7d crop factor confusion

T

tommyo

New member
Hi all, first post here. first let me thank everyone on this forum for their wonderful contributions, i have been following for a while and i wouldnt be able to figure anything out without all the knowledge that is accessible on this site so thanks.

what thing i'm a bit confused about that i can't quite figure out why some crop factor things aren't working out for me.

so i have a 7d, and i got the stock 18-135 and recently picked up the tamron 17-50vc and the EF 50mm 1.8. now because the 50mm should have a 1.6 crop, it should look like an 80mm on my 7d. So when i set the 18-135 to 80, the field of view should be equivalent, correct? unless i'm doing something way off the EF50 is wider then the 18-135 at 80. i also was messing with some canon EF 17-40L glass where my tamron made for an APC-S sensor should be pretty substantially wider right? the canon should be like a 26mm.

can anyone clear up my confusion. thanks
 
what he said. 50mm on your 18-135mm will be equal to your EF50mm.

a 50mm APSC lens is STILL 50mm even though the FOV is "equal" to 80mm on full frame
 
The "crop factor" is a notion that should be sent straight back to the hell from whence it came.

A millimeter is a millimeter is a millimeter. Look at your 18-135 lens, and zoom it all the way out to 18mm. Then put on that 17-50 and zoom it out to 17mm. They should look pretty close to the same, because 18mm is almost the same as 17mm.

Zoom the Tamron to 50mm, and then zoom the 18-135 to 50mm, and compare, and guess what -- they're the same.

The "crop factor" is a "crap factor" that just confuses people and does infinitely more harm than good.
 
From 1930 odd when leica started the craze for using 35mm film in a landscape format in still cameras until 1999 odd when the first digital still cameras came about 35mm still photographers had been subjected one field of view for a given focal length

It is not suprising, therefore, that these first 'small chipped' digital cameras had what was widely described as a crop factor by stills photographers

Of course for this duration cinematograohers had been running thier 35mm film through the cameras in in a 'portrait' manner, rarely did the two comunities swap lenses - or maybe even talk !

Nowadays both still and motion digital cameras have chips of all sizes so the phrase crop factor is indeed somewhat stupid

Field of View is wider when you have less mm or a larger chip or both

Makers of phones and compact digital camera confuse the situation even more by refering to 'equivilent field of view' where the dont tell you the focal lenght of the lens on thier device but equate it to the field of view for a 35mm 'full frame' stills camera

18mm is very wide on a 35mmFF chip camera, kind of wide on a film motion camera and almost tele on a 1/3 inch camera or mobile phone ...

S
 
Thank you for all your responses guys. This is sort of disturbing my whole thought about this, haha, i'm still unclear. It was my impression that the rear element of whatever you would call it for a FF lens is larger then APS-C and therefore FF on APS-C would have a narrower FOV and so thats why I thought my 50EF would look like my 80EFS, bc the smaller sensor wouldn't see the whole picture the lens sees.

But obviously your right all my lenses have the same FOV whether its FF lens or EFS lens, but I just don't understand why. What then is the advantage of an APS-C lenses? simply for wider view, or it is cost? What does an APS-C lens do for me that a FF lens won't on my 7d? If it just a wider view then should I always buy FF for my telephoto?

So crop factor is more a term for people used to 35mm that move to smaller sensor cameras and dont know what the lenses mean?

Any insight anybody can continue to provide I would really appreciate.
 
APS-C lenses only cover the smaller frame. They won't illuminate the whole full frame. So APS-C lenses can be cheaper, wider, and faster, because they don't have to work as hard. A full-frame lens and an APS-C lens will deliver the exact same field of view on the APS-C camera, but if you put the APS-C lens on a full-frame camera you'll get a big massive vignetting circle all around the frame.

As for why the crop factor exists, once upon a time everyone shot on the same format size (35mm still film) so when new formats were introduced, people wanted a way to easily compare. But I think they went around it in a very confusing way. The crop factor has *nothing* to do with the lens, yet everyone seems to want to believe that a 50mm "becomes" an 80mm.

It doesn't. 50mm = 50mm = 50mm. A 50mm APS-C lens, and a 50mm full-frame lens, will deliver an identical picture (on an APS-C camera). Even on a full-frame camera, they'd have an identical picture, except that the APS-C lens would have a big black vignetting circle on it, but everything within the circle would look exactly the same as it does on the full-frame lens.

If you put a 50mm lens on a 1.6x crop camera, and an 80mm lens on a "full frame" camera, you would have the same field of view. But if you put those cameras in the same spot and shot a still life, would you get the exact same photo? No you would not! The field of view would be the same, but the perspective and depth of field would be different!

What happens is that your sensor is smaller, so it only sees a smaller portion of what the lens is relaying. Imagine taking a photo on a full frame camera, and then using scissors to cut off the edges of the full-frame picture, "cropping" it down to the central 60%. That's what the smaller sensor does.
 
It looks different on a non crop camera vs crop camera. On a 5d or 1ds with a full frame sensor a 50mm will look like a 35mm lens does on a 7d. Take your 7d into a camera store and try it.
 
The image looks the same but with the crop camera you only get a crop of the 'full' image

in perspective, DOF the images are the same

so its different but the same

work that one out

S
 
visugeek said:
It looks different on a non crop camera vs crop camera. On a 5d or 1ds with a full frame sensor a 50mm will look like a 35mm lens does on a 7d. Take your 7d into a camera store and try it.
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Of course it does. But it's not the lens that's changing, it's the sensor.
 
It seems like the biggest audience for these DSLRs is the people coming from DVX100, HVX200, HPX500 and shooting 35mm stills. It is easier to visualize what field of view you will get based on thinking in terms of crop factor since shooting on 35mm is so far out of most people's league in terms of budget.
 
saneproductions said:
It seems like the biggest audience for these DSLRs is the people coming from DVX100, HVX200, HPX500 and shooting 35mm stills. It is easier to visualize what field of view you will get based on thinking in terms of crop factor since shooting on 35mm is so far out of most people's league in terms of budget.
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That is, in part, what makes the whole crop factor issue so frustrating to me. Most of the people who need to use it don't regularly use a 35mm Full Frame camera, so the comparison is useless.

It would be like having a "crop speed" for walking in comparison to flying an airplane - it would give you a way to relate the two, but how many of us have a good idea what flying is actually like in the first place.
 
Barry_Green said:
What happens is that your sensor is smaller, so it only sees a smaller portion of what the lens is relaying. Imagine taking a photo on a full frame camera, and then using scissors to cut off the edges of the full-frame picture, "cropping" it down to the central 60%. That's what the smaller sensor does.
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What a great explanation!
 
So if im taking a photo with a 7D using an 85mm full frame lens will I get the same type of background blur as if i used the lens on a 5D? only the zoom appearance changes but not the blur?

Because originally I was thinking that a full frame 85mm would act as a 135mm on my 7D and give me even more blur while taking a portrait of someones face but the way Barry explains it is seems not to be so.
 
Lucas 7D said:
So if im taking a photo with a 7D using an 85mm full frame lens will I get the same type of background blur as if i used the lens on a 5D? only the zoom appearance changes but not the blur?

Because originally I was thinking that a full frame 85mm would act as a 135mm on my 7D and give me even more blur while taking a portrait of someones face but the way Barry explains it is seems not to be so.
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If you take it from the same spot (getting a smaller field of view) the blur will be the same

if you move back to get the same field of view you will be focussed nearer to infinity and have less blur

for a given aperture and field of view you get more blur with a larger chip

S
 
I don't know why some get bent out of shape about talking about the crop factor.

I see both points, and the concern, if one was to be mentioned, is more one of what I will need in a given area. For example, about 10 years ago, I shot a lot of 35mm in NewYork covering fashion. In some venues, we had to let everyone in the building first, and then the cameras would be at the exit shooting in. It was so packed, but in most cases, the 28mm would cover the wide shots.

Now if I were to go back and shoot the same thing, the crop camera would not allow me to do so with that same 28mm. So knowing what I needed, and how much of a "Crop factor" the camera did to the image, is very helpful.
Knowing that I use to use a 28mm, and that to shoot in the same venue to get the same coverage, I need to just multiply by 0.625 to pick the lens needed for the same venue.

For many, it is not one of perspective, but one of coverage.
Afterall, you have two types of WIDE, either fish eye, or not.
Beyond that, your picking your wide shot for coverage.

For me, at least, when I pick something wider than 50mm, I do so for coverage.
Anything longer than 50mm, I pick for perspective.

All this being said, for me, the crop factor is an issue for picking my wides, not so much for the long lenses.
 
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Thanks everyone for your replies. I have a much better understanding of it now.
Barry your books have been a great tool to me while shooting, thanks again.
 
I figured I would bump this instead of making my own, and I hope I can verbalize this question:

So a 200mm lens on a 7d would be the equivalent of a 320mm lens on a 5d, as in they would both have the same field of view. Now if you took that 200mm lens and put it on a 5d some central part of that image would be the field of view that the 7d provided with the same 200mm lens. All other things being equal, which image is better: the slice of the 5d's image that is equivalent to the field of view of the 7d's sensor, or the 7d image created with the 200mm lens?

It seems like the images are equal, right? The lens on the 7d just spills all that extra image off the sides of the sensor, where the 5d still has sensor to go and picks it up.
 
Scott Lovejoy said:
I figured I would bump this instead of making my own, and I hope I can verbalize this question:

So a 200mm lens on a 7d would be the equivalent of a 320mm lens on a 5d, as in they would both have the same field of view. Now if you took that 200mm lens and put it on a 5d some central part of that image would be the field of view that the 7d provided with the same 200mm lens. All other things being equal, which image is better: the slice of the 5d's image that is equivalent to the field of view of the 7d's sensor, or the 7d image created with the 200mm lens?

It seems like the images are equal, right? The lens on the 7d just spills all that extra image off the sides of the sensor, where the 5d still has sensor to go and picks it up.
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You've got the concept. However, both images are the same for the same lens. The only variable is the sensor. The 5D sensor is less dense than the 7D sensor. If you compared only the center cropped region, the 7D sensor will have 18MP worth of data while the equivalent crop of the 5D will only have ~10MP. If the lens can't resolve more than 10MP, then both images will be more or less equal. However, if the lens can resolve more than 10MP, the 7Ds image will contain more valid data.
 
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