AF or Bahtinov?

[rickwayne]

I actually started building a myFocuserPro, Arduino and all, but I could never get it to move the stepper. Dunno if I soldered something wrong or what.

The huge advantage to the Pi/Waveshare route is that it's so simple. You stack the HAT board on top of the Pi. You connect the 4 wires from the stepper to the HAT board (it literally has 3 different ways to plug it into the board). You get Kevin Ross's indi_wmh_focuser driver. You start focusing.

I used a couple of RJ-11 breakout boards with screw terminals so that I wouldn't have to solder anything, and so that the cable between Pi and focuser is light, secure, and absurdly easy to obtain. The mount for the focuser...it is to laugh. Piece of steel strapping with holes in that we had lying around. I drilled more holes, the motor was already tapped for M2.5 bolts.

The timing-belt pulley goes on the motor shaft, and the belt around the pulley and the coarse-focus knob.

[Dazzyt66]

8 hours ago, rickwayne said:

I actually started building a myFocuserPro, Arduino and all, but I could never get it to move the stepper. Dunno if I soldered something wrong or what.

The huge advantage to the Pi/Waveshare route is that it's so simple. You stack the HAT board on top of the Pi. You connect the 4 wires from the stepper to the HAT board (it literally has 3 different ways to plug it into the board). You get Kevin Ross's indi_wmh_focuser driver. You start focusing.

I used a couple of RJ-11 breakout boards with screw terminals so that I wouldn't have to solder anything, and so that the cable between Pi and focuser is light, secure, and absurdly easy to obtain. The mount for the focuser...it is to laugh. Piece of steel strapping with holes in that we had lying around. I drilled more holes, the motor was already tapped for M2.5 bolts.

The timing-belt pulley goes on the motor shaft, and the belt around the pulley and the coarse-focus knob.

Yeah, That’s exactly the version I was going for - I’ve already installed Kevin’s drivers, so I guess I should probably do the hardware at some point 😂 and I think I have a piece of steel with some holes in too! 😂😂

[ollypenrice]

On 22/04/2021 at 09:49, Dazzyt66 said:

I've been considering building my own RPI based autofocuser next month (when I get my next 'spending allowance' 😂). This will initially go on my ST80 (permanently setup). As per usual I keep doing my research and I came across this thread:

So now I'm torn. I can get the AF bits and a new case for the RPI which'll cost about £60 or I can do the 10p mod that @ollypenriceuses (and do it today) and then buy a Bahtinov mask for about £15.

My question is: I want to be able to do my imaging mostly using Ekos scheduling. At the mo I either check the focus before I start, using focus assist in Ekos (manually until I have the best number) and then lock the focus on the ST80. For subsequent nights I just quickly check the focus numbers in Ekos are roughly what they were previously and leave it to go. Does the focus change overnight due to seeing etc (or if I move to a new target) if doing long sessions? Or once its setup generally is that it for the night? If its the latter then 10p and a Bahtinov seems the way to go given that the ST80 is as basic as it gets (although I do love it!!).

Cheers

Daz

Focus certainly moves during the night, though how quickly depends on the rate of temperature change, the thermal stability of the scope and the imaging resolution. (Higher resolution will 'show' focus drift more readily than low.)

I wouldn't use the FWHM value from one night on a subsequent one or in a different part of the sky.  The seeing varies considerably so you might reach a lower value tonight than last night, etc.  And the higher you are in the sky the lower the value is likely to be.

Olly

[Buzzard75]

On 24/04/2021 at 16:05, Clarkey said:

I have found that the AF routine and the mask give different focus points, but it has always been very close and not enough to see donuts when processing. I would hope if you get a good Bahtinov specifically for your scope it would give you accurate results. (Mine is a cardboard special!)

I agree, it shouldn't be that far off. The scope I have is a WO Redcat and the mask is the one that came with it. Sometimes it's just off for some reason. It's integrated into the lens cap. I guess it's possible that when I put it on, I didn't get it flush and perfectly perpendicular to the imaging train which may throw off the Bahtinov pattern. I don't know. I've never actually attempted it or seen anyone else show that to be the case. Might be worth looking into. I've just defaulted to using the Bahtinov to get close and then using the AF routine to guarantee the stars are as small as possible.

[rickwayne]

I use the Linear algorithm with my DIY autofocuser, and a pretty small step size. That converges in 20 frames or less. So, yeah, more wear on the shutter, but not absurd amounts.