Creating a basic set of eyepieces for your new telescope

Discuss telescope eyepieces.
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Lady Fraktor Slovakia
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Re: Creating a basic set of eyepieces for your new telescope

#41

Post by Lady Fraktor »


Avoid the Celestron eyepiece kits as the eyepieces are of poor quality and the filters are not much better.
The GSO Plossl are the cheapest quality Plossl available and are better quality than the kit ones.
With filters it is better to buy filters that will work for the objects you wish to observe but quality ones will cost more of course.
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
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Re: Creating a basic set of eyepieces for your new telescope

#42

Post by turboscrew »


Lady Fraktor wrote: Thu May 23, 2019 2:34 am One of the most asked questions by beginners, What eyepieces should I get?


There is always a lot of discussion from people on what eyepieces to get with their new telescopes.

Most people seem to want to get the most magnification possible right away, but unfortunately, reality in the form of current atmospheric conditions has a lot to say on that subject.

All telescopes, no matter the type, have an “optimal” range where they perform the best. As you gain experience, you will understand when and how to properly go outside those limits.

This discussion will show you how to generate a good optimum set to start out with and get the most from your scope without the pitfalls of buying something that will not be of use to you.

There are 3 formulae that you will need to know to work this all out. For the beginner, it will show the relationship of telescope focal length, eyepiece focal length, exit pupil, and magnification.

AFOV (Apparent Field Of View) is not taken into account as it is more subjective to the target and style of telescope.

The formulae you need to know to do this are:

1) Focal Length of Eyepiece ÷ Focal Ratio of Telescope = Exit Pupil
2) Focal Length of Telescope ÷ Eyepiece Magnification = Eyepiece Focal Length
3) Focal Length of Telescope ÷ Focal Length of Eyepiece = Eyepiece Magnification

The first thing you need to do is find your starting exit pupil. I prefer to start at 0.5mm, which is usually around ½ the Focal Ratio of the telescope.
The scope we are going to use in the example is my SV 80mm f/6.9 (552mm), so we will start with an eyepiece focal length of 3.5mm

HINT: An eyepiece focal length equal to the Focal Ratio of your scope is normally a 1mm Exit Pupil.

1) 3.5mm ÷ 6.9 = 0.507 or 0.51mm
2) 552mm ÷ 3.5mm = 157.7 or 158x magnification

For spacing the eyepieces, we are going to use a magnification decrease of 1.5x so,

158x ÷ 1.5 = 105x magnification

The next step is to use formula 3.

3) 552mm ÷ 105x mag = 5.2mm (eyepiece focal length)

Use the above formula to work out your exit pupil for this eyepiece and then carry on with the next step.

105x ÷ 1.5 = 70x magnification.

As you work through you will have a list that looks like this.

Set 1 (1.5):
3.5mm -- 0.51 ep -- 158x
5.2mm -- 0.75 ep -- 105x
8mm -- 1.16 ep -- 70x
12mm -- 1.74 ep -- 47x
18mm -- 2.58 ep -- 31x
26mm -- 3.81 ep -- 21x
39mm -- 5.71 ep -- 14x
55mm -- 8 ep -- 9x (unusable)**

Work down till you get to just over a 7mm exit pupil as most people will never be able to use anything larger than 7mm.

It can be used in a refractor as it will not affect the view, in a reflector the shadow of the secondary mirror will start to show as a black spot in the view if you exceed the size of your dark adapted pupil.

Notice also in Set 1 that there is no real need for a barlow lens as dividing any of the focal lengths by 2 will put the new focal length within 1-2mm of the next eyepiece.
For a starter set the range of 8mm - 39mm (substitute a 40mm in place of the 39mm) will work very well.

Afterwards if desired you could add one in the 5.5 or 6mm range and a 32mm on the low range.

Now to work out a second set but this time using 1.6 instead.

Using the example scope and formulas/steps above your chart will look like this:

Set 2 (1.6):
3.5mm -- 0.51 ep -- 158x
5.5mm -- 0.80 ep -- 99x
9mm -- 1.31 ep -- 62x
14mm -- 2.05 ep -- 39x
23mm -- 3.33 ep -- 24x
36mm -- 5.33 ep -- 15x

In Set 2, there is potential for using a 2x barlow as the focal lengths will be in between all the calculated focal lengths.

Most eyepiece manufacturers space their focal lengths at 1.4, 1.5 or 1.6x

Congratulations, you have just generated a useful range of eyepieces for your telescope!

The only thing you need to decide on now is what AFOV you wish to use and do you want a barlow or not.

I have found over time that I prefer to view using fixed focal length eyepieces over using a barlow.

I still have a couple and occasionally will use them, normally in a “grab and go” situation of a barlow and 2-3 eyepieces.


In conclusion:

Most new telescopes come with a 9mm and 25mm eyepieces which unfortunately are usually not of the best quality. Most of these are poorly made Ramsden, Huygenian, Kellner or Plossl which is a shame because when made properly they are actually fine eyepiece designs in the right telescope.

The 9mm and 25mm eyepieces can be considered “work horse” focal lengths. They will always work in any style of scope. When considering buying better quality eyepieces right away, my recommendation is to change these for better quality first.
They are eyepieces that will be in your kit for a long time. They do not have to be the same type as supplied with the telescope. This is where you can play with the AFOV, depending on what you normally want to view.

Using your telescope at the lowest possible magnification has a lower limit for every scope which is normally dictated by the size of your dark adapted eye pupil.
This is considered around 7mm which can and will decrease as you get older.
You can exceed it with a refractor as it will not affect the view, though really would just be wasting money as it just becomes “wasted” light.
In a reflector, the shadow of the secondary mirror will start to show as a black spot in the view if you exceed the size of your dark adapted pupil size.

Highest magnification possible will be dictated by the prevailing current atmosphere and style of scope.
Physics says this is what your scope can theoretically do while the atmosphere says this is what it will be allowed to do. Occasionally, when the two are feeling civil towards each other, you will be able to exceed those limits, but it is not an occasion that happens very often, unfortunately.
Inspired by this posting, I made a LibreOffice Calc tables to help selection. It could work in Excel too, I'm not sure. It has too tabs, one for selecting by number of eyepieces and another for selecting by magnification step.
The tables also have fields to experiment with AFOVs and Barlows.
Maybe that's of some help for beginners.
https://www.dropbox.com/s/n7gajmxhgrqjy ... l.ods?dl=0
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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Re: Creating a basic set of eyepieces for your new telescope

#43

Post by SkyHiker »


Lady Fraktor wrote: Thu May 23, 2019 2:34 am The formulae you need to know to do this are:

1) Focal Length of Eyepiece ÷ Focal Ratio of Telescope = Exit Pupil
2) Focal Length of Telescope ÷ Eyepiece Magnification = Eyepiece Focal Length
3) Focal Length of Telescope ÷ Focal Length of Eyepiece = Eyepiece Magnification
There's something wrong with formula 2 here...
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: Creating a basic set of eyepieces for your new telescope

#44

Post by turboscrew »


SkyHiker wrote: Sat Aug 01, 2020 11:17 am
Lady Fraktor wrote: Thu May 23, 2019 2:34 am The formulae you need to know to do this are:

1) Focal Length of Eyepiece ÷ Focal Ratio of Telescope = Exit Pupil
2) Focal Length of Telescope ÷ Eyepiece Magnification = Eyepiece Focal Length
3) Focal Length of Telescope ÷ Focal Length of Eyepiece = Eyepiece Magnification
There's something wrong with formula 2 here...
What is it? I don't see it.
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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Re: Creating a basic set of eyepieces for your new telescope

#45

Post by SkyHiker »


turboscrew wrote: Sat Aug 01, 2020 11:38 am
SkyHiker wrote: Sat Aug 01, 2020 11:17 am
Lady Fraktor wrote: Thu May 23, 2019 2:34 am The formulae you need to know to do this are:

1) Focal Length of Eyepiece ÷ Focal Ratio of Telescope = Exit Pupil
2) Focal Length of Telescope ÷ Eyepiece Magnification = Eyepiece Focal Length
3) Focal Length of Telescope ÷ Focal Length of Eyepiece = Eyepiece Magnification
There's something wrong with formula 2 here...
What is it? I don't see it.
2 and 3 contradict each other. Clearly, 3 is right.

BTW "Eyepiece magnification" should be "magnification", right? A single lens does not have magnification just a focal length.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: Creating a basic set of eyepieces for your new telescope

#46

Post by turboscrew »


SkyHiker wrote: Sat Aug 01, 2020 3:40 pm
turboscrew wrote: Sat Aug 01, 2020 11:38 am
SkyHiker wrote: Sat Aug 01, 2020 11:17 am

There's something wrong with formula 2 here...
What is it? I don't see it.
2 and 3 contradict each other. Clearly, 3 is right.

BTW "Eyepiece magnification" should be "magnification", right? A single lens does not have magnification just a focal length.
Actually, you can think of the focal length of telescope as the product of the two others. Dividing the focal length of telescope with either, gives the other. Don't let the order (result last) lead you astray. ;-)
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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Re: Creating a basic set of eyepieces for your new telescope

#47

Post by notFritzArgelander »


turboscrew wrote: Sat Aug 01, 2020 3:53 pm
SkyHiker wrote: Sat Aug 01, 2020 3:40 pm
turboscrew wrote: Sat Aug 01, 2020 11:38 am

What is it? I don't see it.
2 and 3 contradict each other. Clearly, 3 is right.

BTW "Eyepiece magnification" should be "magnification", right? A single lens does not have magnification just a focal length.
Actually, you can think of the focal length of telescope as the product of the two others. Dividing the focal length of telescope with either, gives the other. Don't let the order (result last) lead you astray. ;-)
This is correct. While in astronomy circles "eyepiece magnification" is seldom used the eyepieces for spotting scopes are often specified by magnification rather than focal length. For instance https://telescopes.net/store/telescope- ... piece.html

JG has pointed out that spotting scope eyepieces often are advantageous for astronomical purposes because of superior stray light control.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: Creating a basic set of eyepieces for your new telescope

#48

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notFritzArgelander wrote: Sat Aug 01, 2020 7:09 pm
turboscrew wrote: Sat Aug 01, 2020 3:53 pm
SkyHiker wrote: Sat Aug 01, 2020 3:40 pm

2 and 3 contradict each other. Clearly, 3 is right.

BTW "Eyepiece magnification" should be "magnification", right? A single lens does not have magnification just a focal length.
Actually, you can think of the focal length of telescope as the product of the two others. Dividing the focal length of telescope with either, gives the other. Don't let the order (result last) lead you astray. ;-)
This is correct. While in astronomy circles "eyepiece magnification" is seldom used the eyepieces for spotting scopes are often specified by magnification rather than focal length. For instance https://telescopes.net/store/telescope- ... piece.html
They specify it as 20x60 zoom for a Swarovski spotting scope, not as a 20x60 zoom for arbitrary objectives. The range of spotting scope focal lengths is narrow enough for it to be practical in that sense. But that is quite different from the OPs message, which is about magnification as in elementary physics not as in commerce.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: Creating a basic set of eyepieces for your new telescope

#49

Post by notFritzArgelander »


SkyHiker wrote: Sun Aug 02, 2020 12:17 am
notFritzArgelander wrote: Sat Aug 01, 2020 7:09 pm
turboscrew wrote: Sat Aug 01, 2020 3:53 pm
Actually, you can think of the focal length of telescope as the product of the two others. Dividing the focal length of telescope with either, gives the other. Don't let the order (result last) lead you astray. ;-)
This is correct. While in astronomy circles "eyepiece magnification" is seldom used the eyepieces for spotting scopes are often specified by magnification rather than focal length. For instance https://telescopes.net/store/telescope- ... piece.html
They specify it as 20x60 zoom for a Swarovski spotting scope, not as a 20x60 zoom for arbitrary objectives. The range of spotting scope focal lengths is narrow enough for it to be practical in that sense. But that is quite different from the OPs message, which is about magnification as in elementary physics not as in commerce.
Still, the formulas are correct. All three of them. :)

Spotting scopes objectives aren't as variable in focal length as astronomical scopes. Makers tend to settle on a focal length. So if you are interested in using a spotting scope eyepiece that formula is pretty handy.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: Creating a basic set of eyepieces for your new telescope

#50

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Oops never mind, they are redundant not contradictory.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: Creating a basic set of eyepieces for your new telescope

#51

Post by denairt »


So I am new to this. I read the article and I am as lost as I was before. I have an Orion Star Seeker IV 150mm reflector, it is a GOTO. Overall I am pleased with it. I am not getting great clarity on anything except the moon and I want to upgrade the lenses. Basically I want to see the planets more clearly and seeing nebula and star clusters would be nice.
I don't know where to start with lenses. Is a Plossi lense good enough? Is it worth it to purchase to purchase something like an assortment of lenses from Orion or Celestron? I don't know anyone who has a telescope and has done anything with it astronomy. I am hoping someone hear can give me some help. I don't want to break the bank and spend around $200. Is this even possible for that much $$$
Any help would be much appreciated!!
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Re: Creating a basic set of eyepieces for your new telescope

#52

Post by Lady Fraktor »


Is your telescope mirrors in good colimation?

A Plossl will work well with your telescope and are a great starting point when beginning.
The GSO Plossl are low priced and good quality, a combination that rarely happens with astronomy equipment.

Your telescope is a f/5 so to start a 5mm would be your high power eyepiece.
If you get a 32mm, 25mm and 9mm GSO Plossl as well as a GSO 2x barlow you can have a basic starter set of 8 focal lengths.

Avoid the eyepiece kits the manufacturers sell as the eyepieces are typically not very good quality.
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
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Re: Creating a basic set of eyepieces for your new telescope

#53

Post by denairt »


Thanks So much!! Exactly what i needed to hear!
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Re: Creating a basic set of eyepieces for your new telescope

#54

Post by Refractordude »


denairt wrote: Sun Aug 16, 2020 4:27 am So I am new to this. I read the article and I am as lost as I was before. I have an Orion Star Seeker IV 150mm reflector, it is a GOTO. Overall I am pleased with it. I am not getting great clarity on anything except the moon and I want to upgrade the lenses. Basically I want to see the planets more clearly and seeing nebula and star clusters would be nice.
I don't know where to start with lenses. Is a Plossi lense good enough? Is it worth it to purchase to purchase something like an assortment of lenses from Orion or Celestron? I don't know anyone who has a telescope and has done anything with it astronomy. I am hoping someone hear can give me some help. I don't want to break the bank and spend around $200. Is this even possible for that much $$$
Any help would be much appreciated!!
Eyepieces are important, but so are the clarity of the skies you are observing under. I live under Bortle Scale 9 skies. I have several dark sites that I travel to for nebula, galaxies, etc.
https://www.lightpollutionmap.info/#zoo ... TFFFFFFFFF

https://www.handprint.com/ASTRO/bortle.html
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Re: Creating a basic set of eyepieces for your new telescope

#55

Post by ChrisP90 »


Lady Fraktor wrote: Sun Aug 16, 2020 4:47 am Your telescope is a f/5 so to start a 5mm would be your high power eyepiece.
Can I ask why that is?

I’m looking to invest in a high power eye piece.
According to my math (could be wrong), a 2.5mm EP would give me a 0.5 exit pupil and 260x magnification.
My scope theoretically should have a maximum useful magnification if 325x.

Is there a reason you would suggest a 5mm for a f/5?

I just want to ensure my understanding is correct. Some of my math is taken from the original post whilst others is from TLAO. So I may be getting confused!

Thanks,
CP.
Telescope: Skywatcher Heritage 130P
Camera: Canon EOS 450D
Complete Novice, hoping to build my collection and in turn my signature! :D
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Re: Creating a basic set of eyepieces for your new telescope

#56

Post by notFritzArgelander »


ChrisP90 wrote: Wed Sep 02, 2020 5:55 pm
Lady Fraktor wrote: Sun Aug 16, 2020 4:47 am Your telescope is a f/5 so to start a 5mm would be your high power eyepiece.
Can I ask why that is?

I’m looking to invest in a high power eye piece.
According to my math (could be wrong), a 2.5mm EP would give me a 0.5 exit pupil and 260x magnification.
My scope theoretically should have a maximum useful magnification if 325x.

Is there a reason you would suggest a 5mm for a f/5?

I just want to ensure my understanding is correct. Some of my math is taken from the original post whilst others is from TLAO. So I may be getting confused!

Thanks,
CP.
I agree with LF's suggestion. I don't presume to speak for her but a 1mm exit pupil will likely work well under a variety of atmospheric conditions. The 0.5 exit pupil might only be usable 2-3 nights per year.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: Creating a basic set of eyepieces for your new telescope

#57

Post by ChrisP90 »


notFritzArgelander wrote: Wed Sep 02, 2020 5:58 pm
I agree with LF's suggestion. I don't presume to speak for her but a 1mm exit pupil will likely work well under a variety of atmospheric conditions. The 0.5 exit pupil might only be usable 2-3 nights per year.
Okay, that’s brilliant.
Makes sense. While the 0.5 exit pupil may theoretically be the better EP, the 1mm exit pupil will be more useful on a regular basis?
Thanks for explaining!
Telescope: Skywatcher Heritage 130P
Camera: Canon EOS 450D
Complete Novice, hoping to build my collection and in turn my signature! :D
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Re: Creating a basic set of eyepieces for your new telescope

#58

Post by notFritzArgelander »


ChrisP90 wrote: Wed Sep 02, 2020 6:04 pm
notFritzArgelander wrote: Wed Sep 02, 2020 5:58 pm
I agree with LF's suggestion. I don't presume to speak for her but a 1mm exit pupil will likely work well under a variety of atmospheric conditions. The 0.5 exit pupil might only be usable 2-3 nights per year.
Okay, that’s brilliant.
Makes sense. While the 0.5 exit pupil may theoretically be the better EP, the 1mm exit pupil will be more useful on a regular basis?
Thanks for explaining!
Also.... a 2mm exit pupil will resolve anything your telescope can resolve. Smaller exit pupils just make things bigger.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: Creating a basic set of eyepieces for your new telescope

#59

Post by ChrisP90 »


Are the Celestron X-Cel Lx eyepieces any good?
Or are there better out there? I’ve seen them for £66 for a 5mm.
Telescope: Skywatcher Heritage 130P
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Re: Creating a basic set of eyepieces for your new telescope

#60

Post by notFritzArgelander »


ChrisP90 wrote: Wed Sep 02, 2020 6:56 pm Are the Celestron X-Cel Lx eyepieces any good?
Or are there better out there? I’ve seen them for £66 for a 5mm.
There are several folks on this board that like them. They are similar to the Meade HD 60 line which I like.

If you compare them to a Plossl, say, they have more field distortion but a wider field and longer eye relief. So if you need to observe wearing glasses they might be a better choice than a Plossl.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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