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Exposure Differences Between Two Similar Lenses

Discussion in 'Adapted Lenses' started by Boatman, May 10, 2011.

  1. I have a Takaumar 1.4/50 and newly acquired Konica 1.8/40 pancake lens for my GH2. My results with the Takumar have been mixed. I have a lot of shots that are very soft which could be due to a number of issues; high iso, poor focusing (on my part), moving subjects, etc. I decided to try some side by side shots in a semi-controlled environment with the Konica lens and see if I got different results. Long story short, I didn't see much difference though I seem to get the focus wrong with the Takumar more frequently. However I got an unexpected result I can't quite explain.

    My methodolgy was to take two groups seven photos, one with the Takumar and one with the Konica. I used aperture priority mode and fixed the ISO at 320 and used aperture f4 for both lenses and all photos. When I reviewed the photos I discovered that in every case the shutter speed was twice as fast with the Konica as with the Takumar. The historgams for the images were very similar indicating that the exposures were equal and correct.

    I'm at a loss to explain why one lens would be a full EV faster than another given the same aperture and ISO. The Takumar lens is somewhat yellowed and it is a 20% longer focal length. Would these explain a 1EV difference in their performance?
  2. Assuming you are photographing a scene with consistent lighting across the image (i.e. your classic brick wall test), you can isolate the discrepancy to one or both of the lenses. Often a legacy lens will require a slight exposure compensation shift in either direction, and this is not always constant so the amount required may vary across the range of apertures.

    Are you using an appropriately sized hood on either lens? These older lenses are very susceptible to stray light and they also project a larger image circle than required . It could also be the reflectivity of the inside of each adapter that is influencing the problem. In leiu of using a hood I've also sometimes used step-down rings on the front of the lens to reduce the transmission of unwanted light through the lens.
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  3. aleksanderpolo

    aleksanderpolo Mu-43 Regular

    Mar 31, 2010
    San Diego, CA
    Is your takumar yellowish (do a custom white balance with the Konica, take a shot of white wall, then take a shot with the takumar with the same white balance setting)? If so, treat it with UV light to de-yellow it, you will get almost one stop more light. 50/1.4 Takumar use radioactive element which over time cause yellowing of glass element that leads to reduced light transmission.
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  4. Good comments, thank you. I took the photos on a porch and outside in overcast conditions that were very steady throughout the process (15 minutes start to finish) so I'm certain that the ambient light stayed the same. Not sure about the internal reflections in the 4/3 adapter. The contrast looks good for both lenses.

    As for yellowing, the Takumar certainly has it. I've left it in the sun a few times to clean it up but never long enough. Perhaps this summer when the sun gets stronger I can get this done right. If the yellowing can cause a full stop of light reduction, that's probably the difference. I have a Takumar 28mm that is not yellowed. I could throw that on there too, and see what it gets for exposure settings.
  5. Luckypenquin; to adress your coments in more detail, I did not use lens hoods but it was sufficiently overcast that I doubt a lens hood would be needed. I do have a 135mm lens hood that fits on the 50mm lens very nicely and does not get into the corners despite the fact that it is quite deep. As for the step down rings, I assume you use these to essentially block the outer part of the lens and shade the portions of the focus circle that are not being used by the m4/3 imager. Sound like a good solution, which I've not heard of before.

    How deep do you typically block? I would assume that the length of the lens and the diameter of the front element would need to be considered. Is there a working rule of thumb one can use?
  6. It depends on the lens. I think a lens hood is most effective but they also add extra bulk. On my Canon FDs which have a 52mm filter thread, I've used 52-37mm step down rings on the 50/1.4 and 35/2 with no vignetting, and both have reasonably large front elements. On a wider angle lens like the 24/2.8 I've fitted 52-43mm rings. I've bought a few step-down and step-up rings on eBay and I think they cost a bit over AUS$1 each.
  7. I guess I could cut out some circles from black construction paper and make some tests. I bought a step up adapter so that I could use a 62mm polarizing filter on a 58mm lens from an outfit called Wholesale Electronics,Wholesale Gadgets,cool gadgets,electronic gadgets,Free Shipping!. It was six dollars and change, direct from China. It took about two weeks to arrive, but hey, this is a pretty low tech item, no point in paying a lot for it. They have step down adapter for similar prices.
  8. WT21

    WT21 Super Moderator Subscribing Member

    Feb 19, 2010
    Those lenses have a differing field of view. The wider lens could be bringing in edge items that are dark or light, and therefore throwing off metering a bit (along with all the other explanations that were given).

    It'd really help if you could post the images.
  9. True. There is a 20% difference in their focal length. However, the subjects I picked wouldn not change a full EV based on small difference what was in the field of view. I suspect that the issue is with the yellowing of the Takumar lens and I'll need to leave it out in the sun some more. I can post the results tonight using Picasa and I can put the vital sitatistics in the comments field so that you don't have to download the image to pull the FX data out of them.
  10. Pan Korop

    Pan Korop Mu-43 Veteran

    Mar 31, 2011
    Phare Ouest
    Don't leave it in the sun. It may overheat, and/or uncement the grouped lens elements. There you'd be in real trouble.

    If you want to give it some UV, use a fluorescent lamp, or a proper "black light".
  11. sprinke

    sprinke Mu-43 All-Pro

    Apr 5, 2011
    Pasadena, CA
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  12. WT21

    WT21 Super Moderator Subscribing Member

    Feb 19, 2010
    There could be other factors, but the FOV is a major difference in some of those shots.

    Look for instance at these two:


    Green especially as a % of the frame can impact the meter reading.

    Though the chair shots, which are pretty similar, do show a one stop difference.

    The first flower shots show the same exposure.

  13. You are correct. It wasn't a very scientific test. Still, I think it is surpising that the shutter speed would be as different as it is. This demonstrates that, in its current condition, the f1.4 Takumar is a slower lens than the 1.8 Hexanon. Given that I use these lenes in low light conditions, that is important to know.

    I looked into the Ikea desk light Sprinke discussed. It's only $10 and would be the best resolution. Too bad there isn't an Ikea within 100 miles of where I live and the lamp is not offered on their website.
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