How do I calculate the field of view for imaging

[WattleHill]

Hi all, I hope everyone is well :)

How can I calculate the field of view using a 18" f4.5 dob using an imaging camera.



I presume the above results would vary according to the camera type so.... I would also appreciate any recommendations on a good make/model of colour imaging camera for the task.

I successfully started doing some basic imaging several years ago with a 16" f4 and would like to get back into it in the new year.

Thanks in advance.
Stephen

[iborg]

Hi Stephan



Using some of the bits in the link may give you the information you are looking for.


https://astronomy.tools/calculators/field_of_view/


Philip

[WattleHill]

Thank you Phillip, that's a great resource. Now I need to establish a good camera

[iborg]

Yeah


Its complicated, I have just gone through the same sort of search myself.

I want something that suits the scope I have, and later, be able to pick a scope and mount, that will still be useful for the camera I intend to purchase.



And then some so-n-so's put for sale a used one, when I want to save my penny's for now.


Philip

[astro744]

Your telescope focal length in mm = 18 x 25.4 x 4.5 = 2057.4mm

Field of view (deg) = linear dimension of sensor x 57.3/focal length of telescope.

E.g. if you had full frame DSLR (36m x 24m sensor) your field of view would be 36 x57.3/2057.4 = 1 deg on long axis and 24 x57.3/2057.4 = 0.67 deg on short axis. You can work out diagonal using Pythagoras. Sqrt(1x1+0.67x0.67)=1.2 deg.

If you don’t have the sensor dimensions but do have the number of pixels and pixel size then first multiply these out to get the linear dimension.

E.g. 6 million x 4 million pixels of 2.2 microns each gives 6000000x2.2/1000000= 13.2mm x 4000000x2.2/1000000= 8.8mm

Field of view = 13.2x57.3/2057.4=0.37 deg by 8.8x57.3/2057.4=0.25 deg. Not enough for a full lunar disk so either use a bigger sensor or shorter focal length telescope (for example).

The 57.3=number of degrees in a Radian. A Radian = The length of the radius of a circle around it’s circumference. Don’t really need to know any of that only the formula.

[Startrek]

Philip,
An alternative to punching in numbers in an auto calculator and spitting out the answer
Here’s the formula to calculate Imaging FOV

Camera sensor size (mm) x 3460 / telescope focal length = FOV ( arc minutes )

Where camera sensor size ( height and width )

Cheers
Martin

[astro744]

I get 3438 or more precisely 3437.747 if using more decimal places for a radian

57.3 x 60 = 3438 minutes of arc.

I always use degrees and multiply x 60 or 3600 if I want minutes or seconds of arc. 57.3 is good enough for me, many use 57.296.

[glend]

Stellarium has a built in tool that will do it for you. You just plug in your equipment "camera, scope" being used and it will give you the field details, plus show you the field on the sky diagram, wherever you aim. If you zoom in or out it will adjust the sky field.
If you have more scopes and cameras, it will calculate and display for those as well. If you want to compare, two cameras, it's just a click away.

[JackWhite]

The best way to learn how to do it is to install and learn Stellarium. I've been with the same problem as you and after spending probably 3-7 days (after job for 1-2 hours) I've got my desired result. Check it out :)

[JA]

Stellarium as already suggested by Glen and Jack is an easy way to go and you get to look at your optic/sensor combination on a sky target of your choice.

Or if you're in the middle of nowhere with no power or caluclator you can just use the fact that a 1000mm focal length optic (actually 1030mm - close enough) with a Full frame Image circle, on a FullFrame (36x24mm) sensor has a 2.00 degree horizontal field of view and scale that linearly up or down for different focal lengths and/or sensor diagonal sizes. For example ....
2000mm optic with ~1 degree field of view horizontally on FF sensor
4000mm optic with ~0.5 degree field of view horizontally on FF sensor
500mm with ~4 degree field of view horizontally on FF sensor, etc...

If you want it more accurately then base it on 1030mm having a 2.00 horizontal FOV, but 1000mm is easier to remember. If you want to known the field of view on something other than a FullFrame sensor you need to scale the result by the ratio of the sensor diagonals (sometimes known as the Field of View Crop factor or simply Crop Factor), for similar aspect ratio diagonals, or revert to other tricks, possibly beyond mental math.



Best
JA

[WattleHill]

Thank you everyone for the help with this.

Now I need to look for a suitable camera.