[texandrews]

I know these other two lenses but I am not interested in using these zoom and focal length.

For almost 10 years now I have been going around with Pentax 67 and always the same 90 mm prime lens, in fact the 645Z is interesting for me because it has a 55mm lens which has almost the same angle as a 90 mm 67.

Thank you,

Enrico

That 55 is one of my favorite lenses. It's on my Z by default.

[enricob]

I think your question might be impossible to answer, because of all the variables involved and these vary for each person. This impossible to transfer that to you.

Perhaps your best option is to "convert/translate" your experience with the 6x7 to what you can expect on the 645z.

For example find a scenario where you are satisfied the micro movements are insignificant enough for your requirement on the 6x7.

Translating that to the 645z you only really have the ISO to play with when you are talking about moving subjects. Because freezing a moment with moving subjects has only one requirement, a fast shutter speed. The shutter speed depends how steady you are holding the camera in relation to the subject, also known as panning in larger movements.

With static subjects you could perhaps lower the shutter speed by one or two stops to account for the lesser mirror slap effect of the 645z compared to the 6x7.

Coming back to the ISO, as others have also mentioned, you can comfortably shoot at 3600 iso, as long as you don't under expose. At 6400 and higher you need to get comfortable with the post cleaning up in ACR/Lightroom.

I can't tell you the difference between the Fuji 50 mpx cameras and the 645z in terms of noise at high iso, because I don't have a Fuji to compare.

I suspect the 645z raw files have less noise than the Fuji, but I could be wrong. I have found in some cases the raw DNG files, ex camera is sharper and cleaner than the png files. Other may have found different results.

Compared to the 6x7 and what I've seen of the Fuji 50mpx cameras I find the 645 system, film and digital to be much better balanced. Even with a longer and heavier lens, the system just feels right and steady. I can take a shot with my one hand without much strain, with a faster shutter speed of course. I can't speak to other systems like Hasselblad and P1 on this topic, and others may not find balance an important attribute.

Everyone rides his horse his own way, as they say.

I hope you find a solution for your problem.

Yes, it's true.

But I would not like to establish an absolute rule which was valid always and for anyone because, as you say, rightly, it would be not possible.

I would like to understand if there is a difference and what's this difference between some references I considered: 6x7 MF, d850 FF and 645z, same condition and same person.

I've already said about my experience: Pentax 67 + 90mm lens freehand MLU at 1/30, 1/250 even walking. D850 + 40mm lens freehand 1/125 may be 1/250 no walking.

I think it depends on quantity of mp and sensor size, is it correct?

In theory, because of mp and sensor size, 645z should allow shooting with longer times that with D850 because the number of MP is the same but the sensor is larger. But it is a theoretical consideration and I try to verify it considering the direct experience on the field of those who use this 645z.

Many thanks for all answer.

Enrico

[kaseki]

An angular rotation is an angular rotation, and thus the image of a point at infinity's focal position movement on the focal plane is proportional to the focal length of the lens times the rotation angle. The field of view of a pixel is the pixel size divided by the focal length (in radians). Hence, a focal plane with double the reference focal plane pixel size using a lens of twice the focal length of that used with the reference focal plane will be equally sensitive to rotational motion.

So, a 100 Mpixel focal plane of the 645z size will have more sensitivity to angular motion -- pixel-peeping-wise -- than the present 51 Mpixel focal plane, whereas a 100 Mpixel focal plane covering the original film plane of 45 x 60 mm will have the same sensitivity. (Roughly)

[texandrews]

I think it depends on quantity of mp and sensor size, is it correct?

An angular rotation is an angular rotation, and thus the image of a point at infinity's focal position movement on the focal plane is proportional to the focal length of the lens times the rotation angle. The field of view of a pixel is the pixel size divided by the focal length (in radians). Hence, a focal plane with double the reference focal plane pixel size using a lens of twice the focal length of that used with the reference focal plane will be equally sensitive to rotational motion.

So, a 100 Mpixel focal plane of the 645z size will have more sensitivity to angular motion -- pixel-peeping-wise -- than the present 51 Mpixel focal plane, whereas a 100 Mpixel focal plane covering the original film plane of 45 x 60 mm will have the same sensitivity. (Roughly)

Yes to the technical aspects outlined above by Kaseki. But also, Enrico, the ergonomics of the camera-lens combination and your reaction to them as it involves your hands and arms holding the camera/lens, your age, the time of day, and any other physical issues that might pertain (excessive heat or cold, wind, and much more) will have a big impact here. That's going to be wildly different for every person. For instance, I have found holding smaller cameras more difficult that larger ones, but others are just the reverse.

[enricob]

An angular rotation is an angular rotation, and thus the image of a point at infinity's focal position movement on the focal plane is proportional to the focal length of the lens times the rotation angle. The field of view of a pixel is the pixel size divided by the focal length (in radians). Hence, a focal plane with double the reference focal plane pixel size using a lens of twice the focal length of that used with the reference focal plane will be equally sensitive to rotational motion.

So, a 100 Mpixel focal plane of the 645z size will have more sensitivity to angular motion -- pixel-peeping-wise -- than the present 51 Mpixel focal plane, whereas a 100 Mpixel focal plane covering the original film plane of 45 x 60 mm will have the same sensitivity. (Roughly)

Does this mean that a 50 MP 33x44 sensor camera should be less sensitive to motion than a 50 mp 24x36 sensor camera?
Does this mean that a 24 MP 24x36 sensor camera should be less sensitive to motion than a 50 mp 24x36 sensor camera?
Did I get it right?

If I get it right, a higher resolution (50mp) camera as 645z is more sensitive to motion and therefore forces shorter shutter speed and upper ISO values. Someone suggests a lower resolution (24mp) camera in case you need shooting with longer shutter speed and lower ISO values because it's less sensitive to motion. Do you agree? What would you prefere?

Thank you,

Enrico

[kaseki]

Does this mean that a 50 MP 33x44 sensor camera should be less sensitive to motion than a 50 mp 24x36 sensor camera?
Does this mean that a 24 MP 24x36 sensor camera should be less sensitive to motion than a 50 mp 24x36 sensor camera?
Did I get it right?

If I get it right, a higher resolution (50mp) camera as 645z is more sensitive to motion and therefore forces shorter shutter speed and upper ISO values. Someone suggests a lower resolution (24mp) camera in case you need shooting with longer shutter speed and lower ISO values because it's less sensitive to motion. Do you agree? What would you prefer?

Thank you,

Enrico

First, it must be emphasized that we are addressing angular motion, and not translation motion, which would have an effect in the near field. (We have to note that it is pixel size vs. focal length that determines image translation due to angular motion.) When you use the word "more sensitive" I interpret it to mean blur extending farther over across some number of pixels. Fundamentally, we are addressing "smear" and any motion will cause smear; the only question is how noticeable it is. In principle, one could take the image from a 50 Mp camera and derez it to a 25 Mp equivalent (to the extent that a linear root 2 derez was achievable) and the blur would be less noticeable even as the pixel resolution would be more noticeable (in a large enough print).

Second, we must keep in mind that pixel size affects the noise level that a given ISO value will yield in that camera, so in reality, smear sensitivity and noise sensitivity may be interactive in a given result. Other ways of looking at pixel size effects include:

• From the point of view of modulation transfer function effects, the product of all the MTFs to yield the MTF of the actual read out image is being compared to the same final MTF times the MTF of a smear motion. The effect will be a reduction of the higher frequencies in the image, but if the pixels are large enough in angle space the effect will be initially hidden for small smears.
• As another attempt at description, assume a diffraction free optical system, and infinitely fine grain film. The image will have infinite resolution. Then read it out by sampling the density pattern over a series of contiguous areas representing pixels. Compare to reading out a smeared version of this image. I can't claim that larger pixels provide an improvement over smaller pixels when the end result is observed with some level of degraded image resolution (eye, monitor, etc.). No matter what the pixel size is, smear always spills the image across more than one pixel, but not necessarily over exactly two pixels.

tl;dr: I think you got it right, given a lot of assumptions (that if ignored may lead to misleading understanding). I think I prefer more resolution because there is more information to work with such that post processing may be able to be more effective (for someone skilled in the art).

[enricob]

Many thanks kaseki for all this information, although perhaps I can only partially understand because it's a little too complicated for my little knowledge and also for my equally poor English.

Yes, there are many variables (micro motion blur, ISO noise, sensor size, mp amount, pixel size), perhaps it's a matter of looking for the best balance among all these variables, but I'd also prefer more resolution.

Practically, I've tested D850 (50mp, sensor 24x36mm), 645z (50mp, sensor 33x44mm) and Pentax67 (film 60x70mm), same focal length, same person, same shots.

D850 is the most sensitive to motion, 645z seems to be just a bit less sensitive and it allows shooting with a longer time for about 1 stop difference, Pentax67 is the least sensitive to motion and it allows shooting with a longer time even about 3 stops of difference than to the D850, which is a big difference.

What does this difference between Pentax 67 and digital D850 / 645Z depend on?

Does it mainly depend on the size of the 60x70mm Pentax67 frame?

Or does it also depend on the nature of the film compared with the sensor, regardless of the size of sensor and film?

Thank you,

Enrico

[kaseki]

I think it depends on the fact that with distributed grain sizes, the film acts like a myriad of different sized tiny pixels being stacked upon one another and providing (as Kodak Portra data sheets show) a gradual roll off in modulation transfer function (MTF) with (spatial) frequency. I forget what transverse blur MTF looks like, but I suspect that when multiplied over the frequency range with a film MTF the result is more benign (in some perhaps non-intuitive way) than when similarly applied to a spatially sampled data system (pixels) MTF (sinc squared function, as I recall).

(An excellent question for a late friend and coworker of mine whose understanding of this topic was unsurpassed, but who unfortunately is not with us to answer. His purchase of a 645 in the 1970s at a Boston area camera show we attended eventually led to my purchases much more recently.)

[enricob]

I finally had the opportunity to try the Pentax 645z.

To answer the thread question, the longest shutter speed I could use with this Pentax 645z freehand (55mm lens, ambient light) without any traces of (micro) motion blur, even at a 100% magnification, is 1/125.

Even in case you raise up the mirror of the Pentax 645z before the shot, as in case of self-timer mode or continuous shooting, there was not any difference, longest shutter speed always 1/125.

Unfortunately, during these tests I also checked some focus problems and I opened another thread in this regard because I would need the opinion of some expert 645Z users to understand if these problems are possible or even common with the Pentax 645z, or if instead in this case it is the problem of a nor properly working camera.

Thank you,

Enrico

[TDvN57]

I finally had the opportunity to try the Pentax 645z.

To answer the thread question, the longest shutter speed I could use with this Pentax 645z freehand (55mm lens, ambient light) without any traces of (micro) motion blur, even at a 100% magnification, is 1/125.

Even in case you raise up the mirror of the Pentax 645z before the shot, as in case of self-timer mode or continuous shooting, there was not any difference, longest shutter speed always 1/125.

Unfortunately, during these tests I also checked some focus problems and I opened another thread in this regard because I would need the opinion of some expert 645Z users to understand if these problems are possible or even common with the Pentax 645z, or if instead in this case it is the problem of a nor properly working camera.

Thank you,

Enrico

The longest shutter speed on any camera depends on the focal length of the lens and the photographer's technique and physical abilities. Sans IBIS the only role the camera plays is the balance of the camera and lens combination.

[Abbazz]

The longest shutter speed on any camera depends on the focal length of the lens and the photographer's technique and physical abilities. Sans IBIS the only role the camera plays is the balance of the camera and lens combination.

Indeed, but For me the 645's heft acts as a stabilizer. I can reliably use 1/30s with the 55mm lens on my 645D (but some people need 1/60s or 1/100s). Of course, longer lenses require faster speeds, like this self-portrait taken handheld at 1/50s in available light with the old 6x7 105mm lens wide open at f/2.4:



Cheers!

Abbazz

[texandrews]

Indeed, but For me the 645's heft acts as a stabilizer. I can reliably use 1/30s with the 55mm lens on my 645D (but some people need 1/60s or 1/100s). Of course, longer lenses require faster speeds, like this self-portrait taken handheld at 1/50s in available light with the old 6x7 105mm lens wide open at f/2.4:



Cheers!

Abbazz

Agreed. I've often gotten sharp images at surprisingly slow speeds. I usually shoot multiple frames for insurance, though.


The OP's original question concerned micro focus, however, and in this case I'd say that to ensure absolute focus (on the plane of focus, because DOF doesn't count here), it can't be reliably managed by anyone not made of stone at under 1/250th of a second with a normal lens, and shorter speeds as the FL's go up. Many years ago in the 1980's a lanscape photographer whose name escapes me now wrote several instructional books, and in one he showed through examples that 1/125th handheld would not give critically sharp results---and this was with film, more forgiving than today's digital sensors, and with that era's lenses.

[TDvN57]

Theoretically you cannot eliminate micro movements, even if you are made of stone or using a super stable steady tripod.

Thus eliminating total micro movements is an impossible target, unless it is described within a reference. For example: Micro movements not visible if the picture is enlarged to a certain size. Pictures intended for social media and book prints may "tolerate" larger micro movements, than say large prints of say 1m x 2m.

All the time I used a 6x7 without a tripod I used mostly two shutter speeds 1/60 and 1/30, which was great for developing technique. Incidentally sharp shooting with a rifle uses similar techniques.

Lately I find it more difficult to achieve slow shutter speeds and prefer to shoot at minimum 1/125. Yet a few weeks ago I visited Hamburg and wanted to take a picture of the high speed train showing its high speed. With no tripod and no nd filters I had one choice, handheld at 1/4. I pulled out all the stops with technique and managed to get a reasonable micro movement free picture of the train with 80mm focal length (FA 80-160mm lens). Is it free of movement for a large print? I guess not, haven't checked it because I have no intention of printing it.

Can I repeat that, be assured I'll try, will be a great personal boost to show myself I can reverse a trend I thought was inevitable.

On a more technical note, I suppose it would be more appropriate to describe the issues involved with the help of circles of confusion, but I'll leave that to others more capable.

[enricob]

It also depends on the way you check the pictures.

For example, I usually check the presence of micromotion blur by comparing shots taken one after the other with gradually longer times and always at 100% enlargement. It would certainly be more difficult to check the micro motion blur in case there was not a comparison between shots made at faster and slower times. Check results would be probably different even in case you check at 25% instead of 100% enlargement.

What's more, the longest shutter speed does not depends just on the focal length and the photographer's technique and physical ability. It also depends on the number of megapixels and the sensor size. For example, the 645d should allow a little longer speed than the 645z because it has a lower number of megapixels with the same sensor size.

Thank you,

Enrico

[TDvN57]

It also depends on the way you check the pictures.

For example, I usually check the presence of micromotion blur by comparing shots taken one after the other with gradually longer times and always at 100% enlargement. It would certainly be more difficult to check the micro motion blur in case there was not a comparison between shots made at faster and slower times. Check results would be probably different even in case you check at 25% instead of 100% enlargement.

What's more, the longest shutter speed does not depends just on the focal length and the photographer's technique and physical ability. It also depends on the number of megapixels and the sensor size. For example, the 645d should allow a little longer speed than the 645z because it has a lower number of megapixels with the same sensor size.

Thank you,

Enrico

Yes I agree the pixel size has some role to play within the same sensor size. For example my KP has a pixel pitch about the same size as the pixel pitch of the Fuji 100. However the KP is not nearly as sharp the the 645z and not even close to the Fuji 100. If you take two equivalent systems with two photographers (not equivalent :-) I hope), then it comes down to technique and ability.

I think it was Gary Player, the South African golf player that said his success in golf is due to luck, although the more he practiced the luckier he got.