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25mm ES 100* confirmed? sale date? preorder?

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#251 Dick Jacobson

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Posted 15 February 2013 - 07:39 PM

I was considering ordering a few EPs over 30mm but read a thread about exit pupil and someone suggested to that person that they exit pupil would be too big to be "favorable."

I have a Zhumell Z10. 1250mm. I don't the forula for figuring exit pupil, but the thread was for a similar scope.

What do you think?

One way to figure the exit pupil is to divide the focal length of the eyepiece by the focal ratio of the telescope. If your Zhumell Z10 is f/5 focal ratio, then a 30mm eyepiece would have an exit pupil of 30/5 = 6 mm. Since most people middle-aged or older have pupil sizes of around 5 mm, some light would be wasted in this case. The eyepiece might still be useful for its wide field of view despite the stars being a little dimmer. Tele-vue recommends not using an exit pupil over 7.5 mm.

#252 rodster

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Posted 16 February 2013 - 10:07 AM

Just had first light last night (between clouds & moon) using a 18 UC Obsession with paracorr. Conditions were not great but allowed time to compare the ES 25 and the Nagler 31, the ES 25 is very comfortable to use, the eye lens is like a movie screen providing a very immersive view, field stop is well defined but I would stop short calling it crisp. Compared to the nagler the field of view was ery similar. The best part was the contrast was much better on the ES 25 (smaller exit pupil). my nagler was giving me a washed out appearance probably due to my aging (64) year old pupils. So objects like the double cluster and galaxies were popping out and much more detailed (same FOV and greater magnification). Stars were crisp of axis basically the same ad the 31 nagler. I also have the ES 20 and the ES 25 views are similar as far as of axis goes, not perfect but very useable, I can focus on a star out on the peripheral view and not loose much focus as the same star is moved to the center. Very similar to all my naglers and ES eyepieces. The only time I felt I was missing the 31 nagler was on the rosette nebula using a filter, here the greater light gathering power of the nagler produced a brighter rendering if the nebulous area but the FOV was similar. I am not a professional, but my viewing was much enhanced using the ES 25 over the nagler 31, the ES 25 is very easy to view through, even relaxing & it will for sure be in my focuser a good share of the time. I highly recommend this EP! Nice work ES!

#253 Fred1

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Posted 16 February 2013 - 07:05 PM

Welcome to Cloudy Nights, rodster. I very much appreciate your post as I've had my eye on the ES 25mm 100° for the exact reasons that you described in your comparison with the TV31NT5. I had presumed that if the ES25mm was designed correctly that it would be a very nice complement to the 82° AFOV and longer focal length of the 31. You've helped keep it on my short list for new purchases. :bow:
Clear and dark skies.

#254 turtle86

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Posted 16 February 2013 - 10:46 PM

Thanks for your post, Rodster, and welcome to Cloudy Nights. The 25mm ES 100 sounds promising indeed. I was just curious about which Paracorr setting works best for the 25mm ES 100. I know that the 31mm Nagler and 21mm Ethos perform best with the tunable top all the way in...

#255 bleep

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Posted 17 February 2013 - 10:15 AM

I just noticed there is one on eBay from high point scientific for $599 plus $5.90 shipping actually says 2 available much to much for me just throwing it out there in case some are interested :)

#256 Fred1

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Posted 17 February 2013 - 12:46 PM

I just noticed there is one on eBay from high point scientific for $599 plus $5.90 shipping actually says 2 available much to much for me just throwing it out there in case some are interested :)


Skip ebay and buy directly from Highpoint's website for free shipping.

#257 careysub

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Posted 17 February 2013 - 07:14 PM

I was considering ordering a few EPs over 30mm but read a thread about exit pupil and someone suggested to that person that they exit pupil would be too big to be "favorable."

I have a Zhumell Z10. 1250mm. I don't the forula for figuring exit pupil, but the thread was for a similar scope.

What do you think?

One way to figure the exit pupil is to divide the focal length of the eyepiece by the focal ratio of the telescope. If your Zhumell Z10 is f/5 focal ratio, then a 30mm eyepiece would have an exit pupil of 30/5 = 6 mm. Since most people middle-aged or older have pupil sizes of around 5 mm, some light would be wasted in this case. The eyepiece might still be useful for its wide field of view despite the stars being a little dimmer. Tele-vue recommends not using an exit pupil over 7.5 mm.


I am 55 and measured my pupils with the hex key method and found it was between 5.5mm and 6.5mm, roughly 6mm.

Other sources indicate that 6mm is common in older people:
http://www.intechope...rams-and-nor...
http://www.intechope...edia/image2.png

http://calgary.rasc....copes/index.htm

It seems the the average approaches 5mm as a limit with increasing age.

#258 rodster

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Posted 17 February 2013 - 11:37 PM

I have the paracorr with tunable top but it is not the newest model, paracorr 1? Anyway I noticed inserting the 25 ES fully into the paracorr would not allow the paracorr travel all the way in, which is my preferred setting for my 31 nagler & the 20mm ES. I just used a setting near the middle of travel and it seemed to work out ok. I would like to try the newest paracorr & see if I can get full range of travel. I will experiment with this next tome out as I only had a couple of hours before it clouded up. Funn EP, can't wait for decent night. Clear skies

#259 leviathan

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Posted 18 February 2013 - 05:34 AM

Just had first light last night (between clouds & moon) using a 18 UC Obsession with paracorr. Conditions were not great but allowed time to compare the ES 25 and the Nagler 31, the ES 25 is very comfortable to use, the eye lens is like a movie screen providing a very immersive view, field stop is well defined but I would stop short calling it crisp. Compared to the nagler the field of view was ery similar. The best part was the contrast was much better on the ES 25 (smaller exit pupil). my nagler was giving me a washed out appearance probably due to my aging (64) year old pupils. So objects like the double cluster and galaxies were popping out and much more detailed (same FOV and greater magnification). Stars were crisp of axis basically the same ad the 31 nagler. I also have the ES 20 and the ES 25 views are similar as far as of axis goes, not perfect but very useable, I can focus on a star out on the peripheral view and not loose much focus as the same star is moved to the center. Very similar to all my naglers and ES eyepieces. The only time I felt I was missing the 31 nagler was on the rosette nebula using a filter, here the greater light gathering power of the nagler produced a brighter rendering if the nebulous area but the FOV was similar. I am not a professional, but my viewing was much enhanced using the ES 25 over the nagler 31, the ES 25 is very easy to view through, even relaxing & it will for sure be in my focuser a good share of the time. I highly recommend this EP! Nice work ES!

Thanks for comparison !

#260 JMW

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Posted 18 February 2013 - 12:12 PM

I have done 3 dark sky public outreach events with the 25mm 100* eyepiece. It is an easy to use eyepiece that is great for showing larger objects with a good deal of magnification. It is nice to not have to nudge the scope as often for the public. I have used it on a TEC 140 and C11 EdgeHD. I plan on buying a Paracorr II before the GSSP this summer. I will be using it in an 20 inch F5 Obsession. I will be curious to compare the Nagler 31T5 to the ES25mm 100* in a large dob.

#261 MitchAlsup

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Posted 18 February 2013 - 08:20 PM

For edge of field sharpness I rank it as follows:

1. 21 Ethos
2. 31 Nagler
3. 25 ES


For me the issue is does the 25ES100 deliver more light to my eye than the 31NT5 in an F/4 scope.

25ES100 has a 6.25mm exit pupil 5.44mm with Paracorr
31NT5 has a 7.75mm exit pupil 6.74mm with Paracorr

Also note my eyes are 60 YO.

I am hoping for better contrast (because my pupil muscles are nto over illuminated) and most of the field decently presented.






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