Brownie Camera: focal length?

Alex_L · Jun 2, 2014

Greetings to all members of this amazing Forum.

Currently, I am conducting a research into some old photographs alleged to have been taken by a 'Kodak (UK) box camera' in 1934. Although I cannot be certain which type of camera was used, I assume that it was one of the following three models:

- No 2 Brownie Junior

- Six-20 Brownie Junior

- Six-20 Brownie Model 4

Now, I was wondering if you could help me in identifying what was the focal length of the lens used in these models (I understand that most models had simple meniscus, fixed lenses)? This datum seems to elude me despite my many inquiries with professional photographers and searches on the internet. I find it quite odd that none of the manuals from the period, nor specialized websites provide this information. Usually, the only 'specification' available regarding the lens is that it is 'meniscus'.

I would be very grateful if you could advise me on this particular matter.

Thankfully,
Alex
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removed account4 · Jun 2, 2014

if it is any help...

some of the hawkeye's had 30mm lenses
and that might have been 127mm film.
my guess is that whatever the the box camera was
the focal length was "medium wide angle"
yes,very vague, but maybe not too far off

good luck !
john

Alex_L · Jun 2, 2014

Thank you jnanian.

Yes, I agree that box cameras had 'medium wide angle'. In fact, the landscape in the 1934 photographs I'm investigating does suggest a smaller or medium focal length lens was used. However, while researching the subject I came upon some (seemingly) confusing data. For example, No.2 box Brownie is stated as having a 105 mm lens! But wouldn't such focal length have 'telephoto properties'? Unless, of course, we take into account that a 6 x 9 mm film was used in which case a corresponding equivalent to a 35 mm film would be a 45 mm focal length.

In other words, does a 105 mm fl in a box camera using 6 x 9 mm film equals to a 45 mm fl for a camera using 35 mm film?

MattKing · Jun 2, 2014

Alex_L said:
Thank you jnanian.

Yes, I agree that box cameras had 'medium wide angle'. In fact, the landscape in the 1934 photographs I'm investigating does suggest a smaller or medium focal length lens was used. However, while researching the subject I came upon some (seemingly) confusing data. For example, No.2 box Brownie is stated as having a 105 mm lens! But wouldn't such focal length have 'telephoto properties'? Unless, of course, we take into account that a 6 x 9 mm film was used in which case a corresponding equivalent to a 35 mm film would be a 45 mm focal length.

In other words, does a 105 mm fl in a box camera using 6 x 9 mm film equals to a 45 mm fl for a camera using 35 mm film?

"Telephoto" actually means a lens that is physically smaller than its focal length - used most often to permit a longer focal length in a smaller construction.

A "standard" focal length is usually equal to the diagonal (approximately) of the film format.

Using modern 35mm film (24mm x 36mm) as an example, 45 mm is approximately standard.

So a camera that creates 6cm x 9cm negatives (note cm, not mm) would have a "standard" lens that was about 10.5 mm in focal length.

pdeeh · Jun 2, 2014

surely 10.5cm (note cm, not mm)

Alex_L · Jun 2, 2014

Thanks for correcting me Matt. I did mean to denote cm instead of mm for 6 x 9 film size.

You said:

'So a camera that creates 6cm x 9cm negatives (note cm, not mm) would have a "standard" lens that was about 10.5 mm in focal length.'

You meant 105 mm (or 10.5 cm), right?

Two23 · Jun 2, 2014

I am a Brownie collector. Their lens seems to be 35mm equiv. to something between 45-50mm. I.e., "normal" lens. Since they are fixed focus, couldn't you simply measure from the lens to the plane of the film?

Kent in SD

Alex_L · Jun 2, 2014

Two23 said:
Since they are fixed focus, couldn't you simply measure from the lens to the plane of the film?

Hi Kent,

Well, no, because I don't have the actual cameras! In my initial post I described I only have photographs from 1934 and the assumption they were made by one of the three models I referred to!

Hence the reason why I'm asking for the information on this forum.

Furthermore, I do have a Zeis Ikon (Box Tengor 54/2 model from 1938) and I did some preliminary measurements using two methods:

(1) I measured the lens to the plane of the film. The result is 105 mm.

(2) I measured the smallest aperture (f/22) which seems to be almost 3 mm. This would make the focal length about 65 mm.

So, which is it then, 105 or 65 mm?

Which method of measuring the focal length is a correct one?

tony lockerbie · Jun 2, 2014

You can be sure that if they are 6x9 negatives, then the lens would be close to 100mm (or 10cm!) and the others guess of around 105mm would seem correct.

tony lockerbie · Jun 2, 2014

Just saw your new post, and with that simple lens your first method of measuring is correct.

Alex_L · Jun 2, 2014

Hi Tony,

The matter complicates even further, it seems. Namely, from which point on the lens should I measure the distance to the film plane? If I use the point on the outer side of the lens (i.e. the part outside of camera), I get roughly 100 mm. However, if I measure from the inner side of the lens (i.e. inside of camera) then I get about 85 mm!

Which reference point should be used?

Jim Jones · Jun 2, 2014

A diagram in Rudolf Kingslake's Lenses in Photography suggests that the focal length of a meniscus lens with the concave side and aperture away from the film is measured from slightly behind the lens.

summicron1 · Jun 2, 2014

Alex_L said:
Hi Kent,

So, which is it then, 105 or 65 mm?

Which method of measuring the focal length is a correct one?

These are simple miniscus lenses, no magnification or anything.Questions of where on the lens to measure are complicating things. This is a one-element lens system, the lens is about 1 mm thick, at least on mine. I can't see whether it makes any difference where you start.

No, you would not measure from where the lens diaphram (f-stop thingy) is located. Focal length is measure from the center of the optical system, wherever that is. In this case, it is the lens.

I have here before me an Agfa Synchro Box, allowing for the thickness of the back, it is about 105mm (10.5 cm) from the rear to the lens.

On a 6 by 9 format, that's a moderate wide angle, about 35mm in a 35mm film camera equivalent, exactly the same as on my Baby Crown Graphic.

Alex_L · Jun 2, 2014

Summicron1,

You missed the point. Ruler is useless if one doesn't have an actual camera to measure it! I don't have the cameras of the models I specified (i.e. - No 2 Brownie Junior, - Six-20 Brownie Junior and - Six-20 Brownie Model 4).

I do have Zeis Ikon Box Tengor, though, which is not the same thing.

I don't think you are right when you say that 'on a 6 by 9 [cm] format' the focal length is '35 mm in a 35 mm film camera equivalent'. The equivalent for a 6 x 9 cm format 105 mm focal length is actually 45 mm focal length in a 35 mm film!

shutterfinger · Jun 2, 2014

About Lens by Eastman Kodak Co., 1921 http://www.cameraeccentric.com/html/info/kodak_5.html on page 14 shows a #0 Brownie to have a depth of field from 10 1/2 feet to infinity, a #2 Brownie 14 ft. to infinity, a #2A, #2C, and #3 Brownie 15 ft. to infinity. On page 31 depth of field table it states "fixed focus cameras are focused on 25 feet.
Now using an older version of fCalc in DOF mode a focused distance of 25 feet that gives a DOF of 10.5 feet to inf @f8 is 52.5mm; 14 ft to inf @f8 is 70mm; 15 ft. to inf is 75mm on 6cm x 9cm format.

http://www.brownie-camera.com/ technical data shows the #2 and #3 box cameras to use f11 to f22 lens and when focused at 25 feet one gets some non common focal lengths to fit the close focus distances to infinity DOF focus range listed for the Brownie cameras.

MattKing · Jun 3, 2014

pdeeh said:
surely 10.5cm (note cm, not mm)

Surely, you are correct sir!

Alex_L · Jun 3, 2014

shutterfinger said:
About Lens by Eastman Kodak Co., 1921 http://www.cameraeccentric.com/html/info/kodak_5.html on page 14 shows a #0 Brownie to have a depth of field from 10 1/2 feet to infinity, a #2 Brownie 14 ft. to infinity, a #2A, #2C, and #3 Brownie 15 ft. to infinity. On page 31 depth of field table it states "fixed focus cameras are focused on 25 feet.
Now using an older version of fCalc in DOF mode a focused distance of 25 feet that gives a DOF of 10.5 feet to inf @f8 is 52.5mm; 14 ft to inf @f8 is 70mm; 15 ft. to inf is 75mm on 6cm x 9cm format.

http://www.brownie-camera.com/ technical data shows the #2 and #3 box cameras to use f11 to f22 lens and when focused at 25 feet one gets some non common focal lengths to fit the close focus distances to infinity DOF focus range listed for the Brownie cameras.

Thank you Shutterfinger for your useful input!
If we assume the models I referred to are foused at 25 ft, and that they are set at f/11, then can we conclude that the lens focal length of such a camera is somewhere in the range between 70 and 75 mm on 6 x 9 cm film (perhaps 72 mm)?
The focal length of 72 mm on a 6 x 9 cm format would correspond to a 31 mm on a 35 mm film.

Until you referred me to the publication by Eastman Kodak from 1921, I was almost certain that the models of camera I am considering in my investigation had 105 mm focal length lens. However, I now have doubts.

See for example this link: http://www.mhs.ox.ac.uk/cameras/item36.htm
That particular model had a 105 mm fl!

shutterfinger · Jun 3, 2014

If there are any objects/people in the photos that are a known height then their size could be used to calculate other dimensions in the photo which will aid in the focal length determination.
The camera you linked to shows a 105mm f18 lens, another non standard lens measurement.

At f11 a 83mm lens has a dof of 14 ft. to 110 ft., angle of view 56.93° vertical, 39.74° horizontal, 66.18° diagonal.
At f16 a 98mm lens has a dof of 14 ft. to 115 ft., angle of view 49.33° vertical, 34.04° horizontal, 57.79° diagonal.
At f22 a 117mm lens has a dof of 14 ft. to 111 ft., angle of view 42.08° vertical, 28.76 horizontal, 49.62° diagonal.

Stated values in the published texts are likely the base standard from which deviations were used to achieve a desired prospective.

A 105mm f18 focused at 25 feet has a dof of 14.14 ft. to 107.35 ft, angle of view 46.4° vertical, 31.89° horizontal, 54.5° diagonal.

The dof and angle of view in the photos are your best clues outside of finding the actual tech data for the camera used.

Also see: http://www.brownie.camera/

Alex_L · Jun 3, 2014

Thanks again for the further information you supplied, Shutterfinger.

You suggested I should use people or objects of known size depicted in the photograph to work through the focal length. But that's just it! There are no people or known objects in the photograph, just a distant background landscape and an expanse of water.

In fact, I'm trying to find out the focal length in order to determine distances and sizes contained in the photograph (a reverse process to the one you proposed). However, I never knew it would be so difficult to get a hold of such technical data for Brownies as the focal length.

For what is worth, The photographs' dimensions are 16.7 cm x 23.7 cm.

shutterfinger · Jun 3, 2014

The "other" key information you need is
Is this a contact print? Contact print=original negative size. Your measurements say NO.
If not a contact print what is the degree of enlargement to fit the existing print?
What is the crop factor, if any?
http://en.wikipedia.org/wiki/Film_format

You may have to buy a few old Brownies and optically measure their lens to find a suitable answer.

Denverdad · Jun 4, 2014

I wish I had the cameras in question - if I did, I would just measure for you and find out! But in all likelihood the focal length for each is somewhere right around the 100mm or 105mm figure many have been suggesting. My experience with medium format boxes and other simple roll film cameras is that this is typical for 6x9, and that relatively few of the genre have focal lengths significantly shorter. Unless these cameras are exceptions in that regard, calculating FOV and object dimensions based on the 105mm figure will most likely be within 5% or so of the true answer. Edit: This is also assuming that the photos are uncropped images (as I think Shutterfinger pointed out). If you have reason to believe that they are cropped, then there is little you can say with certainty.

For reference, your first method of measuring the focal length of your Tengor was correct (as Tony said). There are a couple reasons why the second method will give you a different result, but I will leave that explanation to complicate another discussion. For whatever it is worth, I happen to have measured my own 56/2 Tengor a while back and came up with a focal length of 102mm, with an uncertainty of -3mm to +5mm (no clue at this point how I derived those uncertainty values though!).

Good luck with our quest. Sounds like an interesting project!

Jeff

Alex_L · Jun 4, 2014

shutterfinger said:
The "other" key information you need is
Is this a contact print?

Your are correct at pointing out that these are not contact prints, but rather enlargements printed on one of the standardised photo-paper of the day (approx. 17 cm x 24 cm).
I will employ several methods of analysing the photographs, making certain assumptions along the way and will then cross-reference the results to see what can be concluded.
In addition, one of the photographs does show a part of what looks like a telegraph pole. I'll try to work out fl from the data assigned to this particular object.
Anyway, I appreciate your feedback very much.

Alex_L · Jun 4, 2014

Denverdad said:
I wish I had the cameras in question - if I did, I would just measure for you and find out! But in all likelihood the focal length for each is somewhere right around the 100mm or 105mm figure many have been suggesting. My experience with medium format boxes and other simple roll film cameras is that this is typical for 6x9, and that relatively few of the genre have focal lengths significantly shorter. Unless these cameras are exceptions in that regard, calculating FOV and object dimensions based on the 105mm figure will most likely be within 5% or so of the true answer. Edit: This is also assuming that the photos are uncropped images (as I think Shutterfinger pointed out). If you have reason to believe that they are cropped, then there is little you can say with certainty.

For reference, your first method of measuring the focal length of your Tengor was correct (as Tony said). There are a couple reasons why the second method will give you a different result, but I will leave that explanation to complicate another discussion. For whatever it is worth, I happen to have measured my own 56/2 Tengor a while back and came up with a focal length of 102mm, with an uncertainty of -3mm to +5mm (no clue at this point how I derived those uncertainty values though!).

Good luck with our quest. Sounds like an interesting project!

Jeff

Thank you for your positive feedback and encouragement, Denverdad. I don't think much cropping has been done, perhaps 2 mm on the sides. I base this assumption on the fact that I have other photographs in my collection which were made from 6 x 9 cm negatives in the smaller standardized prints by a professional photographer under my supervision. No cropping occurred during enlargement process and yet the ratio is almost the same as in the prints that I'm currently analyzing.

It is very interesting to hear about your measurements of 56/2 Tengor's focal length. I'm now quite curious to learn more about the cause of your uncertainty regarding the margin of error of -2 to +5 mm? I am asking this because I too had difficulties in measuring my Tengor. To be honest, I haven't used proper measuring tools, just an ordinary ruler. I'll have to repeat the exercise using dividers, small scale rulers, etc.
I'll report about the results here.

Best wishes.

wombat2go · Jun 4, 2014

The original Brownie was a 2.25 by 2.25 inch frame and there are drawings of it in US patent 725,034 of year 1900.
The plan (Fig 3) and elevation (Fig 4) sections are detailed but not dimensioned, I think there is a high probability the aspect ratio scaling is preserved.

Both frame dimensions (Item 24) were set to 2.25 inch on the monitor, and the distance from the film to the front of the meniscus (Item 6) was measured . It is about 3.875 inch (1.72 times 2.25 inch)
That is about 98.3mm. If the lens is focused at 15 ft, by 1/f=1/v-1/u
the focal length (of the lens) would be approximately 96.2 mm
(4 inch is 101.6 mm, and the above estimation could be in error by up to 6 mm or so)

I was not able to find section drawings of the 2 Brownie or the 6-20.

Denverdad · Jun 6, 2014

wombat2go said:
The original Brownie was a 2.25 by 2.25 inch frame and there are drawings of it in US patent 725,034 of year 1900.
The plan (Fig 3) and elevation (Fig 4) sections are detailed but not dimensioned, I think there is a high probability the aspect ratio scaling is preserved.

Both frame dimensions (Item 24) were set to 2.25 inch on the monitor, and the distance from the film to the front of the meniscus (Item 6) was measured . It is about 3.875 inch (1.72 times 2.25 inch)
That is about 98.3mm. If the lens is focused at 15 ft, by 1/f=1/v-1/u
the focal length (of the lens) would be approximately 96.2 mm
(4 inch is 101.6 mm, and the above estimation could be in error by up to 6 mm or so)

I was not able to find section drawings of the 2 Brownie or the 6-20.

So I'm not the only one who measures dimensions off of a monitor? It probably looks a little funny to see me holding a ruler up to the screen, but hey it works!

But I think your method of getting the dimension from the patent drawing is perfeclty fine and should be pretty accurate too. For reference, I think Jim Jones has it right as to where the principle plane is located for a simple meniscus lens (i.e., where from to measure the focal length). This Wikipedia page about cardinal points and principle planes in optics also has a drawing for a meniscus lens. The exact location may depend on the focal length, curvature of the two sides, glass index etc., but I think if you just assume the vertex of the convex side you should be within a millimeter, maybe two at most.

As for uncertainty of my focal length measurement with the Tengor, it is partly due to lack of knowledge of the principle plane locations on that lens since it is actually a cemented doublet meniscus, not a single element lens. And then too, there is just plain old measurement uncertainty due to the fact that it is difficult to get measuring implements into the camera where they need to be to make the measurements.

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