Focusing-Positive (Outward)

[admin]

Hi Jack,

glad to hear that your gear was recovered and made its way back to you in the end. It sounds like a dreadful thing that the system takes more interest in the rights of the criminal than the rights of the honest, but that sort of thing seems to happen everywhere now

It sounds like your settings are a good start. Ideally you make the focuser approach the target position so that it is lifting the camera against gravity. That means towards the telescope and positive if you are using a refractor or SCT. Trickier with a Newtonian as the up/down for the camera may vary as the scope moves around the sky.

200 steps may or may not be enough overshoot - if you find small negative movements don't actually change focus position then try increasing it until they are having an effect.

The refocus button will become available once you have done at least one semi-automatic scan for best focus then 'goto best position' - that first procedure helps SharpCap know what range, how many steps, etc, should be used in the refocus procedure.

cheers,

Robin

[jhopkins]

Hi Robin,

I'm finally beginning to start an autofocus routine with an Ascom driven Canon DSLR on my 500mm telescope . I’ve already established that "Positive" is "In" with numbers increasing.

I started in the daytime, selected Contrast (Edge) Detection. I used the ZWO Focuser box to first push the focus in a Negative direction (Step Size is still to be determined). I started the exposures needed to run the focus routine by clicking Quick Capture to start continuous shooting. Then started the Positive focus direction using the controls in the upper right corner of the Focus Graph. When I did that there was a delay of 2 or 3 captures before I noticed any change in focus like it was taking exposures that weren’t necessary or was not reading them quickly enough. I think I set it somewhere to only look at 1 frame for each position. Maybe the delay is because I'm using a DSLR instead of an astro cam. When I do finally get through this stage adjusting step size, etc. and have a focus pattern established, will clicking on "Automatic Refocus" start the necessary exposures, too? Or do I always start exposing with Quick Capture at the beginning?

Sorry, my 80 year old mind is not serving me as well as it used to.

Jack

[admin]

Hi Jack,

when you are using a DSLR, it all becomes a bit more complex...

SharpCap was originally designed around webcams and high speed planetary cameras, so by default it captures images all the time, one after another. That isn't ideal with a DSLR, so you switch SharpCap into 'Still Mode' instead of 'Live Mode' so that frames are only captured on request.

Now, if you want to do a focus scan by hand, the way to do it is

* Adjust focuser, wait until finished moving / settled
* Use the 'Framing shot' button to take a single frame
* Repeat

This ensures that the images taken for focus scores are only captured when the focuser is stationary (SharpCap will ignore images that are captured while the focuser is moving, which I think is affecting the approach you tried).

Even better is to use the 'Scan' button in the focus graph area - this automates the 'move the focuser, capture an image, repeat' bit, and with the camera in still mode it will ensure the images are only taken when the focuser is stationary.

Hope this helps,

Robin

[jhopkins]

Thank you so much for getting back to me. I'll go ahead and set everything up at the house today and try again with the new instructions. I'll let you know if I have problems. Tomorrow night I'll be able to get up to the mountain for a few nights of shooting.

Jack