And think of long focal length (so much prone to thermal focus shift) on small format film (so much demanding about proper focus). The Graphic is another thing: not enough long focus and not enough small format to show the problem, I guess. I can assure you that precise focus at infinity is a well-known issue among astrophotographers. Please also read my previous message on this same topic.
Dario ----- Original Message ----- From: "Graywolf" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, October 29, 2004 4:41 AM Subject: Re: Lunar Eclipse under way! > What are you guys shooting at? f/1.4 with a 10,000mm lens? For an example with > the 135mm f4.7 on the Graphic set to f/4.7 and infinity everything from 94 feet > to the Andromeda Galaxy is in focus (I use that lens because it is one I have > calculated). So if my focus is set anyplace between 94 feet and infinity, object > at infinity will be in focus. It is not like you don't have any depth of field > to work with when your subject is 235 thousand miles away. Even if your > hyperfocal distance is something like 10 thousand miles your DOF is far more > than enough to insure proper focus. That BTW is why autofocus is so problematic > at infinity. The system can not tell the difference between the hyperfocal > distance and actual infinity. Though as long as you are not blowing the photo up > beyond the value used to calculate the DOF infinity should still appear sharp. > > Now if you are shooting something at 20 feet with a 600mm f/4.0 lens having your > infinity mark off a 1/4mm or so is going to affect scale focusing, but it will > not at infinity you just have too much slack to work with out there. > > -- > > Herb Chong wrote: > > the infinity mark isn't actually focused for an object at infinity except at > > a specific temperature. > > > > Herb.... > > ----- Original Message ----- > > From: "Graywolf" <[EMAIL PROTECTED]> > > To: <[EMAIL PROTECTED]> > > Sent: Thursday, October 28, 2004 1:31 PM > > Subject: Re: Lunar Eclipse under way! > > > > > > > >>Ummmm..? > >> > >>Surely the moon is at infinity. I can not even begin to see how you could > > > > have a > > > >>focus problem. Autofocus problem yes, focus no. > > > > > > > > > > -- > graywolf > http://graywolfphoto.com/graywolf.html > >
