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Pentax Lens Review Database » Pentax 645 Medium Format Lenses » 645 Normal Primes
SMC Pentax 645 LS 75mm F2.8 Review RSS Feed

SMC Pentax 645 LS 75mm F2.8

Reviews Views Date of last review
2 54,500 Thu June 28, 2018
Recommended By Average Price Average User Rating
100% of reviewers $550.00 9.50
SMC Pentax 645 LS 75mm F2.8


Normal lens in the 645 film format. In the 645 digital format it has the field of view of a short telephoto lens. The lens is manual focus only.

This lens has a built-in leaf shutter which allows for high speed flash synchronization. The top speed with flash is 1/500s. The flash must be connected to the lens with an X-synch cord.

The lens can also be used without the leaf shutter as an ordinary 645 lens. It has no A setting so Program and Tv exposure modes are not supported. While the lens was designed for use on Pentax 645 film cameras it will also work on the 645D and 645Z.

smc Pentax 645 LS 75mm F2.8
©, sharable with attribution
Image Format
645 film
Lens Mount
Pentax 645
Aperture Ring
Yes (no A setting)
Automatic, 5 blades
6 elements, 5 groups
Mount Variant
Check camera compatibility
Max. Aperture
Min. Aperture
Min. Focus
75 cm
Max. Magnification
Filter Size
58 mm
Internal Focus
Field of View (Diag. / Horiz.)

645 Digital: 40 ° / 33 °
645 Film: 50 ° / 41 °
RH-A 58mm screw-in
Lens Cap
Plastic clip-on
Weather Sealing
Other Features
Leaf Shutter
Diam x Length
76 x 49.5 mm (3 x 2 in.)
365 g (w/o attachments) (12.9 oz.)
Production Years
Engraved Name
smc PENTAX 645 LS 1:2.8 75mm
User reviews
Fastest flash sync speed: 1/500 s. P and Tv exposure automation is not possible with this lens.
Manual FocusAperture RingMedium-Format SupportAdapter needed for DSLRsDiscontinued
Price History:

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Registered: February, 2018
Location: NoVA
Posts: 635
Review Date: June 28, 2018 Recommended | Price: $400.00 | Rating: 9 

Pros: Leaf shutter, good optics, decent bokeh, useful soft glow at f/2.8
Cons: Cumbersome, not as fully integrated with the 645z as it should be.
Sharpness: 9    Aberrations: 10    Bokeh: 10    Handling: 6    Value: 8    Camera Used: 645N, 645NII, 645z   

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 use case, 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 duration 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). 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, not 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 the zoom is just as sharp, and far more convenient. it's just not as fast. This one's on the bubble for an essential lens on a trip focusing on landscape photography, but for a gig that needs a lens that can do portraits that won't require a touch of softening in post, this one will do very well.

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

Registered: March, 2011
Location: arlington va
Posts: 18

1 user found this helpful
Review Date: April 4, 2011 Recommended | Price: $700.00 | Rating: 10 

Pros: normal angle of view, daylight fill flash
Cons: multiple steps to make an image using shutter

i am posting a review because i have had some past experience using this lens for outdoor fill flash and general photography

if i had one wish it would be that they offered a slightly wider shutter lens perhaps 60mm or even 50mm

my go to prime has always been the 55mm because you can image just about any 'event' with it and get good results

75mm is too tight for larger groups and if you are doing lots of portraits get the 135mm shutter lens.

the lens has a shutter cocking ring, a pc flash sync socket, and shutter speed setting ring with

shutter settings are o, 60, 125, 250, 500

the o setting is used to set the lens to non-lens shutter use

i have had no problems using the hot shue - ps sync cord adaptor to use a 280t or 500ftz flash

the pc socket is safe to use with studio flash units like the photogenic powerlight units

if you forget to cock the lens shutter you will not get an exposure because the lens shutter will remain drop a frame

one must also use caution in cocking the shutter as to not change the shutter speed

my experience has been using the lens with a 645 and 645n and both these cameras the camera shutter goes to 'ls' when the lens is cocked and the lens shutter is set to a speed

i have not been about to distinguish a difference between the 'standard' 75mm lens and the 'shutter' lens

i know the construction formula is different and that means there must be a difference in image quality, but it must be minor

in closing, this is a must have lens for outdoor daylight fill flash

it also makes a good 'standard' lens
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