canon Lee

I have a question. If you are going to FF from aps-c sensor, does the FF give you more light and make it possible to shoot at a faster shutter speed? Then would a F/4 be equal to a F2.8 lens? I am considering the Canon 6D FF, and have F/4 lenses. If a FF can increase my shutter speeds then is there any need to purchase a F2.8? I shoot sometimes in Low light. Or is the increase in light from a FF not that big?

CaptainC Loc: Colorado, south of Denver

There is ZERO correlation to exposure & sensor size. If using a handheld light meter one were to read that the exposure was 1/125 f/8.0 at an ISO of 200, that would be good for APS-C, FF, 645, 4x5, etc.

A sensor size (alone) has nothing to do with how much light the sensor absorbs.

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

The size of the sensor has no effect on aperture or shutter speed.

Longshadow Loc: Audubon, PA, United States

Correct.

TriX Loc: Raleigh, NC

As others have said, there is no direct correlation between sensor size and exposure, but the typically lower noise floor of the FF may allow you to utilize a higher ISO which then allows you to use a higher shutter speed or f stop with equivalent noise (one of the reasons I moved to FF- it was worth 1-2 stops for equivalent noise). Having said that, there are still other reasons to use fast lenses (shallow DOF, superior bokeh...)

PixelStan77 Loc: Vermont/Chicago

Captain C nailed the answer

Peeb Loc: NE Oklahoma

It will affect depth of field.

Article: http://photo.stackexchange.com/questions/12098/why-does-a-bigger-sensor-lead-to-a-shallower-depth-of-field

jcboy3

The answer is YES. The larger sensor gathers more total light, and with the same aperture and shutter speed (and proportional focal length) will tend to have less noise. So you can increase ISO and shutter speed to achieve similar noise levels with faster shutter speeds.

However, that is not the only difference. Different sensors have different noise characteristics. As it stands, the Canon 6D is a good low noise performer; much better than the 5D Mk III, for example. So you might expect even better performance than just from the difference in size.

Note that, for the same ISO, aperture, and shutter speed, the crop sensor and FF sensor should have the same exposure. That is because ISO is essentially calibrated for each sensor to achieve that goal. Because the FF sensor gathers more light, the gain on the amplifiers is turned down for a comparable ISO value. However, ISO calibration is not consistent across manufacturers. Using a good spot meter to calibrate ISO is necessary when comparing different camera models.

I would still get some fast lenses for low light, because you get better focusing. Shooting at very large apertures with full frame has DOF issues, so you generally want to stop down to preserve focus. You will just be able to see more clearly through the viewfinder and get more accurate focus with faster lenses.

TriX Loc: Raleigh, NC

Just to add - pros often shoot fast lenses wide open specifically to limit depth of field so the subject "pops" (stands out) against the background. I recently attended a seminar conducted by pros from our local newspaper (they are relatively large and employ 10 professional photographers) - they had sessions on sports, food, wedding and portrait photography. Among many other things I noted the following: everyone was shooting Canon (the sports photographer shot various models of 1Ds and everyone else was shooting 5D Mk3s), everyone had a 70-200 f2.8 in their kit (along with other lenses), and every one specifically said that they tended to shoot wide open to minimize DOF so the subject would "pop" (their words) against the background. Granted this was a particular segment of photography (photojournalism), and their style would not always be appropriate for other types of photography, but I found their take on DOF interesting.

canon Lee

I did read that FF sensors gather more light than the smaller APS-C, but how much more? Enough so that I don't have to replace my f/4 for a f/2.8? If not then its all about noise?

CaptainC Loc: Colorado, south of Denver

This is a terrible, misleading answer. With regard to exposure - AND THAT IS THE QUESTION - there is ZERO difference in sensor size or film formats. This is a great example of being asked the time and building them a watch - a bad watch. Just showing off arcane and irrelevant information. I guess it is just amazing I can take meter reading, get an exposure, set that exposure exactly the same on my crop frame AND full frame cameras and get the same exact exposure. (Any minor difference is due to individual units, not sensor sizes.

Just FYI - noise difference is due to PHOTOSITE (pixel) size, not sensor size. Assuming equal technology on both, a crop frame camera with larger photosites will have better noise performance than a full-frame unit with smaller photosites.

LoneRangeFinder Loc: Left field

Agree. Obfuscation of the issue. That misleading answer is a bit like saying more light falls on a two acre field as compared to a one acre field.

GoofyNewfie Loc: Kansas City

Forget that misleading post.
It is NOT correct.
Trust the Captain.

Bobbee

Like the light meter example. Simple!

Peekayoh Loc: UK

This is correct, the light flux remains the same for any size of Sensor. The larger Sensor does of course gather more light so noise is reduced.

This however is incorrect although it was a factor in early Sensor designs. Even though a small Sensel will appear to have more noise at high magnification, it is smaller and therefore has relatively less impact. What really counts is Sensor size and the larger area is what brings better low noise performance. Reducing the size of individual Sensels is advantageous because the effect of shot noise is more evenly spread; dark noise is irrelevant assuming that Sensor Technology is the same.