New guy with a stupid? question..

Drano

Hi, found this site today and spent a few hours perusing. Seems like a lot of friendly, knowledgable folks so I thought I'd say hello and jump right in with a question..
I've been trying to wrap my noodle around the whole 1.6 crop factor associated with some digital sensors. I understand that it affects field of view, i.e. a 100mm lense on the 1.6 sensor is roughly equivalent to the FOV of a 160mm on a 35mm. My question is: while the FOV may be equivalent, is the actual image seen the same for both? In other words, will a picture taken with a 100mm on a 1.6 look the same as one taken at 160mm with a 35mm format? I'm thinking they would not, but everything I read indicates that they are identical. Logically, to me, it seems that the 100mm @ 1.6 would have the same FOV as the 160mm @ 35mm, but the image produced with the 160mm would appear closer, with more detail, etc..:scratch I'd appreciate any insight (please use small words..)
From that question you can safely assume that I'm pretty much a beginner when it comes to anything other that point and shoot. I look forward to listening in and seeing what there is to learn, this photography stuff seems fun so far :thumb

Cheers!

LiquidOps

Drano wrote:

Hi, found this site today and spent a few hours perusing. Seems like a lot of friendly, knowledgable folks so I thought I'd say hello and jump right in with a question..
I've been trying to wrap my noodle around the whole 1.6 crop factor associated with some digital sensors. I understand that it affects field of view, i.e. a 100mm lense on the 1.6 sensor is roughly equivalent to the FOV of a 160mm on a 35mm. My question is: while the FOV may be equivalent, is the actual image seen the same for both? In other words, will a picture taken with a 100mm on a 1.6 look the same as one taken at 160mm with a 35mm format? I'm thinking they would not, but everything I read indicates that they are identical. Logically, to me, it seems that the 100mm @ 1.6 would have the same FOV as the 160mm @ 35mm, but the image produced with the 160mm would appear closer, with more detail, etc.. I'd appreciate any insight (please use small words..)
From that question you can safely assume that I'm pretty much a beginner when it comes to anything other that point and shoot. I look forward to listening in and seeing what there is to learn, this photography stuff seems fun so far

Cheers!

First of all, Welcome

Second of all, I think that is a great question. I do not have the answer for it, but would love to hear from some of the more knowledgable peeps here.

Now post some pictures!!!

Steven

wxwax

Welcome drano! Not a stupid question at all, I think the whole crop factor thing is surrounded in controversy.

I'm no expert, but I think the answer is that both images would be identical, depending upon the resolution of the camera's sensor. I think the raging discussion is really a matter of semantics. But I could be wrong, I'm not very technical. :hide

GREAPER

I also could be wrong as well, but I believe they would be "nearly" identicle.

The crop size, or the composition, would be identicle, but due to the difference in the distance form the lens element to the recording medium, I think there would be a slight difference in DOF. (depth of field)

Mitch

Basicly no difference.

I don't remember where, but I read an article some time ago on the subject. Two pictures one shot with a fisheye and the other a 100mm ( I think). Center crop from fisheye to equal 100mm field of view. Same pic.

Now the kicker. Rule of thumb - 1/focal length = slowest hand held shutter speed for 35mm. Right. So now is it 1/(focal length * factor)?

So the hand held speed for a 100mm lens with a 1.6 factor would be 1/160.

Something to think about.

Mitch

Mitch

I was just sitting here thinking about the crop/[font=&quot]magnification factor. I currently own 3 wide angle lenses. They are: 75mm, 50mm, and of course 17-40 zoom. What makes any one of these a wide angle lens? I am sure there will be people that read this and not believe that a 50mm lens is a wide angle let alone the 75mm.

What makes a lens a wide angle is image circle. In other words how big of an area will the lens spread the light inside the camera. Ok...yes it does have a little to do with the size of the light collection medium, but only in realizing the [/font][font=&quot]potential of the wide angle not in the lens being a wide angle.

The 75mm is for my 4X5, the 50mm the blad, and 17-40 for the 10D. All are wide angle lenses and act as such used on the correct format.

I remember some of the hype for the 1/2 frame 35's. You can get twice as many pictures on a roll of film and double the focal length of your lenses.

IMHO there is too much concern about the crop factor. Use the equiptment you have to the best of your ability, shoot more and improve your ability.

Just my 2 cents worth.
[/font]

wxwax

Mitch, it can make quite a bit of difference when you want to shoot wide for landscapes. Andy and his 1Ds is at quite an advantage over David and his 20D. Andy gets an image that's 60% wider. That's significant in anyone's book.

I see your point though. I remember Marc Muench talking about 100 mm lenses being wide on his large format camera. So it is all relative.

DavidTO

wxwax wrote:

Mitch, it can make quite a bit of difference when you want to shoot wide for landscapes. Andy and his 1Ds is at quite an advantage over David and his 20D. Andy gets an image that's 60% wider. That's significant in anyone's book.

I see your point though. I remember Marc muench talking about 100 mm lenses being wide on his large format camera. So it is all relative.

Ah, but Andy can't use the 10-22 on his 1D!

'Course he's got a 20D, too

Mitch

wxwax wrote:

Mitch, it can make quite a bit of difference when you want to shoot wide for landscapes. Andy and his 1Ds is at quite an advantage over David and his 20D. Andy gets an image that's 60% wider. That's significant in anyone's book.

I see your point though. I remember Marc Muench talking about 100 mm lenses being wide on his large format camera. So it is all relative.

Yes is a huge difference, but...if you own a 20D does it really matter what the corp factor is for any lens? I say no. Now if you own a 1Ds and a 20D, like some people, you might be able to make a case.

That's all I'm saying. Oh in addition to that "improve you ability" stuff I should have added "and buy more equiptment"

wxwax

Mitch wrote:

Yes is a huge difference, but...if you own a 20D does it really matter what the corp factor is for any lens?

Sure it does. That's why Canon made the 10-22 for the 20D crowd but not for my body, dammit! :pissed

NHBubba

Pardon me while I dump my brain here in no particular order:

Isn't aperture (and therefore DOF) effected? The aperture is measured relative to the focal length of the lens. However f/11 is always the same size (diameter) for a given lens. So if the effective focal length is now 1.6x as long, isn't the effective f-stop now ... let's see, f/x = y, f1 * 1.6 = f2.. y remains unchanged, so f1/x1 = f2/x2 and so x1 * 1.6 = x2 ... So the effective f-stop is actually 1.6x what it was, no? This means that that fancy 135/2 is effectively a 216/3.2, no?

So that's something the FF guys have over us as well, the ability to shoot an extra shallow DOF at will!

I think I've proven this to myself in practice a few times when going back and forth between my G3 (w/ it's f/2 lens) and my old Pentax MF film rig w/ 50/2 mounted. Everytime I pick up the Pentax I start shooting at f/2 and thinking nothing of it. Then I get the film back and NOTHING is in focus but a very very small section of the subject! Doh!

ubergeek

Crop factor, aperture, DoF, etc.

NHBubba wrote:

Isn't aperture (and therefore DOF) effected? The aperture is measured relative to the focal length of the lens. However f/11 is always the same size (diameter) for a given lens. So if the effective focal length is now 1.6x as long, isn't the effective f-stop now ... let's see, f/x = y, f1 * 1.6 = f2.. y remains unchanged, so f1/x1 = f2/x2 and so x1 * 1.6 = x2 ... So the effective f-stop is actually 1.6x what it was, no? This means that that fancy 135/2 is effectively a 216/3.2, no?

Actually no. The focal length of the lens has not changed, nor has the aperture. The lens still produces exactly the same image--the only difference is that the camera crops the image, in this case to a size 1.6x smaller than a 35mm film frame. So a 50mm f/1.4 is still a 50mm f/1.4, but the crop produces a field of view equivalent to what an 80mm lens would have produced on a 35mm film frame.

So that's something the FF guys have over us as well, the ability to shoot an extra shallow DOF at will!

Now we're talking about something different than field of view. Depth of field is related to the actual focal length--so while a 50mm lens on a 1.6x-crop camera will produce a certain depth of field for a given aperture, an 80mm lens on a full-frame camera will produce the same field of view, but with less depth of field at that same aperture.

I think I've proven this to myself in practice a few times when going back and forth between my G3 (w/ it's f/2 lens) and my old Pentax MF film rig w/ 50/2 mounted. Everytime I pick up the Pentax I start shooting at f/2 and thinking nothing of it. Then I get the film back and NOTHING is in focus but a very very small section of the subject! Doh!

What you've found is consistent with the above--your G3 has a 7.2-28.8mm lens. Its "50mm-equivalent" setting has an actual focal length of about 10mm, and since depth of field is related to focal length, the depth of field is much deeper for a given aperture than with your Pentax, which has an actual focal length of 50mm.

Cheers,
Jeremy

erich6

The wide-angle really is defined by the sensor format and the focal length (not the aperture). The sensor is a field stop which defines how wide the field-of-view is. The closer the sensor is to the lens aperture (short focal length), the wider the projection of each pixel on the scene.

Things do get pretty quircky when it comes to depth-of-field for different formats and different lenses. The problem is that depth-of-field is a subjective measure of how sharp the scene looks so it's going to be influenced by your perspective. Here's an excerpt from an article by Bob Atkins on Photo.net:

"

1. For an equivalent field of view, the EOS 10D has at least 1.6x MORE depth of field that a 35mm film camera would have - when the focus distance is significantly less then the hyperfocal distance (but the 35mm format need a lens with 1.6x the focal length to give the same view).
2. Using the same lens on a EOS 10D and a 35mm film body, the 10D image has 1.6x LESS depth of field than the 35mm image would have (but they would be different images of course since the field of view would be different)
3. If you use the same lens on a EOS 10D and a 35mm film body and crop the 35mm image to give the same view as the digital image, the depth of field is IDENTICAL
4. If you use the same lens on an EOS 10D and a 35mm film body, then shoot from different distances so that the view is the same, the 10D image will have 1.6x MORE DOF then the film image.
5. Close to the hyperfocal distance, the EOS 10D has a much more than 1.6x the DOF of a 35mm film camera. The hyperfocal distance of the EOS 10D is 1.6x less than that of a 35mm film camera.

"
You can read the rest at http://www.photo.net/learn/optics/dofdigital/

Also, check out my post http://www.dgrin.com/showthread.php?t=11015

Erich

GREAPER

Thats what I said.