I did quick simulation using Diglloyd's described chief ray angle=35.8deg.
PCX 2m would be optimal for ZM C-Biogon 2.8/35.
Biogon design gives steeper exit ray than Distagon so such stronger PCX is necessary.
The good news is, additional distortion of this combination is negligible 0.2%.
The problem is, this combination requires 0.6mm shorter adapter to reach infinity.
I hope Chinese manufacturers make such shorter adapter.
Haruhiko
DavidBM wrote:
WOW!
This makes me really tempted by the 28 as well the C Biogon 35: does anyone there know what filter we should use?
Here's why:
The 2/35 Biogon has good or better better MTF than the 2.8/28 stopped down. And yet I agree Fred's samples of the corrected 28 look better than Loxia.
So what was Zeiss doing in generating the correction of Biogon to Loxia? Pure speculation: they wanted a solution that didn't make the lens longer, and didn't make the distortion worse. Perhaps a PCX or other filter is giving better results than the native Loxia correction would, at the slight cost of distortion and focal length change. A cost which, for landscape, I'm happy to pay.
Now since the 2.8 Biogon has somewhat better MTF stopped down than the f2 version, if it can be corrected as much, it ought be both even better than the corrected 28 and the corrected 2/35 (stopped down). In which case.......Show more →
I did quick simulation using Diglloyd's described chief ray angle=35.8deg.
PCX 2m would be optimal for ZM C-Biogon 2.8/35.
Biogon design gives steeper exit ray than Distagon so such stronger PCX is necessary.
The good news is, additional distortion of this combination is negligible 0.2%.
The problem is, this combination requires 0.6mm shorter adapter to reach infinity.
I hope Chinese manufacturers make such shorter adapter.
Haruhiko
Thanks Haruhiko! Very tempting option then as a lower cost and size alternative to the Distagon for landscape use!
At least if we can find a way to shorten the adapter enough....(or remove enough shims)
Can I just add to the thanks others have given you for the pioneering work you have done here!
I do not have the C-Biogon 35mm f/2.8, however, if this lens follows suit like it's bigger brother the f/1.4 Distagon or many other ZM lenses, there's a high chance you could remove shims internally by removing the rear rentention ring and pulling the front lens assembly away from the focusing helicoil.
This may help overcome the need to have the lens sit 0.6mm closer.
Equally, I was able to shave a cheap adapter off an auction website down about 0.6mm off the bayonet face, when I first started to investigate the feasibility of using the correction lenses on my ZM collection.
Both removing internal shims, or shaving an adapter down should be doable.
Nearly any CNC metalwork machine shop could shave the adapter down 0.6mm.
HaruhikoT wrote:
Hi David,
I did quick simulation using Diglloyd's described chief ray angle=35.8deg.
PCX 2m would be optimal for ZM C-Biogon 2.8/35.
Biogon design gives steeper exit ray than Distagon so such stronger PCX is necessary.
The good news is, additional distortion of this combination is negligible 0.2%.
The problem is, this combination requires 0.6mm shorter adapter to reach infinity.
I hope Chinese manufacturers make such shorter adapter.
I'm happy we are finally nearing a solution for these wide angle RF lenses and the Sony stack.
I think the concept from Haruhiko's modelling and the trial and error performed on the ZM lenses have shown us that correcting the astigmatism to achieve sharper corners and flatter focus fields is definitely doable.
And yes, as it was said, the modified ZM 25 and 28mm lenses become very potent landscape lenses in a small package now, and can still AF with TAP as well.
Awesome times we are living in 😀
Fred Miranda wrote:
Thanks for checking @candreyo@ ,
Yes, I realized now why the 1.5m PCX is a better match!.
I tried using TAP with the infinity MF preset and was able to focus at infinity with the 1m Proxar...but to the dot! (and that's without 4 shims)
The results with the Proxar are actually pretty good even with the ZM 28. I can't wait to try the PCX filter on it.
Here are some crops. (Extreme corners)
LEFT: ZM 28/2.8 @f/8 + 1m Proxar
Right: ZM 28/2.8 @f/8 without any front lens.
Both focused at the center of the image (to investigate FC)
PS: I had to lift the shadows on this area, so perhaps there is a loss of contrast)
The mid zone area gets improved as well. It's now a very impressive 200g lens on the A7RII. This could get even better with the 1.5m PCX front lens (instead of the Proxar). To my eyes, this is already better than what I get with the Loxia 35/2 @f/8....Show more →
candreyo wrote:
I do not have the C-Biogon 35mm f/2.8, however, if this lens follows suit like it's bigger brother the f/1.4 Distagon or many other ZM lenses, there's a high chance you could remove shims internally by removing the rear rentention ring and pulling the front lens assembly away from the focusing helicoil.
This may help overcome the need to have the lens sit 0.6mm closer.
Equally, I was able to shave a cheap adapter off an auction website down about 0.6mm off the bayonet face, when I first started to investigate the feasibility of using the correction lenses on my ZM collection.
Both removing internal shims, or shaving an adapter down should be doable.
Nearly any CNC metalwork machine shop could shave the adapter down 0.6mm.
Shaving down an adapter is not as easy as I thought. The area that needs shaving is where the front metal mount sits on to. Perhaps a machining shop can do an even job as any tilt will cause resolution discrepancies in the corners.
(Adding shims to an adapter is easier than shaving it down)
Jim had noted previously on this thread, that TAP (parked at the MF infinity position using aperture the f/36 setting) is able to help a lot. This is actually true as TAP is the only adapter that let's me focus my ZM 28/2.8+Proxar 1m at infinity distance. (All my other adapters including the Hawks's v5 with infinity adjustment do not)
I really like the idea of removing internal shims from ZM lenses. I followed @Candreyo 's video and it was quick and easy as he described.
I'm happy we are finally nearing a solution for these wide angle RF lenses and the Sony stack.
I think the concept from Haruhiko's modelling and the trial and error performed on the ZM lenses have shown us that correcting the astigmatism to achieve sharper corners and flatter focus fields is definitely doable.
And yes, as it was said, the modified ZM 25 and 28mm lenses become very potent landscape lenses in a small package now, and can still AF with TAP as well.
Awesome times we are living in 😀
Yes, I wonder if a Kolari modded sensor could give better results than this. Even if i's equal or a little better, one has to deal with color casts and a reduction in performance for native lenses.
The front-end lens solution is just like having an UV filter on the lens. It only weights 18 grams and actually helps protect the lens from the elements.
When I get my PCX 1500mm, I will compare it to the Proxar 1000mm in standard and reverse mode. (ZM 28/2.8)
Thank you for the comment.
I don't have the C-Biogon, too. I've just simulated it to answer David's question
I agree with you both removing shims and shaving adapter are doable.
But I don't have any experience to outsource such CNC work.
Can such professional machine shop accept one-off order from an amateur individual?
How much does it cost?
Haruhiko
candreyo wrote:
I do not have the C-Biogon 35mm f/2.8, however, if this lens follows suit like it's bigger brother the f/1.4 Distagon or many other ZM lenses, there's a high chance you could remove shims internally by removing the rear rentention ring and pulling the front lens assembly away from the focusing helicoil.
This may help overcome the need to have the lens sit 0.6mm closer.
Equally, I was able to shave a cheap adapter off an auction website down about 0.6mm off the bayonet face, when I first started to investigate the feasibility of using the correction lenses on my ZM collection.
Both removing internal shims, or shaving an adapter down should be doable.
Nearly any CNC metalwork machine shop could shave the adapter down 0.6mm.
@HaruhikoT ,
Would a Proxar 1m lens have similar optical characteristics to a Minolta 1m close-up filter for example? They both seem to be meniscus lenses.
From your modeling, how would do they differ from a PCX lens as far as correcting FC and astigmatism?
If they are similar in your software simulation results, what would be the positive and negatives of each approach?
These days I'm gradually realizing that Meniscus solution is unmanageable for me, unlike much simpler PCX solution.
In theory, meniscus front-end filter can also correct both field curvature and astigmatism, perhaps even better than PCX in some conditions.
However, the correction effect of meniscus lens is very sensitive to the parameters below:
1. Curvature radii of both side: we can't measure these accurately without using professional equipment. Even very small difference of these curvature induce visible correction error.
2. Distance between the meniscus filter and the primary lens: even 1mm difference of this gives visible correction error. Also I can't set this distance precisely in my simulation bench without knowing the primary lens' technical details.
3. Assembly variation of the filter: small decentering and tilt give visible correction error.
When we use PCX, 1. is exactly specified, 2. and 3. give much smaller impact to correction results so things are much easier.
I'm not saying negative to use Proxar lenses for correction by trial and error method, but it seems difficult for me to simulate its behavior
Fred Miranda wrote:
@HaruhikoT@ ,
Would a Proxar 1m lens have similar optical characteristics to a Minolta 1m close-up filter for example? They both seem to be meniscus lenses.
From your modeling, how would do they differ from a PCX lens as far as correcting FC and astigmatism?
If they are similar in your software simulation results, what would be the positive and negatives of each approach?
My (uncoated) 5m PCX from Eksma Optics to be used with the ZM 35 1.4 arrived today.
I only managed to do a very short test before it was too dark, will do it thoroughly tomorrow.
I have already seen improvements regarding bokeh and corner sharpness though.
With my Fotodiox L/M->Nex adapter infinity focus is still possible, with my VM-E close focus adapter it isn't.
I will check tomorrow how big the improvements are and probably try to remove 1 or 2 shims then (camera spanners arrive on thursday) to be able to use it with the VM-E.
Yes, machine shops do custom/ one off orders also. This service may be upwards of £40.00 in Great Britain, but in other countries the service could be much more affordable depending on labour costs.
I would do a search for a CNC / metalwork shop in your local area, then stop by them and explain you want 0.6mm 'lapped' off the front surface of the bayonet. Tell them it's important that the surface that is being lapped down, remain as flat as possible to ensure there is no light leakage.
Ask them for a quotation first, and it may be best to compare 2-3 different quotations to see who is most affordable.
They may have to remove the bayonet from the adapter to work on it, but this should be doable with screws.
HaruhikoT wrote:
Hi Chris,
Thank you for the comment.
I don't have the C-Biogon, too. I've just simulated it to answer David's question
I agree with you both removing shims and shaving adapter are doable.
But I don't have any experience to outsource such CNC work.
Can such professional machine shop accept one-off order from an amateur individual?
How much does it cost?
BastianK wrote:
My (uncoated) 5m PCX from Eksma Optics to be used with the ZM 35 1.4 arrived today.
I only managed to do a very short test before it was too dark, will do it thoroughly tomorrow.
I have already seen improvements regarding bokeh and corner sharpness though.
With my Fotodiox L/M->Nex adapter infinity focus is still possible, with my VM-E close focus adapter it isn't.
I will check tomorrow how big the improvements are and probably try to remove 1 or 2 shims then (camera spanners arrive on thursday) to be able to use it with the VM-E.
Let us know how many shims (if any) you had removed to make it work with your VM-E.
I thought I would report back after a week while travelling with an A7S and the G21 with the 1.5m PCX under certain conditions in the summer sun I am seeing a little bit of colour casting but no other problems.
Slingers wrote:
I thought I would report back after a week while travelling with an A7S and the G21 with the 1.5m PCX under certain conditions in the summer sun I am seeing a little bit of colour casting but no other problems.
I think the colour casting is due to the deep wells of the A7s and all A7 series except rII; you won't get it on the A7rII but I think there'll be at least some on A7s, sii, A7, A7ii and A7r.
I've just got back from a local machine shop.
They say that they can lap off .6mm from the front plate of my Yeenon (VM-E copy) adapter for $AU70 (US$50 at the moment). For an extra 100 they can get it re-chromed. Any idea if that makes any sense? I guess the brass might eventually start leaving green residue on the lens mount.
OK so now I'm waiting to see people's results!
If the Distagon 1.4/35 performs with better bokeh in the mid distance and better mid to corner resolution at wide apertures, and no noticeable impact on flare and contrast (this last is my biggest worry) then I'm in. The Yeenon for landscape, TAP for portraits.
I'm also really interested in the 2.8/35 as a hiking landscaper, and the 28 if it turns out well, as it seems it will!
The 2.8/25 makes a lot of sense, but since it is no lighter than the Batis, and performs similarly, then the extra speed and AF makes the Batis a nice allrounder - and while the ZM would be a bit nicer to carry and use in the bush, I can't justify both.
I own a G21 and have wanted to use it since the original nex5 knowing how well it worked with color positive film on my ContaxG2. I saw results back then that were horrible on the NEX 5. Seemed like ever model someone tried to make that lens work but imo were far from successful compared to the results on the G2.
Now I am seeing this method being used to address corner smears and color shifts with probably the best results so far. My issue is my lens is still uncut but even my 28mmG lens seems to be almost on my sensor when using a kipon adapter on my a7rII. You guys are not worried about lens to sensor contact when stabilization is on? It looks like even cut the lens would be only a fine hair away from making contact if it wasn't already making contact when mounted.
DavidBM wrote:
I've just got back from a local machine shop.
They say that they can lap off .6mm from the front plate of my Yeenon (VM-E copy) adapter for $AU70 (US$50 at the moment). For an extra 100 they can get it re-chromed. Any idea if that makes any sense? I guess the brass might eventually start leaving green residue on the lens mount.
OK so now I'm waiting to see people's results!
If the Distagon 1.4/35 performs with better bokeh in the mid distance and better mid to corner resolution at wide apertures, and no noticeable impact on flare and contrast (this last is my biggest worry) then I'm in. The Yeenon for landscape, TAP for portraits.
I'm also really interested in the 2.8/35 as a hiking landscaper, and the 28 if it turns out well, as it seems it will!
The 2.8/25 makes a lot of sense, but since it is no lighter than the Batis, and performs similarly, then the extra speed and AF makes the Batis a nice allrounder - and while the ZM would be a bit nicer to carry and use in the bush, I can't justify both....Show more →
David,
Just by looking at my adapters, I believe you can't shave down the front plate. That will make your lens not be able to fit in place anymore. (The lens bayonet will be loose when mounting on the adapter)
You need to shave down the surface area where the front plate sits on. It's not very easy to do while keeping things completely flat with no tilt.
These days I'm gradually realizing that Meniscus solution is unmanageable for me, unlike much simpler PCX solution.
In theory, meniscus front-end filter can also correct both field curvature and astigmatism, perhaps even better than PCX in some conditions.
However, the correction effect of meniscus lens is very sensitive to the parameters below:
1. Curvature radii of both side: we can't measure these accurately without using professional equipment. Even very small difference of these curvature induce visible correction error.
2. Distance between the meniscus filter and the primary lens: even 1mm difference of this gives visible correction error. Also I can't set this distance precisely in my simulation bench without knowing the primary lens' technical details.
3. Assembly variation of the filter: small decentering and tilt give visible correction error.
When we use PCX, 1. is exactly specified, 2. and 3. give much smaller impact to correction results so things are much easier.
I'm not saying negative to use Proxar lenses for correction by trial and error method, but it seems difficult for me to simulate its behavior
Thanks for letting me know. I will stick with PCX lenses for the reasons you mentioned, but I have to say that the Proxar 1m (positive meniscus) works great with the ZM 28/2.8 and according to @candreyo , even better on the ZM 25/2.8. I will compare the ZM 28/2.8 side by side with the PCX.
Thanks Fred!
Looking at it, I think you are right. You have just saved my future self from a stupid mistake!
Inspecting my Yeenon I think if the front two rings come off, there's a part that could be lapped and then the whole thing reassembled, but I'm less sure.....
