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ChrisBCS
16-Aug-2014, 20:33
So my grounding is firmly in focal length/areal coverage in full and crop sensor DSLRs.

My primary lens in that realm is a fast 50 mm (f1.4), my secondary (for macro and portrait) is a 90 mm f2.8. I would love to have something even shorter for landscape

I'm trying to understand what lens it would take to get equivalent field of view of say a 35 mm on a full frame DSLR, and the 90 for portraits. Both black and white.

I recognize the need to have the image passing through the aperture project widely enough on the film sheet to prevent unwanted vignetting.

Be well!

Chris

joselsgil
16-Aug-2014, 20:53
Chris,

Click on the LF Home page at the top of the forum header. It will take you to a new screen with a lot of useful information about large format photography.

Happy reading,

Jose

Mark Sawyer
16-Aug-2014, 21:19
If you're using a 4x5, just multiply the full-frame 35mm lens focal length by 3.

3 x 50mm = 150mm. So a 50mm lens on 35mm format is the equivalent of a 150mm lens on 4x5 format.

neil poulsen
17-Aug-2014, 07:35
Not trying to be over-exact with a fuzzy concept, but I would multiply by 3.75. So a 50mm lens on 35mm translates to about a 187mm on 4x5, or about a 180mm lens. I'll explain my logic.

In arriving at a constant, people usually compare diagonals of each format. The diagonal of 35mm is about 1.8". That of 4x5 is about 6", considering that the actual dimensions of 4x5 are about 3.75"x4.75". Dividing would suggest a multiplier of close to 3.33 to convert from 35mm to 4x5.

However, you are converting from 35mm (aspect ratio of 2:3 width to length) to 4x5 (aspect ratio of 4:5 width to length). My problem with the 3.33 multiplier is that it compares two different aspect ratios. (Like, comparing apples and oranges, as they say.) So, I would compare the diagonal of only that portion of the 35mm format that makes a 4:5 aspect ratio, with the diagonal of 4x5. (Put another way, if one's going to think in terms of 4x5 in the target focal length, I would want to "think" in terms of a 4x5 aspect ratio with the smaller 35mm format.)

You can do that in this case by comparing the short sides of the two formats. Short side of 35mm is pretty close to 1". Short side of 4x5 is about 3.75". Dividing the two gives one a multiplier of 3.75. (Not true in this case, but if the target format had a longer aspect ratio, I would divide the long sides of the two formats.)

One can use any multiplier, as long as they know what that represents. The nice thing about "3" is that it's easy to remember and easy to multiply. And, maybe given the fuzzy nature of this conversion, it's good 'nuf.

But then, one really is comparing two different aspect ratios, so . . . etc., etc.

mdarnton
17-Aug-2014, 08:23
And 3.75 is closer to 4, if being simple. However, it seems to work differently in practice. I think it's better just to get a lens and use it, see what happens. In 35mm the 35mm is my least favorite. In 4x5, 135mm is my most favorite. Go figure.

And if you want to get really confused, work in portrait range with 8x10, where 1:2 is two heads height instead of two eye heights and your camera is four feet away to do that.

Ken Lee
17-Aug-2014, 09:29
The choice of 50mm as a "normal" lens on 35mm cameras is based on the diagonal of a square which encompasses the frame: a 36x36 mm square, whose diagonal is 50mm.

For 4x5 film we can take the diagonal of square which encompasses the frame, a 5-inch square - and we get 180mm.

Perhaps it is for this reason that Rodenstock brochures consider the 180mm length as normal for 4x5, and why Fujinon made their A-series lenses in lengths of 180/240/300/360 etc.

Just speculating.

Dan Fromm
17-Aug-2014, 10:39
The choice of 50mm as a "normal" lens on 35mm cameras is based on the diagonal of a square which encompasses the frame: a 36x36 mm square, whose diagonal is 50mm.

Ken, check your concepts.

The normal lens for a format has focal length equal to the format's diagonal. 24 x 36's diagonal is 43 mm. 50 mm is accepted as the normal focal length for 24 x 36 because the most influential early 35 mm camera was usually sold with a 50 mm lens. This reflects its roots in cinematography, where the normal focal length is always longer than the format's diagonal. Yes, the Leica, whose original lens was a 50 mm. Remember that the Leica project started as an exposure tester for 35 mm cine (gate 18 x 24 mm, "normal" focal length 25 mm) that should double frame 35 mm (36 x 24).

Similarly, normal for 4x5 is 150 mm, not the 180 mm you assert. I think you misquoted Rodenstock. If you go here https://skydrive.live.com/redir?resid=8D71BC33C77D1008!324 and read the Sironar brochures you'll see that Rodenstock recommends 150 mm for 4x5.

And if you go here http://www.subclub.org/fujinon/byseries.htm you'll see that Fuji's A series cover 70 degrees. A 150 would cover 4x5 perfectly well. Your reason for Fuji's choice of focal lengths for their A series is, as you said, speculation. Unsupportable, too.

Ken Lee
17-Aug-2014, 13:38
What you say about the 50mm standard having its origin in cinematography is interesting and compelling. Perhaps others have been unaware of it too.

On page 3 of this Rodenstock Analog Lenses (http://www.kenleegallery.com/pdf/2010RodenstockTraditonalLens.pdf) catalog we find the following table (emphasis added) which shows


"...focal lengths (from super wide-angle to long focal length) which have corresponding diagonal field angles and which have been rounded to standard values in comparison with very popular focal lengths for 35 mm photography."

http://www.kenleegallery.com/images/forum/RodLensLengths.jpg

They also make the following statement:


"Because the different taking formats have different 'width-to-height' ratios, the corresponding format diagonal is used as a reference value."

Dan Fromm
17-Aug-2014, 14:07
Ken, thanks for posting the link to the Rodenstock catalog. I've found it and more on Rodenstock's own site and have added a link to my list of links to lens catalogs, which can be downloaded from http://sdrv.ms/1i4czGa

With respect to normal focal lengths, Rodenstock's copywriters have slipped their moorings. Conventional "normal" focal lengths by format are 35 mm, 50 mm (real is 43 mm); 6x6, 80 mm; 6x7, 90 mm; 2x3 (6x9 in metric), 100 mm; 3 1/4 x 4 1/4, 127 mm; 4x5, 150 mm, 5x7 210 mm; and 8x10 300 mm (305, really). Compare with Rodenstock's and weep.

mdarnton
17-Aug-2014, 14:39
Yes. That chart is really strange. The 135 "normal" for 6x9 is especially weird.
The rule I remember from long ago was that normal was the diagonal, and portrait the sum of the two sides.

I think their mistake was in starting with the aberrational 50mm "normal" for 35mm. If they'd started with 75-80mm for 6x6 or some other place, their chart would have aligned itself with reality better.

I think a 35mm single frame movie "normal" lens was 25mm, which is probably where the idea of 2X that for double frame came from.