First Telescopes - Sometimes I feel like an Idiot!

For those of you that have been following my journey towards a
Telescope, and have provided inupt, this is a continuation of the
saga. For the rest of you, a quick recap:

I started off thinking of a 5" Orion Mak, moved to an 8 Inch either
Reflector or SCT. Now that the final decision is close and the budget
is close to set, it will be either an 8 inch Reflector, a 8 inch SCT,
or a 9 1/4 inch SCT. It will have GoTo only if it fits into the
budget.

My big concerns are portability and size (to get into a small
vehicle). My biggest concern about the larger telescopes has been the
increased focal length leading to magnification issues (too much
magnification).

I have also been concerned about Field of View (FOV) but haven't
mentioned it here before. I've noticed that the larger telescopes all
have a narrower FOV with the supplied eyepiece.

Now the "I'm an idiot" part.

I don't know why this took me so long, but I've known that:

RealFOV = ApparentFOV / Magnification = (Apparent FOV * Eyepiece
Focal Length) / Optical Tube Focal Length

This last part of the part was the "duh" that just hit me.

With the larger aperature telescopes, I've always been thinking that
instead of buying eyepieces to INCREASE magnification, I was going to
need to buy one early to DECREASE magnification. Well, it just
occurred to me that the narrower FOV of the larger telescopes was
probably because the supplied eyepiece was the same regardless of
telescope aperature (duh). I checked and found I was right.

So, here is the part that I need you to check. The supplied eyepiece
is a 25mm with a 50 degree ApparentFOV. If I were to get a 40mm
eyepiece with a 60 degree apparent FOV, I should increase the RealFOV
by:

(40 / 25) * (60 / 50) = 1.6 * 1.2 = 1.92

Assuming that the Real FOV for the 25mm 50 degree eyepiece was .55
degree, the 40mm 60 degree eyepiece would yield:

..55 * 1.92 = 1 degree + change

I get about the same number ding the calculation the other way.

So, am I correct in the above? If so, the next question:

All these telescopes come with a 1.25 eyepiece. The longest focal
length eyepiece I've seen for this size is a 42mm and the widest angle
is about 70 degrees. Now that would give a nice, wide field of fiew.
Are there longer eyepieces made in this size? If so, by whom?

As for the above discussion, I realize now that the same logic would
apply by using a focal length reducer. I'm trying to keep as little
glass between me and the subject as possible so I'm trying to avoid
that.

Thank you all for your continued help.

"Edward Smith" wrote in message
...
For those of you that have been following my journey towards a
Telescope, and have provided inupt, this is a continuation of the
saga. For the rest of you, a quick recap:

I started off thinking of a 5" Orion Mak, moved to an 8 Inch either
Reflector or SCT. Now that the final decision is close and the budget
is close to set, it will be either an 8 inch Reflector, a 8 inch SCT,
or a 9 1/4 inch SCT. It will have GoTo only if it fits into the
budget.

My big concerns are portability and size (to get into a small
vehicle). My biggest concern about the larger telescopes has been the
increased focal length leading to magnification issues (too much
magnification).

I have also been concerned about Field of View (FOV) but haven't
mentioned it here before. I've noticed that the larger telescopes all
have a narrower FOV with the supplied eyepiece.

Now the "I'm an idiot" part.

I don't know why this took me so long, but I've known that:

RealFOV = ApparentFOV / Magnification = (Apparent FOV * Eyepiece
Focal Length) / Optical Tube Focal Length

This last part of the part was the "duh" that just hit me.

With the larger aperature telescopes, I've always been thinking that
instead of buying eyepieces to INCREASE magnification, I was going to
need to buy one early to DECREASE magnification. Well, it just
occurred to me that the narrower FOV of the larger telescopes was
probably because the supplied eyepiece was the same regardless of
telescope aperature (duh). I checked and found I was right.

So, here is the part that I need you to check. The supplied eyepiece
is a 25mm with a 50 degree ApparentFOV. If I were to get a 40mm
eyepiece with a 60 degree apparent FOV, I should increase the RealFOV
by:

(40 / 25) * (60 / 50) = 1.6 * 1.2 = 1.92

Assuming that the Real FOV for the 25mm 50 degree eyepiece was .55
degree, the 40mm 60 degree eyepiece would yield:

.55 * 1.92 = 1 degree + change

I get about the same number ding the calculation the other way.

So, am I correct in the above? If so, the next question:

All these telescopes come with a 1.25 eyepiece. The longest focal
length eyepiece I've seen for this size is a 42mm and the widest angle
is about 70 degrees. Now that would give a nice, wide field of fiew.
Are there longer eyepieces made in this size? If so, by whom?

As for the above discussion, I realize now that the same logic would
apply by using a focal length reducer. I'm trying to keep as little
glass between me and the subject as possible so I'm trying to avoid
that.

Thank you all for your continued help.



LOL...find a psychiatrist who has a telescope and talk it out