Lumicon Easy Guider for 2 inch focuers

The Original Off Axis Guider. Patent:4,448,500 - 1981

Part number LG1015 Configured for DSLR Camera setups

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Congratulations and thank you for purchasing one of the most powerful astrographic accessories on the market today – The Lumicon Easy Guider.

Lumicon first patented the Off-Axis Guider in 1981 and has been manufacturing this same device since that time. Lumicon OAG’s have been sold world wide and is the most used off-axis guiding system in the world. We’re pleased to add the performance and quality, that tens of thousands of astronomers have enjoyed, to your imaging setup. With a few short minutes of careful setup you will be enjoying the benefits of off-axis guiding.

Benefits of Off-Axis Guiding

• Guiding occurs with the same light path as the imaging detector thereby eliminating the effects due to differential flexure/slop of the auxiliary guide scope.

• Differential flexure in guiding setups often introduces errors far worse than the actual corrections actually needed. Off-axis Guiding avoids this problem.

• Auxillery guide scopes are blind to image shifting due to primary mirror “flop” in telescopes with moving primary mirrors (SCT’s). Off-axis guiding corrects for this problem.

• Guiding occurs at the same focal length as the main imaging camera. Although CCD guiding software can compute tracking errors to sub-pixel accuracy, many guide scope combinations have marginal or too-short focal lengths to be properly effective. Off-Axis Guiding Avoids this problem.

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Off-Axis Guiding Tips

• First things first. If your mount has a periodic error correction system make sure it is well trained. We recommend using PEMPro.

• Make sure your mount is well polar aligned. Guiding will keep the guide star stationary but the field will still rotate. We recommend learning to use a drift alignment technique with assist software such as PEMPro.

• Adding an Off-Axis Guider to your system adds a layer of mechanical complexity to the imaging train. Make sure all of the connections between the telescope and detector are tight and wiggle/slop free. A tight system is your best starting point for success.

• Make sure the guide camera is equally locked in place. Any movement of the guide camera will introduce artificial guiding errors.

• Off-Axis Guiding is powerful. A common mistake made when configuring guiding software is to set it to be too responsive. If the servo loop is set too tight then the guiding system will attempt to respond to star movement due to atmospheric seeing disturbances.

• Use longer guide camera exposures to help smooth out seeing displacements.

• Use longer guide exposure intervals to avoid responding to seeing displacements.

• An auto-guiding system is working best when it is making the fewest amount of guiding corrections needed to maintain suitable tracking.

• Remember, the goal of guiding is to correct for drive tracking errors and not seeing and wind turbulence errors.

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Guider Layout & Setup

The guider is fairly straightforward and consists of the main guider body, a pick-out prism, guide camera drawtube, and removable/rotating T-thread adapter. To assemble your system, loosen the 3 locking screws that hold the T-thread adapter in place and remove the adapter from the guider body. Thread the adapter into the front of your camera adapter (DSLR T-ring) and firmly tighten. (You may need to use a spacer ring or alternate adapter in order for the guide camera to reach focus; see specific configurations later). Re-attach the adapter and camera to the guider body. Before tightening the locking screws adjust the orientation of the camera so the detector is “square” with the edge of the prism. Look through the guider into the camera to view this alignment.

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Guider Setup Continued

Attach the 1.25” extension tube to the guide camera. DSLR cameras have a larger Back Focal Distance, therefore the guide cameras need to be spaced back further. The extension tube allows for the required back focus spacing.

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Guider Setup Continued

Insert the guide camera into guide camera drawtube, midway down the tube, and lightly lock the thumb screws. In later steps you will adjust the position (focus) of the guide camera and re-lock the screws more firmly. As you insert the guide camera into the drawtube align the orientation of the guide chip with the edge of the pick-out prism in a similar fashion as you did the main camera. However, this time it will be a blind alignment. Just do your best. In the figure below we’ve turned the guide camera transparent for illustration purposes. Again, just do your best to align the long edge of the chip with the long edge of the prism.

Finally, attach your assembled imaging train, plus off-axis guider, to your telescope focuser. Adjust the orientation of the whole assembly as necessary.

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Optical Spacing Configuration

In order for the off-axis guider to work, both the main camera and the guide camera have to come to focus. For this to happen, the distance of both camera detectors must be located the same distance from the center of the pick-out prism.

All units in mm.

Goals: A must = B C must be > 27mm and < 48mm

A = Guide Camera Back Focal Distance + C B = Camera Back Focal Distance + 17.5mm + T Ring thickness – Extension Tube Length C = B – Guider Camera BFD

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Example #1:

• NIKON D7000 DSLR o BFD = 46.5mm

• T-Ring Thickness = 8.0mm o BFD = 20mm

• ZWO ASI “Mini” camera (all models) as guider o BFD = 8.5mm

• Extension Tube Length (Provided with Guider) o BFD = 25.0mm

Calculation: First Calculate B: B = Camera BFD + 17.5 + T-Ring thickness – Extension Tube Length B = 46.5 + 17.5 + 8 - 25 B = 47mm

Next Evaluate C: C = B – Guider camera BFD C = 47 – 8.5 C = 38.5

C is greater than 27 and less than 48 so the guide camera will come to focus.

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Example #2:

• Canon 5D DSLR o BFD = 44.0mm

• T-Ring Thickness = 8.0mm o BFD = 20mm

• ZWO ASI “Mini” camera (all models) as guider o BFD = 8.5mm

• Extension Tube Length (Provided with Guider) o BFD = 25.0mm

Calculation: First Calculate B: B = Camera BFD + 17.5 + T-Ring thickness – Extension Tube Length B = 44+ 17.5 + 8 - 25 B = 44.5mm

Next Evaluate C: C = B – Guider camera BFD C = 47 – 8.5 C = 38.5

C is greater than 27 and less than 48 so the guide camera will come to focus.

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Zwo guiders Back Focal Distance Table

Mini's / Guiders Model Back Focus (mm)

ASI120MM Mini Mono 8.5 ASI174MM Mini Mono 8.5 ASI290MM Mini Mono 8.5

Other Guiders Back Focal Distance Table

Model Back Focus (mm) Lodestar 12.5 QHYCCD5 Version 1 12.5 QHY5III174 11.0 QHY5III178 11.0 QHY5III185C 11.0 QHY5III224 11.0 QHY5III290 11.0

Model Back Focus (mm) Canon EF mount cameras 44 Nikon F Mount Cameras 46.5

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Final Guider Setup – Focusing

Once your camera and OAG setup is attached to the telescope and connected to the control computer: Center a bright star such as Vega or Antares and bring the main camera to focus using the telescope’s focuser. We recommend using a Bahtinov mask to assist if the telescope is manually focused and autofocus software, such as FocusMax, if the focus is controlled by the computer. Next loosen the guide camera lock screws and adjust the focus of the guide frame by moving the guide camera in and out of its draw tube. A Bahtinov mask is very useful for this task. Once best focus is found, lock down the guider camera locking screws. It is imperative that the guide camera have no wiggle or slop or it will introduce guiding errors as it moves relative to the main camera.

Guiding Software

Last, configure your auto guiding software as necessary. Many imaging control software packages now integrate auto guiding features. Prism, TheSky X, MaximDL etc. PHD2 is also a very good open source package.

Now go take some amazing astrophotos or collect some excellent scientific data.

Thank you!

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Lumicon is owned by Optical Structures Incorporated.

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