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Re: [ATM] ATM Digest, Vol 51, Issue 2; a lightweight 12' "hat box" travel dob, 20 pounds
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dob, 20 pounds." Follow the link.
----- Original Message -----
From: <atm-request@atmlist.net>
To: <atm@atmlist.net>
Sent: Saturday, March 01, 2008 9:00 PM
Subject: ATM Digest, Vol 51, Issue 2
> Send ATM mailing list submissions to
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> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of ATM digest..."
>
>
> Today's Topics:
>
> 1. Re: Tool surface medium (Bob May)
> 2. Re: OH (that word again) (Bob May)
> 3. Re: a lightweight 12' "hat box" travel dob, 20 pounds.
> (Jack.Swaton@starryhost.com)
> 4. Re: a lightweight 12' "hat box" travel dob, 20 pounds.
> (Philip Lardner)
> 5. Exit pulil and brightnees (George Nikolidakis)
> 6. Re: a lightweight 12' "hat box" travel dob, 20 pounds.
> (Dave Smith)
> 7. Re: Exit pulil and brightnees (Jan van Gastel)
> 8. Re: Exit pulil and brightnees (Alexis Cousein)
> 9. Re: Exit pulil and brightnees (Ken Hunter)
> 10. Re: Exit pulil and brightnees (Marinus van der Lugt)
> 11. Re: Exit pulil and brightnees (Lawrence D. Lopez)
> 12. Re: Exit pulil and brightnees (Jan van Gastel)
> 13. Re: Exit pulil and brightnees (George Nikolidakis)
> 14. Re: Exit puoil and brightness (James Gort)
> 15. Re: Exit pulil and brightnees (Jan van Gastel)
> 16. Re: Exit pulil and brightnees (Bob May)
> 17. Re: Exit pulil and brightnees (Mel Bartels)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 29 Feb 2008 07:31:19 -0800
> From: "Bob May" <rmay@nethere.com>
> Subject: Re: [ATM] Tool surface medium
> To: <atm@atmlist.net>
> Message-ID: <001601c87ae8$22bd6ce0$ddadfea9@amd>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Lockups generally occur because the two surfaces are not to the
> same curvbe. As a result, the space between builds up a vacuum
> as the hole in the mirror travels from the edge to the center.
> This holds down the glass more and more as the vvacuum builds,
> eventually getting to the point hwere it locks up as the force to
> move the glass is too high for you to move it. The correct
> solution is to work the middle high areas by doing short strokes
> so that the two surfaces get back into shape relative to each
> other. Generally I've noted whenever this happens is that there
> is also astigmatism that goes along with this as certain
> orientations of the glass and tool don't want to lockup. When
> this haappens, it is easier as you jut keep the glass slowly
> rotating and that will work its way out gradually. You do need
> to take care that the two don't lockup tho as well as that you
> just don't go shifting the easy direction around as you go.
> Short strokes again are what is necessary.
> Remember that as long as you are doing long stokes, you are doing
> strokes that will parabolize or worse in the polishing/figuring
> stage. You want to make the mirror and tool spherrical so you
> need to use shorter strokes to maintain that shape!
> Please note that when I say short strokes, I also mean not as
> much side to side on the W part of the stroking.
> Bob May
>
> rmay at nethere.com
> http: slash /nav.to slash bobmay
> http: slash /bobmay dot astronomy.net
>
>
>
>
> ------------------------------
>
> Message: 2
> Date: Fri, 29 Feb 2008 07:39:14 -0800
> From: "Bob May" <rmay@nethere.com>
> Subject: Re: [ATM] OH (that word again)
> To: <atm@atmlist.net>
> Message-ID: <002501c87ae9$3d9988e0$ddadfea9@amd>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Then there's the local business window glass supplier. They have
> glass in up to 25mm thickness available although usually they
> will only keep 19mm stuff in stock of any kind. Tempered glass
> is all special ordered unless you want a standard sizze of glass
> that everybody has in their windows which is really kind of rare.
> One size, I mean. Premade products like tabletops and so forth
> will tend a lot more to be tempered so be aware of that, sort of
> like you have already found out.
> Bob May
>
> rmay at nethere.com
> http: slash /nav.to slash bobmay
> http: slash /bobmay dot astronomy.net
>
>
>
>
> ------------------------------
>
> Message: 3
> Date: Fri, 29 Feb 2008 21:22:12 -0800
> From: "Jack.Swaton@starryhost.com" <jack.swaton@starryhost.com>
> Subject: Re: [ATM] a lightweight 12' "hat box" travel dob, 20 pounds.
> To: <atm@atmlist.net>
> Message-ID: <026301c87b5c$34950c10$0402a8c0@dell2>
> Content-Type: text/plain; charset="US-ASCII"
>
> I've never gotten this link to work. I get, "The site you requested could
> not be found".
>
> Is there another link than the one below?
>
> Thanks,
> Jack
>
>
>
> Message: 1
> Date: Wed, 20 Feb 2008 09:31:11 +0100
> From: "dobson 2005" <dobson.2005@gmail.com>
> Subject: [ATM] a lightweight 12' "hat box" travel dob, 20 pounds.
> To: atm@atmlist.net
> Message-ID:
> <4330d4470802200031t7fda703cxe0302419557f4601@mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hello everybody,
>
> Here is my latest completion, a lightweight 12', f/d 5, travel dob, 20
> pounds, all included.
>
> Easy to carry in a bag, for airflight or a trecking in the montains.
>
> I tried to make it as light, compact and minimalist as possible. I will
> call
> it : "La libellule" (dragonfly).
>
> Please note some particular points;
>
> - When disassembled, all parts are put together in a "hat box", 42 cm
> diameter, 12 cm height.
>
> - The ring base is used as a mirror box.
>
> - The lightweight, low profile and simplified spider,
>
> - The lightweight helical crayford focussor (60 g),
>
> - The truss fixations: made in duran, with double articulation.
>
> - The ring flex rocher and ring base system.
>
> In the pictures, the dobson is shown on a very low profile and simplifiedc
> equatorial platform (4 cm height).which is still waiting for a drive.
>
> All details and pictures, as well as pictures of other dobsons I made,
> are
> here on my web site:
> http://dobson.2005.googlepages.com/un300devoyageultral?ger
>
> Regards,
>
> Pierre DESVAUX
> Bourgogne, France
>
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Sat, 1 Mar 2008 11:38:22 -0000
> From: "Philip Lardner" <philiplardner@eircom.net>
> Subject: Re: [ATM] a lightweight 12' "hat box" travel dob, 20 pounds.
> To: "'Jack.Swaton@starryhost.com'" <jack.swaton@starryhost.com>,
> <atm@atmlist.net>
> Message-ID: <AA011ABF823841E88C48251E576E04BB@Vostro>
> Content-Type: text/plain; charset="us-ascii"
>
> Try: http://dobson.2005.googlepages.com
>
>
> -----Original Message-----
> From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
> Of
> Jack.Swaton@starryhost.com
> Sent: 01 March 2008 05:22
> To: atm@atmlist.net
> Subject: Re: [ATM] a lightweight 12' "hat box" travel dob, 20 pounds.
>
> I've never gotten this link to work. I get, "The site you requested could
> not be found".
>
> Is there another link than the one below?
>
> Thanks,
> Jack
>
>
>
> ------------------------------
>
> Message: 5
> Date: Sat, 1 Mar 2008 16:52:17 +0200
> From: "George Nikolidakis" <geoniko@otenet.gr>
> Subject: [ATM] Exit pulil and brightnees
> To: <atm@atmlist.net>
> Message-ID: <000001c87bab$d866f7f0$8934e7d0$@gr>
> Content-Type: text/plain; charset="us-ascii"
>
> Hello everyone ..
>
> It is known that the diameter of the eye pupil is reduced by the age.
>
> I found some references professing that means to lose in object
> brightness,
>
> looking trough an eyepiece with greater exit pupil than your eyes.
>
> Or, to put it another way, a younger person looking from the same eyepiece
>
> will see the object Brighter.
> So in my view it seems to me that the older person simply lose the edges
> of
> the field
>
> and not in object brightness.
>
> But what view is finally right ?
>
> George Nikolidakis
>
>
>
>
>
>
>
> ------------------------------
>
> Message: 6
> Date: Sat, 1 Mar 2008 07:09:28 -0800 (PST)
> From: Dave Smith <smithersscope@yahoo.com>
> Subject: Re: [ATM] a lightweight 12' "hat box" travel dob, 20 pounds.
> To: "Jack.Swaton@starryhost.com" <jack.swaton@starryhost.com>, ATMLIST
> <atm@atmlist.net>
> Message-ID: <663251.66495.qm@web51806.mail.re2.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> Hi Jack,
> Try backing up one directory in the tree. Then you'll
> be able to see links to all his scopes. And beautiful
> they are.
>
> http://dobson.2005.googlepages.com/
> HTH,
> Dave
> --- "Jack.Swaton@starryhost.com"
> <jack.swaton@starryhost.com> wrote:
>
>> I've never gotten this link to work. I get, "The
>> site you requested could
>> not be found".
>>
>> Is there another link than the one below?
>>
>> Thanks,
>> Jack
>>
>
> http://dobson.2005.googlepages.com/un300devoyageultral?ger
>>
>> Regards,
>>
>> Pierre DESVAUX
>> Bourgogne, France
>
>
>
>
> ____________________________________________________________________________________
> Be a better friend, newshound, and
> know-it-all with Yahoo! Mobile. Try it now.
> http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ
>
>
>
> ------------------------------
>
> Message: 7
> Date: Sat, 1 Mar 2008 16:38:29 +0100
> From: "Jan van Gastel" <jhm.vangastel@wanadoo.nl>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: <atm@atmlist.net>
> Message-ID: <000e01c87bb2$4cee7430$13124751@niks03981037eb>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> For a certain telescope under a certain sky, darkness of the FOV is a
> function of exit pupil. So, if the pupil of your eye doesn't get larger
> then, say 5 mm, no more light will enter your eye then through that 5 mm
> pupil, even if you look through an eyepiece giving you a larger then 5 mm
> exit pupil. So, with a larger then 5 mm exit pupil, the FOV will only be
> as
> bright as if you were looking though a 5 mm exit pupil.
>
> A person with a larger then 5 mm eye pupil, will see a brighter FOV when
> looking through an eyepiece giving him an exit pupil larger then 5 mm.
> When
> that same person looks through an eyepiece giving him an exit pupil of 5
> mm
> or smaller, he will have an equally dark FOV as the person with the 5 mm
> exit pupil through the same eyepiece/telescope combination.
>
> Jan
> http://home.wanadoo.nl/jhm.vangastel/Astronomy/
>
> ----- Original Message -----
> From: "George Nikolidakis" <geoniko@otenet.gr>
> To: <atm@atmlist.net>
> Sent: Saturday, March 01, 2008 15:52
> Subject: [ATM] Exit pulil and brightnees
>
>
>> Hello everyone ..
>>
>> It is known that the diameter of the eye pupil is reduced by the age.
>>
>> I found some references professing that means to lose in object
>> brightness,
>>
>> looking trough an eyepiece with greater exit pupil than your eyes.
>>
>> Or, to put it another way, a younger person looking from the same
>> eyepiece
>>
>> will see the object Brighter.
>> So in my view it seems to me that the older person simply lose the edges
>> of
>> the field
>>
>> and not in object brightness.
>>
>> But what view is finally right ?
>>
>> George Nikolidakis
>>
>>
>>
>>
>>
>> _______________________________________________
>> ATM mailing list http://www.atmlist.net/
>>
>
>
>
>
> ------------------------------
>
> Message: 8
> Date: Sat, 01 Mar 2008 18:00:04 +0100
> From: Alexis Cousein <al@sgi.com>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: George Nikolidakis <geoniko@otenet.gr>, atm@atmlist.net
> Message-ID: <47C98B94.3050909@sgi.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> George Nikolidakis wrote:
>>
>> But what view is finally right ?
>>
>
> Theirs. *All* the parallel ray bundles for all of the objects
> in the field pass through the exit pupil, and all are vignetted
> by the eye's pupil. Losing the edge is when you have an
> aperture stop in a focal system (i.e. somewhere before the eyepiece,
> not one at the exit pupil of an afocal one.
>
>
> --
> Alexis Cousein al@sgi.com
> Senior Systems Engineer/Solutions Architect SGI/Silicon Graphics
> --
> <If I have seen further, it is by standing on reference manuals>
>
>
>
> ------------------------------
>
> Message: 9
> Date: Sat, 1 Mar 2008 09:16:13 -0800 (PST)
> From: Ken Hunter <atm_ken_hunter@yahoo.com>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: George Nikolidakis <geoniko@otenet.gr>, atm@atmlist.net
> Message-ID: <225757.37428.qm@web52707.mail.re2.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> I believe the field is full but reduced in brightness... Think about a
> pinhole camera, it
> still captures the whole field but there is not many photons from each
> point in the field.
>
> Ken Hunter
>
>
>
> George Nikolidakis <geoniko@otenet.gr> wrote:
> Hello everyone ..
>
>
> So in my view it seems to me that the older person simply lose the edges
> of
> the field and not in object brightness.
>
>
>
> ---------------------------------
> Looking for last minute shopping deals? Find them fast with Yahoo!
> Search.
>
> ------------------------------
>
> Message: 10
> Date: Sat, 1 Mar 2008 18:38:45 +0100
> From: Marinus van der Lugt <lugt@xs4all.nl>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: "George Nikolidakis" <geoniko@otenet.gr>
> Cc: atm@atmlist.net
> Message-ID: <CED9417E-C252-4046-B346-51519C43FAAD@xs4all.nl>
> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
>
> For point objects against a black background, the brightness is
> reduced. This equals a reduction in contrast and hence in detectability.
>
> However for extended objects all the brightness is reduced by the same
> factor. There is no chance in contrast and hence no difference in
> detectability.
>
> Rien.
>
>
> On Mar 1, 2008, at 3:52, George Nikolidakis wrote:
>
>> Hello everyone ..
>>
>> It is known that the diameter of the eye pupil is reduced by the age.
>>
>> I found some references professing that means to lose in object
>> brightness,
>>
>> looking trough an eyepiece with greater exit pupil than your eyes.
>>
>> Or, to put it another way, a younger person looking from the same
>> eyepiece
>>
>> will see the object Brighter.
>> So in my view it seems to me that the older person simply lose the
>> edges of
>> the field
>>
>> and not in object brightness.
>>
>> But what view is finally right ?
>>
>> George Nikolidakis
>>
>>
>>
>>
>>
>> _______________________________________________
>> ATM mailing list http://www.atmlist.net/
>>
>
>
>
> ------------------------------
>
> Message: 11
> Date: Sat, 01 Mar 2008 14:07:51 -0500
> From: "Lawrence D. Lopez" <lopez@mv.mv.com>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: George Nikolidakis <geoniko@otenet.gr>
> Cc: atm@atmlist.net
> Message-ID: <47C9A987.8010409@mv.mv.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> I've looked at the other posts and wodner if I have come to a correct
> understanding.
>
> If your eye vignette's the exit pupil (say from 7mm to 5mm)
> then it is exactly the same as if you vignetted the objective (say from
> 7" to 5").
>
> The only problem I have in this is a star image size which will get
> bigger the smaller
> the objective. I'm not sure how that changes things. Certainly for low
> power it wouldn't
> since it would be smaller that the resolving power of the eye.
>
> And it wouldn't matter for high power since the exist pupil will be
> small also.
>
> George Nikolidakis wrote:
>> Hello everyone ..
>>
>> It is known that the diameter of the eye pupil is reduced by the age.
>>
>> I found some references professing that means to lose in object
>> brightness,
>>
>> looking trough an eyepiece with greater exit pupil than your eyes.
>>
>> Or, to put it another way, a younger person looking from the same
>> eyepiece
>>
>> will see the object Brighter.
>> So in my view it seems to me that the older person simply lose the edges
>> of
>> the field
>>
>> and not in object brightness.
>>
>> But what view is finally right ?
>>
>> George Nikolidakis
>>
>>
>>
>>
>>
>> _______________________________________________
>> ATM mailing list http://www.atmlist.net/
>>
>>
>
>
>
> ------------------------------
>
> Message: 12
> Date: Sat, 1 Mar 2008 21:01:12 +0100
> From: "Jan van Gastel" <jhm.vangastel@wanadoo.nl>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: <atm@atmlist.net>
> Message-ID: <000a01c87bd7$00433a10$13124751@niks03981037eb>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> With 5" aperture, you catch less light as compared to a 7". Wit a 5 inch
> exit pupil and a 7" objective you will catch all the light of your 7"
> objective.
>
> Jan
> http://home.wanadoo.nl/jhm.vangastel/Astronomy/
>
>
> ----- Original Message -----
> From: "Lawrence D. Lopez" <lopez@mv.mv.com>
> To: "George Nikolidakis" <geoniko@otenet.gr>
> Cc: <atm@atmlist.net>
> Sent: Saturday, March 01, 2008 20:07
> Subject: Re: [ATM] Exit pulil and brightnees
>
>
>> I've looked at the other posts and wodner if I have come to a correct
>> understanding.
>>
>> If your eye vignette's the exit pupil (say from 7mm to 5mm)
>> then it is exactly the same as if you vignetted the objective (say from
>> 7" to 5").
>>
>> The only problem I have in this is a star image size which will get
>> bigger the smaller
>> the objective. I'm not sure how that changes things. Certainly for low
>> power it wouldn't
>> since it would be smaller that the resolving power of the eye.
>>
>> And it wouldn't matter for high power since the exist pupil will be
>> small also.
>>
>> George Nikolidakis wrote:
>>> Hello everyone ..
>>>
>>> It is known that the diameter of the eye pupil is reduced by the age.
>>>
>>> I found some references professing that means to lose in object
>>> brightness,
>>>
>>> looking trough an eyepiece with greater exit pupil than your eyes.
>>>
>>> Or, to put it another way, a younger person looking from the same
>>> eyepiece
>>>
>>> will see the object Brighter.
>>> So in my view it seems to me that the older person simply lose the edges
>>> of
>>> the field
>>>
>>> and not in object brightness.
>>>
>>> But what view is finally right ?
>>>
>>> George Nikolidakis
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> ATM mailing list http://www.atmlist.net/
>>>
>>>
>>
>> _______________________________________________
>> ATM mailing list http://www.atmlist.net/
>>
>
>
>
>
> ------------------------------
>
> Message: 13
> Date: Sat, 1 Mar 2008 23:42:51 +0200
> From: "George Nikolidakis" <geoniko@otenet.gr>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: <atm@atmlist.net>
> Message-ID: <000301c87be5$331328c0$99397a40$@gr>
> Content-Type: text/plain; charset="us-ascii"
>
>>Theirs. *All* the parallel ray bundles for all of the objects
>>in the field pass through the exit pupil, and all are vignetted
>>by the eye's pupil.
> I thought that the parallel rays simply form the central part of the field
> view thus there is no vignetting for them.
>
>>Losing the edge is when you have an
>>aperture stop in a focal system (i.e. somewhere before the eyepiece,
>>not one at the exit pupil of an afocal one.
>
> I can't understand the difference can you explain it more please !
>
> Also I like to have a more specific question :
> If we suppose there is an object, say a galaxy near to the center of the
> field is
> this object will appear in more details to the person with the larger
> pupil
> ?
>
>
> George Nikolidakis
> http://geonik.homeip.net
>
>
> -----Original Message-----
> From: Alexis Cousein [mailto:al@sgi.com]
> Sent: Saturday, March 01, 2008 7:00 PM
> To: George Nikolidakis
> Subject: Re: [ATM] Exit pulil and brightnees
>
> George Nikolidakis wrote:
>>
>> But what view is finally right ?
>>
>
> Theirs. *All* the parallel ray bundles for all of the objects
> in the field pass through the exit pupil, and all are vignetted
> by the eye's pupil. Losing the edge is when you have an
> aperture stop in a focal system (i.e. somewhere before the eyepiece,
> not one at the exit pupil of an afocal one.
>
>
> --
> Alexis Cousein al@sgi.com
> Senior Systems Engineer/Solutions Architect SGI/Silicon Graphics
> --
> <If I have seen further, it is by standing on reference manuals>
>
>
>
>
>
>
> ------------------------------
>
> Message: 14
> Date: Sat, 01 Mar 2008 17:29:13 -0500
> From: James Gort <jgort@oxford-observatory.org>
> Subject: Re: [ATM] Exit puoil and brightness
> To: atm@atmlist.net
> Message-ID: <47C9D8B9.8010608@oxford-observatory.org>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>
>
>
> Simple experiment. Choose an eyepiece that will give you a 5 mm exit
> pupil. Take a cardboard and drill a 1 mm hole in it. Now, view some
> stars and extended objects, both with and without the cardboard directly
> in front of your eye. Compare what you see.
>
> Cheers,
>
> James
>
>
> ------------------------------
>
> Message: 15
> Date: Sat, 1 Mar 2008 23:33:16 +0100
> From: "Jan van Gastel" <jhm.vangastel@wanadoo.nl>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: <atm@atmlist.net>
> Message-ID: <001901c87bec$3eaa36e0$13124751@niks03981037eb>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> Not necessarily. Only if a large exit pupil (very low magnification) and
> resulting bright FOV is needed to see the detail. A large exit pupil is
> only
> usefull at very low (for the telescope in question) magnifcations. A large
> eye pupil for observation with a telescope is not very important, because
> for most objects and detail in objects, middle or large magnifications are
> necessary. For a rich(est) field telescope, if one wants to have a very
> large FOV it may be important. In that case, a large eye pupil will give
> you
> acces to a low magnification and a resulting wide field, without
> lightloss
> from a too small exit pupil.
>
> Jan
> http://home.wanadoo.nl/jhm.vangastel/Astronomy/
>
>
> ----- Original Message -----
> From: "George Nikolidakis" <geoniko@otenet.gr>
> To: <atm@atmlist.net>
> Sent: Saturday, March 01, 2008 22:42
> Subject: Re: [ATM] Exit pulil and brightnees
>
>> Also I like to have a more specific question :
>> If we suppose there is an object, say a galaxy near to the center of the
>> field is
>> this object will appear in more details to the person with the larger
>> pupil
>
>
>
>
> ------------------------------
>
> Message: 16
> Date: Sat, 1 Mar 2008 02:43:21 -0800
> From: "Bob May" <rmay@nethere.com>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: <atm@atmlist.net>
> Message-ID: <002001c87b89$12743200$ddadfea9@amd>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Look at it this way.
> The telescope magnifies the image you are seeing. What it is
> doing is actually reducing the diameter of the ray bundle by the
> magnification value. Thus the size of the scope of 200mm gets
> reduced to 2mm at 100 power. The 5mm iris will accept all of the
> light from the telescpe, thus not making the brightness of the
> image any less. However, when the magnification is less, lets
> say we're at 10 power, the exit pupil will be 10mm. At this
> size, all will vignette the light with the smaller pupil seeing
> less of the light than the person with the larger pupil.
> The edge of the FOV isn't interfered with any differently as the
> EP puts all of the light in the same area at the correct position
> for viewing (when you barely see the field stop of the EP) so all
> persons will see the same falloff of light the same amount.
> Any more questions on this???
> Bob May
>
> rmay at nethere.com
> http: slash /nav.to slash bobmay
> http: slash /bobmay dot astronomy.net
>
>
>
>
> ------------------------------
>
> Message: 17
> Date: Sat, 1 Mar 2008 17:04:43 -0800
> From: "Mel Bartels" <mbartels@bbastrodesigns.com>
> Subject: Re: [ATM] Exit pulil and brightnees
> To: <atm@atmlist.net>
> Message-ID: <003f01c87c01$67f59b60$63012001@bbad>
> Content-Type: text/plain; charset="us-ascii"
>
>> For point objects against a black background, the brightness is
>> reduced. This equals a reduction in contrast and hence in detectability.
>>
>> However for extended objects all the brightness is reduced by the same
>> factor. There is no chance in contrast and hence no difference in
>> detectability.
>
>
> This last statement is suspect, because while the contrast (difference in
> brightness between object and background) stays constant, the *perceived*
> contrast (the eye's ability to perceive or detect the object) varies with
> changes in the sky background brightness.
>
> Mel Bartels
>
>
>
>
> ------------------------------
>
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> End of ATM Digest, Vol 51, Issue 2
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