The problem with using hyperfocal techniques for astrophotography is that the assumed "acceptable circle of confusion" is not adequate to render stars as sharp points. To compound the problem, variations in temperatures will affect the different materials of your camera system (lens elements made of varying optical materials and densities, metal helical collars, plastic lens tube, etc.) and the skies are usually best suited for astrophotography when the temperature is much lower than for what your lens was optimally designed.

For night sky shots here is what I do. Once my camera is set up on the tripod I enable live view. I start with the brightest star in the sky, point my camera at it and center it on the screen. I do a rough focus and then repeat at x5 and x10 magnification (I'm not sure if the 450D has this). That will get the focus near enough that some dimmer stars that may not have been visible in live view before now will be. Re-point your camera to a dimmer star and carefully refocus (x1, x5, x10). Everything in the sky except the Moon should be as sharp as your lens is capable of at this point. For shutter speeds I use a rule of thumb of 600 divided by effective focal length (include your crop factor if applicable). When using a 17mm focal length I can expose for around 30 seconds and the stars will appear motionless when viewing the entire scene. At a 100% crop the stars will appear as very short trails. By the time I'm at 640mm (200mm x 2X extender x 1.6 crop factor) I'm down to less than 1 second for shutter speed and push the ISO up to compensate. With night sky shots in relatively dim (light pollution free) skies, your exposure level choice will determine how many stars are visible. Only the brightest stars will appear at lower exposure levels and each successive exposure level will increase the number of visable stars in the shot.

The problem with using hyperfocal techniques for astrophotography is that the assumed "acceptable circle of confusion" is not adequate to render stars as sharp points. To compound the problem, variations in temperatures will affect the different materials of your camera system (lens elements made of varying optical materials and densities, metal helical collars, plastic lens tube, etc.) and the skies are usually best suited for astrophotography when the temperature is much lower than for what your lens was optimally designed.

For night sky shots here is what I do. Once my camera is set up on the tripod I enable live view and set my lens to manual focus. I start with the brightest star in the sky, point my camera at it and center it on the screen. I do a rough focus and then repeat at x5 and x10 magnification (I'm not sure if the 450D has this). That will get the focus near enough that some dimmer stars that may not have been visible in live view before now will be. Re-point your camera to a dimmer star and carefully refocus (x1, x5, x10). Everything in the sky except the Moon should be as sharp as your lens is capable of at this point. For shutter speeds I use a rule of thumb of 600 divided by effective focal length (include your crop factor if applicable). When using a 17mm focal length I can expose for around 30 seconds and the stars will appear motionless when viewing the entire scene. At a 100% crop the stars will appear as very short trails. By the time I'm at 640mm (200mm x 2X extender x 1.6 crop factor) I'm down to less than 1 second for shutter speed and push the ISO up to compensate. With night sky shots in relatively dim (light pollution free) skies, your exposure level choice will determine how many stars are visible. Only the brightest stars will appear at lower exposure levels and each successive exposure level will increase the number of visable stars in the shot.

The problem with using hyperfocal techniques for astrophotography is that the assumed "acceptable circle of confusion" is not adequate to render stars as sharp points. To compound the problem, variations in temperatures will affect the different materials of your camera system (lens elements made of varying optical materials and densities, metal helical collars, plastic lens tube, etc.) and the skies are usually best suited for astrophotography when the temperature is much lower than for what your lens was optimally designed.

For night sky shots here is what I do. Once my camera is set up on the tripod I enable live view. I start with the brightest star in the sky, point my camera at it and center it on the screen. I do a rough focus and then repeat at x5 and x10 magnification (I'm not sure if the 450D has this). That will get the focus near enough that some dimmer stars that may not have been visible in live view before now will be. Re-point your camera to a dimmer star and carefully refocus (x1, x5, x10). Everything in the sky except the Moon should be as sharp as your lens is capable of at this point. For shutter speeds I use a rule of thumb of 600 divided by effective focal length (include your crop factor if applicable). When using a 17mm focal length I can expose for around 30 seconds and the stars will appear motionless when viewing the entire scene. At a 100% crop the stars will appear as very short trails. By the time I'm at 640mm (200mm x 2X extender x 1.6 crop factor) I'm down to less than 1 second for shutter speed and push the ISO up to compensate. With night sky shots in relatively dim (light pollution free) skies, your exposure level choice will determine how many stars are visible. Only the brightest stars will appear at lower exposure levels and each successive exposure level will increase the number of visable stars in the shot.

The problem with using hyperfocal techniques for astrophotography is that the assumed "acceptable circle of confusion" is not adequate to render stars as sharp points. To compound the problem, variations in temperatures will affect the different materials of your camera system (lens elements made of varying optical materials and densities, metal helical collars, plastic lens tube, etc.) and the skies are usually best suited for astrophotography when the temperature is much lower than for what your lens was optimally designed.

For night sky shots here is what I do. Once my camera is set up on the tripod I enable live view. I start with the brightest star in the sky, point my camera at it and center it on the screen. I do a rough focus and then repeat at x5 and x10 magnification (I'm not sure if the 450D has this). That will get the focus near enough that some dimmer stars that may not have been visible in live view before now will be. Re-point your camera to a dimmer star and carefully refocus (x1, x5, x10). Everything in the sky except the Moon should be as sharp as your lens is capable of at this point. For shutter speeds I use a rule of thumb of 600 divided by effective focal length (include your crop factor if applicable). When using a 17mm focal length I can expose for around 30 seconds and the stars will appear motionless when viewing the entire scene. At a 100% crop the stars will appear as very short trails. By the time I'm at 640mm (200mm x 2X extender x 1.6 crop factor) I'm down to less than 1 second for shutter speed and push the ISO up to compensate. With night sky shots in relatively dim (light pollution free) skies, your exposure level choice will determine how many stars are visible. Only the brightest stars will appear at lower exposure levels and each successive exposure level will increase the number of visable stars in the shot.