Tele Converter and Downsampling

Discussion in 'Native Lenses' started by deacon, Jul 13, 2015.

  1. deacon

    deacon Mu-43 Regular

    Jul 7, 2015
    I've got a lens related question about the GM1 and its 'Tele Converter' option. I've got the 12-32 kit zoom and a 14mm f2.5. I favor wide lenses for my job. For fun I take pictures and videos of my family, often in low light. Personal photos are mostly viewed on a screen and never printed bigger than A4.

    To avoid unflattering photos, I like to create some space and zoom in. At 32mm, this results in a F5.6 and is often too slow.

    Correct me if I'm wrong, but if I used my 14mm and the Tele Converter option (with size set to S), I get 28mm and keep f2.5 with much more useful shutter speeds. I lose OIS, but that doesn't help with rambunctious toddlers anyway (that would be awesome though). Is the unflattering affect of a wide angle lens a product perspective when you're really close to something?

    In David Thorpe's book about the GM1 controls, he says the camera uses the entire sensor and then downsamples. What's downsampling? The obvious drawback is that the image will be smaller (2272x1704), but do I lose a lot of detail as well?

    I guess I'll have to judge what's acceptable for how I use my photos - small is better than blurry. I'm wondering if the 14mm is worth holding on along with the 12-32. If the tele converter operates like I think, I'll probably keep it and get the wide angle adapter as well to stretch its usefulness out even further.

    Or maybe I sell it and get the 20mm F1.7...

  2. tkbslc

    tkbslc Mu-43 Legend

    Basically the camera is just cropping for you to make it look like you have more zoom. That's why it results in smaller file sizes. You could also do this back on your computer later, and it's really there for video since it results in 1920x1080 anyway, which is already a smaller resolution.

    I don't think there is anything particularly wrong with your idea, but the saying, "there is no free lunch" comes to mind. F5.6 is a slow aperture, which would require increasing the ISO indoors. Increasing the ISO too high increases noise, which reduces pictures quality. However, cropping effectively reduces your sensor size, which also increases noise. At the same display size, the noise, softness and artifacts will be more greatly magnified, so you will have noticeably reduced image quality from cropping. You could certainly test it to see if it meets your needs, though.

    So essentially you can pick between a standard resolution noisy photograph or a low resolution noisy photograph if you use the digital TC option. In the end, you are not gaining anything and maybe losing.

    A longer/faster lens would more adequately solve the problem. 20mm f1.7 may not provide enough focal length separation from your 14mm. You might look at the Sigma 30mm f2.8 or Olympus 45mm f1.8 as affordable alternates (especially used). They aren't pancakes, but they are very small for what they are.
  3. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    To use the teleconverter to change the perspective is correct, if you step back obviously (I suppose "create some space" means that...or magic :) ). If you remain in the same place you get the same unflattering effect but bigger.

    Downsampling is when you have more data then you need and you create a simplified version of something discarding (in a smart way) some of that data. But you get something that is reasonably similar to the original data.

    To be honest I cannot see how downsampling can be involved with a digital teleconverter. If the end image is smaller is just a crop. If it is the normal 16MP size it is an upsampling i.e. a scaled up image.

    You do not actually loose any detail but you get a lower resolution image, like 4MP instead of 16MP (or something like that). So in practice yes, when you'll print you'll notice the different resolution. My advice is to try to print both and see, I use the Oly teleconverter with reasonable results.

    You can also try to push the ISO higher, like 3200, and you could find it better then the cropped images.

    Or buy a Sigma 60mm or a 45/1.8 :)
    • Agree Agree x 1
  4. deacon

    deacon Mu-43 Regular

    Jul 7, 2015
    haha, that's a term I use a lot at work. It does sound kinda off when I'm not talking about buildings...or magic

    I played with the setting some last night. It does appear like it's just a cropped image. Not much use, especially in a dim building and a high ISO. I'm interested to see what it looks like with video though.

    I'll let my wife know you guys told me to buy more lenses. Thanks!
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