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- Name
- Stewart
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There was a decent pass of the International Space Station at a convenient time last night so I thought I'd try to photograph it.
I got the camera and lens set up on the tripod, then looked for a target to focus the lens on. (At 1200mm f/8 on a 7D Mk II, the hyperfocal distance is about 10km, so focusing on an astronomical object means that artificial satellites at ~500km will also be in focus.) I found a bright target in the southern sky, acquired it in Live View and then tried to get the manual focus right. But it just didn't seem to work. At 1x it looked like my target was a tiny disk, but as I went to 5x and 10x I just couldn't get the focus right: instead of a little round disk I kept seeing - or thinking I was seeing - an apparently elongated object.
Now I started worrying about the lens. Maybe something inside was out of alignment? That could be an expensive repair bill on a 600mm f/4.
But before I gave up I thought I might as well take a couple of pictures, then look at them to see if that offered any clues as to what might be going wrong. Live View at 10x is pretty difficult, not least because with a lens this big, the tiniest vibration makes the image jump all over the place. I really need to have the IS on to stabilise the image, but that means my hand is on the camera and my eye is very close to the Live View display. Much easier to take a picture and look at it from a comfortable distance. Maybe there's nothing wrong, and maybe the elongation I thought I could see was just an artefact of squinting at the display at close range through varifocal glasses.
Oh yeah. That'll be the reason.
I got the camera and lens set up on the tripod, then looked for a target to focus the lens on. (At 1200mm f/8 on a 7D Mk II, the hyperfocal distance is about 10km, so focusing on an astronomical object means that artificial satellites at ~500km will also be in focus.) I found a bright target in the southern sky, acquired it in Live View and then tried to get the manual focus right. But it just didn't seem to work. At 1x it looked like my target was a tiny disk, but as I went to 5x and 10x I just couldn't get the focus right: instead of a little round disk I kept seeing - or thinking I was seeing - an apparently elongated object.
Now I started worrying about the lens. Maybe something inside was out of alignment? That could be an expensive repair bill on a 600mm f/4.
But before I gave up I thought I might as well take a couple of pictures, then look at them to see if that offered any clues as to what might be going wrong. Live View at 10x is pretty difficult, not least because with a lens this big, the tiniest vibration makes the image jump all over the place. I really need to have the IS on to stabilise the image, but that means my hand is on the camera and my eye is very close to the Live View display. Much easier to take a picture and look at it from a comfortable distance. Maybe there's nothing wrong, and maybe the elongation I thought I could see was just an artefact of squinting at the display at close range through varifocal glasses.
Oh yeah. That'll be the reason.
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