OT - Flash Photography

[The Natural Philosopher]

Yes, Id say that was about in the ballpark.

The best slow slide film was about 10-15Mpx

[The Natural Philosopher]

Wrong. Theres more dynamic range on a CCD these days

[dennis]

We aren't talking about taking deep space pictures, the noise you get in DSLRs doesn't have much to do with that when the exposures are still subsecond and many thousands of photons are involved.

I don't. I said that lenses made for film do not have the correct characteristics for digital sensors and that they fit filters to the chip as a compromise. More recent cameras that have lenses designed to work with digital sensors don't need the filters and can produce better images. There is also the slight problem that film lenses didn't need to be as good because the film couldn't resolve the defects unlike modern sensors.

[Fredxxx]

So, with a few thousand photons landing in a subsecond interval, even without taking into account the quantum efficiency of the phot0-diode, perhaps you can tell us the signal to noise ratio you will get assuming noise is limited by shot noise?

Do you know why those filters are fitted to the sensor? Can you explain why removing them would improve the image?

[fred]

K which is a measure of resolution. The developing process will have enormo us effect on the resolution of any film regardless of the ASA, though gener ally speaking the lower ASA rating the higher the resolution. I get what yo u are talking about just think the comparison poor.Generally speaking curre nt sensors outperform film.

Utter nonsense. I used Tri X 400 ASA black and white film for all of our we dding work. The grain (Fuzziness ?) size was determined by the developing p rocess (Usually D76). It could be enlarged or reduced as desired. It can no t be directly compared to a camera sensor.

[whisky-dave]

Where's the proof of this ?

Lenses werent as good because the processes topday for making them are better or can be produced more cheaply.

[fred]

If you are talking about anti aliasing filters these were introduced to sol ve a perceived problem with moire. Current sensors are better able to cope with this hence the choice of buying some models with this filter removed. Given that Pentax have a camera on which one can select to have this filter on or off it seems obvious that this 'filter' is introduced via software.

[Tim Streater]

There isn't a filter on these Pentax models. Its simulation is done by hardware. Since Pentax uses in-body optical stabilisation, thereby removing the need to put it in the lens (as others do), they can shake the sensor by 0.5 pixel to produce a similar effect to having a traditional AA filter (which sat in front of the sensor).

Whether you use it in a given shot would depend on whether you expected moire to be a problem in that shot. There are now several Pentax models that follow this path, I would expect all future ones to do so.

[dennis]

I will leave you to find out, you need to do some studying in this area.

[dennis]

There is the slight issue of the angle at which the light hits the sensor. I suggest you investigate why and report back. I will give you a hint, look for some details on the layers in the sensor.

[whisky-dave]

Irrelivent to the main point in question. Around 1609 when Galileo started making his own optic he couldn't make them as good as his vision was, vison being his eyes as sensors. Now we still can't make leneses as good as the sensors can handle so now we use software to filter out the mistakes. They even did this with the Hubble space telescope.

[dennis]

Rubbish, I have several diffraction limited long lenses here ATM. They don't cost much either, the 500 mm F5 being about £100. What I can tell you is that camera lenses are built down to a price and I have never seen one diffraction limited at full aperture although you can see the detail fall off as you get down to F16ish.

The hubble was designed to be diffraction limited too but they cocked it up. It is diffraction limited now, after the fix.

You will never get camera lenses as good while camera users can't tell the difference or don't care.

[Fredxxx]

There are two issues here. First is that most colour sensors use a bayer filter that creates moire type artefacts. The second is that some sensors have pixel sizes that are close to the Airy disk. Sometimes physics gets in the way.

[Fredxxx]

Yes, tell us the Airy disk for a F5 optic. You rightly say that the lens will be diffraction limited.

[whisky-dave]

Not relivent.

So, physics has always been there nothing new. I use to use the GePe glass slide mounts that were either Anti-Moiré or to reduce Moiré.

[Fredxxx]

Apart from the spelling, can you explain why there might be some deliberate defocussing to reduce moire artefacts?

You do know what these are?

I'm struggling here, can you explain how you would use a GePe glass mount to reduce the moire effect when taking a photo with a digital camera?

[whisky-dave]

Because you don;t want to see them, fox tablot never had that problem

are they they same as some called them anti-newton rings.

you wouldn't you use it for mounting slides between glass and projecting th em onto a screen, which could if you had normal glass produce those Moir é patterns on the projected image.

[Fredxxx]

I think you're getting confused how Moire fringes are generated in your slide mount and with a sensor. The second is associated with registration of the image and how it is sampled.

A clue is that pixel elements are small, and worse still have a low fill factor, such that only a percentage of the pixel area is sensitive to light. They Bayer filter makes the active area even smaller and the de-Bayering filter causes defocussing in its own right. Hence why RAW is preferred by purists. There are different algorithms for de-Bayering.

The result is that high frequency image detail creates artefacts. I have called them Moire artefacts, to be distinct from other causes of Moire patterns such as those in your mounting slides.

[dennis]

You have looked it up so quote it yourself. BTW you can't do it for an F5 optic without knowing the rest of the details as anyone that understands optics will know.

[Fredxxx]

Is that an admission that the diffraction limited lenses you have in your possession aren't great performers.