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Thread: 103mm Doublet vs 81mm triplet APO

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    Default 103mm Doublet vs 81mm triplet APO



    I'm having a hard time deciding between the William Optics 103mm Doublet and the 81mm Triplet APO refractors.

    https://williamoptics.com/products/t...ran-turismo-81

    https://williamoptics.com/products/t...zenithstar-103

    They both have FPL53 glass but the triplet is a bit faster: F/5.9 for the 81 vs f/6.9 for the 103

    I'm going to be using the scope primarily for astrophotography but don't have sufficient experience to know which I should buy. Do I want chromatic perfection or added light gathering ability?

    Any advice you can give will be just great!

    Thanks!
    Clete

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    Default Re: 103mm Doublet vs 81mm triplet APO

    That bit faster makes a noticeable difference - at f7, you'll need exposures about a third longer than at f6 (6x6 = 36, 7x7=49).

    Haven't used the scopes in question, so can't say how the performance compares.

    You may also want to play around with stellarium / Astro Aid / the free CCD calculator from The New CCD Astronomy Home Page to see how the framing with the camera you intend to use compares between the two scopes - at around 480mm and 700mm focal lengths, the 103 is going to give you a somewhat larger image scale than the 81.
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    Default Re: 103mm Doublet vs 81mm triplet APO

    The two scopes will have different fields of view, so you really need both.
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    Default Re: 103mm Doublet vs 81mm triplet APO

    Aperture in AP is actually a not very important consideration, focal ratio and focal length are much more important.

    Always go with the better optics unless the field of view overrides that consideration.

    Cheers,
    JT
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    Default Re: 103mm Doublet vs 81mm triplet APO

    Quote Originally Posted by jerryTheC View Post
    That bit faster makes a noticeable difference - at f7, you'll need exposures about a third longer than at f6 (6x6 = 36, 7x7=49).

    Haven't used the scopes in question, so can't say how the performance compares.

    You may also want to play around with stellarium / Astro Aid / the free CCD calculator from The New CCD Astronomy Home Page to see how the framing with the camera you intend to use compares between the two scopes - at around 480mm and 700mm focal lengths, the 103 is going to give you a somewhat larger image scale than the 81.
    Well, that's what I was thinking too! It seems like the added speed would make up for the difference in apature. I hadn't thought about the focal lengths though.

    As for my camera sensor, I use a Canon SL2 with the APS-C sensor with dimensions of 22.3 x 14.9 mm, which is caparatively small actually. (I'm never going to be done spending money on this hobby, am I?! )

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    Default Re: 103mm Doublet vs 81mm triplet APO

    Quote Originally Posted by JML View Post
    The two scopes will have different fields of view, so you really need both.
    Of course!

    Why didn't I think of that?!


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    Default Re: 103mm Doublet vs 81mm triplet APO

    Which leads on to the famous rule:

    The ideal number of scopes is at least N+1, where N is the number you have at the moment.

    There's also the advanced version:

    The ideal number of scopes is at least N+1, where N+1 is the number you have at the moment, and N+1 <= M, where M is the number of goodies you've bought for your significant other.
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    Default Re: 103mm Doublet vs 81mm triplet APO

    I would say the 80mm is a better choice- Not because of doublet or triplet, but because of the focal length. With the AVX, a 480mm refractor is perfect. Even with smaller sensors, you will get a nice field of view and a slightly less steep learning curve than with focal lengths over 600mm.

    The AVX is a WONDERFUL mount that will allow 10+min guided exposures, but it starts to get finicky when pushing the payload too far past 50%... the lighter 80mm will also be better for this once you factor in a flattener, camera and autoguider.

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    Default Re: 103mm Doublet vs 81mm triplet APO

    Quote Originally Posted by Clete View Post
    As for my camera sensor, I use a Canon SL2 with the APS-C sensor with dimensions of 22.3 x 14.9 mm, which is comparatively small actually. (I'm never going to be done spending money on this hobby, am I?! )
    The APS-C sensor is on the large size for AP sensors. The vast majority of consumer grade AP cameras really don't go above the DSLR full-size sensor dimensions. So the APS-C is only 1.5 sizes down from the largest.

    You are learning -- THE SPENDING NEVER STOPS!!!!

    Cheers,
    JT
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    Default Re: 103mm Doublet vs 81mm triplet APO

    Quote Originally Posted by jaetea View Post
    The APS-C sensor is on the large size for AP sensors. The vast majority of consumer grade AP cameras really don't go above the DSLR full-size sensor dimensions. So the APS-C is only 1.5 sizes down from the largest.

    You are learning -- THE SPENDING NEVER STOPS!!!!

    Cheers,
    JT
    I was thinking it was on the smalller end of the scale because of this image, which is found on the speficications page for any one of the W.O. scopes....

    https://williamoptics.com/pub/media/...0320-02-01.png

 

 
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