[rdenney]

Series Contents

So, for the penultimate test, I'm looking at the last prime that I'm testing. The FA75 and the A75 attract considerable favorable comment as being sharp and a good value. These were the standard normals for the 645 film cameras, having a focal length about the diameter of the full 645 frame. They are slightly long on the 33x44 frame of the 645D and 645Z, making it a good short portrait lens for use with studio lights and outside fill flash. I bought this for the latter, as part of my 645NII wedding kit. The lens came from KEH over a dozen years ago, when I paid a little over $400 for it.

On the NII, this lens automatically sets the camera to LS mode, which automatically sets the shutter speed to 1/8. When using the leaf shutter, one had to meter manually (or use an automatic strobe), because the lens does not tell the camera what shutter speed is being used. Likewise, there is no A setting on the aperture ring. When using the focal-plane shutter in the camera, the leaf shutter is cocked and set to "o" for "open", at which point the lens operates with full wide-open metering and can use aperture-priority automatic exposure. Because there is no A setting on the aperture ring, shutter-priority automation is not available. The camera will automatically set the mode to Av even if the mode dial is pointing to some other setting, being M being the only allowable alternative.

But I found that the 645Z provides the same LS display, but for some reason does not set the 1/8 shutter speed. The focal-plane shutter time has to be long enough so that the stop-down lever 1.) stops down the lens, 2.) triggers the leaf shutter cycle, which 3.) closes the leaf shutter right before the focal-plane shutter opens (and this is just a matter of designed timing--there is no mechanical interlock), then 4.) opens and closes the leaf shutter right after the focal-plane shutter opens (again, just a matter of timing--there is no interlock) to make the exposure. The leaf shutter stays closed after the exposure, which is disconcerting for many but not for me. My experience with a range of SLR's of ancient design has taught me that instant-return mirrors are a modern luxury not a human right. If the camera doesn't force the focal plane shutter to 1/8, it will often set the shutter speed automatically and that is usually too fast to ensure that the focal plane shutter is open when the leaf shutter fires. When that happens, one gets an image that looks like this:



I don't know why the 645Z does not operate the leaf shutter lenses as it should. The NII does it correctly, and it seems to me the 645Z firmware could do the same. Even though the camera reports "LS", the selected shutter speed is out of range--the EXIF reports "1/infinity s". It's nuts, but there it is. As has been reported here before, one must tape over the contacts on the lens (of which there are only a few) to prevent any electronic communication between the lens and the camera. Then, one must put the camera in M mode, and set the shutter speed to 1/8 second, at which point the leaf shutter will work as intended. To take a meter reading when using the leaf shutter, here's the process:

1. Cock the shutter.
2. Set the leaf shutter to "o", which opens the shutter for viewing.
3. Set the focal plane shutter to the desired speed (which will be 60, 125, 250, or 500--the speeds provided by the leaf shutter).
4. Adjust the ISO and aperture to center the metering display.
5. Set the leaf shutter to the desired speed.
6. Set the focal plane shutter in the camera to 1/8.

The idea was that one would not need to do this often, because one would only use the leaf shutter with flash, and the exposure would be dictated by the flash and not the meter. But when using fill flash, which is the primary use case, one must meter AND set the flash. I usually set the flash to expose a stop less than the ambient light (with an automatic flash, I set the ISO on the flash to twice that of the sensor, which will give it one stop less exposure), and then set the camera to ambient light. This requires metering the scene. Of course, one can also use an external meter.

So, in practice, the leaf shutter is cumbersome to use. But it's not any worse than it used to be with most commercial cameras--my Mamiya C3 didn't have a meter at all, let alone a fully coupled one, and the leaf shutter was the only option with that camera.

But the lens is fully usable with the focal plane shutter in the camera, with aperture-priority automatic exposure. This is not a spray-and-pray lens, but it works conveniently enough to serve as one's only 75mm prime, for those who have occasional use for synching a flash at speeds higher than 1/125. Note that the 645Z focal-plane shutter syncs with flash up to 1/125, so really only 1/250 and 1/500 leaf shutter speeds provide any real utility.

The flash we are talking about is NOT a Pentax P-TTL speedlight like the AF-540FGz. The flash sync interface is through a PC connector on the side of the lens, not through the hot shoe. This lens works best with an old-fashioned automatic flash like a Vivitar 283 mounted on a bracket that doesn't touch the hot-shoe contacts, or with studio strobes. For set shots (such as outdoor portraits), I would often set up studio lights at the site (I still have that Speedotron 1600ws Brown Line power head with two mains and two fills). The flash power would be set to be compatible with ambient lighting.

For those who never imagine themselves using the leaf shutter, get the A or FA 75mm lenses for the sake of convenience. It's a little like the old joke about the talking dog. A dog trainer comes to a talent agent, and says, "Book me at a circus, I have a talking dog." The talent agent says, "Okay, Fido, tell me what's over our heads." The dog says "woof!" The talent agent angrily kicks them out, and once outside, the dog looks at the trainer and says, "what was wong with that?" The trick is not that the dog speaks well, but that the dog speaks at all. The trick with this lens is not that the leaf shutter is easy to use, but that it's there at all on a camera fully optimized for a focal-plane shutter.

So, are optics worth all this palaver?

Pretty much.

In short, the optics are quite good, even by normal-prime standards.

Here's the full image, at f/11, using the 75mm LS:



Here's a 1:1 crop of the center at f/2.8:


It's sharp enough, but there's a bit of flare that reduces contrast and gives everything a bit of a glow. This is not a bug, but a feature. For a lens that is 1.3 times normal, and thus can serve as a short portrait lens (a useful use case for high-speed flash sync anyway), one wants a bit of softness at maximum aperture. Remember also that the 1:1 clip, when viewed at the 100 pixels/inch of typical monitors, is part of an image seven feet wide. The above is not bad.

For comparison, here's the DFA 55 at 2.8:


The 55 is a lens for making things sharp, not for making things soft, and it really doesn't do soft very well. The 75 can do both.

By f/5.6, though, it's as sharp as anyone would want. Here's a 1:1 clip at f/5.6:


Again, it's not as contrasty as the 55, but it's still quite sharp.

Here it is at f/11:


Which isn't really any sharper than f/5.6.

And at f/22:


Between f/5.6 and f/22, all that gets sharper is the out-of-focus foreground and background.

Again, here's a comparison with the 55 at f/11:


Differences are subtle, if we can barely see them at these magnifications.

So, center performance is excellent by f/5.6, but how does it do in the corners?

Upper right corner. 1:1 at f/2.8:


The leaves that are mostly in focus are also in the focus plane, being about the same distance from the camera as the lamp. No lateral color, no longitudinal chromatic aberration, no appreciable field curvature.

So, how does it compare with the 45-85 zoom, one lens that might keep me from needing this one on many occasions?

Here's the 45-85 at 65, in the center at a good aperture:


Hmmm. The 75 is good, but will I need a fast 75 in Alaska? Maybe, maybe not. The zoom is just as sharp, and far more convenient, but it's not as fast. This one's on the bubble for an essential lens on a trip focusing on landscape photography.

Rick "special-purpose lenses often get left behind even when they are good" Denney

---

Last edited by rdenney; 06-30-2018 at 12:19 AM. Reason: Cannot believe the number of typos I saw this morning.

[supersargas]

Excellent work!

[johnha]

Thanks for the detailed description of how this lens works and it's limitations with the Z (I presume the same process is required for the D?). I've briefly experimented with the 6x7 90mm f/2.8 L/S lens on my D with the Pentax adapter - which seems like a much simpler process: Set the lens to 'U' and cock the shutter, meter the scene in manual, set desired speed on the L/S lens, set focal plane shutter to 1/8th and shoot (the L/S shutter stays open after the shot). Obviously you need to mix your flash with ambient in the 'usual' way based on your aperture.

Your comment about the 283 freaked me out at first - mine exceeds 270 volts across the contacts - no way that's going anywhere near the hotshot - but then I realised the 6x7 90mm L/S sync port has no connection to the camera (and the 6x7 adapter has no electrical connections to the camera either).

[rdenney]

The later made-in-China 283’s had 8-volt triggers. I have four and two are high voltage, two low. I put labels on them to keep them straight.

But the leaf shutter has mechanical switch contacts and will work fine with high-voltage triggers. Just don’t mount a high-voltage flash on the camera’s hot shoe.

Rick “easy to test with a volt meter” Denney

[rajiv]

Great test. Are their any currently still in production automatic flashes (similar to the Vivitar but safe) that you would suggest ? Thanks.

[rdenney]

Great test. Are their any currently still in production automatic flashes (similar to the Vivitar but safe) that you would suggest ? Thanks.

The “new” flash units I have bought recently are all of the TTL type—two AF540FGZ units for the Pentax and another Canon 580EX for the 5Dii. I bought them all pre-owned and they work fine.

Vivitar 283 and 285 flashes are common and cheap, and even still available new. Just be careful of the trigger voltage. The main problem is with the other contacts on the hot shoe, which are more sensitive than the center trigger. Use an external flash holder and a PC wire to the PC port on the side of the lens, which can handle any flash. Vivitar uses a special PC cable, and the only brand I would ever use for that is Paramount.

Rick “not up to date on aftermarket flashes” Denney

[rajiv]

Thanks for the explanation. I have a Vivitar 285 but I have not used it as yet because I have not tested if it is a high voltage version. It works great though on old manual film cameras.

[bstruggles]

Hello! I recently purchased this lens off of ebay and have been following the forums and trying to figure out how to use with flash. I keep reading about “cocking the lens” to open up the viewfinder, but I’m having trouble doing this?

I bought the 135mm LS version off ebay.

When I cock the lens, nothing happens. I look through the viewfinder and it stays open. I’ve even tried to cock the lens on its own expecting it to close or open when cocked.

Could the mechanism in this lens be broken?

I’ve confirmed that LS appears in the viewfinder when switched from O to a shutter speed on the lens.

When in the O position, the aperture blades move according to what shutter speed i’m using on the camera. The speed coordinates with each shutter speed too.

When I switch shutter dial on the physical lens, the shutter speed is constant to whatever is on the camera, it won’t change on the lens itself.

Any help greatly appreciated!

[garywakeling]

Firstly , what camera are you using the lens with.
The way the leaf shutters work in general is that unlike a normal lens, which uses the aperture in the lens and the shutter at the focal plane, both the aperture and the shutter is in the lens. The added fact that there is also a shutter at the film/sensor plane complicates the exposure. When used without cocking the leaf shutter, the lens works like a normal manual lens where you set the aperture on the lens and set the shutter speed on the camera body. When using the shutter in the lens, what happens is first the shutter closes in the lens, then the aperture closes in the lens. Then the shutter in the body opens followed by the shutter in the lens opening to expose the image, sometimes with the flash going off if used, then followed by the lens in the shutter closing and then the shutter in the body closes. Every step needs to happen in sequence for an image to be made. Because the 2 shutters need to be open to expose an image, the body shutter needs to be open much longer than the shutter in the lens otherwise the system doesn't work. As the original poster wrote, it is not an easy or perfect system but it can work and give you the ability to use faster shutter speeds to synch with your flash. Good luck experimenting with your new lens