Estimating magnification of a captured image?

[5ash]

Years ago when I had one of the original G star cameras , we estimated the magnification as about that of a 6 mm eyepiece. Is there a formula to calculate the eyepiece equivalent magnification for a camera.
Regards philip

[Startrek]

Here’s an interesting post and thread from CN

https://www.cloudynights.com/topic/766842-camera-equivalence-to-magnification/

I’m of the opinion it’s almost impossible to make an accurate assessment and comparison based on one formula or calculation as there are no standard or familiarity frames of reference between the two.

The human eye looking through an eye piece and digital camera sensor are incomparable in regards to physics and mathematics.

Probably an ongoing topic , hotly debated I suspect

[JA]

Hi Phil,

The equivalence to me would be achieved when the view through the eyepiece has the same field of view as that from an uncropped image of the same scene. On that basis you could simply plug the various telescope/optical parameters you are simulating in to any of the several Field of View programs available and look to see for what eyepiece focal length the FOV of both systems you are comparing is equal. Then hey presto you have your answer.

Here is an example of just such an FoV Calculator (https://astronomy.tools/calculators/field_of_view/). Select an object first, to see the resultant data.

Another one to help calculate Imaging Sensor FoV (https://www.scantips.com/lights/fieldofview.html) with various focal length lenses/scopes. Not that intuitive at first

As for a direct formula approach, one could be worked out on the same basis as the above, with some underlying assumptions, but given the variables involved would be easier via the programs suggested.

As an aside and for what it's worth, I always like to remember that a focal length of 1031mm on a full frame optical system will give an ~2 degree horizontal FOV on a typical 3:2 format DSLR sensor. From there its possible to work out MANY sensor / scope combinations.

Best
JA

[bojan]

Hi Phil,

As JA said :-)

By definition, magnification is a ratio, number without dimension (unit etc).
So term "magnification" between camera and eyepiece is meaningless..

On the other hand, eyepiece magnification is ratio between two angles : angular size of the object (for example Moon) as seen trough telescope (with eyepiece) vs angular size with unaided eye.

Camera has FOV and "scale" (arcsec/pixel or arcsec/mm for example).

So, the most intuitive/practical number for "magnification" as per your post would be ratio between two FOVs (FOV through telescope and camera FOV).
In case you print the image on paper (or look at it on the screen) , things become much more complicated :-) You have to take into account the physical size of the screen or paper, zoom factor.. You don't want to go into that too far ;-)