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Lens Shading for the 85/1.2

dk0

Active Member
First, I was able to answer my previous question on this forum, namely what did Contax actaully prescribe for its 85/1.2 50-year Anniversary lens. The official answer is the 77/86 Step-up ring and Metal Hood #3. This was verified by the service manuals from Contax.

Now for something more interesting. Another member of this forum made a claim about using Metal Hood #5 on the 85/1.2, which appeared rather dubious. Most other people claim that Hood #4 is the "best". Yet, I was puzzled by all of these claims which confront the work of the actual engineers at Zeiss who on two occassions produced the magnificent 85/1.2 lenses (the 50- and 60-year anniversary lenses), and yet insisted on a smaller hood size of type #3 in each case, even after ten years of re-consideration.

So, I decided to measure the variation of relative illuminance as a function of hood size myself.

Here is one image taken with the 85/1.2 shot wide-open against a uniformly lighted white-card using the 85/1.2 Anniversary Hood:



And here is another image taken wide-open with Hood #5:



I was able to quantify the light fall-off as relative illuminance with respect to the center. Here is a table of the results that show mean percentage of illumination from the edges to the corners (worst case). Higher numbers are better. In other words, in the perfect case of no light fall-off, the entry would be 100%.



For ex&le, the entry which reads 46.1 - 61.9 means that the mean variation of illuminance went from 61.9% at the edges to 46.1% at the corners (darkest).

As you can see, the Anniversary hood appears to be well thought out by the Zeiss engineers. Granted there are other issues like flare control. From this table you can see that deeper hoods such as the Metal Hood #4 are indeed a viable option for those who place more emphasis on this. However, you can see that there is just too much light fall-off when using Hood #5.

For those of you who still want more on lens hoods, check out
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David
 

wang

Well-Known Member
Well, I would like to ask those who has 85 1.2 to put on hood 5 and look at the viewfinder.

For me, I have S2b, AX and RX. When I put on my hood 5 there is no light fall off at the corners. I strongly doubt if the results produced by David are true.

David, what do you use to measure illuminance ? Where did you get those results ? Did you do it yourself or do you have a reference ?
 

dk0

Active Member
Chi, I am a professional physicist, and am very capable of making scientific measurements. Indeed, I made these measurements myself. I do find it offensive that you claim my results are not true (even more so, when you claim that you can look through your viewfinder and instantly claim that my results as well as the engineering work from Zeiss are in error).

If you do not know the basics of measuring illuminance, then you can't possibly be qualified to comment on this at all.
 

wang

Well-Known Member
Well, perhaps what David found out could be right, but it is what you found in theory.
David, you can try yourself, the best is having an RTSIII with full view. You could see if you get dark corners.
For people who has Canon 1DsI or 1Dsll, they can easily test this on their cameras, to me there is no dark corners.
\Part of the reason that I insisted on this is because of the light pathways. This diagram showes the optical elements of 85 1.2. I draw the most marginal light pathway going thro' the lens.

Point A is the most peripheral point of the first frontal lens element. B is the same point of the second element. C belong to the third element. You can look at the this pathway directly with your eye as shown, the three points ABC coincide to become one point.
The photo showed the view of the eye so that ABC coincide to become one point. As you can see, the pathway remains intact with the hood 5 on.


Afterall, in terms of practical photography, the use of hood 5 on 85 1.2 does not produce dark corners in the viewfinder,negatives and prints. Most important of all, I have been shooting my 85 1.2 on hood 5 and never get a dark corners in my prints.
 

dk0

Active Member
Chi, first please do not try to lecture on optics. You are only embarrassing yourself.

Light fall-off is a fact. The illuminance is always potentially higher in the center. The issue here is really whether you can or cannot visually detect a 10% difference in the light fall-off at the corners.

I have physcially demonstrated that there is an additional 10% loss of peripheral light resulting in images when using Hood #5. My gray images posted above were normalized so that the light fall-off can be seen in the corners. In other more realistic images, it may not make a perceptible difference to you, but it is there and it may make a difference to some people.

This will be my last posting on this thread, as there is nothing more of substance that can come from it. I simply tried to contribute something to those who might be interested in this from a purely technical viewpoint.
 

gunteach

Well-Known Member
Aside from the mild acrimony on this thread, probably prompted by a less than ideal use of the word "true"..I found this thread to be of great value in combination with the link David provided. What I gather from this thread is that light fall off does occur with lens hoods, to a greater or lesser degree, it's worse at wide-open than stopped down, in some cases it really isn't visible and flare reduction may be the priority anyway. Hope I got the lessons of this thread right.

I for one always thought a lens hood wasn't really necessary and that size and shape did not matter on anything other than the widest angle lenses. Now I know better. Thanks David.
 

jsmisc

Well-Known Member
Yes, thanks to all and particularly David for his scientific explanation and for the useful link. I have found it interesting too. I invariably use a lens hood but I had no idea that the difference in shapes could make such a difference. I had always felt that the tulip type would be less efficient and that the rectangle shape was strange. It just shows how wrong you can be.
John
 

wang

Well-Known Member
David, on your posting 11, you said I am embarrassing myself. I don't feel that I am embarrassing myself at all. Can you tell me if I have written anything wrong ? I am presenting to everyone that hood 5 is not in the way of the light travelling pathway, this is a decent fact. Can anyone tell me if this is embarrassing ?

David, on your posting 11, you said I tried to lecture on optics. Let me tell you that I did not tried to lecture on optics, but I am stating the truth in optics. Can you tell me if I have written anything which is wrong. Do I have to try ? I am simply stating the correct fact in optics.

Perhaps, the problem is the attitude of David of trying to make other people feel embarrassed. Sorry, I really don't feel embarrassing at all. I am presenting a very decent work.

David, if you are a professional physicist, why don't you divert your effort of trying to make other people feel embarrassing to explaining why there is a 10 % loss of peripheral light when the light travelling pathway is unaffected ? This is something I really wish to know.
 

fotografz

Well-Known Member
Gentlemen, please stop getting personal about this subject. Information is shared, opinions are stated, others can take what they wish and use it or not.

I, for one, use the 85/1.2 with a 77 to 82 ring and #4 hood. I've seen a very slight vignetting in the corners on a few occasions ...
but it has to be a very flat, even tone being shot. In reality, it is a non-issue for 95% of photography. Manufactures always error on the side of being conservative.

If it is a critical issue for some photographers, then a different hood system should be sought out. For ex&le, the Lee system
has adapter rings for all these lenses, and much more effective baffled shades. There are similar systems made specifically for 35mm lenses which aren't as bulky, but also offer baffled shades.

As usual, it comes down to convenience verses effectiveness.
 

wang

Well-Known Member
How about these "hoods" ?



The bigger lens is 85 1.2 60yr, the cardpaper cutting reduces the area of light entering to half of the original area. 85 1.2 becomes 1.7.
The smaller lens is 85 1.4 being converted to 85 2.

I have been playing with these tricks for a while. For 85 1.2, I don't find these occlusive hoods very useful. However, 85 1.4 becomes a very useful lens. The occlusion makes the lens a lot more useable at f2, better than the f2 made by rotating the aperture ring.

These 'hoods" does not vignette at corners, at least in practice. This is why I found it difficult to believe that hood 5 causes darkening of corners. These two lenses, after occlusion, still has the entrance bigger than the lens 85 2.8. So,if 85 2.8 does not vignette, these occluded lenses won't.

If you try this on 85 1.4, it might make the lens so good that you may think 85 1.2 is less indispensible.

By the way, about the question of me spending less than 2 k on a mint 85 1.2. People may think Hong Kong has an endless supply of these expensive lenses.

On that day, the guy selling the lens did not aware how much he could sell the lens in e-bay. He sold the lens in very low price to the shopkeeper. It happens that I was watching them in the shop. If I came to the shop latter not seeing them, the shopkeeper would increase the price to a lot more than 2k.
I brought these lenses in such a low price only because of pure luck. Unfortunately, luck does not come everyday.
 
D

djg

So a piece of cut-out cardboard on top of the 85 1.4 improves the image - who would've thunk?

Chi Yuan, what kinds of image improvements are you finding at f2? Do they carry over to the smaller openings?
 

wang

Well-Known Member
Instead of me posting results, please try it yourself.

The principle of cardboard cutting on 85 1.4 is as follow.

The f2 of 85 1.4 obtained by rotating the aperture ring to f2 is not good enough. Light passes thro' all part of front elements followed by squeezing thro' the aperture. Most aberration occurs at the peripheral part of the front lens elements. The front element is the biggest and marginal aberration do occur badly.

The cardboard cutting ensures light passes only thro' the central part of the front lens elements avoiding marginal aberration of the front elements. It is just like a second aperture infront of the lens.

To me the improvement is such that in the past, I feels sleepy with f2 of my 85 1.4., now the cardboard f2 is comparable to the f2 of 100 f2.

The improvements do carry over to the smaller openings.
 

wang

Well-Known Member
Here is an ex&le of photo taken by the Planar 85 1.4 at f2, subject 1 meter from the camera. I scan the neg. to more than 6 million pixels, then photoshop. The film I used is Kodah 100 Gold.




The second image is taken in similar lighting but I put a second aperture in front of the 85 1.4 so that 50% of the light is being stopped from entering the lens, leaving the remaining 50 % entering the lens at the central part. It effectively converts the lens to 85 f2. So the second image is taken at f2 with cardboard cutting second aperture when the aperture ring remains at f1.4.

The second image is slightly sharper, the eyebrow is defined better.
 

wang

Well-Known Member
The third s&le is taken with the 85 1.4 at 2.8



The forth s&le is taken with 85 1.4 with the card cutting(as the second aperture in front) and aperture ring at f2. The overall effect is having a lens at f2.8. It is quite clear to me that the forth one is better than the third in terms of the lens sharpness and contrast.
(the transverse lines in the third s&le are artefacts)
 

wang

Well-Known Member
I have to mention that the film I used for the first and second are Kodak gold 100, for the third,forth and the rest, I used Kodak HD200.

The fifth is taken by 85 1.4 at f4.




The sixth is taken by the lens with the card cutting and aperture ring at f2.8,making the effective fno. f4.

To me the sixth is slightly better defined than the fifth.

In conclusion, I have preliminary evidence to suggest the cardboard cutting do improve the performance of 85 1.4 at f2, f2.8 and f4, with results most noticable at f2 and f2.8.
 

wang

Well-Known Member
So, DJ, this is the kind of image improvement I meant at f2 and it does carry to the smaller openings.

In 85 1.4,the diameter of the area which allows light to go in is about 60mm, the diameter of the inner circle of card cutting is about 42mm.

85 1.4, even with this kind of occlusive "hood", does not vignette. I must admit that if 85 1.2 is reduced to 42mm diameter, it will vignette.
 
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