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Seppe Van Grieken SBC

Image circle Vs. sensor. Ideally 1 vs 1 or 2 vs1?

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I am looking into large format these days. The question came from the director I'm working with at the moment - and is the following: is there anything gained from using lenses with larger image circles then your sensor?

 

I was suggesting to shoot on the Leica R lenses for various reasons - he asked about the hasselblad whitepoint lenses - presuming they are better cause they cover a 65mm imager.

 

When thinking about this I realized two different bits of information came to mind: my instinct is; the more the lens' image circle exceeds the imager's size, the less quality will be lost towards the edges of the image - lenses perform better in their center and then gradually degrade as you move away from the center.

 

I have also heard people express their believe that you should match Image Circle with imager size - the argument being that this way you get to see the lens' full image, full range (from sharp center to softer edges) "nothing is lost".

 

Is there anyone out there that has tested different IS lenses on LF/FF formats? Did you see any pattern in terms of the relation between IS and size of the imager? Is it just a matter of taste; if you want inperfections 1=1, if you want very consistent images on which the lens is consistent from edge to edge then go 2 vs 1 or even 3 vs 1 (like a 65mm lens on a 16mm sensor?)

 

Many thank!

 

Seppe

 

 

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the more the lens' image circle exceeds the imager's size, the less quality will be lost towards the edges of the image - lenses perform better in their center and then gradually degrade as you move away from the center.

This is true, but it may be at least partially offset by the fact that lenses made for larger formats tend to be less sharp. This was certainly the case in the stills world.

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I've used a Mamiya MF film lens with an adaptor on a Nikon APSC dslr. The image had a soft overall effect but was very flattering for portraits. Some times a defect can be a plus. Some DSLR FF lenses are so sharp you can see the zits and skin pores and imperfections. Only a flawless beauty with makeup and great lighting is going to look good.

Edited by Bob Speziale

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It's generally better to use a lens designed for the format you're shooting, although there are always exceptions to any rule. Some modern large format lenses might be better centre-cropped than using the full image circle of older FF 35mm lenses, but testing is probably the best way to be sure.

 

As Stuart mentioned, larger format lenses almost always resolve less detail overall than smaller format ones, because of the compromises needed to cover the larger field, and because larger formats in general require less magnification at the viewing scale so they can afford to have less resolution. They are also invariably slower at the same focal lengths.

 

In the case of Leica R lenses versus Hasselblad V-series (which I believe are what the Whitepoint rehousings use), there are MTF curves we can compare, to get a limited sense of their difference.

 

post-46614-0-44670100-1550721606_thumb.jpgpost-46614-0-24862500-1550721645_thumb.jpg

 

On the left are curves for a Hasselblad (Zeiss) CF3.5/100mm (a well regarded lens) showing 10, 20 and 40 line pairs/mm. The lowest curve is the 40 lp/mm one, with sagittal and tangential readings shown as continuous and dotted lines. The contrast stays at about 60% until around 15mm from the image centre, where tangential contrast in particular drops substantially. (The variation between sagittal and tangential readings indicates some astigmatism in the lens.)

 

On the right are MTF curves for a Leica R Elmarit 2.8/100mm, with 5, 10, 20 and 40 lp/mm graphs, the lowest again being the 40 lp/mm one. (This is often used as an indication of the fine detail rendering.) In contrast with the Hasselblad, the Leica remains at over 70% contrast until around 15mm from the image centre, and even at 20mm (an image circle therefore of 40mm), the contrast is still around the 60% level, as good as the Hasselblad ever gets. Note also that the Leica lens is at f/2.8 compared to f/3.5 for the Hasselblad.

 

So even using the central sweet spot of the Hasselblad up to a 40mm image circle, at a slower aperture, the lens acuity is not as good as the whole image area of the Leica. You could reasonably assume this to be true for other large format lenses compared with full frame ones too. But as Bob mentions, you might favour a slightly softer lens anyway. As always, the best thing is to do some testing yourself.

Edited by Dom Jaeger
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OP, you have to test the lenses at the stops you are going to use. Some lenses have to be closed down to get the edges doable. Others work pretty good wide open. Just depends. If a lens is adapted, that can make a big difference.

 

Do some tests and pixel peep the edges.

 

As far as your inquiry about using over size lenses to hit the sweet spot? Makes sense. We did it with enlarging to get the center of the lens. If you do test the lenses, send in some photos of the tests.

Edited by Daniel D. Teoli Jr.

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