How do you work out the Apparent field of view of an Eyepiece.

[bomberbaz]

Cant remember how to work it out. I think it is something to do with the field of view and its magnification but cant figure beyond that

[rory]

e/p apparent field divided by the magnification

example. my 25mm e/p has apparent f.o.v of 60 degrees, and with my scope it magnifies at x48 so 60/48= 1.25*

[ismangil]

The AFOV is usually stated from the eyepiece manufacturer.

http://www.televue.com/engine/TV3_page.asp?id=79

The True FOV can be calculated, or deduced accurately from star drift test.

[rory]

i see youre building up some e/ps there bomber, how do you find the hyperions compare to the x-cels ?

[bomberbaz]

I will let you know as soon as I try them, literally only just got em and weather has been... well you know how its been.

However signs are good for tomorrow night, so can't wait to try them out then...

[glowjet]

Another interesting thing you also might like to find out is how many minutes and seconds of arc you can actually see with each of your eyepieces. If you have a stop watch or a second hand on your wrist watch, place any star which is near the celestial equator, you could use Delta Orionis ( Mintaka ) in Orion's belt at this time of the year, with your drive switched off, place this on the Eastern edge of your eyepiece FOV and time how long it takes in seconds to cross through the centre and disappear off the Western edge. Divide the time by four and this should give you the actual field diameter of your eyepiece in arc minutes, if you then multiply by 60, this will convert to arc seconds which you may find useful

John.

[E621Keith]

Generally read what the manufacturer said.

John's drift method will allow you to work out true field of view, but many wide field eyepieces have rectilinear distortion so AFOV calculated from tFOV may not correspond exactly to the AFOV you see.

[bomberbaz]

This is all very interesting and opens up more things to conssider. Question, I haven't got the" turn left at orion" book. Does this also tell you the size of objects in degrees?

[bomberbaz]

This is all very interesting and opens up more things to conssider. Question, I haven't got the" turn left at orion" book. Does this also tell you the size of objects in degrees?

[rory]

This is all very interesting and opens up more things to conssider. Question, I haven't got the" turn left at orion" book. Does this also tell you the size of objects in degrees?

not really, it mentions size on occasions but its kept quite simple in most respects,i suppose thats what is appealing about tlao.

[John]

Stellarium gives you the apparent diameter of the moon and planets at a given date / time.

[Mr Q]

This is all very interesting and opens up more things to conssider. Question, I haven't got the" turn left at orion" book. Does this also tell you the size of objects in degrees?

This large list of DSOs that(most) are detectable with a 250mm reflector in dark skies does list each object's size but for photo images, which are a bit larger than visually, especially with galaxies and nebulae. For any one on the list, I use a 3/4 figure of what's listed for dark skies. Also, the surface brightness of most objects are listed, another aid to determine if an object can be detected for the size scope you are using. The list is very long but since it's formatted by constellations and brightest objects first, I find it very useful when observing visually. Since some sites do disapear in the future, I have printed out the whole list for safe keeping...just in case

7000 DSOs

[J_M_Franklin]

7000 DSOs

Interesting document there Mr Q, thanks for sharing, all you need to do now is turn it into a searchable excel file for everyone

[Spec-Chum]

Blimey, that would make a mad 1 night marathon

[bomberbaz]

I need to play about with stelarium more John. Its a fantastic pice of kit.

[John]

I need to play about with stelarium more John. Its a fantastic pice of kit.

It's the best freeware that I've used, thats for sure

[Alastair Rae]

This is all very interesting and opens up more things to conssider. Question, I haven't got the" turn left at orion" book. Does this also tell you the size of objects in degrees?

Wikipedia's quite good at giving apparent dimensions for individual DSOs.

[Spec-Chum]

It's the best freeware that I've used, thats for sure

**offtopic** I'd give that accolade to linux, hands down **ontopic**