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09-11-2011, 08:58 PM   #1
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Difference between SMC A and LS lenses????

I was looking at 645 lenses at KEH and they have both types with the 75 2.8. The lenses I got for mine are SMC A. What's the difference? I noticed the LS cost more. Better image quality?---Can't wait until my 645 setup gets here!...a few more days...

09-11-2011, 09:20 PM   #2
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LS stands for "Leaf Shutter"- those lenses let you sync flash up to 1/500s, but don't feature the "A" setting.

Pentax 645 LS 135mm F4 Reviews - 645 Telephoto Primes - Pentax Lens Reviews & Lens Database

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09-11-2011, 09:22 PM   #3
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The "LS" should refer to leaf shutter. I don't know that much about the 645 lenses, so I'm not sure if they are any different optically.
Basically the leaf shutter is a special shutter in the lens itself, that allows you to take photos using flash at higher speeds than the normal sync speed.
When taking a photo using the leaf shutter, I believe the normal focal plane shutter is locked open and then the leaf shutter in the lens is allowed to fire.
I've also seen the LS lenses listed as a "flash lens". I'm pretty sure you can use them as a normal lens, without worrying about the leaf shutter too.
If you haven't already noticed, these MF SLRs typically have very slow sync speeds due to the large mirror and FP shutter. The 67 for example is 1/30.
09-12-2011, 12:37 AM   #4
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for the pentax 645 system there are two leaf shutter lenses the SMCP 75mm f/2.8 LS and SMCP 135mm f/4 LS - both are optically identical to their A-Series counterparts, as mentioned in the above posts they possess a built in Leaf shutter -Which has to be cocked each time you use it - which makes LS lenses a bit awkward and slow to use, but with Medium format there is no other way of obtaining 1/500th synch speeds. You do not have to use the leaf shutter mechanism - on the shutter speed dial in the front of the lens there is a circle - set the shutter to that and the leaf shutter will remain open allowing you to use the focal plane shutter. The reason for this function is that Leaf shutters have a substantially shorter longevity than focal plane shutters do - as I recall the average leaf shutter is only rated for 20,000 firings. As far as I know the focal plane shutter in the 645D is rated for 50,000, so having two shutter mechanisms at your disposal is certainly appealing.


Last edited by Digitalis; 01-03-2012 at 01:41 AM.
09-12-2011, 05:23 PM   #5
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Leaf shutter-I should have figured that out. Now I wish I would have got the 75 LS lens.

My Nikon D300 syncs at 1/250, and that has been a problem a couple of times outdoors. My D50 was 1/500, but didn't think about that before I sold it. Actually, if you connected a non dedicated cord between camera and flash, and the D50 did not "know" there was a flash, you could go all the way to top shutter speed 1/4000, and none of the image blacked out. But faster than 1/1000, it would start underexposing a little-compensation is necessary. I think that body did not have a focal plane shutter that's why it was possible. The D300 will do high speed sync with compatible flash, but after 1/320, range is DRASTICALLY reduced.
09-12-2011, 09:31 PM   #6
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QuoteOriginally posted by LightMeter Quote
Leaf shutter-I should have figured that out. Now I wish I would have got the 75 LS lens.

My Nikon D300 syncs at 1/250, and that has been a problem a couple of times outdoors. My D50 was 1/500, but didn't think about that before I sold it. Actually, if you connected a non dedicated cord between camera and flash, and the D50 did not "know" there was a flash, you could go all the way to top shutter speed 1/4000, and none of the image blacked out. But faster than 1/1000, it would start underexposing a little-compensation is necessary. I think that body did not have a focal plane shutter that's why it was possible. The D300 will do high speed sync with compatible flash, but after 1/320, range is DRASTICALLY reduced.
Err, the D50 didn't have a focal plane shutter? Really??

Anyway, I'm sure there's still a lot you can do with the sync speed of 1/60 on the 645.
09-13-2011, 07:45 AM   #7
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QuoteOriginally posted by goddo31 Quote
Err, the D50 didn't have a focal plane shutter? Really?

As a matter of fact, I think it does, for the slower shutter speeds. I'm trying to remember how someone explained it to me. I think after a certain speed, the sensor is "on" for that amount of time. Example- if the highest focal plane speed is 1/500, and you select 1/4000. The shutter opens for 1/500, but the sensor is on for 1/4000. I'd like to find a camera body that does that. About 6 years ago I used to have an Olympus P&S that would sync with its highest shutter speed.
09-23-2011, 08:18 PM   #8
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QuoteOriginally posted by goddo31 Quote
... When taking a photo using the leaf shutter, I believe the normal focal plane shutter is locked open and then the leaf shutter in the lens is allowed to fire. ...
The operation procedure from a 75LS and 135LS user:
  1. Set shutter speed on lens
  2. Cock lens shutter
  3. Set camera shutter speed to 1/8sec.
  4. Fire

The actual steps inside the camera when the shutter button is released:
  1. Mirror flips up
  2. Aperture stop down mechanism is actuated
  3. Lens stops down and shutter closes.
  4. Focal plane shutter on camera body opens.
  5. Lens shutter opens and close for duration of exposure.
  6. Focal plane shutter on camera body closes.
  7. Lens shutter open.
  8. Mirror flips back down

It is an extra step to cock the shutter but it is a natural step when the film is winding to the next frame(645/N/NII) you just grab the shutter cocking ring and twist. IMHO this is faster and less prone to jamming than trying to shoot fast hand winding a Hassy500

09-23-2011, 11:58 PM   #9
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QuoteOriginally posted by D W Quote
...
It is an extra step to cock the shutter but it is a natural step when the film is winding to the next frame(645/N/NII) you just grab the shutter cocking ring and twist. IMHO this is faster and less prone to jamming than trying to shoot fast hand winding a Hassy500
I wouldn't go as far to speculate how natural that extra step is for everyone. I find myself frequently forgetting to arm the lens for the next shot especially after a period of using my 500C/M.
09-24-2011, 03:08 PM   #10
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optically they are the same, but I believe that the LS has five blades, the A (and FA) eight.
I do not know whether there was a lens hood for the 135 LS (the LS 75 shared that of the A version).

Last edited by Smolk; 09-24-2011 at 03:20 PM.
09-26-2011, 06:04 AM   #11
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QuoteOriginally posted by tuco Quote
I wouldn't go as far to speculate how natural that extra step is for everyone. I find myself frequently forgetting to arm the lens for the next shot especially after a period of using my 500C/M.
OK it was natural for me but whenever I use the Pentax it was for hand held fast shooting situations with many shots. I also shot 45 and 810 so the shutter cocking was a routine until the Sinar DB's.

I got the hang of it within minutes just like the grab the knob, turn knob forward and tile the camera back at the same time sequence with a 500C/M.
01-02-2012, 10:39 PM   #12
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i bought the 75mm ls lens, hooked up an old vivatar flash unit with pc cord , and got good exposures at 1/500 sec.the flash unit is 35 yrs, old.
01-03-2012, 08:48 AM   #13
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One other small difference - the LS lens is not an "A" lens, so you have to always set the aperture via the aperture ring on the lens.
01-09-2012, 09:22 AM   #14
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QuoteOriginally posted by D W Quote
The operation procedure from a 75LS and 135LS user:
  1. Set camera shutter speed to 1/8sec.
That is not necessary with the 645N, which automatically recognises the lens as an LS and sets the shutter speed accordingly.
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