VidThreeNorth
No longer a newbie, moving up!
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- Oct 21, 2016
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SLR Magic 8mm F4 M43 lens
Tested on Yi-M1
Primary Use:
I have been recording fireworks for a few years with varying success. Last year I had a problem so bad that I did not make a post-able finished version. I know the problem and I could probably correct it this coming year, but now that I have the Yi-M1, I thought it might be nice if I could get it done with this camera. To do this, I needed a "very wide" lens. My zooms cover 12mm, which is equal to 35mm camera 24mm ("eq 24mm") which is not really wide enough. A few months ago, I decided that I would probably want a Rokinon 10mm F2.8, manual lens. These cost around $400 US, which I could not afford, so I left it at that. There is also a new Venus Optics Laowa 7.5mm F2.0 lens selling for around $500.00 US, which I also cannot afford.
[2018-07-27 Correction: Laowa lens is 7.5mm, not 7.2mm]
B&H recently had a sale on the SLR Magic 8mm F4 for the Micro 4:3 mount which is intended for drone use. This lens normally sells for around $350 US. I bought one for around $180 US. I do not have a drone, but I felt that the specifications could be acceptable for my needs.
I have done some testing to verify its capabilities using the Yi-M1 which has a 20MP sensor, and I have mixed feelings about this. I am certainly glad I did not pay the full price.
I have tested it in UHD (3840 wide) video mode and Yi's unique 4:3 frame format 2K video mode, as well as in still images at full 20MP resolution.
First The Bad News:
The lens I received was assembled/adjusted improperly and the nominal "infinity" is not at infinity. I cannot tell precisely, but I think it might be focusing at around 1.0 M. Infinity is not even covered by depth of field as far as F11. I did not test F16.
Also, colour fringing is evident at all F-stops I tested (down to F11) and is even visible in the middle 1/3 of the image. There is some barrel distortion, and as expected, the sharpness decreases somewhat in the corners, depending on the F-stop.
Any Good News?:
I am not a technician, but I do think that I can probably correct the focus, if I can get the right tool. I think I need a metric 1.0 Allen key (hex key), or similar screw driver. I used to have that size, but I cannot find one now, and I do not know where I can get one.
[2018-02-18 Update]
I found my metric 1.0 hex key and it is too big. I compared the set screws to a ruler and the screw diameter seems to be a bit over 1mm (maybe 1.2mm?). The size of the hole for the hex key looks a bit bigger than 0.5mm (0.6mm?). I am still trying to find a vendor for any hex keys smaller than metric 1.0. Nothing is certain at this point.
Testing:
I have a lot of test images. I needed a lot of them because the depth of field is very large and the lens has issues, so it was very hard to tell what was going on. I am only going to post images from a couple of files. They indicate (somewhat weakly) the improper focus. I do not see any point in posting more at this time. If/when I get this lens adjusted to bring "infinity to infinity" then I expect to post more.
If you look at "industrial" (C-mount) lenses, they are generally rated as "xMP (megapixels)" for a sensor size. For example, a manufacturer might rate a lens at a "2MP lens for a 1/2.3" sensor".This implies that the manufacturer has rated the lens as having 2 megapixel image quality on a 1 over 2.3-inch sensor. That 1/2.3" sensor size will be a real limit, with the image often cut off beyond that size by vignetting. But the sharpness rating is up to the manufacturer and generally is the capability at full aperture. So a "1MP" lens will usually be good for 1280 x 720P ("HD") video work. A "2MP" lens would be recommended for 1920 x 1080P ("Full HD") video work. But a very good "1MP" lens might be good enough for "Full HD" when stopped down.
[2018-02-18]
A slight correction: If the sensor is 3:2, then a Full HD ("1980 x 1080") resolution will be about 2MP, which is what I stated above, but if the sensor is 4:3, then really you need 3MP performance to cover Full HD because the 16:9 frame of Full HD will not use the upper and lower rows of sensors.
My current estimate is that if/when I get it properly adjusted, this SLR Magic 8mm F4.0 lens will probably turn out to be something like a "1MP" lens. It might be usable for "Full HD", stopped down, but it is not going to be acceptable for "UHD".
I have not seen a review of the Rokinon 10mm F2.8 lens yet, but the company has a reasonably good reputation. So I think it is probably the better product. An early report indicates that the Laowa 7.5mm F2.0 lens is a better lens than this SLR Magic lens. It seems to me that it would be better to look for one of these other products instead. And it would be really nice if one of the major lens testers covered these products.
Original image format 5200 x 3902 Pixels
(20MP)
"P2060002.DNG"
Nominal settings:
F4.0, Focus Infinity
Partial EXIF data:
Date: Feb 6, 2018, 14:19:03
Pixel height 3888
Pixel width 5184
Color Space (irrelevant -- RAW)
Exposure program Normal
Scene capture Standard
Exposure mode Auto exposure
Exposure bias 0.00 ev
Exposure time 1/4000 sec.
ISO speed 200
Metering mode Center weighted average
Digital zoom ratio None
Gain control "Low gain up"
The following is not recorded in the EXIF data:
F number [nominal F4.0 -- fully open]
Focal length [nominal 8mm]
Focal length in 35mm [16mm]
All files are un-adjusted except for the conversion from RAW and then either cropping or resizing.
"P2060002-1a-rsz1640-C1.jpg"
- unadjusted conversion from DNG (raw) file, resized to 1640 x 1231
"P2060002-1b-Crop01-C1.jpg"
Crop from (2570,1400), size 1200 x 900
- look at the street light tops left from the billboard
- these are big enough to show the edges blurring from the left most to the right most. The blurring increases with distance.
"P2060002-1c-Crop02-C1.jpg"
Crop from (2100,1400), size -1200 x 900
- The "traffic island" sign and its post are not wonderfully sharp, but it does show the color fringing, and that the sharpness is not being lost in the nearer objects. They are probably a bit sharper, but the difference is so little that I will not claim to be able to tell.
"P2060020.DNG"
Nominal settings:
F8.0, Focus Infinity
Partial EXIF data:
Date: Feb 6, 2018, 14:25:31
Pixel height 3888
Pixel width 5184
Color Space (irrelevant -- RAW)
Exposure program Normal
Scene capture Standard
Exposure mode Auto exposure
Exposure bias 0.00 ev
Exposure time 1/1250 sec.
ISO speed 200
Metering mode Center weighted average
Digital zoom ratio None
Gain control "Low gain up"
The following is not recorded in the EXIF data:
F number [nominal F8.0 -- 2 stops down]
Focal length [nominal 8mm]
Focal length in 35mm [16mm]
"P2060020-1a-rsz1640-C1.jpg"
- unadjusted conversion from DNG (raw) file, resized to 1640 x 1231
"P2060020-1b-Crop01-C1.jpg"
Crop from (2570,1400), size 1200 x 900
- again, look at the street light tops left from the billboard
- The blurring still increases with distance.
This is also true of the hand rail on the far side of the bridge. I think it is more visible in this F8.0 picture than in the F4.0 picture
"P2060020-1c-Crop02-C1.jpg"
Crop from (2100,1400), size -1200 x 900
The "traffic island" sign and its post are sharper, but it still shows the color fringing, and that the sharpness is not being lost in the nearer objects. They are probably a bit sharper, but the difference is so little that I will not claim to be able to tell.
Tested on Yi-M1
Primary Use:
I have been recording fireworks for a few years with varying success. Last year I had a problem so bad that I did not make a post-able finished version. I know the problem and I could probably correct it this coming year, but now that I have the Yi-M1, I thought it might be nice if I could get it done with this camera. To do this, I needed a "very wide" lens. My zooms cover 12mm, which is equal to 35mm camera 24mm ("eq 24mm") which is not really wide enough. A few months ago, I decided that I would probably want a Rokinon 10mm F2.8, manual lens. These cost around $400 US, which I could not afford, so I left it at that. There is also a new Venus Optics Laowa 7.5mm F2.0 lens selling for around $500.00 US, which I also cannot afford.
[2018-07-27 Correction: Laowa lens is 7.5mm, not 7.2mm]
B&H recently had a sale on the SLR Magic 8mm F4 for the Micro 4:3 mount which is intended for drone use. This lens normally sells for around $350 US. I bought one for around $180 US. I do not have a drone, but I felt that the specifications could be acceptable for my needs.
I have done some testing to verify its capabilities using the Yi-M1 which has a 20MP sensor, and I have mixed feelings about this. I am certainly glad I did not pay the full price.
I have tested it in UHD (3840 wide) video mode and Yi's unique 4:3 frame format 2K video mode, as well as in still images at full 20MP resolution.
First The Bad News:
The lens I received was assembled/adjusted improperly and the nominal "infinity" is not at infinity. I cannot tell precisely, but I think it might be focusing at around 1.0 M. Infinity is not even covered by depth of field as far as F11. I did not test F16.
Also, colour fringing is evident at all F-stops I tested (down to F11) and is even visible in the middle 1/3 of the image. There is some barrel distortion, and as expected, the sharpness decreases somewhat in the corners, depending on the F-stop.
Any Good News?:
I am not a technician, but I do think that I can probably correct the focus, if I can get the right tool. I think I need a metric 1.0 Allen key (hex key), or similar screw driver. I used to have that size, but I cannot find one now, and I do not know where I can get one.
[2018-02-18 Update]
I found my metric 1.0 hex key and it is too big. I compared the set screws to a ruler and the screw diameter seems to be a bit over 1mm (maybe 1.2mm?). The size of the hole for the hex key looks a bit bigger than 0.5mm (0.6mm?). I am still trying to find a vendor for any hex keys smaller than metric 1.0. Nothing is certain at this point.
Testing:
I have a lot of test images. I needed a lot of them because the depth of field is very large and the lens has issues, so it was very hard to tell what was going on. I am only going to post images from a couple of files. They indicate (somewhat weakly) the improper focus. I do not see any point in posting more at this time. If/when I get this lens adjusted to bring "infinity to infinity" then I expect to post more.
If you look at "industrial" (C-mount) lenses, they are generally rated as "xMP (megapixels)" for a sensor size. For example, a manufacturer might rate a lens at a "2MP lens for a 1/2.3" sensor".This implies that the manufacturer has rated the lens as having 2 megapixel image quality on a 1 over 2.3-inch sensor. That 1/2.3" sensor size will be a real limit, with the image often cut off beyond that size by vignetting. But the sharpness rating is up to the manufacturer and generally is the capability at full aperture. So a "1MP" lens will usually be good for 1280 x 720P ("HD") video work. A "2MP" lens would be recommended for 1920 x 1080P ("Full HD") video work. But a very good "1MP" lens might be good enough for "Full HD" when stopped down.
[2018-02-18]
A slight correction: If the sensor is 3:2, then a Full HD ("1980 x 1080") resolution will be about 2MP, which is what I stated above, but if the sensor is 4:3, then really you need 3MP performance to cover Full HD because the 16:9 frame of Full HD will not use the upper and lower rows of sensors.
My current estimate is that if/when I get it properly adjusted, this SLR Magic 8mm F4.0 lens will probably turn out to be something like a "1MP" lens. It might be usable for "Full HD", stopped down, but it is not going to be acceptable for "UHD".
I have not seen a review of the Rokinon 10mm F2.8 lens yet, but the company has a reasonably good reputation. So I think it is probably the better product. An early report indicates that the Laowa 7.5mm F2.0 lens is a better lens than this SLR Magic lens. It seems to me that it would be better to look for one of these other products instead. And it would be really nice if one of the major lens testers covered these products.
Original image format 5200 x 3902 Pixels
(20MP)
"P2060002.DNG"
Nominal settings:
F4.0, Focus Infinity
Partial EXIF data:
Date: Feb 6, 2018, 14:19:03
Pixel height 3888
Pixel width 5184
Color Space (irrelevant -- RAW)
Exposure program Normal
Scene capture Standard
Exposure mode Auto exposure
Exposure bias 0.00 ev
Exposure time 1/4000 sec.
ISO speed 200
Metering mode Center weighted average
Digital zoom ratio None
Gain control "Low gain up"
The following is not recorded in the EXIF data:
F number [nominal F4.0 -- fully open]
Focal length [nominal 8mm]
Focal length in 35mm [16mm]
All files are un-adjusted except for the conversion from RAW and then either cropping or resizing.
"P2060002-1a-rsz1640-C1.jpg"
- unadjusted conversion from DNG (raw) file, resized to 1640 x 1231
"P2060002-1b-Crop01-C1.jpg"
Crop from (2570,1400), size 1200 x 900
- look at the street light tops left from the billboard
- these are big enough to show the edges blurring from the left most to the right most. The blurring increases with distance.
"P2060002-1c-Crop02-C1.jpg"
Crop from (2100,1400), size -1200 x 900
- The "traffic island" sign and its post are not wonderfully sharp, but it does show the color fringing, and that the sharpness is not being lost in the nearer objects. They are probably a bit sharper, but the difference is so little that I will not claim to be able to tell.
"P2060020.DNG"
Nominal settings:
F8.0, Focus Infinity
Partial EXIF data:
Date: Feb 6, 2018, 14:25:31
Pixel height 3888
Pixel width 5184
Color Space (irrelevant -- RAW)
Exposure program Normal
Scene capture Standard
Exposure mode Auto exposure
Exposure bias 0.00 ev
Exposure time 1/1250 sec.
ISO speed 200
Metering mode Center weighted average
Digital zoom ratio None
Gain control "Low gain up"
The following is not recorded in the EXIF data:
F number [nominal F8.0 -- 2 stops down]
Focal length [nominal 8mm]
Focal length in 35mm [16mm]
"P2060020-1a-rsz1640-C1.jpg"
- unadjusted conversion from DNG (raw) file, resized to 1640 x 1231
"P2060020-1b-Crop01-C1.jpg"
Crop from (2570,1400), size 1200 x 900
- again, look at the street light tops left from the billboard
- The blurring still increases with distance.
This is also true of the hand rail on the far side of the bridge. I think it is more visible in this F8.0 picture than in the F4.0 picture
"P2060020-1c-Crop02-C1.jpg"
Crop from (2100,1400), size -1200 x 900
The "traffic island" sign and its post are sharper, but it still shows the color fringing, and that the sharpness is not being lost in the nearer objects. They are probably a bit sharper, but the difference is so little that I will not claim to be able to tell.
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