A Review of the A7K (Kolari Thin Filter Conversion)

[pinholecam]

I am not sure how many are aware that this modification is available for the Sony A7 and A7r cameras and other that a little being mentioned on the Sony section of the forums, I've not seen any more info nor discussion continue.


Some Background
The A7 series of cameras have a rather thick filter stack (the stack consisting of the bayer color array, AA filter and the IR/UV block filter).
This may be fine on lenses designed to cater for this stack thickness, but for legacy lenses this can be a problem.
The light rays striking the edges and corners of the sensor from old lenses can be very acute, the result of which is astigmatism on those areas (ie. off the center)
For lenses with a longer exit pupil (to the sensor), there is enough distance to make this angle less steep.
But on those with short exit pupils (especially RF and RF wides), this can result in large image quality drop.

For much more detailed info on sensor stack thinkness, look here :
http://www.lensrentals.com/blog/2014/06/the-glass-in-the-path-sensor-stacks-and-adapted-lenses


The A7 series, So near yet so far

When this camera was first launched, many legacy (esp. RF lens users) were euphoric.
Here was a camera, a fraction of a Leica M9 price with the potential to use RF lenses in a full frame format.

As the camera came out, some shot a few shallow DOF shots with their fast lenses and were sated.
The more careful (and perhaps those shooting genres that required more stopping down to the lens) started to observe that the off-center and/or edges/corners were far from good.

My own experiences, have been the same.
Not all RF lenses work that well on the A7 series of cameras.
Even 50mm lenses the likes of the Leica Summicron V1 and DR can have issues with off center sharpness.
Even on legacy SLR lenses, I felt that they can be better, having experienced better apparent performance on film over what the edges looked like on the A7.


I began to take interest in the discussion that stated in FM Forums regarding the thin filter mod pioneered and offered by Kolari Vision.

Here is a link to the discussion on FM forums.
Its a must read for those who are considering the mod as it also addresses the potential risks and pitfalls.
http://www.fredmiranda.com/forum/topic/1340474/0


The initial problem was that the replacement IR/UV cut filter replacement (as thin as the one used on the M9) suffered the same issues of corrosion in high humidity.
Luckily, Kolari has been able to source a more resistant filter (from Schott)


I decided go for the mod and since little info has been shared here on CS, I will try to do so.


The exact link to Kolari Vision is :
http://kolarivision.com/product/sony-a7-series-thin-filter-legacy-lens-upgrade/



This is a AA filter removal + thin filter modification.
More results will follow as I get to compare against a A7K (modded) vs A7 (unmodded)
Note : I don't have an unmodded A7, so any updates will be dependent on meetups with friends who have the camera.

Here is the first one done for an SLR lens.
All shots in RAW and using the same processing.
If there is anything I adjust between the sample shots, it will be a bit of exposure correction (within 0.5ev) if the exposure don't match up.

Pentax SMC K24/2.8

Full Image

A7_standard Pentax K24 f2.8 at f10 by jenkwang, on Flickr


Center Crop

A7_standard Pentax K24 f2.8 at f10-center by jenkwang, on Flickr


A7K Pentax K24 f2.8 at f10-center by jenkwang, on Flickr

 

[pinholecam]

Left Crop

A7_standard Pentax K24 f2.8 at f10-left by jenkwang, on Flickr


A7K Pentax K24 f2.8 at f10-left by jenkwang, on Flickr


Right Crop

A7_standard Pentax K24 f2.8 at f10-right by jenkwang, on Flickr



A7K Pentax K24 f2.8 at f10-right by jenkwang, on Flickr



There is certainly improvement even on this particular legacy SLR lens.

 

[ricleo]

nice! thanks for trying it out and posting some samples for us.

would be even more informative if you could get hold of some RF ultrawides (like CV 12mm, 15mm v1/2) are known to cause magenta corners / smearing on the A7 series. That would be the real acid test

If you need access to the 12/15mm let me know, can test together

 

[pinholecam]

nice! thanks for trying it out and posting some samples for us.

would be even more informative if you could get hold of some RF ultrawides (like CV 12mm, 15mm v1/2) are known to cause magenta corners / smearing on the A7 series. That would be the real acid test

If you need access to the 12/15mm let me know, can test together

Thanks for the offer, I will certainly keep it in mind.

I have the CV12, and access to the CV15 v1, I will get to them in time for sure.
The problem for me if to find time to meetup with my friends who have a A7 to do the comparisons.


I'll certainly get to the lenses though.

 

[pinholecam]

For those wondering if the thin filter mod reduces the color cast on corners for RF wides, I don't think it does.
(All 3 samples shown here are on my Flickr at full size )

Here is a shot before correction.


A7K CV12 0EV sample by jenkwang, on Flickr

As far as I can recall, the color casting on the corner is the same as before the mod.


Here is the corrected sample.
Basically just call up the CV12 lens profile on LR with vignette correction set to 50.
The color cast is then removed with a brush set to tint -15 (ie. towards green )

A7K CV12 corrected sample by jenkwang, on Flickr

As for sharpness, I did not shoot this shot with a comparative (unmodded) camera.
However, the full size of the 3 samples shown here is on my Flickr.


Final Image with a bit of WB adjustment, 0.2ev exposure and contrast. (~2-3mins from RAW image)

A7K CV12 0EV sample by jenkwang, on Flickr

 

[pinholecam]

Some more updates.
I thought I saw a hint of some sort of color cast, so I compared the unmodded and modded camera shots of the above.
The A7 used a WB of 5200K for proper WB while the modded camera used about 7200K.

Here is the A7 shot at 5200K

A7 unmodded WB 5200K by jenkwang, on Flickr


Here is the A7K (ie. modded camera) using this same 5200K

A7K modded WB 5200K by jenkwang, on Flickr


That said, the modded camera largely takes care of this change with its AWB.

Here is the A7K shot with its AWB.

A7K Pentax K24 f2.8 at f10 by jenkwang, on Flickr
Still a hint of magenta imo.
There might be several ways to get around this like playing with the WB and tint (though I've found it tricky with the AW picker tool in LR)


My thoughts are that this is an advanced mod and its not for the faint hearted causal user who is just thinking of 'sup-ing' up his ride.
The IR/UV blocking filter was replaced and the AA filter removed, the default WB tweaks in the camera is almost very certain to go off since each of these glass will certainly have come with its own color cast of some sort and tweaked 'in factory'.
Maybe IR contamination?

I feel that to even go to the stage of want to mod the camera, the user has got to be aware of the potential pitfalls and maybe some workarounds.
There are some adjustments in the camera profile that can be done to further tweak the colors (or create a custom profile)


I've done one to taste here :

A7K modded AWB custom profile Shadows -3 Green Hue +6 Blue Hue -5 by jenkwang, on Flickr

with AWB
Custom LR Profile
Shadows -3
Green Hue +6
Blue Hue -5

I save this now as a Custom Preset.

 

[pinholecam]

Managed to test out the CV15/5.6 Heliar v1 (ltm version).
(As usual for this review, I've placed full sized shots via the Flickr links)

All done at f11 to be sure that the edges balance up in sharpness as best as is possible on these cameras.
Unfortunately, I did not realize until shooting the series of lenses that my friend's A7 was set to Std Jpg (all settings at 0) instead of RAW.
So I also set the A7k to shoot at the same settings.
I did shoot in RAW+JPG though, and to be fair, I'd say that if I processed the RAW, I'd get a little better results with the more powerful on computer JPG engine, but its really slight and would not really invalidate the test shots done in JPG.

The lighting conditions varied through the test shots.
From bright Sun to Shaded between A7 and A7K shots. (just for additional info)


A7K CV15v1 at f11 by jenkwang, on Flickr


A7 CV15v1 at f11 by jenkwang, on Flickr


Crops


A7K CV15v1 at f11 -center by jenkwang, on Flickr


A7 CV15v1 at f11 -center by jenkwang, on Flickr

 

[pinholecam]

A7K CV15v1 at f11 -left by jenkwang, on Flickr


A7 CV15v1 at f11 -left by jenkwang, on Flickr





A7K CV15v1 at f11 -right by jenkwang, on Flickr


A7 CV15v1 at f11 -right by jenkwang, on Flickr


For color cast on corners, those familiar with it will know that exposure and type of scene can influence it.
So the change in lighting condition between the test can be a factor.
I'd say that it generally does not improve between modded and unmodded cameras.


Sharpness in general, the A7K does give a little bit better edge definition.
But this is really just a little bit to me.
On the sides, also a little bit better edge definition, but imo, not enough to make me go buy a CV15v1 after I have a modded camera.

That said, I am not familiar with the CV15, as I don't own this lens.
Perhaps this really is the max that the lens can do on whatever format (ie. film; M9 )??
Am I expecting too much resolution wise from a 15mm (its already real wide) at far distances?
Or is the copy I tried not as good?
I'm also curious how this lens performs on a camera that is supposed to be catered for RF lenses (ie. the M9)
Do give me some inputs if possible. TIA

 

[hjbyeo]

THanks JK, appreciate the review.

CV15 v1 in my opinion will not work well with A7.

Seems like you've to tweak your workflow a bit to adjust to this new A7'k'.

 

[ricleo]

looking at your results, looks like the purple tint is reduced slightly with the CV15 V1 and A7K. not sure if this is due to the AWB differences or differences in lighting.

can share some shots at F4.5? The corners on my CV15 V1 smear quite alot at F4.5. If the mod improved the corners even at F4.5, i think the mod is worth it.

the best is of course to buy the CV15 v3, which was made for digital, and solved the smearing issue.

 

[pinholecam]

THanks JK, appreciate the review.

CV15 v1 in my opinion will not work well with A7.

Seems like you've to tweak your workflow a bit to adjust to this new A7'k'.

Yeah, imo, no significant an improvement to get a CV15v1 even with a modded A7.
AWB, I wouldn't be too worried about it.
IMO, the user needs to be aware, not afraid.
Aware so that he/she can tweak it if necessary.


I shot a couple of other genres (as you know)
Don't think I saw anything that worried me.

Taken with the A7K

20150721-DSC05247-1 by jenkwang, on Flickr

looking at your results, looks like the purple tint is reduced slightly with the CV15 V1 and A7K. not sure if this is due to the AWB differences or differences in lighting.

can share some shots at F4.5? The corners on my CV15 V1 smear quite alot at F4.5. If the mod improved the corners even at F4.5, i think the mod is worth it.

the best is of course to buy the CV15 v3, which was made for digital, and solved the smearing issue.

Very hard to say if the casting is really reduced.
I'd be conservative and not say that it has improved.

CV15v1, I only tried my friend's lens during that test period.
I did focus wide open using the off center (the right side) to make sure I was taking care of the field curvature.
From that focusing wide open at high magnification, I did not see that big a difference between cameras.
Almost like what has been shown with the f11 samples only more smudged of course at f4.5
The A7K had a little better edge definition which helped with the focus, but that was all.

 

[pinholecam]

Here is another one.
The lens is still marked as 'Cosina' 25/4 (later the Voigtlander Color Skopar 25/4)

Full shot

A7K CV25 at f11 by jenkwang, on Flickr


Center

A7 CV25 at f11 -center by jenkwang, on Flickr



A7K CV25 at f11 -center by jenkwang, on Flickr

Too close for me to tell much.
A few factors can come into play here imo.
The changing intensity of the sunlight can give more apparent sharpness via providing more contrast for one.
My own judgement in focus being the other.


Right crop

A7 CV25 at f11 -right by jenkwang, on Flickr



A7K CV25 at f11 -right by jenkwang, on Flickr

Unfortunately, I think the left side either suffered from a decentered lens or adapter non-planarity, so I won't bother to show/crop it.

For the right side, a bit better for the A7K.
Just a little bit again.
But to me, that little bit does move it a grade in IQ from 'maybe I might use it' to 'still ok, I'll use it'.

The dilemma is this to me.
Its still a compromised IQ imo.
Perhaps moving towards good enough, but certainly not great.
Not to mention the need to clean up the magenta cast.
But the lens is so small that perhaps its a reasonable trade-off for the portability.

 

[pinholecam]

The irony so far for me is that the SLR lenses that I've tried so far seems to have better improvement than the RF ones.
This is so lens specific that its really only via this sort of passed down info or personal try out that one can be sure.


Just to lift the gloom a bit.
Here are sample shots using the Pentax K28/3.5 at f8


Full Image

Constructing the urban future by jenkwang, on Flickr


Center Crop

Pentax K28 f3.5 at f8 -center by jenkwang, on Flickr


Left Crop

Pentax K28 f3.5 at f8 -left by jenkwang, on Flickr


Right Crop

Pentax K28 f3.5 at f8 -right by jenkwang, on Flickr

This to me, probably shows off whats possible with AA filter removal and thin filter.
The first thought that ran through my mind when I inspected the image at 100% was that it so reminds me of my DP1m image (coincidentally also a 28mm eq)

 

[pinholecam]

Update from today.

I had some doubts about the CV15 v1 test above.
Perhaps that sort of distance with atmospheric haze and sheer distance had made it too hard to judge the results.
So here is a simple reshoot at f8 with closer distances where its easier to differentiate differences.

All shots straight off the AWB of both cameras and in RAW processed in LR with the same settings.
No corrections done for the lens.



Full Image

A7 CV15v1 f8 by jenkwang, on Flickr

A7K CV15v1 f8 by jenkwang, on Flickr


Vignette and color cast to me is about the same.
Needs a correction in PP for both.



Center Crop

A7 CV15v1 f8-center by jenkwang, on Flickr


A7K CV15v1 f8 -center by jenkwang, on Flickr

Quite apparent differences this time round.
Certainly sharper for the A7K.
A bit more 'bite' in the image with the better edge definition and a bit more texture detail.

 

[pinholecam]

Upper Left crop


A7 CV15v1 f8-upper left by jenkwang, on Flickr


A7K CV15v1 f8 -upper left by jenkwang, on Flickr

Again clearer advantage to the A7K.
Notice that the text on the "EXIT" signage is more readable.
Better edge definition too.


Right Crop

A7 CV15v1 f8-right by jenkwang, on Flickr


A7K CV15v1 f8 -right by jenkwang, on Flickr

Again much better on the A7K.

 

[pinholecam]

One of the great frustration and IMO unmentioned things about some of these RF lenses on A7 is that its mostly only center good.
Yes, part of this is certainly due to the lens characteristic, however, the thick filter stack is certainly adding to this.

A lens that has caused me some frustration with this is the Voigtlander 35/1.4 Nokton.
Yes, its quite a marvel of a lens, tiny for a 35mm with f1.4.
Problem is that on the A7 (unmodified), just past the center, in the rules of thirds area, its smeared.

This often poses a problem when one composes with the subject in the thirds or in a group shot where at least one or two persons will end up off center where the sharpness is (and hence smeared, even though they are on the same plane of focus)


So here are some test shots between the A7 and A7K.
Handheld, but shot multiple times to make sure about the focus.


Full Image
Subject placed in the 'thirds'

A7 CV35 f1.4 at f1.4 by jenkwang, on Flickr


A7K CV35 f1.4 at f1.4 by jenkwang, on Flickr


100% Crop

A7 CV35 f1.4 at f1.4 -100% by jenkwang, on Flickr


A7K CV35 f1.4 at f1.4 -100% by jenkwang, on Flickr

The difference is significant to me.

 

[pinholecam]

Just in case anyone not familiar with the RF lenses will look at the CV15 samples and immediately declare them as bad due to the color cast, here is a quickly corrected one in LR.
The adjustments can be easily saved as a file 'template' in LR and later just "Copy>Paste" the adjustements for any pict taken with the lens.


20150730-CV15v1 f8 -corrected by jenkwang, on Flickr

Full sized sample on my Flickr as well for those who want to check out the file in detail.

 

[pinholecam]

No comparative samples between stock A7 and A7K, but here is a test shot using the CV21/4 on the A7K.
Both images corrected for color cast on the corners and LR lens profile used.
To see the full sized image, just get it on my Flickr.


At f8

CV21 f4 @f8 by jenkwang, on Flickr


At f4

CV21 f4 @f4 by jenkwang, on Flickr



This isn't my lens, but if I had one, I'd sure be happy thats its decent enough after the mod to be a very portable 21mm option.