There is a function called “Ex. Tele Conv.” on the Panasonic Lumix GX8 camera (and probably on most of the other Lumix cameras) that makes it possible to crop an image in camera. I saw it described as “useless” in a discussion on a Flickr group some months ago which seemed at bit harsh to me. Of course, for RAW shooters, this feature makes no sense as they will get the full readout of the sensor anyway. Ex. Tele conv. can be set to Zoom, which makes it possible to continue to zoom in when using a lens with power zoom (like the Panasonic 14-42 or 45-175) after the optical zoom has reached its longest or shortest focal length, but it can also be set to On to get the maximum zoom with any lens. I am going to talk about the last way to use it here.
What this function actually does is just read out pixels from a narrower part of the sensor and hence it also reduces the number of pixels you get in your image when you use it. In other words, it is not an electronic zoom that scales the image and looses quality, but a narrower readout where each pixel on the sensor becomes a pixel in the JPEG which means that there is no reduction in image quality except that you get a picture with fewer pixels. This function is naturally only available when shooting JPEGs or RAW+JPEG since RAW files are readouts from the whole sensor.
After you have turned “Ex. Tele Conv.” on in the menu, to get it to actually work, you have to set the picture size (for instance through the Quick menu button) to Ex. M to get a 1.4 times crop and a 10 MP JPEG or to Ex. S to get a 2 times crop and a 5MP image. (Assuming you shoot 4:3.) When you want to return to the normal 20 MP images, you can set the camera to shoot L size pictures through the Quick menu again. There is no need to turn Ex. Tele Conv off to use the normal 20 MP picture size.
I think the Ex. M setting can be useful, but personally, I think Ex. S is probably too much of a compromise on number of pixels for the 0.6 times extra crop it gives compared to the Ex. M picture size. Hence, I will disregard the Ex. S. setting and only focus on what the Ex. M setting can be useful for. A 10 MP picture is pixel dense enough that you would have to print really large and look at the print from a really short distance to need more pixels, but a 5 MP image might be a bit low on pixels for a large print.
Recently, I sold the Lumix 20 mm f/1.7 lens not because I dislike the focal length, the optical quality or the extremely compact size and weight, but because the slow autofocus made me miss shots with it. I actually really like the 40 mm equivalent focal length as it is a slightly wide standard lens with none of the perspective distortion of wide angle lenses, but with a slightly wider field of view than my Panasonic Leica 25 mm f/1.4 which sometimes is just a bit too long to fit a wider subject in the frame.
Today, I realised that my Panasonic Lumix 14 mm f/2.5 which is even smaller and lighter than the 20 mm f/1.7 can actually be a useful substitute for the 20 mm with the Ex. Tele Conv. function and Ex. M picture size since 14 mm x 1.4 = 19.6 mm. The 20 mm is better optically, but the 14 mm has fast autofocus and is good enough optically to be useful and has the advantage of being small and light. If you own the Panasonic Leica 15 mm f/1.7, maybe that is an even better substitute for a standard lens since 15 mm x 1.4 = 21 mm which is the diameter of the micro four thirds sensor. It also gives you better optical quality than the 14 mm.
I really like standard lenses because of their lack of proportion distortion and because the focal lengths of these lenses are perfect both for landscapes, portraits, environmental portraits, street photography etc. A standard lens is really versatile as it is neither too long nor too short for most types of subjects. My 25 mm is thus my most used lens. It is also my best lens optically and that is another reason I use it so much. However, sometimes I cannot come far enough from my subject to capture all of it without using a wider lens and then I use my 14 mm. This happens mainly when shooting landscapes or cityscapes. When I am travelling, changing lenses is a bit of an annoyance, so if I could get away with using the same 14 mm lens for both wide angle and standard focal lengths, that would be perfect. It might also mean that I could get away with travelling with fewer lenses and thus reduce the size and weight of my already quite light MFT kit even further.
These thoughts got me thinking about my other lenses and what I could get out of them by using the Ex. Tele Conv. function. The aforementioned 25 mm becomes a 35 mm with the Ex. M picture size. I sometimes felt that the 25 mm was a bit short when I did some street photography this summer. Maybe it is mainly because I am not comfortable getting really close to people on the street and taking their picture, but even when I was really close, sometimes I felt that the clutter of the scene made the pictures less good than if I could have come a tad closer in on the main subject. The Ex. Tele Conv. function gives me that option without having to use another lens.
My Panasonic Lumix 42.5 f/1.7 becomes a 59.5 mm with the Ex. M picture size and Ex. Tele Conv. I actually seldom use this lens even if it is a good lens and comes in a small and practical size. I use it mainly for landscapes and faux macro shots and if I ever get into portraiture, I will use it for that. When doing faux macro, the close focusing distance and the relatively long 85 mm equivalent focal length makes this lens a good choice, but with the Ex. M picture size, it would be even more useful for macro since it would make it possible to make the subject even larger with the same short focusing distance.
My fourth and last lens is my Lumix 45-175. I use it mainly for landscapes when I want the background to come closer to the foreground through compression or when I want to focus in on only one part of my landscape. I sometimes feel that it would have been useful to have an even longer lens, but I can’t justify spending the money for a lens I would only occasionally use and that would weigh my photo bag down. The solution is to use the Ex. M picture size that makes this small and light lens into a 63 to 245. With a 490 mm equivalent focal length at its longest, I should be able to get a narrow enough field of view to focus in on parts of landscapes even if they are on the other side of a fjord or a sound, and I would definitely get enough compression to make majestic mountains get close up behind the serene houses in my townscapes from rural Norway.
All in all, the more I think about it, the more useful this feature seems. I will try it out during the next few days to see how useful it is in reality.