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BRUN

Which 'middle' EP ?

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BRUN    36

i have just bought a Celestron Edge HD 8" and i need to buy some EP's.

I currently have a 24mm 68 degree explore scientific, and a 40mm celestron plossl, so im looking for higher power

I am pretty set on getting the 8.8mm 82 degree explore scientific, but if i have enough money for another i was thinking of what to have as my 'middle' EP, maybe the 14mm ES 82 degree, but ive also noticed the 68 degree is available in 16mm, so not sure which would be the better choice, or other thoughts ?

 

Thanks

Edited by BRUN

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I find 14mm a very useful focal length. I used to have the Meade Series 5000 14mm UWA Mk.1 (which I think has the same optics as the ES 14mm 82 deg). It was a great EP in many respects, showing awesome detail on the moon. Framing the entire moon in the FOV at 145x is amazing. The only reason I replaced it with a Nagler 12T4 and later a Delos 14mm is that the eye relief is just a touch too short for me with my glasses. If you don't wear glasses, ER is fine.

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parallaxerr    511

I have a C8 along with ES 8.8mm 82° and 16mm 68°.

The 8.8mm 82° gives the maximum magnification I find usable under UK skies at around x230, but the seeing has to be good. I often dropped back the the 11mm 82° when viewing Jupiter which sharpened the view up without losing significant image scale.

To be honest I haven't used the 16mm 68° in the C8 much, it tends to live in my frac for DSO as it gives a good exit pupil size. One point to note with the 16mm is that the eye relief is quite tight, I don't wear specs so it doesn't bother me, but may be a consideration.

The 16mm 68° is often said to outperform the 14mm 82° EP on the edge of the FOV and displays less pincushion, but I haven't tried the 14mm myself.

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BTW, the 82 degree series of ES is rated to work well down to F/4, whereas the 68 deg are rated to work in scopes no faster than F/5. The 82 degree is therefore more future proof. I used the Meade 14mm in an F/4.1 Dob (20"), and it worked very nicely (very similar to my 17T4 and 22T4 Naglers). I tried MaxVision 68 degree EPs (20 and 24mm, also said to be of the same optical design as the ES counterparts) in the same scope, and the performance at the edge was not as good.

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Ricochet    454

Thinking only in terms of the focal lengths, I think a set of 8.8-11-16-24 would work well with the 8.8-11 close pair giving options for planetary, but if you only want one option between the 8.8 and 24 then the 14 gives the most "even" split.

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BRUN    36

im thinking my choices are the following

11mm 82 degree and 16mm 68 degree, or

8.8mm 82 degree and 14mm 82 degree

? Im reading conflicting things that the 8.8mm might not be usable most of the time, and that the 11mm might be a better choice, but im also reading many of you guys happy to go to 8mm in this or similar scopes

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parallaxerr    511

You'll get more use out of the 11mm, the 8.8 only comes good with very good seeing in the C8 imho. Also consider that the planets aren't ideally placed for a few years so very high power planetary viewing may be off the table for a while.

For lunar, I think the 11 & 16mm combo would suit and for DSO, look for something longer than and to complement the 24mm you already have. Perhaps take some time to consider your targets and think about exit pupil and TFoV.

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Davesellars    832

I wouldn't recommend the 8.8mm ES82 for that scope at the moment.  You would use it rarely.  The ES82s are great eyepieces for DSOs but imho the lower focal lengths are terrible on bright objects like the Moon.  I'd say the 14mm ES82 would be the best progression from the 24mm to give you a mid-high power at 145x which would be great for globular clusters and planetary nebulae.  For lunar and planetary observation I'd go for an orthoscopic around 10 or 11mm since you have tracking the lower eyepiece AFOV is not a problem

Edited by Davesellars
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BRUN    36

thanks Dave, ive actually done my order today so hope everything works out

ive gone for the 11mm 82 and the 16mm 68

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Highburymark    894

Am sure you'll be pleased with both those eyepieces. They will give great views in the C8 Edge - hope you enjoy it as much as I did

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Special K    942
On 12/09/2017 at 15:00, parallaxerr said:

Perhaps take some time to consider your targets and think about exit pupil and TFoV.

Spot on with what I was thinking. Put a spreadsheet together with formulae for the different EPs to include pupil exit, surface brightness, TFOV, etc.  If you are going after galaxies you may want one that is not too drastic on SB but with enough magnification to satisfy high power viewing. Also, which EP comes closest to 2.5mm pupil exit?  That will cater well to general viewing as this is our sharpest acuity physiologically (if I'm not mistaken!). 

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