GoPro Hero 3 Black minimum focus distance?

Started Jan 8, 2013 | Questions
skiphunt13
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GoPro Hero 3 Black minimum focus distance?
Jan 8, 2013

Anyone happy to know the minimum focus distance of the new GoPro Hero 3 black edition lenses? I know it's fixed focus, but I haven't been able to find any specs regarding what the minimum focus distance for wide, medium, and normal settings is.

One site posts that for the Hero/Hero 2 it's 8in for wide, 9in for med, 10in for narrow. But I don't know if that's true, or why it would be different, or if true... that it's the same for Hero 3. It seems like this would be an easy tech specification to find on GoPro's own site, but I can't find it anywhere.

Anyone know for sure or have a link to the specs of the lens used on the GoPro Hero 3 Black Edition?

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skiphunt13
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Re: GoPro Hero 3 Black minimum focus distance?
In reply to skiphunt13, Jan 8, 2013

Hmmm... I'm surprised this info is so hard to find. I've posted the same question on 2 different gopro forums and gopro's facebook page and no one seems to have the answer. I guess I'll have to just shoot a ruler to see, but if the wide, medium, narrow settings are just sensor crops... it doesn't explain why it's reported the Hero/Hero2 has different minimum focus distances for each setting. Does anyone know why that would be?

It seems to me that if the wide, medium, narrow settings are just different sensor crops, and the lens is a fixed focus 2.8... then the minimum focus distance would be exactly the same for each setting.

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Roger Krueger
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Cropping changes DoF
In reply to skiphunt13, Jan 9, 2013

skiphunt13 wrote:

It seems to me that if the wide, medium, narrow settings are just different sensor crops, and the lens is a fixed focus 2.8... then the minimum focus distance would be exactly the same for each setting.

No it  wouldn't be.
Changing the sensor crop is in effect changing the format. Which changes the CoC for DoF calculations.

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skiphunt13
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Re: Cropping changes DoF
In reply to Roger Krueger, Jan 9, 2013

Roger Krueger wrote:

skiphunt13 wrote:

It seems to me that if the wide, medium, narrow settings are just different sensor crops, and the lens is a fixed focus 2.8... then the minimum focus distance would be exactly the same for each setting.

No it wouldn't be.
Changing the sensor crop is in effect changing the format. Which changes the CoC for DoF calculations.

That's odd, because in my own quick tests with a t-square there doesn't appear to be much DoF difference if at all for each of the three settings.

Odd that a definitive answer to this basic lens spec query is so hard to find.

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skiphunt13
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Re: GoPro Hero 3 Black minimum focus distance?
In reply to skiphunt13, Jan 10, 2013

Here's something interesting related to my post. I found this minimum focus test on YouTube, but the guy is testing stacked macro filters via the BlurFix adaptor which I'll likely pick up myself.

Before he starts stacking filters onto the front of the GoPro Hero3, he shows with a tape measure what the focus distance is without any filters at all. His results are the same as mine, ie. the scene without any filters doesn't look sharp at any distance. It's all sort of soft. Not even the background looks tack sharp. What's interesting is that after he's stacked a few cheap macro filters onto the front of the housing, he actually starts getting images that are impressively sharp. This shows this lens is capable of sharp images.

Here's the video: http://www.youtube.com/watch?v=bDAopwmGXmk&list=PLUW9rRbPGzS3lh5h_aO40b12GShp-nw0r&index=1

Why wouldn't at least the background appear sharp without the filters at all?

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HumanTarget
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Re: Cropping changes DoF
In reply to skiphunt13, Jan 10, 2013

That's not how you figure out DOF.  It's hard to determine the minimum focusing distance, because info on the focal length and sensor size are not readily available.

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skiphunt13
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Re: Cropping changes DoF
In reply to HumanTarget, Jan 10, 2013

HumanTarget wrote:

That's not how you figure out DOF. It's hard to determine the minimum focusing distance, because info on the focal length and sensor size are not readily available.

I'm not so much trying to determine DOF. Because you can't see what you're doing without the optional LCD screen, and even if you have the LCD backpac (which I do) the image is too small to determine focus. If would be nice to know what the closest distance is to the lens is so that you can at least eye-ball it. I don't see why this seems like such an irrelevant question for most.

If you can't see what you're doing, you should at least have a good idea what the distance is. I know this is primarily an action cam, but it is being used on pro shoots and the Discovery channel even uses them. So what if you want that logo on the side of the car you're attached to be in focus? If you're too close to the lens, it'll be blurred. At some point, it'll be in reasonable focus. That's what I'm trying to figure out.

Doesn't pretty much every camera manufacturer out there at least give you what the minimum focus of their lens is? I've been googling and looking for a week now. Have emailed GoPro, have asked on their facebook page, and still... nothing.

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GodSpeaks
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Re: Cropping changes DoF
In reply to skiphunt13, Jan 11, 2013

skiphunt13 wrote:

I'm not so much trying to determine DOF. Because you can't see what you're doing without the optional LCD screen, and even if you have the LCD backpac (which I do) the image is too small to determine focus. If would be nice to know what the closest distance is to the lens is so that you can at least eye-ball it. I don't see why this seems like such an irrelevant question for most.

You might want to get the GoPro remote WiFi app.  It pretty much replaces the LCD backpack, and will display on any size screen.

Seems to me that you should be able to determine the closest focus distance yourself with only a few minutes of planned shooting.  In fact I may do this myself, as I too would like to know what the closest focus distance is.

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skiphunt13
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Re: Cropping changes DoF
In reply to GodSpeaks, Jan 11, 2013

GodSpeaks wrote:

skiphunt13 wrote:

I'm not so much trying to determine DOF. Because you can't see what you're doing without the optional LCD screen, and even if you have the LCD backpac (which I do) the image is too small to determine focus. If would be nice to know what the closest distance is to the lens is so that you can at least eye-ball it. I don't see why this seems like such an irrelevant question for most.

You might want to get the GoPro remote WiFi app. It pretty much replaces the LCD backpack, and will display on any size screen.

Seems to me that you should be able to determine the closest focus distance yourself with only a few minutes of planned shooting. In fact I may do this myself, as I too would like to know what the closest focus distance is.

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Here's the thing... I've already done my own tests. The lens really doesn't look sharp close up at all. If I were to guess the closest where it's the most sharp, it's around 12in. If you look at the youtube video link I provided... check out the test on a tape measure before they guy puts closeup filters on the front. The naked lens simply isn't a very sharp lens... period. However, when he puts the closeup filters on it... it does achieve something close to "tack sharp" which really doesn't make sense.

Regarding the app... it's nearly useless. The LCD back is WAY more useful and totally worth the cost. I tried to get by with only the app and it's got too many problems. I didn't want to buy the LCD back, but I'm so glad I did.

1. You connect via wifi and wifi eats up the gopro battery VERY quickly

2. It only shows you what you're shooting before you actually hit record. After that you're flying blind in the highest resolutions. The live preview works in 720p 30/60fps and I think in 1080 but only at 30p.

3. Have you tried framing your shot on the fly aiming the camera while framing on a mobile device? Not easy. MUCH easier framing while shooting with the LCD back.

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dsjtecserv
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Re: Cropping changes DoF
In reply to Roger Krueger, Jan 11, 2013

Roger Krueger wrote:

skiphunt13 wrote:

It seems to me that if the wide, medium, narrow settings are just different sensor crops, and the lens is a fixed focus 2.8... then the minimum focus distance would be exactly the same for each setting.

No it wouldn't be.
Changing the sensor crop is in effect changing the format. Which changes the CoC for DoF calculations.

Yes and no. The CoC is a factor that enters into an appraisal of sharpness for a given print size and viewing distance. That does indeed change with sensor or film format, because a different degree of enlargement is needed to produce that given print size. But the image on the sensor itself doesn't change if the sensor area is cropped, so what is sharp or not as recorded remains the same. Also, while enlargement affects depth of field, it doesn't affect the focus distance, so the distance from the lens that provides the best focus will also remain the same even as the sensor is cropped.

So, since the videos produced by the GoPro are presumably enlarged to the same screen size for viewing, regardless of whether wide, medium or narrow settings were used, there would be a difference in depth of field, but not focus distance. And since the focal length of the fixed focus lens is so short, and it is probably pre-focused to something around hyperfocal, it is doubtful that you would actually be able to see this difference in depth of field.

And, because the cropping of the sensor means that more enlargement is needed in order to get to the display size, the outcome of using, in effect, a smaller senor is to decrease the depth of field. That may seems counter-intuitive because we have become accustomed to associating smaller sensors with greater depth of field. But where all lens and distance parameters remain the same, and only sensor size (and therefore degree of enlargement and CoC) changes, the depth of field does decrease with decreasing sensor size.

To the OP: If you knew the focal length of the lens, the aperture (above you said it was fixed f/2.8?) and dimensions or size family of the (uncropped) sensor, you could determine the hyperfocal distance for that combination using any number of online DoF calculators. I have no idea if this is actually true, but it would be logical for the GoPro lens to have been focused at the hyperfocal distance in order to maximize the focus range all the way out to infinity.

Dave

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dsjtecserv
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Re: Cropping changes DoF
In reply to dsjtecserv, Jan 11, 2013

Just for giggles I tried to find out the information needed to calculate the hyperfocal distance. In the process I found this website (http://www.eyeofmine.com/gopro/hd/index.html) that estimates the minimum (presumably fixed?) focus distance for the Hero at 8 inches. I have no idea if that's credible, but FWIW.

That site also indicated that the Hero has a 5 mm f/2.8 lens and 1/2.5 (5.76 x 4.29 mm) sensor. If that's the case, then the uncropped circle of confusion limit would be about 0.0048, and the hyperfocal distance would be about 6 feet. That seems too long. So I suspect that the lens is focused at a point much closer than hyperfocal, on the principle that with such a wide lens you wouldn't be able to discern much distant detail anyway, and the primary use is for relatively proximate subjects. On that basis, the above website's measurement of 8 inches or so makes sense.

Not sure I helped you much, but it was an interesting exercise and I learned a little about a camera I've never thought much about.

Dave

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skiphunt13
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Re: Cropping changes DoF
In reply to dsjtecserv, Jan 11, 2013

dsjtecserv wrote:

Just for giggles I tried to find out the information needed to calculate the hyperfocal distance. In the process I found this website (http://www.eyeofmine.com/gopro/hd/index.html) that estimates the minimum (presumably fixed?) focus distance for the Hero at 8 inches. I have no idea if that's credible, but FWIW.

That site also indicated that the Hero has a 5 mm f/2.8 lens and 1/2.5 (5.76 x 4.29 mm) sensor. If that's the case, then the uncropped circle of confusion limit would be about 0.0048, and the hyperfocal distance would be about 6 feet. That seems too long. So I suspect that the lens is focused at a point much closer than hyperfocal, on the principle that with such a wide lens you wouldn't be able to discern much distant detail anyway, and the primary use is for relatively proximate subjects. On that basis, the above website's measurement of 8 inches or so makes sense.

Not sure I helped you much, but it was an interesting exercise and I learned a little about a camera I've never thought much about.

Dave

You actually did help me some. I saw that site, and that's why I started my own tests at the 8in mark. It's definitely not focussed at 8in. Maybe 12in, but still never tack sharp. Not mushy either. Strange thing is that video at full resolution does look pretty sharp. Individual frames, not so much.

This is also the GoPro Hero3 Black Edition in which I believe they changed the lens on and as I recall, that site you referenced is the original Hero and Hero2.

I don't understand the hyperfocal distance stuff. You're a bit out of my pay-grade on this, but would this explain why the YouTube test I referenced... of some cheap macro filters attached to the front of the lens.. achieved a much sharper looking image than the lens with no filters?

If you look at the test video, he first shows the Hero3 on a tape measure with just the stock lens. You'll see that no where on the tape measure actually looks that sharp. Not even that sharp at infinity. It's all sort of soft looking. Then, he tries stacking the cheap macro filters in front of the lens one-by-one. By the time he's got 2-3 filters stacked, the focal distance if obviously changed to very close AND what's interesting is that it's rendering a MUCH sharper (looking) image than with no filter at all.

Here's the video: http://www.youtube.com/watch?v=bDAopwmGXmk&list=PLUW9rRbPGzS3lh5h_aO40b12GShp-nw0r&index=1

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dsjtecserv
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Re: Cropping changes DoF
In reply to skiphunt13, Jan 11, 2013

skiphunt13 wrote:

You actually did help me some. I saw that site, and that's why I started my own tests at the 8in mark. It's definitely not focussed at 8in. Maybe 12in, but still never tack sharp. Not mushy either. Strange thing is that video at full resolution does look pretty sharp. Individual frames, not so much.

This is also the GoPro Hero3 Black Edition in which I believe they changed the lens on and as I recall, that site you referenced is the original Hero and Hero2.

I don't understand the hyperfocal distance stuff. You're a bit out of my pay-grade on this, but would this explain why the YouTube test I referenced... of some cheap macro filters attached to the front of the lens.. achieved a much sharper looking image than the lens with no filters?

If you look at the test video, he first shows the Hero3 on a tape measure with just the stock lens. You'll see that no where on the tape measure actually looks that sharp. Not even that sharp at infinity. It's all sort of soft looking. Then, he tries stacking the cheap macro filters in front of the lens one-by-one. By the time he's got 2-3 filters stacked, the focal distance if obviously changed to very close AND what's interesting is that it's rendering a MUCH sharper (looking) image than with no filter at all.

Here's the video: http://www.youtube.com/watch?v=bDAopwmGXmk&list=PLUW9rRbPGzS3lh5h_aO40b12GShp-nw0r&index=1

The hyperfocal distance is the focus distance from the camera at which, for a given focal length and aperture, everything from half the hyperfocal distance to infinity will be in focus. Focusing at the hyperfocal distance achieves the maximum depth of field for that focal length and aperture, which is why I thought it might be used for this fixed-focus lens. However, it also make sense that it would be biased toward closer subjects, so hyperfocal can probably be dismissed.

I have no idea why the video looks sharper when diopters are added. That's above my pay grade!

Dave

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HumanTarget
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Re: Cropping changes DoF
In reply to dsjtecserv, Jan 11, 2013

Good find.  With all the "8 inches to infinity" talk I've seen mentioned about the camera, though, it does make me wonder where exactly it's focusing.  Perhaps they're using more lax CoC requirements.

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GodSpeaks
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Re: Cropping changes DoF
In reply to skiphunt13, Jan 12, 2013

skiphunt13 wrote:

Here's the thing... I've already done my own tests. The lens really doesn't look sharp close up at all. If I were to guess the closest where it's the most sharp, it's around 12in. If you look at the youtube video link I provided... check out the test on a tape measure before they guy puts closeup filters on the front. The naked lens simply isn't a very sharp lens... period. However, when he puts the closeup filters on it... it does achieve something close to "tack sharp" which really doesn't make sense.

Interesting.  I will have to do some tests myself and see what mine looks like.

Regarding the app... it's nearly useless. The LCD back is WAY more useful and totally worth the cost. I tried to get by with only the app and it's got too many problems. I didn't want to buy the LCD back, but I'm so glad I did.

Personally, I prefer the app.   I have the LCD backpac, but no longer use it because I find the wifi so much more convenient.

1. You connect via wifi and wifi eats up the gopro battery VERY quickly

Everything is a tradeoff.  I added the battery backpac to boost run time.

2. It only shows you what you're shooting before you actually hit record. After that you're flying blind in the highest resolutions. The live preview works in 720p 30/60fps and I think in 1080 but only at 30p.

I use it mainly to frame a shot.  Once framed, the camera is locked down.  At that point, all I need is start/stop.

3. Have you tried framing your shot on the fly aiming the camera while framing on a mobile device? Not easy. MUCH easier framing while shooting with the LCD back.

Trying to frame on the fly is difficuly no matter how you do it.  But yes, I can see using the LCD Backpack like a viewfinder.  Not an issue for me, usually, as I lock the camera down and move on to other tasks.

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skiphunt13
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Re: Cropping changes DoF
In reply to GodSpeaks, Jan 12, 2013

The app does have it's use for sure. If you're placing the camera in a place where you can't get behind it to view, then using the app for framing is definitely useful. And, I can see if you're mostly locking it down, that the LCD wouldn't be that useful.

I'm wanting to use the camera for uses that are not so much action-oriented. I want the high resolution in the small form factor and to be able to take it in the water if I want. But I'd like to play with it in more of a narrative fashion. Or, more of a moving poetic fashion? This video is the closest to what I have in mind, and was made with the gopro hero3 black, shot 720p 120fps: http://vimeo.com/55113238

This camera is capable of beautiful hi-res images and buttery smooth slo-mo if the conditions are right.

I finally heard back from GoPro and they tell me the Hero3's minimum focus distance is 12in to infinity for all crops. I think the reason it looks soft is because I'm mostly shooting in Protune with has NO in-camera sharpening. It's basically a RAW format and you do the sharpening in post.

Here is one of the best blog posts from one of the guys who shoots the stellar gopro promo videos that breaks it down and explains where the real sweet spots are. These results are consistent with all I've discovered so far, but this info is much more detailed. So useful, I've saved it to my iPhone and iPad for reference: http://abekislevitz.com/understanding-your-new-gopro/

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GodSpeaks
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Re: Cropping changes DoF
In reply to skiphunt13, Jan 12, 2013

skiphunt13 wrote:

The app does have it's use for sure. If you're placing the camera in a place where you can't get behind it to view, then using the app for framing is definitely useful. And, I can see if you're mostly locking it down, that the LCD wouldn't be that useful.

Which is what I do with my GoPros.

I finally heard back from GoPro and they tell me the Hero3's minimum focus distance is 12in to infinity for all crops. I think the reason it looks soft is because I'm mostly shooting in Protune with has NO in-camera sharpening. It's basically a RAW format and you do the sharpening in post.

That's good to know.

Here is one of the best blog posts from one of the guys who shoots the stellar gopro promo videos that breaks it down and explains where the real sweet spots are. These results are consistent with all I've discovered so far, but this info is much more detailed. So useful, I've saved it to my iPhone and iPad for reference: http://abekislevitz.com/understanding-your-new-gopro/

Great find.  Yes, indeed, some very useful info about the Hero3 and protune.  I didn't know it was 45Mbps.  I thought it was 'only' 35Mbps 

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Sphenisc
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Re: GoPro Hero 3 Black minimum focus distance?
In reply to skiphunt13, Apr 8, 2013

Are all filter threads the same, or do I have to get something specific to the Blurfix adaptor? Thanks

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cretinhopp
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Re: Cropping changes DoF
In reply to dsjtecserv, 2 months ago

Hope I don't sound like a dummy, first post and all, but why not make life simple and get out a ruler and do a simple camera test? 12 inches out better get the usable shots for me for client work.

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