I was thinking of getting another "finder eyepiece". I've been using a 40 mm Plössl with
AFOV and secondary shadow
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AFOV and secondary shadow
I was thinking of getting another "finder eyepiece". I've been using a 40 mm Plössl with
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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
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Re: AFOV and secondary shadow
This makes the exit pupil of the eyepiece larger than your dark adapted pupil.
What 40mm eyepiece do you have with a 52°
With your telescope a 40mm would give a 10mm exit pupil... how are you seeing anything?
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Re: AFOV and secondary shadow
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Re: AFOV and secondary shadow
The shadow of the secondary is in the centre of the exit pupil. If the secondary is 30% of the objective, the shadow of the exit pupil will be 30% of the exit pupil
When the exit pupil gets bigger than the observer's pupil two things happen:
1. some of the light ends up next to the observer's pupil and cannot enter the eye
2. the shadow of the secondary begins to fill up the observer's pupil
2. can cause the secondary's shadow to become noticeable.
Imagine watching the Moon using an 13mm wide exit pupil with a 3mm shadow at its centre. A 4mm observer's pupil hovering over this exit pupil will lose a lot of light when directly over its centre and taking in the full shadow of the secondary. When it drifts a few mm to the edge of the exit pupil, the shadow no longer obscures the pupil.
Another example: If you have an
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I have a 500mm focal length
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I discovered that I like a 6x30
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Re: AFOV and secondary shadow
Where the
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Re: AFOV and secondary shadow
You're right. It hasLady Fraktor wrote: ↑Sun Oct 11, 2020 5:13 pm AFOV does not increase the secondary shadow it is caused by to low of magnification of the eyepiece.
This makes the exit pupil of the eyepiece larger than your dark adapted pupil.
What 40mm eyepiece do you have with a 52° AFOV? Normally they are between 40° and 45° AFOV.
With your telescope a 40mm would give a 10mm exit pupil... how are you seeing anything?
And I do see enough to get a target from finder into view. When I get the target about centered in the view, I switch to some useful eyepiece - often 25 mm. I'm really using the 40 mm eyepiece only for that.
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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
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Re: AFOV and secondary shadow
I do notice the secondary shadow, but it hasn't bothered its use as a "finder eyepiece". I don't use it for observing at all.Ruud wrote: ↑Sun Oct 11, 2020 5:47 pm Yes, it is the exit pupil's size that causes the problem, and the exit pupil size depends on the focal length of the eyepiece. Example: if you have an f/5 telescope and you use a 30mm focal length eyepiece, you get an exit pupil of 30/5 = 6mm
The shadow of the secondary is in the centre of the exit pupil. If the secondary is 30% of the objective, the shadow of the exit pupil will be 30% of the exit pupil
When the exit pupil gets bigger than the observer's pupil two things happen:
1. some of the light ends up next to the observer's pupil and cannot enter the eye
2. the shadow of the secondary begins to fill up the observer's pupil
2. can cause the secondary's shadow to become noticeable.
Imagine watching the Moon using an 13mm wide exit pupil with a 3mm shadow at its centre. A 4mm observer's pupil hovering over this exit pupil will lose a lot of light when directly over its centre and taking in the full shadow of the secondary. When it drifts a few mm to the edge of the exit pupil, the shadow no longer obscures the pupil.
Another example: If you have an f/4.7 telescope and a 55mm eyepiece, you get an exit pupil of 55/4.7 = 11.7mm and you will definitely notice your secondary's shadow.
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I have a 500mm focal length f/5 refractor and used a 55mm Plössl as finder. Magnification was 9x and the exit pupil was 11mm. A refractor has no central obstruction so I saw no shadow, but I still did not like the eyepiece as a finder. A separate RACI has all the advantages: you can leave it in place when you don't need it, and you don't need to remove an eyepiece to do your finding. On top of this, the cross hairs of a RACI make it a more effective finder than a long focal length eyepiece will ever be.
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I discovered that I like a 6x30 RACI much better than an 8x50. The larger field of the 6x30 is definitely an advantage. My 6x30 RACI is a SkyWatcher and cost just under €50.
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: AFOV and secondary shadow
I would use a 25mm - 28mm and have a proper exposure.
Using the 10mm exit pupil is like hobbling a horse and trying to get it to run fast...
See Far Sticks: Elita 103/1575, AOM FLT 105/1000, Bresser 127/1200 BV, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS 100/1000, Vixen SD115s/885
EQ: TAL MT-1, Vixen SXP, SXP2, AXJ, AXD
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Re: AFOV and secondary shadow
I have been planning to get a
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)
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LAT 61° 28' 10.9" N, Bortle 5
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Re: AFOV and secondary shadow
If they are, the centered object in the finder will be centered automatically in the telescope.
See Far Sticks: Elita 103/1575, AOM FLT 105/1000, Bresser 127/1200 BV, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS 100/1000, Vixen SD115s/885
EQ: TAL MT-1, Vixen SXP, SXP2, AXJ, AXD
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
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, Tak prism, TAL, Vixen
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Re: AFOV and secondary shadow
Yes. I align the finder with every setup. Daylight first for ease then refined alignment with a star.Lady Fraktor wrote: ↑Mon Oct 12, 2020 3:08 pm It sounds like your finder and telescope are not aligned together properly.
If they are, the centered object in the finder will be centered automatically in the telescope.
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Re: AFOV and secondary shadow
It is. It's just that it's hard to get the target centered so well in the finder that it is visible in the telescope view especially when one has to look in weird yoga positions.Lady Fraktor wrote: ↑Mon Oct 12, 2020 3:08 pm It sounds like your finder and telescope are not aligned together properly.
If they are, the centered object in the finder will be centered automatically in the telescope.
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
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Re: AFOV and secondary shadow
Use a convenient daytime object that is somewhat distant and the problem will be solved.turboscrew wrote: ↑Mon Oct 12, 2020 5:09 pmIt is. It's just that it's hard to get the target centered so well in the finder that it is visible in the telescope view especially when one has to look in weird yoga positions.Lady Fraktor wrote: ↑Mon Oct 12, 2020 3:08 pm It sounds like your finder and telescope are not aligned together properly.
If they are, the centered object in the finder will be centered automatically in the telescope.
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Re: AFOV and secondary shadow
If you mean finder alignment? I did it yesterday daytime (while observing the spruce cones). The yoga positions are needed when I try to look up in a straight finder end that's 5 cm higher than my navel. The ground is too wet to kneel, and it still wouldn't help that much.notFritzArgelander wrote: ↑Mon Oct 12, 2020 5:25 pmUse a convenient daytime object that is somewhat distant and the problem will be solved.turboscrew wrote: ↑Mon Oct 12, 2020 5:09 pmIt is. It's just that it's hard to get the target centered so well in the finder that it is visible in the telescope view especially when one has to look in weird yoga positions.Lady Fraktor wrote: ↑Mon Oct 12, 2020 3:08 pm It sounds like your finder and telescope are not aligned together properly.
If they are, the centered object in the finder will be centered automatically in the telescope.
I'm only 57, but not that flexible any more.
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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