Central Obsruction

[RonM64]

For reflecting telescope setup, is the secondary mirror percent obstruction defined based on linear units, (e.g. diameter2/diameter1) or area units (e.g. area2/area1).  I think most often the obstruction is reported based on linear units, but not necessarily always, so I wanted to confirm what SkyTools expects.  Thanks!

[theskyhound]

For reflecting telescope setup, is the secondary mirror percent obstruction defined based on linear units, (e.g. diameter2/diameter1) or area units (e.g. area2/area1).  I think most often the obstruction is reported based on linear units, but not necessarily always, so I wanted to confirm what SkyTools expects.  Thanks!

Hello,

Yes, you are correct. The central obstruction is expressed as a fraction (e.g 39.1% is 0.391) of the diameter of the primary aperture.

That would make a really nice addition to the help.

[RonM64]

Thanks for confirming and for the quick reply. Much appreciated!

[razvan]

Please update the help as it suggests the number is based on the area: "This is the obstruction of the primary mirror by the secondary mirror for a reflecting telescope. This is essentially the area of the shadow that the secondary mirror casts on the primary." Even better, it'd be helpful to have "area" mentioned in the dialog box.

Thanks.

[theskyhound]

Hi,

I will update the help and make this more clear, but the obstruction is in fact an area. Its just that, by convention, it is specified as a fraction of the diameter. Internally, that is converted to area.