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ES 25mm 100 AFOV Shipped

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#51 Darenwh

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Posted 08 January 2013 - 09:56 PM

Sounds like you may need a little more in focus to reach infinity and even more if you want to reach infinity and beyond.

#52 Starman1

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Posted 08 January 2013 - 11:20 PM

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?

#53 jochsner

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Posted 09 January 2013 - 12:32 AM

Did some more quick 25mm-100 tests as the sky cleared here. No problems focusing the 25mm-100 in my 2 SCT's 6" and 8", plenty of focus travel on both sides of prime focus available.
Testing in the 80mm, the 25mm-100 is parfocal with a 1.25" Meade RG-7mm ortho almost perfectly! The RG-7mm has the most in-focus of all my current EP's.
The field stop looks as clean and sharp as the ES 9mm-100 and does have a bluish ring at the edge. The coating somewhat give off a Greenish tingle when held a certain angles.

#54 Dick Jacobson

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Posted 09 January 2013 - 09:01 AM

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.

#55 Manish

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Posted 09 January 2013 - 09:06 AM

>>How big is the eyelens? Any photos?

33mm (1.3").

We have several photos and some additional specs up on our website.
http://agenaastro.co...piece-25mm.html

Regards,
Manish
www.AgenaAstro.com

#56 Dave Ittner

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Posted 09 January 2013 - 09:14 AM

Nice photos! So this eyepieces lists at $599.99 and is not on sale at the moment?

#57 Starman1

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Posted 09 January 2013 - 11:00 AM

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.

There is a drop off visible when looking through the eyepiece at the sky. It certainly doesn't appear to be severe, and it is confined to a fairly small ring near the edge.

#58 Scott in NC

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Posted 09 January 2013 - 01:05 PM

We have several photos and some additional specs up on our website.
http://agenaastro.co...piece-25mm.html


Thanks for posting the stats on your website, Manish! :waytogo:

#59 Starman1

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Posted 09 January 2013 - 01:43 PM

Manish,
Explore Scientific says this eyepiece has 8 elements, not 9.
Just thought you should know. The element count is on the ES website.

#60 pbsastro

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Posted 09 January 2013 - 01:44 PM

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.

There is a drop off visible when looking through the eyepiece at the sky. It certainly doesn't appear to be severe, and it is confined to a fairly small ring near the edge.


That slight drop off was expected given the small size of the eyepiece. Looking at the 20mm and 30mm size and weight, it is clear that the 25mm is smaller than expected.
To me it is clear that ES chose (and well) to offer two different and close products: The 25mm being small, light and cheap, and the 30mm being big, heavy, expensive and optically perfect. I will choose the latter, but the former will be more popular I am sure. I always prefer optical perfection, but the size, weight and price will be irresistible to most people, especially compared to the Ethos 21.

#61 Manish

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Posted 09 January 2013 - 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

#62 pbsastro

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Posted 09 January 2013 - 02:16 PM

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.

#63 pbsastro

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Posted 09 January 2013 - 02:20 PM

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.

#64 JMW

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Posted 09 January 2013 - 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.

#65 Shneor

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Posted 09 January 2013 - 04:15 PM

>>How big is the eyelens? Any photos?

33mm (1.3").

We have several photos and some additional specs up on our website.
http://agenaastro.co...piece-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,

#66 DRodrigues

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Posted 09 January 2013 - 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... :grin:
The ES120 9mm seems to show too much lateral colour on day-light use but with the reduced ER also wasn't for me... :bawling:

#67 MitchAlsup

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Posted 09 January 2013 - 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.

#68 Starman1

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Posted 10 January 2013 - 12:01 AM

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.

#69 FastMike

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Posted 10 January 2013 - 11:26 AM

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.

Attached Files



#70 Starman1

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Posted 10 January 2013 - 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.

#71 Shneor

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Posted 10 January 2013 - 04:17 PM

Got a shipping notice from Astronomics.

Clears,

#72 Dick Jacobson

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Posted 10 January 2013 - 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.

#73 Starman1

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Posted 10 January 2013 - 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.

#74 Fred1

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Posted 10 January 2013 - 09:36 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.


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

#75 Tamiji Homma

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Posted 12 January 2013 - 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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