Soft edges with wide angle lenses on the BMP4K

[kin869]

I'm getting some really soft edges with wide angle lenses on the BMP4K and was wondering if anyone experienced something similar. The lenses I've tried so far are native MFT lenses, the Laowa 7.5mm and the Samyang 12mm. I know the problem is not with the lenses because I use them on the GH5S and the GX85 without any soft edges. Another reason I don't think the problem is with the lens is that I can actually get the edges in focus at the expense of a softer center point. Here are some examples:


BMP4K with Laowa 7.5mm at f/2 - Focus is set to center of frame.

BMP4K with Laowa 7.5mm at f/2 - Focus is set to edges of frame.

GX85 with Laowa 7.5mm at f/2 - Focus is set to center of frame.

=====

BMP4K with Samyang 12mm at f/2 - Focus is set to center of frame.

BMP4K with Samyang 12mm at f/2 - Focus is set to edges of frame.

GX85 with Samyang 12mm at f/2 - Focus is set to center of frame.

Any idea why this is happening?

[ted ramasola]

What about at f4 or f5.6 ?

Lenses are usually not optimal at their full aperture especially at that price level.

Another theory is that the Lumix cameras usually do in camera lens correction, especially so with their own lumix lenses. I would suspect it still does since you have to type in the focal length when you use third party manual lenses.

I have the Laowa and I have good results with it with my GH4. I will test it when my P4k arrives.

[joe12south]

The GH series can only correct the distortion of 1st party lenses with electronic contact. You enter the focal length of manual lenses for IBIS.

[ted ramasola]

The GH series can only correct the distortion of 1st party lenses with electronic contact. You enter the focal length of manual lenses for IBIS.

I think this is correct, so its probably due to having it at full open then. Though I think I havent seen it THAT soft when I used it at f2. Hhmm..

[kin869]

The GH series can only correct the distortion of 1st party lenses with electronic contact. You enter the focal length of manual lenses for IBIS.

That's my understanding as well. The lenses that I'm using are 3rd party lenses and they don't have any electronic contacts to communicate with the camera, so there shouldn't be any corrections at all.

I think this is correct, so its probably due to having it at full open then. Though I think I havent seen it THAT soft when I used it at f2. Hhmm..

I understand that shooting wide open tends to be softer especially for wider lenses, but the focus is perfectly fine when I use those same lenses on my GX85. What's even more weird is that the focal plane isn't even all the way across the frame....makes me think this has something to do with the BMP4K's sensor stack being different from standard MTF cameras. Another reason that leads me to believe that is the "infinity" mark on my lenses are off quite a bit when shooting on the BMP4K compared to my GX85.

[ted ramasola]

Since I happen to have the same GX85 that you have I decided to do a chart test and true enough, at f2 the loawa has soft on on the edges, I noticed that on the left side it is softer than on the right, its a quick and dirty test, and since its wide, I'm very close to the chart so any slight off centering of my camera will probably impact focus across the chart. But yeah soft on the side.
At F4 it negligible.
f2
f2.jpg

f4
f4.jpg

and since the p4k has no digital sharpening like in the lumix cameras, these slightly off focus lenses will be obvious.

[kin869]

Since I happen to have the same GX85 that you have I decided to do a chart test and true enough, at f2 the loawa has soft on on the edges, I noticed that on the left side it is softer than on the right, its a quick and dirty test, and since its wide, I'm very close to the chart so any slight off centering will probably impact focus across the chart. But yeah soft on the sides.
At F4 it negligible.
f2
[ATTACH=CONFIG]26903[/ATTACH]

f4
[ATTACH=CONFIG]26904[/ATTACH]

and since the p4k has no digital sharpening like in the lumix cameras, these slightly off focus lenses will be obvious.

Thanks for taking the time to take those test shots. Did you take both of those with the GX85? Do you have a BMP4K that you can shoot the same thing and compare?

I'm trying to isolate the softness from the lens versus softness from the camera. Since both my Laowa 7.5mm and Samyang 12mm can focus at f/2 evenly across the frame on my GX85, it should also be able to do the same thing with the BMP4K. I don't think it has to do with digital sharpening either, since I can get the edges to focus on the BMP4K at the expense of center sharpness (I've posted examples of this in my first post as well). It's just odd to me that I can't get these lenses to focus evenly across the frame on the BMP4K, but they work perfectly fine on my GX85.

[ted ramasola]

Yes, both with GX85. I have a bigger chart which I use to test my wide lenses years back but I already rolled it into storage, this was on the shelf in my office so I just took it out since this Laowa was relatively new to me and I didnt "properly" test it.

Anyhow, my pocket has not yet arrived but this was also something of a revelation for this lens that, its not evenly sharp AND not evenly soft! I'd attribute it probably to QC in manufacture. If I were you and I want to isolate the issue, I'd test it with a control lens, something thats "industry proven" to be good. If you have a lumix 12-35, I'd use that as its a sharp lens across the frame. I would not use that samyang as basis, though their 35mm f1.4 is good, just not at f1.4, stop it down to 2 or 2.8 and its good.

[Samuel H]

Cameras have a chunk of flat glass in front of the sensor, and the thickness of that glass affects how the image hits the sensor. Lenses are designed for a specific glass cover thickness, and if the sensor has a different thickness then they will become soft, with this being more of an issue for, you guessed it, wide lenses with fast aperture.

With the original 2.5k camera, BM used thinner glass than other m43 manufacturers, because it used canon-like thickness. I would guess they would go thick on the p4k, but maybe they didn't?

https://www.lensrentals.com/blog/201...oes-it-matter/

[kin869]

Cameras have a chunk of flat glass in front of the sensor, and the thickness of that glass affects how the image hits the sensor. Lenses are designed for a specific glass cover thickness, and if the sensor has a different thickness then they will become soft, with this being more of an issue for, you guessed it, wide lenses with fast aperture.

With the original 2.5k camera, BM used thinner glass than other m43 manufacturers, because it used canon-like thickness. I would guess they would go thick on the p4k, but maybe they didn't?

https://www.lensrentals.com/blog/201...oes-it-matter/

That's what I assumed but I couldn't find where the actual sensor stack thickness is mentioned for the BMP4K. I remember having issues with the thinner sensor stack with my original BMPCC as well, although that was sorta fixed when I added the Mosaic OLPF. From my brief experience in shooting with it so far, it seems like the sensor is already really good at suppressing aliasing and IR pollution so I don't think a 3rd party OLPF will be created. I wonder how this problem could be solved then...

[ted ramasola]

I also had experience with a mosaic filter when I used it to suppress aliasing on 5DmkII and I agree that it does changes lens performance. The MOD on my lenses changed to a point you cant rely on the distance scales on the lenses anymore. But in this case I would assume BM made there sensor design with as much compatibility with lenses as possible considering they don't make their own.

Stopping down your lens could give you e to e sharpness, this is a workaround even for lenses from known makers. F2.8 could be a lot better and at f4 this would probably be not an issue. I would not shoot landscapes at f2 anyway.

Here's someone who just posted a laowa 7.5 on an P4k on a gimbal.

https://www.youtube.com/watch?v=Br7L5r86RD4

[kin869]

I also had experience with a mosaic filter when I used it to suppress aliasing on 5DmkII and I agree that it does changes lens performance. The MOD on my lenses changed to a point you cant rely on the distance scales on the lenses anymore. But in this case I would assume BM made there sensor design with as much compatibility with lenses as possible considering they don't make their own.

Another reason why I think it's the sensor stack on the BMP4K is because the witness marks/focus scale is off when I use my lenses on the BMP4K versus the GX85. If I set the lens to infinity (based on the witness mark), then the lens will actually be focused to infinity on the GX85, whereas on the BMP4K, it's off by a few degrees.

Stopping down your lens could give you e to e sharpness, this is a workaround even for lenses from known makers. F2.8 could be a lot better and at f4 this would probably be not an issue. I would not shoot landscapes at f2 anyway.

Right, stopping down will definitely reduce the softness, I purposely shot at f/2 so it's easy to see the problem. It's just a bummer that I can't shoot at wider apertures with my wide angle lenses when I'm shooting indoor or lower light situations.

Here's someone who just posted a laowa 7.5 on an P4k on a gimbal.

https://www.youtube.com/watch?v=Br7L5r86RD4

It says he shot that with the GH5s in the title, not the BMP4K. I actually rented the GH5s a few weeks ago and used it on my Crane with the Laowa 7.5mm. I was able to shoot indoors at f/2 without any of the soft edges that I'm getting with the BMP4K.

[ted ramasola]

It says he shot that with the GH5s in the title, not the BMP4K. I actually rented the GH5s a few weeks ago and used it on my Crane with the Laowa 7.5mm. I was able to shoot indoors at f/2 without any of the soft edges that I'm getting with the BMP4K.

oh shoot... my mind is all P4k P4k P4k I'm beginning to see things! Hahaha!

But, yeah, if its any consolation, a lot of lenses, even from reputable ones, are not good wide open, it would vary from fair to really bad. Even the legendary 11-16 tokina f2.8 has issues wide open. My old nikons, almost all of them are not good wide open. 50mm f1.4, 105mm f2.8, 80-200 f2.8, my mamiya 80mm f1.9 whuch I adapted to nikon mount, they are either soft or exhibit ghosting and flare, CA, in the case of the tokina 11-16, slight softness and chromatic aberration.

Now all of them become awesome when turned down even by 1 stop.

Now with the pocket 4K, it's now feasible to use slow lenses and in our case, we can now stop down the Laowa to even smaller apertures since these new cameras like the Pocket 4K and the GH5S are good with low light at higher ISOs.

[Robert Niessner]

Guys, you are aware that the PCC4K has a bigger sensor?
GH5/s: 17.3 x 9.7 mm
PCC4K: 18.96 x 10 mm

[ted ramasola]

Yes. And that might also contribute to this to a degree. Have you gotten to test it by how much of a crop factor it does compared to 2x crop of GH5? The GH5S is somehwhere at 1.8 ish.

But looking at the area of softness on the chart test and some footage, it is way within the safe spot of the sensor and not really out in the fringes.