Yes, the Tessar isn't derived from the triplet, it came about by combining the front of a Unar with the back of a Protar.
The dialyte is well corrected without an achromat, can't quite think of another one though.
Yes, the Tessar isn't derived from the triplet, it came about by combining the front of a Unar with the back of a Protar.
The dialyte is well corrected without an achromat, can't quite think of another one though.
I knew I'd forget one or two!Originally Posted by Ian Greenhalgh
But such designs are rare...
Trying to remember any others...
"I love my Verito lens, but I always have to sharpen everything in Photoshop..."
You've got me thinking now, there will probably be some uncommon ones, but I really can't think of a well-known and widely-used one apart from the triplet and dialyte (which is really a triplet where the middle glass has been split).
I'll even settle for pics of reflections with a pen light. ;~'))Arhhh... that surely sounds true enough to stop counting reflections in the that-bay pics.
Thank you for the clarification.
... Anybody claiming to own a 355 dagor-type G-Claron is very welcome to post the proof after taking the lens apart!
Thank you for your answers. So my guess was correct - it sounds that's for the in-focus details mainly. Myself, I rather don't like softness. I believe a hard-sharp lens is just fine for me when combined with a film developer yielding no (or, more correctly speaking, very little) edge effects - or in the digital world, with no post-sharpening. The nowadays common compensating development presents a lot of edge effects and makes the picture of a hard-sharp lens unpleasant for me, too. It also makes a just a bit softened lens picture somewhat better for my personal taste. But I still prefer a hard lens and no edge enhancement in post processing.
But the spherical aberration that softens the in-focus image is also the very thing that rules the out of focus rendition, and that's why I prefer the Dagor at f/10 to f/16 when there is a lot of blurred background, and f/5.6 Plasmats wide open when a lot of foreground is out of focus (if only f/5.6 is sufficient for DoF of course.... and unfortunately, it usually isn't).
Wide open, they both have a lot of overcorrected spherical aberration fine for the foreground blur. But the Dagor also has plenty of undercorrected spherical aberration; that results in much worse foreground blur with the Dagor. Also, personally I find the softness both too pronounced and also too "dirty"/"mushy" for my taste when lots of under- and overcorrected spherical aberration are present at the same time. A f/5.6 Plasmat has its undercorrected SA so much weaker that it doesn't spoil the foreground at f/5.6. And I find the character of the in-focus softness to be way better for my needs when only one type of spherical aberration is dominant.
From f/10 on, the overcorrected SA is gone in the Dagor but the undercorrected SA remains so the lens yields great background blur, and its in-focus rendition also becomes just fine for my taste. A typical Plasmat's overcorrected SA is gone from f/11 on, but the undercorrected SA that remains is too week to make the background as good as with the Dagor, and no trace of softness remains in-focus.
... Sorry I'm really not sure if anybody is interested in these longish theorizings of mine, though. :)
I'm having trouble seeing how a lens can display both under- and over- corrected aberration of any type at the same time... and I really should know...Thank you for your answers. So my guess was correct - it sounds that's for the in-focus details mainly. Myself, I rather don't like softness. I believe a hard-sharp lens is just fine for me when combined with a film developer yielding no (or, more correctly speaking, very little) edge effects - or in the digital world, with no post-sharpening. The nowadays common compensating development presents a lot of edge effects and makes the picture of a hard-sharp lens unpleasant for me, too. It also makes a just a bit softened lens picture somewhat better for my personal taste. But I still prefer a hard lens and no edge enhancement in post processing.
But the spherical aberration that softens the in-focus image is also the very thing that rules the out of focus rendition, and that's why I prefer the Dagor at f/10 to f/16 when there is a lot of blurred background, and f/5.6 Plasmats wide open when a lot of foreground is out of focus (if only f/5.6 is sufficient for DoF of course.... and unfortunately, it usually isn't).
Wide open, they both have a lot of overcorrected spherical aberration fine for the foreground blur. But the Dagor also has plenty of undercorrected spherical aberration; that results in much worse foreground blur with the Dagor. Also, personally I find the softness both too pronounced and also too "dirty"/"mushy" for my taste when lots of under- and overcorrected spherical aberration are present at the same time. A f/5.6 Plasmat has its undercorrected SA so much weaker that it doesn't spoil the foreground at f/5.6. And I find the character of the in-focus softness to be way better for my needs when only one type of spherical aberration is dominant.
From f/10 on, the overcorrected SA is gone in the Dagor but the undercorrected SA remains so the lens yields great background blur, and its in-focus rendition also becomes just fine for my taste. A typical Plasmat's overcorrected SA is gone from f/11 on, but the undercorrected SA that remains is too week to make the background as good as with the Dagor, and no trace of softness remains in-focus.
... Sorry I'm really not sure if anybody is interested in these longish theorizings of mine, though.
One man's Mede is another man's Persian.
Yes, a lens is corrected to a certain degree for spherical aberration and that level of correction doesn't change. All that happens when you stop down is you are masking any under-correction.
The two main things I like about the rendering of a lens that has some uncorrected spherical aberration are the diffuse glow on highlights and the smoothness and slight swirl in the oof areas.
The simple difference between an old Dagor and a modern Plasmat is the level of corrections, the modern Plasmats are more highly corrected.
A classic example of how lenses evolved in their level of corrections is the CZJ Biotar 2/58 and the Pancolar 1.8/50 that replaced it. Both are about equal in resolution but the Biotar has some uncorrected spherical aberration at large apertures which gives it glow and swirly bokeh. The main change from Biotar to Pancolar was the correction of spherical aberration and this means the rendering is more clinical without the diffuse glow and swirly bokeh. I have both lenses and prefer the Biotar due to it's character.
For me, the main reason I often chose to use an old lens rather than a more modern one is the character of the rendering, old lenses have more character because they are less highly corrected and some residual uncorrected aberration is the reason why they have more character.
Thanks a lot... I was really in a serious doubt if I should go on on the topic or not.I'm having trouble seeing how a lens can display both under- and over- corrected aberration of any type at the same time... and I really should know...
In fact, both the under- and over- correction words are somewhat slang. Its more correct to speak about negative spherical aberration (a.k.a. undercorrected) and positive (a.k.a. overcorrected) one (I guess I should chose the words better from the start. Sorry). It's called negative when the outer zones of the lens refract stronger then the center, and the rays coming through the edges of the lens are focused closer to the lens then the near-axial rays; the other way around, the SA is called positive.
Most of the actual lenses have both the positive and the negative SA. In the SA graph, that is usually shown with a line that goes left first, then bends back to the right. The branch inclined to the left illustrates the negative SA inherited in the middle parts of the lens pupil, and the brunch turning to the right is for the positive SA corresponding to the edge zones of the lens - those that are actually in use only when the lens is not stopped down at all or is stopped down very little. With the aperture restricted (to f/10 for the Dagor, to f/11 for a typical Plasmat or to about f/5.6 for a f/2.8 mf Planar for example), the outer zones are excluded, and all that remains is the negative (a.k.a. undercorrected) SA. That's true for most of the lenses - except that some have "no outer zone at all", with only the undercorrected SA left.
But the quantity of the remaining SA is obviously very different with different lenses. Some have their positive SA very weak and the negative strong, and vice versa. So some lenses are better for background blur, and others for the foreground blur.
And there is more to it. Not only the amount but also the character of the residual SA is different. The famous (and loved by myself, too) f/6.8 (or f/7.7) Dagor has its negative SA already noticeable even in the very slightly off-center zones of the pupil, and very gently growing up to f/10. That's why the Dagor's background blur is still better then that of the most other lenses even at f/32 and f/45: a small amount of SA is still present. On the contrary, a very beautiful Tessar usually has a lot of negative SA in the middle zones but almost none at the zones in use at f/22 and smaller f-stops, and so it looses all its charm if heavily stopped down. And a Plasmat as good as a f/5.6 Convertible Symmar just has that residual SA in the amounts too small to make the background blur as beautiful as a Dagor's.
.... Sorry Ian but the Biotar has little undercorrected SA. It actually has a lot of overcorrected SA. And sorry again but the Pancolar is quite different in all the other aberrations, too. And it is also much sharper (but not as free from distortion though). And stopping the Biotar down, we are masking not the undercorrection but the overcorrection.
But any swirl in the oof areas actually has nothing to do with the SA at all. The swirly pattern most easily seen with the 1.5/75 Biotar and its cousin 1.5/85 Helios-40 and Petzval's lenses and many RRs (and somewhat less with the 2/58 Biotar, a.k.a. Helios-44) is just produced by the strong vignetting in these lenses. Funny enough, the wide-open Helios-40 picture on a Zenith-B and Zenith-E is very different from a picture by the same Helios-40 on a Pentax Spotmatic because the rear lens element is so large that the camera itself adds its own vignetting! (The later Zenith models make pictures somewhat in-between the Zenith-E's and the Pentax's with this lens. And the early Kine-Exacta combined with the 1.5/75 Biotar is similar to the Zenith-E rather then to a Pentax.)
And this also results in different rendition in the far out of focus subjects at wider f-stops. At about f/11 a good Tessar may be virtually equal to the Dagor in rendering the slightly blurred near-background but it often fails to make the very distant parts of the background look as beautiful at the same time while the Dagor usually has no trouble with that. And the best of the Planars are even less suitable for the job then the Tessars.
That piece of theory corresponds with the practical results very well - at least with my own ones. Though tastes differ of course, and the looks I call good may not be liked by other people as well as those I hate may be (and often are) praised here and there....
Interesting I had never considered that an SLR camera bodies design could have such an affect upon the outcome of a photograph and a lenses rendering of a subject. I have always just considered them to be light tight boxes albeit with some of them being better at preventing non image forming light falling on to the film than others. You live and learn. Thank you Ridax. Is it because the M42 lens mount is relatively narrow?
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