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Mamiya TLR lens test: last time, I promise!


tim_brown

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Conditions:

Film: Tech Pan

Developer: Microphen diluted 1+5, 16 min @ 75 deg. F

Illumination: Multi strobes, max duration 1/1000 sec.

Magnification: 1:34

Lenses: All black, 55, 80, 105D, 135, 180 Super, 250

Body: C330, tripod, cable release

Finder: Beattie Intenscreen w/ split prism, chimmney shade

Target: Tilted wedge, stripes similar to USAF 1951

Neg viewer: Leitz microscope @ 100X

 

<p>

 

F-stop, center lp/mm, edge lp/mm

 

<p>

 

55mm:

4.5--45---40

5.6--50---45

8----63---45

11---71---45

16---63---45

22---45---36

 

<p>

 

80mm:

2.8--45---36

4----50---40

5.6--57---45

8----63---45

11---63---40

16---57---40

 

<p>

 

105mm:

3.5--45---45

5.6--50---50

8----63---63

11---63---63

16---57---57

22---45---45

 

<p>

 

135mm:

4.5--40---36

5.6--45---40

8----57---36

11---57---32

16---50---25

22---45---25

 

<p>

 

180mm:

4.5--80---40

5.6--90---45

8----90---45

11---80---40

16---63---40

22---57---36

 

<p>

 

250mm:

6.3--63---57

8----63---57

11---63---50

16---50---40

22---50---40

32---40---28

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Just wondering the implication of this lens test against the sharpness

of films. Nearly all films are capable of doing over 100 lpmm. Velvia

does 160 lpmm for high contrast objects. Ilforchrome paper resolves

over 60 lpmm. Yet most of your numbers are below 60. Is there any

difference in the definition of lpmm? If a MF lens resolves only

half the number of lines per mm than the film, there is hardly any

gain using MF gear against a good 35mm system except for the grain

issue.

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This test shows why MF is so much better than 35mm in medium wide to medium long focal length. Although Velvia "may" be able to resolve 160 lp/mm under high contrast condition, it is very hard to obtain even 100 under real world condition. Assume that a 50mm (in 35mm format) lens can resolve 100 lp/mm in the center, you get 24mm * 100 lp/mm = 2400lp in a landscape picture while a 80mm in MF will give you 45mm X 60 lp/mm = 2700lp (I use 8X10 as the ratio). So, at the minimum you will get more details and have 1/2 the grain size when enlarge to 8 X 10. Of course, there are a lot more than just lp/mm, contrast, color rendition and distortion are also important factors when evaluating the performance of a lens. I think 35mm format does very well in ultra wide and long tele range, but in the middle range it just can't compete with the quality of MF.
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I'm not sure why the hypothetical numbers given demonstrate the clear superiority of MF over 35mm, at least with respect to resolution. If in fact you get 2700 line of resolution with MF vs. 2400 with 35 mm, that's a pretty insignificant (12.5 percent) difference. I understand that there may be advantages other than just resolution in the final enlarged images. I certainly hope so, given the expense, weight and bulk we all suffer with by using MF gear.
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The hypothetical numbers that I use is more like the theoretical limit achievable by 35mm format versus average/low end MF setup. Even under that condition MF is still better than 35mm. In normal contrast situation one may not get even 60 lp/mm from Velvia. If you compare 35mm with more modern MF lenses, you will see that the film is usually the limiting factor in terms of resolution (unless you use Techical Pan like the poster). Hence, the larger the film size, the better the image will be.
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