Hasselblad Historical - Focal length comparisons

'Equivalent' 35 mm format (24x36 mm) focal lengths

By Q.G. de Bakker

A very frequently asked question is one about the 35 mm format focal length equivalent of the lenses used on Hasselblad's 6x6 format.
It is often asked, perhaps because there is no single answer. The aspect ratios of 6x6 format (1:1) and 35 format (1:1.5) differ considerably, and an answer will depend on what aspect is used in the comparison.

Figure 1
Same diagonal angle of view

Diagonal

Manufactureres usually only state the diagonal angle of view of the lenses they produce. As a result, the diagonal often has to be taken as the basis for comparisons.

In Figure 1, 6x6 format (black outline) and 35 mm format (red outline) frames that have the same size diagonal are superimposed.

As Figure 1 shows, the different aspect ratios of both formats lead to a rather different framing: the 6x6 frame is taller than the 35 mm format frame, yet less wide.
A subject just fitting inside the 35 mm frame horizontally will not fit inside the 6x6 frame, and conversely, a subject just fitting inside the 6x6 frame vertically will not fit inside the 35 mm frame.

Framing in both formats is equivalent only in the rare case that subjects have to be framed diagonally. The differences in both horizontal and vertical aspects then still make it very hard, if not impossible, to crop an diagonally composed image in either format to the image produced by the other format.

Figure 2
Same vertical angle of view

Vertical

Another option would be to select lenses so that their vertical angles of view are the same (Figure 2).
The difference in aspect ratios of the two formats then shows itself in the horizontal angle of view, which is 1.5 times as large on 35 mm format as that of the equivalent lens on 6x6 format.
It obviously is very easy to crop the larger frame to produce an image exactly the same as that produced inside the smaller frame. The (vertical) equivalence is true.

Figure 3
Same horizontal angle of view

Horizontal

Conversely, when the lenses are chosen so that the horizontal angles of view are the same (Figure 3), the difference in aspect ratio leads to a 1.5 times larger vertical angle of view on 6x6 format.
Again, cropping the taller frame to produce an image exactly the same as that captured in the smaller frame is not a problem, i.e. the (horizontal) equivalence is true.

The Hasselblad focal lengths given in the table to the right are nominal. The actual focal lengths differ, not only from this nominal focal length, but also from that of other Zeiss/Hasselblad lenses having nominally the same focal length.

To keep the table simple, the choice was made to use the nominal focal lengths instead of the true focal lengths.
As a result the table only gives an approximation of the equivalent 35 mm format focal lengths.

Since the known focal lengths of 35 mm format lenses are also nominal, with their true focal lengths rarely known, an approximation will be the best a general comparison can achieve. For critical purposes, an actual test of all the lenses involved will be necessary.

6x6 format lens	35 mm format lens having the
	same horizontal angle of view	same vertical angle of view	same diagonal angle of view
38 mm	24 mm	16 mm	21 mm
40 mm	25 mm	17 mm	22 mm
50 mm	32 mm	21 mm	27 mm
60 mm	38 mm	25 mm	32 mm
80 mm	51 mm	34 mm	43 mm
100 mm	64 mm	42 mm	54 mm
105 mm	67 mm	45 mm	57 mm
110 mm	70 mm	47 mm	60 mm
120 mm	76 mm	51 mm	65 mm
135 mm	86 mm	57 mm	73 mm
150 mm	96 mm	64 mm	81 mm
180 mm	115 mm	76 mm	97 mm
250 mm	159 mm	106 mm	135 mm
300 mm	191 mm	127 mm	162 mm
350 mm	223 mm	149 mm	190 mm
500 mm	319 mm	212 mm	271 mm

Figure 4
Same horizontal angle of view

Figure 5
Same vertical angle of view

6 x 4.5 format

Ever since Hasselblad introduced a film magazine producing 16 frames in 6x4.5 format in 1956, 6x6 is not the only Hasselblad film format.

The difference in the aspect ratios of 35 mm format and 6x4.5 format is small. The 6x4.5 format is a little bit taller than the 35 mm format. Consequently, the spread in equivalent focal lengths depending on what aspect is chosen to be equal is also smaller.

Figures 4 and 5 show the difference in framing when lenses are chosen so that either the horizontal or vertical angles of view are equal (blue outline = 6x4.5 format).

6x4.5 format lens	35 mm format lens having the
	same horizontal angle of view	same vertical angle of view	same diagonal angle of view
38 mm	24 mm	22 mm	23 mm
40 mm	25 mm	23 mm	25 mm
50 mm	32 mm	29 mm	31 mm
60 mm	38 mm	34 mm	37 mm
80 mm	51 mm	46 mm	49 mm
100 mm	64 mm	57 mm	61 mm
105 mm	67 mm	60 mm	65 mm
110 mm	70 mm	63 mm	68 mm
120 mm	76 mm	69 mm	74 mm
135 mm	86 mm	77 mm	83 mm
150 mm	96 mm	86 mm	92 mm
180 mm	115 mm	103 mm	111 mm
250 mm	159 mm	143 mm	154 mm
300 mm	191 mm	171 mm	184 mm
350 mm	223 mm	200 mm	215 mm
500 mm	319 mm	286 mm	307 mm

The Hasselblad focal lengths given in the table to the left are nominal. The actual focal lengths differ, not only from this nominal focal length, but also from that of other Zeiss/Hasselblad lenses having nominally the same focal length.

4 x 4 'superslide' format

The third and last Hasselblad format to consider is the 4x4 cm 'superslide' format.
It was introduced in 1957, to produce slides that could be projected using normal 35 mm format projectors.

The aspect ratio is the same as that of the original 6x6 format, so the same considerations apply. Though being much smaller than the 6x6 format, the angles of view will be smaller too. The equivalent 35 mm format focal lengths will be longer accordingly.

4x4 format lens	35 mm format lens having the
	same horizontal angle of view	same vertical angle of view	same diagonal angle of view
38 mm	33 mm	22 mm	28 mm
40 mm	35 mm	23 mm	30 mm
50 mm	44 mm	29 mm	37 mm
60 mm	53 mm	35 mm	45 mm
80 mm	70 mm	47 mm	60 mm
100 mm	88 mm	59 mm	75 mm
105 mm	92 mm	61 mm	78 mm
110 mm	97 mm	64 mm	82 mm
120 mm	105 mm	70 mm	90 mm
135 mm	119 mm	79 mm	101 mm
150 mm	132 mm	88 mm	112 mm
180 mm	158 mm	105 mm	134 mm
250 mm	220 mm	146 mm	187 mm
300 mm	263 mm	176 mm	224 mm
350 mm	307 mm	205 mm	261 mm
500 mm	439 mm	293 mm	373 mm

Figure 6
Relative sizes of 6x6 (black), 6x4.5 (blue), superslide
(green) and 35 mm (red) formats superimposed

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