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Old 16-07-2011, 04:28 PM
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stephenb (Stephen)
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SLR FOV question...

Can someone help me with some my maths.... In general terms, can the size (in mm) of the lens used on a 35mm print be determined by the FOV present on the print?

I know the lens used was an Olympus 35-70mm with an angle of view 63-34 deg.

Now based on this info, I have an attached 6x4 35mm film print of Crux and surrounding area from 21 years ago) which was taken with this lens. I've measured the field of view of this print off Stellarium as approximately 35 deg 42' x 22 deg 47'. I know there is some distortion on the edges, so I'm happy to call it a straight 35 deg.

Can I then assume that this lens was set to it's wide field of 70mm?

Or am I barking up the wrong tree?

Also this was a tripod shot with no tracking, but as you can see, there is a slight trail in some parts of the image only, so determining the exposure from any star trails would be misleading. But if 70mm is correct, as far as an exposure duration, I'm going to say 30 seconds. Would anyone like to hazard a guess as to the exposure time? I'm thinking the film type will be needed to make a guesstimate on exposure?

Regards,
Stephen
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Last edited by stephenb; 16-07-2011 at 07:25 PM.
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Old 16-07-2011, 10:18 PM
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mithrandir (Andrew)
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Feeding CCD Calc a 34x23 mm sensor and 55mm lens gives close to the measured FOV.

UniMap says your image is 33:13:39 by 22:49:31 but given that the constellation figures don't match the stars I'd have to agree there is some distortion so the FOV might be a bit off.

Andrew
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Old 17-07-2011, 11:56 AM
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stephenb (Stephen)
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Cheers Andrew, thanks for that.

I think I am reading the lens specification incorrectly? The "Angle of View" specified in the specs is what we would call in eyepiece terms the "apparent FOV". I am assuming that this is the "actual FOV". So by the calculations you've provided, the lens would have been my 50mm OM lens (I owned 2 lenses and one of those was a 50mm).

It sounds like CCD calc is the application to work these problems out.

Regards,
Stephen

Last edited by stephenb; 17-07-2011 at 02:41 PM. Reason: added comments
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