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05-11-2013, 07:40 AM   #1
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Any updates/tests on 25mm DFA versus DA?

Hello all,

I am potentially interested in picking up a 25mm for my 645D and am interested in the comparison between the DFA and DA versions, both of which can be obtained. I am aware that both versions are rated very highly in terms of resolution, etc. but that the original DFA version supposedly had trouble (for a lens of its price) with aberrations. The DA version, which came later, was aimed at reducing this (though of course Pentax would not quite say so, as that would be an admission of problems with the DFA). However, no one seems to have been quite sure about what changed - it is clear that there were superficial changes and a longer hood - which would of course reduce aberrations associated with flare etc. - but only in situations where a bright light source is around the edges of coverage of the original lens. If it was already out of shot (or shielded by the original hood), or still in frame even with the longer hood, then one would expect no difference (if this is all that has changed). At the time of the change, the DA version was indicated as not being compatible with full frame 645 film, only with the cropped 645D (though whether this is purely because of hood changes or fundamental changes with the lens itself, affecting the image circle, I do not know).

So, my question is this: is there any more up-to-date knowledge and/or testing of the newer DA version, preferably compared to the earlier DFA version, to reveal the performance of the new lens and whether anything changed over than superficial factors and the hood? If it is only superificials and hood, then I might get the DFA version to get the full frame coverage (you never know when that might be desirable) - and simply try to use a longer hood that I will obtain elsewhere. If, on the other hand, the performance is better and/or there are changes more than superificials and the hood, then I might go for the DA version.

Any hard data, tests or clear experiences would be much appreciated.

I am fully aware that both versions perform well much of the time, so, with respect, I am not really after responses that amount to 'both are good, just get one' or 'the old one seems fine to me'. It is specific evidence comparing the performance or clear knowledge of what changed (if anything) beyond superficials and hood size that I am seeking.

Many thanks in advance!

Ed

05-11-2013, 08:21 AM   #2
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QuoteOriginally posted by Ed Hurst Quote
Hello all,

I am potentially interested in picking up a 25mm for my 645D and am interested in the comparison between the DFA and DA versions, both of which can be obtained. I am aware that both versions are rated very highly in terms of resolution, etc. but that the original DFA version supposedly had trouble (for a lens of its price) with aberrations. The DA version, which came later, was aimed at reducing this (though of course Pentax would not quite say so, as that would be an admission of problems with the DFA). However, no one seems to have been quite sure about what changed - it is clear that there were superficial changes and a longer hood - which would of course reduce aberrations associated with flare etc. - but only in situations where a bright light source is around the edges of coverage of the original lens. If it was already out of shot (or shielded by the original hood), or still in frame even with the longer hood, then one would expect no difference (if this is all that has changed). At the time of the change, the DA version was indicated as not being compatible with full frame 645 film, only with the cropped 645D (though whether this is purely because of hood changes or fundamental changes with the lens itself, affecting the image circle, I do not know).

So, my question is this: is there any more up-to-date knowledge and/or testing of the newer DA version, preferably compared to the earlier DFA version, to reveal the performance of the new lens and whether anything changed over than superficial factors and the hood? If it is only superificials and hood, then I might get the DFA version to get the full frame coverage (you never know when that might be desirable) - and simply try to use a longer hood that I will obtain elsewhere. If, on the other hand, the performance is better and/or there are changes more than superificials and the hood, then I might go for the DA version.

Any hard data, tests or clear experiences would be much appreciated.

I am fully aware that both versions perform well much of the time, so, with respect, I am not really after responses that amount to 'both are good, just get one' or 'the old one seems fine to me'. It is specific evidence comparing the performance or clear knowledge of what changed (if anything) beyond superficials and hood size that I am seeking.

Many thanks in advance!

Ed
From what I know, the only difference between the two is the hood.

According to our lens database:

"The SMC Pentax-DA 645 25mm F4 AL [IF] SDM AW lens is identical to its D-FA series predecessor, except that its lens hood has been stretched to better work on the Pentax 645D."

In the US, the DFA lens is no longer available (was replaced by the DA lens).

Adam
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05-11-2013, 08:35 AM   #3
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Thanks Adam. I have seen that - just wondered if it is a firmly established fact that they are otherwise identical (and borne out by actual performance)...
05-11-2013, 09:52 AM   #4
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I think that after they released the 25mm, Pentax realized that the small hood was causing issues. Since I don't think there's much of a market for film lenses any more, they went ahead and stretched the hood at the expense of vignetting on the 645n, etc.


Adam
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05-12-2013, 12:32 PM   #5
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Thanks Adam. Looks like the DA is the one to go for then!
05-12-2013, 10:37 PM   #6
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"...which would of course reduce aberrations associated with flare etc."

Flare is not an aberration.
05-13-2013, 12:55 AM   #7
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Hello there. I didn't actually say it was - I referred to aberrations associated with flare etc.. The words "associated" and "etcetera" gave me enough vague latitude to make it clear that I wasn't saying that. I was mainly referring to CA/fringing, which of course tends to happen in many of the same high contrast situations in which flare can occur.

Anyway, although I didn't say so, one could argue that flare is an aberration. After all, it is not something that is present in the same way when a scene is directly viewed - it is an artefact of the imaging process.
05-13-2013, 03:09 AM   #8
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The older version is said to have marginally higher chromatic aberrations - the newer version is said to have better control of it - mind you the CA on the older version is very well controlled when compared to other 20mm lenses on 35mm format.


QuoteOriginally posted by Silent Street Quote
Flare is not an aberration.
Correct, it isn't. Flare is primarily a characteristic of the design on the lens and the AR coatings used, the number of lens elements in a lens increases the risk of flare and internal reflections - and the AR coatings are used to control the magnitude of flare and internal reflections when it is present. Flare is common in all complex optical systems - it is interesting to note that flare does occur with pinhole cameras, but that is because an Ideal pinhole "lens" has to be 2D, and perfectly round- Many pinhole "lenses" are imperfect though, Zero Image pinhole cameras come very close to embodying the ideal pinhole.


Last edited by Digitalis; 05-13-2013 at 03:19 AM.
05-13-2013, 05:11 AM   #9
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QuoteOriginally posted by Digitalis Quote
The older version is said to have marginally higher chromatic aberrations - the newer version is said to have better control of it - mind you the CA on the older version is very well controlled when compared to other 20mm lenses on 35mm format.



Interesting! Do you know if this marginal improvement is purely a result of the larger hood causing the problem to be provoked less or whether there have been other improvements that mean the lens actually handles the issue better in itself?

I also wonder how the two versions compare in terms of CA with Hasselblad's superwide lens...
05-13-2013, 04:16 PM   #10
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Ed,

There must be something other than the hood that is different. The DA version, despite the larger hood, is listed as 30 g lighter than the D FA
05-13-2013, 06:23 PM   #11
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QuoteOriginally posted by Ed Hurst Quote
I also wonder how the two versions compare in terms of CA with Hasselblad's superwide lens
The hasselblad HCD 28mm f/4 cannot be used on a full frame 645 camera - the H3D will not allow it. the Pentax DFA 25mm f/4 can be used - and its 15mm FOV is quite spectacular. The hasselblad lens uses hard wired software optics correction - which cannot be disabled, which would make any direct comparison between any other ultrawide medium format lens invalid.

QuoteOriginally posted by Thomas Quote
here must be something other than the hood that is different. The DA version, despite the larger hood, is listed as 30 g lighter than the D FA
these lenses are solid metal, a redesigned hood really would drop that much weight from a lens.
05-13-2013, 07:52 PM   #12
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I remember they also changed internal flocking and made some other improvements. Coating was another one I remember. I got the DA and it's an amazing lens.
05-13-2013, 08:06 PM   #13
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I have the original DFA version of the 25mm f/4 -And I have no complaints about its performance. At least if pentax ever decides to release a 645D with a full frame 645 sensor - I will be ready for that day.
05-13-2013, 08:15 PM   #14
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QuoteOriginally posted by Digitalis Quote
The older version is said to have marginally higher chromatic aberrations - the newer version is said to have better control of it - mind you the CA on the older version is very well controlled when compared to other 20mm lenses on 35mm format.




[...] it is interesting to note that flare does occur with pinhole cameras, but that is because an Ideal pinhole "lens" has to be 2D, and perfectly round- Many pinhole "lenses" are imperfect though, Zero Image pinhole cameras come very close to embodying the ideal pinhole.


You bet they have the close-to-ideal pinhole! I like to exploit the potential for flare, but with Zero Image cameras the pinhole is so damn good that flare is either too much (enough to write off an image) or virtually nothing. A friend makes his own pinhole cameras with just tote amazeballs flare: he can aim straight into the sun and still get a beautiful image with quite stunning flare!

I use nano B+W or HMC SHMC filters on all of my apo/asp 35mm and 67 lenses and don't get any flare. Mind you, using a filter also increases the risk of flare.
05-15-2013, 11:11 AM   #15
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QuoteOriginally posted by Digitalis Quote
I have the original DFA version of the 25mm f/4 -And I have no complaints about its performance. At least if pentax ever decides to release a 645D with a full frame 645 sensor - I will be ready for that day.
+1, wonderfull rendering on film 645NII as well, in situations where you need more widthness for framing !
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