Full Frame Convert

[orjanf]

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It seems to me that with the same lens at the same aperture, to fill a full frame you have to step closer than with a cropped which reduces the DOF.

Stepping closer with the cropped frame while substituting a wider lens to get the same field of view as the full frame camera increases DOF when compared to full frame.

 

Of course, to get the same print size with the cropped frame you have to enlarge the image more which will increase the out of focus blur so in the end there is no difference.

[AlanG]

It seems to me that with the same lens at the same aperture, to fill a full frame you have to step closer than with a cropped which reduces the DOF.

Stepping closer with the cropped frame while substituting a wider lens to get the same field of view as the full frame camera increases DOF when compared to full frame.

 

Of course, to get the same print size with the cropped frame you have to enlarge the image more which will increase the out of focus blur so in the end there is no difference.

 

I don't think it is clear to me where you are going with this. Any time you move closer you are changing perspective and dof comparisons become moot.

 

The way it works is for a given sensor size a specific focal length will give a specific angle of view. The smaller the sensor, the smaller the focal length for the same angle of view, and the greater the depth of field. That is all there is to it.

 

Depth of field needs to be calculated in the same way for all comparisons - e.g. a specific circle of confusion for a specific size print. It takes into account that images on smaller sensors must be enlarged more than images from larger sensors.

 

See this calculator:

 

Online Depth of Field Calculator

 

For instance a 28mm f2 on the M8 at 10 ft will provide 3.66 ft of dof. The Circle of confusion will be .023 to allow for the greater enlargment needed.

 

37.5mm (28*1.33 actually is 37.24) at f2 on a 5D at 10ft will provide 2.61 ft of dof. The circle of confusion will be .03. This is the M8's circle of confusion of .023 times the 1.33 crop factor.

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[SJP]

Hi Alan,

 

I think I am slowly getting there, but it has not finally gelled yet I hope you can help me here.

 

If I understand correctly the DOF is determined either by diffraction (Fourier optics) or by what the sensor can handle, where the latter usually dominates. In either case the DOF is governed only by the numerical aperture (1/NA^2 or 1/NA term repectively) so that is independent of the focal length. If we have a 50mm at f/2 on a M8 or a M2, M3, Mx etc (x<8) we get the same DOF but only a different crop of the image plane.

 

I hadn't considered the factor of print size yet in my calculations. If you crop more (ie the M8) then the extra enlargement will foul up the previous argument for resolution & DOF but not for perspective. If I understand correctly e.g. 50 mm perspective remains exactly that irrespective or sensor crop. This would explain the popularity of the 75's for portraits with M8 - nothing has actually changed in the perspective.

 

Stephen

[fotografr]

Hi Alan,

 

I think I am slowly getting there, but it has not finally gelled yet I hope you can help me here.

 

If I understand correctly the DOF is determined either by diffraction (Fourier optics) or by what the sensor can handle, where the latter usually dominates. In either case the DOF is governed only by the numerical aperture (1/NA^2 or 1/NA term repectively) so that is independent of the focal length. If we have a 50mm at f/2 on a M8 or a M2, M3, Mx etc (x<8) we get the same DOF but only a different crop of the image plane.

 

I hadn't considered the factor of print size yet in my calculations. If you crop more (ie the M8) then the extra enlargement will foul up the previous argument for resolution & DOF but not for perspective. If I understand correctly e.g. 50 mm perspective remains exactly that irrespective or sensor crop. This would explain the popularity of the 75's for portraits with M8 - nothing has actually changed in the perspective.

 

Stephen

 

If your goal is to confuse a lot of people about DOF, you probably have just succeeded.

 

Let's keep this simple: DOF is determined by a variety of factors, either together or independently. 1) Aperture. 2) Focal length of the lens. 3) Distance from the camera to the object in focus.

 

Higher mathematics is not needed to figure this out.

[ho_co]

Stephen--

Remember, perspective is determined only by standpoint, not by focal length or sensor size.

 

Suggestion: Photographic optics has excellent and simple descriptions of a lot of terms used in our metier/hobby.

 

But keep in mind that depth of field seems to work somewhat differently with digital as compared to film, as demonstrated at Digital Focusing Part One.

 

--HC

[ho_co]

... go right out and buy a range of Zeiss ZF lenses for his new machine, and report back on any differences between Zeiss and Nikon glass....

Remember that Sean Reid has directly compared the ZF and Nikkor 50/1.4's, and has separately tested the Zeiss 18/4.

[orjanf]

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I don't think it is clear to me where you are going with this. Any time you move closer you are changing perspective and dof comparisons become moot.

You are of course quite correct in this. My input was, in the context, inconsidered and irrelevant.

[ho_co]

I noticed when I was first looking at the unusually low-priced Elmarit 28/2.8 that was released at the same time as the M8, that its MTF curves all had a novel shape -- straight with remarkably high contrast values at each lpmm, and then falling off fairly rapidly at larger radii.

Erwin Puts mentions another possible adjustment in design philosophy for the Summarits at Summarit lenses, part one:

It is intriguing to note for all Summarit lenses that the behavior at apertures from f/5.6 till f/8 is different form that of the Summicron range. Where the Summicron line generally is at its top around /4 and starts to loose some definition at 5.6 and smaller, the Summarit range holds on till /8 and then losses contrast, quite visibly at /16.

--HC

[johnjs]

I have the Zeiss 25/2.8 and have just started to use it again with the D3. On the D2x I used it a lot and it exhibits the same basic performance characteristics of the ZM lenses - i.e. high micro-contrast and beautifully rendered images. On the D3 it's a true 25mm lens again as opposed to just shooting it's sweet spot and effective 38mm.

 

One thing to note with the ZF 25/2.8 is that it can be slow to focus as the ring is quite low geared. The flip side is that it can be very accurately focused close up. It is beautifully constructed too, although the extra hood is a little loose. Zeiss lens cap is horrible - badly designed, just like the ZM versions.

 

As regards the 17-55/12-24 being almost Leica quality ... they're good but lack that special Leica 'sparkle' and phenomenal rendering. I'm a huge long time Nikon system user (heck, fan ...) but unless you look at the special glass like the 28/1,4, 85/1.4 or 200-400VR, there's a big difference in image rendering quality. The 17-35, 17-55, 70-200VR & 200VR are all superb lenses also but even these draw differently than Leica M glass IMHO.

 

The ZF glass is sweet though. I'm tempted by the 100 Makro myself.

 

I've been following the conversation and thinking about this ZF thing with the D3 alot. The 50mm Planar ZF I've been using with the D200 for about a year is an amazing lens, in terms of sharpness, color and bokeh, although sometimes difficult to focus accurately at the wider apertures with the stock screen. Is the finder on the D3 good enough for precise manual focus, or will an aftermarket screen be needed? It is possible to focus the ZF glass with extra concentration and focus-bracketing. Yes, that 100mm.

 

-j

[sdai]

I have only one comment to add ... what Zeiss/Cosina has to offer between 14 and 24mm?

 

Nothing.

 

Absolutely nothing.

[guywalder]

which si which? 1st looks much more pleasing to me. My feeling is that digital has not as smooth transition from sharp to unsharp as film. My theory is that it is not so much about sensor size but more about the fact that film is thicker than a sensor surface. What do you think?

 

Thomas, the top shot is digital (200mm@f2.8) and the bottom is film (300mm@f2.8)

I dont think it has much, if anything, to do with film thickness. I think the effect is due to the differences in focal length (at least for the most part).

Actually my own experience is that the smaller the sensor, the longer the sharp to unsharp transition. That was really noticeable with the Digilux2 at wide aperture. It has a very sharp in-focus plane, but that plane was very narrow. However the transition to obviously unsharp was so wide there were large areas that fell into a no-mans-land of not really sharp, yet not really OOF.

[gwelland]

I've been following the conversation and thinking about this ZF thing with the D3 alot. The 50mm Planar ZF I've been using with the D200 for about a year is an amazing lens, in terms of sharpness, color and bokeh, although sometimes difficult to focus accurately at the wider apertures with the stock screen. Is the finder on the D3 good enough for precise manual focus, or will an aftermarket screen be needed? It is possible to focus the ZF glass with extra concentration and focus-bracketing. Yes, that 100mm.

 

-j

 

It's early days with the D3 but I've had no problems with focusing accuracy with the 25/2.8. On the D2X I had a custom KatzEye screen that had the centre focusing microlens and that was excellent and would really pop when in focus. No D3 or D300 screens available yet though.

 

I agree with the other posts about the FF advantages on rendering - my "lens memory" is returning after being distorted from 7 years of non-FF digital compensation. You live with it, but suddenly I'm finding that I can enjoy my primes again without Frankenstein DoF / effective focal length combinations.

[sdai]

The Katz screens are known to have negative effect on spot and center weighted evaluative metering, plus, the D3 has built in manual focusing assistance/confirmation ... why would you bother?

[jaapv]

Thomas, the top shot is digital (200mm@f2.8) and the bottom is film (300mm@f2.8)

I dont think it has much, if anything, to do with film thickness. I think the effect is due to the differences in focal length (at least for the most part).

Actually my own experience is that the smaller the sensor, the longer the sharp to unsharp transition. That was really noticeable with the Digilux2 at wide aperture. It has a very sharp in-focus plane, but that plane was very narrow. However the transition to obviously unsharp was so wide there were large areas that fell into a no-mans-land of not really sharp, yet not really OOF.

 

Thomas is right about the differences between film and sensors; film has a thickness of between 1/2 and 1 CoC (Circle of Confusion) which means that projecting a dot onto a infinitely thin sensor surface is essentially different from doing so into the semi-opaque film layer, which will diffuse and reflect the light. Compare it to shining a torch into a murky bowl of soup. Also this will elongate the CoC's towards the corners of the image into ellipses. All this makes for a less defined sharp/unsharp transition on film, as opposed to the harsher DOF transition on a sensor.

[Shootist]

The Katz screens are known to have negative effect on spot and center weighted evaluative metering, plus, the D3 has built in manual focusing assistance/confirmation ... why would you bother?

I have no idea about the D3/D300 but on my D200 when I use a MF 55mm Macro Nikkor and use the in focus light conformation that lights up when the camera "THINKS" the lens is properly focuses and take a shot it is ALWAYS out of focus. If I then just use my eye to judge the focus it is in better focus. With AF D or S lenses and MF with conformation light the camera focuses correctly. I'm not sure if it is becasue of the focus shift of the MF lens when stopped down that is causing this but with AF lenses the camera is compensating for focus shift or what. I have a Cats Eye but removed it and put the original back in for verious reasons.

[gwelland]

The Katz screens are known to have negative effect on spot and center weighted evaluative metering, plus, the D3 has built in manual focusing assistance/confirmation ... why would you bother?

 

This time around I'm not sure I'll bother. As regards metering - it never was a problem with the D2x (within a 1/3 on spot, no difference on matrix)' but the split lens definitely was an improvement over a matte screen/focus indicator.

 

The auto focus in my M8 has never worked though ...

[sdai]

I have no idea about the D3/D300 but on my D200 when I use a MF 55mm Macro Nikkor and use the in focus light conformation that lights up when the camera "THINKS" the lens is properly focuses and take a shot it is ALWAYS out of focus.

 

I don't remember it now but this is probably because the old D200 doesn't have a 55mm focal length for you to choose from the menu so you could only match it to the closest thing. With the D3/D300 you can specifically choose 55mm and f/2.8 from the menu so it won't be a hit or miss.

[sdai]

This time around I'm not sure I'll bother.

 

I've no ZF lenses ... never even saw one actually

 

But I've got a handful of non-CPU pre-Ai lenses nobody wants to pay a dime for and tried them all in my standard "ruler tests" ... everything is spot on (with in camera focus confirmation).

[Shootist]

I don't remember it now but this is probably because the old D200 doesn't have a 55mm focal length for you to choose from the menu so you could only match it to the closest thing. With the D3/D300 you can specifically choose 55mm and f/2.8 from the menu so it won't be a hit or miss.

No the D200, at least mine, is set to 55mm f/2.8 in the custom menu.

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[terrycioni]

I have no idea about the D3/D300 but on my D200 when I use a MF 55mm Macro Nikkor and use the in focus light conformation that lights up when the camera "THINKS" the lens is properly focuses and take a shot it is ALWAYS out of focus. If I then just use my eye to judge the focus it is in better focus. With AF D or S lenses and MF with conformation light the camera focuses correctly. I'm not sure if it is becasue of the focus shift of the MF lens when stopped down that is causing this but with AF lenses the camera is compensating for focus shift or what. I have a Cats Eye but removed it and put the original back in for verious reasons.

 

Ed, you might want to have the checked-out by Nikon.

 

Best Regards. Terry.