JW from PA wrote:
My question concerns Adapters vs Extension Tubes:
If an extension tube is used to aloud a lenses to focus closer for macro photography, does an adapter have the same effect on the lenses. Example #1: If I were to buy a Sony Full Frame Camera (A7RIII) and use all my Canon EF lenses instead of buying all new Sony lenses, what effect would that have on light entering the camera? F stops, SS, and ISO. Example #2: If I bought a Canon R6 or R5 and used an adapter for my EF lenses, what effect would that have on the light entering the camera? F stops, SS and ISO.
I hope I explained my question so its understandable, if not I am sorry.
Thanks in advance for your replies.
My question concerns Adapters vs Extension Tubes: ... (show quote
The flange to sensor distance in Canon DSLRs is 44mm. The flange to sensor distance in Sony e-mount is 18mm and in Canon RF-mount, 20mm. The difference between these is where the adapter comes in. So in one case it's 24mm and in the other it's 26mm... that's about an inch in both cases (1 inch = 25.4mm, if I recall correctly).
This is minimal when it comes to light fall off that might effect any exposure considerations (f-2top, SS, ISO).
An adapter is usually a tube without any optics, but it is NOT a macro extension tube. It is a precise conversion from the original long "back focus" design of the DSLR lens (which was necessary to allow the mirror mechanism to move freely) so that the lens is able work with the shorter back focus design of the mirrorless camera. An adapter maintains correct focus all the way out to infinity, while a macro extension tube moves the lens farther from the camera so that it will focus closer, but giving up the ability to focus all the way to infinity while the tube is installed.
Macro extension tubes are also tubes without optics, sold in various lengths in order to change close focusing ability more or less (basic rule of thumb, the longer the lens focal length, the more extension you will need to make a significant change in lens close focusing ability and magnification). While most macro tubes are 12mm, 20mm, 25mm and 36mm long, there are some more than 50mm and they all can be stacked together for additional length. For that matter, the "old school" macro bellows is nothing more than an adjustable tube, which can be up to 250mm long (approx.) It would be possible to use an adapter AND macro tubes together.
Because macro tubes can mean a lot of "extension" behind the lens, light fall off within the tube can be a concern. But that can be the case even with high magnification lenses. For example, the Canon MP-E 65mm "super macro" can do up to 5X magnification (in fact, the least it can do is 1X... there's no shooting infinity or anywhere even close to it with this lens). When it's at minimum focus, the smallest selectable aperture is f/16. Once that lens is fully extended to it's maximum 5X magnification that same setting becomes an effective f/96 aperture!
Some of this occurs any time a lens is put onto an extension... or the lens itself extends (note that many zooms have variable apertures). But it is usually minimal. And because the camera's metering system takes its readings "through the lens" (TTL), a smaller effective aperture and light fall off are compensated for at the moment the measurement is made. Where you can get in trouble with effective apertures and light fall off are when using fully manual control and a separate meter, such as a hand held flash meter.
Also, there are adapters that are "speed boosters". They are also sometimes called "turbo" or "accelerator" adapters. Unlike the various "plain" lens adapters, these have built-in optics that somehow increase the effective brightness of the attached lens. I have no idea how this works and imagine these more costly types of adapters need some pretty advanced optics to maintain good image quality. The primary use of these appears to be video.... in particular when shooting 4K in the crop mode required. This is not to say they can't be used for still photos, though that seems more secondary. These adapters are intended for use on APS-C or similar crop. If working with a full frame camera, the resolution will be substantially reduced. For example, a 45MP R5 set to APS-C crop mode ends up under 20MP. That might be sufficient for a lot of things. It would be a bigger concern with a lower resolution FF camera, like the 20MP R6, which will end up around 8MP in APS-C crop mode.
These speed boosters may have more application with actual APS-C cameras, like the new Canon R10 or R7. On those the 0.71X booster makes the lens "act like" it would on full frame. For example, if you put a 50mm focal length lens directly onto one of these Canon APS-C cameras, or use a plain adapter to fit one, it will give you an angle of view similar to what an 80mm lens would on full frame. By using the booster you get the same angle of view a 50mm on FF. In other words, it "corrects" the APS-C crop effect back out of the angle of view. I believe it also effects depth of field the equivalent of one stop. So if that were a 50mm f/1.4 lens it will render depth of field more similar to f/1.0. There would be no loss of resolution using the speed booster on an APS-C camera.... so the 24MP R10 will still render 24MP images.
The least expensive 0.71X Canon EF to RF speed booster I could find is the Viltrox that sells for around $268. I found Viltrox also offers a Canon EF to Sony e-mount (APS-C) for $139. But other brands of speed boosters cost over $500 and even as much as $700.
Note that the Canon EF to RF adapters... both "plain" and "booster" types... generally give full support to autofocus, image stabilization, etc. Adapting Canon to Canon here is very little if any loss of performance. The same can't be said adapting Canon EF mount lenses to Sony e-mount... there's usually a noticeable drop in AF performance and other functions may not be fully supported either.