
20 Comments
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Jay
Thorough and exceptionally helpful.
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Domingo Riesco
Thanks for your full explanation Alex! Just landing to your blog. It is hard for me to fully grasp how distance to subject affects DOF, but I have a question. What would happen in terms of depth of field, when attaching a speedbooster to a 24mm f2 FF lens, onto a FF camera? Lots of vignetting, but after cropping... I guess the result would be the equivalent to a ~35mm f2? That means one extra stop depth of field shallowness than before? Or just the same DOF as before but simply brighter? I already own a 24mm f2 and I'm evaluating the difference between adding a focal length reducer to it, or having (another) 35mm f2 lens.
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Alaaddin
Dear Alex: Thank you very much for this article. My question is simple: does it make sense to use a Speedbooster on a full frame? I am considering a Villtrox speedbooster ot use Nikon Lenses on my EF sony mount camera. Thanx.
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Gabriel Goncalves
Hi! I'd like to pose a question. Imagine I have an APS-C camera and I choose an FF lens 35mm 1.4 lens. I then could couple - or not - that lens to the APS-C camera with a speedbooster 0.71x. (Of course the number 0.71 is not by accident: it is the inverse of the squared root of 2, a fundamental number in f stops.) Please correct if i'm wrong, because i'm completely new to this thing of speedboosters. (But not to crop factor and all the nonsense written about it and "equivalences" and all that stuff around aperture and DoF in different cameras - as if the sensor size could modify the lens!...) Is it true that without the speedbooster, I would have, mounted on the APS-C camera, a lens (the FF 35 mm 1.4) that would give me an angle of view roughly equal to that of a 50mm 1.4 lens mounted on a FF camera? The angle of view would be the same of a 50mm 1.4 mounted on a FF... However, not the depth of field, since a 35mm 1.4, the lens I really mounted (regardless of what camera is mounted in, of course, although many people have wrong ideas about this) has a not so shallow depth of view as a 50mm 1.4. Correct me if I'm wrong, but this is because of the focal length, which is shorter in the 35mm lens (all other things being equal: distance to subjet, and both having been set to the same 1.4 aperture), and therefore would be the sole responsible for the difference in depth of field. (By the way: conversely, if I were to use a 35mm lens on both cameras, the depth of view would be the same (again, and sadly, many people are wrong about this, as you obviously know), but not the "shot", since we now would have a different, narrower, angle of view when we put the 35mm on the APS-C camera.) In order to have the same characteristics (both angle of view and depth of field, thus giving us the famous "same shot") I would either have to put a 24mm 1.0 lens on the APS-C camera so I could have the same angle of view AND the same depth of field that I would have with the FF 35mm 1.4 lens mounted on a FF camera (I checked this on a DoF calculator and it agrees) OR I could mount the FF 35mm 1.4 on the APS-C camera with a speedbooster - necessarily 0.71x, as to reach the same angle of view of a 24mm on the same APS-C camera without the speedbooster. And the DoF would be the same as of a 24mm 1.0 lens in the APS-C camera. Is there a flaw in my reasoning in the last sentence? If there is not a flaw in my reasoning (and only if), aren't somehow right those who say that a speedbooster makes depth of field shallower? What I think they mean - using my example - is that using a lens designed for FF cameras, a 35mm 1.4, for instance, and using a speedbooster with this lens, this combo will give a shallower DoF than a 24mm 1.4 would. I really think this is what they want to say - but I might be wrong! If I'm not wrong (and I ask your favour to assess this) I think this might be the source for so many misunderstandings about this subject of speedboosters. Any comment from you would be really appreciated! One thing I don't understand: you wrote «Let’s say we add a Speedbooster to our 50mm f/2 lens. It has a magnification of 0.71x, therefore, we can multiply the focal length by this factor: 50*0.71=35.5. The lens is now a 35.5mm lens» I don't get it. Does the speedbooster actually change the focal legth of a lens, shortening it, or were you refering to "35.5mm lens" considering only angle of view, and not focal length, which it a physical property of the lens? Thanks a lot for any comment of yours! Happy New Year 2023 and Thank You so much for the video, explanations, and comments!
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Niek Deventer
Hi Alex, good story! The depth of field part is even simpler when you look at the 'image size' on the sensor (that's how Google translates 'Afbeeldingsmaatstaf' from Dutch...) Example: A close-up of Pinocchio with a 50 mm lens at 2 meters distance. To get eyes and nose tip exactly in focus you need aperture F8. The same close-up can also be made with a 25 mm lens at 1 meter distance, a 500 mm lens at 20 meters distance or a 2000 mm lens at 80 meters distance. If you take those shots with F8 then in all cases Pinocchio's head is and the same size and in all those shots the sharpness is exactly from his eyes to his nose. If Pinocchio starts to lie in that close-up then the ONLY way to keep eyes and nose tip sharp is to stop down to F11 or even smaller. If that's not enough you have to use a wider lens or step back. But then your 'image size' gets smaller and your close-up becomes a medium shot. So if you take a knee-shot of an actor and you want another actor a half meter behind him also in focus then you need a certain aperture. And with that aperture it doesn't matter what kind of lens you use to make the knee-shot, close with a normal lens or from a distance with a telephoto lens, the depth of field, or how sharp the other actor becomes in your image stays the same.
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Roman
Hello dear Alex thank you for this article it help me understand better the way lenses work because you used simple language not technical misleading terms, thank you for that. I must inform you that although your article is technically sound and mostly correct i find it lacks deeper explanation of how lens work and could potentially lead readers that have little understanding about lens mechanics to the wrong conclusions about effectiveness of Speed Boosters. I find important omission to not mention that FF 50mm f/2.0 lens mounted on APS-C camera would be actually reduced to f/3.0 aperture since the projection image it outputs is intended for 35mm sensor when actual sensor is 25mm (more details in links below). Indeed its marketing statement that speed booster makes 50mm f/2.0 lens into f/1.4 lens, it simply changes it from f/3.0 back to f/2.0 by focusing entire projection on the sensor. Readers could benefit greater from more physical explanation rather than pure mathematical one. Speed Booster physically takes place of 35mm sensor and receives 35mm projection FF lens generates then outputs smaller 25mm projection to into APS-C sensor. Please see second page for diagram. Two pages https://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care Please see diagram under "Why do you say a smaller sensor sees less light?" https://www.dpreview.com/articles/5365920428/the-effect-of-pixel-and-sensor-sizes-on-noise
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Ola
I’ve got a question about using a speed booster with a standard zoom lens. I’ve got a viltrox speed lens that I attached to a recently bought 28-80mm f2.8-4. My observation is that the aperture does not open wider than the f2.8. This is not the case with the nifty 50 f1.8 that I have as it opens up to f1.2 when used with the speed booster. I guess my question is, does zoom lens open any wider when used with the speed booster? N.B Camera is canon m50 and the lens is also a canon, L series
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Bob
Actually, very informative and helpful in understanding exactly what and how a speed booster works!
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YX
as far as conclusion goes about depth of field: Vladimir is correct; Alex Stone is wrong.
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Vladimir
Wow, you just made everything even more confusing and complicated :) The main thing about the speedbooster is, it makes your 50mm on a crop body to behave like 50mm on a FF, everything will be exactly the same as if you have a FF sensor, and that means your FOV is the same, your DOF is the same, your bokeh is the same, the amount of light hitting the sensor is the same, that's all. It's like moving your sensor back and gathering all the light lens is projecting, that's why you get all the properties of a FF sensor. There is no need for confusing theory, you could just post a photo with and without a speedbooster and you will see both are identical, given the speedbooster is making the exact 1.0x crop. If not, everything still applies, but you will have 1.05 or 1.1x or 1.3x, but a speedbooster is working exactly like cropping backwards and all the image properties are affected.
Mladen
You are confusing people (unnecessarily) with your approach to this issue. Nobody is measuring equivalence the way you have done it here. At least, not in a photographic world. I don't see why videographers would be any different. ''50*0.71=35.5. The lens is now a 35.5mm lens'' You reversed the order of how most people measure equivalence. I wouldn't go about this issue in that order. A 50mm lens on APS-C sensor will be equivalent to 75mm on full frame (35mm). That is the crop factor. That is the ''equivalence''! Period. Now, one of the functions of a focal reducer (Speed Booster, Lens Turbo, Pixco...) is to ''reduce'' the focal length according to a focal reducer specification - 0.7X or whichever, to make it closer back to 50mm (specified focal length)!