Author Topic: Need advice on new zoom lens  (Read 85 times)

James Pederson

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Need advice on new zoom lens
« on: January 09, 2018, 12:54:46 AM »
I have 2 scopes, both are used for terrestrial viewing. we are looking down about 1000 ft over a river and can see the boats and marina about 2.5 miles away. The wife uses both daily.
One is a cheap 80 mm 400 mm fl. the other is a Celestron Nextstar 127SLT @ 127 mm 1500 mm fl.
We are very happy with both.
Currently I have a very cheap 3x barlow and a 25 mm eyepiece = 48 X mag.
Currently I have a 25 mm eyepiece = 60 X mag.
Both have 16 mm eve relief.

I want to buy a cheap zoom lens to get a tad more mag. I'm looking at the Celestron.
This lens is a 8 - 24 mm with 15 mm eye relief at 8 mm.

Opinions please. Don't forget we're happy with the cheap 80 mm 400 mm one and the barlow.



Jaye Agting

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Re: Need advice on new zoom lens
« Reply #1 on: January 10, 2018, 12:51:47 AM »
I have the Celestron 8-24. It is my most used eyepiece in my 80 mm refractor and my 8" Dob.  Love it.

zoom eyepiece review
http://www.chuckhawk...m_eyepieces.htm
BaaderHyperian III Clickstop zoom review
http://www.weasner.c...iece/index.html
Baader Zoom Vs Fixed Eyepieces - This will open your eyes
http://www.cloudynig...m-vs-fixed-eps/
http://www.cloudynig...l=+baader +zoom
Celestron 8-24 Zoom
http://www.cloudynig...celestron +zoom
http://www.cloudynig...celestron +zoom
http://www.cloudynig...del-93230-r2106

Mortimer Concepcion

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Re: Need advice on new zoom lens
« Reply #2 on: January 10, 2018, 04:22:51 AM »
The first 3 are not cheap. The last one is the Celestron and the reviews look very good. Thank you.

I also found anOrion Explorer II 7-21mm Zoom Telescope Eyepiece about the same price but 1 mm more eye relief. Ans 7 - 21 mm but the field of view is much smaller at 33 to 43 degrees as opposed to the Celestron with 40 to 60 witch I believe would be better for terrestrial viewing. Both are about the same price. < $60

David Corder

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Re: Need advice on new zoom lens
« Reply #3 on: January 10, 2018, 06:25:11 PM »
Get the older Celestron zoom from the 1980's -- the glass is probably a lot better than the newer ones. I have one of those and it works well.

Michael Robinson

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Re: Need advice on new zoom lens
« Reply #4 on: January 11, 2018, 01:11:24 AM »
How would you suggest I do that? I dont see any advertised.

genssizafa

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Re: Need advice on new zoom lens
« Reply #5 on: January 12, 2018, 05:39:58 AM »
Cosmic Ron in L.A. sells them periodically here on CN; and, George at Astro Parts up in Frazier Park has a huge inventory of used astro gear. I'll find his website and get back to you in a little while.

vidysriret

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Re: Need advice on new zoom lens
« Reply #6 on: January 12, 2018, 09:11:37 PM »
Im a little confused. I see the Celestron has a Field of View: 40° (at 24mm) to 60° (at 8mm). I thought the more magnification the less FOV. Isn't 8 mm more magnification than 24 mm?

Another question, how does eye relief correspond to exit pupil size? My Celestron 25 mm lens has a rear lens width of 16 mm. Is that the same as the exit pupil?

should I post this back in the beginner section?

ivirlocri

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Re: Need advice on new zoom lens
« Reply #7 on: January 13, 2018, 04:36:21 PM »
Quote
Cosmic Ron in L.A. sells them periodically here on CN; and, George at Astro Parts up in Frazier Park has a huge inventory of used astro gear. I'll find his website and get back to you in a little while.

Thank you, that would be great. BTW a new Celestron is under $60

brigtigeartgib

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Re: Need advice on new zoom lens
« Reply #8 on: January 16, 2018, 04:20:59 AM »
It's Don Rothman not George (I confused him with another guy in NY state). Rothman may have one -- I didn't look at his inventory nor have I lately but he usually has some interesting old astro stuff for sale. Here's Don's website: http://www.astronomy...o.parts.outlet/
 By the way, I have one which I will not sell.

xenjavabve

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Re: Need advice on new zoom lens
« Reply #9 on: January 25, 2018, 02:03:15 PM »
I took a cursory look through his listing and I didn't see one listed but that doesn't mean that he doesn't have one. Give him a phone call -- it doesn't hurt to ask -- he may have one or he may know someone who does. Good luck with your endeavor. One will turn up.

Duane Berhane

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Re: Need advice on new zoom lens
« Reply #10 on: January 31, 2018, 02:16:18 AM »
He lists a Celestron for around $75, but doesn't say its age.

rennlispuring

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Re: Need advice on new zoom lens
« Reply #11 on: January 31, 2018, 03:10:49 AM »
I didn't note it when I went through that extensive typewritten listing but I'm tired and my eyes are tired so maybe I missed it. This appears to be the modern version of the one with the better glass from the early 1980's that I was talking about. It's more expensive but it is probably worth the extra bucks -- better glass by far and far better eye relief and a better eye cup to view through. It will be a whole lot more comfortable and a lot more enjoyable of an experience viewing through this one while seated. If I were going to buy a modern one -- this is probably the one to get -- a lot of bang for the dollar. The question is whether it will fit into your scopes; and, I don't know the answer to that but I think that it probably will.
http://celestron.fac...tron-82003.html

esicnatka

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Re: Need advice on new zoom lens
« Reply #12 on: February 08, 2018, 07:48:43 PM »
Quote
Im a little confused. I see the Celestron has a Field of View: 40° (at 24mm) to 60° (at 8mm). I thought the more magnification the less FOV. Isn't 8 mm more magnification than 24 mm?

Another question, how does eye relief correspond to exit pupil size? My Celestron 25 mm lens has a rear lens width of 16 mm. Is that the same as the exit pupil?

should I post this back in the beginner section?

Larry:

- The AFoV, the apparent field of view, increases as the magnification is increased but the TFoV, the true field of view, decreases with increased magnification. The true field of view can be estimated using the approximation:

TFoV = AFoV/Magnification.

Using your ST-80 as an example:

At 24mm, the magnification will be Mag = 400/24mm = 16.7x so the TFoV will be 40 deg/16.7 = 2.4 degrees.

At 8mm, the magnification will be 400mm/8mm = 40x so the TFoV will be 60deg/40x = 1.5 degrees.

- Eye relief versus exit pupil: The exit pupil is the beam of light that leaves the eyepiece and enters your eye. You can see it as a bright circle on the eyepiece if you look at it from a distance. The diameter of the exit pupil depends only on the aperture of the telescope and the magnification:

Exit pupil = Aperture/magnification

The Eye Relief is the distance from the eyepiece where the image is fully formed, this is the optimal position for your eye. It depends on the particular eyepiece and it's design. Quite a different thing.

Regarding zoom lenses:

If I understand correctly, the 24mm-8mm Zoom that Tarzanrock is encouraging you to purchase is the older made in Japan version of the standard 24mm-8mm zoom. These were sold by nearly everyone, Vixen, Celestron, Meade, Orion, even TeleVue sold a version, probably the only TeleVue eyepiece that was not designed by TeleVue. I am not exactly sure who manufactured the eyepiece but I believe most were sourced through Vixen, the Celestron and Orion version would have been.

The Vixen LV zoom is still available, it's $182 from Agena Astro. I have a Vixen LV zoom. It's a decent eyepiece, I use it mostly in my solar scope because the narrow AFoV doesn't matter and F/10, it performs well enough. In my other scopes, it's range is insufficient and I find the views of my fixed focal length eyepieces superior...

Whether the increased cost of the Vixen Zoom is worth it to you, I cannot say. Zooms are complicated eyepieces with moving elements so that unlike fixed focal length eyepieces, the design cannot be fully optimized at each focal length, there are compromises.

Jon