How do I calculate magnification with a t-adapter

gavinadams (Gavin) · #1 06-12-2009, 08:39 AM

Hi All,
I have a celestron Nexstar 6SE.
This has a focal length of 1500mm and the standard eyepiece is 25mm.
So 1500mm divided by 25mm gives a magnification of 60x.

So I have my t-ring for my nikon d70 and a 32mm camera projection eyepiece. Which is fine and easy to calculate the magnification for that.
(approx 47x)

I'm considering the celestron t-adapter (#93633-A).
There seems to be no specs as to the focal length of this unit. As it contains no optics, maybe it has no focal length?

And from basic maths 1500mm divided by zero is zero, so that can't be right.

So the question is when I mount my d70 onto the back of 6SE with a t-apater what magnification should I get?

Cheers,
Gavin

dannat (Daniel) · #2 06-12-2009, 09:08 AM

with the T adaptper you will be operating at prime focus..and the old rule for 35mm cameras is 50mm = 1x, so 1500mm divided by 50mm should be about 30x magnification. I am not sure if the aps sized sensors alter this rule

astro744 · #3 06-12-2009, 09:14 AM

The T-adaptor is a short tube that places your camera film plane (CCD chip plane) at the focal plane of the telescope. Your telescope becomes a 1500mm 'lens'.

eg. A 50mm standard camera lens attached to an film SLR camera produces a 1x image. A 1500mm camera lens attached to the same camera would produce an image 1500/50 = 30x bigger (closer).

Not familiar with the D70 but I think the chip would be 2/3 film size so there is a 1.5x factor applied to the lens focal length to bring it up to film size. Therefore the mag factor would be 45x. If you had a digital camera with a full 35mm film size chip the magnifying factor would be 30x. I think I'm right this time.