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01-25-2014, 02:25 PM   #1
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Not impressed with MTF program line...

Just for kicks, I wanted to see how "smart" the K-3 algorithms are for different program lines.

Now, as a software architect, I'm not a fan of "hard and fast" rules -- I like software that is "flexible". (better yet, I like software that is user-configurable!!)

Given that, my expectation was that MTF *should* mean: bias the settings towards obtaining the most sharpness out of the current lens but also taking into account all the other factors that affect "sharpness". In other words, I expected it to behave analogously to the way that "Depth of field priority" biases the lens to open the lens up, but doesn't blindly open it up to the maximum and keep it there always.

Instead, what the MTF program line appears to do is chose the lens' known ideal f/stop then never deviate from that setting. I find this nearly useless (and not in keeping with the "priority" behavior of other program lines), especially on a prime lens. I would have expected the algorithm to attempt to keep as "close" as it could to the best MTF but allow it to move a little in either direction depending on the current situation. E.g. if the best MTF for a given lens is at f/2.8 then allow the MTF program line to vary (as in a bell curve) between f/2 and f/4. After all, what's the purpose of blindly sticking to f/2.8 but then auto specifying ISO3200? Clearly a "sharper" image would be had at f/2 and ISO1600 in the same situation, but the way Pentax implemented MTF doesn't appear to work that way. It basically is no different than using Av mode with the "A" part automagically chosen for you -- that's nice, but it simply doesn't go far enough. Clearly I can see this as a convenience feature aimed primarliy at non-professionals who may not really understand how their complex lens behaves at different focal lengths, and especially designed with super zooms in mind, but given the way it currently is implemented, I seriously doubt I could ever imagine using it. I would much rather have something that was completely manual versus an algorithm that I feel is patently flawed. I would rate this feature as "close but no cigar". Ah well. On to the next test...

YMMV

Michael

01-25-2014, 04:10 PM   #2
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I think its been like that since the mtf program line came out many years ago. The info comes from the lens itself and the camera just rolls with that.

I agree that a "smart" program line would be nice. Though that's sort of what autopict does.

Adam
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01-25-2014, 04:35 PM   #3
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I'm actually keen to know how many people use MTF and has it worked for them?
01-25-2014, 05:19 PM   #4
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QuoteOriginally posted by MJSfoto1956 Quote
...also taking into account all the other factors that affect "sharpness".
Nope, it reads the chip in the lens which gives the "general" best setting (determined by engineers) for that type of lens - but not even that particular lens. That is all. Never used it :-) If I'm trying to get there (rarely) I just stop down 2 stops and go with it. I'm not a infinite pixel peeper :-)

01-25-2014, 05:27 PM   #5
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QuoteOriginally posted by Teal Quote
I'm actually keen to know how many people use MTF and has it worked for them?
I have been running in modulation transfer function for several years. Seems to work fine for my shooting needs.
Granted, there were couple times I should have intervened and opened up the aperture, for desired effect.
01-25-2014, 06:54 PM   #6
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Ok, I did a little bit more digging and I was wrong in my analysis. The MTF program *DOES* open up/stop down above and below the "optimal" aperture for the given lens, but it seems to be somewhat "sticky" -- you really need to have extreme low-key or high-key situation to force the program to consider anything other than the "optimal" aperture. So in that way, it does behave somewhat analogous to the other modes, with the proviso that it "appears" to be more biased than the other modes. It would be awesome if they would publish the lookup tables they use the program lines use to make the decisions. It would be even better if we could "tweak" these lookup tables to our own purposes. Suffice it to say I take back my initial criticism and now have a more favorable view of what they have implemented. Still not sure I will use it though. Need more testing. Hopefully, Pentax engineers will agree that letting end users customize their systems is in everyone's best interest.

Cheers,
Michael
01-25-2014, 09:08 PM   #7
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I like it for walking around. I leave ISO on auto with the range appropriate for the lighting conditions. It usually chooses an appropriate aperture and if I want something different I choose something different. The Pentax program line really is an excellent feature.
01-25-2014, 10:39 PM   #8
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QuoteOriginally posted by MJSfoto1956 Quote
Now, as a software architect, I'm not a fan of "hard and fast" rules -- I like software that is "flexible". (better yet, I like software that is user-configurable!!)
Nice to see a colleague in the software field with a similar mindset to mine. There are definitely not enough of us.

QuoteOriginally posted by MJSfoto1956 Quote
Given that, my expectation was that MTF *should* mean: bias the settings towards obtaining the most sharpness out of the current lens but also taking into account all the other factors that affect "sharpness".
Wrong expectation My thought is that DOF is perceived sharpness, not absolute sharpness.

01-26-2014, 04:56 AM   #9
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I like DxO's concept of "visual acuity" better than a single mathematical MTF "sharpness" value. Acuity in this sense takes into account "the system": i.e. noise, sharpness, vignetting, etc. Consequently, if the "MTF" program line meant instead "try to obtain the best acuity out of the system" instead of "use the single sharpest aperture setting for all photos unless there are no other options", then I would be much happier with it.

Michael
01-26-2014, 08:26 AM   #10
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I use the MTF program line on my K-5IIs for a certain reason.

I have my camera with my DA*300 mounted and always at the ready on the top of my book shelf. We always get wildlife coming by the house. There have been many times where we only had a couple seconds to grab the camera and shoot before said critter disappears. With the MTF program set, I can be partially confident that I might get a shot. If the time allows, it is so easy just to flick the control wheels to change the aperture or shutter speed setting. Also, with my wife who shares my hobby but is not interested with anything to do with camera settings, she also can just grab the camera and shoot without having to ask me to change any settings.

So for my kind of shooting, the MTF program is just a basis for a quick point and shoot and so easy to change with the flick of a control wheel.
03-10-2014, 07:24 AM   #11
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thanks Michael and all for the interesting details. Learning a lot here
03-10-2014, 11:45 PM   #12
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Found that on my f/2.8 200mm lens, that it set the aperture at f/4. But this lens is sharpest at f/5.6 to f/8... and I use f/8 a lot for depth-of-field. In practice, I don't think MTF matters much.
03-11-2014, 03:30 AM   #13
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QuoteOriginally posted by MJSfoto1956 Quote
It would be awesome if they would publish the lookup tables they use the program lines use to make the decisions.
It's tempting to think of a program line as a lookup table. But it's more like a function of a ton of inputs, yielding an output triplet of (shutter, aperture, iso).

Inputs beside the metering reading is also stuff like shutter speed limitations (flash sync etc), iso limitations (autoiso, highlight protection), variable aperture zoom settings and probably tons more.

It's quite complex in its full level of detail. That's probably why you can't just program a simple table with one line per light level.

Regards,
--Anders.
03-11-2014, 12:33 PM   #14
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QuoteOriginally posted by MJSfoto1956 Quote
Instead, what the MTF program line appears to do is chose the lens' known ideal f/stop then never deviate from that setting. I find this nearly useless (and not in keeping with the "priority" behavior of other program lines), especially on a prime lens. I would have expected the algorithm to attempt to keep as "close" as it could to the best MTF but allow it to move a little in either direction depending on the current situation. E.g. if the best MTF for a given lens is at f/2.8 then allow the MTF program line to vary (as in a bell curve) between f/2 and f/4. After all, what's the purpose of blindly sticking to f/2.8 but then auto specifying ISO3200?


If you don't use auto ISO, I believe it actually works better. I find that it tries to stick to around 1/50, 1/60 speed and if it can, then it goes to the sharpest aperture. Otherwise, it will open up the aperture. This way it never closes it down, but it might open it.


I confess that I trust it only so far, I use P mode as a "av on demand" and frequently change the aperture value.

QuoteOriginally posted by Teal Quote
I'm actually keen to know how many people use MTF and has it worked for them?


I do, always.
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