Magfilter adapter on G7X II

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tokumeino Senior Member • Posts: 1,009
Magfilter adapter on G7X II
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IMO, CPL filters are much more important than perfect sharpness on corners. So as to adapt filters on a G7X / G7X II / G5X and more, I have found the Lensmate solution and the Magfilter solution. Both permit to adapt threated filters. I've chosen Magfilter mainly because I was afraid to hurt the lens if the attached lensmate hooks on something.

But the Magfilter comes into 3 sizes : 52mm, 55mm, 58mm. What should you choose ? Contacting the Magflter support by mail is usless : they don't seem to have tested the product on a variety of cameras. Anyway, the 58mm would be larger than the lens ring, and probably would exceed the bottom of the camera. So... 55mm or 52mm ?

Basically, up to that point, it is about vignetting at WA. I've ordered a 55mm so let me show my conclusion. You would have liked to read clear points about that, so I post for future Google searches.

I've taken a quick snap out of my window : with the Magfilter in red, and without the Magfiter in blue. On the Magfilter, I've put a CPL filter (Marumi DHG Super Circular PL 55mm). It is quite slim, but thicker than an ultra slim UV filter.

So... the results.

24mm, lens distortion 100% corrected

The angle of view is the one you would get OOC : equivalent to a 24mm FF. This picture is WITHOUT the filter, so no vignetting of course.

With the filter at 24mm, no vignetting

So far, so good.

Wider than 24mm, lens distortion 100% corrected

The G7X lens is sharp but heavily distorted. And OOC JPEGs are produced from a sensor crop. By reading the whole sensor outpout, one gets a significantly wider angle, at the expense of corner sharpness (no free lunch). So, what's going on with the Magfilter if one wants to unleash the G7X wide angle ?

Widest possible angle while keeping lines straight (rectilinear projection obtained by a 100% corrected lens distortion)

With the Magfilter + CPL attached under the same conditions, no vignetting. Sweet !

There is actually vignetting with the 55mm Magfilter, and we are getting close by going beyond 24mm

Full sensor capture, uncorrected distortion

So as to figure out how much the Magfliter vignetes at widest angle, let's have a look at the full sensor capture, without lens correction.

Even without the Magfilter, the lens vignettes at such a WA.

Vignetting is more pronounced with the 55mm Magfilter + CPL, but it remains OK, and anyway very far from the 24mm AOV boundaries

Widest angle without vignetting, adapted correction percentage

Here, we try to show the widest possible angle with a 2/3 aspect and without vignetting. To do so, the lens distortion correction percentage is adpated to maintain the widest angle, yet eliminating vignetting.

37% correction for the widest angle without vignetting

With the Magfilter 55mm, 65% correction. It's not as good because of the Magfilter vignetting, but it remains very nice...

... just remember what you would get OOC.

Conclusion

  1. With the 55mm, there won't be vignetting with an OOC picture, nor with an image processed by a basic RAW interpreter such as Lightroom.
  2. If you want to retain lines straight, then the Magfilter won't prevent you from going a wider as the G7X lens can go (perhaps like 22mm or such).
  3. It's only when you relax the "straight lines" constraint vignetting might become a concern.

So 55mm is probably the best size with a G7X :

  • With the 52mm, the feature (2) would probably not be verified
  • The 58m is too large for the body

Hope it helps...

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