Geometrical optics and focuser
- turboscrew
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Geometrical optics and focuser
What's the role of the focuser?
I've been playing with geometrical optics of two lens system, and it looks like the image is always formed, either true or false - except when the object to a lens is at its focal point.
Is it because of the eye, or because of other properties not described by geometrical optics?
And why should the focal lengths of the objective and eyepiece overlap (false image)?
I've been playing with geometrical optics of two lens system, and it looks like the image is always formed, either true or false - except when the object to a lens is at its focal point.
Is it because of the eye, or because of other properties not described by geometrical optics?
And why should the focal lengths of the objective and eyepiece overlap (false image)?
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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: Geometrical optics and focuser
Yes, image is formed by telescope objective in the focal plane. The role of EP is to magnify this image. Since EPs have different focal lengths you need focuser to converge the focal planes of EP and telescope objective. Any time you add additional elements to the optical train (observe eye, diagonal, barlow, etc.) you need to do further adjustments.
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Re: Geometrical optics and focuser
A single lens will form an image but with convergent rays towards the focal point and divergent from there on. In order for the human eye to see an image, the light rays must come in approximately parallel. That's why you need a second lens, the eyepiece. It will make the divergent rays parallel tuned by your hand turning the focuser.
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Re: Geometrical optics and focuser
I've read that the focal lengths have to overlap a bit. if the object of second lens is exactly in its focal point, there is no image, true or false. If the object is outside of the focal point, the image is true, an if it's inside of the focal point, the image is false. And since the image of the objective forms at its focal plane (its object in optical infinity)...
Also the angle that a lens "bends" the beam doesn't depend on the distance.
But I guess, it has to do with the eye: whether or not the image forms on the retina, in front of it, or behind it?
To get it, I should study 3 lens systems with true final images?
Also the angle that a lens "bends" the beam doesn't depend on the distance.
But I guess, it has to do with the eye: whether or not the image forms on the retina, in front of it, or behind it?
To get it, I should study 3 lens systems with true final images?
- 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.
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: Geometrical optics and focuser
Yes.turboscrew wrote: ↑Tue Jan 12, 2021 4:56 am But I guess, it has to do with the eye: whether or not the image forms on the retina, in front of it, or behind it?
No because the shape of the human eye leads to a nearly fixed focus lens. For comfortable viewing the rays must come in parallel. They may diverge a bit but then the eye's lens must work to focus. So just assume parallel. Then there's not that much to study really.turboscrew wrote: ↑Tue Jan 12, 2021 4:56 am To get it, I should study 3 lens systems with true final images?
... Henk. 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: Geometrical optics and focuser
Re-reading it, what I meant to say is that a parallel light bundle (for instance from a star at infinity) must be processed by the optics into a parallel light bundle emerging from the eyepiece, for most comfortable viewing by the human eye. Of course the rays coming from different stars are not parallel but the rays contained in the light bundle of each individual star, are.SkyHiker wrote: ↑Tue Jan 12, 2021 9:31 amYes.turboscrew wrote: ↑Tue Jan 12, 2021 4:56 am But I guess, it has to do with the eye: whether or not the image forms on the retina, in front of it, or behind it?No because the shape of the human eye leads to a nearly fixed focus lens. For comfortable viewing the rays must come in parallel. They may diverge a bit but then the eye's lens must work to focus. So just assume parallel. Then there's not that much to study really.turboscrew wrote: ↑Tue Jan 12, 2021 4:56 am To get it, I should study 3 lens systems with true final images?
... Henk. 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: Geometrical optics and focuser
https://www.physicsforums.com/attachments/3-png.184389/
In the above image, the role of the focuser is to place the
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