Digital vs. Film lens openings

My friend and I were talking about the 16-35 f/2.8 vs. the 17-40 f/4 and I told him that for his shooting needs, which don't require a lot of low light, the 16-35 isn't worth the money. Then he said that he didn't know about that and wanted to have the f/2.8 to be able to blur out backround better. Fair enough.

Then he said that digital cameras require more light (larger apetures) than film cameras do. I had to leave at that point, so I didn't question him, but I don't know what he is talking about. In fact, even with a 1.6x camera, which we both have, I can't think of why that would matter.

Does anyone know what he might mean...or if there is any truth to that?

The only thing that makes any sense to me is that ISO 100 is the slowest normal ISO that I know of in the digital world. Perhaps a Kodachrome 25 sensor is a couple of years down the road?

Have Fun,

Partly correct.

When you want to have the same DOF given:
- two camera's: one FF, one with crop factor
- same field of view (i.e. on the FF camera an 80mm, on the 1.6 crop camera a 50mm)
...then you need a larger aperture on the camera with the crop factor.

Regards,
David

The ISO settings are calibrated (possibly badly) to give a certain exposure with a given amount of light, regardless of the camera. I'm fairly certain he's wrong.
The ISO settings are purely a fudge factor, not something intrinsic to the sensor. So unless digital ISOs are consistently badly calibrated, ISO x is ISO x.

To be clear, I am not speaking about DOF. Just the sensitivity.

Why would you need a wider aperture on the one with the crop factor? Assuming an evenly-lit scene, what's the difference?

I've never done a test myself but I figured that if you had ISO 100 film in a film SLR and ISO 100 on a digital camera and pointed them both at exactly the same thing from the same point you'd get the same f/stop/aperture settings (depending on if you were in aperture or shutter priority).

Same thought goes for FF and 1.6... Surely they'd have exactly the same readings, unless the ISO were actually not to the same standard?

I think I disagree. The ISO defines the amount of light (luminance x exposure time) required to record the image correctly, and the point I was making is that there are no ISO 25 digital sensors available, and that might be interpreted as 'digital needs more light.'

Have Fun,

Have you ever used ISO (ASA at the time) 25 film? That stuff really need more light. Shutter speeds were four times as long as with ISO 100 film.

The sensitivity of any given ISO is the same whether you are shooting digital or film. At any given shutter speed you need the same aperture for both to get the correct exposure.

It is true the cropped frame sensors give slightly more depth of field when using comparable lenses. For example, in order to take the same picture you would use a 50 mm lens on a 1.6x crop camera and an 80 mm lens on a full frame picture if you did not move either the camera or the subject. Also, if your object is to make an 8x10 inch print, the 1.6 crop image will have to enlarged more than the full frame crop, so the maximum circle of confusion allowable for the smaller sensor also has to be smaller. By the time you calculate all those variables you will find that the smaller sensor has slightly more depth of field.

If you object is to keep as much of the image as possible in focus this is great. If you want to selectively focus and blur the background or other parts of the image you will have to use a slightly larger aperture with the smaller sensor.

The way he said it - he's wrong.

Film cameras with slow film require larger apertures. Which makes it easier to blur the background.

Sometimes I'd want to have ISO 25 or ISO 12 at my disposal! Try shooting at f/2 in full sun

Gee, I guess I am bass ackwards here (no reference to our member with the same name)

Having the ISO 25 sensor would mean it needs more light -

(CoolToolGuy backs out, excusing himself profusely)

Have Fun,

CoolToolGuy - I didn't read the whole thread. My reply was directed at the original poster. (just in case)

DocFrankenstein wrote:
CoolToolGuy - I didn't read the whole thread. My reply was directed at the original poster. (just in case)

Don't worry - after I thought about it, I realized what I was saying was 180 degrees out. Its been a long day. . .

Have Fun,

Don't know. Unless he read something that whatever ISO algorithoms that run on digital cameras underexpose compared to film of the same rating. I haven't heard anything about the ISOs not being equivolent.

Also, (for debunking misconceptions) crop factor or not, an 80mm lens on a FF will not have the same DOF as a 50mm on a 1.6 camera. It will have the save FOV. DOF is an intrinsic property of the lens, not the sensor or a combination of the lens and sensor.

I'd say DSLRs require less light in general than film cameras. The latest sensors perform pretty well at ISO 1600 and you can shoot quite happily at ISO 800 with very little noise. Film at those ISO levels is very grainy by comparison.