6x7 back on a 4x5 Linhof Canera ==> sharper?

[pensacolaphoto]

Hi,

If I use a rollfilm back on a large format camera, am I not shooting

only through the middle part of the lens, resulting in getting

sharper images (on a medium format scale) since most lenses are

sharper in the center than in the edges? Food for thought :-)

[nicholas_t.]

Raid, yes but you have to offset the lessened negative 'real estate' of 6x7 vs 4x5 in your equation of 'what is sharper?' to balance it out.<p>

Also, using a 4x5 lens to do the work of a 6x7 lens creates a certain kind of ineffeciency as well. Lenses designed for a 6x7 (ie a 100mm Symmar vs a 150 Symmar) will have better correction all round. That is, the lens has to work less for the same amount of negative square inches.<p>

I know AA recommended a focal length up from the one used for enlarging (ie 135 for medium format, 80-90 for small format). Personally, I think if you are trying to get the most out of your lenses, using the appropriate lens for the format is the way to go.<p>

Although, all of this is within limits, there is a common practice to use, for instance, a 210mm as a standard lens for 4x5 and a 63mm enlarging lens for 35mm for the reasons exactly as you have stated. And for all intents and purposes this sounds reasonable and justified to me...

[igor_johanson]

All are true myths. What magnifications are your final prints? If 30 times, than these arguments can make sense. If 10 x they do not.

[dave_t]

OK, take a decent lens, say you get 65 lpmm with 6x7, 50 lpmm at 4x5. Make 8x10 (or whatever) prints from each. What's the on-print resolution? More food for thought ...

[kelly_flanigan1]

These are not myths; but basic optics. The best lens performance is on axis; lens performance drops when going off axis. The 127mm Kodak Ektar here from circa world war 2 of mine has an on axis resolution of 80 line pairs/mm; at a 1:10 ratio; at the far edges of a 4x5 negative; it peaks at about 17 line pairs/mm...Using lenses over a narrower field is using the better part of the lens.....This is basic stuff. One can use a 35mm Nikon F slr lens on a 16mm movies camera and get great results; the lens is using the best central core/on axis part of the lens...Long ago we used Nikon F lenses and Leica M series lenses on regular 8 and 16mm cameras; using a Nikon or Leica to C mount; and a C mount to D mount adapter for 8mm....Using the 50mm F1.4 or a 105mm F2.5 at F5.6 or F8 yields a fantastic sharp LONG telephoto lens; for 16mm or 8mm movie work.............

[nicholas_t.]

Ok, the original question guys.<br> ...Sharper?<p>

If the original thesis were true we would all be running around with Super Rollex backs on our Linhofs, or using 8x10 lenses on 4x5's instead of using medium format lenses which are designed for Rolleis, Hasseys, Konis or actual 150 Symmars for 4x5 or whatever...<p> A tautology...

[michael_briggs2]

You need to decide if you want to compare apples to apples, or apples to oranges.

 

As an example, suppose you are taking a photo with a 75 mm lens on 4x5. The 75 mm lens was selected because you as artist-photographer or your customer wants a wide-view. Let's call the wide view "apples".

 

The sharpness of the image will be not as good in the corners compared to the center. You notice this and use a 6x7 roll film back with the 75 mm (or cut away all but the center 6x7 cm of your 4x5 negative). It is true that the worst sharpness on the cut-down negative is better than the worst sharpness on the 4x5 negative. But now the amount of the scence included on the negative isn't wide -- it is about a normal view -- an "orange". The artist or the customer wanted a wide view ("apples"), so this won't do.

 

The next idea is to continue with the 6x7 roll film back, but with a 45 mm lens. The wide-view (apples) has been recovered, so now we can do an apples-to-apples comparision. Medium format lenses may be sharper than LF lenses, so let's guess that the 4x5 negative might have 30 lppm resolution, the 6x7 cm 40 lppm. Enlarging to 16x20, the print from the 4x5 will have (ignoring losses in the enlarging process) 7.5 lppm, and the print from the 6x7 cm negative 5.5 lppm.

These numbers, for the same size print with the same view of the scence, are very similar. My guessed numbers gave a small edge to the print from the 4x5 negative.

 

Other guessed numbers might make the MF print better, but the reduction in sharpness from enlarging (which I neglected) will favor the print from the larger negative -- less grain and sharpness loss from the film. In many cases both prints will be either equally sharp or both will be judged sharp enough by most observers.

[fred_de_van]

May be your thoughts need to be focused on better food... You are what you eat. Sharper?? Exactly how would a 6x7 roll film image be sharper than the same 6x7 area cut from a sheet of 4x5? This is the only way you have equal images with which to pose your question. Anything else is comparing apples and oranges.

[colin carron]

Raid,

 

As a 6x7 back on 4x5 user I know what you mean. I have put it down to my nice shiny new(ish) rfb being in better register than my assorted tatty dark slides.

[Troll]

The wavy film plane of roll film (compared to sheet film) may more than negate the advantage of using the sweet spot of your lens.

[bob_salomon]

In the 3/92 edition of ColorFoto magazine from Germany they did head to head to tests.

 

They tested Rollei 6008, Rollei SL66, Hasselblad 500, Hasselblad 205, Mamiya 6, Mamiya

C 330 Pro-S, Exacta 66, Bronica SQ AI, Mamiya RZ 67, Pentax 67, Mamiya RB, Bronica GS

1, Fuji GX 680, Linhof Super Technika V with then current Rodenstock lenses.

 

Tests were scored on resolution, distortion, contrast, vignetting, etc.

 

If you are in the U.S. we would be happy to mail or fax you a copy of the test results, If you

are not in the U.S. you can contact the magazine. The report is in German, however.

 

 

You will find that this test showed the view camera with Rodenstock lenses out performed

all of the roll film cameras (View camera used 6x7 format Super Rollex back).

[dee_seegers]

I also use 6x7 and 6x9 roll film backs on a 4x5. My reason is my current enlarger can't use negs larger than 6x9. Otherwise I would be using 4x5 negs. That being said, I found that when I shoot wide lenses on these two formats; (75mm, and 90mm, 6.8's), I don't see the light falloff as much on the smaller negs even with normal movements. To me, this is what I consider to be "using the sweet spot" of the lens. I do not have center filters. (The 90mm of course offers more room to play, but is not as wide as I usually like, Thus the 75mm.)

 

I agree with others above that the center of a given lens is going to be sharper. How much? Who knows. Also I think that the bigger the neg, the sharper the image. It's all tradeoffs in this world.

[wieslaw1]

I do not care about resolution tests. I am using top German optics and worries like �resolution� or �sharpness� are not part of my photography. Were I in microdocumentation, semiconductor business or murals-making that would be a different story. For the type of fine art photography (and print sizes between 11x14 to 16x20 inches) which I make, who cares about on axis or corner resolution? You see the impression a photograph makes, not some �mythical� lens performance, diffractions, etc., due to the laws of optics, important in technical photography or lab tests, but not in a gallery.

 

For all sharp freaks here is a fragment of a 35mm which I photographed from the WTC and magnified to over 1 meter size. Oh - it is taken near lens axis. If you want to see how the lens performs (Tele Tessar 200mm for Contax RTS) at the edge, please see the entire article posted on these pages.<div></div>

[pensacolaphoto]

I know that a 4x5 lens results in an overall "better looking" iamge due to its large size. The reason I am planning to use a 6x7 back is to avoid using film backs that are slow and can be rather annoying. I recall from years ago when I used 35mm lenses on half-frame cameras that I would get sharper images with more magnification, so I extrapolated that result to my intend in using a 6x7 back on a 4x5 camera. Maybe I am trying to convince myself that my loss will not be large! Actually, the use of a roll-film back is not that bad idea since it is far more economical and still results in rather good images compared to using 4x5 backs.

Do I need now to get a wider lens for using a 6x7 back onb my 4x5? I have a 180mm (convertible) lens and nothing else.

 

Lastly but not leastly I want to thank all of you for this interesting and informative discussion.

 

Raid

[michael_briggs2]

"Do I need now to get a wider lens for using a 6x7 back on my 4x5? I have a 180mm (convertible) lens and nothing else."

 

If you want the same view on 6x7 as you get with the 180 mm lens on 4x5, then you need a shorter focal length lens. On 4x5, 180 mm is a slightly long lens and is used by many as their "normal" lens. On 6x7 it would be a long lens. If you like the angle of view of the 180 mm on 4x5, then to get the equivalent view on 6x7 you would need a lens of about 105 mm focal length. Depending on the precise size of the formats (e.g., the gate on your roll film holder), the focal length conversion factor between the two formats is about 1.7.

[pensacolaphoto]

Thanks for the hint. I still have to take a photo with the 4x5 camera and any useful information will be made use of.<div></div>