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Using Pentax legacy lenses on MFT Bodies

Discussion in 'Adapted Lenses' started by Dave Reynell, Aug 5, 2013.

  1. Dave Reynell

    Dave Reynell Guest

    I've a few Pentax legacy lenses which I use on my Panasonic G1. These are the highly rated Pentax-M 50/f1.7 and the Pentax-M 135/f2.5.

    Just recently I have been comparing the resolution of the 50/1.7 with that of my G1's kit, which is the excellent 14 ~ 45. With the 50/1.7 on the G1, set up on a tripod, manually focussed and the shutter set on a 10 second delay (in other words, I am not in contact with the camera when the the shutter is released) I am not getting the results I would expect from a quality lens.

    On inspection, the images are a tad "softer" than those of the 14 ~ 45 (also manually focussed).

    I know that some PK/MFT adaptors tend to cause focussing problems at infinity and mine is an ebay "cheapie". Do you think that there is a possibility that this "effect" manifests itself throughout the entire focussing range i.e. from close-up to infinity. ? In other words "What you see (in the EVF) is NOT what you get (on the sensor)"
     
  2. fredlong

    fredlong Just this guy...

    Apr 18, 2011
    Massachusetts USA
    Fred
    No. The problem with cheap adapters is that they are usually very slightly shorter than they should be. This means a lens focused to infinity is actually focused slightly past infinity. All the intermediate positions of the focusing ring have to be focused somewhere. What you see in the viewfinder ( or rear screen) is what you get.

    Many, most really, older "highly rated" lenses are softer than cheap modern lenses. Especially wide open. Most will perform at their best closed down two to three stops form wide open.

    Fred
     
  3. dougjgreen

    dougjgreen Mu-43 All-Pro

    Jun 5, 2013
    San Diego
    Doug Green
    You didn't say what the aperture setting of the 50mm lens was. If it was wide open, I am not surprised. The 50mm f1.7 lens is soft wide open on the digital sensor. It should improve noticeably at f2.8, and more so at f4. If the focus is sharp in the finder, you probably are properly focused. But the results with that lens are going to be soft wide open.
     
  4. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    The other thing I would check is the diopter setting (if using the EVF). Have had a few times where I bumped it and everything was off by the same amount. Generally this would result in focus being in a different spot, rather than overall softness.
     
  5. Dave Reynell

    Dave Reynell Guest

    Interesting comments, for which I thank you.

    Doug, I did my test of the 50/1.7 at f4.0, but having said this, Cruzan may have a point. I must check the diopter setting on my G1 - one tends to ignore this.

    Fred, my adaptor is fairly hefty and the lens stands 26mm (a tad over one inch) clear of the G1's body. I have seen a Novoflex PK/MFT adaptor (seriously expensive) which is only about 10mm in thickness.
     
  6. fredlong

    fredlong Just this guy...

    Apr 18, 2011
    Massachusetts USA
    Fred
    The Novoflex adapter you saw must have been for 4/3 bodies not m4/3. The adapter HAS to place the adapted lens at exactly the same distance from the sensor as the what the lens was designed for. The inaccuracies that I mentioned before are only a fraction of a millimeter.

    Fred
     
  7. Petrochemist

    Petrochemist Mu-43 Top Veteran

    651
    Mar 21, 2013
    N Essex, UK
    Mike
    Exactly

    IIRC the Pentax rear focal distance is 45.46mm whilst ยต4/3 is 19.25mm (4/3 is 38.67mm)so a adapter needs to make up the difference (26.21mm) If your adapter is 26mm it will reach beyond infinity focus as the lens will be 0.21mm to close from the sensor.
    This would of course be more useful than it being too long preventing infinity focus, the lenses focusing movement easily providing the extra. I suspect your 26mm is actual slightly more but the principle remains the same.

    Errors converting between metric & imperial units for these sorts of measurements have allegedly made some very expensive mistakes in these sorts of matters.
     
  8. dwig

    dwig Mu-43 Top Veteran

    621
    Jun 26, 2010
    Key West FL
    Unless you are relying on the focus scale on the lens to set the focus, any error in the length of the adapter, whether small or large and whether overly long or short, will have absolutely no impact on your test.

    You do need to be certain that the eyepiece diopter is set properly. You should be able to see some aliasing (pixel stair stepping) on the edges of the VF text displays when the eyepiece is set correctly. If you can't achieve this, you eyesight is not good enough for manual focusing without engaging the magnification function (which I recommend for such tests, anyway).

    When comparing old lenses with new you often encounter similar issues. You need to keep in mind that fact that "sharpness" doesn't exist in the real world. It is merely an illusion formed in your brain. What exists are resolution and contrast. Older lenses are often lower contrast than today's lenses. It's quite possible for a lens with higher resolution, but lower contrast, to seem less sharp. When doing the test, you need to adjust the contrast of the images so that they match.

    You may find that the adapter is causing some additional flare. This will lower the impression of sharpness. I've seen this with the two middle priced adapters I have for M42 and P/K. IQ improved when I added a mask at the rear of the adapter and added some flocking to reduce reflections on the inside of the adapter. My thin Leica M adapter from the same supplier doesn't have this problem, but is so thin that there is little of the adapter exposed.

    In practice, I've found my Panny 14-45 to be "sharper" than either my rather excellent Takumar 55mm f/1.8 and my Leitz Summicron-DR 50mm f/2. Actually, the Tak preforms as well as the Summicron and has become the only "nifty fifty" in my regular kit, there when I need the speed or shallow DOF.
     
  9. Dave Reynell

    Dave Reynell Guest

    Fred, I have double-checked the Novoflex info (see Novoflex - _info) and can confirm that their listed adaptor is for MFT. They refer to it as MFT/PENT, price a huge Euro 169.00. But if it means that it will make the difference and allow me to use my Pentax-M's to the full then I'm happy to spend that.

    Dwig, As mentioned, I shall most certainly check the diopter setting on my eyepiece and thanks for the tips on how to do this properly. As for the flare bit, well, I'll just have to leave it at that. I feel that if one has to go through a complex series of modifications in order to get an adaptor to work well, then maybe, just maybe, it'd be better to stick with MFT lens options and forget about legacies.

    Interesting to read about your Takumar 55mm f1.8. Back in the 1960's when I purchased my first Asahi Pentax (they were named Honeywell Pentax in the U.S. - I think) it came with a 55mm f2.0 as the so-called "standard" lens. I never liked the focal length, far too tight for my liking, and in the end I treated myself to the 35mm/f3.5 Super-Takumar, which was a gem. Also interesting to read that the Tak could keep up with the stellar Leitz Summicron, that's saying something !

    And, in closing, I gather from Mike that the chances of getting the perfect MFT/PK adaptor are not that great.

    Your comments have been most helpful and are appreciated. I'll now go off and work at it.

    Dave
     
  10. tjdean01

    tjdean01 Mu-43 Top Veteran

    842
    Feb 20, 2013
    The adapter is not your problem because when you spin the ring to focus it increases/decreases distance anyway
    (often I focus by moving my arms back and forth on closeup shots). I recently did the same test with the Pentax M
    (and A) 50mm 1.7 vs the modern Olympus 40-150. The results at 5.6 (where both of them are at their best) follow.

    I don't use the Pentax for its sharpness over the 40-150. I use it because I enjoy the metal "feel." I like the manual
    focus. I feel accomplished when getting a shot. I can't explain it really. I just enjoy using it. Autofocus is for sissys!
    I've also read that since we're using the lens on a HALF format-size sensor the sharpness is reduced by half. Makes sense.

    [​IMG]
     
  11. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    Sorry, but this makes no sense to me. You are cropping out ~50% of the image (the corners, where most lenses are not as sharp), and keeping just the center. There is something to be said for it being optimized to hit a digital sensor at the right angle, but that is simply film/digital, and nothing to do with the size. If you are still getting the same results, you may just have to concede that it is not as sharp. Then make the judgement call as the photographer which to use. The size of the sensor would make no difference to sharpness.
     
  12. tjdean01

    tjdean01 Mu-43 Top Veteran

    842
    Feb 20, 2013
    Like I said, I read it and don't personally know for sure, but when I don't have a definite answer I always lean towards the explanation that makes the most sense to me. I agree with you, but not in certain situations.

    * You have a Nikon 10MP FF sensor with a cheap lens. You get soft corners. You use the same lens on on a 10MP HALF-frame (m4/3s) sensor and you don't get soft corners (assuming a low ISO to make up for the FF's obviously superior noise performance and obviously taking into consideration the smaller sensor's DOF advantage). If I understand this correctly, this happens because the FF sensor's corners go to the edge of the glass where the light is hitting it at more of an angle whereas the m4/3s is getting only the center of the glass.

    * Take a very GOOD lens on these same two cameras and at low ISO they are both good (factoring in the smaller one's DOF advantage).

    * However, let's take the SAME two sensors, and the VERY good lens with SHARP corners. Heck, we'll even take a huge lens made for a Phase One or for a telescope to guarantee sharp corners on the FF. Now, if we make the sensors 100MP, we get a sharper picture with the full-frame camera because it's using the whole of the glass whereas the half frame sensor is using only a quarter (not 50%) of the area of that glass as the FF. I know I've read, "smaller lenses are sharper because they have to be" and I believe this is why.

    Call me wrong, as I might be, but if you do, please provide an alternate explanation. I like to learn this kind of useless info! (Actually, it's not useless, I guess. It shows that a cheap native lens can beat an expensive well-regarded one that was designed for full frame. I'd guess people upgrading from a 10MP D700 to a 36MP D800e have noticed the imperfections of some of their lenses.)
     
  13. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    Why would it be sharper with the corners, if they are both 100MP? The corners (to my knowledge) have always been the same as or weaker than the center for almost all lenses. The m4/3 sensor is 1/4 (thanks fredlong) the area of the 135mm format. The difference would come in that a current generation m4/3 has up to 18MP (theoretically on the GX7) whereas the 135 format has 36MP (call it double). So it would be the same level of sharpness, assuming an ideal lens that is sharp across the frame equally, that was mounted on each camera, with all other things with the sensor being equal. Not sure where the smaller are sharper because they have to be comes from. Possibly the same part where smaller equals cheaper. :rolleyes:

    (*Note* The last sentence is not a jab at you, simply at others who have ideas which don't hold weight. The internet is horrible at conveying tone and sarcasm).
     
  14. fredlong

    fredlong Just this guy...

    Apr 18, 2011
    Massachusetts USA
    Fred
    m4/3 is approximately 1/4 the area of 24x36mm film or "full frame". It is about 1/2 the size in TWO dimensions.

    Fred
     
  15. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    Sorry, my mistake. Edited the post to reflect that.
     
  16. juangrande

    juangrande Mu-43 Top Veteran

    805
    Dec 2, 2012
    COLORADO
    If the area of the sensor is approx. 1/4 smaller, then wouldn't it make sense that the image projected by the lens would only be the center 1/4 of the image, thus making it sharper, as generally, the center part of the projected image of a lens is sharper? Or same logic for 1/2 the size in 2 dimensions?
     
  17. tjdean01

    tjdean01 Mu-43 Top Veteran

    842
    Feb 20, 2013
    We're all saying mostly the same thing here. Yes, it's only using 25% of the light that a FF sensor. Yes, the corners will be better. And we're assuming we have two noiseless sensors and ignoring different DOF.

    But what I'm talking about is the physical composition of the glass and the impossibility of keeping it perfect at infinitely small sizes.

    Test: Take a 12MP Nikon D700 with a cheap off-brand 35mm lens and take a shot of a resolution chart at 10 feet. Adapt the same lens lens to a 12MP Olympus PL3 and take a photo of the chart at 20 feet. Assuming the sensors are equal, forgetting DOV, and ignoring corners, the full frame camera will win because it's using the entire image circle whereas the m4/3s is only using the inside 25% yet showing the same resolution chart, which will magnify any impurities in the glass.

    So I'm also saying that if you mount this highly-regarded Pentax lens on a FF 16MP camera the resulting image will be sharper than on m4/3s because it's using the entire image circle.

    I could be wrong, but that's what I believe until someone shows me otherwise! :thumbup:
     
  18. Dave Reynell

    Dave Reynell Guest

    tj, coming from decades of using manual-focus Pentax lenses, I know exactly what you are referring to ! I too enjoy the feel of those beautifully built, heavy, solid lenses. Thanks for the demo pictures.

    I shall now stop worrying about the slight differences in definition and live with them.
     
  19. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    At this point, we are debating different parts. I understand what you are saying about impurities in the glass, but if it is taken on a 135 sensor and cropped, you are using the same area of the glass. What I am saying is that the corners will inherently be worse than the center, and removing these "less sharp areas" would, IMO, result in a sharper picture generally than the small impurities that may be magnified. If you are simply comparing the center-most resolution, then yes, the bigger sensor would win. However, on a weighted scale (including corners), the smaller sensor (depending on lens corners and impurities) could be equal to or better than the larger one.

    At this point, I think we both agree with each others logic, and it is simply different ways of determining sharpness that we have differing opinions on. Correct, or did I misunderstand or sidestep part of your reasoning?

    Sent from my LG-P769 using Mu-43 mobile app
     
  20. Ulfric M Douglas

    Ulfric M Douglas Mu-43 Hall of Famer

    Mar 6, 2010
    Northumberland
    No.

    I had ONLY ONE lens that outresolved my Lumix 14-45 across the garden, and that's my own Yashinon 45mm converted off a rangefinder, and that's only sometimes and only in the centre.
    At the time I didn't have the Olympus mZuiko 45mm so sometime I'll do my tests again,
    but I'll say it is no surprise your Pentax isn't as sharp.
    My Cosina50mmF1.8 PK-fit isn't as sharp, my Helios isn't as sharp.