[biz-engineer]

In this year's A1 print set received from the lab, two of the prints showed out of focus areas that were looking fine on my (smaller) display. So, I revisited how I selected my exposure setting (see P mode / hyper program thread), but also I checked again the depth of field matter, opened up the online advanced DoF calculator from photopills here https://www.photopills.com/calculators/dof-advanced. However, after entering a few value sets , I got confused by the depth of field results the simulator provided me with. , until I realized that the classic format equivalence doesn't work for me (unless I didn't understand correctly).

Considering prints (or display), it looks like classic equivalence only work if display output size, viewing distance and viewer visual acuity are all fixed (e.g fixed to 8x10" at 14" viewing distance, 20/20 vision). For example, for same display / viewing conditions, the perceived depth of field from an FF 85mm f/8 image would be matched by an APSC 56mm f/5.6, that's the classic equivalence. Now, considering that a FF 85mm f/8 image would be enlarged 1.5x more than the APSC image for display (e.g taking advantage of the extra resolution of the FF camera), the classic equivalence is broken, and that case the depth of field (blur) of the FF 85mm f/8 image would be perceived like an APSC 56mm f4 image.

So, in practice, there isn't only one stop difference between FF and APSC , but it's two stops. Taking another example, from FF image to Phase One image printed 2x larger than the FF one (crop factor 0.5x), for the Phase One to match the FF depth of field its lens should be stopped down by as much as 4 stops, that's huge. And from FF to 4x5 (crop factor = 0.27), for making 3x larger prints out of the LF camera, I would have to stop the LF lens by 8 stops from FF aperture values (e.g FF lens aperture f/5.6 => LF lens aperture ~ f/100), leading to super slow shutter speeds in the LF camera. Did I understand correctly?

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Last edited by biz-engineer; 12-08-2021 at 04:37 AM.

[GUB]

Now, considering that a FF 85mm f/8 image would be enlarged 1.5x more than the APSC image for display (e.g taking advantage of the extra resolution of the FF camera)

Have you got that the right way round?

[biz-engineer]

Have you got that the right way round?

Humm , yeah I meant the FF image printed (or displayed) 1.5x larger than the APSC image, both viewed from the same distance by the same viewer.

[UncleVanya]

The moment you decided to print at different sizes you broke any equivalence. At that point you switched over to driving a relationship between your results. Equivalence however you feel about it has typically been based on the same output not on similar output density.

[Dartmoor Dave]

Considering prints (or display), it looks like classic equivalence only work if display output size, viewing distance and viewer visual acuity are all fixed (e.g fixed to 8x10" at 14" viewing distance, 20/20 vision). For example, for same display / viewing conditions, the perceived depth of field from an FF 85mm f/8 image would be matched by an APSC 56mm f/5.6, that's the classic equivalence.

Classically, depth of field is based on a point of light looking like a point rather than a blurry disc, when viewed at a certain print size and a certain distance by someone with normal eyesight. What looks like a point of light on a smaller print can easily become a blurry disc, if you make a bigger print from the same original and view it from the same distance. So yes: the bigger print will therefore have less depth of field. But take a step or two backwards so that the blurry disc looks like a point of light again and, oh look, you've got your depth of field back.

That's one of the reasons why so much of the nonsense about equivalence spouted by people on the internet is just. . . well, nonsense. Because they obsess and obsess about sensor size, while utterly ignoring the intended viewing size and distance.

[steephill]

The key thing about depth of field is that it is a subjective term and will vary depending on the viewer. One person's acceptably sharp is another's blurred.

[VictorDA]

On format equivalence (again)

Yeah, just what I was waiting for to make my 6 posts
Here's 1 anyway

[Rondec]

Typically you should be comparing images printed or displayed at the same size, otherwise none of this makes sense. Typically you would say that the APS-C image has to be enlarged more to reach the same size image as the full frame image.

If your goal is printing A1 then that should be your goal for both cameras and go from there.

[StiffLegged]

… after entering a few value sets , I got confused by the depth of field results the simulator provided me with …

Well of course you did, that’s why depth of field is defined in terms of circles of confusion. Here we go round again….

[ChristianRock]

Are you pixel peeping your A1 images? Sounds like it....

I'm still of the opinion that an image has to be seen as a whole, and if you print large it's because you are supposed to view it from a distance...

[bertwert]

On format equivalence (again)

[luftfluss]

Have you ever watched the entire video? It was the bomb back in the day.

[pschlute]

If an image is good enough for screen viewing when viewed at 100%, it will be good enough to be printed by a reputable printer at 300 ppi.

[Michail_P]

Don’t confuse Dof with dpi... you could be printing the photo, looking through the viewfinder and viewing it on a screen and still think the focus range is different. Distance makes resolution. That’s a rule. I guess A1 should be viewed from at least 3ft

[GUB]

Humm , yeah I meant the FF image printed (or displayed) 1.5x larger than the APSC image, both viewed from the same distance by the same viewer.

The automatic coc in the calculator (.03 for FF and .02 for apsc) is intended to make up for the fact the FF image doesn't have to be enlarged so much. By printing larger you needed this stay the same.