Crop Factor - A Different Approach

[photo_chick]

So I am a mere mortal? Here I thought being able to hurl a poop filled diaper 20 feet across the room into a trash can made meant I had super human powers. Granted that is the only truly exceptional talent I have!!

I was thinking on this while I was at Wal-Mart waiting in line. Lets take the moon example. Even if it is larger in the frame the actual magnification power of the lens has not been increased. So it is not magnified at all. When you go to make a print it is merely enlarged. You really are not getting a closer view of the object.

Yes, like so many other things in my life it finally started to make sense in line at Wal-Mart. It was actually the cheap telescopes at the check out that got me thinking on it again. Stupid Wal-Mart. Making me think.

 

[MarkBarbieri]

magnifying the image after it is captured is digital zoom.

I can sort of see your point, but I don't think that is how the term "digital zoom" is typically used. "Digital zoom" strongly implies the creation of new pixels through interpolation.

You are very likely to print or display your image larger than the image on the sensor. So if you want to call it "digital zoom", then all photographers use the technique. Only the degree varies between "full frame" and "cropped."

Even if it is larger in the frame the actual magnification power of the lens has not been increased. So it is not magnified at all. When you go to make a print it is merely enlarged.

Just what is the difference between magnifying and enlarging?

I think that we all agree on the many of the core facts:
1) A "cropped" sensor does not see a magnified image, just a subset of what a "full frame" sensor would see.
2) All images captured by a sensor are "enlarged" when they are printed.

The uncertainty appears to be around what the effects of cropping and enlarging more are as compared to capturing a larger image and enlarging it less. I have tried to argue that the following two items are not different between two different "effective focal lengths".

Whether from zooming or cropping, the field-of-view is the field-of-view. The pixel quality may suffer, the effect of depth-of-field may differ, but the composition and perspective of the image is identical. Also, there is no free lunch on hand-holdability gained by capturing a smaller image and enlarging in post production. The inverse focal length rule, to the extent that it is meaningful, must take into account the crop factor...handholding a 320mm lens on a FF requires the same shutter speed as handholding a 200mm lens on a 1.6x sensor, all other things being equal.

 

[boBQuincy]

So I am a mere mortal? Here I thought being able to hurl a poop filled diaper 20 feet across the room into a trash can made meant I had super human powers. Granted that is the only truly exceptional talent I have!!

But is it a cropped or full frame trash can? Either way, yours is truly an awesome power to be reckoned with!
What does your superhero costume look like and even more importantly, what is your superhero name?

 

[photo_chick]

But is it a cropped or full frame trash can? Either way, yours is truly an awesome power to be reckoned with!
What does your superhero costume look like and even more importantly, what is your superhero name?

I am Super Diaper Flinging Mommy and my costume is an unassuming pair of pj pants with super pockets, a super bag that rivals Dora's backpack, and a faded MIckey t-shirt. I will repel evil doers with each poopie fling!

And if I took a self portrait it would be cropped, as I have a Rebel XT.

Now I do have a legitamate question in this post... Does the crop factor changing the field of view affect the EF-S lenses, or are they different because they are made for the 1:6 Canons only?

 

[Groucho]

Well, my "mere mortals", I meant those who can't look at a scene and instantly decide what, say, a 100mm "frame" will look like, and furthermore, how much of that the crop factor will remove.

I can do poopy diapers pretty effectively too but I generally don't throw them, the consequences would be dire if I missed!

As for digital zoom, I'd recommend never using it - you'll get as good and almost certainly better results by resizing it yourself on your PC.

I think part of the problem is that manufacturers have sold consumers on the idea that megapixels are equivalent to film size - like how there used to be 110, APS, 35mm, medium format, even disc film... and the bigger the film, the higher the quality.

In reality, it's all the sensor, and the megapixels are just like what size you get your prints. A higher mp camera is like getting all your photos printed in large size.

Anyway, if you think about the difference in physical size between a 35mm sensor and the usual APS-sized sensor in most DSLRs, that should help visuality the crop factor. (Similar to 0bli0's illustration.) Again, just picture the edges being removed.

 

[boBQuincy]

I am Super Diaper Flinging Mommy and my costume is an unassuming pair of pj pants with super pockets, a super bag that rivals Dora's backpack, and a faded MIckey t-shirt. I will repel evil doers with each poopie fling!

And if I took a self portrait it would be cropped, as I have a Rebel XT.

Now I do have a legitamate question in this post... Does the crop factor changing the field of view affect the EF-S lenses, or are they different because they are made for the 1:6 Canons only?

Yow, evildoers beware!

The EF-S lenses are still measured in true mm of focal length and will still exhibit the crop factor. I have a Canon 10-22 EF-S, at 10mm with my 30D it has the viewing angle of a 16mm on a full frame.

 

[jann1033]

I have noticed some confusion with regards to what the crop factor does to a lens, and have a new approach on how to relate to crop factors, one that may be more intuitive than what we often read.

With a wide angle lens the primary concern is field of view. Here it is convenient to redefine the focal length in 35mm/fullframe terms since that is a good way to imply what the field of view would be. If we mount a 24mm lens on a 1.6x camera we can expect it will give approximately the field of view of a 38mm. If we are looking for a really wide angle we know we will have to spring for something under 18mm.

Where this equivalency doesn't work as well is at the long end. Here field of view is not much of an issue, it is already small and 1.6x less may not be important. In many cases the lens is not as long as we would like anyway and our subject only covers a small area of the viewfinder, cropped or not. What can really be considered misinformation is equating a 200mm to a 320mm. The 200 on a crop camera only gives the field of view of a 320, but with a long lens what is really important is the magnifcation, and the crop factor does not change the magnification at all. An image of the moon projected on the sensor will be the same size with a given lens, no matter what camera it is mounted on.

So the first point is: the *only* thing that changes when moving a lens from a full frame camera to a crop camera is the field of view. The second point is that field of view is often not the most important issue when using a long lens. Magnification is generally the main reason for using a long lens and magnfication does not change with a crop camera.

To reduce confusion I prefer to consider lenses as whatever the focal length actually is, and just realize that 24mm is not very wide on a 1.6x camera.

Right or wrong, I expect to hear more about this, and that's what makes this board so good!

i don't even need the alchoholic beverages to agree ...good way to put it...and am shocked at how many camera salespeople say it makes it the "same as" the larger focal length ...now will read the other 24 posts for no doubt alternative views

ok read them , a couple comments

a) if you make sure and securely fasten the velro like tabs it is perfectly safe to throw poop filled diapers great distances , unless someone mistakenly steps into that field of view post toss and gets it in the face...then great harm could be inflicted on the tosser due to outraged unintended target, divided by the speed by which the tosser's feet accelerate after initial contact of diaper. crop factor does not apply in this case but substitute an "a" in crop and that crop factor is multiplied 10x per square foot of contact area. anecdotal evidence not scientifically tested

b) imo as a submortal species, the enlargement is another good way to mentally picture it....in the olden days when i used an actual enlarger to make a photo bigger, only the size changed and due to the size change the larger it got the less sharp it would appear which happens when i crop more than my present lens allows, it gets blurry since i'm not really taking a photo with a 320 lens, i'm taking it with a 200 lens..it looks larger/closer but isn't any more detailed. any loss of sharpness could not have anything to due with lens shake, cause i never shake

c)now i am wondering what a teleconverter would throw into the mix since it "supposedly" is actually magnifying it or is it really just enlarging it? ie would it show more detail than a 200mm lens( no matter what the crop factor) or just enlarge that 200mm photo to 280mm( or what ever, figuring in crop factors, time of day, hair color, gravitational pull etc etc etc)

 

[MarkBarbieri]

Just to be clear, diapers are not impacted by the "crop factor." For diapers, you use the crap factor."

 

[ukcatfan]

Just to be clear, diapers are not impacted by the "crop factor." For diapers, you use the crap factor."

I really hope I never come across an Olympus baby. I do not even want to think about that with a 2X factor!

Kevin

 

[photo_chick]

I really hope I never come across an Olympus baby. I do not even want to think about that with a 2X factor!

Kevin

My youngest had a bit of shutter lag, and his files were always very compressed. This resulted in him frequently regurgitating RAW data.

 

[jann1033]

maybe his aperture was to narrow ? granddaughter has usually been the opposite, very large files. and i wish she would start using the "creative" mode instead of the "auto" side of the dial.

 

[ukcatfan]

maybe his aperture was to narrow ? granddaughter has usually been the opposite, very large files.

You don't want an aperture that is too wide b/c with that you get a narrow DOF and that can just be messy. DD's DOF was too narrow once to the point of needing a hose down in the shower!!!

Kevin

 

[photo_chick]

This is indeed a very different approach to the crop factor!