WO Z73 back focus question

[ninjageezer]

ok so i ve had my wo z73 for a few months and used it to good effect with my canon 60d but now i wish to get a dedicated astro camera ,ZWO ais533 mc pro.

i have the wo adjustable field flattener fitted and its adjusted to 11.4 mm on the scale as per wo instructions for the canon ,my question is do i need to change this or leave it and just add the zwo spacers up to the 55mm ,confused......😕

[symmetal]

With the flattener adjustment at the zero mark the back focus for the Z73 flattener is 66.2mm. The DSLR and canon T adapter has a distance of 55mm from the front of the T adapter to the camera sensor, (commonly also called back focus just to add to the confusion).

Therefore the extra FF backfocus required is 66.2 - 55 = 11.2mm. This is the distance you set on the FF adjustable scale.

11.4mm is quoted which is possibly due to the DSLR T adapters  varying slightly in thickness.

Your ASI533 MC has a sensor to flange distance of 17.5mm, (called back focus in the manual) so you need to make up the extra spacing of 66.2 - 17.5mm = 48.7mm.

The FF adjustment can be set from 0 to 15mm so you need to add a spacer distance from 48.7 to 33.7mm and make up the difference to 48.7 on the FF adjustment.

If you left the FF adjustment at 11.4 you would need to add 48.7 - 11.4 = 37.3mm spacing. Much easier to use common spacer lengths like a 20mm plus a 15mm and set the FF adjustment to 13.7.

Hope that makes sense. 🙂

ALan

[ninjageezer]

1 hour ago, symmetal said:

With the flattener adjustment at the zero mark the back focus for the Z73 flattener is 66.2mm. The DSLR and canon T adapter has a distance of 55mm from the front of the T adapter to the camera sensor, (commonly also called back focus just to add to the confusion).

Therefore the extra FF backfocus required is 66.2 - 55 = 11.2mm. This is the distance you set on the FF adjustable scale.

11.4mm is quoted which is possibly due to the DSLR T adapters  varying slightly in thickness.

Your ASI533 MC has a sensor to flange distance of 17.5mm, (called back focus in the manual) so you need to make up the extra spacing of 66.2 - 17.5mm = 48.7mm.

The FF adjustment can be set from 0 to 15mm so you need to add a spacer distance from 48.7 to 33.7mm and make up the difference to 48.7 on the FF adjustment.

If you left the FF adjustment at 11.4 you would need to add 48.7 - 11.4 = 37.3mm spacing. Much easier to use common spacer lengths like a 20mm plus a 15mm and set the FF adjustment to 13.7.

Hope that makes sense. 🙂

ALan

cheers alan

[symmetal]

I'm sure you got it ok ninjageezer, but one statement I said may have been a bit confusing. 🤔

When I said you need to add a spacer distance from 48.7 to 33.7, I meant to say that the fixed spacing distance you need to add, can be anywhere between 48.7 and 33.7mm, and any spacing below 48.7mm you then make up on the FF adjustment. 😊

Alan