My first Astronomy Sketch

[Davekyn]

Hi,
It's not breath taking, but for my first go, I don't mind saying that the idea of sketching really does help me to better observe. What is the formula for finding Mag and also FOV.
I'll try to include some more details next time with labels and so forth. Any recomend a good site that gives tutorials? I used my ED80 with a 25mm EP [I think]
http://i181.photobucket.com/albums/x30/davekyn/bd348163.jpg

[Robh]

Dave,
Nice drawing.
Magnification=aperture focal length/EP focal length.
If your telescope has a 600mm focal length the magnification=600/25=24.
The 25 is the 25mm focal length of your EP.
True FOV=apparent FOV/magnification.
The true FOV will depend on your eyepiece's apparent field of view.
If it's around 60 degrees (check its specs) then the true FOV=60/24=2.5 degrees. The 24 was your magnification.

Regards, Rob.

[Coen]

Magnification = focal length of scope / eyepiece.

Your ED80 is F7 so has focal length 7*80 = 560mm therefore your 25mm eyepiece would have an approximate magnification of 560/25 (about 22x).

The true field of view is apparent field of the eyepiece / magnification.

For Plossl's apparent field is approximately 55 degrees so your 25mm eyepiece (assuming Plossl) will have a true FOV approximately 55/22 or about 2.5 degrees (just under at about 2.46).

These are theory numbers - for better accuracy and to take into account that the numbers quoted are not always exact you are better off timing how long it takes a star to transverse the centre of the field (i.e. turn off the motor drive and turn on the stopwatch). 240 seconds equates to 1 degree.

RE: sketching tutorials

Try: http://perezmedia.net/beltofvenus/archives/000567.html
and: http://www.cloudynights.com/ubbthreads/postlist.php/Cat/0/Board/Sketching

As possible starting points.

[Davekyn]

Thanks guys,
that sorts out my issues with FOV. Checking links now. Thanks again :)

[xnomad]

I really like it. Forgive my ignorance but is that white pencil on black paper or has the colour been digitally inverted?

[dannat]

good work dave, have just started some bino sketching myself - of ic2602, beehive etc. I am also doing the IFAS bino challenge which has room for many sketches, atelast 20 to qualify for their award

[Davekyn]

Not at all xnomad...I used paint shop pro & simply pressed the button to turn it into a negative.(First I scanned my sketch) I am really excited about doing more sketches. Since playing around with a pencil and sketch pad, I have scanned a few pages from my star atlases and turned them into negative, then cropped and magnified ect...making up a PDF for my iPhone. I've really taken a deeper interest and am starting to find targets I'd been scratching my head about. FOV has a new meaning, and my eyes seem to see further than before. Each veiwing session is now more concentrated and somewhat more relaxing at the same time.
Yea Dan.....I been looking into the Bino sketching too.....Wider veiws good for learning the sky quickly. Please let us have a look when you get somthing going :). I've been caught up digitizing my maps for iPhone, with good results...I can even flipmy maps without the screen readjusting the pic...good for flipping the atlas veiw Vs EP veiw...nice and quick.

Can't wait to put a bigger effort in on my next pic...I found heaps of sketching options in paintshoppro to enhance the finish product.
No time for spell check...on the phone...goto go.

Later all