ZWO FF130 APO + ZWO ASI294MC PRO, CANNOT FOCUS

SF1jVe1b

Good day,

I have recently purchased and received the FF130 APO from ZWO. I am attempting to focus the telescope with the 294MC PRO directly attached (no spacers for back focus) and cannot achieve focus.

Can anybody tell me what the issue is?

I have cycled through settings, but can say I tried all binning modes, adjusted exposure for each, attempted at day and night. I do not have any knowledge on ADU? being below 65000, just saw it as I was perusing the internet, so maybe this is the case.

Of note, physical inspection without the camera of the telescope looks fine. I did notice that when I was about 2 feet behind the telescope, the image did come into focus, but I am also aware our eyes and the camera are two different things so I apologize if that is irrelevant.

Hoping for some education-

Thank you.

V/r,
Drew-
Bin 1X1

w7ay

SF1jVe1b Hoping for some education-

The ZWO FF130 is just a rebadged Askar 130PHQ OTA. (Given how ZWO appears to treat warranty requests, buying an Askar OTA from a local vendor would have given you better warranty protection.)

When used without a reducer, to find the focus location of the Askar 130PHQ, first rack the focuser so that the drawtube is fully retracted. At that point, the focal plane is 99mm away from the metal back of the 54mm adapter (79mm from the metal back of the 48mm adapter). This is the maximum distance your camera's sensor can be away from the OTA and still be able to focus.

Mark that location on your table. Now rack the focuser all the way out. If the metal back of the drawtube does not reach the maximum position in the previous paragraph, you will need to add spacers.

If you use a reducer from Askar, the camera sensor needs to be precisely 55mm from the metal back of the reducer when using the 48mm adapter (62.5mm from the reducer's 54mm adapter).

Remember to subtract 17.5mm for the distance of the ASI294 flange to its sensor. And add 1/3 the thickness of the filter glass, if you have a filter in the light path.

Chen

SF1jVe1b

w7ay

Chen, thanks for the response. Through my research, I found the same info you provided irt the Askar 130PHQ. My solution for 1000mm, w/o the 0.7x reducer, was using the stack provided for the focal reducer plus my 16.5 & 21 mm spacers to provide enough distance between the telescope optics and the camera to achieve focus. All, said I achieved focus in the day and will seek the next opportunity to confirm good focus in the evening...as it goes, I get a new scope and the forecast shows 12 days of cloud coverage.

Thanks again for the response-

CS, Drew-

w7ay

SF1jVe1b All, said I achieved focus in the day and will seek the next opportunity to confirm good focus in the evening

This is the focus delta (back focus vs object distance) that I had made up for a 901 mm focal length scope (using the thin lens approximation):

I.e., if you are focused in the daytime at a tree 100 m away, the back focus is 909.192 mm instead of 901 mm (i.e., ∆ of 8.192 mm from infinity focus). So, for infinity at night, you would need to reduce the drawtube length by 8.2 mm.

Your 1000 mm focal length will be a little more than that. Depending upon the daytime object, this delta it is not small, so best to set it up before nightfall.

Chen