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How to calculate max. TFOV of scope
Posted: Tue Dec 14, 2004 2:53 pm
by carlogambino
How to calculate max TFOV of scope? I know it is dependent on f/ratio, but how to exactly calculate? (e.g my f/13 4" Mak has a max. TFOV of 1.3 degrees). I dont think AFOV of ep and magnification matter in this case, since we are talking about max. TFOV without vig/obvious secondary obstruction, not magnification here.
Posted: Tue Dec 14, 2004 5:45 pm
by ariefm71
you will need to measure the inside diameter of your mak's baffle tube, eg c5 baffle tube i.d. is 25mm, c8 is 38mm, c9.25 is 48mm.
tfov = field stop/scope's focal length * 1 radian
Treating the central baffle as the limiting field stop:
C5 at F10: 25/1250*57.3 = 1.15 degrees
C8 at F10: 38/2032*57.3 = 1.08 degrees
C5 at F6.3: 25/787.5*57.3 = 1.8 degrees (e.g. pentax xl 21mm)
C8 at F6.3: 38/1280*57.3 = 1.7 degrees (e.g. pentax xw 30mm)
Posted: Tue Dec 14, 2004 8:19 pm
by weixing
Hi,
tfov = field stop/scope's focal length * 1 radian
Don't need to be so "deep" lah!!
True Field Of View = Eyepiece Apparent Field of View / Magnification
But this will be an estimate only, because the focal length of telescope and eyepiece and the Apparent Field of View of eyepieces may vary a bit with each eyepiece. The more accurate method is to measure the time a star travel across the centre of your field of view.
Have a nice day.
Posted: Tue Dec 14, 2004 8:24 pm
by ariefm71
True Field Of View = Eyepiece Apparent Field of View / Magnification
The question is related to compound scope (sct/mct) tfov. This formula can not be used to calculate the max tfov for such scopes. The limiting factor is the diameter of the primary mirror baffle tube.
Carlo, i bet your Nexstar 4 baffle i.d. is 30mm, since you said the max tfov is 1.3*. Use a caliper to measure.
cls,
arief
Posted: Tue Dec 14, 2004 8:59 pm
by weixing
Hi,
How to calculate max TFOV of scope?
Oops... :oops: never see that he want to find the max TFoV for his scope.
C5 at F10: 25/1250*57.3 = 1.15 degrees
By the way, I think the max TFoV for C5 should be greater than that.
To Kayheem: You have try the 1rpd 30mm 80 degree with C5 @ f10... may be you can measure the TFoV that this combination give.
Have a nice day.
Posted: Tue Dec 14, 2004 9:30 pm
by carlogambino
Yep, thnx alot, Arief. My N4 baffle field stop is arnd 30mm.