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  1. #1
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    Default Minimum Magnification?



    I'm a bit hazy on the concept of minimum magnification. What happens when you go below it?
    I was interested in a wide angle, low power EP for an 8" F5 reflector (1000mm FL). A 2" 32mm 70 degree (maybe the Orion Q70) would be about 31x, is this too low to be usefull? If I went down to 28mm 70 degree could I go to 1.25" to save money without any of the FOV being blocked? And finally, with a fairly fast scope like this (F5), is it a mistake to get a cheaper EP like the Q70, or Meade 4000? I was under the impression that an F5 tends to make cheaper EPs look rather fuzzy away from the center.
    Thanks

  2. #2
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    Default

    Shouldn't be too low. I use a 30mm with my 6"dob (focal length 1200mm) which magnifies 40x and it works really well; especially for star clusters.

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    Default

    Hi simon , As far as the powers goes , i have a 2000mm 8in. f10 with a focal reducer of 6.3 and i use 40mm and 50mm eyepieces ... Great fields of view ...The meade series 4000 stuff is pretty good quality as is the series 5000 stuff ... You could get a series 4000... 36mm qx wide angle 70 degree field from meade for 99 dollars or a series 5000 plossl 40mm for 149 with a 60 degree field ...Just a thought ...
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  5. #4
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    Default

    Quote Originally Posted by Simon01351 View Post
    I'm a bit hazy on the concept of minimum magnification. What happens when you go below it?
    I was interested in a wide angle, low power EP for an 8" F5 reflector (1000mm FL). A 2" 32mm 70 degree (maybe the Orion Q70) would be about 31x, is this too low to be usefull? If I went down to 28mm 70 degree could I go to 1.25" to save money without any of the FOV being blocked? And finally, with a fairly fast scope like this (F5), is it a mistake to get a cheaper EP like the Q70, or Meade 4000? I was under the impression that an F5 tends to make cheaper EPs look rather fuzzy away from the center.
    Thanks
    My telescope is a F/5 also. Just a smidge bigger than your telescope but that doesn't change anything. You can effectively use a 32mm eyepiece in your telescope. My most used eyepiece is a Televue 32mm Widefield with an apparent field of view of sixty five degrees. They are no longer manufactured and have been replaced by Televue's Panoptic series of eyepieces that have an apparent field of view of sixty eight degrees. My skies limiting magnitude is around six however I used to use my 32mm eyepiece in magnitude 3-4 skies for many years. Recently I had the opportunity to try a 35mm Panoptic in my telescope. I prefered it perhaps five percent more than my 32mm Widefield optically. But there is no way that I could presently afford one.
    The above mentioned eyepieces provide a very good field pretty sharp right out to the edge of the field of view. But the price is steep. Once I tried a Hyperion and I was disappointed in the soft outer half of the field of view. It was similarily disappointing in a 12.5" F/5.3 telescope. Eyepiece utility is a very user dependent quality. It depends on how good your eyesight is, and in your case a newtonian reflector with a F ratio of five, and how picky you are about seeing sharp stars out to the edge of the field of view, and how much money you can afford to spend. It is better to attend a star party and try other eyepieces before purchasing them, especially if you can plop them into your telescope for a few minutes of test driving. If you cannot attend a star party and think that you may be fussy about image quality then by all means save your money for a higher end eyepiece.

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  7. #5
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    Default

    .. you know .. great question ... I made up a excel spreadsheet that I can plug in each of my scopes and every EP variation and get all that useful information like "minimum useful magnification" ... yeah ... then you can easily scan down the chart and find out the range of EPs that would function most effectively in each scope ... I once spent several days digging through all that information so that I could maximize my EP selection ... fat load of good that did ... for instance ...

    Celestron C6-R 150mm @ 1200mm = f/8.0 lending a Maximum Useful Magnification of 300x and a Minimum Useful Magnification of 19.5x (or for better contrast using a factor of .2 = 30x) ... which supposedly translates to using a 15mm EP to achieve 20x, or a 10mm to get 30x ... so I tried that ... and promptly went out and got some lower power EPs anyway ...

    ... those charts also mean that I have to use a 2x Barlow to even think of getting near the maximum magnification, even when under most atmospheric conditions it is hard to push past about 200x ...

    ... bottom line ... don't spend to much time not enjoying the lower power EPs if you want to enjoy the wider views ... but for planetary and lunar viewing you will find that the min/max "guidelines" can be somewhat useful, even though chances are you are going to ignore those rules and still end up with some lower power EP in the 40mm range ...

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  9. #6
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    Default

    Thanks for all the useful information, I really appreciate all the help. Right now I'm leaning towards the

    "Meade 32mm Series 5000 2" Plossl Eyepiece with 60 Degree Field of View".

    It's not as wide as some, but it's only $129 at Adorama.

  10. #7
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    Default

    Simon, I have also heard it said that fast reflectors suffer more at the edge of view than fast refractors. I can't explain it, as I don't know enough, but thought I'd mention it. As for lowest power, I have used a 40mm Plossl in my ST80, giving me 10x. It is below what is stated as the lowest theoretical magnification, but it works, nonetheless. Not clear to the edge, but I don't mind as I'm only using it for finding purposes. Another thing about low power is that the exit pupil size can get bigger than your eye pupil, making the background sky too bright. I have used a mask to offset that effect.

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  12. #8
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    Default

    Hi, I ended up getting the Baader Planetarium Hyperion 21mm. Unfortunately, as a natural consequence of getting a new eyepiece, it has been cloudy every night. The Baader is huge and heavy, and I like the fact that you can unscrew the 1-1/4" end to get a 32.2mm 2" EP. Baader also sells what it calls "Fine Tuning Rings" fairly cheaply which can change the FL to 17.6mm, 15.5mm and 14mm. I'm really looking forwards to playing with it, if the weather ever cooperates.

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    Simon, I said something wrong in that last post. I meant to say that fast refractors suffer more at the edge than SLOW refractors.

    The Hyperion you got is a great eyepiece. I opted to avoid heavy eyepieces because my scopes are so short that I can't slide the tube much to get balanced. May get one eventually, though, anyway.

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