FOV for a Finder Scope?

[johnd]

Hi, quick question and hopefully obvious answer to you?

I'm looking at buying a "Altair 10x60mm Right Angled Illuminated Finder Scope" and was working out my FOV sizes for my EP's i.e. 1500 Focal Length Dob and a BST 12mm EP (AFOV of 60) gives a 0.5 degree FOV. I'm looking to work out a couple of little circle rings for my Star Atlas to assist in my plotting across the sky's. So I wondered what would my Finder scopes FOV be in degrees?

Can someone advise on this?

Thank you.

[Laurie61]

It would depend, up to a point, on the Apparent field of view of the eyepiece used by the finder. This site allows you to put the spec's in of the Altair finder and simulate the f.o.v   http://www.nightskies.net/scopetest/scopecalc/index.html 

It looks as though you will get around Six degrees. 

[johnd]

It would depend, up to a point, on the Apparent field of view of the eyepiece used by the finder. This site allows you to put the spec's in of the Altair finder and simulate the f.o.v   http://www.nightskies.net/scopetest/scopecalc/index.html

It looks as though you will get around Six degrees. 

Thanks, yes the websites that show this scope give every piece of info about it except the AFOV?

[Davey-T]

There is a thingy in Stellarium where you can input scope aperture. focal length etc and it shows the FOV.

Dave

[Laurie61]

Another alternative is to point the finder at the night sky and see how many stars, in a constellation, fit in the f.o.v, not an exact method but should be OK for making a f.o.v ring for a star atlas ? 

[AlexB67]

I believe the sky-watcher DOBs in that range come with this one, be it a right angle or not I think has the same specs anyway

http://www.firstlightoptics.com/finders/skywatcher-9x50-finderscope.html

http://www.firstlightoptics.com/finders/skywatcher-9x50-right-angled-erecting-finderscope.html

according to that  a 5.6 degree FOV should be observed .

[johnd]

Just found this so looks like as you say 6 degrees   Thanks

"Specifications:


Optics: Achromat
Aperture: 60mm
Focal length: 225mm
F-ratio: 3.75
Eyepiece: 23mm wide angle with crosshair
Illuminator: LED, variable brightness
Focuser: Helical
Tube rings: Aluminium with 2x3 adjustment screws
Finder base: Fits most SCTs and refractors
"

[johnd]

I believe the sky-watcher DOBs in that range come with this one, be it a right angle or not I think has the same specs anyway

http://www.firstlightoptics.com/finders/skywatcher-9x50-finderscope.html

http://www.firstlightoptics.com/finders/skywatcher-9x50-right-angled-erecting-finderscope.html

according to that  a 5.6 degree FOV should be observed .

Hi Thanks, I got my 300p second-hand and it didn't come with a FS. The previous owner upgraded several elements and he also went with this Altair 10x60 scope but it wasn't in the sale.

[AlexB67]

John, I completely misread the post after getting sidetracked by your equipment signature and making some stupid assumptions_.   

[johnd]

 So.... got out at about 9:00pm Thursday evening and got in an hour before the high cloud rolled in. But, I did get a chance to test (sort of) my new Pocket Atlas. I say sort of as I hadn't got my FOV templates made yet but I had a cap that is 5degs. I also mounted my BINs 10x50 in the place where a proper Finder Scope would go and although I can only use 1 lens it did confirm the ease of locating at 5-6degs FOV.  I used Gemini as its 6degs between the Castor-Pollux to see if the Bins were indeed 6degs. I'm wondering if my BINs might be enough use rather than spending another £170's albeit for a rather nice scope? If only I had more viewing nights I could see how well I get on but SW London/Southern England seems to be remiss of clear skies at present.  

But I do see now how I can go from Rigel to BINS/FS but now I think my 25mm BST EP might still be a little small in FOV terms (1 degree) and a 32mm( or bigger?) might be another interim EP to assist in my star hopping in washed out skies?

Any thoughts on this for DSO/Double Star finding?