Puzzled by 35mm equivalence
Jan 21, 2017 12:34:56 #
I took out my trusty Canon 7D camera with its 24-105mm lens to take a picture of a nearby large ship, but it would not fully "fit" at 24mm in my APS-C camera viewfinder. That should have been 38mm equivalence (X1.6) I think. No, problem I thought, I will get my Olympus OM-D E-M1 camera which has a lens that starts at 14mm (2x=28mm). But to my surprise, even less of the ship showed in the viewfinder.
What am I missing here? Does the Olympus have some setting like the Sony's to take in crop mode? Or is this simply a case of the lenses not really matching their advertised values? I have never knowingly activated any crop mode in either camera.
What am I missing here? Does the Olympus have some setting like the Sony's to take in crop mode? Or is this simply a case of the lenses not really matching their advertised values? I have never knowingly activated any crop mode in either camera.
Jan 21, 2017 12:44:49 #
The 7D doesn't have a 'crop mode'. The Canon has a crop-sensor camera with a 1.6x factor. Isn't it more likely your distance to the large ship was too close for either a 38mm or 28mm perspective? Relative to show, does the Olympus have a 100% view finder? What showed in the image when captured / replayed?
Jan 21, 2017 12:47:55 #
CHG_CANON wrote:
And/or did the ship move closer while changing cameras? ... Relative to show, does the Olympus have a 100% view finder? What showed in the image when captured / replayed?
Jan 21, 2017 12:51:31 #
Jan 21, 2017 12:53:36 #
Different aspect ratio? It looks like the EM1 is 4:3. Comparing crop factor is only valid if both cameras have an aspect ratio of 3:2.
Jan 21, 2017 12:57:36 #
The ship was stationary in dock. I was at the same spot in both instances. I took no pictures because I did not want a picture of 3/4 of a ship! Does the EM1 have a digital crop mode? If so, I will try to find it in the menus and see what the setting is at.
Jan 21, 2017 13:01:48 #
Algernon
Loc: Milwaukee, Wisconsin
It seems to me the answer is that the EM1 is a 2x crop factor and the Canon is a 1.6 crop factor. That alone explains why the two camera show different views.
Jan 21, 2017 13:11:27 #
Dragonophile wrote:
Does the EM1 have a digital crop mode? If so, I will try to find it in the menus and see what the setting is at.
Yes, it's called telconverter 2x.
It can be turned on in the menu (Menu>Camera 1) or by a button of your choice which you can assign in the menu (Menu>Gears>B Button/Dial>Button Function). If you allocate it to a button the button toggles it on and off. When it is turned on a magnifying glass icon appears at the LCD in settings display mode.
Jan 21, 2017 13:14:04 #
Algernon wrote:
It seems to me the answer is that the EM1 is a 2x crop factor and the Canon is a 1.6 crop factor. That alone explains why the two camera show different views.
You miss the point. After applying those, what should have been the smaller equivalence was actually the larger.
Jan 21, 2017 13:15:03 #
Jan 21, 2017 14:51:32 #
Thanks for all the responses. It was operator error! The teleconverter option was on. I didn't even know I had that option. When I turned it off, indeed an image seemed to recede. So, my fault and my ignorance of the camera.
Jan 21, 2017 15:49:26 #
fetzler
Loc: North West PA
The focal length of a so-called normal lens is determined by by the diagonal length of the sensor or film. You can calculate this using the formula f = SQRT( length^2 + width^2). SQRT = square root. n^2 = n squared.
For 35mm Film: f= SQRT[ 36 ^2 + 24^2) = 43mm usually rounded to 50mm for lens manufacture
For 6 x 4.5 cm film f = SQRT[60^2 + 45^2] = 75mm
For Nikon DX f = SQRT[23.6^2 + 15.7^2] = 28.3 mm usually rounded to 35mm for lens manufacture. Do the math an you will understand.
to calculate the crop factor between Nikon DX and 35mm film
43mm/28.3 = 1.52
For a DX camera with a 35mm lens the corresponding focal length for 35mm film would be 35 x 1.5 = 52.5mm A 35mm DX lens is approximately equal to a 50mm film lens. For a 6 x 4.5 cm the corresponding lens would be 75mm
For 35mm Film: f= SQRT[ 36 ^2 + 24^2) = 43mm usually rounded to 50mm for lens manufacture
For 6 x 4.5 cm film f = SQRT[60^2 + 45^2] = 75mm
For Nikon DX f = SQRT[23.6^2 + 15.7^2] = 28.3 mm usually rounded to 35mm for lens manufacture. Do the math an you will understand.
to calculate the crop factor between Nikon DX and 35mm film
43mm/28.3 = 1.52
For a DX camera with a 35mm lens the corresponding focal length for 35mm film would be 35 x 1.5 = 52.5mm A 35mm DX lens is approximately equal to a 50mm film lens. For a 6 x 4.5 cm the corresponding lens would be 75mm
Jan 21, 2017 16:41:43 #
Dragonophile wrote:
Thanks for all the responses. It was operator error! The teleconverter option was on. I didn't even know I had that option. When I turned it off, indeed an image seemed to recede. So, my fault and my ignorance of the camera.
If you shot raw the files would have come across as the normal crop. Glad I could help. I'll be honest, these are complex cameras and it's easy to inadvertently turn an option on. You should also notice an increase in image quality, now that it is not digitally cropping
Jan 21, 2017 16:46:01 #
fetzler wrote:
The focal length of a so-called normal lens is det... (show quote)
Did you read my original question? I was not asking about a math exposition. The simple answer is that somehow I triggered a menu button that activated a teleconverter enhancement So my Olympus 14mm setting was not 28mm equivalent as I expected but much more.
Jan 21, 2017 19:49:56 #
http://www.tawbaware.com/maxlyons/calc.htm
50 degrees for the 24mm
65 for 14mm at 3:2 aspect or 63 degrees at 4:3 aspect
34 degrees for 14mm with 2x teleconverter function!
50 degrees for the 24mm
65 for 14mm at 3:2 aspect or 63 degrees at 4:3 aspect
34 degrees for 14mm with 2x teleconverter function!
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