Calculation for lenses

L

Luzer

Active member
Hi all

Im not exactly sure if the thread is aptly titled but I've been wondering about a few things.

I know that if a 35mm SLR lens when placed onto a 16mm film camera, theoretically, the image would look twice as big. What if a wide angle converter meant for 1/3" cameras is put onto a 35mm SLR lens?
 
Luzer said:
Hi all

Im not exactly sure if the thread is aptly titled but I've been wondering about a few things.

I know that if a 35mm SLR lens when placed onto a 16mm film camera, theoretically, the image would look twice as big. What if a wide angle converter meant for 1/3" cameras is put onto a 35mm SLR lens?
Click to expand...

Okay, slow down, man. Your terminology might be the source of confusion. A 35mm lens "seem" longer in a 16mm film camera, because the gate is smaller. That means, only a small center of the image is used, even though the image formed is big enough to extract a 35mm still from it. It works like a "digital zoom" in a way. That is very different than using a longer lens in a 35mm picture frame. Because longer lenses change the spacial relationship between foreground and background subjects, besides having a shorter DOF. So even thou a lens might "seem" longer, it isn't.

An adapter made for a 1/3" image sensor wouldn't fill the whole frame of the 35mm image, resulting in an image formed only in the central parts of the frame.
 
Ah....thanks for clarifying all that! But is there a way to calculate the size of image formed?
 
Yes, there are some calculators, most relating to FOV (Field of view) and some programns that give you a visual representation, such as PCAM and PCINE for Palm OS. so you can dial, for instance: "a person, 20 ft from a 50mm lens" and it gives you a little drawing of what the shot looks like. For most time though, we use directors finders, because there are several nuances that are best analyzed with our own eyes.

I believe there is a FOV calculator in this site:

www.panavision.co.nz

Cheers!
 
taubkin said:
Okay, slow down, man. Your terminology might be the source of confusion. A 35mm lens "seem" longer in a 16mm film camera, because the gate is smaller. That means, only a small center of the image is used, even though the image formed is big enough to extract a 35mm still from it. It works like a "digital zoom" in a way. That is very different than using a longer lens in a 35mm picture frame. Because longer lenses change the spacial relationship between foreground and background subjects, besides having a shorter DOF. So even thou a lens might "seem" longer, it isn't.

An adapter made for a 1/3" image sensor wouldn't fill the whole frame of the 35mm image, resulting in an image formed only in the central parts of the frame.
Click to expand...

I have a book with all the calculations you could ever want, just can't locate it right now. I will look up FOV and post it for you when I find that darn book! I would like to make one small correction to the above statement.
You said "Because longer lenses change the spacial relationship between foreground and background subjects,..." While in practice that may be true, technically it is not. Lenses do NOT change perspective. If I have a 35mm lens on my camera, and change to a 500, the perspective, (here meaning the relative location of objects) will remain EXACTLY the same. If the exit sign over the door was just over someone's head with the 35mm lens, it will be the same amount over their head with the 500mm. Only thing is with the 35mm we had the person from head to toe with the sign, and with the 500mm perhaps we have only the top of the head and sign. What changes perspective is camera to subject distance. And since when we go to a longer lens we usually move the camera further away, we get into the habit of saying that the "lens" has changed the perspective while it is in fact the camera distance.
Sorry, just one of those very technical type guys, and only post this because I think it would be useful info to the original poster, please don't take this as I am "correcting" anyone here. I know most of you here know a lot more than do I.
 
I think you wanted a field of view calculation. Here it is. (SD/FL - 1) x FL = FOV. Where SD is Subject Distance, FL is focal length, FF is film format, and FOV is field of view.
So with a 35mm still camera, (film measures closer to 36mm in reality) If I am going to take a photo of a 6 foot 6 inch person, (1981.2mm) and the camera will be 10 feet away, (3048mm), and I am using a 50mm lens,then (3048/50-1) x 36 = 2158.56 so I can see that I will get my full 6 foot 6 inch person in the frame, with a little room to spare. In fact, there will be about 11% of the frame free, or the subject will be filling 89% of the frame.
If you want any other calcs, let me know.
 
Sorry it took me so long to reply, didn't have email notice turned on. Yes you are correct in "portrait" mode. As I said, I am a still photogrpher, so I may do things in an unusual manner for you folks! Of course, my 36mm would still be correct if you where shooting a cruise ship and wanted to be sure you filled the frame horizontally. <;o)
 
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