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

[Rokkor]

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vor 6 Minuten schrieb wlaidlaw:

I would be very suspicious of an APO Rodagon 50/2.8 at that price. The normal price for a used APO Rodagon is $300 to $600. The new price for an APO Rodagon 50mm is $960. Are you sure it is the APO version you are being offered, as that price is much more in line with the price for the non-APO version and even cheap for that one. A 50mm/2,8 Componon S Green Stripe (they have a lever at the side unlike the non-green stripe version) will sell for around $150 to $200. 

Wilson

It is from a camera store / portrait photographer. So should be ok. The price is almost too good I know. Seems serious. I have sent you a picture per DM.

[Guest]

3 hours ago, Steve Ricoh said:

With my Summilux 50/1.4 mounted, the Beoon column height is approximately mid height, meaning there’s adequate adjustment to acquire critical focus. With either of the two enlarger lenses mentioned above, the Beoon column ‘bottoms out’ and it’s impossible to adjust either side of critical focus, which isn’t helpful.

I would like to understand this. Deviations between effective and nominal focal length cannot explain this result. The Summilux has an effective focal length of 51.6mm. If you combine BEOON extension rings to obtain an overall extension of 51.6mm, then you obtain 1:1 with your Summilux at infinity focus position. I think extension rings A+D (+ some thickness of the BEOON device) provide this extension.

Now assume you use an enlarger lens instead with an effective focal length of 51.6mm as well. Assume the flange focus at infinity of the lens is 46.4mm (about 10% less than the focal length, that's what I have for my M-Componon lens, for example). The Leica M flange focal distance is 27.8mm. Assume you again combine BEOON extension rings to obtain an overall extension of 51.6mm. Then your effective extension is now 51.6 + 27.8 - 46.4 = 33mm. Thus, with the same BEOON extension, you now only achieve a magnification of 33/51.6 = 0.64 (1:1.5636). The reason is that the Summilux mount already provides sufficient internal extension to cover its flange focus at infinity. The enlarger lens does not provide this extension. Hence you need an additional 51.6 - 33 = 18.6mm to achieve 1:1.

At 1:1 the distance between sensor and object is 4x the focal length. This is the same in both cases (Summilux and enlarger lens). Therefore if you use both lenses at 1:1, you should get exactly the same BEOON column extension. If you use the Summilux at 1:1 and the enlarger lens at 1:5636, the latter requires an extra 7.3mm column extension because the distance between sensor and object increases from 206.4mm to 213.7mm.

If I understand you correctly, your problem with enlarger lenses is that the BEOON column is already too long at its minimum extension. I am puzzled. Just to be very clear, I am not doubting your experience at all, just trying to understand it. But I am absolutely sure that deviations from the nominal 50mm focal length cannot explain your result.

[Steve Ricoh]

1 hour ago, Studienkamera said:

I would like to understand this. Deviations between effective and nominal focal length cannot explain this result. The Summilux has an effective focal length of 51.6mm. If you combine BEOON extension rings to obtain an overall extension of 51.6mm, then you obtain 1:1 with your Summilux at infinity focus position. I think extension rings A+D (+ some thickness of the BEOON device) provide this extension.

Now assume you use an enlarger lens instead with an effective focal length of 51.6mm as well. Assume the flange focus at infinity of the lens is 46.4mm (about 10% less than the focal length, that's what I have for my M-Componon lens, for example). The Leica M flange focal distance is 27.8mm. Assume you again combine BEOON extension rings to obtain an overall extension of 51.6mm. Then your effective extension is now 51.6 + 27.8 - 46.4 = 33mm. Thus, with the same BEOON extension, you now only achieve a magnification of 33/51.6 = 0.64 (1:1.5636). The reason is that the Summilux mount already provides sufficient internal extension to cover its flange focus at infinity. The enlarger lens does not provide this extension. Hence you need an additional 51.6 - 33 = 18.6mm to achieve 1:1.

At 1:1 the distance between sensor and object is 4x the focal length. This is the same in both cases (Summilux and enlarger lens). Therefore if you use both lenses at 1:1, you should get exactly the same BEOON column extension. If you use the Summilux at 1:1 and the enlarger lens at 1:5636, the latter requires an extra 7.3mm column extension because the distance between sensor and object increases from 206.4mm to 213.7mm.

If I understand you correctly, your problem with enlarger lenses is that the BEOON column is already too long at its minimum extension. I am puzzled. Just to be very clear, I am not doubting your experience at all, just trying to understand it. But I am absolutely sure that deviations from the nominal 50mm focal length cannot explain your result.

I wish I could add to your excellent explanation... 

All I can say is the BEOON column has plenty of adjustment with the camera ‘taking’ lens installed, whereas the column bottoms with either enlarger lens. 
I’ve tried various spacers, but not to the dimensions you mention above. Perhaps a suitable helix would be beneficial, but I’m more or less convinced the Summilux 50 is adequate.

[pop]

vor einer Stunde schrieb Studienkamera:

If I understand you correctly, your problem with enlarger lenses is that the BEOON column is already too long at its minimum extension. I am puzzled. Just to be very clear, I am not doubting your experience at all, just trying to understand it. But I am absolutely sure that deviations from the nominal 50mm focal length cannot explain your result.

I have no other explanation. In fact, I did a number of tests some time ago with two Leica M mount lenses with nominal focal lengths of 50mm. One could focus at a scale of 1:1, the other could not:

(Is the camera mentioned in your user name the Linhof? - Are you actually using it?)

[a.noctilux]

I think that the answer is the physical size of the lenses, for fixed 1:1 repros,

as I use two Focotar 4.5/50 of different size on Beoon, the distance (and rings to use on each) is different a couple of millimeters, not exactly same set-up.

 

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[Steve Ricoh]

1 hour ago, a.noctilux said:

I think that the answer is the physical size of the lenses, for fixed 1:1 repros,

as I use two Focotar 4.5/50 of different size on Beoon, the distance (and rings to use on each) is different a couple of millimeters, not exactly same set-up.

 

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I’m not sure, but finding exact spacers in small numbers of mm could be tricky. A helix coupler might be more suitable (in M39 if available ???)

[wlaidlaw]

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I tried and failed to get a 50mm VM Zeiss Planar and a 2.8/50 Elmar-M to work on the BEOON. No focus at any distance with any combination of extension tubes. I put both the 50mm Componon S and the borrowed APO Rodagon N lenses and they both focussed immediately in about middle of the range. I cannot recall now what extension tubes I use but I did post earlier, on I think this thread. It may have been A, B and D. 

Wilson

[Rokkor]

vor 4 Minuten schrieb wlaidlaw:

I tried and failed to get a 50mm VM Zeiss Planar and a 2.8/50 Elmar-M to work on the BEOON. No focus at any distance with any combination of extension tubes. I put both the 50mm Componon S and the borrowed APO Rodagon N lenses and they both focussed immediately in about middle of the range. I cannot recall now what extension tubes I use but I did post earlier, on I think this thread. It may have been A, B and D. 

Wilson

That is encouraging. The Rodagon was mentioned often to pair well with the BEOON. First I was tempted trying a Minolta Rokkor but haven’t found anything on this lens and BEOON combination.

[Guest]

9 hours ago, pop said:

I have no other explanation. In fact, I did a number of tests some time ago with two Leica M mount lenses with nominal focal lengths of 50mm. One could focus at a scale of 1:1, the other could not

I see. If the combination of extension rings A+D yields a magnification of 1:1 with the Elmar, then they would produce a magnification of m = 51.6/50.1 (1.03:1) with the Summarit. This roughly fits the object size you mentioned. The distance between sensor and object is d = (1+m+1+1/m) x f, where m is the magnification and f the focal length. For the Elmar at 1:1, we obtain d = 206.4mm. With the Summarit at 1:03:1, we obtain d = 200.4mm. Thus, if your Elmar at 1:1 is placed within about 6mm of the minimum extension of the BEOON column, then this would explain why you can't focus the Summarit at 1.03:1. If that's the case, then indeed deviations in the focal length from the effective focal length of the Elmar (51.6mm) can explain the findings of Steve and others. I stand corrected. 

(Yes, my name here refers to the Linhof Studienkamera 70, which is also pictured in my user photo. I still use it with a roll film back in Idealformat and a Symmar-S 100mm lens.)

 

[Guest]

9 hours ago, a.noctilux said:

I think that the answer is the physical size of the lenses, for fixed 1:1 repros,

as I use two Focotar 4.5/50 of different size on Beoon, the distance (and rings to use on each) is different a couple of millimeters, not exactly same set-up.

The physical size can play a role if (and in my opinion only if) it affects the lens' flange focus at infinity. It then affects the extension required to reach 1:1 in line with your experience. Otherwise, it obviously affects the working distance from the front of the lens to the object. However, it will not affect the distance between sensor and object, which only depends on the magnification and the focal length as described in my last post.

[michaelcole]

I bought a BEOON a few weeks ago and then found a Focotar 4.5/50mm in great condition to use with it and it works great.  The images are nice and sharp right to the corners.

Before I got the Focotar, I tried my 50mm Summilux ASPH, and for this use it was as sharp as the Focotar in the center, but not in the corners.