Camera repair: are the diaphragm blades correctly installed?

[mellais]

Hi, 

Please have a look at the attached two photos for reference. I have a newly acquired Minolta Minoltina-s rangefinder camera and I am cleaning its lens elements. While at it, I keep looking at the diaphragm and the aperture opening vs aperture ring setting; I am not sure if the blades are correctly installed (by some previous owner). The smallest f16 setting looks really small in my experience and the widest f1.8 does not seem to open up as wide as it should be. 

So my question is: if the measurement for the smallest aperture available is approximately 1,4mm in diameter, and the widest is 14,6mm, can I just check the corresponding f values by dividing the focal length 40mm by these values? It gives me roughly f28 and f2.8, telling me that the blades are not correctly installed.

I am trying to avoid rebuilding the diaphragm if possible because it is clean and smoothly functioning and difficult to access but of course it would have to be correctly built as well. 

Many thanks for your comments,

Regards 

Otto

[John Seaman]

I don't see how the assembly of the blades themselves could cause this, more likely there is some issue with the linkage between the blades and aperture ring. I would be inclined to leave it and compensate for the error by selecting an aperture one stop wider than that required.

Edited April 6 by John Seaman

[mellais]

1 hour ago, John Seaman said:

I don't see how the assembly of the blades themselves could cause this, more likely there is some issue with the linkage between the blades and aperture ring. I would be inclined to leave it and compensate for the error by selecting an aperture one stop wider than that required.

Thanks John, 

I'll have a look at the aperture ring and its linkage, possible stoppers etc. At the moment the ring turns seemingly correctly from f1.8 position to f16 position and stops at both ends. So there's no room for correction at these extreme values. The aperture openings still look odd to me, usually even f22 is not that tiny and I feel it should open up wider at the lenses max aperture.

[kmac]

8 hours ago, mellais said:

I am not sure if the blades are correctly installed (by some previous owner)

The aperture blades look ok, you can't really make a mistake reassembling them, as long as their pins are set in their positions correctly. The aperture opening on yours looks the same as my Minolta 7S, which is 45mm focal length, but f16 is still pretty small.

[arthur_mcculloch2]

6 hours ago, kmac said:

The aperture blades look ok, you can't really make a mistake reassembling them, as long as their pins are set in their positions correctly. The aperture opening on yours looks the same as my Minolta 7S, which is 45mm focal length, but f16 is still pretty small.

Hi kmac. 'You can't really make a mistake reassembling them': I have (at least on a synchro compur), by putting the blades in back the front. They still fit the pins, look proper, but when actuated, close, then reopen in the rest state. From the photo, it does look more like f22 than f16 to me. But that is guessing. For the widest aperture, I've heard that, for instance, that the f2.8 xenon used in the retina IIa was simply the f2 lens with the aperture not opening as wide - but that could be an urban myth. Regards, Arthur.

[kmac]

5 hours ago, arthur_mcculloch2 said:

Hi kmac. 'You can't really make a mistake reassembling them': I have (at least on a synchro compur), by putting the blades in back the front. They still fit the pins, look proper, but when actuated, close, then reopen in the rest state. From the photo, it does look more like f22 than f16 to me. But that is guessing. For the widest aperture, I've heard that, for instance, that the f2.8 xenon used in the retina IIa was simply the f2 lens with the aperture not opening as wide - but that could be an urban myth. Regards, Arthur.

Yes, I take photos of shutter parts as I disassemble them, so by studying the photos I can see which way things go back.

Without posting a pic of my Minolta 7S, I can say the aperture opening at f16 is very small, as is the one in the OP, but for a 40mm lens, the f16 opening will be slightly smaller than that of the 45mm 7S lens, but not by much.

For some of my larger cameras, I could easily stick a pencil through the f16 aperture opening. Longer focal lengths need more light.

 

 

 

Edited April 7 by kmac

[arthur_mcculloch2]

4 hours ago, kmac said:

Yes, I take photos of shutter parts as I disassemble them, so by studying the photos I can see which way things go back.

Without posting a pic of my Minolta 7S, I can say the aperture opening at f16 is very small, as is the one in the OP, but for a 40mm lens, the f16 opening will be slightly smaller than that of the 45mm 7S lens, but not by much.

For some of my larger cameras, I could easily stick a pencil through the f16 aperture opening. Longer focal lengths need more light.

 

 

 

Thanks kmac. That's good to know. Regards, Arthur.

[mellais]

10 hours ago, arthur_mcculloch2 said:

Hi kmac. 'You can't really make a mistake reassembling them': I have (at least on a synchro compur), by putting the blades in back the front. They still fit the pins, look proper, but when actuated, close, then reopen in the rest state. From the photo, it does look more like f22 than f16 to me. But that is guessing. For the widest aperture, I've heard that, for instance, that the f2.8 xenon used in the retina IIa was simply the f2 lens with the aperture not opening as wide - but that could be an urban myth. Regards, Arthur.

Arthur, and all others, 

Thank you for your comments. I got this camera in very clean condition but certain things indicated that someone had at least taken out the front lens group earlier. In addition to that the rear lenses were oily. I'm starting to believe there is something misaligned around the diaphragm.  Whether it's aperture blades placed upside down or what I can't tell yet. But here's an update explaining why I still think there's something wrong. 

The 1st photo here shows the linkage between the aperture ring and a lever moving the blades; it's pictured here with the aperture ring turned all the way to its widest f1.8 end, and you can see how the sort of "fork" holding the lever actually makes the lever stop before the blades are fully open, as seen in the 2nd photo here. Without the fork in place, the lever can move all the way to the stop (Photo 3). 

Everything seems to be in their proper places and you get the feeling that this aperture ring linkage is working as it should, the fork and lever and everything fitting together perfectly. Yet the max aperture you get with this lens as it is now is still only roughly 14-15mm in diameter. My math says it's not equal to f1.8. 

I will have to take out the whole shutter mechanism to access the diaphragm. 

 

[arthur_mcculloch2]

mellais, am I right that it's a seikosha shutter? You may be able to get some further advice on the Learn Camera Repair' facebook site. I am about to open up my first seikosha-rapid in the next couple of weeks - it's in an airesflex TLR that has been sitting around for some decades, and is gummed up. Regards, Arthur.

[mellais]

4 hours ago, arthur_mcculloch2 said:

mellais, am I right that it's a seikosha shutter? You may be able to get some further advice on the Learn Camera Repair' facebook site. I am about to open up my first seikosha-rapid in the next couple of weeks - it's in an airesflex TLR that has been sitting around for some decades, and is gummed up. Regards, Arthur.

Arthur,

I'll see if I can get further assistance in that fb group. The shutter here is Seiko-SLV and it's pretty robust, well-built. I hope you will have a good time with the Airesflex, those are interesting cameras! 

[mellais]

Ok everybody,

Problem solved. I didn't take into consideration that when calculating the aperture f-value, we have to use  the diameter of the lenses so called  entrance pupil — not the actual size of the iris, but rather its magnified image as seen through the front of the lens as Jay Holben points out in an article published on the American Association of Cinematographers' website (visited on April 8, 2024, see https://theasc.com/blog/shot-craft/the-entrance-pupil-of-the-lens).

So the camera should work as intended - time to put it back together and start shooting. 

P.S. 

This made me think of a possible modification; since there is room for wider movement in the diaphragm itself than what is being used, I will see if I could rebuild the linkage between the aperture ring and the lever making it possible to use the aperture to its full potential. At the very least one could get f22 instead of f16 min aperture and possibly a max aperture beyond f1.8, if the lens design allows it.

[arthur_mcculloch2]

On 4/9/2024 at 2:43 AM, mellais said:

Ok everybody,

Problem solved. I didn't take into consideration that when calculating the aperture f-value, we have to use  the diameter of the lenses so called  entrance pupil — not the actual size of the iris, but rather its magnified image as seen through the front of the lens as Jay Holben points out in an article published on the American Association of Cinematographers' website (visited on April 8, 2024, see https://theasc.com/blog/shot-craft/the-entrance-pupil-of-the-lens).

So the camera should work as intended - time to put it back together and start shooting. 

P.S. 

This made me think of a possible modification; since there is room for wider movement in the diaphragm itself than what is being used, I will see if I could rebuild the linkage between the aperture ring and the lever making it possible to use the aperture to its full potential. At the very least one could get f22 instead of f16 min aperture and possibly a max aperture beyond f1.8, if the lens design allows it.

Good outcome.  As noted before, I've been told that the xenon f2.8 used in some kodak retinas is the same lens as the xenon f2 but with the aperture stopped before getting to f2.  That may be an urban myth, like the notion that the ektar used in the retina I's was simply a rebadged xenar to get around US post war import controls. Let me know how you go. Regards, Arthur

[winfried_buechsenschuetz1]

Yes, the diaphragm diameter cannot be measured directly, you always have to take into accout the magnifying factor of the lens. 

The thing about the f/2 and f/2.8 of the Retina is no myth. I think Rick Oleson described the method of removing the stop on one of his fabolous camera repair pages - if they still exist, must be a decade or so since I last visited them.