Focal Reducers and Macro Photography

Discussion in 'Adapted Lenses' started by ibd, Aug 6, 2017.

  1. ibd

    ibd Mu-43 Regular

    90
    Jun 5, 2016
    Hey there!

    I was wondering if pairing a macro lens, for example the Vivitar 105mm f2.5, with a focal reducer would make sense.
    - Will the maximum reproduction ratio / magnification be preserved? For example, if the original lens goes to 1:1, would one paired with a 0.7x speed booster only go to 1:1.4 (calculated as 1/0.7)? My reasoning behind this is that the focal reducer effectively makes the projected image smaller, thus losing the original magnification ratio. However, I am not sure how the optics work exactly.
    - Since macro lenses are often used stopped down to get some usable depth of field, and focal reducers make the lens faster, would it even be desirable to use a focal reducer? My reasoning is that it would be desirable because it can make the lens sharper. Also not sure if the diffraction limit would be affected at all, I think it is purely given by the sensor characteristics (sensor size and pixel count).

    If anyone has any experience with this kind of setup, please share it!

    Cheers
    ibd
     
    Last edited: Aug 6, 2017
  2. magIBIS

    magIBIS Mu-43 Regular Subscribing Member

    88
    Jun 8, 2016
    Central Europe
    I'm no expert here, but try some basic logic - more knowledge (and not assumptions like mine) will follow by some other for sure. Meanwhile...
    The lens specification does not change at all.
    A simple adapter gives you the same characteristic of the picture, like a 2x crop of the intended lens spec. So a macro lens with 1:1 on 35mm will give you a 2x bigger magnification on 4/3 sensor in the first place, on the expense of light loss and possible loss of detail.
    The focal reducer will bring back some light and can improve the details on the expense of some magnification. Usually you gain a stop of absolute light and will loose half of the magnification. The details might improve in a 100% view but if that will be the same with cropping to the same magnification as with a simple adapter is not probable.
    On the other hand, looking at the full picture: it gains probably details and you can stop down the lens. So if the still bigger magnification than on the 35mm film is good enough for you, you get a nice compromise with bigger dof than with the simple adapter.
    A focal reducer is a option, not a 100% better solution to a simple adapter.
    (edited for missunderstanding)
     
    Last edited: Aug 6, 2017
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  3. bikerhiker

    bikerhiker Mu-43 All-Pro

    Dec 24, 2013
    Canada
    David
    Hi,

    Yes, you will loose the original magnification and reproduction ratio because the angle of view had changed and thus your focusing distance will change as well. I own a 55mm f/3.5 Micro-Nikkor (one of Nikon's sharpest macro lens) mated to a focal reducer and it does make the lens so sharp and more contrasty as opposed to my native Panasonic Leica 45mm Macro which does 1:1. My Micro-Nikkor does 1:2. I rarely use the Micro-Nikkor now, but was thinking of converting it to a slide duplicator btw because of its super sharp resolving power..
     
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  4. ibd

    ibd Mu-43 Regular

    90
    Jun 5, 2016
    Interesting. Would the depth of field change when I stop down a lens that is made faster by a focal reducer? In other words, if I reduce a f/2 lens to f/1.4, then stop it down to f/2.8 (to make it effectively f/2 with the reducer), would the optical properties change at all compared to the original f/2 lens? Besides a sharper image maybe, if using a good focal reducer.

    Thank you for the insight. Is the magnification loss proportional to the focal reduction?

    What focal reducer do you recommend? The Metabones might be a bit out of reach for me pricewise. On the other hand, the cheaper alternatives might degrade the picture quality. Is the lens turbo II by Zhongyi still the go-to cheap-ish option or are there better ones available now?
     
  5. bikerhiker

    bikerhiker Mu-43 All-Pro

    Dec 24, 2013
    Canada
    David
    I am not sure if the magnification loss is proportional to the focal reduction, though it does sound logical. I use it with the Zhongyi Lens Turbo and I got as good of a copy as it can be. It's sharp in the centre, but gradually soften on the corners. The Lens Turbo II is better especially with its improved coating which does not show as a red blob when exposed to a strong light source, but the Metabones is the best. Metabones is a bit too much and you're probably be better served to get a dedicated Macro lens instead.

    I bought the Zhongyi because it was then tested to be the 2nd best to the Metabones and it was significantly cheaper. I bought it to adapt 2 full frame lenses, one still in use for astrophotography of the Milky Way. But the Micro-Nikkor languished in my photo bag after since I got a great deal on a used Pana Leica 45mm. I sometimes take out the Micro-Nikkor out with the Zhongyi just to get a unique bokeh look.
     
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  6. magIBIS

    magIBIS Mu-43 Regular Subscribing Member

    88
    Jun 8, 2016
    Central Europe
    Yes, because you get a wider focal length with the same f-stop, so a bigger dof. Simply put, with the lens turbo II you get from a "full frame" lens an image, like on an aps-c body. The exact focal reduction is 0.726, so effectively you can work with a dof chart of a 1.4-crop sensor.
    I have the lt II - it really is great, but I did no testing others, just research. With my telelenses I get a small vignette in the very corner of the 4/3 image. No big deal, just to mention. I believe the metabones was not cured of that either, but the price difference makes it a no brainer to me and my needs anyway.
     
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  7. ibd

    ibd Mu-43 Regular

    90
    Jun 5, 2016
    Ah, I understand now. Makes sense. Interesting that you get vignetting, are you adapting/"speed boosting" full frame lenses on m4/3 bodies?

    Thank you all for the valuable insights!
     
  8. TheMenWhoDrawSheeps

    TheMenWhoDrawSheeps Mu-43 Veteran

    447
    Jun 15, 2016
    Stopping down the lens to f2.8 to get yourself f2 will have many effects - first of all, the image will be sharper. That's also the main reason I use it - same light gathering ability for sharper results.

    With dof, it gets bit complicated you get wider, but faster lens - so at the same distance, at same f-stop, you should get almost same dof, with wider fow.

    I wouldn't worry much about magnification ratio - 1:1on ff is 2:1 on mft - the whole concept is getting bit out of Hand as you start using crop sensor bodies.
    Just use distance to your Subject, achieving desired magnification/dof ratio.
     
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  9. magIBIS

    magIBIS Mu-43 Regular Subscribing Member

    88
    Jun 8, 2016
    Central Europe
    I did some Vignette test on the fly - note: none is a Macro

    All:
    Em1 + LT II (EF)+ M42-EF + Lens (M42)
    minimum focus distance, auto ISO, IBIS off

    Aperture open, F8, closed

    Tokina RMC II 80-200 @ 100 (to match your Vivitar): F4, F8, F22
    Em1-LTII-Tokina-100_F4_web. Em1-LTII-Tokina-100_F8_web. Em1-LTII-Tokina-100_F22_web.

    Pentacon auto MC 135: F2.8, F8, F22
    Em1-LTII-Pentacon-135_F2.8_web. Em1-LTII-Pentacon-135_F8_web. Em1-LTII-Pentacon-135_F22_web.

    Auto Revuenon MC 50: F1.8, F8, F16
    Em1-LTII-Revuenon-50_F1.8_web. Em1-LTII-Revuenon-50_F8_web. Em1-LTII-Revuenon-50_F16_web.

    Zeiss MC Flektogon 35: F2.4, F8, F22
    Em1-LTII-Zeiss-35_F2.4_web. Em1-LTII-Zeiss-35_F8_web. Em1-LTII-Zeiss-35_F22_web.
     
    Last edited: Aug 7, 2017
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  10. Christop82

    Christop82 Mu-43 Top Veteran

    504
    Sep 10, 2016
    Taken with a Sigma 105 2.8 macro adapted with a metabones s Speedbooster.
    74mm (reduced) f8
    OI000061.
     
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  11. Bytesmiths

    Bytesmiths Mu-43 Top Veteran

    A lot of people in this thread have claimed "the image will be sharper" with a focal reducer, but let's think about that a bit.

    First off, you're adding glass elements in the light path. This almost always reduces sharpness!

    But then, you're increasing the reproduction ratio, which causes an apparent increase in sharpness, because you're "pushing away" optical quality problems, not because anything in the light path is actually somehow making the image sharper.

    If you crop a focal-reduced image to be the same size as the non-focal-reduced image, I'm willing to bet that you will see no increase in sharpness, and more likely, you will see somewhat reduced image quality.

    Focal reducers are great for 1) getting more light, if you need it, so you can shoot at a faster shutter speed, and 2) reducing depth-of-field. Neither of these seem particularly useful for macro, although shooting a stop faster may make a difference with scurrying bugs and wind-blown flowers. On the other hand, if you are using an extension (including a long helicoid focus built into a macro lens), you probably won't realize the faster shutter, as your reduced effective "T Stop" will consume your increased F Stop — moving the lens elements away from the focal plane uses up light, by spreading it out in a larger-than-required image circle!

    Entropy rules. There's no free lunch. In fact, the energy expended to get what looks like a free lunch may well consume more calories than are in that lunch!

    But another aspect makes focal reduction even less useful for macro: you generally already have control over the reproduction ratio, so why use a focal reducer if you can simply move back a bit and re-focus, in order to get the desired reproduction ratio? Your resulting image will be no less sharp then getting closer and using a focal reducer — and it may well actually be sharper.

    So I propose that the opposite approach is actually more useful: use a tele-extender for macro, rather than a focal reducer. That at least allows you a smaller reproduction ratio, if you need it.
     
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  12. Christop82

    Christop82 Mu-43 Top Veteran

    504
    Sep 10, 2016
    I'm not sure where the sharper image thought originated? This was the first thread that I had seen that. In general focal reducers of high quality should retain the original sharpness of the lens.
     
  13. Bytesmiths

    Bytesmiths Mu-43 Top Veteran

    Well, it does look sharper for the same reason that viewing it from double the distance makes it look sharper!
    But I haven't seen any that actually do "retain the original sharpness of the lens."

    However, I have not used a ~$600 Metabones; I've only used ones under $200, and they all degrade the image, at the same crop, to some extent.

    Here's a comparison of one under $200 and one under $100. I think it is clear that, at least at this level, you get what you pay for, and I'd discourage anyone from using a low-cost focal reducer on a high-cost macro lens. :)
     
  14. WhidbeyLVR

    WhidbeyLVR Mu-43 Top Veteran

    841
    Feb 14, 2014
    Whidbey Island
    Lyle
    Probably came from here: Metabones®

    If the addition of a focal reducer does increase the acuity of a given lens (as Metabones argues), and if you can achieve your desired reproduction ratio with the focal reducer in the optical path, then it seems like it could be a win. This is not the same thing as cropping a focal reduced image taken at the same distance to the same framing as without the focal reducer.
     
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  15. Christop82

    Christop82 Mu-43 Top Veteran

    504
    Sep 10, 2016
    Makes me want the ultra. I wonder if the older models have any optical performance increase?
     
  16. Christop82

    Christop82 Mu-43 Top Veteran

    504
    Sep 10, 2016
    Perhaps I'll try to do some comparison shots with the metabones s Speedbooster.
     
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  17. Bytesmiths

    Bytesmiths Mu-43 Top Veteran

    Can you explain why?

    It seems to me it is exactly the same.

    I read the Metabones link posted. It says nothing about comparisons of the same crop.

    I do understand that focal reducers reduce the excess image circle, which may result in less flare from internal reflections, but I know of no way that a focal reducer can improve the optics of the lens it is reducing.

    The Metabones is undoubtedly a fine product, and I am not trying to run it down at all.

    But as a systems engineer with signal processing background, I just need help understanding how an add-on can provide something that was never there in the first place. It reminds me of the movies where I totally lose "suspension of disbelief:" when the good guys are looking at the bad guy via a grainy security camera, and they say, "Zoom in. Enhance." and then you can read his destination from the plane ticket in his pocket.
     
  18. Bytesmiths

    Bytesmiths Mu-43 Top Veteran

    I would especially appreciate comparisons at the same crop.

    Otherwise, it's an apples-and-oranges comparison. I can make any photo "look sharper" by moving it further away!
     
  19. ibd

    ibd Mu-43 Regular

    90
    Jun 5, 2016
    Could you tell me how to discern an "apparent" increase in sharpness from an "actual" increase in sharpness? ;)

    Of course, focal reducers are imperfect. However, the fact that you're projecting a bigger area (including more details) onto the same sensor area as before will by definition lead to an increase in sharpness. This may well offset any optical imperfections the focal reducer has otherwise.

    Your physics-based approach is an interesting one, however it is an oversimplification. First, entropy does not tell you anything about the conservation of energy, rather it tells you about the quality of the energy. Second, the additional energy comes from the light that would otherwise fall outside of the sensor -- by using a focal reducer, you are converting the incoming energy of the light into electrons (hitting the sensor) instead of turning them to heat (hitting other parts of the camera)!

    Let's assume, for simplicity, that we have a perfect focal reducer of 0.5x. Let's assume we have a 1:1 capable macro lens, and it can also cover a sensor twice as big as m4/3. Now, let's say the desired magnification is only 1:2. We can either:
    1. Put the lens on a dumb adapter, and focus to 1:2
    2. Put the lens on our imaginary 0.5x focal reducer, and focus the lens 1:1.
    It is obvious that the second setup will result in a sharper image. We are not cheating by "moving the photo further away"! Instead, we are projecting light and absence of light (contrast) on a smaller part of the sensor, and sharpness will increase.

    The final question then remains: Does the increased sharpness from the focal reduction overcome the worsening of the optical setup by the additional glass? This is solely dependant on the quality of the focal reducer.
     
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  20. 3dpan

    3dpan Mu-43 Veteran

    263
    Mar 11, 2017
    Far North, New Zealand
    Alec

    You could read this test from Jim Chung,

    Evaluating the MTF Improvements of Speed Booster Focal Reducers