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    Default TeleVue PowerMate 2.5x not parfocal with Everbrite 1.25" Diagonal?



    Hi,

    So sorry, this question probably belongs in another forum, but I'm so embarrassed that I don't know the answer I thought I'd post it here! I was under the impression that if I have properly focused the view with an EP -- any EP -- and then inserted a PowerMate 1.25" 2.5x between diagonal and EP, I wouldn't need to re-focus. And yet, despite my "staying in the family" by using a TV 1.25" Everbrite diagonal all of my EPs require re-focusing. Perhaps related is that the PowerMate 2.5x doesn't fully "sit" in the Everbrite diagonal, i.e. a bit of the silver 1.25" barrel peaks through the top of the diagonal.

    The part where I'm embarrassed is that I may have misunderstood the definition of "parfocal." I am prepared for the public humiliation, as long as I learn the right answer.

    Thanks as usual for all your help!

    Best,
    KJ

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    Default Re: TeleVue PowerMate 2.5x not parfocal with Everbrite 1.25" Diagonal?

    No need to feel embarrassed ..within a specific line of eyepieces you may find that most of them are parafocal IF the manufacturer claims them to be..BUT even then you will still normally have to refocus a hair between the individual eyepieces ...

    I highly suspect that even if your present eyepieces are all the same brand and type and are also claimed to be parafocal by the manufacturer the use of a Barlow or a POWERMATE will still need to be refocused..

    All parafocal means to me is that while I still have to refocus when I switch individual eyepieces I do not need to make much of an adjustment as I would if the eyepieces were not parafocal...

    Bob G
    CPC1100 housed in a slotted domed observatory (Exploradome) 4 and 5 inch refractors for use from the lawn, a 8" Sct (NS 8i) for star parties...
    I Hate the winter so I use heated Motorcycle clothing to stay warm while observing in winter
    Retired, also have 2 other hobbies
    1. tinker with older Corvettes (6 in garage)
    2. make a heck of a lot of sawdust in my wood shop.

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    Default Re: TeleVue PowerMate 2.5x not parfocal with Everbrite 1.25" Diagonal?

    I've never heard of a barlow/powermate being parfocal. It changes the light path too much not to need refocusing.
    Clear Skies

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    120ST, GoScope 70, Lunt LS50TH
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    Plossl 25mm, 10mm, Series E 20mm,10mm,6.3mm,3.6mm , 2x Shorty Barlow, AstoTech ED II 12.5mm, 5mm, Orion .5X FR
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  5. #4
    Albireo's Avatar
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    Default Re: TeleVue PowerMate 2.5x not parfocal with Everbrite 1.25" Diagonal?

    Quote Originally Posted by Bob327 View Post
    No need to feel embarrassed ..within a specific line of eyepieces you may find that most of them are parafocal IF the manufacturer claims them to be..BUT even then you will still normally have to refocus a hair between the individual eyepieces ...

    I highly suspect that even if your present eyepieces are all the same brand and type and are also claimed to be parafocal by the manufacturer the use of a Barlow or a POWERMATE will still need to be refocused..

    All parafocal means to me is that while I still have to refocus when I switch individual eyepieces I do not need to make much of an adjustment as I would if the eyepieces were not parafocal...
    Suddenly, it makes sense now. Thanks a lot!

 

 

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