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  1. #1
    C.Worley's Avatar
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    Default Exit Pupil Question



    I am looking to round out my eyepieces with a wide angle low power ep. The minimum magnification for my scope (Z10) is 35mm. I am wondering if a larger ep is a waste of time or if there are advantages to it for DSO's.
    Clarence
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  2. #2
    KathyNS's Avatar
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    Default

    IMO, a wide angle eyepiece is not a waste of time.

    Some of the most gorgeous sights are open clusters seen through a wide angle eyepiece. I vividly remember the first time I turned my Pan27 on M44, the Beehive Cluster. Wow, beautiful!

    Wide angle is an excellent tool for finding many DSOs. The smaller magnification increases their surface brightness, plus the wider field of view makes then easier to spot.

    Definitely go for it!

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  4. #3
    C.Worley's Avatar
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    Default

    Thanks Keith, but I'm wondering more about the difference between a 35mm and a 40+mm ep. Optcorp.com has the ES 70 35mm 2" on clearance for $50.
    Clarence
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  5. #4
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    Default

    Some people would say it is a waste going any lower than that while others would say it is not. I don’t worry about the exit pupil getting too large. More importantly, when you are trying to get to a super wide TFOV, you need to consider not only the FL of the EP, but also the AFOV of it.

    For example: A 35mm 52 degree AFOV EP on a 1200mm FL scope will give you a 1.52 degree TFOV at 34.29X magnification while a 30mm 82 degree AFOV EP on the same telescope will give you a 2.05 degree TFOV at 40X magnification. The later will give you better contrast and the “larger, wide screen view.” My choice was to buy the 30mm 82 degree EP (of course you have to pay a lot more for it and it is big and heavy).

    It’s really all a matter of choice and what is important to you. There are objects out there that are 3 degrees wide and more, so at some point the most practical answer is to switch over to binoculars.

    Good luck and clear skies, whatever you decide to do!
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  7. #5
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    Default

    Quote Originally Posted by C.Worley View Post
    I am looking to round out my eyepieces with a wide angle low power ep. The minimum magnification for my scope (Z10) is 35mm. I am wondering if a larger ep is a waste of time or if there are advantages to it for DSO's.
    The 35 mm gives you a 7 mm exit pupil and 36x magnification. That's a limit for young eyes that are very dark adapted. My old eyes may only get to 5 mm. If so the equivalent aperture would be about 180 mm instead of 254 mm.

    Just multiply the magnification times your eye pupil to get the equivalent scope aperture.

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  9. #6
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    Default

    Hello Clarence,

    there are basically two things about the EPs to consider: the true field of view you'd like to enjoy, and the the level of light pollution at your observing site.

    Suburban skies with their typical light pollution allow for the exit pupils 3-4mm, to get the contrast of the DSOs. Here it is nice to have a very wide fileld of view. Going any higher with the exit pupil may make some DSOs disappear (due to the background sky glow), and independently, if your eyes are young or aged. According to my experience, the large exit pupils make sense only if you are using filters to reduce the background sky glow. Then, you can go for very large fields of view at some lower magnifications.

    Best

    JG
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  11. #7
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    Default

    Quote Originally Posted by C.Worley View Post
    I am looking to round out my eyepieces with a wide angle low power ep. The minimum magnification for my scope (Z10) is 35mm.
    I want you to reconsider basing the decision on power (i.e. magnification). Consider, instead, on basing the decision on Field of View. The 35mm Panoptic has the same FoV as a 31mm Nagler; yet the Nagler has a darker background and a smaller exit pupil. The 26mm Nagler has the same FoV as a 21mm Ethos, yet the Ethos has a darker background and a smaller exit pupil (it appreast better corrected at F/4 than my Naglers do also).

    The intent of the repurposing from magnification to FoV is to get you thinking about the more important things EPs do! EPs create a viewable image at a computable magnification; to be sure. However the Size of the FoV is at least as important as the magnification, and as magnification goes up the sky background gets darker. You you can see the same FoV at higher magnification and more contrast with shorter wider FoV EPs.

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  13. #8
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    Default

    Quote Originally Posted by MitchAlsup View Post
    I want you to reconsider basing the decision on power (i.e. magnification). Consider, instead, on basing the decision on Field of View. The 35mm Panoptic has the same FoV as a 31mm Nagler; yet the Nagler has a darker background and a smaller exit pupil. The 26mm Nagler has the same FoV as a 21mm Ethos, yet the Ethos has a darker background and a smaller exit pupil (it appreast better corrected at F/4 than my Naglers do also).

    The intent of the repurposing from magnification to FoV is to get you thinking about the more important things EPs do! EPs create a viewable image at a computable magnification; to be sure. However the Size of the FoV is at least as important as the magnification, and as magnification goes up the sky background gets darker. You you can see the same FoV at higher magnification and more contrast with shorter wider FoV EPs.

    Well said. You made the same point I was trying to make, but you did a better job.
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