cp 5000 f stop settings

I was asked this question recently and did not want to give a less than fully accurate technical answer as to why the stops only go to f8 on the cp5000.

James do you want to take a run at the detailed explanation. Thus how in film for macro you would set for F16 yet cannot now with cp5000.

Thanks

Hi Todd,

I can't explain all the technical details, but I'll give it a shot based on what I have read, etc.

It's not a difference between film and digital that we're dealing with - it's the actual physical size of the lens - namely, the diameter. The lens is small and the aperture opening is small. A Nikkor lens has a fliter thread of 62mm for example, compared to something like 28mm for the Coolpix (just an example).

Fstop is derived from a combination of focal length and aperture size. Look at the ACTUAL focal length of the 5000 (not the 35mm equivalent) and you'll see that it is really LOOOOOOOOOW. To get to f22 with the coolpix cameras your aperture would have to be TINY.

If you did that, you'd be esentially taking pictures with a pinhole camera - not the best way to get good photos...

Does that make sense?

This is why Kasey and others have mentioned that it's difficult to use your manual strobe power equations (based on guide numbers, distance, fstop) to shoot manual strobes with consumer digital cameras. That's why most consumer UW shooters use the "trial and error" method to determine strobe power. Not the most "elegant" method, but people say it works.

Cheers

James

Thanks you explained it much better than I could have.

Actually, it's the size of the pixels that limit the usable fstops. It's not that they can't make a smaller hole.

Fstop = aperture width/ focal length. Consumer digital cameras have small CCD's with small pixel. There's a fundamental property of light going through small holes call diffraction which cause a blurring of the image over a size inversely proportional to the fstop. Small fstop causes blurring over a larger area. The 5Mpixel CCD's have a 3.5 micron pixel size, for that size pixel fstop smaller than f/8, like f/22, will cause the image to blur over an area greater than the 3.5 micron pixel. The blurring also depends on the color, but that's too much details to go into here.

Because the way fstops are written there's sometimes a confusion over which way is bigger. The way I'm writting it f/22 is smaller than f/8.

That's awesome Herb!

I had no idea that we were getting down into that range (diffraction of nM lightwaves) with the size of the sensor sites. Whoa!

Cheers

James

It's not just the pixel size, although it is contributory. The issue exists even for film cameras.

Aperture is the size of the hole through which the light must pass. It is expressed numerically as the relationship between focal length and the diameter of the opening.

e.g. A 10mm opening with a lens with an 80mm focal length yields a designated f-stop of 8. If I double the area of the opening it will result in a diameter of 14.15mm. The resulting f-stop designation will be 5.6.

Since the f-stop designations are relative, the smaller lenses of digicams require smaller actual openings for the same f-stop designation.

e.g. The CP5000 at a focal length of 7.1mm requires an opening of .89mm for an f-stop of 8.

Now, the reason we don't see higher f-stops on digicams is two fold: 1) The smaller the phyiscal size of the aperture blades, the more difficult it is to precisely control their positioning, especially on an adjustable aperture cameras. 2) The primary difficulty as outlined by herbko is diffraction. The smaller the actual opening, the more diffraction. It is dealing with this diffraction that limits the use of usable smaller f-stops.

The pixel size and density of pixels contribute to the camera's ability to deal with the diffraction problem, as does the glass itself.

Of course, because CCDs are smaller than 35mm film, the need to stop down for greater DOF is greatly reduced.

I think I started something here.

So, then mathematically if someone was saying that on a wideangle shot on film they usually shot F5.6 then, is there a formula that could be used to actually convert that to a camera like the cp5000 for an equivilent?

I have a feeling this is not a simple answer.

How about this for a simple answer: no

I'm just kidding!

In theory, f5.6 is f5.6 no matter what. However, with a consumer digicam, you will get more DOF at f5.6 than you will w/ a film camera or a film sized sensor.

How about this question:

Film and digicams at f5.6 both shooting at 1/125th - will the same amount of photons hit the sensor as will hit the film?

Cheers

James

So, then mathematically if someone was saying that on a wideangle shot on film they usually shot F5.6 then, is there a formula that could be used to actually convert that to a camera like the cp5000 for an equivilent?

Yes and no.

I have a feeling this is not a simple answer.

Correct.

Equivalent what? Light/Exposure? It's the same.

DOF? Yes, you can calculate it. Let's see, I need the f-stop, exact focal length at which you are zoomed, circle of confusion...If a train leaves Philadelphia going 60mph.....

Exactly.

I know enough engineers that love these kind of questions so I was baiting a little bit.

So on a macro shot, assuming 1 foot distance and setting to F8 at 1/60 on the cp5000 then this does not equal F16 or F22 at 1/60. Or does it?

Or, if you take the square route of pi and multiply by the inverse of....

Sorry, a little accountants humour.

If anything, it's the other way around.

I found that I have PLENTY of light w/ the CP5000 but need a LOT more with the S2pro.

Say a fish portrait, a shot that I would shoot that I would shoot at f8 with the coolpix would be an F4 or even 3.5 shot with the S2pro. This is just my personal observation though.

Cheers

James

You guys are making it seem lots more complicated than it needs to be. As I wrote earlier Fstop = Aperture width(size of hole) / focal length. So the size of the hole as seen by the CCD or film can be described by the fstop ONLY. The diffraction blurring width is inversely proportional to the size of the hole as seen by the CCD; therefore, smaller fstop, bigger diffraction blur. Actual hole size and focal length are already figured in. When the diffraction blur gets bigger than the pixels, you loss resolution. A bad thing. If you go through the number for the 3.5 micron pixels in the CP5000 CCD, you'll find that f/8 is as small as you want to go before resolution is degraded. That IS the reason the CP5000 is limited to f/8. There is really no need to assume anything about how well camera makers can make and align holes. Do you really know that? My first digicam, an Olympus C2020, goes to f/11. Do you think the skills of camera makers have degraded since then? It's okay to go to f/11 in that camera because the pixels were actually bigger. Lower resolution, smaller CCD but still bigger pixels.

The diffraction limit also applies to film. The resolution of 35mm film is better than the cp5000 because film is 35mm across vs the 9mm CCD. That difference in size is big enough that the image on the film actually does not have to be as sharp for the 35mm slide to have higher resolution. So 35mm cameras can go to f/22 or so before lossing resolution.

I think I started something here.

 

So, then mathematically if someone was saying that on a wideangle shot on film they usually shot F5.6 then, is there a formula that could be used to actually convert that to a camera like the cp5000 for an equivilent?

 

I have a feeling this is not a simple answer.

In theory this should be simple. If the ISO or ASA rating of the digicam and film are the same, then the same fstop and shutter speed should give the same exposure. That's why they go through the trouble of giving an ISO rating. However, CCD's have a linear response while film saturates slowly. So it's eaiser to over expose the CCD and blow out the highlights in your digital photo. I really don't have enough experience using film to comment on what really happens in practice, but I would guess you'd need to slightly under expose the CCD vs film for good results in most cases.

How about this question:

 

Film and digicams at f5.6 both shooting at 1/125th - will the same amount of photons hit the sensor as will hit the film?

 

Cheers

James

A simple question at last

Yes. Shutter speed and fstop are properties of the camera body and lens and is independent of whatever you put at the focal plane.

Thanks Herb.

I agree with your explanation - but it doesn't appear to hold true for me in practice. I wonder why???? Could it be the ISO 100 on the coolpix is really more like ISO 150? I don't think that's it, but it's the only possibility I can see left - after taking out the other variables.

Cheers

James

As I mentioned earlier, I don't have enough film experience to give a first hand perspective. The only thing I can add is this. About a year and a half ago I took an afternoon lesson with Cathy Chruch, she had just started working on digital and did a couple weeks of tests with the Olympus C3030. She told us that the ASA100 rating is wrong; it's at least 200 and maybe even higher. I think her conclusions were based on tests with calibrated strobe settings and placements.

Yes. Shutter speed and fstop are properties of the camera body and lens and is independent of whatever you put at the focal plane.

True.

The same light is either hitting either the CCD or the film. The sensitivity, as a rated ISO, is the third part of the equation.

I think the reason many feel that consumer digitals are more light senstive is the fact they do not have the dynamic range of film because of the small pixel size. If your scene has 6 stops of light variation, the digicam would blow out the brightest part or the scene. The first reaction is, "Too much light". We notice slight underexposure less. I have an Olympus D-340R from several years ago. It rarely exposed anything correctly.

I guess I could do some tests, since I've still got the CP995, a D100 and and film SLR or two.

So on a macro shot, assuming 1 foot distance and setting to F8 at 1/60 on the cp5000 then this does not equal F16 or F22 at 1/60. Or does it?

No. Nothing seems equal from the digicam to the SLR. I shot the CP995 at all sorts of apertures and shutter speeds from 1/60 to 1/250 with my strobe set on 1/8 power with and without a diffuser. Nothing really clicked as being a good starting point. I ended up at 1/125, 1/8 strobe power and adjust f-stop since the f-stop change allowed partial stop adjustment. It didn't seem to matter what f-stop, DOF was always good enough. I then switched to fixed shutter and f-stop and using EV for adjustment. I then drop kicked the unit into my camera gear graveyard. The grand total was 6 dives over two trips with 6 usable images.

Now, with the CP5000 and a TTL strobe, things will be much easier. I'd just pick 1/60 and f/8 and let the strobe do the rest. If the results are consistently under or over exposed, I'd use the EV adjustment. I'm not sure if you get f/8 over the entire zoom range. It's not that important. You will easily get the DOF of a 35mm camera at f/16 or f/22.

Hmm...the CP995 and the CP5000 both have Flash +/- adjustment. They both have the same TTL setup too.

I used both cameras (actually, CP990) and found that they both behaved pretty much the same. The only difference was that I had to go into the menu to do the Flash +/- on the 990 - which was sort of a pain whereas there was a nice button on top of the 5000.

So...I'm confused again scorpio - a more and more common state of mind for me as I get older.

Cheers

James

Aquatica housing, no TTL strobe control. A real detriment to shooting. The housing failed to take advantage of an important camera feature.

Ah yes, the housing blocks the TTL sensor on the popup flash. Doh.

Cheers

James Wiseman