ZWO Canon Lens adaptor

[peeb61 (Paul)]

Hi All, I want to set up a rig using a ZWO dslr adaptor to my Canon 28mm to 80mm Canon EF lens and as the imaging camera a ZWO183MC Pro. On the front of the Canon lens it states 58mm and In order to plate solve in APT I need to enter the focal length and diameter of the lens.. I have attached a grab from Astronomy Tools showing hopefully the correct values I need to add in order to achieve plate solving...
Can anyone confirm I have entered these figures are correct?
Many thanks in advance.
Paul

[ronson]

Hi Paul,

the 58mm on the lens is usually the filter diameter which is different from the lens aperture.

The lens aperture is calculated by dividing the focal length by the f-number. Here is a simple calculator: https://www.omnicalculator.com/physics/aperture-area

[peeb61 (Paul)]

Hi Ronson,

Many thanks for your reply and for the link....

So if the f ratio is 5.6 and f/l is 80mm, this works out to be 14.286 diameter?

As in the attached?

Paul

[Drac0 (Mark)]

Hi Paul,

Yes, that is correct. Just remember when using a zoom lens, as you change the focal length/f-ratio the aperture changes. As an example, with the 28-80mm you get the ~14.3mm wide open (f5.6), but wide open at 28mm (f3.5) the aperture is only 8mm. It's fine if you only use one focal length but can be annoying if you change a lot, especially with zooms that have a wider range.

Cheers,
Mark

[peeb61 (Paul)]

Originally Posted by Drac0

Hi Paul,

Yes, that is correct. Just remember when using a zoom lens, as you change the focal length/f-ratio the aperture changes. As an example, with the 28-80mm you get the ~14.3mm wide open (f5.6), but wide open at 28mm (f3.5) the aperture is only 8mm. It's fine if you only use one focal length but can be annoying if you change a lot, especially with zooms that have a wider range.

Cheers,
Mark

Thanks Mark for the confirmation.... Great work!