Anonymous
Unregistered
|
|
Post deleted by night watch
|
btschumy
Think Astronomy
Reged: 04/13/04
Posts: 1110
Loc: Austin, TX, USA
|
|
NW,
How can objective diameter be related to TFOV? It is AFOV / mag. Right?
--------------------
Bill Tschumy
Where is M13? Freeware -- Add a new dimension to your observing.
|
milt
sage
Reged: 09/13/04
Posts: 430
Loc: Arizona
|
|
Quote:
It [TFOV] is AFOV / mag. Right?
Hi Bill,
Just for the record (I know you know this) TFOV is 57.3 times the field stop diameter of the eyepiece divided by the focal length of the scope. 57.3 is the number of degrees in a radian, i.e. 360°/2Pi.
Using the eyepieces's AFOV divided by magnification is a shortcut that doesn't always work, like on the 24Pan where Uncle Al cheated a little calling it a 68° AFOV eyepiece - from the field stop it is more like a 64.5° eyepiece (however IMO still the best thing going for widefield binoviewing).
I'm off to RTMC and will let you guys carry on.
--------------------
Clear skies, Milt
|
btschumy
Think Astronomy
Reged: 04/13/04
Posts: 1110
Loc: Austin, TX, USA
|
|
Thanks Milt,
Yeah, I'm aware that AFOV / mag is a shortcut. It's just that sometimes the field stop diameter is a harder parameter to come by. Nevertheless, it is good for you point this out for other readers that may not have heard this.
Hope everyone has fun at RTMC.
--------------------
Bill Tschumy
Where is M13? Freeware -- Add a new dimension to your observing.
|
Anonymous
Unregistered
|
|
Post deleted by night watch
|
btschumy
Think Astronomy
Reged: 04/13/04
Posts: 1110
Loc: Austin, TX, USA
|
|
NW,
I don't think your formula
TFOV = [(EP field stop diameter)/(objective diameter)]*(360/2-pi)
is correct. I believe Milt is right. Your "objective diameter" should be "telescope focal length".
--------------------
Bill Tschumy
Where is M13? Freeware -- Add a new dimension to your observing.
|
Anonymous
Unregistered
|
|
Yep, Milt is correct. I was looking at the wrong notes. I deleted all my ill-posts. My apology.
|
Jeff Morgan
Carpal Tunnel
Reged: 09/28/03
Posts: 1531
Loc: Prescott, AZ
|
|
Quote:
... but in short,
as you use higher magnification in an equivalent aperture (up to a point) contrast detection becomes easier.
The 20x100 binoviewer will appear to have better contrast.
edz
Perhaps this is the same mechanism described by Roger Clark in the book Visual Astronomy of the Deep Sky. Basically, the brain is more likely to recognize and process a signal when more rods and cones are reporting it. More magnification means more cells are covered by the signal. Likewise, he states that the brain also compares signals between eyes.
--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12566
Loc: Cumberland, R I , USA42N71.4W
|
|
yes.
In some post up above, I refered a link to Clark's and Bartel's sites.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
KennyJ
Reged: 04/27/03
Posts: 10143
Loc: Lancashire UK
|
|
It's great we can discuss these things.
Image if for some reason the internet crashed tomorrow and NEVER came back !
I think research from the likes of Bartel , Clark and Zarenski represent strong desires to grasp and share knowledge, which if ever to be fully understood , cries out for understanding of optometry.
The chances of any such person happening to become as active and reliable a contributor to this Cloudy Nights binocular forum as Ed Zarenski has been since it's inception might be more remote than I would prefer.
On a more optimistic note , what were the chances of Liverpool ( who have just finished only 5th in the English Premiership ) winning the greatest prize in world club soccer last night , when they were 3 -0 down at half -time against a talented Italian team ?
I live in hope !
Kenny
--------------------
Two eyes and a preference to use both
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
|
Joad
Wordsmith
Reged: 03/22/05
Posts: 11919
|
|
"That is not the question. I am comparing views at the same magnification between 70 mm binoculars and a binoviewed 100 mm refractor."
I probably shouldn't be wading in here, but you know what Alexander Pope said about fools and their tendencies to rush where angels fear to tread . . . .
At any rate, by carefully reading Kenny's and Professor's EdZ's responses, the simple answer (in regard to the same magnifications) seems to be that a bino-viewed 100mm telescope powered at 14X will produce the same perceived brightness as a 14X70 binocular but with better resolution and better apparent contrast. Do I have that right?
|
craig_oz_land
sage
Reged: 01/21/04
Posts: 343
Loc: Sydney, Australia
|
|
Some may say at 14x you won't see a difference in resolution.
An optical test target will prove or disprove that belief decisively.
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12566
Loc: Cumberland, R I , USA42N71.4W
|
|
It will produce the same brightness in the image delivered to the eyes.
On the point of resolution, theoretically yes, the 100mm scope with binoviewer has finer resolution. However, I test binoculars for on-axis resolution all the time. Even though I know a 100mm binocular creates a spurious disk smaller than a 70mm binocular, I have never recorded a significant measurable difference in low power resolution that I could attribute to the difference in aperture. In the case of low power resolution, I believe it is far more dependant on the quality of the optics. I have achieved finer apparent resolution with a 16x70 Fujinon than with almost any 100mm at 20x or 25x.
On the point of contrast, I'm not sure but I think the binocular will produce a better contrast. The scope with binoviewer has a larger aperture. It would be capable of producing much more contrasty images, but only once you begin to employ higher magnifications.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
Joad
Wordsmith
Reged: 03/22/05
Posts: 11919
|
|
Super, I was hoping to elicit a nice tight summary of the situation and that's what's appeared. The brightness all comes down to the amount of light that is getting to EACH eye and the bino-viewer really takes a whack out, but resolution and contrast seem to be, more or less, six and one half dozen or the other. Thanks, prof. EdZ, for all the elucidation.
The practical solution is to have both a giant binocular setup and telescope--as I discovered last night when I set up both my 40X100 Oberwerks and my Meade LX10 together for the first time under dazzling Mt. Pinos skies (not the top of the mountain, though, from my house at 5600 ft). Wow. Wide field space walks and zoom in looks.
|
Shneor
super member
Reged: 03/01/05
Posts: 121
Loc: Northern California
|
|
I finally had a chance last Saturday night to compare a pair of 24mm Panoptics to my 30mm Rini Widefields in my Denk Standard. The Rinis give a wider true field (maybe 6-8%?) but of course the Panoptics gave better image quality. Of ocurse the Rinis cost 10% what the Pans do...
--------------------
Shneor
22" f/4 Sayre Monocular+Tom O. Eq. Platform
Burgess 25x100 Binos+T&T Mount
Denkmeier Binoviewer
Assorted small telescopes, 90-114mm
13.1" Travel Telescope
|
Anonymous
Unregistered
|
|
I'd like a pair of TV panoptics for my BT, but their too dang expensive for me right now. I heard that the TV 24mm pans are super nice.
|
Previous
Index
Next
Threaded
[Re: 
Edit
Reply
Quote
