MTF Program

has anyone else tried this yet?

I have my K10D set to MTF program. Now perhaps I am being naive, but I was expecting this program to bais towards the lens best aperture, but that isn't what I'm seeing.

It seems to select wide open in 90% of situations. Initially I thought it was just that I was shooting in low light, but earlier on today it picked 1/1000th at F4.5 with the kit zoom. Now I'm sorry but the kit zoom is not at its best at F4.5, surely in that situation it ought to be biasing towards something more like F8?

am I doing something stupid here?

Interesting...
I use MTF all the time. I always did on the *ist-D, and did on the Z1 before that.

However, I do know that the MTF data is contained in the lens, and the body needs to read that information. Additionally, the K10D will balance the MTF with the available light - it's not that it uses the MTF aperture all the time, just that the program is weighted towards using that.

Either the Z1 or the *ist-D (probably the Z1) manual had the graphs of each of the program lines so you could see how it was weighted.

HTH!
Matt

thanks for your reply Matt, I figured that would be the case hence I wasn't initially bothered by it, it's when it starts picking combinations like 1/1000th at F4.5 that I start to get a little confused.

I'm going to have to play with it some more I think since MTF-priority generally seems like a very good idea. It's always possible (indeed likely!) that I am doing something stupid and unintentionally telling it to open wide.

I'd picked up on this when having a re-read of the manual on a long plane ride the other day. Does anyone know if the K10D can pick up this sort of data from Sigma EX lenses?

My initial feeling is 'I doubt it'...

Will

I use MTF program line, but switch program with Hypershift in P mode.

I checked the Z1 and Z1p manuals and they have the graphs that give you a pretty good idea of what's going on.

I'll also check the MTF of the 18-55 kit lens when I get a chance
Matt

What I don't understand is why bother with that, you could just set the lens to f8 in Aperture Priority and let the camera set the shutter speed. Obviously a tripod could be needed in dimmer light.

In any event, in real-life photography we are unlikely to see much difference in resolution or sharpness between perhaps f8 and f16 with a zoom lens, and even wider with a prime.

When the operation of the camera starts to get too complex I'm sure that we can simplify things and get back to basics. And switch our attention to the image rather than the technicalities.

Sigma tend to reverse engineer things. If they can't figure out what something is for, they leave it alone and pray that it works. You can see this if you mount an old Sigma AF lens on a DSLR. Pentax have always encoded the names of their lenses even though AFAIK there was no reason for them to do this before the *istD came along (unless the data back for the Z1-P recorded the lens name?). Hence my Sigma made Zeiss 75-300 claims to be a Pentax SMC 80-210, while my Sigma 28-200 identifies itself as an SMC 35-135.

I therefore suspect that even if the Sigma lenses contain MTF data, it is quite possibly the MTF data for whichever lens they copied the electronics from rather than that of the lens itself.

On this note, has anyone studied/been told what the camera does if it can't get MTF data? does it revert to normal program, assume F8 is best, or what?

The *istD manual has the charts for the 18-35mm kit lens at the back of the manual. At 18mm, the camera should choose f/5.6-6.7, at 35mm it would be f/8. But that's for that lens, not your 18-55, but I would have thought, like you, that it would be along those lines.

Might need to give the contacts on the lens a good clean? Or pop into a friendly shop and try another lens, just to make sure yours isn't missing something.

Dan

I checked with Sigma last year and they said they don't contain mtf data. I imagine only Pentax FA and DA lenses would do.

I tried it with a 43mm and with normal program line, I was on f/2.8, when i switched to MTF line, it went to f/4.

Please excuse my ignorance . . . what does MTF mean exactly?

Here here what is MTF?

something like Median Transfer Function

whatever it stands for, it is a measure of lens resolving power

Thanks Mongoose

Will have to keep an eye open for that in any new lenses I buy

Thanks Mongoose,

but in terms of Pentax DSLR's and Pentax lenses . . . what does it mean?
What are the benefits of using this setting, and what camera/lens capabilities does it use that other modes don't use?

In a nutshell, when & why should we use it?

Anybody know, I mean really know?

Try this

http://www.normankoren.com/Tutorials/MTF.html


(It may be more than you needed to know)

G