35 mm film v APS sensor

just jon

just jon

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Jonathon
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I have a old SLR and a DSLR with an APS sensor

When I look
though the view finder of my SLR then aim my camera at a window I get the whole window .

When i use my DSLR with APS sensor and try to same window from the same distance i get less of the window .

Is that because an APS Sensor is smaller
 
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Assuming you're in the same position and using a lens of the same focal length on both cameras, the effect is due to the 'crop factor' of the smaller APS sensor. You're effectively seeing a central crop, as If you'd cropped the 35mm negative centrally to the same size as the APS sensor,
 
just jon said:
Is that because an APS Sensor is
Click to expand...

An APS sensor is..... certainly it is. Well I think it is. Whether it thinks it is, I don't know...:lol: /night have to get Descartes onto this one... A table cant think, but it still is, where I think, I is there for I might be:thinking:

Am I right in thinking that there was more to this proposition than made it to diaglogue box?

Is the amount of window in the viewfinder less, because the APS sensor is.... smaller?

If so... probably.

35mm film or 'full-frame' digital has a frame size 24mm tall by 36mm wide.

Lens projects image over that viewing plane... at a certain magnification ratio, which is 'roughly' proportional to the lens length.

So, if your windows were, for the sake of easy numbers, 3.6m wide by 2.4m tall... and you stood back just far enough to get the entire window frame in your image frame... then you would have a scale of 100:1... every 100mm or 10cm of window would be represented by 1mm of image.

Now.... the APS sensor is 24x16mm... same lens will focus the 100:1 magnification down onto that image frame, but half of it would be hanging over the edge of the viewing frame. You'd STILL get 1mm if image for every 100mm of Window... but as the sensors smaller, 24mm wide, you would only 'see' 2.4m of window width not the full 3.6m.

So! Take the captured image off the sensor... and make a picture of it on a screen or on a print... for easy numbers... magnify the 'film' or 'sensor' image 6x.

Viewed for a 36x24mm frame is now 216x144.. or in old money, near as makes no odds, 8.5x5.5"...

Viewed for 24x16 frame, is now 144x96.. or 5.5x3.7" err, one print size down...

So. to get the same size prints... we use more enlargement.... 9x actually, and that would make a print from APS the same size as 6x enlargement for a 35mm frame.

Common misconception, lenses on smaller format cameras don't give more 'reach'... they simply capture less of the scene... and it is enlargement to similar size that gives the effective image magnification.

However... SLR's, Single-lens-Reflex.... the name derived from the 'reflex' or periscope mechanism by which the view-finder looks through the same lens as takes the photo.....

Nearly all SLR cameras 'mask' a certain amount of the image as seen by the film or sensor... typically around 5% give or take a couple or three.

If you have a 35mm camera with 50mm 'standard' lens, that ought to show about the same angle of view as an APS or Crop sensor Digital with a 30mm lens... but one might show the whole window in the view-finder, while the other might trim off a little wood-work, depending on the view-finder crop %.
 
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