Speedbooster question

I see references to speedboosters on various threads. Would there be any advantage to using one with a lens such as the new Tamron 35-150 on a crop sensor camera?

There are only speedboosters available for a small set of mirror-less cameras.

In Canon's lineup, only the M series has one available currently I believe.

So only for use with one of the M system cameras. Got it.

In a M series camera, it would effectively change the 35-150 f2.8-4 to a f2-2.8? Do I understand it correctly?

Something like the Viltrox will take the EF image circle that it produces and shrinks it down so that more of it will fit on an APS-C sensor like the M50.

It effectively reduces the 1.6 crop factor down to 1.1, and in doing so, sends a stop more light to the sensor due to the increased scene making it to the sensor.

So the 35-180, on a crop, effectively becomes a 39-198, rather than the typical equivalent view of a 56-288. Then you get the added light being thrown to the sensor, so the booster reports a lower aperture to keep your metering more exacting, else the images would be blown out.

Thanks for the explanation.

A "speed booster" basically works as an optical magnifier for larger format lenses to smaller format sensors. We now have them for DSLR lens => smaller frame mirror-less. They've been around for various larger video lenses to super-35 sizes.

I've been using them for about 2 years now. Love them. Like mentioned about, they focus the light one to the sensor, and one of the side benefits is it also then helps with Autofocus performance. The only down side I have found so far is if a lens vignettes, that effect is also increased - more dramatic - and not in a good way. I crop to 16x9 so rarely is an issue, but it is there.

duckster wrote in post #18887366
So only for use with one of the M system cameras. Got it.

It is just like a TC, but inverse. If it is 0.71X, then the resulting optics is a real 0.71x factor of the main lens' focal length and open f-number.

davesrose wrote in post #18887487
A "speed booster" basically works as an optical magnifier

This device shrinks the image circle; it doesn't magnify it.

John Sheehy wrote in post #18887727
This device shrinks the image circle; it doesn't magnify it.

In photography, you can have either positive or negative focal length in magnification

A speed booster is really a wide-converter, where conventional converters are considered tele-converters.

A .71x is still a positive multiplier as is 1.4x and 2x, thus not a negative magnification.

https://www.whatdigita​lcamera.com …ce-technology-guide-60994

It isn't a negative magnifier, because as I understand it, a negative focal length or negative magnification is where the image becomes inverted and farther away, nothing gets inverted here.

I was referring to the magnification equation in optics (not the whole lens). Edit: I see references saying negative focal length also inverts image. My main point was that it's optical elements that are magnifying in the sense of reducing image.

A 24mm image, being smaller, than an 85mm doesn't imply negative magnification. Why would it here as well?

Regardless, the simplest explanation for the lay person is that a speed booster effectively removes most, if not all, the crop factor of a crop sensor from a FF supporting lens. If they want more info than that, we can get into the physics.

What do you mean by 24mm image vs 85 (sensor or focal length)? Your link says that a teleconverter has negative lens elements and speed booster has positive elements, for example. Sorry, I think I just confused things as whether magnification always means enlargment of image or if it can mean reduction. My assumption with lens elements is that they can do either. And I'll leave it there because we're not arguing principles.

A teleconverter changes the effective focal length, as does a wide converter, ie speed booster.

A 35mm becomes a 25mm with a .71x, a 2x makes the view look like a 70mm. Neither is negative, the converters just change the effective lengths.

The crop factor of 1.6 then applies to this new effective FL.

That is all I am saying. I feel this description is more technically correct than some sort of negative versus positive effect. I hope that clears up matters. A picture would probably describe this even better for those just learning about speed boosters.