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SPC900 on a Canon 600mm prime

Photosbykev

By Photosbykev
in Imaging - Discussion

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Photosbykev

Photosbykev

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Following the purchase of a handful of SPC880 and reflashing them to the 900 firmware I've manage to mount one on the rear of a Canon 600mm f4L prime lens and damn it gives some serious magnification. At first I thought I had dirt all over the sensor but when I moved the camera I realised they were small dirt marks on the wall lol

Can someone verify my numbers I think using the 1/4" sensor the new focal length is about 6500mm with a FoV of about 0.3 degrees.

This is the view captured at about 6-7 metres, not exactly a starfield but at least I know it works ok :)

Cratlerlet.bmp

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Photosbykev

Photosbykev

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Hi Kev,

Re the focal length. If you're using the lens with just the camera, the focal length stays at 600mm?? I don't think it matters what the chip is.

Dave.

The focal length of the Canon 600mm is based on using a 35mm film format. So you are correct, the actual FL doesn't magically change. What does change is the field of view (magnification) and the effective FL of the lens if you use a smaller sensor than the lens was designed for.
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davew

davew

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Yep, know what you mean.

This is a topic that ran and ran a few years ago. The reason we use " Effective " focal length is because the camera makers thought the public couldn't understand the narrow field of view of the smaller cameras. They were probably right.

If you used a telescope and put differing camera chips on it you wouldn't even consider the focal length, just the field of view.

The truth is, I can't remember the formula for field of view so have to waffle :)

Dave.

Edit. I'd love to see what a 285 chip could do with it wide open.

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Photosbykev

Photosbykev

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Yep, know what you mean.

This is a topic that ran and ran a few years ago. The reason we use " Effective " focal length is because the camera makers thought the public couldn't understand the narrow field of view of the smaller cameras. They were probably right.

If you used a telescope and put differing camera chips on it you wouldn't even consider the focal length, just the field of view.

The truth is, I can't remember the formula for field of view so have to waffle :)

Dave.

Edit. I'd love to see what a 285 chip could do with it wide open.

The video was shot with the aperture at f4 which is the aperture the lens defaults to when it is not coupled to a DSLR. It is possible to force an aperture change but the lens is very sharp wide open :) If I knew what a 285 chip I might be excited lol

edit: I'm now drooling over the QHY cameras, damn you ! :icon_eek:

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Photosbykev

Photosbykev

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Just one caution ... the Canon supertele lenses seem to be a bit prone to changing focus with temperature ... doesn't matter when used with an autofocus camera, of course, but the focus drift can easily bloat stars.
Thank you Brian, with all the glass inside it doesn't surprise me too much.
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