And of course lens have done this but only expensive lens that needed to. Now all lens with a shot enough focal length NEED TOO. When they didn't used to need to.
ugh, the Otus ISNT a distagon it borrows from its design to elongate the lens so that the littlefinal aspherical element group can help collimate the light as it leaves the lens.
ugh, the Otus ISNT a distagon it borrows from its design to elongate the lens so that the littlefinal aspherical element group can help collimate the light as it leaves the lens.
On Wed, Mar 25, 2015 at 1:07 PM, Randy Little <randyslittle@xxxxxxxxx> wrote:
Last I checked the aperture is in the middle of the lens group so collimating the light AFTER that would be an issue why?On Wed, Mar 25, 2015 at 12:55 PM, Pablo Coronel <pablo.coronel.70@xxxxxxxxx> wrote:Interesting discussion.... from a bottom-feeder view I hae found that odl glass works as well in digital camerasIn my view a few lenses that were less than stellar in the 80s due to edge softness or vignetting, are pretty good now, since the APS-C sensors "crop" away the edges of the old lensesIf you already have the lenses give it a try..... if you are buying new ones then it maybe worth going with new and improvedWouldn;t the XE1 a 28 be more "normalish" than a 35?On Wed, Mar 25, 2015 at 12:07 PM, Randy Little <randyslittle@xxxxxxxxx> wrote:Why do you supose the Otus 55 f1.4 is using the distigon design? Cause everyone wants a bigger lens?
why do you suppose the Nikon 24-70 grew by nearly and inch in length? Same with the 16-35mm.
Not all are telecentric but most use a final Aspherical element to collimate the light. Telecentric basis for their design work better for you?On Wed, Mar 25, 2015 at 10:48 AM, Randy Little <randyslittle@xxxxxxxxx> wrote:You are wrong.Lenses in the digital era[edit]
At first glance, digital photography would seem not to affect lenses, since it is a camera technology for the capture and storage, but not the creation, of images. However, intrinsic limitations of digital image sensors have pushed lens designers toward different designs. Furthermore, electronic image processing provides an opportunity to improve lens images far beyond simply applying unsharp mask to boost sharpness.
Unlike film, silicon-based digital image sensors accept light best when it lands squarely on the sensor rather than at a grazing angle.[citation needed] For this reason, lens designs in which all the rays land squarely on the sensor, known as image-space telecentric designs, are preferred as opposed to having incoming rays emerge at the same angle they entered as in a pinhole camera. Sensors microlensescan help alleviate this, by making the optimal chief-ray angle vary across the field.
On Wed, Mar 25, 2015 at 9:33 AM, karl shah-jenner <shahjen@xxxxxxxxxxxx> wrote:
----- Original Message ----- From: "Randy Little" <randyslittle@xxxxxxxxx>
To: "PhotoForum educational network" <photoforum@xxxxxxxxxxxxx>
Sent: Tuesday, March 24, 2015 12:36 AM
Subject: Re: Use of Film-camera lenses with Digital
The image quality can suffer because the angle the light strikes the
sensor. With film it didn't really matter that the light was hitting at
angles. With a sensor when the light is hitting at a strong enough angle
it occludes it from the photosites farther out on the sensor. That being
said it really only matters with wide angle lens and there are fixes that
can be done in software to account for the falloff. You can also profile
the lens via a diffuse cap and then software. I use a 28mm Zeiss G lens
on my Nex 7 and it fringes purple like crazy but I fix it in post since the
lens is insanely awesome everywhere else.
Digital lens are telecentric in design which is why they are longer at the
same focal length. They use Aspherical elements to collimate the light so
it strikes the sensor straight or nearly straight on.
THis has been discussed here before at length..
I adhere to the principles of science, basically 'take no one's word' so I tend to test and evaluate things I hear - and telecentric lenses have some very useful properties - so I had a good look at a few and found no such thing at all.
However I keep hearing these claims, and while some marketing material from the digital dawn claimed this, later material claimed semi telecentric designs or *alluded* to collimating properties, thereby making their lenses 'special' and it made them so mystical that few bothered to even ask why they couldn't use their old lenses on these new cameras. Nowdays you do not see these claims anywhere nnear as much. However telecentric lenses behave totally differently to what we know as normal lenses and they do strage things like make subjects further away appear LARGER than closer subjects - they also have a very narrow DOF compared to 'normal' lenses, and this along with the following has led me to conclude the claim was marketing hype.
to test the claims, I stuck some Sony and Canon 'digital' lens on a board and had a look at the way the light behaved behind the lens - I found as with film lenses, it formed a projection that dropped in and out of focus exactly the same way a Canon film camera lens did. I then did my old laser trick and shone that through the lens from the back - I used this as a focus aid with large format cameras (there you go, a free tip from me) - basically you point the laser at the ground glass screen causing a very bright dot of light to form, this is projected out through the lens and .. if the lens is out of focus, it causes the light to diverge - however when the lens *is* in focus, an intense bright dot appears on the subject - a TTL laser focus aid.
'digital' lenses cause the light to diverge the same as a film camera lens does, covering the same area.
Reversing the lens and shining the light from the front of the lens,(not as a beam focusing the camera on a dot on a sheet of card in front of the camera projected by the laser) the light will again behave the same way as a film camera lens, it also diverges *unless* the lens is focused correctly on the subject, and the dot is brought into focus *at the film plane* (you can get it in focus at other distances, but this again is exactly how a film lens works and is the principle behind old Mamiya and Contax focusing - shifting the film plane and not the lens).
At no time was a digital lens able to collimate the light - at no time did any 'digital' lens behave any differently to a film lens of the same focal length..
I did of course see different film plane / sensor plane distances, just as I would see them differing between a Nikon and a Pentax, I also saw differing sized image circles just as you'd expect with differing formats (just as a 5x4 has a huge image circle compared to the lens designed for 35mm coverage). In fact I saw what appeared to be greater divergence in some lenses designed for digi-cams as they has much shallower sensor registration distances... (#1 notes on this below) for example the Sony E mount has a registration distance of a mere 18mm - the Pentax Q mount is a tiny 9.2mm - compare this to a Pentax K mount which has a whopping 45.46mm film registration distance.. the light from the old Pentax lens must be far more collimated than these tiny digital registration distances.
#1 - Of course the q mount has a sensor of 7.44 x 5.58 mm (9.3mm diagonal) while the K mount has a sensor (film size) of 36 x 24mm.. (diagonal 43mm) - but calculate the angle of divergence and it's around 60 degrees for both.. the apparently greater divergence was a presumption of mine, the calculations proved it incorrect.. but in doing so it also showed the lenses were projecting light out at near exactly the same angle - this blows away any claim of special collimating properties altogether.
As a final note near all digital sensors have micro prismic arrays atop the actual sensors - small hemispherical lenses which acto to gather the light and focus it on the sensor. Rip apart a flatbed scanner and you'll see the same thing - the sensors are small compared to the size of the flatbed but they're actually still quite large (long) - the lens which focuses the light on these sensors still has quite a wide 'angle of coverage' though .. it's the prisms over the linear sensor however that makes sure the obliquely angled light acually makes it to the sensor via additional light pipes.
Anyway, that is my take on it backed by evaluating the lenses and doing some maths, finding no special properties of digital lenses - certainly nothing even close to the properties of telecentrics - a shame really, I'd love to have a play with one of those things - they look like a lot of fun :)
The article http://en.wikipedia.org/wiki/Telecentric_lens has an unreferenced statement which contradicts all my findings, stating "Many lenses that have been specially optimized for digital SLR cameras are nearly telecentric on the image side, to avoid the vignetting and color crosstalk that occur in color filter array-based digital image sensors with oblique incident rays. The Four Thirds System uses this approach"
(were this true, there would be no need for microlenses above the sensors at all) They cite no references or examples which strikes me as odd given the number of 'digital' lenses out there in the world - the only link that is relevant also seems to contradict the above, along with a rather nice image of what telecentrics can do (the link is http://www.lhup.edu/~dsimanek/3d/telecent.htm )
the relevant bit in the article also suggests 'digital' lenses do not comply with telecentricity "Telecentric lenses tend to be larger, heavier, and more expensive than normal lenses of similar focal length and f-number. This is partly due to the extra components needed to achieve telecentricity, and partly because the object or image lens elements of an object or image-space telecentric lens must be at least as large as the largest object to be photographed or image to be formed."
Make of this what you will - trust the manufacturers statements, trust mine, or go test this yourself (something I'd strongly advocate) and see if your lenses are bigger than your subjects, whether more distant subjects are captured larger than nearer subjects, and whether you have infinite depth of field. I suspect you'll find none of these things
k
