tupp

9 hours ago, noone said:

I cringe now when i look at some colour photos in old glossy magazines from the 70s and 80s taken with film.

Yeah.  All of those photos by Richard Avedon, Irving Penn and Victor Skrebneskiphotos were terrible!

 

 

9 hours ago, noone said:

The best image quality metric that correlates with color depth is color sensitivity, which indicates to what degree of subtlety color nuances can be distinguished from one another (and often means a hit or a miss on a pantone palette).  Maximum color sensitivity reports in bits the number of colors that the sensor is able to distinguish.

"Color sensitivity" applied to digital imaging just sounds like a misnomer for bit depth.  Bit depth is not color depth

 

I have heard "color sensitivity" used in regards to human vision and perception, but I have never heard that term used in imaging.  After a quick scan of DXO's explanation, it seems that they have factored-in noise -- apparently, they are using the term "color sensitivity" as a term for the number of bit depth increments that live above the noise.

 

 

9 hours ago, noone said:

My lowly aging 12mp A7s still fairs very well for portrait colour depth.

That's a great camera, but it would have even more color depth if it had more resolution (while keeping bit depth and all else the same).

 

 

9 hours ago, scotchtape said:

A good image starts with good lighting.

That is largely true, but I am not sure if "good" lighting is applicable here.  Home movies shot on film with no controlled lighting have the "thickness" that OP seeks, while home movies  shot on video usually don't have that thickness.

 

 

19 hours ago, tupp said:

Color depth in digital imaging is a product of resolution and bit depth (COLOR DEPTH = RESOLUTION x BIT DEPTH).

2 hours ago, kye said:

Interesting.  Downsampling should give a large advantage in this sense then.

No.  There is no gain of color depth with down-sampling.  The color depth of an image can never be increased unless something artificial is introduced.

 

On the other hand resolution can be traded for bit depth.  So, properly down-sampling (sum/average binning adjacent pixels) can increase bit depth with no loss of color depth (and with no increase in color depth).

 

 

2 hours ago, kye said:

I am also wondering if it might be to do with bad compression artefacts etc.

Such artifacts should be avoid, regardless.  "Thick" film didn't have them.

 

 

2 hours ago, kye said:

Converting images to B&W definitely ups the perceived thickness

There is no chroma sub-sampling in a B&W image.

 

I really think color depth is the primary imaging property involved in what you seek as "thickness."  So, start with no chroma subsampling and with the highest bit depth and resolution.  Of course, noise, artifacts and improper exposure/contrast can take away from the apparent "thickness," so those must also be kept to a minimum.

4 hours ago, kye said:

My question is - what aspect of the image shows thickness/thinness the most?

As others have suggested, the term "density" has a specific meaning in regards to film emulsions.

 

I think that the property of "thickness" that you seek is mostly derived from color depth (not bit depth).

 

Color depth in digital imaging is a product of resolution and bit depth (COLOR DEPTH = RESOLUTION x BIT DEPTH).  The fact that resolution affects color depth in digital images becomes apparent when one considers chroma subsampling.  Chroma subsampling (4:2:2, 4:2:0, etc.) reduces the color resolution and makes the images look "thinner" and "brittle," as you described.

 

Film emulsions don't have chroma subsampling -- essentially film renders red, green and blue at equal resolutions.  Almost all color emulsions have separate layers sensitive to blue, green and red.  There is almost never a separate luminosity layer, unlike Bayer sensors or RGBW sensors which essentially have luminosity pixels.

 

So, if you want to approximate the "thickness" of film, a good start would be to shoot 4:4:4 or raw, or shoot with a camera that uses an RGB striped sensor (some CCD cameras) or that utilizes a Foveon sensor.  You could also use an RGB, three-sensor camera.

 

 

5 hours ago, bwhitz said:

2. Some people actually LIKE the boomer-protectionism of the 1980's technology markets. I.e. hacks can just say "I own X or Y expensive camera! You HAVE to hire me now!"

No need for ignorant bigotry.

 

The notion that camera people got work in the 1980s by owning cameras couldn't be further from the truth.  "Hiring for gear" didn't happen in a big way until digital cameras appeared, especially the over-hyped ones -- a lot of newbie kids got work from owning an early RED or Alexa.  To this day, clueless producers still demand RED.

 

Back in 1980's (and prior), the camera gear was almost always rented if it was a 16mm or 35mm shoot.  Sure, there were a few who owned a Bolex or a CP-16 or 16S, or even an NPR with decent glass, but it was not common.  Owning such a camera had little bearing on getting work, as the folks who originated productions back then were usually savvy pros who understood the value of hiring someone who actually knew what they were doing.  In addition, camera rentals were a standard line-item in the budget.

 

Of course, there was also video production, and Ikegami and Sony were the most sought-after brands by camera people in that decade.  Likewise, not too many individuals owned hi-end video cameras, although a small production company might have one or two.

 

Today, any idiot who talks a good game can get a digital camera and an NLE and succeed by making passable videos.  However, 99% of the digital shooters today couldn't reliably load a 100' daylight spool.

53 minutes ago, BTM_Pix said:

Working space inside the adapter is going to be the issue with any solution.

With a non speed boosted adapter it is less of an issue.

Yes.  It might be best to run the leads outside of the adapter/speedbooster, and epoxy or hot-melt-glue the switch to the adapter housing.

 

By the way, the pictured dip switch is tiny. 

6 hours ago, BTM_Pix said:

This means that you should be able to bring those out those externally and power the adapter from an external source that you would then be able to engage and disengage with a switch as required.

Why not just put a switch inline on the "hot" power lead of the adapter instead of powering with an external source?  That way, OP can just enable and disable the electronics by merely flicking the switch.

 

Incidentally, here is a small dip switch that might work:

1 hour ago, tupp said:

This should read:  "Once again, I have repeatedly suggested that it is NOT the sensor size itself that produces general differences in format looks..."

28 minutes ago, noone said:

Great so you DO you think the sensor size has nothing to do with any difference so we do agree!

The paragraph reads:  "I have repeatedly suggested that it is not the sensor size itself that produces general differences in format looks -- it is the optics designed for a format size that produce general differences in format looks."

 

Again, you somehow need to get that point through your head.

 

 

28 minutes ago, noone said:

Of course if you do not agree with that, you would be able to prove it with science since you cannot prove it with photos (as any differences in photos taken with systems not identically scaled can be explained by difference in the systems.).  Now unless you CAN provide something (ANYTHING) showing how  (often tiny) differences in photos  could not even remotely be explained by differences in the equipment, I think we have gone several pages too far and I am out Really really really this time).

Perhaps you should merely address my points individually and give a reasonable counter argument each one.  Unless, of course, you cannot give a reasonable counter argument. 

58 minutes ago, tupp said:

Once again, I have repeatedly suggested that it is the sensor size itself that produces general differences in format looks

This should read:  "Once again, I have repeatedly suggested that it is NOT the sensor size itself that produces general differences in format looks..."

2 hours ago, noone said:

I do not need to address each point as I disagree with YOUR (no one else its seems) theory that you have shown

You certainly don't need to address each of my points, and, indeed, you have avoided almost all of them.

 

In regards to the your parenthetical insinuation, I would never claim that the number of individuals who agree/disagree with one's point has any bearing on the validity of that point.  However, please note how this poster unequivocally agrees with me on the problems inherent in your comparison test, saying, "I certainly can see what you're talking about in the areas you've highlighted. It's very clear."

 

 

2 hours ago, noone said:

NO, zero, nil, zilch nix, NOTHING in evidence to support  other than saying there are (often tiny) difference so it MUST be because of the sensor size difference.

In regards to my not providing evidence, again, are you referring to evidence other than all the photos, video links, and references that I have already provided in this thread, which you have yet to directly address?

 

Additionally, you have misconstrued (perhaps willfully) my point regarding sensor size.  I have continually maintained in this thread that it is the optics designed for a format size -- not the format size itself -- that produce general differences in format looks.

 

 

3 hours ago, noone said:

That article explains things pretty well to me and I can not understand how YOU can not understand that ANY difference in a system can explain very tiny differences in photos while at the same time you think those differences are explained by sensor size difference without a shred of evidence why ?

The paper that you linked does address points made in this thread, but a lot of the paper discusses properties which are irrelevant to DOF equivalency, as I pointed out in my previous post.  Interestingly, the paper frequently suggests that larger format optics have capabilities lacking in optics for smaller formats, which is what I and others have asserted.  Not sure how you missed those statements in the paper that you referenced.

 

Regardless, I have more than once linked Shane Hurlbut's example of an exact focus match between two different lenses made from two different manufacturers.  So, there should be no problem getting such a close DOF/focus match from other lenses with the proper methods.

 

Once again, I have repeatedly suggested that it is the sensor size itself that produces general differences in format looks -- it is the optics designed for a format size that produce general differences in format looks.  Somehow, you need to get that point through your head.

 

 

3 hours ago, noone said:

The fact that this amounts to many many pages of yes, no, yes, no is reason enough to end it now.  This thread should be locked.

Your thoughtful consideration and open-mindedness is admirable.

7 hours ago, noone said:

I Disagree!

Well, I certainly appreciate your thoroughly addressing each one of my points and your giving a reasonable explanation of why you disagree.

 

 

7 hours ago, noone said:

Got ANY shred of evidence to support your case?

You mean, do I have any evidence other than all the photos, video links, and references that I have already provided in this thread, which you have largely avoided?

21 hours ago, noone said:

This is as good a read on this as any.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-57/issue-11/110801/Equivalence-theory-for-cross-format-photographic-image-quality-comparisons/10.1117/1.OE.57.11.110801.full?SSO=1

It's not a good read on this at all, as most of the information given is irrelevant.

 

Furthermore, many of the conclusions of this paper are dubious.

 

 

21 hours ago, noone said:

"Nevertheless, real world IQ differences (including total image noise) will inevitably occur in practice even when equivalent photos are taken. These will arise due to differences in the underlying camera and lens technology, such as:  • sensor quantum efficiency;

How is "sensor quantum efficiency" relevant to optical equivalency?

 

 

21 hours ago, noone said:

• read noise;

How is "read noise" relevant to optical equivalency?

 

 

21 hours ago, noone said:

• lens aberrations;

Lens aberrations are absolutely relevant to optical equivalency and DOF/focus.

 

According to Brian Caldwell, aberrations can affect DOF and lenses for larger formats generally have fewer aberrations.  Hence, the refractive optics of larger formats generally influence DOF differently than lenses for smaller formats.

 

Keep in mind that the DOF/equivalency formulas do not account for any effects of refractive optical elements, yet optical elements can affect DOF.

 

 

21 hours ago, noone said:

• JPEG tone curve; and

Again, this property is not really relevant to optical equivalency and DOF/focus.

 

 

21 hours ago, noone said:

• image processing.

This property is not really relevant to optical equivalency and DOF/focus.

 

 

21 hours ago, noone said:

In other words, since the total light received by each format is the same when equivalent photos are taken, it is factors such as those above that explain real-world cross-format IQ differences rather than format size. These factors will be discussed further in Sec. 4."

Only one of these six factors (aberrations) that you and the paper present are relevant to optical equivalency and DOF/focus.  So, why is this paper quotee/linked?

 

On the other hand, here is a choice sentence from he paper that immediately follows your excerpt:

Quote

Although real-world IQ differences could favor any of the cameras being compared when equivalent photos are taken, the advantage of a larger format is that it offers extra photographic capability over a smaller format.

 

There are other similar passages in that paper suggesting differences in image quality between different sized formats.

 

If the intention of quoting/linking that paper was to assert that it is difficult to get an exact match between two different lenses made by two different manufactures, I  once again direct you to Shane Hurlbut's test in which he compared two different lenses made by two very different manufacturers (Panasonic and Voigtlander), that exactly matched in regards to the softness/bokeh of the background, with only a slight difference in exposure/color.

 

So, a more exact match can be achieved than what we have seen so far in "equivalency tests."  In addition, we can compare the actual DOF, instead of seeing how closely one can match an arbitrarily soft background set at some arbitrary distance, while relying on lens aperture markings and inaccurate math entries.

On 9/23/2020 at 11:30 AM, noone said:

1) Equivalence theory HAS been tested and is accepted by the majority of photographers and scientists.

It is doubtful that any of the equivalency tests presented so would be accepted by "scientists" as a valid DOF/equivalency comparison.

 

 

On 9/23/2020 at 11:30 AM, noone said:

Most accept it even though no one has done an EXACT match (IE the photos LOOK very similar but someone will always point out a tiny difference) to the satisfaction of SOME but the deniers have never shown evidence that it is wrong either.

In regards to your claim in this thread that it is impossible to exactly match the focus between two lenses of the same focal length made for the same format from different manufacturers, I have already linked a comparison conducted by Shane Hurlbut in which the focus matches precisely -- much more exactly than any equivalency comparison presented here.

 

So, we probably can get a significantly closer match in a DOF equivalency test than what we have seen so far.

 

 

On 9/23/2020 at 11:30 AM, noone said:

The problem in getting an EXACT match is you would have to scale the equipment for an EXACT match and that would be near impossible.

This is false, as exemplified by the Shane Hurlbut test mentioned above.

 

On 9/23/2020 at 11:30 AM, noone said:

To the point the EASIEST way might be to build from scratch very simple low element number formulas that test this (but may not be great images).

That might work, especially if one likes to do things the hard way.  Not sure what the point is regarding low element numbers.

 

 

 

On 9/23/2020 at 9:09 AM, Jay60p said:

A few thoughts on this topic:

1) I would have expected this equivalency theory would have been tested more reliably by still photographers at the numerous photography forums long ago.  They use a much wider range of format sizes than the video people here at EOSHD.  If not, it could be there is just too many variables to control, or no consensus on the methods to use.

The reason why we don't have a proper test of DOF equivalency from still photographers (nor from cinematographers) likely doesn't involve involve the number of variables.  The true reason would probably require some philosophizing.

 

 

On 9/23/2020 at 9:09 AM, Jay60p said:

2)  I would suggest using a 4x5 sheet film camera (8x10 is at $15 a shot!) and limit the test to manual lenses.

Mount all lenses on a 4x5 lens board and take a 4x5 shot for each, to be scanned for viewing.

This way the camera does not change, the sensor does not change, no digital transformations are done in camera.

The different lenses would have different size image circles in the 4x5s, so would be of different resolutions,

but that should not effect the depth of field comparisons much.

It probably would not be wise to shoot DOF/equivalency comparisons using the same emulsion for different formats.  The smaller format on the same emulsion could appear to have a lower resolution, more softness and more grain, which would invalidate the results.

 

On the other hand, digital formats lend themselves perfectly to such a test, as they have standardized resolutions.  So, a Super16 full HD camera will have the same digital resolution as an 8"x10" full HD camera.

 

 

On 9/23/2020 at 9:09 AM, Jay60p said:

I did look at the SLR primes with the Turbo II speedbooster. It shrinks the first fringing seen, but it includes more of the edges of the

image circle, with more CA, so overall the fringing looked the same.

Yep.  Focal reducers tend to transfer the qualities of the larger format lens to the image of the smaller format.

 

 

On 9/23/2020 at 9:09 AM, Jay60p said:

Here is a review of my favorite Fuji lens that includes comments on the in-camera corrections (CA, vignetting, distortion) for anyone

unfamiliar with this: https://opticallimits.com/fuji_x/887-fuji1024f4ois?start=1

Thanks for the link!

 

For the benefit of those who are unfamiliar with in-camera corrections for chromatic aberration, vignetting, barrel/pincushion distortion, etc., such features have been implemented in digital cameras for a long time, and these corrections are not unique to Fuji cameras.

Okay.  Thanks!

54 minutes ago, ZEEK said:

For the EOS M ML RAW Modes, Jip-hop a while back posted the calculations of how the modes compare relative to the width of a full frame sensor (The Crop Factor).
1080 RAW Mode [1736x976] = 1.6x Crop Aps-c
1080 RAW Mode + x3 Crop Mode Enabled 1800px wide = 4.61x Crop (1.6x * 2.88x) 
2.5K RAW Mode @2.35:1 = 3.29x Crop (1.6 * 2.06) 
2.8K RAW Mode @2.35:1 = 2.96x Crop (1.6 * 1.85) - (Closest mode to Super16 or the BMPCC FOV)

Thanks!  Very helpful!

 

So, the 2.5K raw mode @ 2.35:1 vignettes with 16mm lenses?   Does the 2.8K mode vignette with Super 16 lenses?

36 minutes ago, Anaconda_ said:

Sorry to quote you again, but there's a new test build with complete realtime preview, non-cropped for 5k modes now. I just shot 2 minutes of 16:9 12bit raw without any dropped frames. I could see my framing perfectly as though I was using a native camera mode... almost. 

What is the crop factor of these modes (what lens formats match the cropping)?

13 hours ago, Jay60p said:

There is another factor with the new digital cameras which will complicate DOF/format test results.  My Fuji X-T3 recognizes specific Fuji lenses and automatically corrects aberrations for those lenses in camera.

That's a good point, and such in-camera "lens correction" features have existed for a long time and are not unique to Fuji cameras.

 

The primary in-camera feature that might affect DOF tests would be the chromatic aberration correction.  In-camera reductions of barrel distortion, vignetting, and local color changes (from frame center to edge) are less involved in DOF/focus.

 

 

13 hours ago, Jay60p said:

I have FF Canon, Takumar, Minolta 35mm prime lenses with dumb adapters, and none of them are as sharp and clean as the two APS-C Fuji zoom lenses I use. The Fuji zooms don't show color fringing. My FF 35mm primes and Nikon F zooms do (on very close examination).

A few things come into play here.

 

Firstly, Fuji is no slouch in regards to lenses.  Their optics are known for exceptional quality, and I would bet that most Fuji lenses today need very little digital, in-camera corrections.

 

In regards to comparing your APS-C Fuji zooms to FF Canon, Pentax, Minolta primes and Nikkor zooms, keep in mind that when you crop into the image circle of those FF lenses, you are throwing away resolving power and lens character.  A good focal reducer will transfer most of the FF resolution and the lens character to the smaller format.

 

Also, it's not surprising that chromatic aberration appears on some of your non-Fuji lenses that are modern, as camera manufacturers have a tendency these days to rely more on digital correction over optical correction.  So, of course, if your X-T3 isn't correcting the chromatic aberration on the non-Fuji lenses, that would further explain the difference.

 

Keep in mind that these minor in-camera features will not change the DOF nor focus to make APS-C lenses (especially zooms) render images like those from 8"x10" lenses.

I think that this ffmpeg command will create a new file that runs all the frames at 120fps without transcoding:

       ffmpeg -r 120 -i original30fps_file.MOV 120fpsoutput_file.mov

 

If it doesn't transcode, it should make the 120fps copy  quickly.  Also, it would be easy to make a script based on this command that would batch convert a bunch of files.

 

Of course, you could always convert the frames to run at 120fps in an NLE.

23 hours ago, noone said:

A 40mm 1.2 would give a close enough photo. but you could even use an existing Kipon 40mm f0.85 (a lens for both M43 and APSC formats) and keep the change!

That 40mm Kipon f0.85 is designed for APS-C, so it should be slightly closer in look to larger formats than a lens designed for M4/3.  Also, as I have mentioned, cropping into a lenses image circle will change the look and make the image softer.

 

However, I found examples of that lens wide with a open aperture on an APS-C sensor.  Although that lens is not an equivalent focal length to the lens of the 8"x10" image I linked earlier in this thread, it yields comparably shallow DOF, so it should give us a rough idea of how lenses for smaller formats behave in such shallow DOF scenarios.  Here is one example.

 

Of course, the Kipon APS-C lens looks softer and more mushy wide open, with the 8"x10" lens exhibiting more resolving power and a crisp image.  Also, the plane of focus with the 8"x10" lens seems more solid and well defined than that of the APS-C lens.  The APS-C lens additionally suffers from chromatic aberration (remember, Caldwell confirmed that lenses for smaller formats are more prone to aberrations).

 

I think that these differences between these two lenses are common to most lenses made for lager and smaller formats, and that the such results will largely be consistent in any proper DOF/format comparisons that might follow.

 

 

On 9/20/2020 at 2:04 PM, noone said:

Just found that interesting and I would love to see someone do a direct comparison (between an 8x10 camera anyone got a digital back that size with a 600mm f8 lens who also has M43 with a Kipon  40 f0.85?   Great! I look forward to the tests).

I too would like to see a proper DOF/look comparison done between larger and smaller formats.

14 hours ago, SteveV4D said:

This argument overlooks the use of speedboosters,

We haven't directly touched on speedboosters in this thread, but there have been other discussions about how speedboosters/focal reducers are involved in format looks.

 

 

14 hours ago, SteveV4D said:

the fact that smaller sensors can via adapters use lenses designed for larger sensors and the issue that many fullframe lenses have crops for certain frame rates.. ie Panasonic for 60p.  

The adapter/crop issue has been addressed in this thread.

 

 

14 hours ago, SteveV4D said:

For me the visual qualities I require come with codec and colour science.  Not sensor size.  

The format looks in question do not involve sensor size, per se.

17 hours ago, hyalinejim said:

On the contrary, the last few pages of discussion gets right to the heart of the question raised.

Exactly.

18 hours ago, SteveV4D said:

None of it is even proving that fullframe is necessary.   I could argue why shooting film is necessary and produces a look different to digital, but it still doesn't prove it necessary.

What makes a format necessary are what someone considers to be desirable qualities.  We are discussing the desirable qualites of larger formats vs. smaller formats -- which involves FF.

22 hours ago, noone said:

You think the tests get close enough but then when you see a(often very small) difference you attribute that to a difference between formats instead of between the optics.

No.  You are mistaken.  You need to more carefully read what I have said.  I usually attribute differences in equivalency comparisons to failures of the testers.

 

 

22 hours ago, noone said:

There is no reason you would get a difference in vignetting if you used identical formula lenses to match the crop (IE scaled).

It might be helpful for you to actually read what I wrote.

 

 

22 hours ago, noone said:

I simply can NOT match my ancient 300 2.8 with M43 (other than the $35000 plus Arri 150 1.3) or my ancient 24 1.4 (because there are no 12mm m43 f0.7 lenses) or my ancient 85 1.2 (again, no 42.5mm f0.65 lenses which is approaching the limit in air).   No high quality tilt shift lenses either like my favourite 17 f4.

How is this relevant?

 

By the way, if you use mirrorless cameras with shallow mounts, a tilt/shift adapter works with many lenses.

 

 

22 hours ago, noone said:

If I could do what i can with m43 (or Pentax Q) what i can with FF, I would only be using that.

So, are you saying that larger formats have qualities that are lacking in smaller formats?

 

 

22 hours ago, noone said:

A 600mm 8x10 f9 lens would be equivalent to about a 90mm 1.4 FF (so about a 45mm f0.7 M43).

600mm 8"x10" lens is more like an 80mm FF lens (or like a 40mm M4/3 lens).

 

 

22 hours ago, noone said:

If you COULD get a lens to match it  (it IS possible even if there are none) it would yield a very similar photo even without being the exact same lens design.

There are a few 80mm FF lenses.

 

There would likely be a difference between the look of two formats with such a narrow focal length and with the apertures set for a shallow DOF.

 

 

22 hours ago, noone said:

If the lens was 600mm f8, then that would be almost impossible to match with m43 as that would be about a 90mm f 1.2 FF so you would need an aprox 45 f0.65 to even give a similar if not exact photo.

Well, that would actually qualify as a look inherent in a larger format that is impossible in a smaller format, wouldn't it?

 

 

23 hours ago, noone said:

You have yet to show that there is ANY difference BECAUSE of the differences in sensor size and so far all difference have been because of the optics and not getting an exact match.

You really need to read what I wrote in regards to optics and sensor size.

 

The failure to get a match is usually due to tester mistakes.  In addition, all of the testers so far were not actually testing DOF.

 

Incidentally, in regards to your earlier claim about it being impossible to get an exact match with two lenses that have the same focal length and that are designed for the same format, here is that very comparison by Shane Hurlbut.  It looks like an exact DOF/focus match to me, but the exposure is slightly different (likely due to a difference in lens transmission).  So, exact focus matches are possible.

9 hours ago, noone said:

But if you use the same optics in different formats you get the same result...it is not the format that makes the difference it is the lenses.

Well, not exactly.  If you use a S16 lens on a 4"x5" sensor, you will likely see substantial vignetting that won't appear with the same lens on a S16 sensor.  The image inside the vignette probably will appear softer, as the pixels on the 4"x5" sensor are likely coarser.

 

Likewise, if one applies a S16 crop inside the image circle of a lens made for 4"x5", most of the lines of resolution will be thrown away, and the image will appear much softer (which can affect the appearance of the DOF) than using that same lens on a 4"x5" sensor.

 

 

9 hours ago, noone said:

To get an exact match to satisfy everyone,  You would need to firstly pick your cameras of different formats and get the EXACT crop factor.  Next you need a lens for one format. You would need to know the actual focal length (not just the marked focal length),

That's not too difficult.  Earlier in this thread, I picked the S16, M4/3 and 8"x10" formats, and I found several manufactured lenses for those formats that gave around a 98% match on the equivalence calculator that was linked earlier in this thread.  That's a good start, and most of the other variables can be adjusted slightly without suffering invalid results.

 

In regards to knowing the exact focal length when it changes after focusing on the subject, as long as the focal lengths remain in a nominal range there really is no problem, as one can make adjust the aperture so that the results match more closely (as I have already explained in this thread).

 

 

9 hours ago, noone said:

You would need the  diameter and could then work out the exact f stop.

This is where you (along with the legions of equivalency testers that precede you) and I depart.

 

There is absolutely no need to stand on the formality of getting the numbers to exactly match the figures dictated by the DOF/equivalency formula, and trying to do so will only lead to difficulty and mismatched, invalid results.

 

The aperture markings on lenses are not accurate enough (and T-stops are useless for such a test).  Also, aperture markings don't account for the change in focal length when the lens is adjusted to put the subject in critical focus.  If you wanted to get a precise number match to the DOF formula, you would have to measure the exact focal length when focused and the exact aperture diameter, which is somewhat challenging considering there is no tangible focal point marking on  lenses and considering that the aperture is usually inside the lens.

 

Trying to get the numbers to precisely match the DOF/equivalency formula is a fools errand.

 

On the other hand, there is nothing wrong with setting up the test with two camera/lens combinations that match as closely as possible, and then merely adjusting the aperture ring on one of the cameras until the two DOF ranges match by eye.  If the adjusted aperture reads a little off from where the DOF/equivalency formula says it should be, simply make a note of that adjustment and include that note in the test report.

 

 

10 hours ago, noone said:

Using the crop factor to get an exact match, you would then need to do the same for the second format.

That's unnecessary, and you would only need to crop one of the images if you want to exactly match the frames.

 

 

10 hours ago, noone said:

You will also probably need to have the exact same lens formula though to get the same T stop (and take away any possibility of being a difference for other reasons).

No.  If you use T-stops markings, you are making an even bigger error than if you just rely on the accuracy of F-stop markings.

 

The aperture markings on the lens are inaccurate and mostly irrelevant.

 

 

10 hours ago, noone said:

Yeah, it probably IS possible (maybe even easy for some).

Well, if you like to do things the hard way as prescribed in your method, you will have a tough time and will unlikely get valid results.

 

 

10 hours ago, noone said:

I could not do it in a lifetime though and again, beyond being a academic exercise, what is the point?

I agree that your method might not work in a lifetime.

 

I would think that this point of this exercise was obvilus by now -- to demonstrate similarities and/or differences between optics made for different formats.

 

 

10 hours ago, noone said:

So, unless you (or someone else) does THAT, I will always accept that the theory matches the practice and to date, all tests have satisfied me they do

Good for you!

 

 

10 hours ago, noone said:

Are there ANY tests that have been done matching equipment EXACTLY?

There are tests that got a close enough match with the equipment.  However, they suffered the maladies that afflict most other tests:

• they didn't show the delineation of the DOF limits;
• they used wide angle lenses and/or deep DOF; they used a zoom lens;
• they had camera sharpening enabled;
• and, of course, they didn't adjust the aperture by eye to match the DOF.

4 hours ago, hyalinejim said:

Can you link to those posts?  I'm still no clearer on what the differences in DOF rendering due to large/small format lenses actually looks like in an image.

I'll just repeat what has been mentioned in this thread.

 

The lenses for the smaller formats have to use larger apertures to match the DOF of larger format lenses.  So, if one is shooting large format with shallow DOF (as in the above photo), matching that DOF with a with a smaller format lens will require its aperture to be wide open, which not only affects the overall sharpness (As you surmised), but it can also produce a difference in the relative sharpness between center and edges of the frame.  This characteristic with the smaller format lessens as the aperture is reduced.

 

The above 8"x10" photo was shot with a roughly 600mm lens (not sure on the aperture), and the closet lens match that I could find in a smaller format is the Nokton 42.5mm f0.95 for M4/3.  Here is a test of that lens set at f.0.95 that not quite as close/tight as the above photo, but it gives a rough idea of how it might behave close and wide open.  It doesn't seem as sharp wide open as it does at smaller apertures, and, unfortunately, the DOF isn't quite shallow enough to match that of the above 8"x10" lens.

 

In addition, at wider apertures,  there generally seems to be a faster transition from sharp to soft at the rear DOF limit on lenses made for larger formats.   This quality might relate to why the plane of focus seems more solid, more well-defined and flatter on larger formats.

 

Also, the softness/bokeh outside of the DOF seems cleaner and less mushy.

 

Here is a photo shot with an 8x10 camera that shows that shows a solid, flat focus plane (although the lens appears to be swung slightly to the right), with the subject nicely separating from the clean and not too mushy background.

1 hour ago, hyalinejim said:

Are there any conclusions you would draw on the pros and cons  of large formats versus small in terms of the qualities of images afforded by the glass associated with each? For example, are large format lenses well suited to narrow DOF pics that maintain sharpness and small format lenses well suited to deep DOF without suffering as much from diffraction?

I don't have any conclusions in regards to larger formats vs. smaller formats other than the ones I have mentioned in this thread and in other threads.

 

Larger formats don't usually suffer from diffraction with deep DOF, hence the f/64 club.