Sinead, this thread is just riddled with inaccuracies, false statements, and general errors.

First, there are no such things as “35mm sensors," unless you're talking about film.

A full frame sensor is NOMINALLY 36mm wide by 24mm tall.

An APS-C Canon sensor is NOMINALLY 22.5mm by 15mm. A Nikon DX or Sony or Fujifilm APS-C sensor is slightly larger.

A Micro 4/3 or Four Thirds sensor is 17.3 x 13 mm.

The format used by Panasonic and Olympus is called Micro Four Thirds, Micro 4/3, or m4/3 or m43… NOT Micro 2/3. The Four Thirds dSLR format is defunct, but the sensor size carried over into m4/3.

A change in sensor size NEVER affects the focal length of a lens… It only changes its perceived magnification, or the field of view recorded. A given lens focal length projects the same image over the same area. A lens may be designed to cover an 8x10 sheet of film, or a Micro 4/3 sensor, but it can be 300mm in both cases. Only the field of view changes! And it is the same over the same area. Oh, the image circle projected by the lens is wider on larger formats, but then so are the lenses! A 300mm lens made for 8x10 is pretty large, compared to a 300mm lens made for m43.

Depth of field does not increase due to a reduction in sensor size. It does increase when you reduce the focal length of your lens to match what you would have used on a larger sensor! In other words, f/2.8 on Micro 4/3 at 25mm provides about the same depth of field as f/5.6 at 50mm on full frame film. And the field of view is about the same, too. To match that “look” on APS-C, you would need a 35mm lens used at about f/4.

Bokeh is not hard to achieve on smaller sensors IF you use a lens with a wider maximum aperture. It needs to be one stop wider on APS-C and two stops wider on Micro 4/3 (compared to full frame). This is why lenses with maximum apertures of f/0.95 or f/1.2 are popular with Micro 4/3 users! No, you’re not going to get the absolute most bokeh on any of these formats… For that, you’ll need a huge view camera, a very long lens, and 20x24 inch sheet film!

“Crop” sensors do not limit the size of a print you can make from their images! You can make a 40 inch by 30 inch print of the same scene from an iPhone or a Canon 5Dsr or a Nikon D7200. They won’t have the same resolution, but you can make them! The only limits on print size are the limits we have in our minds. I have seen many Apple billboards that were made with iPhones. I’ve seen plenty of crappy 8x10s made from full frame dSLR images. There is MUCH more to image quality than just sensor size! Whole books have been written about it, along with endless rants on the Internet.

A crop sensor dSLR only samples a small area of the image circle of a *lens designed for full frame*. But if you put a DX lens on a DX body, you’re cropping *a lot less,* because the smaller, lighter lens designed for DX projects a smaller image circle! Put that lens on an FX (full frame) Nikon, and you get vignetting or fewer usable pixels… because the projected image circle of a DX lens won't cover an FX sensor.

Full frame/FX sensors, APS-C/DX sensors, and Micro 4/3 sensors are all designed for different purposes… for different blends of capabilities, possibilities, and applications. One format is only better than another in a relative sense, because it is only ONE PART of a larger, broader system! If your sensor is the largest available, with the widest dynamic range, lowest noise, etc., BUT you’re not printing on a high end Epson or Canon photo printer, directly from Lightroom (etc.), from raw files adjusted on a calibrated monitor capable of 100% Adobe RGB color gamut, are you realizing the full potential of your camera? No... regardless of the camera format, brand, etc. (If you took Humanities in college, and studied Plato's Forms, you know what I mean.)

Those who fixate religiously on sensor size dogma are often incapable of seeing beyond the camera technology to the true purposes of imaging, and the importance of the entire imaging SYSTEM. They’re too busy *gloating* about owning full frame bodies to actually go out and use the things!

Consider this: WAY over 90% of today’s images will be viewed ONLY on screens — tablets, smart phones, computers, 4K and HDTV monitors. Very few of those screens have a resolution of over 1920x1080 pixels, and those that do are mostly 4K TV sets with 3840x2160 resolution. A 60” wide screen HDTV or 4K monitor looks GREAT when viewed six feet away.

Yes, prints can look much better. But to really eke out the most from a Nikon D810 or Canon 5Dsr image, you need to make a really big print on a state-of-the-art inkjet printer. Do you make prints like that on a regular basis? Do you own one of those big Epson or Canon printers, or work with a service bureau that does?

Use the right tool for the job. But don’t think you have to lug a full frame body and heavy lenses 100% of the time, when 90% of the time, it won’t make a visible difference in what people see in your photography!

Photography is a broad field with many applications — nearly as many as there are photographers. Don't be so hung up on the technology of it all that you forget to record the images you started out to make. You're writing with light. The MESSAGE is far more important than the medium.