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Old wide-angle lenses with dSLR - most telecentric ones?
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PostPosted: Fri Jun 05, 2009 6:44 pm    Post subject: Old wide-angle lenses with dSLR - most telecentric ones? Reply with quote

Hi,

Film emulsion is much more tolerant of the angle at which light rays falls on it's flat surface.
Digital imaging sensors are equipped with microlenses, which really do not like rays falling at the narrow angle.
Lens that projects rays which fall at the angle as close to the right angle as possible is telecentric one.
It is well known that many old wide-angle lenses are not telecentric enough for modern dSLR's sensors.
Especially these which have small diameter of rear element, which additionally protrudes towards the sensor when
set to infinity.
In such design, light rays aimed at the corners of the image are forced to fall at more and more narrow angle -
closer to corner = more narrow angle of light path.
The lens that is sharp from corner to corner on full frame of 35mm film, does havoc on the smaller APS-C sensor,
details in the corners are just like smeared, with low contrast and dull colours.
Usually such lenses are much better at shorter distances, when rear element is farther from the projected image.
I have several cheap 28mm primes, which are better or worse at this point:

Porst Weitwinkel 28/2,8 - corners OK at close distances, havoc at infinity, better stepped down to f11- f16.
Hanimex (Tokina) 28/3 - corners OK at close distances, havoc at infinity, - better stepped down to f11- f16.
Kenlock MC-Tor 28/2,8 - soft lens overall, but corners not much worse than centre at infinity.

I have tested Pentax SMC-M 28/2,8 - it has very good quality of the corners, even maximum aperture.

Now I've a chance to buy cheap Tokina RMC 28/2.8 and I wonder how this little beast works with dSLR?
Any suggestion from the owner of this little Tokina would be appreciated Smile.

I think, that it would be nice idea to prepare a list of "most telecentric lenses wide angle lenses",
or "almost dSLR-unusable ones" - collecting old lenses is very interesting hobby, but it is much
better when most of the drawer inhabitants are really usable Smile


PostPosted: Fri Jun 05, 2009 7:53 pm    Post subject: Reply with quote

Interesting point.

Would not the smaller size of the APS-C sensor reduce the problem ?

The people who would suffer the most seem to be those with full frame sensors.

Also it seems that the small protruding rear elements are seen mostly in older lenses. My most protruding one is a 1958 Fujita 35/2.5. That one seems OK in the corners, but I will look again.

The old S-M-C Takumar 28/3.5 is very good at the corners.

I don't recommend the Tamron Adaptamatic 28/2.8 for edge quality, its not great.

The RMC Tokinas are from the late 1970's-early 1980's, so should not have such problems. I have RMC Tokina 28-80 zoom with no real bad edge/corner problems.


PostPosted: Sat Jun 06, 2009 1:27 am    Post subject: Reply with quote

The is a way to test for more telecentric lenses characteristics.

As you said, the angle towards the corners is quite large for older non-telecentric, while telecentric lenses are designed so that the light falls onto the sensor closer to perpendicular.

Take a modern telecentric lens, and get an LED flashlight with only one LED.
With a piece of white paper, almost side on, check the straight, then angled light path.
Then do the same for an old wide angle lens.
e.g.

Telecentric straight:


Then Telecentric at an angle:


Now Non-Telecentric at an angle(old lens, Minolta MD 28mm):


You can see how much more of an angle the old wide angle (non-telecentric) lens makes. Some of the old wide angle lenses have a less pronounced angle, and I guess these are the ones to use.


PostPosted: Sat Jun 06, 2009 5:20 am    Post subject: Reply with quote

dnas wrote:
The is a way to test for more telecentric lenses characteristics.

As you said, the angle towards the corners is quite large for older non-telecentric, while telecentric lenses are designed so that the light falls onto the sensor closer to perpendicular.

Take a modern telecentric lens, and get an LED flashlight with only one LED.
With a piece of white paper, almost side on, check the straight, then angled light path.
Then do the same for an old wide angle lens.
e.g.

Telecentric straight:


Then Telecentric at an angle:


Now Non-Telecentric at an angle(old lens, Minolta MD 28mm):


You can see how much more of an angle the old wide angle (non-telecentric) lens makes. Some of the old wide angle lenses have a less pronounced angle, and I guess these are the ones to use.


Thank You for excellent "live" example of telecentricity idea!
People who do not like to dig through white papers concerning optical phenomenons
shall catch the point at once Smile
IMHO this thread shall be renamed to wide angle/telecentric lenses and made sticky Smile


PostPosted: Sat Jun 06, 2009 6:28 pm    Post subject: Reply with quote

I thought this was a vogue idea a few years ago that turned out to be a non-issue.

I've certainly been happy enough with most of my manual focus wide angles and the camera makers do not make special lenses for full frame DSLRs, they still sell the same lenses as they sell for film cameras. How come a 24-70 f2.8L film lens is OK for a pro using digital, but amateurs need a special digital lens that prevents light angle problems? It doesn't make any sense.


PostPosted: Sun Jun 07, 2009 2:46 pm    Post subject: Reply with quote

I bought one of these lenses back in May, an RMC Tokina 28mm f/2.8, and I summarise my findings with some sample pictures, taken with a Cand 5D, and this Photo.net thread here.

In my opinion it's decent but not exceptional. Mine was in the Contax / Yashica mount. The lens is small and snappy but still soft in the corners on a manly, full frame body. On a digital SLR with a smaller sensor it would probably be pretty good across the frame at f/5.6 and beyond, although I suspect it would be no better than a typical modern digital SLR kit lens at 28mm and f/5.6.

Based on subsequent research I eventually decided on an Olympus 24mm f/2.8, as mentioned in another thread and also over at 16-9.net, where the webmaster did an extensive test shoot of wide angle lenses. Amongst manual focus lenses he spoke highly over the Zeiss 21mm, which is far too expensive, and the Olympus 24mm, which is cheap as chips.


PostPosted: Sun Jun 07, 2009 3:23 pm    Post subject: Reply with quote

PaulC wrote:
I thought this was a vogue idea a few years ago that turned out to be a non-issue.


It is a issue with non-SLR lenses (e.g. on view cameras or the Leica MCool, where film wide angles often fail miserably. SLR lenses are quite telecentric in any case as they have to clear the mirror - the practical relevance there is small to none.

Sevo


PostPosted: Sun Jun 07, 2009 10:03 pm    Post subject: Reply with quote

PaulC wrote:
I thought this was a vogue idea a few years ago that turned out to be a non-issue.

I've certainly been happy enough with most of my manual focus wide angles and the camera makers do not make special lenses for full frame DSLRs, they still sell the same lenses as they sell for film cameras. How come a 24-70 f2.8L film lens is OK for a pro using digital, but amateurs need a special digital lens that prevents light angle problems? It doesn't make any sense.


Well, the answer is that 24-70 f2.8L is telecentric lens...
Old, non telecentric lens was not as bad on film.
AFAIK, improved telecentricity reduces such not wanted phenomenons as vignetting, when we think "photographic emulsion way".
So the lens design was improving objective's telecentricity even when the film was the only option.
But when digital SLR's appeared, telecentricity appeared to be a big problem not only for for weird amateurs who can not afford such 24-70 f2.8L and who like to use old Flektogon from the grandpa's drawer, but for lens designers as well.
You shall look at the content of this page, from last year...

I'll quote that they quote Smile
==============================================
"Here's a brief quote from the backpackinglight.com article:

Of great importance, if not well understood, is the relaxation of Four-Thirds' rigid telecentric lens standard. CCD imaging chips used in early digicams need light to hit the chip surface at a perpendicular angle, as their photosites sit in depressions that off-angle light can't reach evenly. This creates havoc that the original Four-Thirds standard addressed by demanding system lenses be perpendicular (telecentric). However, newer NMOS chips new used by Olympus and Panasonic don't suffer fatally from angled light, and advanced in-camera processing can address intensity differences that still occur across the frame.

This allows the Micro Four-Thirds rear lens element to sit closer to the chip which, in turn, allows lenses to be smaller. Thus unleashed, camera and lens designers can now employ classic wide angle lens designs unusable in SLRs, create zooms with rear elements that protrude into the camera body, and shrink many lens parts."
==============================================

So, as stated above - the problem is that "classic" wide angle lens designs is very often unusable in modern dSLRs, due to high standard of telecentricity demanded by most imaging sensors.

Typical "corner disaster" of non-telecentric wide-angle lens, on APS-C size sensor:


PostPosted: Mon Jun 08, 2009 5:43 am    Post subject: Reply with quote

Ashley Pomeroy wrote:
I bought one of these lenses back in May, an RMC Tokina 28mm f/2.8, and I summarise my findings with some sample pictures, taken with a Cand 5D, and this Photo.net thread here.

In my opinion it's decent but not exceptional. Mine was in the Contax / Yashica mount. The lens is small and snappy but still soft in the corners on a manly, full frame body. On a digital SLR with a smaller sensor it would probably be pretty good across the frame at f/5.6 and beyond, although I suspect it would be no better than a typical modern digital SLR kit lens at 28mm and f/5.6.

Based on subsequent research I eventually decided on an Olympus 24mm f/2.8, as mentioned in another thread and also over at 16-9.net, where the webmaster did an extensive test shoot of wide angle lenses. Amongst manual focus lenses he spoke highly over the Zeiss 21mm, which is far too expensive, and the Olympus 24mm, which is cheap as chips.


Thank You,
at the moment I've decided to buy Pentax SMC-M 28/2,8 as it does great job at small sensor dSLR, and the Tokina as well to test it Smile
If it would be better than my EOS Kit lens in case of flaring and chromatic aberration, it would be worth to be kept.


PostPosted: Mon Jun 08, 2009 6:17 am    Post subject: Reply with quote

wariag wrote:

Thank You,
at the moment I've decided to buy Pentax SMC-M 28/2,8 as it does great job at small sensor dSLR, and the Tokina as well to test it Smile
If it would be better than my EOS Kit lens in case of flaring and chromatic aberration, it would be worth to be kept.


It's a great lens, the SMC-A28/2.8 is said to be even better, but it wasn't the case with my copies.

You shouldn't have any problems with CA or flare with it.


PostPosted: Tue Feb 28, 2012 1:56 pm    Post subject: Reply with quote

one simply question... is CZJ Flektogon 35mm f/2.4 a telecentric wide?


PostPosted: Tue Feb 28, 2012 3:07 pm    Post subject: Reply with quote

Ashley Pomeroy wrote:
I bought one of these lenses back in May, an RMC Tokina 28mm f/2.8, and I summarise my findings with some sample pictures, taken with a Cand 5D, and this Photo.net thread here.

In my opinion it's decent but not exceptional. Mine was in the Contax / Yashica mount..


The best C/Y mount 28mm lens is the Carl Zeiss 28mm f2.8 Distagon T*...Simply is'nt worth trying any other 28mm lens once you have one because there is nothing better Wink


PostPosted: Tue Feb 28, 2012 3:24 pm    Post subject: Reply with quote

Sevo wrote:
PaulC wrote:
I thought this was a vogue idea a few years ago that turned out to be a non-issue.


It is a issue with non-SLR lenses (e.g. on view cameras or the Leica MCool, where film wide angles often fail miserably. SLR lenses are quite telecentric in any case as they have to clear the mirror - the practical relevance there is small to none.

Sevo


Your spot on Sevo!...The relatively large registration distance of most DSLR's makes this a complete non issue...It only becomes an issue with cameras that have small registration distances...Mirrorless cameras like the Sony NEX range for instance, which can be thought of as digital rangefinders.
And indeed I see telecentricity issues with most NEX samples when they are used with older manual focus lenses. But even when the lenses are designed specifically for the NEX range, like the Sony 16mm f2.8 Pancake for instance, the issue is still noticable. It makes it appear that the 16mm pancake is only sharp in the centre of frame and that it has major edge of frame issues, but really its probably just a telecentricity issue.


PostPosted: Tue Feb 28, 2012 4:53 pm    Post subject: Reply with quote

I use my Tokina 3.5/17 and Konica 4/21 a lot on my NEX-3 and I haven't noticed any corner issues. I also shoot them both on film with my Konica SLRs.

When we have some sunlight, I'll see if I can arrange some sort of test of my ultrawides on film and NEX.


PostPosted: Tue Feb 28, 2012 5:28 pm    Post subject: Reply with quote

DSG wrote:
Sevo wrote:
PaulC wrote:
I thought this was a vogue idea a few years ago that turned out to be a non-issue.


It is a issue with non-SLR lenses (e.g. on view cameras or the Leica MCool, where film wide angles often fail miserably. SLR lenses are quite telecentric in any case as they have to clear the mirror - the practical relevance there is small to none.

Sevo


Your spot on Sevo!...The relatively large registration distance of most DSLR's makes this a complete non issue...It only becomes an issue with cameras that have small registration distances...Mirrorless cameras like the Sony NEX range for instance, which can be thought of as digital rangefinders.
And indeed I see telecentricity issues with most NEX samples when they are used with older manual focus lenses. But even when the lenses are designed specifically for the NEX range, like the Sony 16mm f2.8 Pancake for instance, the issue is still noticable. It makes it appear that the 16mm pancake is only sharp in the centre of frame and that it has major edge of frame issues, but really its probably just a telecentricity issue.


I don't understand how the registration distance makes a difference in corner performance when using film lenses with digital sensor. To focus, the lens is positioned exactly the same distance from film/sensor on both cameras, no matter the registration distance differences. So I think the telecentricity issue is due rather to tightly packed sensor microlenses not have wide enough angle. A less tightly-packed sensor would have better wide-angle microlenses I think.

I think I understand there might be light-angle problem using wide angle lens from camera with short registration distance, such as lens made specifically for NEX. I think the size of the rear lens element (or more correctly, the lens exit aperture size) is the factor controlling the angle of light onto the sensor.


PostPosted: Tue Feb 28, 2012 8:01 pm    Post subject: Reply with quote

DSG wrote:
The best C/Y mount 28mm lens is the Carl Zeiss 28mm f2.8 Distagon T*...Simply is'nt worth trying any other 28mm lens once you have one because there is nothing better Wink

Leica Elmarit 28/2.8 v2 beats it easily, especially wide open.


PostPosted: Tue Feb 28, 2012 8:06 pm    Post subject: Reply with quote

I think worth to try any lens , even if not better than you have already. Sometimes shocking result come from cheap 'unknown' lenses.


PostPosted: Tue Feb 28, 2012 9:18 pm    Post subject: Reply with quote

I somehow can't understand why the final image wouldn't be sharp because of the microlenses on the chip. I would assume that just because light rays trave at a narow angle to the microlens the microlenses aren't able to divert the light rays to the "sweet spot" of the detector. For me the only understandable consequence could be higher vinetting.

You are so right Attila!, just for fun (and to learn the skills) I converted a lens, 28mm f2.8 Admiral from Minolta mount to EOS. I was just amazed how sharp it is. At f2.8 it is quite sharp, at f5.6 pixel sharp from edge to edge. Conserning sharpness at edges I think it performes better than Flektogon 35mm f2.4


PostPosted: Tue Feb 28, 2012 9:21 pm    Post subject: Reply with quote

sammo wrote:
I somehow can't understand why the final image wouldn't be sharp because of the microlenses on the chip. I would assume that just because light rays trave at a narow angle to the microlens the microlenses aren't able to divert the light rays to the "sweet spot" of the detector. For me the only understandable consequence could be higher vinetting.

You are so right Attila!, just for fun (and to learn the skills) I converted a lens, 28mm f2.8 Admiral from Minolta mount to EOS. I was just amazed how sharp it is. At f2.8 it is quite sharp, at f5.6 pixel sharp from edge to edge. Conserning sharpness at edges I think it performes better than Flektogon 35mm f2.4



Quiet a big think from a non-respected brand like Admiral!


PostPosted: Thu Mar 01, 2012 8:00 pm    Post subject: Reply with quote

sammo wrote:
I somehow can't understand why the final image wouldn't be sharp because of the microlenses on the chip. I would assume that just because light rays trave at a narow angle to the microlens the microlenses aren't able to divert the light rays to the "sweet spot" of the detector. For me the only understandable consequence could be higher vinetting.

It's not just the microlenses, but the anti-aliasing filter that plays a role in the reduced corner performance. With steeper incident ray angles, the effect of the AA filter increases astigmatism.
On top of this, steep ray angles also make light bleed into the wrong subpixels, which causes color shift (usually red/magenta and green/cyan color cast in parts of the frame).