Is this FOV calculator okay for telescope lenses?

http://www.bdimitrov.de/kmp/technology/fov.html

Mentions rectilinear lens.

Or is there a better FOV calculator for telescope type lenses on the
net? (I'm thinking telescope lenses maybe are not rectilinear).

Richard wrote:
http://www.bdimitrov.de/kmp/technology/fov.html

Mentions rectilinear lens.

Or is there a better FOV calculator for telescope type lenses on the
net? (I'm thinking telescope lenses maybe are not rectilinear).

I'm talking about prime focusing of course.

I don't understand this calculator when I think about it. Because I must
input at least two values, something like focal length and the diagonal
measurement of a CCD active surface. In this calculator, how do I input
the diagonal value. I don't think this is the type of calculator I am
after.

I've seen other calculators, but they involve eyepeices.

http://www.twcac.org/Tutorials/magnify4.htm

I'm just interested in prime focusing. And must be able to input a
custom diagonal value at the focal plane.

Richard wrote:
http://www.bdimitrov.de/kmp/technology/fov.html

Mentions rectilinear lens.

Or is there a better FOV calculator for telescope type lenses on the
net? (I'm thinking telescope lenses maybe are not rectilinear).

I'm talking about prime focusing of course.

I don't understand this calculator when I think about it. Because I must
input at least two values, something like focal length and the diagonal
measurement of a CCD active surface. In this calculator, how do I input
the diagonal value. I don't think this is the type of calculator I am
after.

I've seen other calculators, but they involve eyepeices.

http://www.twcac.org/Tutorials/magnify4.htm

I'm just interested in prime focusing. And must be able to input a
custom diagonal value at the focal plane.

"Richard" wrote:

Richard wrote:
http://www.bdimitrov.de/kmp/technology/fov.html

Mentions rectilinear lens.

Or is there a better FOV calculator for telescope type lenses on the
net? (I'm thinking telescope lenses maybe are not rectilinear).

I'm talking about prime focusing of course.

I don't understand this calculator when I think about it. Because I must
input at least two values, something like focal length and the diagonal
measurement of a CCD active surface. In this calculator, how do I input
the diagonal value. I don't think this is the type of calculator I am
after.

I've seen other calculators, but they involve eyepeices.

http://www.twcac.org/Tutorials/magnify4.htm

I'm just interested in prime focusing. And must be able to input a
custom diagonal value at the focal plane.

Why not just try? Point it at the Pleiades or the Moon, work out what
is at the edge of the field you can see and then find work out the
angular separation from a star chart or Mood Atlas. My CCD camera
(Mintron) at prime focus of a 1000mm f8 refractor gives a very very
small field of view and I'm guessing yours will too.

Whether you can put in a diagonal depends on the amount of travel of
your focusser. Some scopes need extension pieces because they haven't
enough out focus, others can't use a diagonal because there isn't
enough in focus - you just have to experiment, see what works for you.

Cheers

Martin

--------------
Martin Frey
N 51 02 E 0 47
--------------

"Richard" wrote:

Richard wrote:
http://www.bdimitrov.de/kmp/technology/fov.html

Mentions rectilinear lens.

Or is there a better FOV calculator for telescope type lenses on the
net? (I'm thinking telescope lenses maybe are not rectilinear).

I'm talking about prime focusing of course.

I don't understand this calculator when I think about it. Because I must
input at least two values, something like focal length and the diagonal
measurement of a CCD active surface. In this calculator, how do I input
the diagonal value. I don't think this is the type of calculator I am
after.

I've seen other calculators, but they involve eyepeices.

http://www.twcac.org/Tutorials/magnify4.htm

I'm just interested in prime focusing. And must be able to input a
custom diagonal value at the focal plane.

Why not just try? Point it at the Pleiades or the Moon, work out what
is at the edge of the field you can see and then find work out the
angular separation from a star chart or Mood Atlas. My CCD camera
(Mintron) at prime focus of a 1000mm f8 refractor gives a very very
small field of view and I'm guessing yours will too.

Whether you can put in a diagonal depends on the amount of travel of
your focusser. Some scopes need extension pieces because they haven't
enough out focus, others can't use a diagonal because there isn't
enough in focus - you just have to experiment, see what works for you.

Cheers

Martin

--------------
Martin Frey
N 51 02 E 0 47
--------------

Richard wrote:

Well, I think this calculator works out the FOV with a default value
for x. It's probably based on 35mm film.

Anyhow the formula is: FOV (degrees) = 2 * arctan (x / (2 f)).

Applying this for a lens of 1200mmm focal length with x = 10mm, I get
a FOV of appx. 0.477462 degrees.

FOV = 2 * arctan 10mm / (2 * 1200mm)

FOV = 2 * arctan 10mm/ 2400mm

FOV = 2 * arctan 0.416667

FOV = 2 * 0.238731

FOV = 0.477462 degrees.

I assumed to put in dimentions in mm. Anyone know if my calculation
is correct?

I'm cooking on gas!

This figure looks good because there is another formula that gives the
same figu

FOV (arcseconds) = 3438 * x / f

FOV = 3438 * 10mm / 1200mm

FOV = 3438 * 0.0083333

FOV = 28.65 arcseconds

FOV (degrees) = 28.65 / 60

FOV = 0.4775 degrees.

Okay, next, need to figure out focal distance.

Richard wrote:

Well, I think this calculator works out the FOV with a default value
for x. It's probably based on 35mm film.

Anyhow the formula is: FOV (degrees) = 2 * arctan (x / (2 f)).

Applying this for a lens of 1200mmm focal length with x = 10mm, I get
a FOV of appx. 0.477462 degrees.

FOV = 2 * arctan 10mm / (2 * 1200mm)

FOV = 2 * arctan 10mm/ 2400mm

FOV = 2 * arctan 0.416667

FOV = 2 * 0.238731

FOV = 0.477462 degrees.

I assumed to put in dimentions in mm. Anyone know if my calculation
is correct?

I'm cooking on gas!

This figure looks good because there is another formula that gives the
same figu

FOV (arcseconds) = 3438 * x / f

FOV = 3438 * 10mm / 1200mm

FOV = 3438 * 0.0083333

FOV = 28.65 arcseconds

FOV (degrees) = 28.65 / 60

FOV = 0.4775 degrees.

Okay, next, need to figure out focal distance.

Richard wrote:


Okay, next, need to figure out focal distance.

Okay, let me see:

I think this is the formula:

1/di = 1/f - 1/do

Where di is the distance from the lens to the focal plane, do is the
distance from the object to the lens, and f is the focal distance of the
lens.

So:

1/di = 1/1200mm - 1/infinity

1/di = 1/1200mm

di = 1200mm.

Okay, let me think. We are saying that for a telescope of 1200mm focal
length the telescope body has to be appx 2400mm in length, in order to
place a focus plane in the rightspot?

If the object were 10 metres away, di would be:

1/di = 1/1.2m - 1/10

1/di = 0.833333m - 0.1m

1/di = 0.733333m

di = 1.36m or 1360mm.

So total distance from lens to focal plane is: 1200mm + 1360mm = 2560mm.

So focus tube would have to travel 160mm to cater from infinity to 10m.

Richard wrote:


Okay, next, need to figure out focal distance.

Okay, let me see:

I think this is the formula:

1/di = 1/f - 1/do

Where di is the distance from the lens to the focal plane, do is the
distance from the object to the lens, and f is the focal distance of the
lens.

So:

1/di = 1/1200mm - 1/infinity

1/di = 1/1200mm

di = 1200mm.

Okay, let me think. We are saying that for a telescope of 1200mm focal
length the telescope body has to be appx 2400mm in length, in order to
place a focus plane in the rightspot?

If the object were 10 metres away, di would be:

1/di = 1/1.2m - 1/10

1/di = 0.833333m - 0.1m

1/di = 0.733333m

di = 1.36m or 1360mm.

So total distance from lens to focal plane is: 1200mm + 1360mm = 2560mm.

So focus tube would have to travel 160mm to cater from infinity to 10m.

Among 14 related free programs, you can try «T-Calc», «TelOpticulator»
and «Telescope Optical Parameters Calculator». Perhaps one of them
will suite your needs.

Take a look at:

http://astrotips.com

Downloads Windows Telescopes, ATM & optics

Regards,
HDV

"Richard" wrote in message ...
http://www.bdimitrov.de/kmp/technology/fov.html

Mentions rectilinear lens.

Or is there a better FOV calculator for telescope type lenses on the
net? (I'm thinking telescope lenses maybe are not rectilinear).