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01-12-2017, 04:13 AM   #1
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D-FA Pentax 90mm F2.8 Macro performance on K1

Just a simple question this time. From what I have been able to gather, the 90mm Macro is arguably the sharpest 645 lens available. If Pentax/Ricoh ever get their butts in gear a release a proper adapter between 645 lenses and K mount bodies retaining all features (AF, OS etc), the final question would be if the lens would resolve well on a 35mm sensor. I suspect it would, but what are your thoughts?

01-12-2017, 05:11 AM   #2
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I doubt it would be any better than the DFA 100mm macro or Tamron 90mm macro, which are a fraction of the price and weight.
01-12-2017, 05:36 AM   #3
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Like Paul said, it seems like too many problems.
a) Lens hood is for bigger format, so it is probably not 100% effective (this can cause problems with internal reflections, contrast loss, because so much extra light for the bigger image circle is entering the camera)
b) Lens is big, heavy (DFA 100mm is really compact)
c) Lens price - the 35mm FF macro primes are very fairly priced
d) You need adapter (even in best case scenario you would have problems with exif, lens profiles, etc.)
e) DFA 100mm, Sigma 105mm, Sigma 70mm, DFA 50mm, Tamron 90mm, Samyang 100mm (and also legacy lenses like FA and F series) are all very sharp, with 1:1 magnification, at good price points.
f) And finally, the camera itself probably won't be able to resolve much more. You can compare the pixel density of the 645Z and the K-1 (and the K-1 with Pixel shift). There is a point where even a sharper lens will not appear to be that much sharper due to the camera's limitations.

I remember someone using old manual 645 lens on a K-5 had big problems with contrast and flare, but that was not a top level digital 645 lens. That said, feel free to try it out Empirical evidence is more fun than theory

Last edited by Na Horuk; 01-12-2017 at 05:43 AM.
01-12-2017, 06:31 AM   #4
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The Pentax 645 sensor has an area of 1452 square mm, the K1 sensor has 864 smm, all Pentax APS-C sensors have 370 smm. So mounting the lens on a K1 is equivalent to cropping off about 41% of a 645 image, mounting on a K3 is equivalent to cropping off about 75% of the 645 image. 645 lenses are designed to provide a larger image circle ("circle of confusion") which involves a trade-off in all parameters of IQ (resolution, color fringing, edge-to-edge uniformity, etc). A lens designed for optimum performance on a FF or APS-C sensor will almost always outperform a lens designed for a larger format. We are not generally tempted to adapt lenses designed for 4X5 or 8X10 cameras to FF or APS-C sensors, even if they are outstanding optics for those large formats.


Last edited by WPRESTO; 01-12-2017 at 06:38 AM.
01-13-2017, 02:36 AM - 1 Like   #5
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Whilst I do agree on many of the points you guys have brought up (but not all, won't specify, I'm not interested in *equivalency* debates), I was more interested in this due to my want to eventually transition to a 645 body at some point in the future. I would just like this for a transitional stopgap solution, as whilst I could probably justify spending ~$2500-3000 on a high quality lens, the $6000+ one needs to pick up a digital 645 body is quite out of the question at this point in time, and adapting the lens to a K-1 body would ease the cost over a longer period of time.

As for the D-FA 100mm Macro, whilst I find this lens quite sharp, it does suffer quite strongly (compared to the D-FA 70-200 & 18-35 ART) when it comes to chromatic aberrations and other colour fringing, and for Macro work, any extra sharpness would be welcome, as would DC focusing and a focus limiter. As an aside, if they could also include tilt and shift capabilities (I know, quite the long shot, would probably have to provide two separate adapters in this case), it could make quite the formidable combination for professional macro/reproduction work!

That said, it would prove an expensive option, but for those more budget strapped, if the adapter would also function with the FA 120mm F4 Macro, it could prove quite popular.

---------- Post added 01-13-17 at 07:51 PM ----------

QuoteOriginally posted by WPRESTO Quote
The Pentax 645 sensor has an area of 1452 square mm, the K1 sensor has 864 smm, all Pentax APS-C sensors have 370 smm. So mounting the lens on a K1 is equivalent to cropping off about 41% of a 645 image, mounting on a K3 is equivalent to cropping off about 75% of the 645 image. 645 lenses are designed to provide a larger image circle ("circle of confusion") which involves a trade-off in all parameters of IQ (resolution, color fringing, edge-to-edge uniformity, etc). A lens designed for optimum performance on a FF or APS-C sensor will almost always outperform a lens designed for a larger format. We are not generally tempted to adapt lenses designed for 4X5 or 8X10 cameras to FF or APS-C sensors, even if they are outstanding optics for those large formats.
Though I would agree that lenses optimized for a certain sensor size would perform best when utilized on the 'correct' sensor size, I will bring up a few points of discussion (and please, I promise I'm not trying to argue that I'm right, I just like scholarly debate!)

1 Consider that the 645z sensor is ~%59 (FF area/645z area x 100 [just to show working incase I've fudged anything]) larger than a K-1 sensor, whilst a K-1 sensor is ~42% larger than a K-3 sensor.

2) It would be safe to say that when it comes to quantifying things as photographers, we rarely work in anything smaller than 1/3 stop margin of error (this is my opinion, definitely not a rule!) Thus, the area difference between 645/FF (59%) and FF/APS-c (42%) is smaller than a 1/3 stop.

3) I frequently use D-FA lenses optimized for a FF sensor, with no apparent* disadvantages when it comes to sharpness, flare etc.
*definitely warrants further investigation

4) Seeing that the D-FA 90mm Marco lens is actually specified for a 55x44mm sensor (hence it not being issues as a DA lens), would it be safe to assume that utilizing it of a 645z sensor is already compromising it's resolving/rendering power?

5) If point 4 is corrected, then I would agree with your comment that this MF lens would perform worse than a FF equivalent lens, otherwise, all things considered equal*, I would expect this lens to perform equally well across different bodies dues to logical deduction.
*that said, things cannot be considered equal due to adapter mount tolerances, see Roger Ciala's post for more info: https://www.lensrentals.com/blog/2013/09/there-is-no-free-lunch-episode-763-lens-adapters/ (though I expect you've read this already, you seem well informed)

Hopefully you'll reply in kind, I look forward to you response

Last edited by Joshua A; 01-13-2017 at 02:45 AM.
01-13-2017, 03:37 AM   #6
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QuoteOriginally posted by Na Horuk Quote
Like Paul said, it seems like too many problems.
a) Lens hood is for bigger format, so it is probably not 100% effective (this can cause problems with internal reflections, contrast loss, because so much extra light for the bigger image circle is entering the camera)
b) Lens is big, heavy (DFA 100mm is really compact)
c) Lens price - the 35mm FF macro primes are very fairly priced
d) You need adapter (even in best case scenario you would have problems with exif, lens profiles, etc.)
e) DFA 100mm, Sigma 105mm, Sigma 70mm, DFA 50mm, Tamron 90mm, Samyang 100mm (and also legacy lenses like FA and F series) are all very sharp, with 1:1 magnification, at good price points.
f) And finally, the camera itself probably won't be able to resolve much more. You can compare the pixel density of the 645Z and the K-1 (and the K-1 with Pixel shift). There is a point where even a sharper lens will not appear to be that much sharper due to the camera's limitations.

I remember someone using old manual 645 lens on a K-5 had big problems with contrast and flare, but that was not a top level digital 645 lens. That said, feel free to try it out Empirical evidence is more fun than theory
Just want to express an opinion on point 'd'. I would be very disappointed if Pentax/Ricoh, having the full diagrams/engineering/electronic specifications of both lens mounts, in addition to both power of body and lens firmware, couldn't design a fully fledged adapter supporting EXIF/Lens Corrections. Considering that Sony* has made this work with the use of the LA-EA3 & LA-EA4 adapters, I'd expect Pentax/Ricoh could do the same (if they wised too). Even most FA primes and all FA* zooms now have automatic corrections when used on the K-1, so it surely bodes well for Pentax/Ricoh being quite forward thinking in this regard!

*though they seemed to have slowed down development, much to the sadness of transitioning α-mount users
01-13-2017, 04:31 AM   #7
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QuoteOriginally posted by Joshua A Quote
4) Seeing that the D-FA 90mm Marco lens is actually specified for a 55x44mm sensor (hence it not being issues as a DA lens), would it be safe to assume that utilizing it of a 645z sensor is already compromising it's resolving/rendering power?
Not necessarily. At least not on resolution. Things like flare could be a problem if the lens hood is not tight enough, low contrast if the image circle is too big. For resolution I would look at testing websites to see what resolution they measured on this (and competing) lenses. You have to compare the measurements done on the same camera, though. Then you can look at cameras with similar pixel density.
I think the main point we are tying to get across is that there are many problems other than resolution.


Last edited by Na Horuk; 01-13-2017 at 04:36 AM.
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