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07-12-2010, 06:20 AM   #1
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Film Plane/Sensor Face

I'm currently using a Model K110 and a K100D Super.

Were on these camera bodies would represent the film plane or the sensor face?

The old 35mm cameras usually had these reference planes marked the body.

Thanks
Bert

07-12-2010, 06:27 AM   #2
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45.46mm back from the lens mount.
07-12-2010, 06:31 AM   #3
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Film Plane/Sensor Face

Wheatfield,

Thanks for the speedy reply, greatly appreciated.

Bert
07-12-2010, 08:39 AM   #4
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QuoteOriginally posted by Wheatfield Quote
45.46mm back from the lens mount.
Thanks for the info. I also was wondering this.

07-12-2010, 09:52 AM   #5
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You can also see the sensor directly if you put the camera in sensor cleaning mode (which flips the mirror up).

BTW, is there a reaono you're wondering?
07-12-2010, 03:36 PM   #6
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The K-7 has a sensor plane reference mark on the top plate to the right of the LCD. These reference marks started to disappear from cameras in the 1970s. My Ricoh Singlex TLS has one as does my Mamiya/Sekor 1000 DTL (both about 1969-70). My Pentax KX (1976) does not.


Steve
07-15-2010, 07:49 AM   #7
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Stevebrot,

Am trying to set these cameras up to check the front and rear focus.

I thought the more accurate the camera was set-up the better the results would be.

Thanks for your interest, any further input would be greatly appreciated.

Bert
07-15-2010, 09:32 AM   #8
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I can't imagine any valid way of testing focus that would care in the slightest where the sensor plane is.

07-15-2010, 11:10 AM   #9
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QuoteOriginally posted by brieck Quote
Stevebrot,

Am trying to set these cameras up to check the front and rear focus.

I thought the more accurate the camera was set-up the better the results would be.

Thanks for your interest, any further input would be greatly appreciated.

Bert

I think maybe you wanted to direct your comment to another user. I agree with Marc, however in wondering how you would use the sensor plane in a focus test.

As for how the index mark has been traditionally used...That one is fairly easy. For macro work, knowing the exact distance and the focal length allows calculation of the size of an object being photographed.


Steve
07-15-2010, 11:45 PM   #10
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I believe that knowing the location of the sensor plane helps with controlling parallax effects with doing panoramic shots. If you had a camera that had the mounting point offset from the film/sensor plane, if you snapped a panorama, you could have double images as the view would shift through the movement.

Software has helped this process quite a bit over the years.
07-16-2010, 06:51 AM   #11
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QuoteOriginally posted by smigol Quote
I believe that knowing the location of the sensor plane helps with controlling parallax effects with doing panoramic shots. If you had a camera that had the mounting point offset from the film/sensor plane, if you snapped a panorama, you could have double images as the view would shift through the movement.

Software has helped this process quite a bit over the years.
Actually, you need to know where the rear nodal point of the lens is, as you need the camera to rotate around that for perfect panoramics.
In practice it isn't that big a deal though.
07-16-2010, 07:04 AM   #12
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QuoteOriginally posted by stevebrot Quote
As for how the index mark has been traditionally used...That one is fairly easy. For macro work, knowing the exact distance and the focal length allows calculation of the size of an object being photographed.


Steve
except that this is only correct for a simple lens, not the complex optics of today.

It is probably much more accurate to know the subject to front element distance, and focal length than the focal plane location and focal length.

THis is especially true for true telephoto lenses, and recall telephoto by definition is not a lens longer than 50mm, but a lens with an effective focal length that is longer than the physical length of the lens.
07-16-2010, 08:09 AM - 1 Like   #13
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On the K20D, ~45.5 mm from the lens mount (the nodal point for pano shots) is at the back of the flash shoe. The center of the tripod socket is ~38mm from the mount, so some sort of adapter (I made a cheap one from angle brackets etc) is needed to fix tight pano parallex problems. I'll echo the above -- with modern optics, I don't see other significant operational reasons for knowing where the sensor plane is. But maybe I'm just uninspired.
07-16-2010, 09:16 AM   #14
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QuoteOriginally posted by Wheatfield Quote
Actually, you need to know where the rear nodal point of the lens is, as you need the camera to rotate around that for perfect panoramics.
In practice it isn't that big a deal though.
Of course! I forgot about the way that the rays would cross as being the pivot point.
07-16-2010, 08:12 PM   #15
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QuoteOriginally posted by Lowell Goudge Quote
except that this is only correct for a simple lens, not the complex optics of today.

It is probably much more accurate to know the subject to front element distance, and focal length than the focal plane location and focal length.

THis is especially true for true telephoto lenses, and recall telephoto by definition is not a lens longer than 50mm, but a lens with an effective focal length that is longer than the physical length of the lens.
Ummmm...that is interesting.

I was basing my comment on the closeup tables that were included in the instructions for Pentax-brand bellows. Focal plane to subject distance was one option for determining magnification using the table. A different table was supplied for each focal length. (See http://www.pentaximaging.com/files/manual/Auto_Bellows-M__Slide_Copier-M.pdf)


Steve
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