Sirius with M41 sketch

[mark81]

I received a new batch of black card, a nice white gel ink pen and pencil and a red light torch from my son.  I sketched this outside with a pair of Olympus 10x50s handheld.  

 

[Shaun_the_Sheep]

Nice sketch. Good match with DSO Planner. 

[AlexK]

Or, also in DSO Planner, but now with the virtual 12" binoculars:

It's easy to fake the AFOV circle of the binos knowing the equation: EpAFOV * EpF = ScopeFOV * ScopeF (or AFOV * f = FOV * F)

To the OP. I had no idea it is possible to sketch with some white ink so nicely! By the way, I've been experimenting with sketching on my Galaxy Note 3 with its Wacom S Pen some years ago. Though just virtually. CN folks are saying that it went out quite interestingly:

[Shaun_the_Sheep]

3 hours ago, AlexK said:

Or, also in DSO Planner, but now with the virtual 12" binoculars:

It's easy to fake the AFOV circle of the binos knowing the equation: EpAFOV * EpF = ScopeFOV * ScopeF (or AFOV * f = FOV * F)

Hi Alex

I have been messing about with this as well.  I've my Vixen EP's input Ok and the FOV is an excellent match.  I also have a pair of 15x70 bino's which I have also been trying to input via the eyepiece database.  The problem is that I know neither the focal length nor AFOV of the bino eyepiece.  Will have to be trail and error.  The bino FOV is around 3 degrees which probably equates to a Fl of approx 30 to 35 mm. AFOV probably quite high, 50 degrees or above I would guess. 

[Fraunhoffer]

nice sketch ?

 

[AlexK]

I hope it's not an off-topic yet. From the formula I have provided (AFOV * f = FOV * F) you can derive that AFOV = FOV * (F/f) = FOV * Zoom. So, you don't have to know the focal ranges of the objective and eyepiece, zoom is enough. In unaware of the zoom app just make it up. E.g. your 15x = 15/1 = 300/20 = 225/15 - any combination will have the same effect on the eyepiece FOV rings drawing on the star chart. 

To determine the FOV (if not provided in the documentation, or to find it more precisely) the best method is the timing of the star's transit:

Where β is the derivative of the transit time measured, γ - the FOV you trying to find.

For convenience just observe a star traveling a -> b horizontally (near the meridian).