Field Of View

majestic · Post by **majestic** » Tue May 25, 2010 2:53 pm

I'm hoping someone can help me out with a question re the Field Of View. If I understand correctly, my scope has a true FOV of 0.62 when using the 25mm eyepiece supplied with it. What does this number mean though? Can I use it to determine how big an object will appear when viewed through my scope?

For example, the Starmap app I use says that NGC 5139's dimensions are 36.30'. How does this correlate to the true FOV of my scope with the default EP?

eMinity · Post by **eMinity** » Tue May 25, 2010 3:18 pm

from what i know, FOV is the "area" of the sky you can see through your telescope. the lower the number, the less you can see. which also means higher magnification. that is for normal eyepieces. unless using "specialised" eyepieces which has higher FOV even at high magnification.

correct me if im wrong

orly_andico · Post by **orly_andico** » Tue May 25, 2010 4:14 pm

Ok with a 0.62 degree TFOV this is 0.62 * 60 = 36 arc-minutes

(1 degree = 60 arc-minutes = 3600 arc-seconds)

So Omega Cen would exactly fit in your field of view. (a minute is ' and a second is ")

The moon is 0.5 degree (30 arc-minutes) and so would mostly fill your field of view.

majestic · Post by **majestic** » Tue May 25, 2010 4:28 pm

Ah, of course - that's fantastic, thank you!!! Yes, it did basically fill the view when I took a look at it last Friday night. This is great - I can see that Jewel Box is 10 arc-minutes and False Comet is 15 arc-minutes, and it's correct - Jewel Box is about 2/3 the size of False Comet in my scope.

orly_andico · Post by **orly_andico** » Tue May 25, 2010 4:41 pm

@stuart,

I didn't go into that to avoid confusion. :-)

One other thing to mention is, AFOV isn't everything. You can get a cheap 80-degree eyepiece, or a crushingly expensive one. And although they both are 80 apparent degrees.... one of them will probably only be usable in the center 40 degrees.....

majestic · Post by **majestic** » Tue May 25, 2010 11:53 pm

Thanks Stuart et al, they were really helpful posts. I'm checking the dimensions of DSOs now and...whoah...Andromeda is huge! So I guess this is the main purpose of the f6.3 reducer for the C8 (but that's another thread).

Post by **weixing** » Wed May 26, 2010 8:45 am

Hi,

majestic wrote:Thanks Stuart et al, they were really helpful posts. I'm checking the dimensions of DSOs now and...whoah...Andromeda is huge! So I guess this is the main purpose of the f6.3 reducer for the C8 (but that's another thread).

IMHO, with 1 degree max TFoV and you'll be able to cover most of the objects. The rest of the very large objects, use a bino to view them might be better. Also, M31 is huge, but you'll basically only see the core in Singapore.

Happy observing and have a nice day.