Which Eye Piece?

[solissydney]

I am l looking for an eye piece for the specific purpose of locating an object when the object is not in the field of view using the go-to before taking images through my DSLR
on my 12 inch f/5. My present 2 inch only covers 1 inch plus of sky.
I need a minimum of 6 degree field of view, say medium power of app. 18 mm, zoom maybe, 20 mm eye relief with rubber cup. Choice of 2 or 3 eye pieces
Advice would be much appreciated.
Ken

[dannat]

At 1500mm f/l I dont think 6 deg fov Is achievable, r wanting if on the main scope or r u talking about using a finder scope?
You would need a 4" focuser & Siebert observatory style ep to get the wide views you're after
Even a 40mm swa 2" ep , 1500/40 = 37x, evn a 72 deg ep is only giving yo 2 degrees of view

[Tom Hancock]

Agreed...just not practical.
You will need an an ep in excess of 40mm focal with a afov above 220 deg!
Such an ep is no where to be found.
Extreme ultra wide field of view is currently at 120 deg afov.
Perhaps your fov can be improved with a focal reducer but then you will be adding more glass and your light transmission will suffer.

[solissydney]

Thanks for your replies, just learned something.
Back then to my Finder Scope

[dannat]

with a counterweight/balnce you could rig up the megrez 72 - would be an excel finder

[solissydney]

That would bugger up the focus of the auto guider
which then needs the laptop to re focus.
Thanks

[solissydney]

Oops, I got the Megrez mixed up with the Orion.
I did consider what you suggested, I also considered an right-angle finder, because my problem is that when the scope is pointing towards the Zenith it is difficult bending down looking through a straight-through finder. I might just get the right-angle finder instead.
ken

[MattT]

Hi Ken,
Go to the Tele Vue web site and in the eyepieces section is calculator that you put in whatever scope you have and it spits out all the AFOV, magnifications etc. Will cut and paste when I can....very helpful site. http://www.televue.com/engine/TV3_page.asp?id=89
Matt

[Tom Hancock]

Hi Ken,

Just divide your scope focal (1500mm) by the eyepiece focal to get the magnification.
Then divide the eyepiece afov by the magnification to give you the true field of view...it really is that simple.

[solissydney]

The Tele Vue table is an real eye (piece) opener Matt. Hope to see you soon again.
Thank you both
Ken