hi,
i need to know how to focusing while the camera into the visual back with no eyepiece. i am using canon 300D, it is a Dslr camera. it dsn't have live view.
is there any other way can focus the object?
thank you
DSLR camera focusing
there are several ways to focus with a DSLR on prime focus mode (like your setup):
1) Hartmann Mask Method
You may like to use a piece of cardboard cut to the size that just fits your imaging objective (like the dew shield of a refractor, etc). Cut two triangles which is spaced equally apart from the center of the circle. Some may recommend cutting out two smaller circles instead of triangles but the triangle way worked better for me. When you focus on a star, adjust the focusing distance until the both images of the star come into precise alignment (two into one), then you are in focus. Using triangles, you will be able to see the same effect with the additional diffractive spikes that will also merge when focused.
2) Right-angled Finder
You can buy a right-angled finder (magnified) for the 300D that will help in ease of focusing but method (1) will still be more precise.
3) Fisherman String Method
Place two strings across the objective's dew shield such that you get a cross. You can focus a star until the diffractive spikes are clean and sharp.
4) Ronchi Method
You can buy off-the-shelf ronchi devices (specifically for the 300D) that will help in precise focusing. Note however that this method might be time consuming and you need to replace the camera with the device when focusing, and then take out the device and put the camera back in.
Reference:
http://www.astropix.com/HTML/I_ASTROP/FOCUS/METHODS.HTM
Mastering the art of focusing in astrophotography is one of the most important and critical fields in achieving excellent images. Do spend sometime in focusing well!
1) Hartmann Mask Method
You may like to use a piece of cardboard cut to the size that just fits your imaging objective (like the dew shield of a refractor, etc). Cut two triangles which is spaced equally apart from the center of the circle. Some may recommend cutting out two smaller circles instead of triangles but the triangle way worked better for me. When you focus on a star, adjust the focusing distance until the both images of the star come into precise alignment (two into one), then you are in focus. Using triangles, you will be able to see the same effect with the additional diffractive spikes that will also merge when focused.
2) Right-angled Finder
You can buy a right-angled finder (magnified) for the 300D that will help in ease of focusing but method (1) will still be more precise.
3) Fisherman String Method
Place two strings across the objective's dew shield such that you get a cross. You can focus a star until the diffractive spikes are clean and sharp.
4) Ronchi Method
You can buy off-the-shelf ronchi devices (specifically for the 300D) that will help in precise focusing. Note however that this method might be time consuming and you need to replace the camera with the device when focusing, and then take out the device and put the camera back in.
Reference:
http://www.astropix.com/HTML/I_ASTROP/FOCUS/METHODS.HTM
Mastering the art of focusing in astrophotography is one of the most important and critical fields in achieving excellent images. Do spend sometime in focusing well!
"The universe is composed mainly of hydrogen and ignorance." 
Re: focus
Michael,
I bought mine at this website for $110. I use it also for macro photography when I can bend my head too far to the ground.
http://forum.clubsnap.org/showpost.php? ... ostcount=2
I bought mine at this website for $110. I use it also for macro photography when I can bend my head too far to the ground.
http://forum.clubsnap.org/showpost.php? ... ostcount=2
Hi Michael, the camera's lcd is good enough to aid focusing. Just zoom in on the last play back, and centered on a bright star. Along with the other focusing devices mention earlier like the Hartmann mask or cross hairs, the enlarged view will show the diffraction features , and you can use that to fine tune the focusing.it dsn't have live view.
Lazy people like me, uses software, hehe.
1) DSLRFocus
2) DSLR Shutter
3) ImagesPlus
The FWHM (full width half max) and half flux diameter is very accurate. I am trying to set up a autofocus system, meaning closing the loop of telescope focus and camera. Using these software, you can also program exposure series (you need more accessories).
Ok, these are some suggestions from a lazy person.
1) DSLRFocus
2) DSLR Shutter
3) ImagesPlus
The FWHM (full width half max) and half flux diameter is very accurate. I am trying to set up a autofocus system, meaning closing the loop of telescope focus and camera. Using these software, you can also program exposure series (you need more accessories).
Ok, these are some suggestions from a lazy person.
Photo Album:
http://www.flickr.com/photos/14113965@N03/
http://www.flickr.com/photos/14113965@N03/