Stellarium Image sensor frame

[masjstovel]

Hi,

I'm totally New to this hobby and i'm having trouble understanding something in stellarium.
I have ordered (not recieved) a Sky-Watcher Explorer 150PDS, which has a 25mm eyepiece 50degrees FOV as a default.
I also have a Nikon D810.

I wanted to get an idea of what my field of view would be with the 25mm eyepiece (30x on 750mm focal length), 
and also what it would be With my Nikon D810 mounted shooting prime Focus - no eyepieces.

What surprised me was that it wasnt much difference between the frame and size of the object i get with 30x magnification (25mm eyepiece), and what i get with the Nikon D810 mounted. 
I dont get this. What magnification do i get With my DSLR mounted with no eyepiece?

[vlaiv]

There is no magnification associated with DSLR or other sensors.

Magnification is ratio between angular extent in the sky when viewed with naked eye vs apparent angular extent when viewed thru the eyepiece.

Image on the other hand has no magnification because it depends on both screen size and observer distance to that screen. Put the same image on your computer screen and view it from 2ft away and then move 20ft away - image will look smaller when you look at it (regular perspective, whole computer screen will look smaller as well).

What can help when thinking about extent of target visible in the eyepiece vs extent of it on surface of the sensor is actual focal plane size of things. Your sensor has 35.9mm x 24 mm - which makes diagonal of it 43mm. 25mm eyepiece has field stop of about 22mm, or about half of your sensor diagonal.

So if M31 fits on your sensor diagonal in length, you will be able to see about half of it in your 25mm eyepiece. Above Stellarium plugin shows this nicely.

[masjstovel]

Thank you. I THINK i understood what you were explaining. If i had a 43mm Eyepiece, it would have the same "magnification"  as the Nikon, right?

[vlaiv]

37 minutes ago, masjstovel said:

Thank you. I THINK i understood what you were explaining. If i had a 43mm Eyepiece, it would have the same "magnification"  as the Nikon, right?

If you had eyepiece with 43mm field stop (not focal length of eyepiece - that is different thing), then galaxy would fit inside eyepiece FOV in the similar way it fits on the sensor, yes.