this post was submitted on 26 Oct 2023
1 points (100.0% liked)
Photography
24 readers
1 users here now
A place to politely discuss the tools, technique and culture of photography.
This is not a good place to simply share cool photos/videos or promote your own work and projects, but rather a place to discuss photography as an art and post things that would be of interest to other photographers.
founded 1 year ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
A 50mm lens at F2.8 on a crop sensor camera will give you exactly the same depth of field and light as a 50mm lens at F2.8 on a full frame.
The difference is that the crop sensor uses less of the image circle so appears to be a narrower lens. This is where the crop factor comes into effect. The crop factor was invented in the early days of professional digital cameras, when there were no sensors that covered the full frame at the time.
It is a concept invented so that professional photographers who had years experience using 35mm film cameras could compare the field of view on the new digital cameras and select the correct lens.
After years of using the 35mm lenses they could look at a scene and know which lens they needed, but with the new smaller sensor digital cameras this would result in to cropped an image so the crop factor was used to make it easier to work out that they needed a 25mm lens when their eye's told them a 50mm full frame lens was needed.
So now that 25mm lens gives them the field of view of the 50mm, but it's still a 25mm and as the short focal length you use the deeper the depth of field you get for a given aperture, you would still have the depth of field of a 25mm at f2.8.
This is when they realised that the crop factor would also work in the description of the depth of field. So this meant that they would say that a 25mm f2.8 is the equivalent of a full frame 50mm f5.8 – but this only equated to the depth of field and not the light gathering capabilities of the lens.
All of these are parameters of the lens, they don't affect the shutter speed so the shutter speed stays the same. It also only relates to the physical size of the sensors and does not take into account the resolutions of the sensors being compared.
what confuses me is aperture diameter in aps-c 23mm f/1.4 is 16 while 35 in f/1.4 is 25. we all know that the bigger the aperture diameter, the more light comes inside the sensor, the more light, means faster shutter speed.
For the same lens?
The f stop is the relationship to the apparent aperture opening (as looked at through the front of the lens) and the focal length of the lens. This doesn't matter if it is on a crop sensor, full frame sensor, medium format sensor or just sitting on your desk not connected to a camera as looking through the front will always give you the same size for the same fstop.
Different light actually. Cropping throws away light.
And diffent DOF as you enlarge the images from image plane by different amounts to the viewing size, though as the field of views are also diffent, comparing DOFs isn't IMHO too meaningful.
The light collecting is a function of several parameters: scene luminance, field of view, exposure time and aperture size.
We're only interested in the aperture size here. 50mm/5.6 and 25mm/2.8 both have about 9mm aperture diameter, or area of 63mm^2 or so. Thus the same amount of light goes through.
The practical implication of this is that the pictures from these systems would look identical to each other.
If we were to increase the light collecting of either system via making the aperture larger, we'd improve the image quality (noisewise) but also decrease the depth of field.