mFT - will diffraction be a problem with smaller lens?

Started Aug 10, 2008 | Discussions
Joesiv Veteran Member • Posts: 5,497
mFT - will diffraction be a problem with smaller lens?

Just curious since the lens' will be smaller, won't more detail per mm be required of the glass... and as such, will diffraction be more of a problem than with full size fourthirds lens'?

Already with fourthirds, I find flash photography a bit of a problem as slow sync speeds require me to to to f16 or so to balance light levels outdoors.

Right now I find f12 where I like to stop if I want lots of detail, if that's pushed back f8 or bigger, this would be a significant disadvantage for mFT.

(by the way, I'm really looking forward to mFT!)
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OP Joesiv Veteran Member • Posts: 5,497
On the flip side perhaps we'll have faster flash sync

Since no mirror box, perhaps we'll get faster flash sync speeds, and my worries won't really be as much of a problem?
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sherwoodpete
sherwoodpete Veteran Member • Posts: 7,767
Re: mFT - will diffraction be a problem with smaller lens?

Joesiv wrote:

Just curious since the lens' will be smaller, won't more detail per
mm be required of the glass... and as such, will diffraction be more
of a problem than with full size fourthirds lens'?

It should make no difference at all.

The sensor size is unchanged, so the lens focal length will remain the same. Consequently the effect of the aperture will be the same as existing 4/3. The lens is smaller only in terms of physical bulk and weight, not optical characteristics.

Regards,
Peter

Laurens Senior Member • Posts: 1,391
Re: On the flip side perhaps we'll have faster flash sync

I'm afraid you're rather confused on both accounts.

The diffraction limit does not depend on focal length or lens size, it's purely a function of permissible blur disk radius, which depends on pixel pitch. For the same pixel count, mFT and 4/3 diffraction limits will be identical.

The mirror box doesn't limit flash sync - it's the shutter curtain that limits it. So again, there is no reason that mFT will be any better in this regard.

Laurens

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PhotoTraveler Forum Pro • Posts: 11,700
Re: mFT - will diffraction be a problem with smaller lens?

It's not driven by the size of the lens. Defraction is driven by the sensor size, along with the photosite size caused by the size of the sensor (smaller sensor, smaller photosites for same resolution).

mFT will help them as they won't have to make retrofocal lenses anymore. So optically simpler.

The lens size is shrinking because of the loss of retrofocal and tele-centricity. The other aspects stay the same.

OP Joesiv Veteran Member • Posts: 5,497
Re: mFT - will diffraction be a problem with smaller lens?

Ok thanks for the explanation guys!

Ok so shutter is the limitation on flash curtain then.... Good to know!
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SteB
SteB Veteran Member • Posts: 4,526
Flash Synch Speed

Everyone else has answered the diffraction issue and it is true that if a normal focal plane shutter is used that synch speeds will probably be similar. However, I think there still remains an open question on the type of shutter that will be used with this system. I have not seen anything definite on it in the release. My guess is that it will be some sort of focal plane shutter, which will allow easy compatibility with existing 4/3 lens. However, there always remains the possibility of a digital type shutter, or even a shutter built into the lenses and some sort of shutter in the 4/3 adaptor. I think the last possibility is the most improbable as this type of leaf shutter is normally lens specific (having said this I don't know enough about the technicalities of this to know of the possibilities here).

Also I do not know enough about video photography to know how the shutter requirements of the proposed integrated high quality video and stills for the future will influence its design. It is also possible that the first cameras could have say a conventional mechanical focal plane shutter, and later cameras a digital type shutter.

JoePhoto Veteran Member • Posts: 6,916
yes ... "timing" of shutter curtains

Joesiv wrote:

Ok thanks for the explanation guys!

Ok so shutter is the limitation on flash curtain then.... Good to know!

Yes ... you just have to realize that with a focal-plane shutter .... after you exceed the "native" flash sync speed, there is never a time when the film/sensor is fully exposed. The light is literally "painted" across the film/sensor by a small "slit" of light.

In other words .... with a slow exposure (ala 1 second), the first curtain fully opens, and the film/sensor is fully exposed for 1 second, and then the second curtain starts to close.

This is true up to (and including) the "native" sync speed. At one shutter speed above that "native" speed, the first curtain only gets "half" way across before the second curtain starts to follow. At the next higher speed, the first curtain only gets 1/4, and 1/8 at the next higher speed. (The slit gets very small by the time you reach 1/8000 sec.)

Some people think the actual travel time changes with each shutter speed, but it does not ... only the "timing" between the opening of the first curtain and the start of the second curtain starts closing.

(But it is true that the speed of the newer -vertical- -metal- curtains is faster than the old days when horizontal traveling cloth curtains limited sync speeds to 1/30 sec. Eventually we got 1/60, then 1/125, and now 1/250 sec.)

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bobn2
bobn2 Forum Pro • Posts: 61,125
Re: On the flip side perhaps we'll have faster flash sync

Laurens wrote:

it's purely a function of permissible blur disk radius, which depends
on pixel pitch. For the same pixel count, mFT and 4/3 diffraction
limits will be identical.

This is a really misleading way of putting things, which leads people to the false assumption that fine pitch sensors are worse with respect to diffraction than coarse pitch ones. The 'permissible blur disk radius' dependes on the magnification at which you wish to view the final image and the resolution you demand in that final image. It has nothing whatever to do with pixel pitch. The pixel pitch places a lower limit on the size of the 'blur disc' (Airy disc) which can be rendered, and there's no point bothering about diffraction below that limit, but that's because you've lost potential resolution, not gained it.

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Bob

JoePhoto Veteran Member • Posts: 6,916
Casio EX-F1

SteB wrote:

Everyone else has answered the diffraction issue and it is true that
if a normal focal plane shutter is used that synch speeds will
probably be similar. However, I think there still remains an open
question on the type of shutter that will be used with this system. I
have not seen anything definite on it in the release. My guess is
that it will be some sort of focal plane shutter, which will allow
easy compatibility with existing 4/3 lens. However, there always
remains the possibility of a digital type shutter,

I think the answer could be the technology behind the new sensor being used in the Casio EX-F1.

I do not yet consider it mature enough for true "professional" applications, since its writing speed is not fast enough to prevent distortion; (and only 6mpx which may not be competitively acceptable).

And I am most upset that Casio (admittedly) deliberately chose a "lo-resolution" EV because they didn't think anyone cared. (They said their --opinion-- was that people would prefer the rear-LCD and the EV was only added as an afterthought.)

In my opinion, they/we lost an opportunity to prove the viability of a high-quality, high resolution, EV ..... (and with the addition of -hi quality- Interchangeable Lenses, we could have the first EVIL).

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Darrell Spreen Forum Pro • Posts: 10,528
another approach

A few P&S cameras are now using internal neutral-density filters to achieve the same exposure values you would get with small apertures. This allows them to keep the minimum apertures to f/5.6 or f/7 (as I recall) and alleviate some diffraction losses. Something like that could be used I presume.

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Darrell

Rriley
Rriley Forum Pro • Posts: 21,846
flash sync may not be not limited

Laurens wrote:

The mirror box doesn't limit flash sync - it's the shutter curtain
that limits it. So again, there is no reason that mFT will be any
better in this regard.

as you say, the shutter limits the flash speed
we dont know enough about the shutter, or even if there is one to say here
not yet anyway
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SteB
SteB Veteran Member • Posts: 4,526
Re: Casio EX-F1

You make some very good points. I don't know much about the technical details of the Casio EX-F1, although I have very much enjoyed watching some of the slo-mo clips people have made with this camera. As you say it is very much first generation.

However, I very much had the EX-F1 in mind when I have made all my posts on this subject. To me this is very much the direction things will be going in. The technology is as you say not yet quite good enough. In a few years though it will very different. This is why I think the micro 4/3 system is very interesting because clearly it is a platform that is designed to incorporate these developement in the future, as and when they become available. Although it remains to be seen how important interchangeable lenses will be on this type of product.

SteB
SteB Veteran Member • Posts: 4,526
Re: flash sync may not be not limited

My point exactly.

Thom Hogan Forum Pro • Posts: 13,659
Re: mFT - will diffraction be a problem with smaller lens?

PhotoTraveler wrote:

It's not driven by the size of the lens.

Correct.

Defraction is driven by the sensor size

Incorrect, mostly. Diffraction is a property of light hitting edges, in particular, the aperture opening. What confuses some people is that there is a small interaction with photosite size in some cases. If the diffracted light is still hitting the same photo diode as the primary light, then it wouldn't show up in an image. Because of the Bayer pattern and the demosaic used to create pixels from it, diffraction doesn't start to be completely recorded until the diffraction equals 2x the photosite size.

But to answer the OP's question: no, diffraction would be about the same on m4/3 as it is on 4/3. I say "about the same" because the position of the aperture blades relative to the sensor has a bit of an impact. But I wouldn't expect any significant change.

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Thom Hogan Forum Pro • Posts: 13,659
Re: Flash Synch Speed

SteB wrote:

However, I think there still remains an open
question on the type of shutter that will be used with this system.

An EVIL type camera requires an "electronic" shutter, not mechanical. This would, in theory, allow flash sync at any speed (assuming the flash is fast enough; Nikon had to arbitrarily limit their electronic shutters on the D50/D70/D70s to 1/500 because at full power some of the Speedlights are only slightly faster than that).

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Rriley
Rriley Forum Pro • Posts: 21,846
Re: Flash Synch Speed

what signalled to me about the shutter, was Joinson making a comment about it in a thread elsewhere. When the post was later removed, i figured he was wrong for some reason, that reason is of course there isnt a physical shutter

Panasonic managed a max sync of 1/2000th sec on the 2/3" sensor LC1
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SteB
SteB Veteran Member • Posts: 4,526
Re: Flash Synch Speed

Some interesting points here. I always suspected that Nikon limited the flash synch on the D70 because if it had been any faster it would have been faster than the duration of the flash on full power, however I'd never seen this confirmed before. So thanks very much to Thom Hogan for confirming this.

Even if the first micro 4/3 cameras did have a mechanical focal plane shutter I see not reason that later cameras could not have a digital shutter, there be no system incompatibility because of this. Obviously, it caused no problems for Nikon.

I think the higher flash synch speed on the Panasonic LC1 was probably because it had a leaf type shutter rather than a focal plane shutter (I haven't checked on this so it is only an assumption on my part and I am more than fallible). Whilst is would in theory be possible to build in lens shutters for the micro 4/3 system I would have thought this unlikely due to the difficulties of then making the system compatible with 4/3 DSLR lenses. Again this is merely an assumption on my part and if any one has any insight or technical knowledge to contradict my assumption I would be genuinely interested in their insight into this.

Rriley
Rriley Forum Pro • Posts: 21,846
Re: Flash Synch Speed

LC1 are electronic shutter
1/2000th is both the highest shutter speed and max sync
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avidday Senior Member • Posts: 2,082
Re: Flash Synch Speed

Rriley wrote:

LC1 are electronic shutter
1/2000th is both the highest shutter speed and max sync

So was the D70/D50.

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