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

The amazingly high resolution of a Helios 44M-4
Post new topic   Reply to topic
Home   Manual Focus Lenses
View previous topic :: View next topic  


PostPosted: Sun Apr 13, 2014 4:56 pm    Post subject: The amazingly high resolution of a Helios 44M-4 Reply with quote
The Russian Helios 44 lens is often underestimated, but nearly all agree on one thing: the Helios 44 optics is quite good. Some even say it is exceptional. Then, when someone said other day that the resolution of the Helios 44 is only 40 lines/mm, I decided to measure myself the resolution of the Helios 44M-4 I own. The end result was amazing.

What I measured was the so-called "limit resolution", which is the number of parallel lines per millimeter, lp/mm, that can be resolved just before the lines disappear into a blur. The resolving power is the traditional figure of merit of a lens, but nowadays MTF50 measurements are increasingly popular.

The equipment
My Helios 44M-4 is a like-new, never abused lens, no better or worse than millions of other Helios 44 made in the former USSR.





The camera used in the test was a Sony A99 with a 24MP 6� pixel pitch sensor. A 6000 x 4000 sensor can, in theory, resolve 4000 lines width per picture height (LWPH), but in practice resolves only 3000~3200 LWPH. In terms of lp/mm, 3000~3200 LWPH correspond to 62.5~66.7 lp/mm ( lp/mm is calculated by dividing LWPH by the double of the sensor height given in mm).

The test chart was of size 1000 x 667 millimeters. The converging lines allow measurements in the center from 1000 LWPH up to a "full-scale" 4000 LWPH. The markings are in hundreds of LWPH, so marking 10 is 1000 LWPH, 20 is 2000 LWPH, and so on.

The picture bellow is the actual shot with the Helios 44M-4 working wide open.





The test � Stage I
The distance from camera to chart was adjusted to a tight framing. Otherwise the marking would not give the correct resolution.

The focus was carefully adjusted with the aid of the 11.7X magnification of live view of the Sony A99. The RAW file was converted to JPG by ACR with sharpening control sets to zero.

The measured corner resolution was:
Radial: 2000 LWPH = 42 lp/mm
Tangential: 2500 LWPH = 52 lp/mm

These values are not bad, but the main interest was to investigate the center resolution. So let's take a look at the 200% crop of the center:



The low contrast is typical of fast lenses wide open. The converging lines mix at about 3000 LWPH = 62.5 lp/mm. It is important to note that this resolution is not the lens'; it is basically the sensor's resolution. We have here a situation where the lens out-resolves the sensor.

The test � Stage II
What we need is a camera with a sensor with resolution so high that it out-resolves the lens. The trick was to use a tele-converter to magnify the image produced by the lens under test. This way, the A99 sensor's effective resolution is doubled. A tele-converter acts as the Barlow lens in a telescope. A Barlow lens magnifies the image produced by the telescope but cannot increase the intrinsic resolution of the telescope. Likewise, the tele-converter cannot increase the intrinsic resolution of the Helios 44M-4 lens.

I used a Komura Telemore II MC7, a 7-element 2X tele-converter that has very good on-axis correction (off-axis is another history). The distance to the test chart was increased to double the distance used in Stage I, so the chart is framed tightly again, like in Stage I. It is important to note that now the real resolution is the double what the markings say. The marking 10 is now 2000 LWPH, 20 is 4000 LWPH, etc.

Below a 200% crop of the center:



The contrast is even lower than in Stage I. The chromatic aberration is much more apparent, too. The lines blend at marking 30, what means the Helios 44M-4 out-resolves the sensor again, in spite of the sensor has been "boosted" by a tele-converter.

The test � Stage III
A second Komura Telemore II MC7 was added to the setup. The distance to the chart was doubled again. The markings are corrected by multiplying the values by 4X.

The 200% crop of center of image is:



The contrast is very, very low, but it is still possible to see that the lines blend at the marking 26, which corresponds to a resolution of 10400 LWPH = 217 lp/mm.

The resolutions for other apertures were also measured. The table below shows the measured resolutions in lp/mm and the theoretical resolution given by diffraction. The diffraction-limited resolutions were calculated by the formula: resolution = 1600/Fnumber

F number ........ Resolution (meas.) ........ Resolution (diffr.)
=====================================
2 ........................... 217 .............................. 800
2.8 ........................ 225 .............................. 565
4 ........................... 233 .............................. 400
5.6 ........................ 217 .............................. 283
8 ........................... 158 .............................. 200
11 ......................... 125 .............................. 141

Final note
The real resolutions of the Helios 44M-4 should be even greater than the numbers above because the tele-converters are not ideal, and their aberrations certainly impact the measurements.

Last edited by Gerald on Tue Dec 20, 2016 4:18 pm; edited 1 time in total


PostPosted: Sun Apr 13, 2014 7:32 pm    Post subject: Reply with quote
Indeed your Helios 44M-4 lens have amazingly high resolution. This cheap Russian lenses are REAL GEMS.
I've been always surprised by my 44M-2 old Helios resolution, too.
At this link:
https://drive.google.com/file/d/0B4dENtC-VAIhQUp6Sm41enRUaHM/edit?usp=sharing
you can download a 52,1 Mpx full frame test image taken with it. If you download the jpg and view it at 100% you'll see that the old Helios 44-2 indeed seems to match or even outperform, in the center at least, a 50Mpx FF sensor!!!


The test image is made by 3 stitched shifted frames taken with my shift adapter (presented here: http://forum.mflenses.com/diy-shift-adapter-for-ff-lenses-on-nex-cameras-completed-t60109,highlight,%2Bshift+%2Badapter.html ) and a Sony NEX-7 camera.


PostPosted: Sun Apr 13, 2014 8:57 pm    Post subject: Reply with quote
We know the Russians love their children and make lens too.


PostPosted: Sun Apr 13, 2014 10:04 pm    Post subject: Reply with quote
I've got a 1960's Helios-44 with a 00 serial that is probably sharper, it's a truly stunning lens. 00 serials are special production items and the one I have is certainly special.

People who talk down Russian lenses (an there are a few of them on this forum) are full of it, quite frankly. I have a J3 that is sharper than my Sonnar 1.5/50 and a J11 that is every bit as sharp as my Sopnnar 4/135. The Helios-103 I bought NOS was better all round than the 200ukp Summicron-R 2/50 I had for a while, so the Russian copy outshone the over-hyped German original. Smile


PostPosted: Mon Apr 14, 2014 12:00 am    Post subject: Reply with quote
Quote:
People who talk down Russian lenses (an there are a few of them on this forum) are full of it

Ian, try and not make statements like this,have your opinion but please think about the wording.


PostPosted: Mon Apr 14, 2014 2:55 am    Post subject: Reply with quote
Edited

Last edited by bernhardas on Tue May 10, 2016 7:32 am; edited 1 time in total


PostPosted: Mon Apr 14, 2014 6:06 am    Post subject: Reply with quote
I generally like all this praise to helios. What is the long term market estimation? Should I sell my stock of brand new, unused ones now, or should I wait for higher price increase? Smile


PostPosted: Mon Apr 14, 2014 6:37 am    Post subject: Reply with quote
Well I suppose you could add:- The Helios is a sharp lens but so are many other 50mms and the difference is negligible. So e.g for £10 would you rather have a Zuiko or Minolta 50mm etc.......... or Helios

This guy has an interesting view http://www.theonlinedarkroom.com/2014/04/why-do-we-talk-such-rubbish-about_7.html


PostPosted: Mon Apr 14, 2014 12:58 pm    Post subject: Reply with quote
bernhardas wrote:

You used the limit where you can't see anything anymore however the usual test criteria is way above these threshold. It is a minimum contrast.

How high a contrast?



I thought it was clear in my post that the criterion I used to measure the resolution was the same used in the photographic world in the last 100 years, ie to visually determine where the parallel lines can barely be seen separately. This occurs when the contrast drops to approximately 10%.


PostPosted: Mon Apr 14, 2014 2:58 pm    Post subject: Reply with quote
I love to see these tests, far beyond my ability to replicate them. The best I can manage is to put up boxes of cereal and dog food and take pictures of them with the camera on a tripod.

Would it make any difference if the test chart had its lines printed in different colours? Would some lenses manage green lines better than blue ones, for instance?


PostPosted: Mon Apr 14, 2014 3:03 pm    Post subject: Reply with quote
scsambrook wrote:
I love to see these tests, far beyond my ability to replicate them. The best I can manage is to put up boxes of cereal and dog food and take pictures of them with the camera on a tripod.

Would it make any difference if the test chart had its lines printed in different colours? Would some lenses manage green lines better than blue ones, for instance?

Take a look of this test in dpreview.
http://www.dpreview.com/reviews/sigmadp1/page20.asp

Different lens will responds to different wavelength differently. So, a lens may be better manage green lines while other lens are better in red.


PostPosted: Mon Apr 14, 2014 3:51 pm    Post subject: Reply with quote
Gerald wrote:
bernhardas wrote:

You used the limit where you can't see anything anymore however the usual test criteria is way above these threshold. It is a minimum contrast.

How high a contrast?



I thought it was clear in my post that the criterion I used to measure the resolution was the same used in the photographic world in the last 100 years, ie to visually determine where the parallel lines can barely be seen separately. This occurs when the contrast drops to approximately 10%.


Actually this is not MTF 10, but rather MTF 2. Personally, I can easily distinguish MTF 2 lines in his chart (on a laptop screen), and my vision is far from perfect.

Quote:
The old resolution measurement— distinguishable lp/mm— corresponds roughly to spatial frequencies where MTF is between 5% and 2% (0.05 to 0.02). This number varies with the observer, most of whom stretch it as far as they can.


http://www.normankoren.com/Tutorials/MTF.html


PostPosted: Mon Apr 14, 2014 5:06 pm    Post subject: Reply with quote
fermy wrote:


Quote:
The old resolution measurement— distinguishable lp/mm— corresponds roughly to spatial frequencies where MTF is between 5% and 2% (0.05 to 0.02). This number varies with the observer, most of whom stretch it as far as they can.


http://www.normankoren.com/Tutorials/MTF.html

Imatest, which makes the program more professionally used to evaluate the performance of lenses, says:

"Traditional “resolution” measurements involve observing an image of a bar pattern (often the USAF 1951 chart), and looking for the highest spatial frequency (in lp/mm) where the bars are visibly distinct. This measurement, also called “vanishing resolution”, corresponds to an MTF of roughly 10-20%"

http://www.imatest.com/docs/sharpness/#sharpness

Most authors consider that the contrast at the point at which the lines appear mixed is something between 5% and 15%. That is why I mentioned the value of 10%.


PostPosted: Mon Apr 14, 2014 6:14 pm    Post subject: Reply with quote
fermy wrote:
Actually this is not MTF 10, but rather MTF 2. Personally, I can easily distinguish MTF 2 lines in his chart (on a laptop screen), and my vision is far from perfect.

Quote:
The old resolution measurement— distinguishable lp/mm— corresponds roughly to spatial frequencies where MTF is between 5% and 2% (0.05 to 0.02). This number varies with the observer, most of whom stretch it as far as they can.


http://www.normankoren.com/Tutorials/MTF.html


You only could distinguish lines with 2% contrast in Koren's illustration because it is noiseless. It is not a real Picture.
This a crop of my test Picture; the contrast is roughly 7-10% under the mark 26. Note the inevitable noise (I shot ISO 100).



PostPosted: Mon Apr 14, 2014 6:41 pm    Post subject: Reply with quote
Edited

Last edited by bernhardas on Tue May 10, 2016 7:33 am; edited 1 time in total


PostPosted: Mon Apr 14, 2014 6:51 pm    Post subject: Reply with quote
Gerald wrote:


You only could distinguish lines with 2% contrast in Koren's illustration because it is noiseless. It is not a real Picture.
This a crop of my test Picture; the contrast is roughly 7-10% under the mark 26. Note the inevitable noise (I shot ISO 100).



Good point on the noise, but when you take the noise into account strictly speaking it is not clear how MTF x is defined. Btw, how does 7-10% figure was obtained, is it what Imatest spits up?


PostPosted: Mon Apr 14, 2014 7:00 pm    Post subject: Reply with quote
Edited

Last edited by bernhardas on Tue May 10, 2016 7:33 am; edited 1 time in total


PostPosted: Mon Apr 14, 2014 7:35 pm    Post subject: Reply with quote
bernhardas wrote:
I am sorry, but my profession has made me into a professional sceptic.

Frankly the estimate of 10% contrast is in my experience as successful as using your hand to feel when the tap water reached 23 degrees. It is in 95% of estimates wrong.

And isn't there a significant difference in the numerical value of the result whether the cut of is at 2% 7% 10% or 12% ???



Very Happy the 100 year old tradition is that everybody does what he wants!
I am sure there is an ISO norm somewhere defined, but even they sometimes grant you latitude in selective input parameters as long as the process and methodology are adhered to.


Let's get the un abbreviated quote from imatest. (Emphasis by me)
Quote:
.
Traditional “resolution” measurements involve observing an image of a bar pattern (often the USAF 1951 chart), and looking for the highest spatial frequency (in lp/mm) where the bars are visibly distinct. This measurement, also called “vanishing resolution”, corresponds to an MTF of roughly 10-20%. Because this is the spatial frequency where image information disappears— where it isn’t visible, and because it is strongly dependent on observer bias, it’s a poor indicator of image sharpness. (It’s Where the Woozle Wasn’t in the world of Winnie the Pooh.) The USAF chart is also poorly suited for computer analysis because it uses space inefficiently and lacks a low frequency reference.
[/b]


Maybe you knew better and should have explained to the USAF, that created the famous USAF 51 chart, that tests of ultra high definition lenses used in military reconnaissance aircrafts based on traditional resolution measurements were a "poor indication of image sharpness". Maybe the whole industry of television equipments was wrong in using a test system based on parallel lines. Maybe Nikon, Zeiss, Leica , were all wrong when they measured the performance of their lenses by the traditional method. Maybe ...

Returning to the real world, it is understandable that Imatest exaggerates the limitations of traditional test. After all, Imatest sells a computerized test system, and has no interest that people continue testing the lenses by the traditional method. The claim that the in the traditional method "the result "is strongly dependent on the observer bias" is not true! The observer to observer variation is only about 5%. The limitations of the traditional method are others. But this a story for another day ...

Last edited by Gerald on Mon Apr 14, 2014 8:15 pm; edited 1 time in total


PostPosted: Mon Apr 14, 2014 7:55 pm    Post subject: Reply with quote
fermy wrote:

Good point on the noise, but when you take the noise into account strictly speaking it is not clear how MTF x is defined. Btw, how does 7-10% figure was obtained, is it what Imatest spits up?




I estimated the contrast by using Photoshop to measure the levels. The white level of the image is ~ 200, and the black level is ~ 50 (the black region of the image is not shown in the crop).

The level of the black lines is ~ 130, and the level of white lines is ~ 140.

The contrast is calculated as follows:
Contrast = (140-130) / (200-50) = 7%

These values are approximate due to the noise. Another person could find slightly different values.


PostPosted: Tue Apr 15, 2014 1:09 am    Post subject: Reply with quote
I wonder if Russia and China had test charts like these:

http://www.dailymail.co.uk/sciencetech/article-2280445/The-mysterious-barcodes-painted-ground-world-actually-used-calibrate-airborne-cameras.html


PostPosted: Tue Apr 15, 2014 1:26 am    Post subject: Reply with quote
Edited

Last edited by bernhardas on Tue May 10, 2016 7:33 am; edited 1 time in total


PostPosted: Tue Apr 15, 2014 1:40 am    Post subject: Reply with quote
Edited

Last edited by bernhardas on Tue May 10, 2016 7:33 am; edited 1 time in total


PostPosted: Tue Apr 15, 2014 1:43 am    Post subject: Reply with quote
bernhardas wrote:


The lens alone is tested on an optical bench.


I fear you do not know that an optical bench uses optical sensors and auxiliary optics. Conceptually, it is not much different from my setup.


PostPosted: Tue Apr 15, 2014 1:53 am    Post subject: Reply with quote
Quote:



I estimated the contrast by using Photoshop to measure the levels. The white level of the image is ~ 200, and the black level is ~ 50 (the black region of the image is not shown in the crop).

The level of the black lines is ~ 130, and the level of white lines is ~ 140.

The contrast is calculated as follows:
Contrast = (140-130) / (200-50) = 7%

These values are approximate due to the noise. Another person could find slightly different values.


This method is guaranteed to give you exaggerated MTF values A more reasonable approach would be to subtract the noise level from the peak white level. For a strong signal the difference at ISO 100 is probably insignificant, however al low MTF the signal is weak and therefore the noise significantly affects the peak values. So it is quite likely that real MTF at the extinction level in your test is somewhere in 2-5% range as Norman Koren claims.

For the sake of the argument, let's assume that the noise level is 1%. That corresponds to the level of white lines with noise subtracted of 140-0.01*200=138 and MTF value of 8/150=5.3

Last edited by fermy on Tue Apr 15, 2014 2:16 am; edited 1 time in total


PostPosted: Tue Apr 15, 2014 1:55 am    Post subject: Reply with quote
Edited

Last edited by bernhardas on Tue May 10, 2016 7:34 am; edited 1 time in total
Post new topic   Reply to topic
Home   Manual Focus Lenses
Goto page 1, 2, 3  Next
Page 1 of 3