Ugly Hedgehog - Photography Forum
Home Active Topics Newest Pictures Search Login Register
Main Photography Discussion
Real Focal Length
Page 1 of 9 next> last>>
Aug 22, 2019 10:05:49   #
Imageandart
 
Does anyone know why manufacturers don't use the correct focal length on their lenses for crop sensors? Why do we have to constantly figure that a lens marked 18-200mm is in actuality a 27-300mm lens with a 1.5 crop factor?

Reply
Aug 22, 2019 10:11:24   #
agillot
 
if the lens is made for a crop sensor camera , it will be right .if for a full size sensor it will not , or older film era lenses are full size .i use them on a crop sensor camera .

Reply
Aug 22, 2019 10:14:59   #
GoofyNewfie Loc: Kansas City
 
Imageandart wrote:
Does anyone know why manufacturers don't use the correct focal length on their lenses for crop sensors? Why do we have to constantly figure that a lens marked 18-200mm is in actuality a 27-300mm lens with a 1.5 crop factor?


They do list the correct, actual focal length.
The focal length doesn't change just because it's on a different sized sensor.
Do you really "constantly figure" the FF equivalent while you're shooting?
Just look through the finder and shoot!

Reply
 
 
Aug 22, 2019 10:22:30   #
srt101fan
 
Imageandart wrote:
Does anyone know why manufacturers don't use the correct focal length on their lenses for crop sensors? Why do we have to constantly figure that a lens marked 18-200mm is in actuality a 27-300mm lens with a 1.5 crop factor?


To your first question, I think they do...

Second question; why do you need to compare? Unless you have a mixed bag of full frame, crop and old 35mm lenses, is there a need to think of equivalence?

Reply
Aug 22, 2019 10:25:52   #
MT Shooter Loc: Montana
 
agillot wrote:
if the lens is made for a crop sensor camera , it will be right .if for a full size sensor it will not , or older film era lenses are full size .i use them on a crop sensor camera .


ALL lenses are designated in 35mm film focal length terms. When mounted on any camera with a different sized sensor, the "crop factor" needs to be applied to determine its equivalent fueld of view. Yes, even lenses designed for crop sensor cameras are designated in 35mm (full frame) terms so the correct crop factor needs to be applied to them as well.
As Goofy correctly stated, just look in the viewfinder and shoot. What you see is what you will get.

Reply
Aug 22, 2019 10:27:41   #
fetzler Loc: North West PA
 
The focal length of a lens is a physical characteristic of the lens. The focal length does not depend on the film size or sensor size.

The field of view (FOV) changes with sensor size, however. A 25mm micro 4/3 lens has a similar FOV as a 50mm on a FF camera if the camera is focused to the same distancethe same distance. Using a 50mm lens on a FF camera and cropping to the size of a micro 4/3 image. Will give the same image as using a 50mm lens on a micro 4/3 camera.

Many photographers grew using 35mm cameras and thus are familiar with the images that can be taken with a particular focal length (FOV) hence the use of equivalent focal lengths.

Indeed my old 6 x 4.5 cm camera uses a 75mm lens as its "normal" lens. Its field of view was similar to a 50mm lens on a FF camera.

The normal focal length is determined by the diagonal length of the sensor. Manufactures then round to convienient numbers when making lenses.


BTW crop factor is only a convenience some and need not be used. I never used it with large format Cameras.

Reply
Aug 22, 2019 10:30:51   #
GoofyNewfie Loc: Kansas City
 
srt101fan wrote:
To your first question, I think they do...

Second question; why do you need to compare? Unless you have a mixed bag of full frame, crop and old 35mm lenses, is there a need to think of equivalence?


A 35mm Full Frame or 35mm DX lens will give the same field of view on a DX (or crop sensor) camera. If the lenses were marked with the FF equivalent and used on a DX camera it would make things even more confusing! One would be marked 35mm, the other 52.5mm. Then if you tried using them with an adapter on a micro 4/3rds camera, it would make someone's head explode!

Reply
 
 
Aug 22, 2019 10:33:27   #
Imageandart
 
Thanks for your comments.

Reply
Aug 22, 2019 10:40:02   #
GoofyNewfie Loc: Kansas City
 
MT Shooter wrote:
ALL lenses are designated in 35mm film focal length terms. When mounted on any camera with a different sized sensor, the "crop factor" needs to be applied to determine its equivalent fueld of view. Yes, even lenses designed for crop sensor cameras are designated in 35mm (full frame) terms so the correct crop factor needs to be applied to them as well.
As Goofy correctly stated, just look in the viewfinder and shoot. What you see is what you will get.


All lenses are marked for their actual focal length, no matter what format camera they are designed for. (there may be a few dumbed-down exceptions on some bridge cameras)
A 200 mm lens for a large or medium format camera will give the same field of view on a FF or crop sensor camera as a 200 designed for a full-frame or crop sensor camera.

Reply
Aug 22, 2019 13:11:36   #
speters Loc: Grangeville/Idaho
 
Imageandart wrote:
Does anyone know why manufacturers don't use the correct focal length on their lenses for crop sensors? Why do we have to constantly figure that a lens marked 18-200mm is in actuality a 27-300mm lens with a 1.5 crop factor?


Manufacturers always do show the correct focal length for their lenses - period!!

Reply
Aug 22, 2019 16:04:18   #
RWR Loc: La Mesa, CA
 
GoofyNewfie wrote:
All lenses are marked for their actual focal length, no matter what format camera they are designed for.

Of course. And that dates way back before the 35mm format was ever thought of.

Reply
 
 
Aug 22, 2019 16:20:42   #
rehess Loc: South Bend, Indiana, USA
 
Imageandart wrote:
Does anyone know why manufacturers don't use the correct focal length on their lenses for crop sensors? Why do we have to constantly figure that a lens marked 18-200mm is in actuality a 27-300mm lens with a 1.5 crop factor?

They do show actual, physical focal length.

If I put a Takumar lens {built before Asahi was using the name "Pentax"} labeled "50mm" it on my camera, will give me exactly the same view I got with the Pentax-M lens labeled "50mm" that was kitted with my first SLR in 1979 and exactly the same view I would get with a recent Pentax-DA lens labeled "50mm" that is intended for the APS-C KP camera I purchased on this most recent Black Friday.

Focal Length is a physical quality of the lens - it has nothing with the sensor it is intended for.

Reply
Aug 22, 2019 16:37:20   #
CO
 
It's interesting about focal lengths. Some manufacturers have started to produce 45mm lenses. 50mm lenses have been the traditional "normal" lens. Now Tamron, Samyang, Sigma, and Rokinon are producing 45mm lenses for full frame cameras. A focal length of 43.5mm on a full frame cameras gives about the same perspective as the human eye sees. I have the Tamron 45mm SP VC f/1.8 that I use on my Nikon D750.

Reply
Aug 22, 2019 16:42:07   #
rehess Loc: South Bend, Indiana, USA
 
CO wrote:
It's interesting about focal lengths. Some manufacturers have started to produce 45mm lenses. 50mm lenses have been the traditional "normal" lens. Now Tamron, Samyang, Sigma, and Rokinon are producing 45mm lenses for full frame cameras. A focal length of 43.5mm on a full frame cameras gives about the same perspective as the human eye sees. I have the Tamron 45mm SP VC f/1.8 that I use on my Nikon D750.
My first two 35mm cameras, both range-finder types, were constructed with 45mm lenses.

Reply
Aug 22, 2019 16:49:39   #
mwsilvers Loc: Central New Jersey
 
Imageandart wrote:
Does anyone know why manufacturers don't use the correct focal length on their lenses for crop sensors? Why do we have to constantly figure that a lens marked 18-200mm is in actuality a 27-300mm lens with a 1.5 crop factor?

It is a common mistake made by many people that the focal length somehow changes when you put a lens on a crop camera. It doesn't. The focal length indicated on the lens is the actual focal length regardless of the size of the sensor it's mounted over. It is the smaller sensor size of crop cameras, not the lens, that results in an angle of view which is different from when that same lens is mounted on a full frame camera. That is why they're called crop sensors. The resulting image is like a crop of the same image on a full-frame camera. Additionally, it makes no difference if the lens in question is one designed for full frame sensor or one designed for crop frame sensor. The focal length marked on the lens in either case is correct.

Reply
Page 1 of 9 next> last>>
If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.
Main Photography Discussion
UglyHedgehog.com - Forum
Copyright 2011-2024 Ugly Hedgehog, Inc.