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Archive 2016 · Front-End Filter Improves Corner Smearing

  
 
Fred Miranda
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p.32 #1 · p.32 #1 · Front-End Filter Improves Corner Smearing


DavidBM wrote:
I thought that ypthe shims are for calibrating the lens to the rangefinder mechanism (certainly it's a shim change that optimizes the 1.5/50 for wide open or f2.8 accuracy with the rangefinder. Must that's all irrelevant with mirrorless...


I think you got that right. The internal shims for the ZM 35/1.4 are probably there for rangefinder calibration. They have no relevance to focus distance.
However the rear shims do adjust focus distance. With the front-lens, keeping a gold and silver works for the Hawks (hard stop) and overshoots for TAP. It does not quite reaches infinity with my Novoflex and my cheap adapters like Fotasy and Pixco. (For those you may need to replace the silver shim with a thinner one)

The good news is that it's super easy to remove the rear shims. All you need is a flat screwdriver to remove 4 screws. The shims are visible as soon as the rear bayonet comes off.



Jan 22, 2017 at 11:56 AM
jhinkey
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p.32 #2 · p.32 #2 · Front-End Filter Improves Corner Smearing


OK, so trying to follow along:
- At f/5.6 or so the stock 35/1.4 ZM is just as good in the corners as the 35/1.4 + Front lens (assuming careful mid-field, etc. focusing)- correct?
- Playing around with the internal shims does or does not positively affect the infinity field curvature of the 35/1.4?

You guys are changing many things (thanks!), but it's hard to follow what was changed and what the resulting change in optical performance is.

Working up to purchasing one for my A7RII (un-modded) and would really love to NOT have to put a front filter on it if at all possible.

Thanks for all the work!

- John



Jan 22, 2017 at 12:10 PM
Fred Miranda
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p.32 #3 · p.32 #3 · Front-End Filter Improves Corner Smearing


jhinkey wrote:
OK, so trying to follow along:
- At f/5.6 or so the stock 35/1.4 ZM is just as good in the corners as the 35/1.4 + Front lens (assuming careful mid-field, etc. focusing)- correct?


Almost. With the front-lens it's still marginally better even at f/8. (You will have to look hard to see improvement though)
However, you must focus on the mid-field without the front-lens and the optimum aperture is f/6.3. With the front-lens, focus position is no longer critical and the optimum aperture is f/4.5. (Excellent across the field)
At apertures from f/1.4 until f/4, it's night and day difference.

Playing around with the internal shims does or does not positively affect the infinity field curvature of the 35/1.4?

There are 8 shims: 4 internal, and 4 located at the rear. Only the rear shims have any effect on distance for the Sony A7 series. You may have to remove a couple of them depending on your adapter.

You guys are changing many things (thanks!), but it's hard to follow what was changed and what the resulting change in optical performance is.

That's because this is a trial and error process. At least, you don't have to experiment too much.

Working up to purchasing one for my A7RII (un-modded) and would really love to NOT have to put a front filter on it if at all possible.

I don't see any significant negatives for the front-filter. I posted the (cons) in a previous post. Mainly you won't be able to attach the original Zeiss hood and there is a very slight decrease in contrast in some scenes.



Jan 22, 2017 at 12:21 PM
jhinkey
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p.32 #4 · p.32 #4 · Front-End Filter Improves Corner Smearing


Thanks Fred - just to clarify:

"Playing around with the internal shims does or does not positively affect the infinity field curvature of the 35/1.4?

There are 8 shims: 4 internal, and 4 located at the rear. Only the rear shims have any effect on distance for the Sony A7 series. You may have to remove a couple of them depending on your adapter."

So the field curvature/corner issues don't change with shim combination (w/o front lens)?

I can see this to be true if the shims don't affect any optical spacings - if the shims just affect infinity adjustment and M-mount camera calibration then it wouldn't affect the curvature.



Jan 22, 2017 at 12:32 PM
jhinkey
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p.32 #5 · p.32 #5 · Front-End Filter Improves Corner Smearing


Also - is there a picture of the 35/1.4 ZM with the adapted front filter attached?

- J



Jan 22, 2017 at 12:33 PM
Fred Miranda
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p.32 #6 · p.32 #6 · Front-End Filter Improves Corner Smearing


John,
Without the front-lens, there will be no change in field curvature since these improvements only happen because you are using a front-lens with the correct strength. (5000mm)

Adjusting the rear shims is only needed for the lens to achieve infinity focus whenever using the front-lens. After this adjustment, infinity distance is achieved at around 5m without the front-lens. (Which on the lens focusing ring, it's not that far from infinity)



Jan 22, 2017 at 12:47 PM
jhinkey
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p.32 #7 · p.32 #7 · Front-End Filter Improves Corner Smearing


Fred Miranda wrote:
John,
Without the front-lens, there will be no change in field curvature since these improvements only happen because you are using a front-lens with the correct strength. (5000mm)

Adjusting the rear shims is only needed for the lens to achieve infinity focus whenever using the front-lens. After this adjustment, infinity distance is achieved at around 5m without the front-lens. (Which on the lens focusing ring, it's not that far from infinity)


Fred - perhaps my questions are ill-posed.

I'm just trying to figure out if you've changed any element spacings by taking out/adjusting the front shims. I've not seen any images of the 35/1.4 ZM taken apart.
Changing element spacings or messing with floating element positions can change the optical properties, one of which is the field curvature (usually at the expense of something else).

It was not clear from all the posts if the field curvature characteristics of the 35/1.4 was changed at all with different shims installed (likely just affected by the front shims if at all).

On a side note, does anyone think it's possible to put the corrective lens element at the rear of the 35/1.4 since one has to use an adapter anyways to put it on an A7 series camera? The corrective element could then be much smaller . . .

Thanks -

J



Jan 22, 2017 at 01:00 PM
artur5
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p.32 #8 · p.32 #8 · Front-End Filter Improves Corner Smearing


After reading the last pages of this thread, specially Candreyo, Fred and Guy findings with the shims ( thanks guys), it seems clear that lenses with floating elements, like the ZM35, are much more complex to fix/correct for infinity adjust with a front filter than old style glass which moves back and forth the whole optical block to achieve focus.
For one thing, adding a front filter modifies the focal length of the combo, so the optimal placement of the floating elements to the focal plane possibly changes with respect to a ‘naked’ lens. What I have no idea is if this (possible) change requires moving back or forth the floating element. Hence, if removing shims helps or it’s detrimental.
Anyway, if finding the correct front filter/infinity adjust for normal focusing lenses is already tedious, requiring trial and error, lenses with internal focus/floating elements are worse still. Until somebody with advanced knowledge in optics chimes in here (Candreyo, Haruhiko ..? ) we’re like a blind man trying to find his way out of a maze.



Jan 22, 2017 at 01:59 PM
navmannz
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p.32 #9 · p.32 #9 · Front-End Filter Improves Corner Smearing


artur5 wrote:
After reading the last pages of this thread, specially Candreyo, Fred and Guy findings with the shims ( thanks guys), it seems clear that lenses with floating elements, like the ZM35, are much more complex to fix/correct for infinity adjust with a front filter than old style glass which moves back and forth the whole optical block to achieve focus.
For one thing, adding a front filter modifies the focal length of the combo, so the optimal placement of the floating elements to the focal plane possibly changes with respect to a ‘naked’ lens. What I have no idea is if
...Show more

I agree that there's some complexity in here that we're not necessarily on top of, but is your assessment perhaps a little pessimistic, given the marked improvement in the tests that Fred showed a couple of pages back? For me, the fact that Zeiss even uses shims at the rear to allow adjustment of infinity focus indicates that removing one or two of them is probably fine - like you, I'd be much more wary of touching the internal ones. In particular, Fred's post on this page where he describes the gains in flat field infinity performance at more open apertures highlights the gains I would want to exploit, i.e., use of a front filter for night sky photos, and I'm currently investigating ways to purchase one in NZ. As for understanding exactly what's going on, it would be brilliant if we could get an optics engineer (ideally Zeiss) to comment, even if off the record. Perhaps one of us should write a brief summary, send it to them, and see if they will engage?

-John (NZ)



Jan 22, 2017 at 02:20 PM
Fred Miranda
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p.32 #10 · p.32 #10 · Front-End Filter Improves Corner Smearing


@jhinkey
If removing some or all the front shims help with field curvature without any front-lens, I am not sure as I didn't test for this. All my tests were done with the front-lens in place.
What I saw is that removing all 4 front shims (Not the rear shims) had no effect in focus distance. (The rear ones do)

I'm still not sure what the front shims are used for. It could be floating element adjustment OR some sort of adjustment for rangefinder bodies. Perhaps other may pitch in.

Regarding the front-lens and removal of some rear shims affecting IQ by changing the position of the floating elements...That's possible, but even if there is a small deterioration of IQ, the benefits of using the front-lens are so much bigger than any possible loss. (I just don't see any loss)

When removing rear shims to be able to focus at infinity with the 5m front-lens, infinity focus changes to ~5m without any front-lens. (So, that's the distance difference)



Jan 22, 2017 at 02:32 PM
artur5
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p.32 #11 · p.32 #11 · Front-End Filter Improves Corner Smearing


Your findings agree with the theory. Adding a 5m filter to a 35mm. lens changes the focal length of the combo to 34.75mm. 35-34,75=0.25mm. That must be the thickness of the shims that you removed. And 0.25mm. is exactly the distance that you have to move forward a 34.75mm lens from the infinity mark to focus at an object located 5mtr. away


BTW : anybody else getting a 'deceptive site' warning when entering here ?. It just started to happen today. I'm using Windows 7 and Mozilla Firefox as a browser. I tried now Microsoft's Internet Explorer and no warning. So this must be a Mozilla thing ?



Jan 22, 2017 at 03:04 PM
Fred Miranda
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p.32 #12 · p.32 #12 · Front-End Filter Improves Corner Smearing


BTW: There is another way to build the filter for these front-end lenses.
In the case of the Zeiss 35/1.4 ZM, you can use a 49-52mm and buy a regular 52mm UV filter. (Amazon basics is fine)

Remove the retention ring and the glass from the UV filter. Attach the empty 52mm filter to the 49-52mm and insert the retention ring on top (52mm). It works but the original hood still does not fit.

At least there is less room for the front-lens to move around making it easier to center it inside.



Jan 22, 2017 at 07:23 PM
jhinkey
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p.32 #13 · p.32 #13 · Front-End Filter Improves Corner Smearing


Thanks Fred - I've done similar things for other lenses for other reasons.
I'd likely want to go to a 52mm thread as there are a couple of Nikon 52mm snap in (meaning they also snap in reversed) metal hoods that look like they would fit snugly over the 35mm when reversed and be fine when in the correct position.

This is in fact what I do for my 180/4 CV - step up to 52mm from 49mm and use a Nikon metal snap in hood that fits perfectly over the lens for storage.

Getting closer to the 35/1.4 ZM I feel . . .



Jan 22, 2017 at 09:19 PM
jhinkey
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p.32 #14 · p.32 #14 · Front-End Filter Improves Corner Smearing


Also, if a 5m fl PCX lens on the front works, should not, in theory the same strength lens on the rear work just as well?

Thinking about added the corrective lens inside the M to E mount adapter. Don't know if this would be the optimal position relative to the rear element or the sensor plane, but it sure would be more convenient as you could still use the native hood.



Jan 22, 2017 at 09:51 PM
HaruhikoT
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p.32 #15 · p.32 #15 · Front-End Filter Improves Corner Smearing


jhinkey wrote:
Also, if a 5m fl PCX lens on the front works, should not, in theory the same strength lens on the rear work just as well?

Thinking about added the corrective lens inside the M to E mount adapter. Don't know if this would be the optimal position relative to the rear element or the sensor plane, but it sure would be more convenient as you could still use the native hood.


Hi @jhinkey@,

Unfortunately this PCX solution won't work on the rear, in theory. I've tried some simulations with several types of correction lenses placed on the rear side of primary lens, but couldn't get any good results.



Jan 22, 2017 at 10:10 PM
ceder
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p.32 #16 · p.32 #16 · Front-End Filter Improves Corner Smearing


If someone would make a video while removing internal and external shims, I for one would appreciate if it was posted here


Jan 23, 2017 at 04:27 AM
jhinkey
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p.32 #17 · p.32 #17 · Front-End Filter Improves Corner Smearing


ceder wrote:
If someone would make a video while removing internal and external shims, I for one would appreciate if it was posted here


+1

Or even a series of still images showing the steps



Jan 23, 2017 at 09:32 AM
jhinkey
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p.32 #18 · p.32 #18 · Front-End Filter Improves Corner Smearing


HaruhikoT wrote:
Hi @jhinkey@@,

Unfortunately this PCX solution won't work on the rear, in theory. I've tried some simulations with several types of correction lenses placed on the rear side of primary lens, but couldn't get any good results.


Thanks for trying!! If you do find a solution for optics at the rear - it would certainly be much more elegant than the front filter solution + shim changes (though the optics at the rear solution would indeed require shim adjustments for infinity focus I suspect).



Jan 23, 2017 at 09:40 AM
GMPhotography
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p.32 #19 · p.32 #19 · Front-End Filter Improves Corner Smearing


On the 25mm I did not have the lens set corectly in the step down. So 46-55 than 55 to 52 step down than my issue was the 52mm retaining ring was not set correctly. That's set now than I put a empty 52mm filter ring on as hood which works well. So have to look at infinity and shims again but of course it's raining again. I can tell though even at 2.8 in the corners looks really good compared to without. You need a 25 this maybe what your after. I'll get tests going soon. Sorry for the delay been painting the exterior of my home between the rain storms we been getting


Jan 23, 2017 at 10:00 AM
Fred Miranda
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p.32 #20 · p.32 #20 · Front-End Filter Improves Corner Smearing


GMPhotography wrote:
On the 25mm I did not have the lens set corectly in the step down. So 46-55 than 55 to 52 step down than my issue was the 52mm retaining ring was not set correctly. That's set now than I put a empty 52mm filter ring on as hood which works well. So have to look at infinity and shims again but of course it's raining again. I can tell though even at 2.8 in the corners looks really good compared to without. You need a 25 this maybe what your after. I'll get tests going soon. Sorry for the
...Show more

It's raining non-stop here in San Clemente, CA as well. There is nothing better than painting the exterior of your house with flash food warnings!


You could probably do 46-52, add an empty 52mm, place the lens inside and then add the retaining 52mm ring.



Jan 23, 2017 at 10:30 AM
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