BEOON - enlarger lenses to avoid / recommended (Open thread - please add your experience for benefit of others)

[Steve Ricoh]

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Thanks once again, Pop, you are a real star!!

I will do as suggested, but to put all this into context I must study the relevant optical laws, otherwise I'm just following instructions. Even though I'm disappointed with my BEOON and sometimes wish I hadn't bothered, I'm actually learning quite a bit along the way, so really my financial outlay on the BEOON and 2 enlarger lenses (not including the light-pad since that's required irrespective of camera scanning) can be classed as the cost of education.

[pop]

There are only two equations involved in this particular business.

 

The first describes how the distance of the lens to both the object and the image depends on the focal length:

 

(1)  1/B + 1/G = 1/F

 

where:

B is the distance between lens and image (sensor)

G is the distance between lens and object (slide)

F is the focal length of the lens.

 

All three measures presume that the thickness of the lens is zero. In practice, the distances refer to the "optical plane" of the lens.

There are two special cases for this equation:

B=F is the infinity setting.

B=G is the setting used for reproducing slides at a scale of 1+1 in which case B=G=2*F.

 

(2) The second one describes the scale at which the object will be reproduced on the image (sensor):

 

s = G/B

 

s is the scale, obviously  a ratio. B and G are the same  as above.

Again, we're interested in the special case where G=B.

 

For a lens with a built-in helicoid, we can presume that it's mounted such that the distance of the optical plane from the sensor is exactly the focal length, such that it will focus correctly on "infinity" at the infinity setting. This is what's missing in an enlarger lens.

 

This article in the Wikipedia might be helpful: https://en.wikipedia.org/wiki/Lens_(optics)#Imaging_properties

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[Steve Ricoh]

Thanks Pop. I've gone through the Wiki link quite quickly, so need to return and read again to comprehend.

 

So, using the thin lens equation (as you've used), where is the optical plane (or optical node) of a complex lens consisting of n elements. We can't use measuring sticks for this, or can we?

[pop]

Thanks Pop. I've gone through the Wiki link quite quickly, so need to return and read again to comprehend.

 

So, using the thin lens equation (as you've used), where is the optical plane (or optical node) of a complex lens consisting of n elements. We can't use measuring sticks for this, or can we?

We don't have to know where it is. We can reckon its position from the magnification scale and the distance between the object and the sensor. We then can calculate how far we have to move it towards or away from the sensor; that gives the length of the extension tubing needed.

[Steve Ricoh]

Steve - agreed with your findings.

Let's take a look at other possible variations.

Fitting the lens to tubes B,C and D I have a total length from the collar of the first tube to the tip of the lens of exactly 90mm

When fitting the three tubes and lens to the Beoon column and 1:1 critical focus set (as per my above image) I have a distance of 80mm from the tip of the lens to the film base. This may vary slightly with some film being thicker than others. With the Beoon column collapsed to its minimum height I have 73mm. Therefore 7mm of adjustment. Removing all I have a minimum Beoon height of 153mm from the collar to the film base. The lens is 29mm from its collar to the end. The final distance is that of the top fixing where the camera is mounted. With the M39-M adapter fitted I have 12mm.

In all the above measurements I've excluded the thread length.

Assuming all your measurements agree, the only other variation is camera sensor/flange measurement I suppose but this is above my head.

Hope this helps

Ray,

I have measured and here are my results:

1) B,C+B plus Componon S = 90mm

2) Critical focus is not conclusive with my set up, since the BEOON is on minimum height when approaching critical, making the measurement of item 3) applicable, ie 73mm or less

3) With BEOON collapsed I measure 73mm

4) From the underside of the BEOON collar to film base = 163mm (was your 153 a typo?)

5) Measuring the physical length of the lens I get 29mm

6) I'm a bit confused about the final measurement with the M39-M adapter. I believe you're using this to obtain a datum only, since it has no purpose with an M240. My measurement from the top of the M39-M adapter (ie where the threaded portion begins) to the underside of the BEOON flange (referenced in 4) above) is 17mm.

 

Apart from the discrepancies and uncertainties mentioned, I think the plot thickens because the optical node of the enlarger lens is an unknown.

Steve

 

Edit: In between posting this, Pop has just responded to my question about optical node.

Edited September 30, 2017 by Steve Ricoh

[Steve Ricoh]

We don't have to know where it is. We can reckon its position from the magnification scale and the distance between the object and the sensor. We then can calculate how far we have to move it towards or away from the sensor; that gives the length of the extension tubing needed.

Sorry for the ping-pong messaging, Pop, which magnification scale are you referring to? If the BEOON, the scale is far too coarse to determine this accurately - but I'm guessing it's something else.

 

Taking the figures obtained from your experiment in post #37, where you able to correctly confirm the FL of the lens, the 50mm, and the requisite length of the BEOON extension tubes for 1:1? (I suspect you didn't calculate because these values are already known to you.)

[Reeray]

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Ray,

I have measured and here are my results:

1) B,C+B plus Componon S = 90mm

2) Critical focus is not conclusive with my set up, since the BEOON is on minimum height when approaching critical, making the measurement of item 3) applicable, ie 73mm or less

3) With BEOON collapsed I measure 73mm

4) From the underside of the BEOON collar to film base = 163mm (was your 153 a typo?)

5) Measuring the physical length of the lens I get 29mm

6) I'm a bit confused about the final measurement with the M39-M adapter. I believe you're using this to obtain a datum only, since it has no purpose with an M240. My measurement from the top of the M39-M adapter (ie where the threaded portion begins) to the underside of the BEOON flange (referenced in 4) above) is 17mm.

 

Apart from the discrepancies and uncertainties mentioned, I think the plot thickens because the optical node of the enlarger lens is an unknown.

Steve

 

Edit: In between posting this, Pop has just responded to my question about optical node.

 

Apologies Steve, 153 was a typo and 163 is correct. Also, using your distance I also see 17mm as you put forward.

 

We therefore totally agree on all measurements.

 

I get critical focus, you don't !

 

The mind boggles.

[pop]

This is the work flow I used in the above experiment.

 

When taking the shot of the ruler, I noted the distance from the ruler to the camera's sensor. That will not be frightfully accurate, as I can't determine the position of the sensor within the camera with any precision. The distance measures 461.5mm

 

In the picture of the ruler I measured the width of the part of the ruler that's visible in the picture.

 

I then presume that the sensor has a width of 36mm.

 

Hence: 

 

Width of the picture = 36mm

Length of the ruler in the picture = 238.2mm

Scale = 238.2mm / 36mm = 6.6167. 

 

(meaning: The actual size of the ruler is about 6.6 larger than shown in the image taken by the camera).

 

From equation (2) in my previous post, we know that the scale of the image is given by the relative position of the lens between the object and the image. 

 

Hence: G = 6.6167*B. 

(The distance between the ruler and the lens is about 6.6 times the distance between the lens and the sensor.)

 

The sum of those distances is (as noted above) 461.5mm. We now know that

 

G+B = 461.5mm and G = 6.6167 * B, therefore

(6.6167*B ) +B = 7.617*B = 461.5mm. Dividing both sides by 7.617 yields

B=60.588mm.

 

This is the distance between the optical plane of the lens and the sensor.

 

The distance between the optical plane and the ruler must therefore be 461.5mm-60.588mm = 400.912mm 

 

Now that we know the distances on both sides of the lens, we can use equation (1) from above to calculate the focal length of the lens.

 

Remember: (1) 1/B + 1/G = 1/F

 

(1/60.588mm)+(1/400.912mm) = 0.018999 (digits omitted) = 1/F

F = 52.634mm

 

The Elmar is actually 51.8mm, but the  error is quite reasonable, given the setup I used.

 

Subtract the focal length from the distance between the lens and the sensor and you get the extension in use: 7.95mm which is the BEOON without any of the additional rings (8mm as measured by caliper)

 

Sorry for the lengthy post. 

[pop]

I get critical focus, you don't !

 

The mind boggles.

Not really. The exact placement of the optical plane within the assembly is not important for an enlarger lens, and neither is the exact focal length. Any difference will be compensated for by the bellows of the enlarger and by manually focusing.

[Steve Ricoh]

 

Sorry for the lengthy post.

 

Not at all, Pop, I have to thank you for taking the time and effort for performing the worked example, your generosity of time amazes me!

 

I'm not really equipped to do the same measurements, as my tripod isn't exactly suitable - I would be concerned about the camera slipping when inverted.

 

In practical terms, in addition to the tubes supplied with the BEOON, I have a two 26mm, a 20mm and a 5mm extension tube. I've tried all logical combinations without success. As Reeray said, the mind boggles.

[Steve Ricoh]

Apologies Steve, 153 was a typo and 163 is correct. Also, using your distance I also see 17mm as you put forward.

 

We therefore totally agree on all measurements.

 

I get critical focus, you don't !

 

The mind boggles.

It certainly does Ray. You get critical focus with 7mm margin, whilst I get margin in negative figures. Great disappointment to me, but I'll get over it I'm sure. I try to reconcile the situation by reminding myself the BEOON was designed to be used with a 50mm camera lens set to infinity, and not with an enlarger lens using tubes B,C and D.

[pop]

It certainly does Ray. You get critical focus with 7mm margin, whilst I get margin in negative figures. Great disappointment to me, but I'll get over it I'm sure. I try to reconcile the situation by reminding myself the BEOON was designed to be used with a 50mm camera lens set to infinity, and not with an enlarger lens using tubes B,C and D.

Try using your 5mm tube instead of the 8.5mm B tube.

[Guest Nowhereman]

Steve - You could sell your two enlarger lenses and get a Focotar 2 50mm lens, which works substantially better than a Leica 50mm camera lens. For some of my Tri-X digitalizations the difference is not important, but I came very conscious of the difference when I started digitalizing Kodachrome and Ektachrome film.

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[Steve Ricoh]

Try using your 5mm tube instead of the 8.5mm B tube.

Results:

C+D+5mm ring - can't focus at minimum BEOON height with Componon 50mm attached

C+D ditto, can't focus

B+D can focus but BEOON is below the 1:1 marking. Negative does not fill the frame, can see sprocket holes top and bottom, plus adjacent film strip. BEOON column is close to bottoming, and about 5mm lower than shown in Reeray's set up pictured above

 

I'm not sure this is logical, not making much sense to me!

 

Edit typo in above corrected

Edited September 30, 2017 by Steve Ricoh

[Doug A]

Steve - You could sell your two enlarger lenses and get a Focotar 2 50mm lens, which works substantially better than a Leica 50mm camera lens. For some of my Tri-X digitalizations the difference is not important, but I came very conscious of the difference when I started digitalizing Kodachrome and Ektachrome film.

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That won't address the issue of finding a combination of extension tubes to work with an enlarger lens in a copy stand designed to work with a 50mm camera lens. For what it's worth, early in my experiments I used an LTM 50/2.8 Elmar lens with the BEOON and an APSC camera and was happy with the results with some of my old half frame (24x18) negatives. (I rotated the camera 90º and used the BEOON 1:1 mask.)

Edited September 30, 2017 by Doug A

[Steve Ricoh]

Steve - You could sell your two enlarger lenses and get a Focotar 2 50mm lens, which works substantially better than a Leica 50mm camera lens. For some of my Tri-X digitalizations the difference is not important, but I came very conscious of the difference when I started digitalizing Kodachrome and Ektachrome film.

_______________

Alone in Bangkok essay on BURN Magazine

Mitch, until I can get my head around why I'm only acquiring focus with B+D only, and still have marginal column height adjustment (can't see the 1:1 markings) I think there's something seriously wrong that even a Focatar 2 would not resolve. However, dimensionally the BEOON is correct, ie it agrees with Reeray's measurements. As far as the camera is concerned, it is sharp at infinity and works well with the 50 lux on the BEOON.

I can't figure this, but Doug A is on the ball I think.

[pop]

Results:

C+D+5mm ring - can't focus at minimum BEOON height with Componon 50mm attached

C+D ditto, can't focus

B+D can focus but BEOON is below the 1:1 marking. Negative does not fill the frame, can see sprocket holes top and bottom, plus adjacent film strip. BEOON column is close to bottoming, and about 5mm lower than shown in Reeray's set up pictured above

 

I'm not sure this is logical, not making much sense to me!....

I'll have to do some calculations later, perhaps today. In the meantime: Are you sure yours is a 50mm lens? Can you show a sample with the sprocket holes and so on?

[Steve Ricoh]

I'll have to do some calculations later, perhaps today. In the meantime: Are you sure yours is a 50mm lens? Can you show a sample with the sprocket holes and so on?

Thanks Pop, yes it's a Componon S 50mm f2.8. I also have an El-Nikkor 50mm f2.8, but all the recent measurements were with the Componon.

[Doug A]

The difficulty with using any enlarging lens with the BEOON is assembling the exact length of extension tubes that will focus the lens on the negative and provide the desired reproduction ratio. Small differences in tube length result in large differences of magnification. I finally solved the problem by buying one of these. Combined with various combinations of the tubes supplied with the BEOON, it should cover almost every setup.

 

(I hesitated to mention this before because, in my experience, these are even harder to find than a BEOON, but it occurs to me that there may be other ways to include a helical focus in the setup.)

Edited September 30, 2017 by Doug A

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[Guest Nowhereman]

That won't address the issue of finding a combination of extension tubes to work with an enlarger lens in a copy stand designed to work with a 50mm camera lens...

 

Doug - Not sure what you mean. The Focotar-2 50mm works well with a full frame camera on the BEOON using the B+C+D tubes and the 1:1 mask for 35mm film. I'm not the only who has experienced this: I was put on to this by postings from several other people — on RFF, if I remember correctly.

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Edited September 30, 2017 by Nowhereman