AFD MTFs?

[Stuart Richardson]

Thanks for the information Thierry. This clears things up nicely. Now people can make an informed decision about whether they want to embrace the new lenses or make do with the old.

 

[David Klepacki]

...
- AFD lenses take in count the focus difference (longer path) due to the IR filter on top of the sensor. The glasses, though not newly designed, have been adapted for this.
...

Thanks Thierry. As always, excellent information.

Can you tell us how this particular difference affects the actual image quality? Does it affect resolution, contrast or CA (or all three?) of the image at the sensor? It would be interesting to know why this had to be done in the optics, as opposed to compensation via the focusing electronics.

Thanks again,

David

 

[thsinar]

I don't think that this correction has any influence on IQ (negative or positive) other than making sure that the focus is exactly in the sensor plane.

Why doing it in the optic itself is a good question: I believe that it is not an optical modification but a mechanical in the lens as well as in the AF system in it.

Thierry

Thanks Thierry. As always, excellent information.

Can you tell us how this particular difference affects the actual image quality? Does it affect resolution, contrast or CA (or all three?) of the image at the sensor? It would be interesting to know why this had to be done in the optics, as opposed to compensation via the focusing electronics.

Thanks again,

David

 

[David Klepacki]

Thanks Thierry.

So, if I understand correctly, the Hy6 is able to tell whether there is a film back or a digital back attached, and is able to dynamically adjust the lens for more accurate focus in either case.

Whereas, the older non-AFD lenses would not be able to be adjusted by the Hy6 to compensate for the IR plate of the digital back, since those lenses were designed when only film backs were in use. Is this correct?

David

 

[Mitchell]

If David is right, (what he says seems reasonable) I would hope that there would be some sort of manual adjustment so you can set the camera for a digital back or film. I'm thinking of getting an Hy6. I will rarely if ever use it with film. I don't want my two manual 6008 lenses to be at a focusing disadvantage.

But, I'm confused. If you were to focus an AFD lens manually, I would think it would be subject to the same focusing error as pre-AFD lenses, i.e. that the distance to the viewing screen from the mirror, while the same as to the film plane, is different than the distance from the sensor to the mirror. So there would have to be an auto adjustment made when you pressed the shutter button or you couldn't manually focus accurately.

I plan on using all manual lenses if I get a Hy6. I hope (and think) I'm not understanding this, but it would be good to hear the facts. But, Theirry is probably asleep now.

Best,

Mitchell

 

[David Klepacki]

Mitchell,

According to the information above from Thierry, only the AFD lenses are able to compensate for the IR glass in front of the sensor. If this compensation could have been done in the camera or back, there would not be any need to modify the lens.

However, I am not sure exactly what happens when you switch to a film back while still using an AFD lens. In this case, I would think the camera or back must somehow "ignore" the additional compensation that was introduced by the AFD lens for the digital sensor. Or, maybe the AFD lenses are really not recommended for use with film backs. I guess we need more information here.

David

 

[Stuart Richardson]

I am guessing that manual focus will be unchanged, given that this camera has been setup with a normal viewfinder and that there are several manual focus lenses still sold with the camera. I doubt this compensation will make much of a difference for film. Digital sensors are perfectly flat and make extremely high demands on the plane of focus being absolutely spot on. Film has a natural curvature and depth to the emulsion that makes these focal issues not quite as critical. I would assume that Sinar, Rolleiflex and Leaf are wise enough not to ship a camera that can shoot film, but does not correctly focus with it. I think this is one of the cases where it is angels dancing on the head of a pin...that 1mm or less difference in focal plane will not likely make a difference unless you are looking at 100% pixels on a 33mp or above back.

 

[thsinar]

That's what I think as well. I believe the issue has been thought through to the last detail. With the exception that some older AF and non-AF are not communication properly with the Hy6 (and which can be sent for an update), there should be no issue.

Best regards,
Thierry

I am guessing that manual focus will be unchanged, given that this camera has been setup with a normal viewfinder and that there are several manual focus lenses still sold with the camera. I doubt this compensation will make much of a difference for film. Digital sensors are perfectly flat and make extremely high demands on the plane of focus being absolutely spot on. Film has a natural curvature and depth to the emulsion that makes these focal issues not quite as critical. I would assume that Sinar, Rolleiflex and Leaf are wise enough not to ship a camera that can shoot film, but does not correctly focus with it. I think this is one of the cases where it is angels dancing on the head of a pin...that 1mm or less difference in focal plane will not likely make a difference unless you are looking at 100% pixels on a 33mp or above back.

 

[David Klepacki]

OK, got it.

So, what this all adds up to is that if you want the highest degree of focusing accuracy for use with a digital sensor (like the eMotion 75), the AFD lenses will have an edge over the non-AFD lenses, since the AFD lenses have been specifically modified to take these digital sensors into account.

I think this explains why Sinar made these newer AFD lenses, so that every last bit of focusing precision could be extracted from their latest digital sensors with the Hy6. Apparently, there was room for improvement over the older non-AFD lenses in this regard.

Thanks!

 

[Mitchell]

I'm afraid I'm still a little lost.

Given that one can focus at any distance within the range of a manual lens, it seems very unfortunate if only AFD lenses can focus with complete accuracy with a digital back because of some auto compensating mechanism. If we are just talking about the depth of the IR filter, there should be a way to compensate for that. It sounds as if with non-AFD lenses, you can focus with greater accuracy with film than with digital, just the opposite from what I would choose.

I think for the price of the camera, manual lenses with focus compensation should focus as well as AFD.

I know this is all speculation, and suspect I'm not understanding, but I'd like an explanation.

Best,

Mitchell

 

[David K]

Mitchell,
I can tell you that I have no problems manually focusing either my AFD or non-AFD lenses, even wide open at f/2. As for the technical differences I'll leave that for others more qualified to debate.

 

[thsinar]

Hi Mitchell,

this is definitively only speculations. I would not worry as you do. First we have already a bunch of photographers shooting with the Hy6 on film, and they didn't complain about focus issues, secondly I believe that one simply has to take as a fact that AFD lenses are built for digital and that they are optimized for it. Why should this not be the case? In the contrary, it is good to know that one can do this.
This being said, I believe and have trust in our technicians and R&D people to built a camera that is able to focus under each circumstance, being it with film or with a digital back.
To re-assure you even more: most of my lenses for the Hy6 are either non-AF or AF lenses from my 6008. Up to now I did not have any problem.

Best regards,
Thierry

I'm afraid I'm still a little lost.

Given that one can focus at any distance within the range of a manual lens, it seems very unfortunate if only AFD lenses can focus with complete accuracy with a digital back because of some auto compensating mechanism. If we are just talking about the depth of the IR filter, there should be a way to compensate for that. It sounds as if with non-AFD lenses, you can focus with greater accuracy with film than with digital, just the opposite from what I would choose.

I think for the price of the camera, manual lenses with focus compensation should focus as well as AFD.

I know this is all speculation, and suspect I'm not understanding, but I'd like an explanation.

Best,

Mitchell

 

[Mitchell]

Thanks Thierry,

You are probably right. It's just that based on what's been said ( a little knowledge is a dangerous thing), it's reasonable to suspect that non-AFD lenses will be out of focus by the depth of the IR Filter when using the digital back but right on when using film.

David, glad to hear you are seeing no problems.

Best,

Mitchell

 

[David Klepacki]

Thanks Thierry,

You are probably right. It's just that based on what's been said ( a little knowledge is a dangerous thing), it's reasonable to suspect that non-AFD lenses will be out of focus by the depth of the IR Filter when using the digital back but right on when using film.

David, glad to hear you are seeing no problems.

Best,

Mitchell

Michell,

Sinar made these finer corrections in the AFD lenses for the digital backs because it may make a difference to some of their customers. Obviously, there is a difference, but as DavidK and Thierry say, the non-AFD lenses are good enough for most photographers with the current backs.

Perhaps the difference will become more apparent to more photographers with future backs and cameras. Otherwise, it would not make sense for a company to make such an engineering investment without realization of any difference at all, at least someday.

I also use some non-AFD lenses for now, but I look forward to more AFD lenses from Sinar. I think it is good for Sinar to strive for the best possible capability in their products, even if the improvement is subtle and incremental. Over some period of time, I do expect at least some of the non-AFD lenses to become obsolete because of the continued engineering improvements targeted for digital capture.

David

 

[David Klepacki]

Hi Mitchell,

this is definitively only speculations. I would not worry as you do. First we have already a bunch of photographers shooting with the Hy6 on film, and they didn't complain about focus issues, secondly I believe that one simply has to take as a fact that AFD lenses are built for digital and that they are optimized for it. Why should this not be the case? In the contrary, it is good to know that one can do this.
This being said, I believe and have trust in our technicians and R&D people to built a camera that is able to focus under each circumstance, being it with film or with a digital back.
To re-assure you even more: most of my lenses for the Hy6 are either non-AF or AF lenses from my 6008. Up to now I did not have any problem.

Best regards,
Thierry

Yes, well said Thierry. ALL of the lenses will work great on the Hy6, and the newer AFD lenses are made to work better with digital.

David

 

[Mitchell]

Thanks Thierry and David,

I'm wildly speculating to kill the time between here and mid-July when I get to test drive a Hy6 and H3D.

The difference between anticipating and using a camera can't be overstated.

Best,

Mitchell

 

[EH21]

I hadn't thought about until now but some of the multishot backs might be able to take advantage of the tighter AFD lenses even though I'm not sure the single shots can.