Extending aperture – 7artisans 12mm F2.8 lens

Typically lens are designed to have perfect round aperture opening circle at maximum value. It looks unusual that 7artisans 12mm F2.8 lens works differently.

7artisans 12mm F2.8 lens aperture mechanism is purposely limiting 7 aperture blades to open completely at F2.8. It’s observed on all lens samples I had chance to see or explored online. So its not a single sample flaw but technical decision, and your lens sample is a good one if you have the same : )

I’m disassembling the lens again to experiment with its aperture. I’m going to set blades opened completely and see how it is affcting the image.

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7artisans 12mm F2.8 – aperture blades at F2.8 value are not opened to the hole borders. That is correct behaviour! : )

Lens modification

First steps are described in 7artisans 12mm F2.8 partial disassembly guide . At this point I’m adding extra marks on aperture transmission ring to indicate positions at different values. I’ve also unscrewed outer brass pin from that ring.

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7artisans 12mm F2.8 lens at F2.8

Short marks there are indicating transmission ring position at F2.8. Normally outer brass pin move ends here due to upper rotation stopper of lens frame. Without that pin the ring can be rotated CW a bit further.

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7artisans 12mm F2.8 lens at a bit more wide aperture, let cal lit F2.?

Long marks are indicating transmission ring position at widest aperture possible.

Next steps is not reversible (bit not affects lens performance). I’ve took the transmission ring out, then drilled 1.2mm hole on the side of the ring near the upper long mark. Then I’ve made temporary pin replacement from soft copper 1.2mm wire. It sits firm inside and can’t escape the position due to outer aperture ring will hold it pushed into the hole. I’ve temporary screwed back the original brass pin to show the position offset.

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7artisans 12mm F2.8 – aperture transmission ring with mod.

Brass pin need to be unscrewed again, and then lens can be assembled. The temporary pin should fit the corresponding slot of the outer aperture control ring.

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After re-assembly I’ve added gray mark on the body that shows new (shifted) position for actual F2.8 value. You may simply set normal F4 value near central dot – it will be F2.8 opening, so I’ve put that mark near F2.8.

Now is the fun part – when you rotate the ring to fully open blades, you can mark the uknown “F.?” position on the aperture ring for better usability while shooting.

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Test shot samples

Nono is my never complaining model available 24/7 : ) So here are three shot samples, 100% crop, at F2.8, “F2.?-1/2”, and “F.?”.

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7artisans 12mm F2.8 shot at F 2.8 X-E2s , ISO800, S1/20
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7artisans 12mm F2.8 shot at F 2.?-1/2 X-E2s , ISO800, S1/20
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7artisans 12mm F2.8 shot at F 2.? X-E2s , ISO800, S1/26

Sharpness is great at F2.8, though event half way to “F.?” details start to look much softer, and F.? shot is very soft with significant glow and fringe in bright areas. That could be good for portraits, but it’s ultra-wide 12mm lens. I can imagine the use of this soft-focus look for some cases of creating dreamy landscape shots, however it can be also done in post processing. Particular shots don’t benefit much from increased amount of light and a bit faster shutter speed (1/26s at F.? vs 1/20s at F2.8).

Most of indor samples are often too artificial, also above shots are close ups. So let check how it works outdoor. Here’s another set of three shots taken at same camera settings with only increasing aperture value. I’ve just cut 100% crop central area.

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7artisans 12mm F2.8 shot at F 2.8, X-E2s , ISO800, 1/5400s
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7artisans 12mm F2.8 shot at F 2.?-1/2, X-E2s , ISO800, 1/7000s
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7artisans 12mm F2.8 shot at F 2.?, X-E2s , ISO800, 1/8000s

Shutter speed differences are more noticeable here – 1/8000s at F.? vs 1/5400s at F2.8.

The image look just reminds me Fujifilm built in JPEG processing Adv. filter called “Soft Focus”. I don’t see real need of opening 7artisans 12mm F2.8 aperture more than F2.8 so far. Probably 7artisans engineers made same decision, so all production samples are calibrated at F2.8 max opening.

Last thing I wanted to check how this aperture mod affects the OOF areas, in particular light sources. Here’s the sequence of 100% crops of OOF in the frame center ad different aperture values from F4 till F2.?

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7artisans 12mm F2.8 – OOF look at F5.6
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7artisans 12mm F2.8 – OOF look at F4
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7artisans 12mm F2.8 – OOF look at F2.8
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7artisans 12mm F2.8 – OOF look at F2.?-1/2
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7artisans 12mm F2.8 – OOF look at F2.?

I don’t notice significant shape or size changes of OOF light circles, which means that aperture blades at F2.8 form the maximum opening for the light passing tunnel. At F2.?-1/2 the circle shape is just become perfect while F2.8 circles have 7 slight angles.

At F.? I can see brigh dot in the OOF circle centers.

Someone may like the F2.?-1/2 OOF circles more, that’s the only reason for me that justifies mod of this lens. But it’s not important to keep, so I basically reverted the mod after this experiment.

Another trade of current mod solution is that minimal aperture become only F5.6 and you can’t use F8-F16 range that is useful in many cases. I think it may be reasonable to extend the normal range of 7artisans 12mm F2.8 from F1.8 – F16 to e.g. F2.?-1/2 – F8.

 

3 comments

  1. I like your experiments. Currently I’m trying Minolta Rokkor lenses and Carl Zeiss Jena (Praktica East Germany-) lenses via adapter at my brand new X-T20.

    By the way, my WordPress.com account is currently only in rough building status. 😉

    Like

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