HyperStar backfocus.

[Grierson]

I have recently purchased the latest version of HyperStar for my Edge HD 8”. The spec. on the website indicates the back focus should be 39.8mm but there is no clear indication of where this measurement is taken FROM. There is some text that suggests that the 39.8mm should be the distance between the camera mounting thread and the sensor but the thread is c. 6.0mm deep and there is no indication wether this means the start or end of the thread. In addition the HyperStar is supplied with a filter drawer so the question arises is ‘the camera mounting thread’ the one on the lens body or the filter drawer body. I wonder if any of you kind people with a similar set up have faced a similar question and managed to fit the correct spacer depth. (The camera will be a ZWO 294 with a front to sensor measurement of 6.5mm.)

[Fegato]

Hi - did you sort yourself out with this? I have the Edge 8HD, Hyperstar v4, and ASI294MC Pro too. I have spent ages trying to get the collimation right, including making sure the corrector plate is centred, and endless looking at defocused stars.  But despite very carefully getting the "doughnuts" as right as I can, I always have coma in all 4 corners facing in to the centre, implying collimation not right or spacing not right. I'm starting to worry that the spacing is the problem although that seems weird -  I assumed that having specified the right camera, I would just stick the camera with its standard nosepiece onto the Starizona adapter and all would be well, and  a very rough measurement suggests I'm about right for 39.8 from the start of the adapter to the sensor.

So - sorry, not providing any answers, just interested in your experience.

[Stef1980]

Hi I have the same setup, v4 for my edge hd 8, zwo 294 and have the exact same problem. Any updates? Thanks

[michael8554]

One site says you must specify which camera you are using, to ensure the correct unit and spacers are supplied.

Why not contact Starizona ?

Michael

[Stef1980]

i did this but not much help tbh. im going to try increasing/decreasing back focus to see what happens. everything appears to be inline and collimated. i do use a cheapish lpf which may cause issues..i wil remove that first. judging by tbe fact im not the only person with this issue something is a miss! i bought my unit last year, when did you guys buy yours? 

[b36lbx]

Hi all, I also use a V4 with the filter drawer on a EdgeHD 8 with a 2600 and a 1600, both mm. Did any of you guys managed to find a solution?

[HeyJP]

Solved:

Wow, unanswered after 3 years.  I was looking for this same info and found this in 2024.  Then I figured it out and thought I’d answer for the next generation.

the backfocus on the Hyperstar is measured from the flange (shoulder) from which the male threads project out. Don’t count the thread length.  Total backfocus must be within .5mm of the target 39.8mm.

The backfocus consists of three components (only 2 if no filter tray).

• Camera:  most ZWO cameras have 17.5mm backfocus from camera base to sensor.
• Filter tray:  The Starizona filter tray is 17.5mm thick (0 if you don’t use it!)
• Adapter:  the adapter will wither be 4.8mm if you use filter tray or 22.3mm without the tray.
  • With tray:  17.5 + 17.5 + 4.8 = 39.8mm
  • no tray:      17.5 + 0 + 22.3 = 39.8mm

there ya go!

 

Jim in Boulder