Which focuser

Hans Tucker (Hans) · #1 01-05-2018, 08:10 PM

Is there any advantage in fitting/using a FLI PDF instead of installing an electronic focuser control direct to control the focuser. Would the PDF be more precise?

Joshua Bunn (Joshua) · #2 02-05-2018, 02:28 PM

Hi Hans.

That would depend on what focuser you want to motorise.
I have no experience with the PDF.

Josh

AstroApprentice (Jason) · #3 02-05-2018, 02:37 PM

Hi Hans, PDF are meant to be very accurate - plus one of the advantages I see is that their weight is evenly distributed. Most add-on motors, even the super $$$ Feather-touch HSMs have most of their weight sticking out one side which can make balancing more challenging depending on the peculiarities of your mount. I prefer the Rigel in-line design.
Colin had a PDF for sale in classifieds a while back...not sure if it sold?

Atmos (Colin) · #4 03-05-2018, 11:29 AM

I’ve used a PDF, Atlas and I’ve just had a SharpSky Pro arrive on Tuesday (although I haven’t had a chance to actually use it yet) and I’d say it all depends on what you’re using it on.

I’ve been forced into motorising the current focuser on my refractor due to back focus issues. Theoretically the PDF should have a more accurate and repeatable autofocus but it is better as a focuser replacement than an addition on top of another one.

If you are using it as an addition you do have to take into consideration the extra weight that the PDF adds and whether the extra weight could flex the focuser.

Hans Tucker (Hans) · #5 03-05-2018, 09:48 PM

Thanks all, a few good points to consider. I have three refractors (AP 130GTX, TEC 160FL and APOMAX 130 f/12) and was looking for an alternative solution to fitting electronic focuser/motors to each of these scopes. Yes I plan to see if I can image with a f/12 scope even though some have said you can't. Though I need to replace the current 4" focuser with something better so I am looking at the AP 4" Giant Focuser.

Atmos (Colin) · #6 03-05-2018, 10:01 PM

Depending on how easy it is to remove the focuser on any of them all you'd need is an OTA to PDF adapter. Unscrew the focuser and screw on the PDF. This would give your the most rigid imaging train.

Although you could just attach it to the end of the draw tube but then you increase the amount of weight/torque on the draw tube. This is what I did with my refractor when I was using an ASI1600 but thinking back now, I think that is what was causing some of the tilt that I struggled to remove.