ES ED102 Help: Having to add and remove extenders for different eyepieces?

We all started somewhere! We are a friendly bunch! Most of your questions can be posted here, but if you are interested in Astrophotography please use the new Beginner Astrophotography forum. The response time will be much better.
Post Reply
brownbrady
Earth Ambassador
Articles: 0
Offline
Posts: 8
Joined: Thu May 21, 2020 8:56 pm
3
Location: Oshawa, ON
Status:
Offline

ES ED102 Help: Having to add and remove extenders for different eyepieces?

#1

Post by brownbrady »


Hi group, I have an Explore Scientific ED 102 which I took out to first light last night with an ES 2" eye piece (24mm). This OTA has a 714 mm focal length with a 44 mm focus travel but I could not reach focus until I attached the 2 extenders with the star diagonal. During star alignment, I used my Celestron CrossAim illuminated Crosshair Eyepiece which is a 12.5 mm but I could not reach focus until I removed one of the extenders. I find this to be an inconvenience because I risk disturbing the alignment when re-attaching the second extension to use my 2" eyepiece. Is this normal or am I missing something? I do not know the physics behind prime focus so I don't understand why I have to do this. Thanks in advance.
User avatar
KathyNS Canada
Co-Administrator
Co-Administrator
Articles: 0
Online
Posts: 2584
Joined: Thu Apr 25, 2019 11:47 am
4
Location: Nova Scotia
Status:
Online

TSS Awards Badges

TSS Photo of the Day

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#2

Post by KathyNS »


The scope produces a focused image at exactly one, and only one spot, known as the focal point. To see clearly through an eyepiece, which has its own focal point, the eyepiece's focal point has to be moved to coincide with the scope's focal point.

If all eyepieces had their focal point at the same position relative to the barrel that inserts into the focuser tube, then focusers would need very little travel, because all eyepieces would focus at the same place. Unfortunately, there is absolutely no standard for where an eyepiece's focal point should be. You will find some that have their focal point way down at the bottom of the focuser barrel, and others that have it well inside the eyepiece itself, and everything in between.

Since eyepieces have such a broad range of focal positions, focusers need to have a long range of motion to accommodate them all. Some don't have enough.
Image
DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,Oiii,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier); Helena Observatory (H2O) Astrobin
User avatar
Lady Fraktor Slovakia
Co-Administrator
Co-Administrator
Articles: 0
Offline
Posts: 9860
Joined: Mon Apr 29, 2019 9:14 pm
4
Location: Slovakia
Status:
Offline

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#3

Post by Lady Fraktor »


What diagonal are you using with the telescope?
See Far Sticks: Antares Elita 103/1575, AOM FLT 105/1000, Bresser BV 127/1200, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS100/1000, Vixen SD115s/885
EQ: TAL MT-1, Vixen SXP, AXJ, AXD
Az/Alt: AYO Digi II/ Argo Navis, Stellarvue M2C/ Argo Navis
Tripods: Berlebach Planet (2), Uni 28 Astro, Report 372, TAL factory maple, Vixen ASG-CB90, Vixen AXD-TR102
Diagonals: Astro-Physics, Baader Amici, Baader Herschel, iStar Blue, Stellarvue DX, Takahashi prism, TAL, Vixen flip mirror
Eyepieces: Antares to Zeiss
The only culture I have is from yogurt
My day was going well until... people
Image
brownbrady
Earth Ambassador
Articles: 0
Offline
Posts: 8
Joined: Thu May 21, 2020 8:56 pm
3
Location: Oshawa, ON
Status:
Offline

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#4

Post by brownbrady »


KathyNS wrote: Wed May 27, 2020 4:09 pm The scope produces a focused image at exactly one, and only one spot, known as the focal point. To see clearly through an eyepiece, which has its own focal point, the eyepiece's focal point has to be moved to coincide with the scope's focal point.

If all eyepieces had their focal point at the same position relative to the barrel that inserts into the focuser tube, then focusers would need very little travel, because all eyepieces would focus at the same place. Unfortunately, there is absolutely no standard for where an eyepiece's focal point should be. You will find some that have their focal point way down at the bottom of the focuser barrel, and others that have it well inside the eyepiece itself, and everything in between.

Since eyepieces have such a broad range of focal positions, focusers need to have a long range of motion to accommodate them all. Some don't have enough.
Thank you for the explanation. The 2 eyepieces are made by different manufacturers (ES vs. Celestron) and probably have too much distance between each focal points.
brownbrady
Earth Ambassador
Articles: 0
Offline
Posts: 8
Joined: Thu May 21, 2020 8:56 pm
3
Location: Oshawa, ON
Status:
Offline

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#5

Post by brownbrady »


Lady Fraktor wrote: Wed May 27, 2020 4:32 pm What diagonal are you using with the telescope?
I am using the one that came with the ES ED102 OTA which also has an ES branding on it.
User avatar
Lady Fraktor Slovakia
Co-Administrator
Co-Administrator
Articles: 0
Offline
Posts: 9860
Joined: Mon Apr 29, 2019 9:14 pm
4
Location: Slovakia
Status:
Offline

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#6

Post by Lady Fraktor »


2" or 1.25"?
Strange that it will not focus between a 12.5mm and 24mm eyepiece though, there should be enough focuser travel to accommodate.
See Far Sticks: Antares Elita 103/1575, AOM FLT 105/1000, Bresser BV 127/1200, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS100/1000, Vixen SD115s/885
EQ: TAL MT-1, Vixen SXP, AXJ, AXD
Az/Alt: AYO Digi II/ Argo Navis, Stellarvue M2C/ Argo Navis
Tripods: Berlebach Planet (2), Uni 28 Astro, Report 372, TAL factory maple, Vixen ASG-CB90, Vixen AXD-TR102
Diagonals: Astro-Physics, Baader Amici, Baader Herschel, iStar Blue, Stellarvue DX, Takahashi prism, TAL, Vixen flip mirror
Eyepieces: Antares to Zeiss
The only culture I have is from yogurt
My day was going well until... people
Image
brownbrady
Earth Ambassador
Articles: 0
Offline
Posts: 8
Joined: Thu May 21, 2020 8:56 pm
3
Location: Oshawa, ON
Status:
Offline

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#7

Post by brownbrady »


Lady Fraktor wrote: Wed May 27, 2020 5:19 pm 2" or 1.25"?
Strange that it will not focus between a 12.5mm and 24mm eyepiece though, there should be enough focuser travel to accommodate.
The star diagonal takes a 2" eyepiece. The 1.25" adapter adds around 8 mm of length.
User avatar
Lady Fraktor Slovakia
Co-Administrator
Co-Administrator
Articles: 0
Offline
Posts: 9860
Joined: Mon Apr 29, 2019 9:14 pm
4
Location: Slovakia
Status:
Offline

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#8

Post by Lady Fraktor »


Looking at various reviews of this telescope everyone seems to state you normally will only need one extension to achieve focus.
Keep trying but if you cannot get it figured out do not hesitate to call ES and talk to them about the issue.

Try using one extension and see if you are running out of inward travel or outward.
See Far Sticks: Antares Elita 103/1575, AOM FLT 105/1000, Bresser BV 127/1200, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS100/1000, Vixen SD115s/885
EQ: TAL MT-1, Vixen SXP, AXJ, AXD
Az/Alt: AYO Digi II/ Argo Navis, Stellarvue M2C/ Argo Navis
Tripods: Berlebach Planet (2), Uni 28 Astro, Report 372, TAL factory maple, Vixen ASG-CB90, Vixen AXD-TR102
Diagonals: Astro-Physics, Baader Amici, Baader Herschel, iStar Blue, Stellarvue DX, Takahashi prism, TAL, Vixen flip mirror
Eyepieces: Antares to Zeiss
The only culture I have is from yogurt
My day was going well until... people
Image
brownbrady
Earth Ambassador
Articles: 0
Offline
Posts: 8
Joined: Thu May 21, 2020 8:56 pm
3
Location: Oshawa, ON
Status:
Offline

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#9

Post by brownbrady »


Lady Fraktor wrote: Wed May 27, 2020 5:39 pm Looking at various reviews of this telescope everyone seems to state you normally will only need one extension to achieve focus.
Keep trying but if you cannot get it figured out do not hesitate to call ES and talk to them about the issue.

Try using one extension and see if you are running out of inward travel or outward.
I just tried some more and was able to achieve focus on both eyepieces using 2 extenders BUT the object is a neighbor's rooftop that is only 100 meters away. With the 2" eyepiece, the focuser is extended by 22 mm. For the 1.25" eyepiece, the focuser is extended by 1 mm. This eyepiece has a focusing ring for the illuminated crosshairs. If I fully retract it, the crosshairs become blurred but it gives me an extra 1 mm of focuser travel and can put the object further away into focus. It is very close to the edge of the focal travel but I will try to focus on a star tonight with this setting.
brownbrady
Earth Ambassador
Articles: 0
Offline
Posts: 8
Joined: Thu May 21, 2020 8:56 pm
3
Location: Oshawa, ON
Status:
Offline

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#10

Post by brownbrady »


Lady Fraktor wrote: Wed May 27, 2020 5:39 pm Try using one extension and see if you are running out of inward travel or outward.
Using 1 extension, I run out of outward focus travel when using the 2" eyepieces on an object that is 100 meters away. I can reach focus by loosening the bolts that tighten down the star diagonal and extend that by about 10 mm but I'm not sure if it is advisable to be doing that. Another place I can extend is the eyepiece holder where I loosen the bolts and extend the eyepiece out by about 10 mm. Again, i'm not sure I should be doing that.
User avatar
KathyNS Canada
Co-Administrator
Co-Administrator
Articles: 0
Online
Posts: 2584
Joined: Thu Apr 25, 2019 11:47 am
4
Location: Nova Scotia
Status:
Online

TSS Awards Badges

TSS Photo of the Day

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#11

Post by KathyNS »


brownbrady wrote: Wed May 27, 2020 6:34 pm I just tried some more and was able to achieve focus on both eyepieces using 2 extenders BUT the object is a neighbor's rooftop that is only 100 meters away.
That means that you extended it too far. Try focusing on the Moon with that same combination. If it won't focus, remove one of the extensions.
Image
DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,Oiii,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier); Helena Observatory (H2O) Astrobin
User avatar
Lady Fraktor Slovakia
Co-Administrator
Co-Administrator
Articles: 0
Offline
Posts: 9860
Joined: Mon Apr 29, 2019 9:14 pm
4
Location: Slovakia
Status:
Offline

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#12

Post by Lady Fraktor »


Also that target is quite close, for infinity focus I imagine one extension will do fine.
See Far Sticks: Antares Elita 103/1575, AOM FLT 105/1000, Bresser BV 127/1200, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS100/1000, Vixen SD115s/885
EQ: TAL MT-1, Vixen SXP, AXJ, AXD
Az/Alt: AYO Digi II/ Argo Navis, Stellarvue M2C/ Argo Navis
Tripods: Berlebach Planet (2), Uni 28 Astro, Report 372, TAL factory maple, Vixen ASG-CB90, Vixen AXD-TR102
Diagonals: Astro-Physics, Baader Amici, Baader Herschel, iStar Blue, Stellarvue DX, Takahashi prism, TAL, Vixen flip mirror
Eyepieces: Antares to Zeiss
The only culture I have is from yogurt
My day was going well until... people
Image
User avatar
Bigzmey United States of America
Moderator
Moderator
Articles: 8
Online
Posts: 7551
Joined: Sat May 11, 2019 7:55 pm
4
Location: San Diego, CA USA
Status:
Online

TSS Awards Badges

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#13

Post by Bigzmey »


I used to have ES 102mm APO, and with supplied ES 2" dielectric diagonal and one extension I was able to achieve focus on astronomical targets with all EPs from 3mm to 40mm.

For terrestrial targets you can get zoom EP, or a set of parfocal EPs which require the same focal travel (Pentax XWs, Vixen SLVs, most of Televue EP lines).

A side note, if you align finderscopes on terrestrial targets close by, it will be somewhat off for astronomical targets. You should re-check the alignment at night on the Moon or another easy to find object. Polaris is convenient, since it does not move.
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
Mounts: SW: SkyTee2, AzGTi; iOptron: AZMP; ES: Twilight I; Bresser: EXOS2; UA: MicroStar.
Binos: APM: 100-90 APO; Canon: IS 15x50; Orion: Binoviewer, LG II 15x70, WV 10x50, Nikon: AE 16x50, 10x50, 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV.
Diagonals: Baader: BBHS mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: 2" prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S, 6-color set; Astronomik: UHC.

Observing: DSOs: 3106 (Completed: Messier, Herschel 1, 2, 3. In progress: H2,500: 2180, S110: 77). Doubles: 2382, Comets: 34, Asteroids: 255
User avatar
NGC 1365 Australia
Saturn Ambassador
Articles: 0
Offline
Posts: 368
Joined: Mon Dec 02, 2019 8:30 am
4
Location: NSW Australia
Status:
Offline

TSS Awards Badges

TSS Photo of the Day

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#14

Post by NGC 1365 »


I had the ES 127 triplet and used a Televue 2 inch diagonal with 2 inch extension tubes screwed directly to the diagonal( I think I had two 35mm tubes screwed together) and this had enough range for all my eyepieces, easier than adding and removing from focuser.
Ivan
User avatar
Baurice
Vendor
Vendor
Articles: 0
Offline
Posts: 1321
Joined: Sun Aug 18, 2019 10:42 pm
4
Location: England
Status:
Offline

TSS Awards Badges

TSS Photo of the Day

Re: ES ED102 Help: Having to add and remove extenders for different eyepieces?

#15

Post by Baurice »


KathyNS wrote: Wed May 27, 2020 4:09 pm The scope produces a focused image at exactly one, and only one spot, known as the focal point. To see clearly through an eyepiece, which has its own focal point, the eyepiece's focal point has to be moved to coincide with the scope's focal point.

If all eyepieces had their focal point at the same position relative to the barrel that inserts into the focuser tube, then focusers would need very little travel, because all eyepieces would focus at the same place. Unfortunately, there is absolutely no standard for where an eyepiece's focal point should be. You will find some that have their focal point way down at the bottom of the focuser barrel, and others that have it well inside the eyepiece itself, and everything in between.

Since eyepieces have such a broad range of focal positions, focusers need to have a long range of motion to accommodate them all. Some don't have enough.
I find this a problem with my Coronado PST. It's limited focus travel means that few accessories work with it and I've had to resort to afocal photography.
Post Reply

Create an account or sign in to join the discussion

You need to be a member in order to post a reply

Create an account

Not a member? register to join our community
Members can start their own topics & subscribe to topics
It’s free and only takes a minute

Register

Sign in

Return to “Beginners forum”