Cartes du Ciel Eyepiece circle question

[ballaratdragons (Ken)]

Does anyone know the FOV (in arc minutes) of the GS 8x50 right-angle finderscope?

I need it to place the correct circle in Cartes du Ciel.

I can't follow the instructions in the Help file coz I don't know what the 'apparent FOV' of anything is.

Thank you

Pic 1 shows where I have to put the value.

Pic 2 is the instructions that I can't follow coz I don't know the AFOV of EP's and finders.

[bojan]

This can be calculated by multiplying the actual FOV with magnification.
8X50 is usually 10 degrees, so apparent FOV is 40 degrees, 2400.
B

[ballaratdragons (Ken)]

Thanks B,

but 2400 can't be right.

I set 2400 into CDC and the circle encompassed LMC, SMC and Acrux! My 8x50 finder doesn't have a FOV that huge.

[sheeny (Al)]

My 7x50 Pentax binos have a field of view of 7.1 deg, so I would expect the 8x50 finder to be similar or a bit smaller... perhaps.

Al.

[bojan]

Actually you are right :-)
Enter just 7.1*60 = 426 arcmins
Sorry.. I was confused this with Apparent Field of View :-)
When I checked in CdC, it is just FOV (that is not apparent, but real field of view).
Bojan

[ballaratdragons (Ken)]

Thanks guys, I'll try 426

[Starkler (Geoff)]

Easiest way Ken is to measure it with stars that you can just fit in the fov .

[middy]

Hi Ken,

If it's any help I have a 9 x 50 finder and I use a value of 280.

[ballaratdragons (Ken)]

ahhh, yep, 426 looks about right

Just about matches my Finderscope view of Octans & SCP.

Thanks Al, Bojan, Geoff & Andrew

[ballaratdragons (Ken)]

Actually, Geoff came up with an easy solution. Just check what stars are in my FOV, then I will make the circle match.

Cloud has just rolled in so I will give it a go as soon as they move away again.

Thanks Geoff

[ballaratdragons (Ken)]

While I have been waiting for the clouds to clear I browsed the net for 8x50 FOV statistics.

They are all different!!! By googling I was given figures of 345, 336, 252, 420 etc.

EVERY site I went to had a different FOV figure for the same right-angled GS 8x50 finder!

Definately makes Geoffs idea the best way. Once I get the stars in the FOV in my finder I will do a drawing of it, compare in CDC, then I will know what my finders FOV is!

Sheeesh, and I thought this had a simple stock-standard answer.

[Gargoyle_Steve (Steve)]

Ken I have a GSO 8x50 RA finder (which hasn't been used for a while) but from memory it's FOV is almost exactly the distance between Alpha and Gamma Crucis, which should be an easy and readily checkable angular distance in CDC, etc.
For newbies (like myself a few months ago) that's the top and bottom stars of the Souther Cross "kite".

My finder either just barely fits both of these stars in at once, or just barely doesn't ... I'll check for you tomorrow night (locked away inside at work now until 7am, can't get to the sky - or finder - right now).

[ballaratdragons (Ken)]

Thanks Steve, the Crux is what I intend to use as my measuring stick

Hopefully I will get to see sky tonight to do it.

[ballaratdragons (Ken)]

OK, I have just placed the Crux in my GS Rightangle 8x50 finder. Gacrux and Acrux lay just on the perphery.

I placed that size circle into CDC to exactly match my view and the FOV of the ring in CDC is '350'.

Thanks Geoff

[erick (Eric)]

Ken, so that's 350 arcminutes? Some 5.8 degrees? Just wanted to be sure as I'm trying to learn more about angular separation etc.

[Merlin66 (Ken)]

If you look at, or close to, the celestial equator; set a star at the xtreme edge of the field, the time it takes in minutes, without a RA drive, to drift from one edge to the other times 15 will give the field of view in minutes of arc.