Home

Please support mflenses.com if you need any graphic related work order it from us, click on above banner to order!
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

Goerz Dogmar 6.3/135 (1916) on 350D
Post new topic   Reply to topic
Home   Manual Focus Lenses
View previous topic :: View next topic  


PostPosted: Wed Apr 30, 2008 5:28 am    Post subject: Goerz Dogmar 6.3/135 (1916) on 350D Reply with quote
A few shots with the Dogmar from 1916, at least temporarily extracted from my Voigtlaender Avus 9x12.

The contrast of an uncoated dialyt type lens (4 elements in 4 groups) can be quite abysmal with a lot of veiling glare, note the difference between the two groups of people due to the different backgrounds:



The above photo would require regional adjustments, but usually things aren't that bad and a global adjustment will do:





Despite a slight double edge, the bokeh usually remains quite decent:


Alder cones at nearly 1:2




A crop, note the noise which is somewhat reminiscent of film grain:


As a comparison, here is a crop from a similar shot with the CZ Sonnar 2.8/135 at f/5.6:


In the OOF area, the difference in noise is even more evident, first the Dogmar:


then the Sonnar, which is much smoother - and perhaps a little bit sterile:


More photos at http://galactinus.net/vilva/retro/eos350d_dogmar.html

Veijo


PostPosted: Wed Apr 30, 2008 6:11 am    Post subject: Reply with quote
The DEPTH...the dimensionality! Wow! The full size image with the ram, looking down the avenue....stunning sense of dimension, it draws me in.


PostPosted: Wed Apr 30, 2008 8:11 am    Post subject: Reply with quote
Having seen your previous samples of older lenses I should no longer be so surprised at how well they perform, but always am Smile


PostPosted: Wed Apr 30, 2008 8:13 am    Post subject: Reply with quote
Why the noise, Veijo? What causes it?


PostPosted: Wed Apr 30, 2008 9:31 am    Post subject: Reply with quote
Richard_D wrote:
Having seen your previous samples of older lenses I should no longer be so surprised at how well they perform, but always am Smile


Ignoring the effect of coating, which could as well be applied to these simpler lenses, more complex lens designs bring very little if any advantage at moderate and small apertures and narrow FOVs. An f/2.8 triplet isn't perhaps so very good, but a properly designed and built f/5.6 triplet using only the best part of the image circle is so good that exceeding its performance in practical photography is very difficult, probably unnecessary and certainly not cost effective.

Here I'm using only a very small part, something like the center 26 mm of the perhaps 160 mm wide image circle of the Dogmar, which on the other hand is known for its good edge performance. The main factor limiting the performance is the veiling glare, which certainly affects the resolution - at pixel peeping level.

Veijo


PostPosted: Wed Apr 30, 2008 10:24 am    Post subject: Reply with quote
Orio wrote:
Why the noise, Veijo? What causes it?


The culprit is the veiling glare, the internal reflections within the lens. You can observe the same phenomenon in most photos taken with uncoated lenses. However, this type of noise is, IMHO, rather unobtrusive and benign compared to sensor noise, especially if you are accustomed to film grain. Under some circumstances this noise may even mask the sensor noise and also prevent pixelation in a way very difficult to emulate convincingly in PP, roughly like the deliberate noise injection used in digital audio recording to improve the low level resolution. This noise can also serve to eliminate most of the plasticky appearance many people attribute to digital photos.

Veijo


PostPosted: Wed Apr 30, 2008 1:31 pm    Post subject: Reply with quote
It is completely new to me that noise can be caused by a lens.
I would have lost any bet on that.
And to be honest, I still do not understand how this can happen. Usual sensor noise is caused by a too high sensitivity of the sensor (as in high ISO) which causes pixels to react to light that fell on neighbouring pixels. How can such an effect be caused by a lens? I understand that you mention veiling glare but how does that produce noise in detail?


PostPosted: Wed Apr 30, 2008 1:55 pm    Post subject: Reply with quote
Did you use a lens hood?
I use this old uncoated lenses with a extra large lens hood from black matt paper. The contrast is much better.

Ingo


PostPosted: Wed Apr 30, 2008 3:22 pm    Post subject: Reply with quote
LucisPictor wrote:
It is completely new to me that noise can be caused by a lens.
I would have lost any bet on that.
And to be honest, I still do not understand how this can happen. Usual sensor noise is caused by a too high sensitivity of the sensor (as in high ISO) which causes pixels to react to light that fell on neighbouring pixels. How can such an effect be caused by a lens? I understand that you mention veiling glare but how does that produce noise in detail?


I constructed a perfect example of this the other day, when I bodged up an adapter to try out the Aldis lens (the one in front of my face in my avatar) on the 10D. The uncoated optics and the reflective interior of the lens tube (a piece of black plastic pipe) combined to produce a horribly low-contrast, noisy, coma-ed image. Some might like it, but I found it just too bad.
I'll re-do the experiment and matt-black the inside of the pipe.

In my opinion, the noisiness of my images was caused by the random light rays striking pixels at all sorts of angles.
I'll put it up later and show you.


PostPosted: Wed Apr 30, 2008 3:53 pm    Post subject: Reply with quote
LucisPictor wrote:
It is completely new to me that noise can be caused by a lens.


Well, it isn't really noise, it just looks like noise.

Quote:
Usual sensor noise is caused by a too high sensitivity of the sensor (as in high ISO) which causes pixels to react to light that fell on neighbouring pixels.


Sensor noise has pretty little to do with light. Every electronic device will produce thermal noise, i.e. a noise voltage which depends on the temperature of the device. If you put a lens cap on so that no light can enter the camera and take a very long exposure shot, you'll get a pure noise image. Cooling the sensor down will decrease this noise, with some sensors about 1 stop/6 degrees centigrade. When photons hit the sensor they will generate a voltage which depends on the number of photons "accumulated" during the exposure. If there are enough photons, the light dependent voltage will be higher than the thermal noise voltage of the sensor, and with an increasing exposure level a more and more noise free image will emerge.

Quote:
How can such an effect be caused by a lens? I understand that you mention veiling glare but how does that produce noise in detail?


Part of the light reflected within the lens will hit the sensor at a lower intensity and slightly displaced from the original destination, at an increasingly lower level and more displaced after each additional reflection. The intensity of this reflected light is several stops below the main "signal" so it mostly looks like noise.

Veijo


PostPosted: Wed Apr 30, 2008 4:00 pm    Post subject: Reply with quote
Ingo wrote:
Did you use a lens hood?
I use this old uncoated lenses with a extra large lens hood from black matt paper. The contrast is much better.


I know the advantage of using a hood, but for these test shots I didn't use one as I didn't have a suitable one and I was mainly interested in the sharpness of the lens - I'll later on construct a hood specifically for this lens. Besides, a hood doesn't always help much, e.g. in the low contrast example here, most of the stray light came reflected from the target, i.e. the very white cathedral.

Veijo


PostPosted: Wed Apr 30, 2008 5:49 pm    Post subject: Reply with quote
I repeat:
This noise is a re-reflection from the lens?
At first, I mean, it is from the old glass.
Interesting thing.

regards Peter


PostPosted: Wed Apr 30, 2008 7:11 pm    Post subject: Reply with quote
padiej wrote:
I repeat:
This noise is a re-reflection from the lens?


You can get a fair idea of the re-reflections if you look at the first photo and compare the dark clothes of the people at the top of the stairs to the clothes of the people lower down, or even compare the faces.

Quote:
At first, I mean, it is from the old glass.


The glass will also have a slight effect, there certainly is some dispersion within the glass, but the reflections are probably the main factor, the total cumulative effect is perhaps something like 5 stops or even less below the main image.

As a comparison, here is a crop from a photo taken with the CZ Sonnar 2.8/135 on the same steps, there is quite a difference in the dynamic range, note especially the black:



Veijo


PostPosted: Wed Apr 30, 2008 8:01 pm    Post subject: Reply with quote
LucisPictor wrote:
It is completely new to me that noise can be caused by a lens.
I would have lost any bet on that.

Same here, new to me.

LucisPictor wrote:
And to be honest, I still do not understand how this can happen. Usual sensor noise is caused by a too high sensitivity of the sensor (as in high ISO) which causes pixels to react to light that fell on neighbouring pixels.


No, I disagree. Sensor noise is thermal or electrical excitation. Its unrelated to the light falling on the sensor. Indeed, in astronomy, its common to take a 'dark field' exposure and subtract.

The influence of ISO is because a sensor, like a film, has a single real or 'natural' ISO. Getting to other settings involves amplifying the signal, which also amplifies the noise. (Rarely, it involves attenuating the signal slightly, to get one stop lower than the natural ISO. Mostly though the base ISO is the lowest ISO available).

This by the way is why the 6MP sensors with 200 lowest ISO gave better results than the 10Mpx sensors with 100 base ISO. At 200, the 10Mpx sensors were amplifying the signal (and the noise) by 2.

Unfortunately, people more familiar with film than with electronics saw a lower base ISO as an improvement (thinking of 'fine grained' low sensitivity film, probably).

This is why I bought a D40 after the D40X came out. But I digress.
Post new topic   Reply to topic
Home   Manual Focus Lenses
Page 1 of 1