Nikkor-SW 90mm f/8 in an f/4.5 shutter?

[mhelminski]

I recently found a good deal on a mint Nikkor-SW 90mm f/8. It arrived today and while the lens is in great condition, but it's mounted in an original Nikon-branded Copal 0 marked for a Nikkor-SW 90mm f/4.5, not an f/8.

In theory the aperture scales should still be accurate, since this is an official Nikon-marked Copal for the same focal length, right? But with the aperture set to f/8, the blades are still clearly visible through the lens. They don't actually disappear until about f/6.8.

Can still I assume the aperture scale is accurate across the entire range, since an aperture of f/8 on either lens should the same or am I likely to have problems with exposure accuracy?

 

[Dave_B]

Nikkor lenses

Putting a new shutter on a lens can't turn an f8 into an f4.5. If that could happen, we would all turn our f8's into f1's for the cost of a new Copal shutter and no company would bother to build fast lenses. The maximum aperature of a lens is determined by the diameter of the glass elements and the focal length, period. The shutter for any given lens system is chosen by the manufacturer to not limit it beyond what the glass elements are designed for. I have both Nikkor lenses and the f4.5 is a beast in comparison with the f8. Sorry, if you want the f4.5 you have to buy a big heavy pile of glass and metal. You will need to recalibrate your lens-you have a hybrid that someone put together from spare parts.
Cheers,
Dave B.

 

[robsoe]

ALL nikkor SW f/8 lenses have a thin brass shim between the front cell and the shutter to optimize the optical performance. Your lens doesn't come with the original shutter, so it might not have the shim. You can check it by unscrewing the front cell out from the shutter. If there is no shim, I would return it to the seller. If the shim is there, then you need to rescale the aperture.

 

[Tom Hoskinson]

ALL nikkor SW f/8 lenses have a thin brass shim between the front cell and the shutter to optimize the optical performance. Your lens doesn't come with the original shutter, so it might not have the shim. You can check it by unscrewing the front cell out from the shutter. If there is no shim, I would return it to the seller. If the shim is there, then you need to rescale the aperture.

If needed, SK Grimes can calibrate your lens and shutter and engrave an Copal fstop plate for you. If your lens needs a shim, SK Grimes can take care of that, too (been there, done that).

 

[robsoe]

If needed, SK Grimes can calibrate your lens and shutter and engrave an Copal fstop plate for you. If your lens needs a shim, SK Grimes can take care of that, too (been there, done that).

I'm always curious to know whether Nikon had to adjust the spacing of each individual nikkor 90mm f8 lens (means different serial number has different shim thickness) or the shim is the same thickness for all 90mm f8? If the shim thickness are all the same, why didn't nikon just machined the front cell mount, so that no shim is needed anymore? How did SKG determine how thick the shim should be? Did they test it optically to find out that?

 

[Roger Hicks]

I recently found a good deal on a mint Nikkor-SW 90mm f/8. It arrived today and while the lens is in great condition, but it's mounted in an original Nikon-branded Copal 0 marked for a Nikkor-SW 90mm f/4.5, not an f/8.

In theory the aperture scales should still be accurate, since this is an official Nikon-marked Copal for the same focal length, right? But with the aperture set to f/8, the blades are still clearly visible through the lens. They don't actually disappear until about f/6.8.

Can still I assume the aperture scale is accurate across the entire range, since an aperture of f/8 on either lens should the same or am I likely to have problems with exposure accuracy?

I'd certainly suspect that the diaphragm should be accurate at f/8 and below, because as far as I recall they're both symmetrical designs and as they're both 90mm your assumption seems reasonable to me.

As for the spacing issue, as long as the lens is the right overall thickness, i.e. the shutter is the right thickness of spacer, there's no reason why you should have a problem there either. In the Photo School at www.rogerandfrances.com, go to 'How do I...?' and then to '...re-shutter an LF lens' which gives some more hints on this, including varying the separation. As someone else pointed out, there must be several sizes of shim, and it is entirely possible that some lens/shutter combinations do not need shims.

As ever, of course, the easiest way to find out is to shoot a few pictures, preferably with a roll-film back in the interests of economy. Try shooting wide open, obviously, and try another lens at f/8 to see if the trannies have the same density.

In other words, I am not on the side of those who tell you that you have just bought a load of junk. It's probably OK anyway, and if it isn't, there's a good chance you can make it OK without sending it away.

Cheers,

R.

 

[mhelminski]

Thank you all for your replies. I don't see a shim. Plus, I'm in Japan, so sending to SK Grimes isn't practical. But I spoke to the shop, which hadn't noticed the incorrect shutter and seemed embarrassed about overlooking it. So I'm sending it back at their expense. If they discover the correct shutter sitting in the shop, great, otherwise I'll continue my search. It would have been a good deal for a mint f/8 in correct shutter, but wasn't cheap enough to turn into a project.

Dave B - I didn't believe the lens had suddenly become an f/4.5 lens, just wondered about the accuracy of the scales from f/8-64, since it was clearly the wrong shutter.

 

[Dave_B]

Nikkor 90mm f4.5 and f8

I'm sorry if I misunderstood your question. I appreciate that the topic is now moot but if you had kept the lens, you would have needed to recalibrate the aperature scale. As you note, the zero was off. If you had re-shifted the zero, the scale would have been out some as well. By rough eyeballing the scales on the two lenses I have (the f4.5 and f8) it looks like they differ by roughly 1/3-1/2 stop if you merely tried to use one scale on the other lens. A 1/3 of a stop is not much but it might matter in some cases.
In the future, you can check the aperature scales on a lens with a dark room, a piece of cardboard, a light box and an exposure meter. You cut a hole in a piece of cardboard just larger than the lens input opening and place the cardboard and lens on the lightbox. You want a light source that is uniform and constant-a light box is perfect. You then use the light meter to measure the light leaving the lens. You need a dark room to eliminate stray light and you need to make sure the exposure meter reading area completely covers the output of the lens. A one degree spot meter can cause problems if you are too close. The absolute values are hard to get right-you assume that the largest reading is the maximum aperature that the lens is capable of and use the exposure meter to scale things from there. This works pretty well and is easy to do.
As mentioned above, S.K. Grimes can calibrate a lens for you and engrave a new aperature scale. They can do 1/3 stop increments which is a nice feature. I have been happy with their work.
It sounds like the shop where you bought the lens was decent about it. I'm glad it worked out OK for you.
Best wishes,
Dave B