Crop Factor and Stabilization

sfoster

sfoster

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Hopefully this question isn't too stupid.. but here we go..

A moving, handheld 10mm lens is going to produce a more stabilized image than a 30mm lens.. lower the focal length, more perceived stability.

If we're dealing with a crop factor of 3x then the 10mm will have a a smaller field of view.. a field of view that matches the 30mm.

Will it have the same handheld look as a 30mm as well?

The only confusion I have here is that if I took a huge super hd image from a full frame 10mm lens and cropped out the middle, in this digital post-production crop it would have the field of view of a 30mm but the stabilization of a 10mm.. does crop factor in-camera work the same way, or is it truly identical to filming with a 30mm lens and full frame sensor?
 
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photon said:
If I understood correctly, than technically yes.
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thanks! sorry if i was talking in circles there.
put succinctly, I was asking if a 10mm with 3x crop factor will be identically shaky as a 30mm with 1x crop factor.

i read one post on a forum describing it as

you were to use a movie projector and movie screen and you projected an image so that it fit perfectly on a 12' x 8' screen and called that "full frame", then a "crop frame" would be derived by shriking the movie screen down to about 8' wide by about 5-1/3' tall but (and here's the key) without doing ANYTHING to the movie projector. Essentially that means you're projecting an image intended to fit ona 12x8' screen... but the real screen is smaller. What happens to the part of the image that doesn't fit on the screen? It just spills off the sides and is lost. That is EXACTLY what happens inside a crop-frame camera.
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and to me that sounds like the shaky wouldn't be the same
 
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thinking about this more.. typically with a long focal lens it makes background and foreground objects appear closer together.

i'm guessing you don't get this effect with a crop factor
 
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photon said:
No. Tried to use logic and apparently failed:D.
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:lol: okay thanks. i think i understand this then. was making my head spin for a minute.
anyway just having someone to talk this through with helped. i wasn't even thinking about investigating via the compression of space at first
 
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There's a final missing bit to the projector/screen example. After you attach the image to the smaller screen, you stretch it to the size of the original screen, thereby amplifying the movement - a move that covered 2" on the smaller screen would now move 6" on the 3x larger one.

Yes, it would have the same movement as the 30mm.
 
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knightly said:
There's a final missing bit to the projector/screen example. After you attach the image to the smaller screen, you stretch it to the size of the original screen, thereby amplifying the movement - a move that covered 2" on the smaller screen would now move 6" on the 3x larger one.

Yes, it would have the same movement as the 30mm.
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Thanks knightly, I would've missed that final point
What a nuanced subject this turned out to be!
 
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knightly said:
There's a final missing bit to the projector/screen example. After you attach the image to the smaller screen, you stretch it to the size of the original screen, thereby amplifying the movement - a move that covered 2" on the smaller screen would now move 6" on the 3x larger one.
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You also have to take in to account the distance of the screen to the viewer on a large screen. For a viewer up close, that 6" of movement covers more degrees of view than for someone in the back of the theater, so what's acceptable for one part of the audience may make other audience members sick.
 
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sfoster said:
okay i just googled it and got a different answer, so confusing.
http://forums.popphoto.com/showthread.php?625220-Sensor-crop-factor-and-macro-photography

they say that "neither magnification nor depth of field/apparent compression depend on the size of sensor; they are characteristics of the lens only."

are you speaking from experience here, this is very confusing to me with different answers coming up
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just when i thought i was out.. they pull me back in
From the book Cinematography - Theory and Practice by Blain Brown

Second edition, page 61
"This is a drawback of 16mm film and some high def cameras. because they often have smaller sensors, they have far more depth-of-field than 35mm film, thus making it more difficult to use focus in this way. Depth-of-field is a product of the sensor size"

Why can't I seem to find a straight answer :weird:
it's hard enough to learn all this information already, much less when i get contradicted at every turn :bang:
 
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sfoster said:
Second edition, page 61
"This is a drawback of 16mm film and some high def cameras. because they often have smaller sensors, they have far more depth-of-field than 35mm film, thus making it more difficult to use focus in this way. Depth-of-field is a product of the sensor size"
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Depth of field doesn't affect stability. Longer lens, larger sensor, wider aperture ----> shallower DOF
 
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i know the thread is titled about stability, just noting the contradiction from the quote i had posted from the other orum.

this book gives equations to figure out depth of field but sensor size does not factor into the equation.. they just kind of casually mention it then ignore it
 
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DOF is a characteristic of the lens, not the sensor size.

The confusion comes from the fact that the smaller your sensor, the wider your lens needs to be to maintain the same field of view.

So for example you can frame up the same shot with a full frame sensor at 50mm, or a super35 sensor at 30mm, or a super16 sensor at 16mm, or a 1/3" camcorder sensor at 7mm. All of these combinations will show the same image on screen, but as you have to use wider and wider lenses the DOF will increase. So while it seems like smaller sensors produce deeper DOF, the reality is it is the need to use wider lenses that is actually responsible for it.

Likewise, take all the sensors above and shoot with the same 50mm lens and the DOF will remain constant - but as the sensor size gets smaller the lens will appear more and more zoomed in. In fact the smaller sensors may appear to produce shallower DOF (although technically they don't) because they'll be zoomed in so far that out of focus items in the background will appear much larger on screen and seem softer.
 
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ItDonnedOnMe said:
DOF is a characteristic of the lens, not the sensor size.

The confusion comes from the fact that the smaller your sensor, the wider your lens needs to be to maintain the same field of view.

So for example you can frame up the same shot with a full frame sensor at 50mm, or a super35 sensor at 30mm, or a super16 sensor at 16mm, or a 1/3" camcorder sensor at 7mm. All of these combinations will show the same image on screen, but as you have to use wider and wider lenses the DOF will increase. So while it seems like smaller sensors produce deeper DOF, the reality is it is the need to use wider lenses that is actually responsible for it.

Likewise, take all the sensors above and shoot with the same 50mm lens and the DOF will remain constant - but as the sensor size gets smaller the lens will appear more and more zoomed in. In fact the smaller sensors may appear to produce shallower DOF (although technically they don't) because they'll be zoomed in so far that out of focus items in the background will appear much larger on screen and seem softer.
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I understand what you're saying, it's just crazy that this book would be straight-up lying to me.

On page 275 it says

A number of factors affect depth-of-field

Focal length of lens
Aperture of lens
Object distance. Closer the subject is to the image plane, less depth-of-field
Sensor Size
The circle of confusion selected for the situation
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you're saying it's only different because the lens changes, but it already lists lens as one of the factors and directly states sensor size as a stand alone influence of dof. your explanation seems to make sense with my understanding, i am inclined to agree with it, but wish there wasn't all this contradiction. i mean wtf blain brown, your book was not cheap

i'm trying to google this, i haven't been this confused since i tried to study perception of opposing objects traveling at near light speed

http://photo.net/learn/optics/dofdigital/

2 Using the same lens on a small-sensor camera and a full-frame camera, the small-sensor image has 1.6x LESS depth of field than the full-frame image would have (but they would be different images since the field of view would be different)

3 If you use the same lens on a small-sensor camera and a full-frame camera and crop the full-frame image to give the same view as the digital image, the depth of field is IDENTICAL
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this guy is full of shit right? what does cropping have to do with altering depth of field. i can't take an image into photoshop, crop it and have that alter the depth of field
 
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sfoster said:
I understand what you're saying, it's just crazy that this book would be straight-up lying to me.
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It's not lying, they're just taking a shortcut to the truth. Yes, sensor size will have a big impact on the DOF you'll get - but the underlying reason for that is that you'll choose different lenses for a given situation based on the composition you're trying to achieve.

3 If you use the same lens on a small-sensor camera and a full-frame camera and crop the full-frame image to give the same view as the digital image, the depth of field is IDENTICAL
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this guy is full of shit right? what does cropping have to do with altering depth of field. i can't take an image into photoshop, crop it and have that alter the depth of field
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No, he's saying it doesn't alter the depth of field compared to the image coming from the small sensor. You can crop in camera (with a smaller sensor) or crop in post and the DOF will remain the same - because it's a function of the lens.
 
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ItDonnedOnMe said:
It's not lying, they're just taking a shortcut to the truth. Yes, sensor size will have a big impact on the DOF you'll get - but the underlying reason for that is that you'll choose different lenses for a given situation based on the composition you're trying to achieve.



No, he's saying it doesn't alter the depth of field compared to the image coming from the small sensor. You can crop in camera (with a smaller sensor) or crop in post and the DOF will remain the same - because it's a function of the lens.
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Okay i really appreciate you responding here, and you've always had great answers. Plus everything you have said corresponds to my understanding on how this should work.

but in regards to his other point from before

2 Using the same lens on a small-sensor camera and a full-frame camera, the small-sensor image has 1.6x LESS depth of field than the full-frame image would have (but they would be different images since the field of view would be different)
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by him noting the field of view would be different, it sounds like if you had a stationary tripod, swapped out a lens with a full frame camera, and then with a half frame camera, the camera with a half-frame sensor would have less depth of field. so identical position, identical lens, the only thing that is changed here is sensor size and he is saying the dof is altered. making it not just purely a function of the lens
 
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In that case, the DoF is the same, but it's magnified due to the last scaling up bit I mentioned before… so the effect is exaggerated with a smaller sensor, although technically, if you take the image from the Full frame camera and blow it up 1.6x to match the crop sensor's FoV, the DoF looks the same with the same lens, it's just magnified and therefore more obvious on the cropped sensor.
 
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Exactly - remember that 'blur' is essentially just spreading detail across multiple pixels. So when you crop something and blow it up (whether via the sensor or in post) you're spreading the same blur across even more pixels which makes it look even softer.
 
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