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Equipment Discussions >> Eyepieces

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Manish
Vendor (AGENA AstroProducts)
*****

Reged: 02/22/05

Loc: Los Angeles Area, CA
Re: ES 25mm 100 AFOV Shipped (Pictures) new [Re: Starman1]
      #5613795 - 01/09/13 02:13 PM

>>Explore Scientific says this eyepiece has 8 elements, not 9.

Thanks very much Don! We cloned another EP page from our site to create this one and overlooked editing this.

Regards,
Manish
www.AgenaAstro.com


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pbsastro
professor emeritus
*****

Reged: 03/21/07

Re: ES 25mm 100 AFOV Shipped (Pictures) new [Re: Dick Jacobson]
      #5613804 - 01/09/13 02:16 PM

Quote:

Is there any noticeable fall-off in brightness near the edge? One post in this forum claimed that it is impossible to create an eyepiece with these specs in a 2-inch barrel without some loss of light at the edge.




Even though this 25mm may have a slight loss at the edge, of course it is possible no light loss in 2-inch barrel. Only it would require more infocus.
Anyone can see that any eyepiece with an eye lens clear aperture smaller than 46mm can be made 2” just by attaching a 2” barrel with no lens inside.
Although a field lens clear aperture may be smaller than 46mm, the total lens may not fit inside the barrel, so lenses must start after the barrel.
Even the ES 30-100 can be used with a 2” adapter, as ES demonstrated, although in that case as the field lens is 52mm it is really vignetted by the 2” barrel 46mm ID.


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pbsastro
professor emeritus
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Reged: 03/21/07

Re: ES 25mm 100 AFOV Shipped (Pictures) new [Re: Starman1]
      #5613812 - 01/09/13 02:20 PM

Quote:

I notice the example I have doesn't have a sharply-focused field stop and has a blue ring around the edge of the field near the edge.
Any of you see the same thing?




Maybe your eyepiece does not have field stop, like one ES9-120 reported to be 140 degrees?
Jochsner mentions clean and sharp field stop.


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JMW
Pooh-Bah


Reged: 02/11/07

Loc: Nevada
Re: ES 25mm 100 AFOV Shipped (Pictures) new [Re: pbsastro]
      #5613834 - 01/09/13 02:31 PM

It is the third most expensive eyepiece in my collection. It is the heaviest and you can see from my picture that it is still a pretty big eyepiece.

I wouldn't say 'small, light and cheap'. Definitely smaller, lighter, cheaper' than the 30mm with 3 inch barrel. My TEC-140 is the only scope I have that has a focuser that could use a 3 inch eyepiece. I think the market will be pretty small for the 30mm 100 degree eyepiece.


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Shneor
scholastic sledgehammer
*****

Reged: 03/01/05

Loc: Northern California
Re: ES 25mm 100 AFOV Shipped (Pictures) new [Re: Manish]
      #5614001 - 01/09/13 04:15 PM

Quote:

>>How big is the eyelens? Any photos?

33mm (1.3").

We have several photos and some additional specs up on our website.
http://agenaastro.com/explore-scientific-100-deg-series-eyepiece-25mm.html

Regards,
Manish
www.AgenaAstro.com



Hi Manish,
Any info on the field stop? I noticed that there's no photo of the field lens on yur site.

Clears,


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DRodrigues
super member


Reged: 08/08/11

ES 25mm 100 AFOV ER new [Re: Shneor]
      #5614364 - 01/09/13 07:38 PM

The values of eye-relief mentioned seem to indicate that this is the ES100 more user friendly to eye-glass users like me. Can someone please compare the useful ER with the one of Ethos 17?
I'm also interested of knowing if this ep shows much lateral colour during the day - this ep might be the best solution for day-light low power wide field fanatics, unlike me since I'm a high power wide field fanatic...
The ES120 9mm seems to show too much lateral colour on day-light use but with the reduced ER also wasn't for me...


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MitchAlsup
Pooh-Bah


Reged: 08/31/09

Re: ES 25mm 100 AFOV ER new [Re: DRodrigues]
      #5614686 - 01/09/13 11:15 PM

I added one to my collection tonight. Thanks for the AgenaAstro link.

Since I have a 9ES120 I will be able to compare and relate the blue flame at the edge. I have been waiting for this thiing to finally arrive to cycle out my 31NT5 in my F/4 for a smaller exit pupil. I will let you know how this goes. If it is anything lke the 9ES120 its going to be superb.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: ES 25mm 100 AFOV Shipped (Pictures) new [Re: pbsastro]
      #5614738 - 01/10/13 12:01 AM

Quote:

Quote:

I notice the example I have doesn't have a sharply-focused field stop and has a blue ring around the edge of the field near the edge.
Any of you see the same thing?




Maybe your eyepiece does not have field stop, like one ES9-120 reported to be 140 degrees?
Jochsner mentions clean and sharp field stop.




Too bad the others were already sent out or I'd compare them.
It's completely overcast here tonight or I'd see what's up.


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FastMike
sage


Reged: 09/22/10

Loc: Florida 27° 15' N
Re: ES 25mm 100 AFOV Shipped new [Re: JMW]
      #5615313 - 01/10/13 11:26 AM Attachment (71 downloads)

Here is a picture of the field lens.

I measured the lens to be about 41.5mm wide using a digital caliper. The reading is not 100% accurate because I hovered the caliper over the lens and eyeballed it to avoid scratching the lens.

Hopefully it will work well in my NP101 but haven't tried it yet.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: ES 25mm 100 AFOV Shipped new [Re: FastMike]
      #5615383 - 01/10/13 12:01 PM

If the bottom lens assembly is negative, then the field stop for the eyepiece is going to be internal.
And probably not measurable easily.
You can time the passage of a star on the equator to get an idea of the true field.
And you can back into the size of the field stop by converting the true field to degrees (with decimals) and using the following formula:

Field Stop = (True Field X Telescope focal length) / 57.3

It will be not the actual field stop, but the derived field stop, and useful for TFOV guesses in different scopes.


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Shneor
scholastic sledgehammer
*****

Reged: 03/01/05

Loc: Northern California
Re: ES 25mm 100 AFOV Shipped new [Re: Starman1]
      #5615819 - 01/10/13 04:17 PM

Got a shipping notice from Astronomics.

Clears,


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Dick Jacobson
scholastic sledgehammer


Reged: 12/22/06

Loc: Plymouth, Minnesota, USA
Re: ES 25mm 100 AFOV Shipped new [Re: Starman1]
      #5615821 - 01/10/13 04:18 PM

Another way to approximate the Field Stop is to multiply the eyepiece focal length by the apparent field, and divide by 60. There is also the Field Stop Calculator which produces an estimate of 40.8 mm for this eyepiece.

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: ES 25mm 100 AFOV Shipped new [Re: Starman1]
      #5615832 - 01/10/13 04:23 PM

Brief look with the 25mm through a TeleVue NP101 today as a daytime spotting scope with wide flat field, producing 22X.
Comments about the 25mm:
--field doesn't appear any larger than 100 degrees. Maybe a little less. I'll have to time a star to find out.
--almost parfocal with TeleVue 24mm Panoptic in a High-Hat adapter.
--when eye is a little too far back, there is a profound yellow-orange ring around the outside 25% of the field. At the proper exit pupil (it feels tight), the very edge of the field (maybe 5%) has a slight yellowish tint, but it's minor--not like a color filter of any kind.
--the exit pupil is definitely too tight for glasses to be worn and too tight for a DioptRx-style lens to be added to the eyepiece.
--The very edge of the field (1 degree of field max) shows a sharply blue thin ring. There is a way to hold the eye to reduce the thin ring to just the very edge but it is visible with direct or peripheral vision.
--the field stop is NOT in focus when the eyepiece is. Wearing reading glasses did not help. It's close, but not exact.
--the image was quite sharp, on a par with the 24 Panoptic.
--the edge of the field has serious rectilinear distortion (as expected)--much more significant than the much narrower 24 Panoptic (as expected).
--the image was fairly sharp right near the edge.
--there is vignetting in the last 5-10 degrees of field at the edge. It is not significant in daytime use. It is visible with peripheral or direct vision. I've seen eyepieces with worse.
--I could not notice any angular magnification distortion or astigmatism. That will have to wait for nighttime use. However, most binoculars with much narrower fields have some of both, so this is obviously an eyepiece aimed at astronomers.

This is not an eyepiece likely to be used as a daytime eyepiece, but the colors near the edge and vignetting were more likely to be visible in daytime use, so I'm reporting here. So far, I'm encouraged by what I see that this could be a very nice astronomical-use eyepiece.


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Fred1
Carpal Tunnel
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Reged: 09/19/07

Loc: Somewhere in the Orion Spur
Re: ES 25mm 100 AFOV Shipped new [Re: Dick Jacobson]
      #5616311 - 01/10/13 09:36 PM

Quote:

Another way to approximate the Field Stop is to multiply the eyepiece focal length by the apparent field, and divide by 60. There is also the Field Stop Calculator which produces an estimate of 40.8 mm for this eyepiece.




Interesting. The N.A.A. Telescope Math Calculator says 43.6mm. Scroll down after entering your scope specs to see the FS value.


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Tamiji Homma
Post Laureate
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Reged: 02/24/07

Loc: California, USA
Re: ES 25mm 100 AFOV Shipped new [Re: Fred1]
      #5619350 - 01/12/13 04:06 PM

I measured TFOV and calculated field stop of ES25-100 along with Nagler 31T5.

41.1mm ES25-100 (last 1% vignetting/fuzzy field stop)
42.2mm Nagler 31T5 (clean to the very edge)

Tammy


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mountain monk
Carpal Tunnel
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Reged: 11/06/09

Loc: Grand Teton National Park
Re: ES 25mm 100 AFOV Shipped new [Re: Tamiji Homma]
      #5620039 - 01/12/13 11:54 PM

Tammy,

Thank you for that post. Since I have the 31mm Nagler, I don't even have to think about the ES 25!

Dark skies.

Jack


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: ES 25mm 100 AFOV Shipped new [Re: mountain monk]
      #5620159 - 01/13/13 03:22 AM

Quote:

Since I have the 31mm Nagler, I don't even have to think about the ES 25!




Maybe not and maybe yes. I don't think the reason to get a 100° eyepiece should be to get a bigger true field, but to get a bigger true field in that given focal length. I can personally attest that the increase in apparent field of view can be most impressive and clearly worth upgrading to, if you can afford it. I couldn't so I went with some 82° ES eyepieces, since I could get three really useful focal lengths for the price of one 100° eyepiece. But I'd still like to have a couple 100° eyepieces. They sure are intoxicating, much like binoviewers.


Clear skies!
Thomas, Denmark


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Dick Jacobson
scholastic sledgehammer


Reged: 12/22/06

Loc: Plymouth, Minnesota, USA
Re: ES 25mm 100 AFOV Shipped new [Re: Astrojensen]
      #5620347 - 01/13/13 09:27 AM

Quote:

Quote:

Since I have the 31mm Nagler, I don't even have to think about the ES 25!




Maybe not and maybe yes. I don't think the reason to get a 100° eyepiece should be to get a bigger true field, but to get a bigger true field in that given focal length. I can personally attest that the increase in apparent field of view can be most impressive and clearly worth upgrading to, if you can afford it. I couldn't so I went with some 82° ES eyepieces, since I could get three really useful focal lengths for the price of one 100° eyepiece. But I'd still like to have a couple 100° eyepieces. They sure are intoxicating, much like binoviewers.


Clear skies!
Thomas, Denmark



Another reason to prefer the ES 25/100 is that it has a smaller exit pupil, meaning that for many people the stars will be brighter. If you have an f/5 scope, the 31mm Nagler gives an exit pupil diameter of 31/5 = 6.2mm so a substantial amount of light is wasted if you're a typical middle-aged person with 5mm pupils. As I see it, the ES 25/100 is the only eyepiece in existence that delivers nearly all of the light that enters a 2" drawtube into your eye (again, for the f/5, 5mm pupil case).

Astrojensen, I have a binoviewer and a couple of 100° eyepieces, and I agree 100% they are intoxicating!


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Tamiji Homma
Post Laureate
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Reged: 02/24/07

Loc: California, USA
Re: ES 25mm 100 AFOV Shipped new [Re: mountain monk]
      #5620878 - 01/13/13 02:07 PM

Hi Jack,

You're welcome. Field stop size of ES25-100 was one of interest as well.
I uploaded closeup ES25-100 photo of side-by-side with Nagler 31T5.

Regarding visual experience, I have nothing to add beyond Don described earlier. I agree with him in all accounts.

ES25-100 needs about 2.8mm Inward focus distance lesser than N31T5 but if your diagonal 2" holder hits bottom, you loose the advantage. It happened with Baader 2" diagonal. Astro Physics MaxBright was OK. I mean nosepiece went in all the way.


Field lens side, trying to show blue fuzzy field stop that people are talking about:


Eye lens side:


Upper body shot:


Tammy


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mountain monk
Carpal Tunnel
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Reged: 11/06/09

Loc: Grand Teton National Park
Re: ES 25mm 100 AFOV Shipped [Re: Tamiji Homma]
      #5621040 - 01/13/13 03:17 PM

Thomas,

I understand the infatuation with 100 degrees. I have four Ethoi---17mm, 13mm, 8mm, and 6mm--and they have provided me with an enormous amount of pleasure in my scopes. I do not have have the extraordinary amount of knowledge you all display here on CN, but I can report that none of the above spends more time in the focusers than the 31mm Nagler. For me, it is the magical eyepiece, though the 13mm is close...

Dark skies.

Jack


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