Fisheye overexposure

[Bongwater Mojito]

I have GH5S and Samyang 7.5mm fisheye. In a bright overcast or a direct sunlight environment, there is noticeable overexposure if I use the F3.5, which I assume is best for picture quality. Is there any other way to address the overexposure than to close down the aperture? It seems I need to use F22 for good results. Camera's ISO scale does not help, not even on L80. Does F22 matter in terms of picture quality?

[OnSlapAtWork]

Kind of confusing what you are asking, but you will get a deeper depth of field (more objects in focus) by using a wider aperture (F22).  This would be more noticeable on a longer length lens.  i.e. with F22 and long lens, you will have more objects in focus.  When filming fisheye, because it is such a short focal length, the majority of items in the frame will be in focus regardless of aperture.

You will want to adjust aperture, shutter speed and ISO to get a correctly exposed image.

[OwlGreen]

Are you worried about diffraction robbing you of sharpness at f22? Unless that lens can take rear filters, stopping down is your only option. Raising the shutter speed is a bad idea as you'll end up with staccato motion. Use the lowest ISO you have and stop down.

[bataaard]

in theory the best quality would be around F5.6 / F8. Lenses tend to get a better quality at the middle of their range of aperture. But honestly, to film skateboarding with a fisheye you can use whatever aperture you want.

From my own experience filming fisheye, I would actually avoid the more open apertures (low number) because depending on the lens, it could make it harder to focus and induce blur near the vignetting.

also this:

Raising the shutter speed is a bad idea as you'll end up with staccato motion.

[fisheye talk]

Do you know how iso, shutter speed and aperture affect exposure?

If you are shooting with plenty of light I recommend the lowest iso possible, a shutter speed that gives a motion that you want (around 1/125 or 1/250) and then close the aperture until you get the correct exposure.

[Bongwater Mojito]

Thanks, I am somewhat familiar of aperture effect on photography side with normal lenses, but was in belief that for fisheye it's different and remember hearing from somewhere that wide aperture is better than narrow. No ND filter available on that particular fisheye, so I'll stop down. Shutter is at 180 (GH5S has angle setting). I've been using auto ISO with reasonable upper limit just for convenience. The lens is manual focus anyway, has been working well at around infinity.

[Bongwater Mojito]

This would be more noticeable on a longer length lens.  i.e. with F22 and long lens, you will have more objects in focus.  When filming fisheye, because it is such a short focal length, the majority of items in the frame will be in focus regardless of aperture.

You will want to adjust aperture, shutter speed and ISO to get a correctly exposed image.

This was what I thought but had wrong belief that focus or image quality would be significantly worse with higher aperture values. Thanks.

[Gnar_Gnar]

Expand Quote

This would be more noticeable on a longer length lens.  i.e. with F22 and long lens, you will have more objects in focus.  When filming fisheye, because it is such a short focal length, the majority of items in the frame will be in focus regardless of aperture.

You will want to adjust aperture, shutter speed and ISO to get a correctly exposed image.

[close]

This was what I thought but had wrong belief that focus or image quality would be significantly worse with higher aperture values. Thanks.

Like others said 5.6 or 8 is probably best but I've used 11 and 16 especially with studio strobes.  Main thing is keeping that shutter speed high and going wide open on your aperture helps with that.  I wouldn't really be shooting fisheye without some kind of flash though personally.

[OwlGreen]

You could also try something like this.

[Bongwater Mojito]

Thanks for replies. Closing down aperture helped. Was just too used to evenings and indoors. Works as should now. Also had completely wrong assumptions about fisheye focus and aperture value, no idea where that hearsay was from.

[OwlGreen]

I thought a bit more about your issue. I hadn't fully considered that the focal length of your lens is so short. Try shooting some tests in an environment where you can control the lighting. You might really find that f22 on that 7.5mm lens is unacceptably soft. The reason is because the aperture diameter of a 7.5mm lens at f22 is (7.5/22)mm, which is ~0.3mm. This is the size of a pinhole. At such small physical apertures, the wave nature of light starts to behave "sub-optimally". It kind of starts to interfere on itself. The full explanation is beyond me, but its called diffraction, and its a basic feature of all light and optical systems. It affects every aperture, but you really start to notice it the smaller your physical apertures become. If in your tests you find apertures above f8 or so are too soft, your best bet is taping a bit of gel, or perhaps exposed film, behind the rear element.

[Bongwater Mojito]

I thought a bit more about your issue. I hadn't fully considered that the focal length of your lens is so short. Try shooting some tests in an environment where you can control the lighting. You might really find that f22 on that 7.5mm lens is unacceptably soft. The reason is because the aperture diameter of a 7.5mm lens at f22 is (7.5/22)mm, which is ~0.3mm. This is the size of a pinhole. At such small physical apertures, the wave nature of light starts to behave "sub-optimally". It kind of starts to interfere on itself. The full explanation is beyond me, but its called diffraction, and its a basic feature of all light and optical systems. It affects every aperture, but you really start to notice it the smaller your physical apertures become. If in your tests you find apertures above f8 or so are too soft, your best bet is taping a bit of gel, or perhaps exposed film, behind the rear element.

Thanks, I will check the footage for softness. In a bright sunny day, it felt like the lowest ISO value (L80) still left too much overexposure, unless the aperture was almost closed down (ie. >f16). For various reasons I'm shooting 30p and am using shutter angle 180.

[fisheye talk]

I wouldn't shoot at L80 but at the lowest ISO available without the L (not too sure which is it on GH5s). You can look up the technicalities but when shooting at L80 the camera is shooting at the lowest regular ISO and underexposing the footage on post.

There is the crude rule for exposure, the sunny 16 rule, that states that on a sunny day shooting at ISO x you have to set the shutter speed to 1/x and the aperture to f16 to get a correctly exposed image. For example, if you are using ISO 200, set the shutter speed to 1/200 and the aperture at f16 (or the shutter speed to 1/100 and the aperture to F22).

30p and shutter angle of 180 is equivalent to a shutter speed of 1/60 I think. Depends on the look that you are going for but in my opinion it gives too much motion blur for skating. I would shoot at 1/120 or 1/250. That would also allow you to not use f22.

[Bongwater Mojito]

I wouldn't shoot at L80 but at the lowest ISO available without the L (not too sure which is it on GH5s). You can look up the technicalities but when shooting at L80 the camera is shooting at the lowest regular ISO and underexposing the footage on post.

There is the crude rule for exposure, the sunny 16 rule, that states that on a sunny day shooting at ISO x you have to set the shutter speed to 1/x and the aperture to f16 to get a correctly exposed image. For example, if you are using ISO 200, set the shutter speed to 1/200 and the aperture at f16 (or the shutter speed to 1/100 and the aperture to F22).

30p and shutter angle of 180 is equivalent to a shutter speed of 1/60 I think. Depends on the look that you are going for but in my opinion it gives too much motion blur for skating. I would shoot at 1/120 or 1/250. That would also allow you to not use f22.

Thanks, this was good information! I'm a hobby-level filmer with my first M43 setup (GH5s, Samyang fisheye, Lumix G 12-32, Sirui Nightwalker 35mm), had a GoPro before. So, lots to learn. Been using 180 angle as baseline, understood that should be still somewhat sharp, as no slow motion is planned. But might try 90 degrees, ie. 1/120 and see how it looks. It's not going to be my edit, but faster shutter and crisper picture might work better.