant correspond to the (black) star images of the lower left quadrant (flip the upper right quadrant left-right and up-down). We are currently working on software to correct for this effect.
 [34] |
A reduced 2048x2048 frame (quad readout) showing examples of "crosstalk" (click on the image for an expanded view).
|
Links:
[1] http://www.chara.gsu.edu/~thenry/SMARTS/
[2] http://www.ctio.noao.edu/noao/content/Tek2K
[3] http://www.ctio.noao.edu/noao/content/ctio-3x3-inch-and-4x4-inch-filters
[4] http://tycho.usno.navy.mil/what1.html
[5] http://www.ctio.noao.edu/noao/content/09-m-Welcome-Overview
[6] http://www.ctio.noao.edu/noao/content/09-m-Duties-Service-PIs
[7] http://www.chara.gsu.edu/~thenry/SMARTS/smarts.template
[8] http://www.ctio.noao.edu/noao/content/09-m-Template-Tips
[9] http://www.ctio.noao.edu/noao/content/09-m-Overhead-Times
[10] http://www.ctio.noao.edu/noao/content/09-m-Duties-Classical-PIs
[11] http://www.chara.gsu.edu/~thenry/SMARTS/smarts.observing.2010.0312
[12] mailto:<span class=
[13] http://www.ctio.noao.edu/forms/supportforms/ccd_direct.php
[14] http://www.ctio.noao.edu/noao/content/09-m-History
[15] http://www.ctio.noao.edu/noao/content/CTIO-3x3-inch-and-4x4-inch-Filters
[16] http://www.ctio.noao.edu/instruments/filters/index.html
[17] http://www.chara.gsu.edu/~thenry/SMARTS/smarts.0.9m.filters.pdf
[18] http://www.chara.gsu.edu/~thenry/SMARTS/smarts.0.9m.filters.text
[19] http://www.chara.gsu.edu/~thenry/SMARTS/smarts.0.9m.tcs
[20] http://www.ctio.noao.edu/noao/sites/default/files/telescopes/smarts/tele09/badpix.pl.txt
[21] http://www.briancasey.org/artifacts/astro/airmass.cgi
[22] http://www.chara.gsu.edu/~thenry/SMARTS/smarts.overheads
[23] http://www.ctio.noao.edu/forms/supportforms/visitor_support.html
[24] http://www.ctio.noao.edu/noao/content/SMARTS-Imager-Exposure-Calculator
[25] http://www.chara.gsu.edu/~thenry/SMARTS/scheduleYYYYA.htm
[26] http://www.chara.gsu.edu/~thenry/SMARTS/scheduleYYYYB.htm
[27] http://www.chara.gsu.edu/~thenry/SMARTS
[28] http://www.ctio.noao.edu/diroff/obser_trav.htm
[29] http://www.ctio.noao.edu/travel/itinerary.php
[30] http://www.ctio.noao.edu/forms/
[31] http://www.chara.gsu.edu/~thenry/SMARTS/smarts.observing.YYYY.MMDD
[32] http://www.ctio.noao.edu/noao/sites/default/files/telescopes/smarts/tele09/0.9zero.jpg
[33] http://www.ctio.noao.edu/noao/sites/default/files/telescopes/smarts/tele09/0.9vflat.jpg
[34] http://www.ctio.noao.edu/noao/sites/default/files/telescopes/smarts/tele09/0.9crosstalk.jpg