hyperfocal distance and IOS calculators

[donboys]

My Fuji xT-1 has a scale showing the dof and focal distance viewable in the LCD and view finder which is very useful to determine hyperfocal distance. By adjusting manual focus twist till the right end of the blue (focus range) band touches infinity. The focus distance, shown in white, is your hyperfocal distance. An iPhone app Tack Sharp, gives the hyperfocal distance for an APS-C sensor, given the focal length and aperture. The two, TS and Fuji, disagree considerably. At 18 mm focal length, f/16, Fuji says hyperfocal about 14 ft, min focus about 7 ft., TS says (for 17mm - doesn’t do 18) hyperfocal distance is 3.2 ft., near focus, 1.5 ft. Why?  After contacting Rico Pfirstinger, author of a book on the XT-1, I now know why they differ. Tack Sharp by default uses a 19 micron CoC for the APS_C sensor, Fuji (according to Rico) uses 5 micron CoC for their camera calculation. Tack sharp lets you, in the info panel, adjust the COC. Set it to 5 micron and the Tack Sharp answer agrees a lot better with Fuji. I guess this means unless you need the precision of focus Fuji is trying to achieve don't believe the blue range of focus band.

 

Another iPhone app, Lens-Lab agrees well with Tack Sharp. A Wikipedia article uses 19 micron for the CoC of a APS-C (Nikon) sensor. 

 

So what does this all mean?

 

Here is the Tack Sharp for 5 micron CoC

 

 

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and for 19 micron

 

 

[jlmphotos]

ISn't te C of C lens specific?  No?  I would LOVE to know that.  I tried using DOFMaster on  my iPhone but don't trust it.  If the CofC is 5 for Fuji, then I can plug that in.

[CRAusmus]

The way I've always understood it, and please someone correct me if I'm wrong, you need three factors to determine your DOF...

 

Aperture, Focal Length, and distance to focal plane.

 

Having not known what CoC was until I googled it, I'm assuming that helps the app determine that distance to more accurately calculate your DOF/Hyperfocal Distance.

 

 

Again, if I'm wrong please correct me so I don't continue thinking about it this way.

[donboys]

I'm not able to reply to the details but it seems CoC is dependent upon the size (diameter) of the image (i.e. sensor). But the calculation of CoC also depends on arbitrary criteria of acceptable image resolution, arbitrary being the important word. Different standards seem to exist. The purpose of these calculators is to determine the hyperfocal distance, that giving the greatest dod and extending to infinity. 

[CRAusmus]

The more I think about it, the more I feel as though I have twisted this up a bit.

 

I'll be happy to have someone who understands this better jump in this discussion and set my confusion straight as well.

[madmaxmedia]

I'm not able to reply to the details but it seems CoC is dependent upon the size (diameter) of the image (i.e. sensor). But the calculation of CoC also depends on arbitrary criteria of acceptable image resolution, arbitrary being the important word. Different standards seem to exist. The purpose of these calculators is to determine the hyperfocal distance, that giving the greatest dod and extending to infinity. 

 

Being that this is the case, I think personal experimentation with different CoC values and some controlled test shooting will help each person determine what is acceptable level of sharpness.

 

Maybe the Fuji value is too stringent for some, or maybe not. But then you can plug in whatever CoC value roughly works best for you into an app like Tack Sharp.

[Larry Bolch]

To understand depth of field, the key is understanding the Circle of Confusion. It is defined as eight optical engineers sitting around a table and arguing about the definition.   

The problem is a simple one. Sharpness drops off gradually at any aperture. If it went from _|¯|_ there would be no problem at all. The argument depends upon where the individual engineer decides the image is sufficiently out of focus to make that the basis for the circle of confusion. It is entirely possible that no two charts or apps will ever agree. Using the internal hyperfocal function with the X-cameras guarantees success since it is extremely conservative. There may well be charts and apps kicking around that were based upon early films without anti halide coatings that were based upon the flair within the film itself and way too loose for our 2015 sensors.

[flysurfer]

Fuji is using the sensor resolution as its benchmark, which is the only objective measure, anyway: pixel-sharp DOF on the sensor level. In other words: Fuji's electronic DOF zone is the zone where the image is as sharp as the sensor's pixel-pitch can resolve light. Makes sense to me, so I like it. Everything in this DOF zone will look equally sharp when viewed at pixel-level (100%) resolution.

 

Of course, the DOF markers on those "clutch lenses" are different and mostly just for show, they are about 2 stops off (as in less conservative). 

[Burb]

Am I right to say that Fuji is using a "save" CoC (probably the mentioned 0.005mm) because everything then will always be sharp at that hyperlocal distance? But if you push it a bit by using the values from certain DOF calculators at a CoC of 0.02mm you will be able to gain a bit extra sharpness in the near distance?

 

With my Samyang 12mm I focussed at 1 meters@f8 and get a sharp images from very close (±0.5m) to the far distance. If I had used a CoC value of 0.005mm I have to focus around 3.6 meters and the closed near distance will be around 2 meters! So I'm "loosing" almost 1.5 meters in nearby sharpness.

[madmaxmedia]

Am I right to say that Fuji is using a "save" CoC (probably the mentioned 0.005mm) because everything then will always be sharp at that hyperlocal distance? But if you push it a bit by using the values from certain DOF calculators at a CoC of 0.02mm you will be able to gain a bit extra sharpness in the near distance?

 

With my Samyang 12mm I focussed at 1 meters@f8 and get a sharp images from very close (±0.5m) to the far distance. If I had used a CoC value of 0.005mm I have to focus around 3.6 meters and the closed near distance will be around 2 meters! So I'm "loosing" almost 1.5 meters in nearby sharpness.

 

Yes, it seems like you would gain a bit of extra sharpness in the near distance, and lose a little sharpness in the far distance.

 

I think Rico (not surprisingly) is correct in his assessment of Fuji CoC. When I read about traditional CoC values, I read about taking into account viewing distance from printed image, etc. so there is a lot of wiggle room generally speaking.

 

But I think if DOF and hyper focal shooting are important to you, you should experiment and then determine how far you can push the near focus distance and still get acceptable sharpness to infinity.