Photo # NH 69722 distance evaluation

Discussions about the history of the ship, technical details, etc.

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marty1
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Post by marty1 »

Hello Antonio:

Thanks for the summary. I should have realized I was looking at the stern of the PE just from the wake. Again -- my bad for not studying the thread a bit closer before posting.

I do have an additional question. Please see the attached image. Is the feature I have circled in yellow on the plan view the same feature on rear of the closest 20,3cm gun turret? What is this thing?

Thanks
marty

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Antonio Bonomi
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Detail

Post by Antonio Bonomi »

Ciao Marty and all,

not a problem, we all make mistakes sometimes :D

YES, but on the photo it is different than in the drawings.

The drawing shows the original plan for that piece ( short ).

The photo shows how it was on May 1941, as it was made longer with an addittional piece.
That is why it appears like that reaching the bottom of the turret.

You can notice the same thing on D turret.

More details of it you can see here in :

http://www.prinzeugen.com/PGWeapons.htm

Ciao Antonio :D
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Antonio Bonomi
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Bismarck shadow

Post by Antonio Bonomi »

Ciao all,

@ Turlock,

sorry I did not read at first your post :D

Good points well taken :D

Bismarck shadow is one of the difficulties of this photo.

I am suer you have seen the shadow comparison I have posted.

What I can tell you more is that Mr. Lagemann ( the photographer ) was standing on the upper bridge at 9 meters from the sea level with his feet, so assuming him been 1.75 meter tall the camera should have been at 9+1.6= 10.6 meters from the sea level.

Hope this helps, and lets see what you experience can add to this discussion.

Surely Bismarck hull was partially immerged on the sea on that moment and not completely showed up, as Bismarck was moving from the wake to starboard of Prinz Eugen on that moment so not perfectly in line.

Ciao Antonio :D
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Post by marty1 »

I have two more things I want to clarify regarding what we are looking at in the range estimation photo. Please see the attached image.

I want to make sure that the two reference points that I have circled in yellow and blue are the same points on each of the four images. This may be rather obvious to most folks here, but after I had mistakan stern for bow I figure I better ask before proceeding with my final range estimate.

Thanks for any help

regards
marty

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Ulrich Rudofsky
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Post by Ulrich Rudofsky »

Is this really a shadow of a machine gun and a sailor with earphones or was the lighting so poor that morning that this is actually a real MG and real person? Photo from P.K. Lagemann, "Schlachtschiff 'Bismarck' feuert die erste Salve auf den Schlachtkreuzer 'Hood' ", in: Fritz Otto Busch"s "Prinz Eugen im ersten Gefecht", 1943. [A full copy of this book is available on this web site].

http://i18.photobucket.com/albums/b138/ ... /Extra.jpg
http://i18.photobucket.com/albums/b138/ ... yscale.jpg
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Javier L.
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Post by Javier L. »

To Marty1: The reference points that you have circled are correct as I see.

To Ulrich: It is a real man and gun to the right of the photo not a shadow. Did I say shadow? :oops:
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Ulrich Rudofsky
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Post by Ulrich Rudofsky »

But there is a problem I have with this photograph. The depth of focus seems obviously not at all like the unaided human eye would see the scene. So how do you calculate and extrapolate distances that are in such an "unnatural" perspective? :lol:
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Post by marty1 »

I approached the problem from the perspective of looking through an imaginary optical range finder. The angular relationship is 1mil = 1meter at 1000meters. 6400mils = 360-degrees.

The challenge is developing an appropraite pixel to mil scale relative to the perspective of the photographer. Fortunately the various high quality plan views available from: http://www.dreadnoughtproject.org/plans ... Eugen_1940 make the scaling part possible. The vertical surfaces on the Prinz Eugene’s turrets are easy enough to develop vertical and horizontal dimensions. Combine these vertical dimensions with horizontal distances to each of the Prinz Eugenes vertical surface features – measured from the presumed Lagemann’s position. This allows you to develop the appropriate angular scale for the photo – your optical range finder specific to the presumed position of the photographer.

The problem is the level of accuracy as a function of edge fuzziness. in the Lagemann photo You are basically counting photo pixels and equating them to a vertical scale and angular scale. The level of error is fairly small for objects that are closer to the photographer’s position. But as you move “deeper” into the photo – i.e. away from the photographers presumed position -- edge fuzziness can increase the potential error. This becomes particularly acute with the smudge we are calling the Bismarck. So while the closest 20,3cm gun turret has well defined edge features, and represents a surface that is over 150 pixels in length, the Bismarck smudge is less than 30 pixels tall (depending on how you expand your working image of the Lagemann photo), and it's edges are not well defined. Moreover, you need to fix what you are calling the edge of an object within the photo. In the case of the closest 20,3cm turret to Lagemann; if your pixel count is off 2 or 3 pixels over 150-pixel total length, your range estimate from the photographer to that object is not affected very much. However with the Bismarck smudge if you define an edge that is 2 0r 3-pixels less or more than the true edge, your range estimate can be off 200-meters or 300-meters.

I used the several of the dimensions defined earlier in the thread. I assumed the Bismarck to be 33m in height, and that Lagemann is located about 16.5m from the rear corner of the closest 20,3cm gun turret (I assume this is Turret-C?). Beyond that I scaled everything from the plan views provided on the Dreadnought Web Site.

I estimate the angular height of Bismarck – as measured from Lagemann’s presumed position (and my imaginary optical range finder) – to be about 14-mils. Thats less than 1-degrees. An object with a known vertical dimension of 33-meters and an angular height of 14-mils yields a range of approximately 2400-meters.

This not to say that other estimates are not correct. As I say the Bismarck is just a smudge, and where I decided to call it’s top and bottom edge could vary by a couple of pixels from someone elses best guess. But by blowing up the smudge several hundred percent – as was done by Antonio already – you can reduce the effect that each pixel has on your final estimate of the pixel height of Bismarck.
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Antonio Bonomi
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Photo distances and more

Post by Antonio Bonomi »

Ciao all,

@ Ulrich,

I see your point, but we are assuming that this photo was taken with a Leica ( or similar ) standard 50 mm lens ( so fixed focal lenght and 45° degrees angle ) as well as all the other photos of Denmark Strait.

We are trying several photogrammetry approaches ( Bill Jurens used at least 4 different ones ).
I have used Tangent X trigonometry evaluation as well ( based on how many times Bismarck shadow fits into the Prinz Eugen visible lateral plates of C and D turrets that we know as dimensions ), than assuming same photo angle and known distances we can calculate Bismarck one.
In addittion I have worked also on simulating the negative enlarged 5 times.
Recently some others methodology have been used as you can read by Marc and Marty ( very interesting one ).

Very good to realize now is that we are closing the gaps among our evaluations between 2300 and 2500 meters, and you at first look evaluated between 2500 and 3000 meters if I recall correctly, so we are close :D .

I think we cannot pretend to reduce the gap to zero, as of course we will be always having tolerances and opinions on what we are looking at and the way we do things, but it is good to have a very close call that at least can be taken as current best estimate of this photo if we will be able to agree on a final result after our evaluations, that should be our goal and I hope everybody will agree on the approach :D

@ Marty,

I find you methodology very interesting ( like the recent one used by Marc :D ), and as said the result is very close and centered with our evaluations.

Yes that turret is the C ( Ceasar ) as you estimated at 16.5 meters.

I am very glad that my shadows comparison of Bismarck helped you on evaluating correctly the '' smudge '' of the Bismarck down there.
That in fact is one of the biggest difficulties of this evaluation and I only had that idea to realize how that '' smudge '' could be compared to the real ship profile, by putting aside a real better photo of Bismarck and compare the whole lenght and width up until I was close.

Of course similarly to Marc I can provide also to you addittional material support ( bigger scans ) of anything you may find useful to use, just write me an e-mail.

On your Blue-Yellow pic the references are all correct and you properly modified the drawing for the duct.

Your 2400 meters evaluation with this new method really impressed me, BRAVO :clap:

Keep on the good work and talk to you soon my friends.

Ciao Antonio :D
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Lets Try it Again

Post by marty1 »

I thought Marc’s estimate was 2749meters? That’s why I added the qualifiers regarding the sorts of challenges one runs up against in counting pixels when “edge fuzziness” begins to kick in. I can also get 2700meters if I assume the top and bottom edge of Bismarck are slightly different, or I assume the visible height of Bismarck is slightly different.

I’d like to give this methodology another whirl on similar type of photo. Perhaps another Bismarck and PE photo since we all probably have the the essential Prinz Eugen plans stored on our hard-drives; or PE and another ship off in the distance. Once we agree upon the photographer’s position on PE, and visible height of the “other ship” than we email our respective answers to Javier and see how close they are to each other.

I have always been interested in this subject but have never tried to work through the mechanics of the problem before. I’d like to see how repeatable answers are via the various methods each of us are using.
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Antonio Bonomi
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Distances

Post by Antonio Bonomi »

Ciao Marty and all,

well that was Marc real first evaluation ( with Bismarck been 36 meters ).

I am sure that now Marc will come out with something different ( and lower ) after the recent work he is doing.

But lets see what comes out at the end.

So far I am with a range of 2325 - 2457 meters with my trigonometry ( tg x ) evaluation of the 2 turrets.

Following my current calculations :
with C plate :

33 x 7,22 x 16,5 / 1,6 = 2457 meters

and

with D plate :

33 x 4,16 x 27,1 / 1,6 = 2325 meters

were :

33 is Bismarck heigth in meters

7,22 is the ratio between C turret plate and Bismarck shadow
( so how many times Bismarck shadow fits on C turret plate 130/18 mm )

4,16 is the ratio between D turret plate and Bismarck shadow
( so how many times Bismarck shadow fits on D turret plate 75/18 mm )

16, 5 meters is the camera distance from C turret plate

27,1 meters is the camera distance from D turrret plate
( 16,5+10,6=27,1 )

1,6 is the C or D turret lateral plate in meters
So as you can see you 2400 meters are just in the middle of them, but it can come out been 2500 or 2700 easily given the tolerances as you said.

That is why I would use right now a range 2300-2700 as current best estimate and 2500 as unique single shot current evaluation.

If you want to play with another photo just look at this one and let me know :

http://hmshood.com/cgi-bin/i/denmarkstr ... ridges.jpg

as you can see Lagemann took this photo from the platform were the 105 mm A/A gun was, so it should be ok for your evaluations.

Now I take some days off on the seaside, see you next week :D

Ciao Antonio :D
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Ulrich Rudofsky
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Post by Ulrich Rudofsky »

"Bismarck in the wake of 'Prinz Eugen' after the battle............spent cartridges of the aft turret group on the poop deck....... and at forecastle spent cartridges of the forward turret group"......... Fritz Otto Busch (1943)............... http://i18.photobucket.com/albums/b138/ ... ky/PG1.jpg
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Re: Distances

Post by marty1 »

Antonio Bonomi wrote:If you want to play with another photo just look at this one and let me know :

http://hmshood.com/cgi-bin/i/denmarkstr ... ridges.jpg

as you can see Lagemann took this photo from the platform were the 105 mm A/A gun was, so it should be ok for your evaluations.
I'll give it a whirl. My first impression is that the Bismarck is closer to the stern of PE than the previous photo we've been examining.

Unfortunately the turrets of the PE are mostly obscured or masked in this new picture. The shell casings are bit more of a challenge as a reference point as they are in random positions around the deck of the PE. Moreover it isnt as simple to figure out horizontal distances from the presumed photographers position to known reference points on the Prinz Eugen.

On the other hand the depth charge rack is a promising reference point. Anyone know how high this feature sticks up above the deck? -- 1.0meter? -- 1.5meters?
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Post by marty1 »

Hello Everyone:

I have a couple of additional questions before I make my range from PE to Bismarck estimate. Basically I wish to make sure I am looking at the same feature in each of the four photos as well as the one plan view of the PEs stern area.

First: The depth charge racks at the very stern of PE; is this same rack as shown in Photo-2? The yellow lines connect each of what I think is the depth charge rack in each of the photos I have posted. I have also shown in red where I think the depth charge rack would be located on the plan view. Does my location look about right? Lastly, I have guessed that the depth charge rack is approximately 0.8meters to 0.85m in height. Does this seem about right?

Second: The big black cylinders I have identified with blue; Are these bollards? I’d guess that these bollards (or whatever they are) are about 0.7m high. These features\bollards don’t seem to be located in the positions shown in the original plan view of PE. Were these things relocated in the final PE design?

Third: In photo-1 and photo-4 there is what appears to be a man\sailor located just to the left of 20,3cm Turret-D. Is this indeed a man – or is this something else?

Thanks again for any replies.
Marty

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Post by marty1 »

This is my take on the photographer’s position for the shell casing picture. I think he has just caught a bit of the elevation(?) wheel on the 2cm flak gun. In addition we are seeing what I think is the barrel of the 2cm flak gun.

The closest 20,3cm shell casing is a bit tricky to place. It is an important vertical scaling feature, as is the depth charge rack in my previous posted image. I need to be able to establish horizontal distance from the photographer to both the depth charge rack as well as the shell casing. I have shown in green where I think the shell casing is.

Any other opinions on where people think the depth charge rack is located on the plan view, and where the shell casing is located.

There are a couple of other features on Turret-D and the 2cm flak gun which can be used for scaling. If everything is correct regarding where I have placed the photographer – the shell case – the turret-D features and 2cm gun features, than the relative mil/pixel ratios for each feature should be about the same. This gives the angular scale relative to the photographers presumed position. I can than determine the mil height of Bismarck and subsequently back calculate the range from the photographer to the Bismarck.

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