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How good it gets the photochain and its limiting factors


How good it gets - the photo-chain and its limiting factors

I find it interesting to know, what can actually influence the “perfect” image/picture and what is limiting the theoretical potential of very good lenses.

First you have to look at the different parts which are involved in the picture-making process/chain.

1. The lens
2. The film
3. The camera
4. You

The lens is the first limiting factor. Even an absolute perfect lens, which does not exist, has resolution limits. If we would imagine that perfect lens, without any lens error, the resolution limit depends on diffraction and therefore on the aperture you are using.

If you shoot fully open, you have a higher resolution number. If you shoot with the smallest aperture, you get the lowest resolution. Of course there are also other factors important for a good picture i.e. the depth of field and therefore you make always a compromise between as much resolution as possible and as much depth of field as needed.

For a better understanding I put here some numbers down, which are published in “camera lens news” (CLN) # 2 from Carl Zeiss Germany.

You can access all issues of camera lens news on the Zeiss homepage. They have them in English and German as a pdf-file.

F-Stop/ Resolution in lp/mm

2.8/ 560
4.0/ 400
5.6/ 280
8/ 200
11/ 140
16/ 100
22/ 70
32/ 50
45/ 35

These numbers show how dramatically the resolution drops, the more you stop down. This is just the diffraction. But there are also lens errors, which are not taken into account in this table.

If you look now closer to modern films you will see, that even the best films do not exceed a resolution of 200 lp/mm (Kodak Ektar 25, Fuji Velvia). Looking at both numbers, you see that just aperture 8 is needed for the best possible result, because the film can not record more anyway.

Normal films are in the range of 140 lp/mm, so even an f-stop of 11 is sufficient – assuming you would have the only perfect (error free) lens in the world.

And if you want to have in landscape photography everything sharp from the front to the horizon, you must stop down and give up even more resolution.

The camera plays also a role. Carl Zeiss made tests already in the 70s with different systems of holding the film flat in the camera body.

They realized, that the film flatness has a bigger influence on the resolution potential than everybody expected. This is an excerpt of the Zeiss article of 1979 in the download-section:

“…Film flatness measurements which we have recently performed on 35 mm SLR cameras have led to results which have surprised and indeed alarmed us. According to our measurements, the film generally displays a convex curvature in the camera aperture in the direction of the lens. The most pronounced deviation from flatness is always displayed by the first frame which is transported into the camera aperture after a period of non-use…...

...In this ex&le, the largest deviation, which mostly occurs in the image centre, is 80 jim; in some cases, we measured even larger curvatures….

Flatness errors of this type suffice to conspicuously change the image quality of fast lenses. This pronounced defocusing, for ex&le, causes a drop in contrast in the 50 mm Planar f/1.4 lens from 60 to about 20% at 20 cycles/mm (Fig. 11). This phenomenon was more or less exhibited by the films of all manufacturers….”

I guess that was at the end of the day the reason, why Contax came out 1990 with the RTS III and the RTV-system.

But there is even more, which can destroy your “resolution dreams”. It is you! If you are shooting handheld instead of using a tripod you are the biggest limiting factor. Camera lens news #2:

“…even a seasoned photographer with a very “calm” camera will hardly find resolutions higher than 40 lp/mm in his photographs unless he uses an adequate tripod….”

And what Zeiss means with an adequate tripod, they mention in CLN #4. :

“…photo tripods usually prove insufficient for real high performance photography. You may wish to use a carbon fibre television tripod instead. With a fluid head featuring adjustable d&ing devices….”

I do not know whether you want to carry a television tripod with you around, nor whether you have the money for it. This all sound extreme. I think the use of an average good tripod helps also already, but the target here is to show, what you have to do to really exploit the maximum potential of Carl Zeiss lenses.

The next thing would be an obvious one. Once you are using a tripod, you should also use a mirror lock up. Otherwise carry on and shoot handheld …

Also quiet obvious is the film processing and printing. If you buy equipment for 6-10k and the best film available, you should neither use an one hour lab, nor any other non-professional lab. And not every so called “pro-lab” is one just because of the name written on the entrance.

Forget the attraction of saving 2-3 Euro here and there. Either you use top equipment and you are also doing this in the whole value-chain, or think about different systems
. This is a pain I know, but hopefully in 3 years time, we can do it cheaper digital.