Daves Focus Meter

[The Thing]

Has anyone tried this? It looks very interesting as it reckons it can correct focus automatically as each sub is displayed. I'll have to give it a go.

Dave's Focus Meter (DFM) gives you a visual indication of just how sharp your current video screen or image is. It will work with any video source, live or recorded, and any image format. It is designed for astronomy, microscopy, security and any area where precise focus is important.

[Mike]

have you tried this out yet Dunc?

[The Thing]

I gave it a go last night and it just said I was perfectly in focus but I wasn't quite - blobby stars if you look closely at the M31 image. I suspect there is some configuring to do and someone like Mark may like to comment on the method used. If it works as advertised it wil be a boon to those of us with ASCOM focusers and those with twiddly knobs.

[MarkS]

"Dave" doesn't state exactly how it is done except to say that it is based on image contrast.  There are a number of algorithms that might be used to measure contrast.  However, I would think they would be more suitable to moon/planetary image feeds with obvious surface features rather than deep sky images that typically contain very faint and noisy structures.  It is possible the contrast of stars is being measured, in which case the usual FWHM and Max Pixel value probably work just as well.

I prefer Bhatinov because it actually provides a measure of precisely how out of focus a star is - at least it does once you've averaged the readings over the fluctuations caused by the seeing. I then tend to bias the focus slightly in the direction of the drift caused by future temperature drops.

[The Thing]

Anyone got nimble enough fingers to cut a Bahtinov mask for a 50mm lens!

[MarkS]

Anyone got nimble enough fingers to cut a Bahtinov mask for a 50mm lens!

I focus during daylight hours and then tape the focus ring it so it can't be moved.  It's a real pain trying to focus a 50mm at night.

[The Thing]

I've made a minute B-mask, I have card but no tape at this rather too nice gaff in Les Alpilles Parc Naturel etc etc.

[MarkS]

Minute?

I thought you meant it took 60 seconds to make.  I now realise you meant it's tiny!

Les Alpilles Parc Naturel?  That's not Normandy!

[The Thing]

No, it's not Normandy. About 7 degrees further south