“Full Frame Equivalence” and Why It Doesn’t Matter

Started Feb 4, 2013 | Discussions thread
qianp2k
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Re: “Full Frame Equivalence” and Why It Doesn’t Matter
In reply to thxbb12, Feb 7, 2013

thxbb12 wrote:

Really? There are two AF related performances - a) AF speed (CDAF no match to PDAF) and AF accuracy (still, moving and tracking). All my DSLRs don't have AF accuracy issues including 1D3 (which is a late batch) as proved in my tons of photos. I don't think any mirrorless can compete to 5DIII AF speed and accuracy (yes accuracy) especially when use thin DOF lenses. My old 5D and 5D2 don't have AF accuracy issues either but slow in AF burst speed nor my 60D. In reality I can capture those critical and precise moments your mirrorless will surrender or in much low hit rate.

I can't care less about your camera/lense case. I'm talking about the technology behind it. The PDAF system relies on very complex and tight calibrations to be accurate enough (the more resolution the sensor, the more tricky the calibration is). It's just the reality of the technology. It requires perfect alignment between the lens, the AF sensor and the image sensor. Any slight misalignment will lead to less than perfect focus. Again, it's not a myth but simply the reality of the beast. Over time, due to mechanical constraints, the AF can slightly change requiring the lens+body to be calibrated.

Let's talk about.  Show me any scientific analysis suggests CDAF has more AF accuracy?  I also can say CDAF based on contrast that is tricky on different lights and difficult in low light. PDAF is a proven technology for decades and is very reliable and accurate (with appropriate QC).  Calibration is still the key.  MFA is useful in further fine-tune an already calibrated lens especially with TC on a super-tele lens.  Personally I have not used MFA on all my cameras and I don't have AF accuracy issues really.

CDAF on the other hand, doesn't suffer from any of these constraints or limitations. It works on the final image to assess whether it's in focus, based on the contrast calculated at the pixel level. No calibration required. Period.

But on different surfaces, different light and especially low light CDAF is not very reliable. You know contrast is not very reliable by itself in its nature.

Why in the world do you think high end DSLR bodies "feature" AF adjustments? Do you think it is a feature? It's simply a way for user to calibrate their lenses with their particular body. Featuring per lens calibration is nothing else than manufacturers acknowledging the potential PDAF issue with calibration.

For further fine tune an already calibrated lens.  Ironically two cameras 60D and 5Dc don't have MFA have very accurate AF accuracy.

The fact you didn't encounter AF mis-calibration doesn't mean the problem doesn't exist. The higher resolution your body, the more likely you will be to encounter the issue. You can dig your head in the sand and be in denial, but it still doesn't change the fact.

Check these samples. I have not read any complaints against 5DIII AF. 1DX is in another level.

http://forums.dpreview.com/forums/thread/3368723 (with Sigma 35/1.4 lens, no such lens in mFT)

http://forums.dpreview.com/forums/thread/3363386 (with 85L/1.2, no such lens in mFT that you only can dream about).

I can also show you tack sharp pictures I took at f/1.4 with my DSLRs. This proves nothing in regard to the limitation of the PDAF system.

Tons of tack sharp DSLR photos vividly proved PDAF is very reliable.  There are no evidences in photos that CDAF is more accurate, simply not, sure partially I am used to FF sharpness and mFT suffers 2.0x crop penalty that affects sharpness.

Wait and see. I see lots of Canon and Nikon (more Canon) at sidelines of NFL on TV, but have not seen a single mFT sport PJ

Read my post again. I talked about focus accuracy, not focus speed. Today CDAF lags way behind PDAF in terms of speed. However, the days of PDAF are counted. Maybe not tomorrow, nor in 2 years, but eventually the PDAF technology will be a thing of the past.

Sure wait and see.  But I am sure CDAF will get better and better but PDAF also improving, similar to mFT sensors getting better and better, so do APS-C and FF sensors.

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