Focusing a big lens in EQ mount

I have a Sigma 150-500 and a 2x teleconverter on a sky-watcher star adventurer eq mount.
With this lens and teleconverter i can't use AF, so i have to focus (moon for example) using the focus ring.
But when a i move the ring it is very hard (live view enabled) to focus ... the image "shakes" (sorry for my english)
Anybody has any idea how can i improve focus?

Will this device will work ?
http://www.amazon.com …ords=usb+focus+​controller

I know one disadventage is focus is not lineal, move with steps ... but maybe it will work anyway ...

I use an app called dslr controller on my tablet to focus the lens when mounted on my star adventurer. It can shoot tethered to a tablet or with the use of a small wifi router it can be wireless. More information in the link below!

http://dslrcontroller.​com/

At focal lengths of 400mm and greater, I have found using a “Bahtinov Mask” to be an effective way of getting good manual focus.

The “Bahtinov Mask” can be home-made or purchased and is a diffraction mask placed over the lens cap end of the lens. You then point the lens at a bright star and inspect the Live View image at x10 magnification to see if the star is focused or not.

When the star in at focus you should see a nice diffraction patter, similar to a squashed X with a bar running through the centre of the X.

In Australia you can purchase one for say, $30 or $40. I find it difficult to see the diffraction pattern in Live View, even at x10, with lenses of focal lengths much smaller that say 300 or 400mm.

I also turn on Exp.SIM (Exposure Simulation) so I can take, say, a 1 to 2 sec exposure so the diffraction pattern is quite bright during Live View.

Here is a Live View image taken with my Canon 40D through a 1800mm fl telescope showing the normal mode and the x10 magnified view.

Here are some links to websites that explain what a Bahtinov Mask is and how to make one. Generally, they work best on telescopes, typically with focal lengths of 800mm or more as the diffraction pattern is easier to see on the Live View display.

http://www.deepskywatc​h.com …s/make-bahtinov-mask.html
http://www.spike-a.com/
http://astrojargon.net​/maskgen.aspx

Cheers

Dennis

JohnPh wrote in post #17642091
I use an app called dslr controller on my tablet to focus the lens when mounted on my star adventurer. It can shoot tethered to a tablet or with the use of a small wifi router it can be wireless. More information in the link below!

http://dslrcontroller.​com/

Thank you John, i'll try the router and the app, i have both, i wasn't aware about controlling focus.

nardes wrote in post #17642555
At focal lengths of 400mm and greater, I have found using a “Bahtinov Mask” to be an effective way of getting good manual focus.

The “Bahtinov Mask” can be home-made or purchased and is a diffraction mask placed over the lens cap end of the lens. You then point the lens at a bright star and inspect the Live View image at x10 magnification to see if the star is focused or not.

When the star in at focus you should see a nice diffraction patter, similar to a squashed X with a bar running through the centre of the X.

In Australia you can purchase one for say, $30 or $40. I find it difficult to see the diffraction pattern in Live View, even at x10, with lenses of focal lengths much smaller that say 300 or 400mm.

I also turn on Exp.SIM (Exposure Simulation) so I can take, say, a 1 to 2 sec exposure so the diffraction pattern is quite bright during Live View.

Here is a Live View image taken with my Canon 40D through a 1800mm fl telescope showing the normal mode and the x10 magnified view.

Here are some links to websites that explain what a Bahtinov Mask is and how to make one. Generally, they work best on telescopes, typically with focal lengths of 800mm or more as the diffraction pattern is easier to see on the Live View display.

http://www.deepskywatc​h.com …s/make-bahtinov-mask.html
http://www.spike-a.com/
http://astrojargon.net​/maskgen.aspx

Cheers

Dennis

Hosted photo: posted by nardes in
./showthread.php?p=176​42555&i=i110124707
forum: Astronomy & Celestial

Hosted photo: posted by nardes in
./showthread.php?p=176​42555&i=i132183192
forum: Astronomy & Celestial

I didn't know about it, is good to know, thank you for your help.
Without any doubts this will help me focusing stars.

I rarely use a bahtinov mask. Also, with teleconverters it is unlikely you will yield a very good quality image..and it will require very long exposures. Try using the lens alone. Download a demo of backyard eos and hook up the camera via usb. Set the lens to autofocus. BYE has a function that allows you to control the motor in the lens manually at 3 different speeds. With this you can focus on a bright star using the computer instead of touching and wobbling the lens all over the place. This will help you to get a really goo focus, though honestly I have no problem hand focusing at 500mm F5.6 The tighter the aperture, the easier it is to focus on a star.