Altair lightwave 0.8 backfocus

[Mark 2020]

Hi guys

I have an altair lightwave 0.8 reducer, i believe its 55 mm backfocus to sensor. Asi 294mm pro camera. 6.5mm from front of camera to sensor. Do you measure from the back edge of the reducer or from the actual glass in the reducer which is around 5mm in from the back edge of reducer? To get the 55mm total...thanks in advance.

[michael8554]

On 16/04/2022 at 12:22, Mark 2020 said:

Do you measure from the back edge of the reducer ?

Yes Mark, though I'd describe it as the front edge.

But according to the Altair spec, 55mm is approximate:

• Spacing of approx. 55mm to Sensor, which can be fine-tuned with our T2 spacers.

Suggesting you tweak the 55mm to get best star shape in the corners of the image.

Michael

[Mark 2020]

Thanks fella, its the fine tuning that takes the time, especially when clear nights are premium 

 

[adyj1]

The diagrams on the ZWO website are surprisingly helpful and tell you exactly what you need;

https://astronomy-imaging-camera.com/tutorials/best-back-focus-length-solutions-55mm.html

NIINA has an option in the 'image' tab to show a 3x3 crop mosaic which shows you a magnified view of all four corners that I have found useful when checking backspace...

Ady

[Mark 2020]

Thanks, i didnt know that about nina..although ive not i.aged for about a year now 

 

[adyj1]

I think it is called the 'aberration inspector' on the Imaging tab (has a grid of 9 squares in the icon. Here I'm trying without success to get the wrong Atair field flattener/reducer to work with my AA66ED-R.

The other AP apps may well have something similar.