SJ8 Pro minimal focus distance

Discussion in 'SJ8 Series' started by Sauron, Dec 8, 2018.

  1. Sauron

    Sauron New Member

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    Hi,

    Does anyone of you know the minimal focus distance for this camera? I cannot find it in papers.
    I'm just checking my underwater videos from recent trip and it seems like most of closeup is out of focus. I've used to use sj4000 and it was ok on close distance :(
     
  2. Sulev Svilponis

    Sulev Svilponis Elite

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    Underwater minimal focus distance may be different than minimal focus distance in the air. It is different even on dry land, depending on whether the camera is in the casing or not. Besides, every camera is slightly different, than the others, therefore there are slight variations in distance between individual units. And users have different expectations for sharpness. For exact data you should measure your own camera, underwater. Just use a measuring tape or a long ruler and place it under your camera, starting from the sensor plane and directing away from the camera, and take some shots. Afterwards, you can find the border, where the sharpness is satisfactory for you, by inspecting those pictures on the computer screen.
     
  3. Sauron

    Sauron New Member

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    Well yes, I can measure it and I'll have to - since there is very little information on this camera. Something so basic as minimal focus should be on paper.
    But I can't agree with other things you said. About user expectations - focus is measurable and does not depend on user. Also this value should be consistent to every camera - if it's otherwise this is manufacturer error/low production quality.
    I assume (no information about it also) this camera has fixed focus lenses. This is also something to test (I don't have it right now with me)...

    Sadly this camera is getting worst and worst...
     
  4. Sulev Svilponis

    Sulev Svilponis Elite

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    Yes, the focus of the lens is fixed, there is no focusing ring for changing the focus. But the lens is connected with the camera body by joining two threaded tubes and these threaded tubes let to set different flange focal distances, before they are clued together in the factory. And you must keep in mind, that there are always certain tolerances in production. Always! And with an ultra wide lens like this, a tiny shift of the lens position (flange focal distance) will result rather large shift in the nearest focusing distance.
    There is no exact distance from where objects become unsharp. The fuzziness is growing gradually the more the subject is closer to the camera (away from the nearest distance of the sharp focus range). Therefore it is subjective how close the camera is usable.
    This distance depends even on how high or deep above/below the sea level you are using this camera, because refraction is dependant on fluid (or air) density.
    Rough estimation about the nearest focusing distance is ca one metre. If the exact distance is important for you, then simply measure it in the environment, where you use the camera.
     
  5. Sauron

    Sauron New Member

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    This has nothing to do with it. Small cameras can have autofocus (nothing to do with ring for manual focus) with, sometimes, "point to focus" on screen (like most of the smathphones now) or fully automated focus (camera itself chooses what should be in focus). It can be also done with fixed focus - where minimal distance to infinity is always focus (like DJI Mavic Air camera for example) - this depends how the lenses are designed. To be fully true, of course "large" cameras can be done the same way - but they usually aren't.
    And the rest is true - but it's, like I said, poor production quality or environment dependant situations. But all specs "on paper" are usually laboratory specs and this way they are easily comparable.

    Anyway - initial questions was, if anybody has more specification for this camera (like minimal focus distance) - and this questions still stands :)
     
  6. Sulev Svilponis

    Sulev Svilponis Elite

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    I can assure you, that SJ8 cameras have no autofocus.
    That's fully true.

    The lens is fixed focus lens, therefore there is no nearest focusing distance for the lens. The lens can give sharp images as close as one millimetre, if not even closer.
     
    Last edited: Dec 9, 2018
  7. RBEmerson

    RBEmerson Humbled by events

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    I dragged my SJ8 out of hibernation to measure the minimum distance between the lens and a page of text. Very loosely, the limit is about 8 cm. Or, don't expect the SJ8 to work well for macro imaging. No blame attaches. :)
     
  8. Sulev Svilponis

    Sulev Svilponis Elite

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    The lens of the SJ8 is very capable for macro shooting, if to increase the distance from the sensor, like by adding a macro ring to some fixed focus lens of a DSLR camera. As the lens has joined threaded tubes (screw in) type lens mount, the nearest focusing distance could be easily decreased just by unscrewing the lens a bit. In case if the 8 cm (like RBEmerson suggested) or ca 30 cm, that is my estimation, is not close enough.
     
  9. RBEmerson

    RBEmerson Humbled by events

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    Adding an auxiliary lens will certainly support macro work. IMHO it's about the last thing the SJ8 is intended to do.
     
  10. Sulev Svilponis

    Sulev Svilponis Elite

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    Sauron is obviously trying to use this camera for shooting macro (or close shot) videos/photos, otherwise he has no need to know the exact value of the closest DOF value.
     
  11. RBEmerson

    RBEmerson Humbled by events

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    This should have been asked sooner: how close is "close" in the video you shot and was out of focus? How close do you want to get with your camera?
     
  12. Sauron

    Sauron New Member

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    I'm still cutting my footage from my two last trips (snorkelling and diving) - so I'm "learning" what this camera can and can't do. So far I was using SJ4000 and assumed SJ8p will be working in similar fashion - and I learned hard it does not ;)
    There is plenty wrong with this camera - but to narrow it down to this topic - since it has wide angle lens (170deg) to fill the screen with small fish I usually tried to take a close up with camera on the stick (José Jalapeno on a Stick ;) - joke). It could be 10cm from object or less. With sj8 it's all out of focus. Sadly I haven't notice it underwater, but there was no way I could humanly see it on this small screen. Now I know, but for further usage I wanted to know more.

    I've already printed test charts for focus testing, but my first results are terrifying - so I have to do it again. Terrifying because of image quality and sharpness/focus in general.
     
  13. RBEmerson

    RBEmerson Humbled by events

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    Much as there is to complain about in the SJ8, trying to make little fish, that hide in the niches in coral, fill the frame is wishful thinking. A 170° FOV lens is never going to be a macro lens. It's rather like using a tennis racket to bail out a sinking rowboat. You might splash some water out of the boat, but expect to go swimming shortly...

    Asking the SJ8 lens to be what it never will be isn't the camera's fault.
     
  14. Sulev Svilponis

    Sulev Svilponis Elite

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    It is actually pretty easy to do great macro shots with an ultra wide action camera lens. By simply unscrewing the lens a bit. But there is a caveat - it may be problematic underwater, because the lens should fit into the watertight casing and must not touch the front window of the casing, and therefore it has only very limited space for unscrewing it.
     
  15. RBEmerson

    RBEmerson Humbled by events

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    And you can hammer nails with a screwdriver handle. It's possible to use the wrong tools do a job, but that doesn't mean it'll produce the best results.
     
  16. Sulev Svilponis

    Sulev Svilponis Elite

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    Using camera for recording videos or taking photos is not exactly an abuse. Ultra wide lens gives unique touch to macro shots, that is not achievable with regular macro lenses.
     
  17. karjak

    karjak New Member

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    Note out to Sauron. You mentioned you were doing some testing with the SJ8 Pro to determine the minimum distance for a clear image. What were your findings? I noticed that RBEmerson gave a figure of 8cm as minimum distance for SJ8. I recently purchased a SJ8 Plus which has the same lens as the Pro. I too was disappointed. In my preliminary tests, my image doesn't clear up untill past 20 cm. Is this just a matter of lens not being threaded in the correct distance? Bad QC? I would be happy to have a clear focused image at 8cm. In checking my Thieye T5 edge another true 4K action cam, objects become clearly in focus at 10cm.
     
    Last edited: Feb 16, 2019
  18. Sauron

    Sauron New Member

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    Hi,

    Assuming the sensor of JS8p is good quality - the lens in this camera is a joke (as the customer support and firmware). I've did some testing (but not in the underwater case and not underwater :) ). But it looks like (despite terrible - also joke - photo quality) the focus is much further then 20cm. Center of the focus chart is 26cm here, and it still does not look focused. I simply cant understand how photo quality can be so bad (I've forced ISO100, used tripod and good light).
    [​IMG]
    Also the chromatic aberrations is enormous (this is 1:1 crop from underwater video) + rather poor video bitrate... ehhh
    [​IMG]
    This are bitrates measured with "moded" firmware (In my opinion - moding hasnt change anything - moded value is MAX, real value is AVG)
    [​IMG]
    Anyway, 60Mb/s for 4k/30fps is muuuch to low value :(
     
    Last edited: Feb 16, 2019
  19. karjak

    karjak New Member

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    I also couldn’t believe how terrible my close ups were. Read such great reviews and how they hype the lens at SJCAM “7 layers of glass lens (including 2 layers of Asperic lens) allows for a distortion-free, high resolution, 170-degree Field Of View, perfect for capturing everything that is in front of the camera with absolutely crisp and vibrant detail." I expected more. It may be true these cameras not primarily intended for the closer recording. I have used 3 other makes of action cameras and have gotten great results. The best camera was the APEMAN Action Camera (fake/interpolated) 4K 20MP. I returned but wish I hadn't. I thought the more distant objects maybe not quite crystal clear. I then purchased a true 4K Thieye T5edge and it has clear focus around 10 cm.

    Quite honestly it was also hard to determine what the actual minimum focus distance was because quality of image was so bad. I said after 20 cm and I think more likely between 30 and 45 cm. I was influenced by RBEmerson’s evaluation that the distance was 8cm. I have some screen grabs from test video of the SJ8 Plus and Thieye. The dog biscuit box is 18cm from front of lens. Also included a extreme closeup screen grab from the Apeman where lens probably no more than 8cm from the bird. Yes these little cameras should be capable to take great closeup nature videos.
     

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    Last edited: Feb 17, 2019
  20. Sulev Svilponis

    Sulev Svilponis Elite

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    It is too much to expect, that the out of focus area should look sharp on images. The lens is ok, but its focus is fixed more distant than any macro shooter likes it to be. As I wrote earlier, the closest border of a sharp area starts somewhere at ca 30 cm (depending on how high are your expectations).
    Ultra wide lenses are prone to cromatic abberation. Especially wide open. Even Nikon AF-S NIKKOR 14-24mm f/2.8G ED with a price tag close to 2000 bucks has plenty of CA, when wide open.
    Besides, it is not so fair to use regular focus distance charts for ultra wide lenses, as at the distance, where the closest sharp area begins, those symbol on chart appear too small to be perceived sharp. This is like you evaluate normal lens by the upper row of a optometrist's chart (large symbols) but for ultra wide lens you use the lowest row (withe the smallest symbols).
     

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