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Lens Image Circle ?


colinbm

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I am looking at the question of 'Lens Image Circle' ?

Is there a way to know what a Lens' Image Circle is ?

Obviously, when you buy a lens for a camera system you know that the Lens' Image Circle, will cover the cameras sensor or film format.

But if you want to use non-standard lenses on your camera, is it a gamble you take that it may or may not cover your sensor ?

Col

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The native format the lens is intended for will give you a useful clue. The lens ought to cover a circle the diametre of which is at least the diagonal of that format.

 

Thus, be aware that most if not all C-mount lenses will not fully cover the m43 frame.

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Thanks Bjorn

The C mount example is only one area of interest. I have one, C mount, that covers the m4/3 sensor & I was wondering what others may cover the m4/3 sensor.

The other area of interest is for tilt / shift on the m4/3 sensor too. It would appear to me that there is a limit to the movement of a tilt / shift lens, & that is, half the m4/3 sensor size, about 10mm ?

Col

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The maximum tilt/shift movement has more to do with mechanical construction than image size as such. Thus, if you imagine having unlimited movement (an approximation would be a view camera with ultrawide-angle bellows and fitted with a lens able to cover many times the image circle required for the actual format), max. shift could be very large and might even exceed the frame size if no obscuration intervened, whereas max. tilt would be
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enricosavazzi

Just as additional information, the illumination circle (i.e. the area on the focal plane illuminated by light passing through a lens) can be larger than the image circle (where the lens projects an image of reasonably good resolution and image quality). If you don't really mind image quality in the corners, you may get away with a lens that projects a larger illumination circle than its image circle, because illuminated but blurry image corners, at least at first sight, don't look as bad as black image corners.

 

A well-designed lens usually has an illumination circle barely wider than its image circle. This is because light from the unused portion of the illumination circle can scatter inside the camera and cause flare and reduced contrast.

 

Tilt-shift lenses must of course be designed with an image circle much wider than the sensor. This is necessary to allow certain combinations of tilt and shift, e.g. shift left and tilt right, which both move the center of the image circle away from the sensor center and in the same direction. Other combinations, e.g. shift left and tilt left, which move the center of the image circle in opposite directions on the sensor, sort of cancel each other out with respect to the need for a large image circle. They do not cancel out with respect to perspective rendering and inclination of the plane of focus, which are of different types for tilt and shift, respectively.

 

In practice, an ordinary (non-tilt-shift) lens designed for APS-C should allow you enough tilt and shift to work well in a tilt-shift adapter on a Micro 4/3 camera. A lens designed for the 35 mm (= "full-frame") format also works, but is a bit of an overkill and illuminates so much of the Micro 4/3 camera interior and of the Micro 4/3 adapter interior, especially with extreme amounts of tilt and shift, that one might start worrying about internal flare. Adding some flocking inside the adapter, if it is not properly light-absorbing, might be a good idea.

 

Another thing to consider is that most tilt-shift lenses and tilt-shift lens adapters allow tilt only in a plane perpendicular to the shift plane. This is somewhat less versatile than the complete freedom of tilt and shift afforded by a large-format studio camera.

 

If you can live with a moderate loss of image resolution, you can get exactly the same geometric results as shift in post-processing by deforming the image. You cannot instead achieve the exact effects of tilt with post-processing. Some photographers roughly fake these effects in post-processing by selectively blurring parts of the image in landscape photography, but this is not the same thing. So tilt is the one camera movement you really need, while shift in the same plane is handy but not equally indispensable if you have a sufficiently large image circle.

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Thanks Enrico for the very detailed explanation :D

I'll get an m4/3 tilt adapter soon & have some fun with it.

Cheers

Col

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Thanks Enrico

I have no OM lenses & I haven't seen any M42 tilt adapters for m4/3 cameras. I have seen the Canon tilt adapter for m4/3, & Canon has the same FFD as the Sigma SA mount, so that is probably the way I will lean & convert the Canon tilt adapter for m4/3 to Sigma SA mount. That is do-able for me.

Col

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Colin,

Some bellows have tilt/shift movements and the EL Nikkors many of us are familiar with have relatively large image circles in the longer focal lengths as they were made for larger format negatives. Perhaps this might be an affordable avenue to explore if you already have one of those lenses.

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enricosavazzi

I tried tilt-shift bellows and even made some custom ones. However, the main problem with commercial ones is that they get very stiff at low bellows extensions, which allows very limited tilt and shift and essentially negates their usefulness. Commercial tilt-shift bellows can be quite expensive, too.

 

http://savazzi.net/photography/tiltshiftbellows.htm

http://savazzi.net/photography/oddbellows.htm

 

I think for experimenting a cheap tilt adapter is the most reasonable solution, especially with mirrorless cameras and legacy SLR/DSLR lenses.

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Have you tried a double- or triple-layered black plastic bag ? The superwide-angle bellows "pouch" essentially is a superexpensive version in leather or leatherlike material.
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enricosavazzi

Have you tried a double- or triple-layered black plastic bag ? The superwide-angle bellows "pouch" essentially is a superexpensive version in leather or leatherlike material.

I made the one at the second link in my previous post from a synthetic leather pouch that came for free with some filter ring or adapter from China I bought on eBay.

 

Years ago I even bought a large-format Sinar with both long and bag bellows, which was the inspiration for building my freebie short bellows. It was already after the digital revolution, so it cost only a small fraction of the original price. All very nice and memorable experiments, although not very productive in terms of practical results. But of course we don't usually do these things for the purpose of achieving practical results in our day-to-day photography. I don't, at any rate, after reaching the insight that experimenting for the sake of it has a far higher intrinsic value than actually using these improbable contraptions.

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Col,

 

Do I recall correctly that you had transplanted a reasonably UV capable lens from an old folding camera of some type?

 

I don't know much about those old cameras but many of them used larger format film. If so then the image circle of that lens at INF would have to cover that format.

 

That could be a relatively large image circle and many times larger than your G3 µ4/3 sensor or APS-C or even a 35mm frame for that matter.

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Years ago I tried an old B&L Tessar from a large format camera. I couldn't get good results due to the haze of the glass, IIRC, not the image size. I do use some triplet lenses from Reflex Korelles with no issues on my GF1, even though the Korelle film format is 60 x 60mm.

 

If you use black plastic, be sure that it is NIR opaque. Some black plastic is transparent to NIR. Just a thought.

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enricosavazzi

If you use black plastic, be sure that it is NIR opaque. Some black plastic is transparent to NIR. Just a thought.

That is a real concern. Even some cheap bellows are made of material that transmits enough NIR to fog UV pictures.

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Yes, John, you are correct, I have a, Scheinder-Kreuznach Radionar f2.9 / 80mm lens, from an older folder, Franka Solida II MF camera.

I could adapt this to a m4/3 tilt mount adapter, no problem, & I should, but I was thinking of something with a bit wider angle of view.

Col

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Hi, hi colin!

 

The 28mm is a very useful focal length for tilted use on my APS-C cams in my opinion. MFT is similar to that. I already made 2 modifications on that lenses.

 

One is a 28mm f2.8 branded as "Porst" a former supplier for photo equipment. It was equipped with Fuji's FX bajonet before, now it is on a PK mount.

 

The other is a "Revue" branded lens 28mm f2.8 from the former german mail order house "Versandhaus Quelle". It was M42 and the modified adapter ring to PK even allows to rotate the lens to change tilt direction.

 

On both lenses I had to shorten aperture setting ring and the barrel to keep the PK flange focus distance.

 

Some of the samples show how the tilt can even be used to decrease the virtual DOF. In my opinion the most beautiful effect.

 

baffe

 

http://up.picr.de/22119739ma.jpg

 

http://up.picr.de/22119740ox.jpg

 

http://up.picr.de/22119741od.jpg

 

http://up.picr.de/22119742ht.jpg

 

http://up.picr.de/22119743zs.jpg

 

http://up.picr.de/22119744wr.jpg

 

http://up.picr.de/22119745kh.jpg

 

http://up.picr.de/22119746yg.jpg

 

http://up.picr.de/22119747yh.jpg

 

http://up.picr.de/22119748dq.jpg

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Thanks for this Steffan, this looks very interesting.

I'll have to get into looking at some of my M42 lenses & adapting them onto a m4/3 tilt adapter........via an other adapter ;)

Col

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I'm dreaming of a Carl Zeiss/Hasselblad Distagon (50 or 35mm) onto EOS 24x36mm Chip...

 

The 80mm 2.8 Planar CZ/HaBla performs very well but focal length (for tilted use) is too big i my opinion.

 

Both lenses have "big circles" but are proarbly not woking in uv. (I never tested)

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  • 2 weeks later...

Thanks & quite interesting Enrico

So all Nikon lenses are still manual aperture adjustment ?

Obviously that makes Nikon lenses, ideal for adapting to other formats.

Col

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enricosavazzi

Thanks & quite interesting Enrico

So all Nikon lenses are still manual aperture adjustment ?

Obviously that makes Nikon lenses, ideal for adapting to other formats.

Col

As far as I remember (I left Nikon for Micro 4/3 over two years ago), there are four ways Nikon cameras control the lens aperture. Not all cameras allow all ways, nor all lenses. There are variations within each category.

- Aperture is only operated manually via an aperture ring on the lens. There may be mechanical couplings to send the aperture information to the camera, but the camera cannot actively change the aperture. Some cameras cannot meter with these lenses. Third-party tilt-shift lenses, and possibly some older shift or tilt-shift Nikon lenses, fall into this category.

- There is a mechanical lever in the lens mount for the camera to close the aperture, and an aperture ring. This is not just a way to close the aperture to the manually set value. The camera can set the aperture value via the lever if the aperture ring is set to fully closed. Alternatively, the user can manually control the aperture via the aperture ring. Some cameras cannot meter in the latter case.

- There is a mechanical lever but no aperture ring. The user can manually control the aperture via the camera or (roughly and approximatively) via an adapter that varies the amount of travel of the lever. Without anything to operate the lever, e.g. with an ordinary Micro 4/3 adapter, the aperture remains fully closed (usually f/22 or f/32, which is beyond usability).

- There is no mechanical lever, and the aperture is only controlled with electronic signals sent by the camera through the electrical contacts of the lens. If I remember correctly, some tilt-shift Nikon lenses work in this way.

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