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  1. #1
    WWPierre's Avatar
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    Default Seben Barlow Comparison



    The clouds cleared for a couple of hours tonight and I got a chance to compare my cheap Seben barlow with a no-name barlow belonging to one of my tenants.

    The Seben is about twice as heavy and seems of general better quality than the no-name, which seems to be mostly plastic. I tried to determine how many elements each lens has, and I think the Seben has at least 2. In any case, the entry surface of the Seben is concave, while that of the cheapie is flat.

    I pointed at the Pleiades, and fitted my 35mm Siebert with each barlow in turn. There was no discernable difference in the view at the center of the FOV, but while stars remained crisp and white to the edge of the Seben while the no-name exhibited chromatic aberration towards the edge.

    Conclusion: The Seben barlow, generally available on E-Bay for around $20, (I think mine cost about $35 delivered to my post box) is not the worst barlow you can buy. I don't mean to damn with faint praise, as soon as I have access to another barlow, I will repeat the test.

    While researching the workings of barlows, I ran across this page, showing the light path through various eyepiece designs.
    Last edited by WWPierre; 10-26-2009 at 04:48 AM.
    Meade 16" LightBridge; Celestron G-8N Bird-Jones/motorized EQ5; Orion 127 Mak/go-to EQ5; Burgess 127f8 refractor; Sky-Watcher 5" F/5 collapsible dob; 90mm Mak/motorized EQ2; Royal Astro 76/910-GEM; Meade 60x700 refractor/alt/az; Zhumell 25x100 Coin Ops; GalilleoScope. Celestron 8mm-24mm zoom; lots of fixed EPs,some good, some..not so much. A small collection of surveying instruments; a forest of tripods; Canon Rebel Xti. Confirmed gadget junkie; Custodian of the Magnetic North Pole (Send $1.00 to Pierre each time you use a compass.)
    49-41-37.03N 123-09-29.61W Calculated magnetic declination: 17° 39' East

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  3. #2
    MarkM's Avatar
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    Default

    Thanks Peter for your work on this study--look fwd to seeing more data as you collect it.
    Location: 30° 19' N; 97° 54' W; elev 248 meters; yellow/green zone; NELM 5.7
    Instruments: Obsession 15" Dob; Orion XT8i; 2" refractor (Galileoscope); Televue EP arsenal; Bushnell 7X50 binos
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  4. #3
    WWPierre's Avatar
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    Default

    Here are the two barlows for visual comparison. Seben on the right.

    I forgot to mention that the no-name was a lot farther from the focus point after fitting it.
    Attached Images Attached Images
    Meade 16" LightBridge; Celestron G-8N Bird-Jones/motorized EQ5; Orion 127 Mak/go-to EQ5; Burgess 127f8 refractor; Sky-Watcher 5" F/5 collapsible dob; 90mm Mak/motorized EQ2; Royal Astro 76/910-GEM; Meade 60x700 refractor/alt/az; Zhumell 25x100 Coin Ops; GalilleoScope. Celestron 8mm-24mm zoom; lots of fixed EPs,some good, some..not so much. A small collection of surveying instruments; a forest of tripods; Canon Rebel Xti. Confirmed gadget junkie; Custodian of the Magnetic North Pole (Send $1.00 to Pierre each time you use a compass.)
    49-41-37.03N 123-09-29.61W Calculated magnetic declination: 17° 39' East

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    Default

    Great review Peter! I'm looking at new Barlow lenses now...very helpful.
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    Default

    Nice data point. How about buying their zoom eyepiece and comparing it to yours?

    I've often wondered about the Seben accessories. After all they are comming from the same Chinese factories that make stuff for other brands.

    I think that Seben gets its not so great reputation from the Newtonian scopes they sell with spherical mirrors and a small corrector lens that seem to be difficult to collimate and to achieve a sharp focus. Seben also has a series of small inexpensive MAKs but I've never seen anything written about one of them .... good or bad.

    In the accessory area, they have the barlow you are testing. They also have a zoom eyepiece, a binocular eyepiece as well as a VGA eyepiece. Again, except for your comparison test, I've never seen anything written about any of these accessories, good or bad.

    While I've sure that these products are outclassed by their more expensive competitors, they may be a viable alternative for folks, like me, who have a hard time justifying spending almost as much for an eyepiece as I did for my telescope.
    SXINIAS

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