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Thread: Aligning and Autoguiding iOptron EQ mounts

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    Post Aligning and Autoguiding iOptron EQ mounts



    Thought this article I posted to the iOptron Yahoo users group might be a help to those who don't access Yahoo groups?

    Setting up, Polar Aligning and Auto-Guiding an Equatorial Mount
    By: Paul Chasse

    This is a basic 'How-To' of preparing your mount and your basic setup with PHD or PHD2 with an equatorial mount. I will attempt to explain my method and supply you with the tips that I use to ensure that an imaging session will be a successful one. My experience is based on iOptron telescope mounts but the basics apply to all types of equatorial mounts, regardless of manufacturer.

    SETUP

    Prerequisites: You just can't assemble your mount, place a telescope on it with a camera and guiding equipment and start imaging. You can, but your results will not be very good. Read the User Manual and become familiar with your mount's operation and controls before attempting polar aligning and imaging in the dark of night. Observe all safety precautions noted for your mount, including using the safety stop on the counterweight to prevent personal injury in the event of failing to lock the counterweight securely. Never attempt to slew any mount with only a counterweight or only a telescope on the mount. Either have no counterweight and no telescope, or have a balanced telescope/counterweight installed. Failing to observe this basic rule may result in damage to the mount, the telescope and your pride.

    Level: The first thing you should do is become familiar with leveling the bubble level by adjusting the lower tripod legs up and down to achieve a perfect level. Use the bubble level in the mount as it will always be your reference point when setting up. Naturally the mount should be attached to the tripod, don't bother leveling the tripod, just level the assembly.

    Note: Do not over-tighten the leg locks, brute force is not necessary and will eventually result in the steel ends of the locks wearing through the plastic tension pad and gouging and denting the tripod wall.

    Note: On the subject of tightening, the RA lock(s) that holds the mount to the tripod only needs to be tightened enough to keep the mount flat on the tripod surface and prevent it from tipping. Excess tightening of the RA lock(s) will result in making azimuth adjustments when polar aligning very difficult.

    Squaring the mount: The mount’s RA and DEC axes should (must) be square and orthogonal to the bubble level. This is easily accomplished at night by just leveling the mount, pointing the mount to True North and centering Polaris in the polar scope reticle.

    RA Axis: To square the RA axis, loosen the RA lock(s) slightly and then just move the mount using the azimuth adjusters all the way to the left and then to the right. While observing through the polar scope, Polaris should remain on the horizontal line all the way across the reticle line. If it does not, use the left/right slew buttons to adjust the level of the reticle line until Polaris stays on the line when moved from left to right using the azimuth adjusters. Once you have done this and are satisfied that the RA axis is level, you can mark the RA joint using a label or marker to indicate the RA ‘Zero Point’.

    DEC Axis: To square the DEC axis, after establishing the RA zero point, you must place a telescope in the DEC saddle. Install a wide eyepiece (25mm or larger). While viewing through the eyepiece using the up/down slew buttons, slew the mount in DEC until Polaris is centered from side to side in your eyepiece.

    Once you are satisfied that Polaris is centered as closely as possible, mark the DEC joint with a label or marker. This is your DEC ‘Zero Point’
    You have now established a mount/ota Zero Point.

    Note: A crosshair eyepiece would be the most accurate way to center Polaris side to side, but most users have 10mm crosshair eyepieces and Polaris may be out of the field of view above or below your field of view due to cone error. With some telescope dovetails it is possible to remove this vertical cone error and perfectly center Polaris, but just centering Polaris horizontally is sufficient for a basic setup.

    Note: This procedure can also be performed with a dSLR camera’s Live View screen in lieu of an eyepiece as the field of view is sufficient.

    Mount time/date setup: Now that the mount is level and the RA and DEC axes are squared to the level it’s almost time to polar align the mount. In order to achieve an accurate polar alignment the mount must know your location on the planet. This requires you to input the exact latitude and longitude of your current location into the hand controller in the Setup menu. The mount also needs to know your exact time, date and UTC offset. If any of this information is incorrect, your polar alignment will be incorrect.

    Note: Polaris is always moving around the North Central Pole in a counter-clockwise rotation at Sidereal speed approximately 40-45 arc-minutes from the exact center of the NCP. Sidereal speed is approximately 15 arc-seconds of movement per second. There are 60 arc-seconds per arc-minute, so if you are off by just 30 seconds in your time setting you have introduced 7.5 arc-minutes of error automatically to your polar alignment accuracy. I use the iOptron Polar Scope App and I synchronize my hand controller time to the App to within 2 seconds

    Polar Scope alignment (Collimation): For the most accurate alignments the polar scope must be pointing to the same part of space as the mount’s axis. Polar scope alignment can be checked during the day. No telescope or counterweight is required. The mount must be lowered enough for you to see a distant object at least 500 yards away (further is better). The mount must be in the Zero Position. Center the distant object, like a flagpole, chimney or window frame in the center of the polar scope reticle crosshairs. Now release the RA locks and while observing the object in the polar scope, rotate the mount to the right and then to the left until it is horizontal. While rotating left and right, the object should stay in the center of the crosshairs of the polar scope if it is perfectly aligned. The small center circle in the polar scope is 4 arc-minutes in diameter and can be used as an error reference point. If your object stays within the 4 arc-minute circle it is close enough for auto guiding the mount. If it is substantially outside of the 4 arc-minute circle when rotating the mount then the polar scope should be aligned per the manufacturer’s procedure.

    Note: The procedure for focusing and aligning a iOptron polar scope is available in the iOptron Forum in Yahoo Groups or may be obtained by emailing the manufacturer.

    Note: Focusing the polar scope reticle is done by rotating the knurled ring on the end of the polar scope. If you can get the reticle in perfect focus but cannot get focus on the star or target simultaneously, then the polar scope must be removed and the front cell adjusted to achieve focus with your eyes. You must focus the reticle perfectly before adjusting for target focus, once both are perfect tighten the front cell adjusting ring and reinstall the polar scope.

    Polar Aligning

    I recommend following the instructions in the User’s Manual for polar aligning the mount with the following tips.

    With a balanced ota and counterweight installed and the mount in the Zero Position, start by centering Polaris perfectly in your polar scope reticle’s crosshairs.

    With Polaris centered, check the level of your crosshairs by moving the mount in azimuth using the mounts azimuth adjusters. Polaris should remain parallel to the horizontal reticle line, if not you can use the left/right ascension slew buttons to adjust the angle until it remains horizontal from one end of the line to the other end. Your polar scope is now level with the cosmos.

    With Polaris back in the center of the polar scope reticle, turn on your camera’s Live View and center Polaris by using the up/down declination buttons to move Polaris to the center of your Live View screen. (Using the left/right ascensions buttons will not work here, don’t bother trying) Polaris may not be centered vertically due to cone error between your ota and mount, if you have an adjustable dovetail you can center it perfectly, if not, at least you have eliminated half the cone error present and improved pointing accuracy.

    Note: If you have PHD setup and operating, use the bullseye overlay to center your guide scope at the same time, now all your optical axes are pointed at the same place in space and pointing errors have been minimized.

    Once you are satisfied that your setup is as level and square as you can get it, it’s time to position Polaris in the correct place in the polar scope reticle. Using the mounts latitude and azimuth adjusters, move Polaris to the position indicated by the hand controller. This is obtained by opening the HC Alignment menu and scrolling to Pole Star Position. Selecting this option will display a graphical representation of Polaris’ position in the polar scope reticle. It also displays an hour figure and a radial offset figure, ie; 9h20m and 40.5m.

    You must place Polaris at those exact spots in the polar scope reticle by using the latitude and azimuth adjusters, not the HC slew buttons. Once positioned correctly, snug down your lat and az adjusters and recheck and readjust as necessary since snugging down the adjusters may sometimes move the position.

    Note: Do not overly tighten the RA lock knob as this will result in sticky or jerky movements when adjusting in azimuth. The RA lock knob(s) only needs to be tightened enough to prevent the mount from tipping on the tripod or pier.

    Note: I recommend using a 30mm rubber eyecup on the polar scope to reduce parallax and increase positioning accuracy when polar aligning.


    Autoguiding

    Now that your mount is properly prepared, set up and polar aligned it’s time to actually auto guide and start imaging with the mount.

    Prerequisites: A laptop computer, a guide camera and a guide scope. You will need to download and install to the laptop the following software programs:

    PHD or PHD2 (free software) or any other guiding software.

    Ascom Platform 6.1

    iOptron’s current Ascom drivers

    Your guide camera’s Ascom drivers

    Setting up auto guiding: Install your guide scope and camera on to your ota using the supplied bracket or rings and tighten firmly. Whether you mount the guide scope vertically parallel to the ota or offset to the ota is not important, what is important is that you orient the guide scope so that its sensor is square to the axis of the mount, ie; not tilted or offset. You want the guide camera sensor as level as possible. This will minimize cone error and make camera corrections more accurate.

    Note: In PHD you can use the bullseye overlay to assist in leveling the guide camera sensor in the same way you level the polar scope.

    In the hand controller of the mount, go to the Guide Rate settings tab and open it. Set the guide rate of the mount to 1.0 if possible. Some mounts will only allow a max setting of .90 (CEM60 series)

    Balance your ota heavy in both axes to keep the worm against the ring wheel and prevent ‘bouncing’ of the worm between the ring gear faces. Always balance in DEC first! From a perfect balance I balance 1/2” heavy in both axes.

    Note: To prevent your cables from dragging or causing flexure in your images they should be looped from the camera and guide camera to a point midway on the ota and secured there with a bungee or gaffers tape. If that’s not possible at least loop them over your ota’s mounting ring knobs. This will eliminate cable drag entirely.

    Connecting your mount with PHD: For basic (recommended) ST4 guiding you must connect the ST4 cable from the guide camera to the mounts ST4 port. The USB cable from the camera is inserted to an available USB port on your laptop. You will receive confirmation of a connection in the form of a ‘ding’ from your laptop as it loads the appropriate camera drivers. Open PHD and select your camera from the Camera Icon tab, then open the Mount tab at the top of the PHD screen and select ‘On Camera’. Set the camera exposure tab to 1.0 second.

    Now you must click on the blue arrow tab to turn on your camera. If your connections are correct the PHD screen will now show a live image complete with stars. Adjust the focus of your guide camera by moving the guide scope focuser in or out until the stars are nicely resolved. Good focus can be determined by observing the dimmest, smallest stars in the field of view and focusing until they appear the brightest. They don’t have to be sharp or have crisp edges, PHD will function just fine.

    Basic settings in PHD: Now that you have an image it’s time to make some basic settings in the ‘Brain Icon’ or advanced section of PHD.

    Under Calibration steps set the steps to a value of 2500-3500.

    Set the Noise Reduction value to 2x2 mean.

    Set the Star Mass value to .90 (this will eliminate the annoying warning ding if a cloud moves over the guide star, your image is ruined anyway).

    Set the Min Motion value to no more than .20 pixels. A setting of .40 pixels means that no guide corrections will be sent until the guide camera sees a movement of .4 pixels or greater, which means your stars will be elongated by default and your graph line will be very jagged.

    Start Guiding: Assuming you are now setup and have focused your guide camera and also your imaging camera (I recommend using a Bahtinov mask on your ota for perfect focus) it’s time to start the auto guiding process. Select a bright star in the PHD screen field of view and select it by clicking on it. The star will now be highlighted in a green box. Click on the PHD bullseye button and actually start the process. Once you hit the bullseye icon button PHD will start it’s calibration routine and once complete will start auto guiding on your target star.

    During calibration the star will be located in a set of yellow crosshairs, when calibration is complete the crosshairs will turn green. Green = good.

    Note: You should strive to complete calibration in 10-12 iterations. If the iterations are too few or too many you can adjust the calibration steps in the Brain settings until you achieve this. Iterations of over 10-12 steps do not improve guiding accuracy, it only increases the wait time until PHD starts guiding and you can start imaging. I have achieved excellent results with as little as 5 iterations, your results may differ.

    Guiding adjustments: PHD or PHD2 will usually function adequately and deliver round stars with just the default guiding settings, ie; RA Agg 100%, Mx RA 1000 and Mx Dec 150.

    If you want to fine tune the guiding graph you will need to experiment with the base settings and adjust them while observing the guiding graph to determine how it affects the graph. After an adjustment, observe the guiding graph for at least 10 frames to avoid ‘knee jerk’ reactions to a temporary change in graph spikes.

    Note: If you are using PHD2 I recommend setting the guide graph to the Pixel scale rather than Arc-Seconds, since pixel movement is all you are concerned with when imaging. PHD and PHD2 will display guide corrections in pixels at the bottom margin of the PHD screen every time a correction is sent to the mount. You should strive to get this pixel movement as small as possible, about .3 pixels or smaller to ensure round stars and minimum movements of the mount in either axis.


    Summary: There is no “One Size Fits All” solution to auto guiding and images with perfectly round stars. Different mounts and auto guiding configurations will require different settings to produce acceptable results. It’s not unusual at all to spend several nights auto guiding to find the sweet spot for your particular setup. No matter what your settings, round stars at the end of the night is the goal, no matter how you achieved them. A graph that looks like the profile of a timber saw blade is fine as long as you get round stars
    As long as you have setup your mount as closely as you can and have polar aligned as closely as you can, your results will be good.

    Disclaimer: These are my personal opinions and are a result of my particular usage with iOptron mounts and PHD and PHD2. I have not attempted to explain everything that is involved in auto guiding, like guide camera sensor resolutions, over-sampling, on axis guiding, guide scope focal lengths, go-to accuracy, etc. All this information is available from several sources and can be obtained once you are comfortable with the basics. A few excellent sources on aligning a polar scope, PHD and PHD2 can be obtained at the following links:

    How to align a polar scope (Video) by Mitch Arsenault: How to align your Celestron POLAR finder scope - YouTube

    Push Here Dummy (Pdf) by Craig Stark: What to do When PHD Guiding isn't Push Here Dummy - Fishing for Photons - Articles - Articles - Cloudy Nights

    A Guide to PHD guiding (Pdf) by Greg Marshall: http://www.rosecityastronomers.org/r...eToGuiding.pdf

    PHD2 User’s Manual by OpenPHDGuiding: PHD2 v2.3.1 User Manual

    IMG_2114 (1280x960).jpgIMG_1732 (1024x768).jpgCEM60EC_071814_AR152mm (1024x768).jpgzeq_043013_90mm.jpg

    Hope this helps somebody dial in their efforts.

    Cheers...Paul
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    Default Re: Aligning and Autoguiding iOptron EQ mounts

    A discussion thread for this great information from Paul has been created at: Discussion Thread for "Aligning and Autoguiding iOptron EQ mounts"

    This "sticky" is closed...
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