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  1. #1
    mikec's Avatar
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    Default Eyepiece for PEC



    I'm just getting started in imaging and was looking at PEC for the possibility of longer exposures enroute to the eventual purchase of a guide scope. This is what Skywatcher says I need to do PEC.

    Required accessory: Illuminated reticle eyepiece with double crossline pattern capable of producing at least 300X magnification in combination with your telescope. The true field of view should not exceed 10 arc min.
    In calculating the EP needed for my SW120ED (specs below), I came up with a 3mm/50 afov EP. This can't be right, can it? I must have done something wrong in my calculation.
    Mike
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    Skywatcher ED120 Refractor (fl=900mm - f/7.5) on an EQ5 mount, Zhumell Z-10 Dobsonian (fl=1250mm - f/4.92). Canon 15x50 IS Binos, Canon Rebel XI DSLR (1000D), Orion Starshoot DSI II and all the accessories I can afford for now (unless you guys tell me different)
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  2. #2
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    Default

    Mike,

    Your calculation is correct. Whether or not you need 300x, I'll leave to people who know more about PEC correction than I do.
    SXINIAS

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  3. #3
    mikec's Avatar
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    Default

    Thanks for the verification Joe. I thought it must have been a math error on my part. So you're thinking the 300x may have been an exaggeration or a typo.
    Mike
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  4. #4
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    Default

    I'm just following upon the original post. Could someone with some insight on PEC training please tell me how well this would work? It would give me 72x and a 42' tfov which isn't what SW specs say I need, but I can't find a 3mm/50fov illuminated double crosshaired EP. I'm not sure I would want it if I could. Thanks for any info.
    Mike
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  5. #5
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    Default

    Mike,

    Here's some more options. My suggestion would be to call OPT and discuss what your attempting to do. They have been very helpful with my questions in the past.

    Illuminated Reticle Eyepieces, Astrometric, #909 - OPT Telescopes

    PS. I did my PEC correction but used a completely different method.

    My attempts at PEC
    Last edited by ghswen; 02-23-2010 at 06:20 AM.
    Gordon
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  7. #6
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    Default

    Thanks so much Gordon for your help. I assume you got the bugs worked out?

    My attempt at using the corrected PEC didn't work out very well last night. Going to have to do some more experimenting. I think I may have accumulated some drift in the PEC file I recorded. Will keep playing with it.
    Mike
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  9. #7
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    Default

    I was finally able to figure out what I had done wrong when I ran the raw data through PECprep. I apparently forgot a few steps that the tutorial had buried in the appendix section. I re-ran the raw data and found my error (I had left the "drift" in the smoothed data). Now that I had clean data I had used the scope another time and neglected to park the mount (you have to park / unpark the mount EVERY time if you use PEC so the mount knows the position of the worm gear / stepper motors.) So I can no longer use that data. Plan is to run new raw data when I get some time and make my corrections then. I will do an update once I get it finished and working.
    Gordon
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  11. #8
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    Default

    The 300X / 10-degree FOV are not critical - what the illustrious technical writers are trying to convey is the need for a high-magnification, illuminated reticle eyepiece with a relatively narrow FOV...

    Any standard double-line reticle illuminated guiding eyepiece will suffice. The critical components:

    - double-line "box" reticle
    - illuminated (preferably controllable intensity)
    - reasonably high magnification

    The reason for the narrow FOV is to help reduce the visual clutter in the guiding field. It is easy to lose track of the actual guide star if the FOV is really wide.

    The remainder is somewhat subjective opinion...

    Manual guiding is very, very tedious. It is visually fatiguing, and demands a lot of concentration. For PEC training, it is probably tolerable, as you only need to handle the concentration and visual task over the mount's PEC cycle (usually 8 - 10 minutes or thereabouts for one of the Synta EQ5/EQ6 derivatives).

    Most of the time, PEC training gets performed in conjunction with an ST-4 compliant auto-guider. The result is greater precision in guide corrections, made at a higher frequency than is possible with manual guiding.

    Not to say that PEC training can't be performed with manual guiding, it's just much more difficult...
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  13. #9
    mikec's Avatar
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    Default

    Thank you very much Joe, Gordon and Austin for your help and invaluable information. I can't wait to be able to pay it forward one day!
    Mike
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