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  1. #1
    MarkM's Avatar
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    Default The Next Level of Fine Detail: Paracorr



    After six weeks of waiting I finally took receipt of a parabola correcting lens (Paracorr; Tele Vue Optics Article Page) which I purchased at a substantial discount through Hayneedle (Telescopes.com).

    This lens is most often used to correct “coma” which is the streaky or comet-shaped appearance of stars prevalent when using longer focal length eyepieces in fast telescopes (usually Newtonians and more obvious in the outer, off-axis FOV). While I do conduct some low power, wide-field viewing of open clusters, the bulk of my observing involves work at higher magnification (e.g., planets, faint galaxies, tight double stars). My hope was that this lens would substantially sharpen the views of planets and stars in my 15” f/4.5 reflector while using both longer and shorter focal length EP’s. My hunch was correct.

    Results:
    In some instances I was able to obtain head-to-head results with and without the Paracorr in place. It should be noted that the lens adds 15% magnification to any EP used while also increasing the f ratio of a telescope by this same amount. I was fortunate to have a very clear, moonless night to try out the lens on a variety of subjects, the results of which are reported below. Collimation was checked and adjusted as needed several times during the course of the night.


    Jupiter: The planet was viewed in the early evening.
    With a Nagler 9T6 installed and no Paracorr in place a crisp view of the planet was seen which exhibited four colored bands at 190x. Using the Paracorr, one of the lower bands was further resolved into two bands yielding a total of five bands.


    Mars: The planet was viewed first at 10 PM and then at 1:30 AM. This subject provided some very interesting, unexpected results when the Paracorr was in place.
    The early view was pristine at 220x (Nagler 9T6). Out of curiosity, I cranked up the magnifications successively to 569x (Stratus 3.5mm) and then to 664x (3mm Planetary Edge-on). The view at 569x was surprisingly clear considering the magnification, while 664x was not as good but still reasonable to discern surface features. The Paracorr has given these EP’s new life when used in my 15” reflector.
    The later view at 398x using the Nagler 5T6 was simply stunning—easily the best view of the planet I have ever seen: the dark areas on the surface were resolved to the point of appearing filamentous (vs. blotchy) and the bright white polar cap had a decisive edge to it.


    Saturn: The planet was studied extensively between 2:30 AM and 3:00 AM while it was at least 50 degrees elevated.
    While the view at 220x was picture perfect, it was the view at 398x that convinced me that this purchase was worth every penny: after months of trying to see Cassini’s Division (CD) a tiny black space was finally glimpsed with certainty as a slight dimming of the bright yellow ring. This picture taken by CN user MvZ back in December shows how small the CD is at the moment []Telescope Reviews: Saturn - December 15, 2009.. Next time I get a good look at Saturn, I will try to see the shadow of the rings on the planet.


    Hu 559: This very close, faint double star in Auriga (magnitudes 9; 10; s= 0.6”) is itself the faint companion of a magnitude 6.4 star comprising STT 103.
    Without the Paracorr, I could (at times) discern two tiny orange points of light with fresh collimation at 345x (Nagler 5T6).
    With the Paracorr, the two points of light were steadily held at 398x (Nagler 5T6) and a thin black line could finally be seen when using the 3.5mm Stratus (569x). Thanks to the Paracorr, a sufficiently sharp image was obtained at high magnification to allow true separation of this challenging double star. This result simply would not have been possible without the Paracorr using the available eyepieces.


    Trapezium E and F: The goal was to determine the lowest magnification possible to view these Theta Orionis components.
    Previously without the Paracorr, I had determined that I could not distinguish Trapezium stars E and F from their brighter neighbors using the 32mm Q70 (54x).
    With the Paracorr and extended viewing of the subject using the 32mm Q70 (62x), Trapezium F was seen as a tiny pinpoint of light sitting above star C. At times, I thought I could also see E, but this observation is tenuous. The extra magnification afforded by the Paracorr helped to see F, but my feeling is that the sharpness of the stars was a larger factor.


    G1: Magnitude 13.8 globular cluster within M31.
    The clarity at high magnification afforded by the Paracorr allowed me for the first time to not only see G1 and its two flanking field stars as three distinct objects [398x; 5T6], but also to make out a degree of fuzzy extent in G1 indicating its non-stellar nature.


    M1: The Crab Nebula.
    I can’t say that the Paracorr improved the image of M1 when using a Nagler 9T6, but it was decidedly different in that the nebula took on a ghostly 3-D appearance hanging there in space.

    M79: A mid-sized globular cluster within the constellation Lepus.
    As noted with M1 above, the image in the presence of the Paracorr was different, not necessarily better. At 220x the enlarged view of the globular cluster and its numerous resolved stars took on substantial structural aspects that had the effect of being pulled into a tunnel towards the bright core. I was very pleased to see how pinpoint the stars were even at 398x.

    Pros: The Paracorr generally showed more detail at every magnification due to sharpening of the both stellar and non-stellar features. This allowed additional features to be seen on planets, higher magnification to be used while giving still giving a crisp image, and greater enjoyment of low magnification, wide-field views of star clusters. Of course, coma is almost completely eliminated as well when using longer focal length EP’s.

    Cons: I was disappointed that my 24mm Hyperion (which I use mostly as a low power finder EP) would not come to focus when inserted as a 1.25” EP—it does fine when put in as a 2” EP—I just don’t like having to take the 2” to 1.25” adapter ring in and out. Weighing in at a little over a pound, the Paracorr is pretty heavy and requires a sturdy focuser and appropriate counterweighting.
    The lens complicates the collimation process a bit but that should work itself out with practice. Interestingly, the magnifying capacity of the lens allows it to be used in place of a Barlow when performing the Barlowed laser technique of Nils Olof Carlin for primary mirror adjustment (Obsession Telescopes / Learning Center).

    Conclusion: In my hands, observing with a Paracorr is like observing with a new, more powerful telescope. It has resurrected my least used eyepieces. It will allow me to go after still tighter double stars as I get ever closer to the Dawes’ Limit of my telescope. And I will have no coma-qualms about viewing open cluster gems such as M37 in their entirety. Opinions regarding the Paracorr run deep and are divided; I am now a believer.
    Last edited by MarkM; 01-16-2010 at 06:27 AM.
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  2. The Following 6 Users Say Thank You to MarkM For This Useful Post:

    AustinPSD (01-16-2010),dmbryan (01-16-2010),klaatu2u (01-16-2010),Lenbo (01-16-2010),Nitrox (01-18-2010),sxinias (01-17-2010)

  3. #2
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    Default

    Great review Mark I know a lot of folks with fast newts/dobs that consider the Paracorr mandatory...

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    Default

    Thanks for the detailed review Mark!
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  5. #4
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    Default

    Mark, thanks for taking the time to report so comprehensively on your findings. All-in-all, it must have been a memorable night for you, and another chapter in your history of progress as an observer.

    -Crandell

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    Default

    Thanks for the great info on paracorr. I have been looking around for more information on one and this has been very helpful

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