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06-28-2012, 11:32 AM   #1
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High speed sync flash with manual non-A lens?

Is it possible to do as the title? Do I need to short the A pin?

06-28-2012, 11:47 AM   #2
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You can only do high sync flash in P-TTL mode.
06-28-2012, 02:03 PM   #3
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QuoteOriginally posted by baby007 Quote
Is it possible to do as the title? Do I need to short the A pin?
QuoteOriginally posted by Anvh Quote
You can only do high sync flash in P-TTL mode.
= no, you can't do HSS with manual lenses.

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06-28-2012, 10:27 PM   #4
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QuoteOriginally posted by Adam Quote
= no, you can't do HSS with manual lenses.
I think Im confused already. While waiting for replies, I tried to short the A pin and put the sigma 610 super on HSS. Now I can set the shutter speed beyond 1/180 and take picture with flash. Is it real HSS? and I don't know if it is "P-TTL" flash or not. Is there anyway to check? It does show "P-TTL" on the sigma though. I use 50mm 1.4 M lens.

06-29-2012, 01:51 AM   #5
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Yes, by shorting the A pin, you'll be able to enable full P-TTL features on a non-A lens (PK-m or m42).
But you have to pay attention to the following point : using an unmodified PK-m lens, you'll be stuck to its widest aperture available.

In order to be able to close down your PK-m lens, you'll have to transform it into a pre-set lens, either by bending/cutting its aperture coupler (eeeeerk! Butcher's work!) or by simply drilling another locking hole so the lens will lock halfway turned into the mount (great as if you ever want to use it as a PK-m lens again, you just have to use the original locking hole instead).

It will then behave just like a m42 lens, meaning that adjusting the aperture will instantly darken the viewfinder.
In all cases, the aperture displayed on the camera (not the lens) will have to be at the widest value available.

Voilą!
06-29-2012, 06:40 AM   #6
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QuoteOriginally posted by dlacouture Quote
Yes, by shorting the A pin, you'll be able to enable full P-TTL features on a non-A lens (PK-m or m42).
But you have to pay attention to the following point : using an unmodified PK-m lens, you'll be stuck to its widest aperture available.

In order to be able to close down your PK-m lens, you'll have to transform it into a pre-set lens, either by bending/cutting its aperture coupler (eeeeerk! Butcher's work!) or by simply drilling another locking hole so the lens will lock halfway turned into the mount (great as if you ever want to use it as a PK-m lens again, you just have to use the original locking hole instead).

It will then behave just like a m42 lens, meaning that adjusting the aperture will instantly darken the viewfinder.
In all cases, the aperture displayed on the camera (not the lens) will have to be at the widest value available.

Voilą!
Heavens no! So long as the lens meters wide open and stops down during exposure, you can do P-TTL without making any permanent modification to the camera body or lens.

baby007 had the right idea, just stopped short. You short the 'A' pin and you'll get P-TTL capability. The next step requires a chart, magictape, scissors and less than 10 minutes to manually indicate the aperture range available on the lens.

https://www.pentaxforums.com/forums/pentax-camera-field-accessories/113756-pk...ml#post1965512
If you scroll down a couple postings - I did a second posting with pictures. The only difference is you will apply the tape to the lens mount rather than extension tube.

There is a chance of slight overexposure when using a lens older than A series. You can do test shots and/or post processing to correct for this.
06-29-2012, 12:29 PM   #7
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Jim, you're right, it can work with some lenses, but true pk-m lenses (nearly all Pentax ones, anyway) are not pk-A compliant, and you'll have severe overexposure with your method at anything but wide open setting, because PK-m lenses do not have a surface-related aperture link.

But you're right, before modifying your lens, it's worth trying its PK-A compatibility (the Porst 55/1.2 is a good example of a working PK-A candidate).
06-30-2012, 05:38 PM   #8
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diacouture- what do you consider "severe" overexposure? Other than some highlights already right at the edge, 1 to 1.5 stops are usually well within post processing tools; even 2 stops can sometimes be made acceptable.

On an A series lens, the desired aperture is reached by the body moving the lens' aperture level a percentage of the arc between min and max aperture. This is why it is important to let the body know via the contact pins what the min and max is for a lens.


A M series lens doesn't have the same percentage movement. If you give the body the M series lens min and max aperture and manually set the desired aperture on a M series lens, take a couple test shots, then set the body's exposure compensation, you should be able zero in on the difference with at worst only moderate overexposure that can be fixed post processing. And of course short the A pin on the camera body.

07-01-2012, 12:54 PM   #9
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The problem is that you won't be closing your lens all the way down to your selected aperture... M-lenses need more lever movement than A lenses to get down to the same aperture. So by selecting the aperture on the camera, you'll be in fact using a wider aperture than what the camera (and you!) expects, thus getting overexposure (flash exposure being computed from wide open to the selected aperture).

But with pre-set lenses (such as m42 or sideway-mounted PK-m), all you need to do is to select the widest aperture available on the camera, then use whatever real aperture you want on the lens. No overexposure, no complexity, instant satisfaction...

Only downside is a darker viewfinder...
07-01-2012, 06:18 PM   #10
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I know I'm being picky - but I'd like a numerical value for the amount of overexposure using a Pentax-M series lens when:
  • The A contact on the body has been shorted.
  • The lens mount has insulator patch(es) so the body knows the min/max aperture range of the lens.
  • Both the lens and the body have the same selected f/stop.
  • The photo is taken using P-TTL flash within a usable flash range for that aperture.

Are we talking less than a stop, more than one but less than two, or more than two stops overexposure?
Is the overexposure consistent? (should be for any given f/stop - there may be a minor variation between different f/stops) And is the overexposure within the limits of the camera's exposure compensation scale?
07-01-2012, 11:46 PM   #11
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I did both the drilling and taping method, the exposure is not consistent. Is that only me?
07-02-2012, 01:30 AM   #12
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Jim: it will depend on the lens used, and the aperture selected!

PK-A lenses work by using a standardized, surface-related lever motion. Every A lenses will lose the same amount of stops when actuated the same way. Moving the lever by, say, 1mm will close the lens by one stop, and this for any PK-A lens used.

On the other hand, older lenses just rely on a full lever move in order to bring the aperture down to the selected value, without any rules on what effect the lever has on the aperture's surface in-between.
So, with some lenses you have a good PK-A compatibility, and with some it will be an utter mess. And it obviously also depends on the selected aperture.

Say you have a f/2.8-22 PK-m lens. It will reach f/22 only when the lever is fully engaged.
But the PK-A mount is able to handle a f/2.8-45 lens at its widest swing! So, by using your method, you'll not be able to really use the f/22 aperture, as the camera will never fully close the lens (having no need to go below what it thinks is f/22).
Said like this, you'll think you only lose the last stop (the difference between f/22 and f/45), but there is really no way to know, as how the aperture behaves when the lever is engaged stays unknown...
07-02-2012, 09:00 PM   #13
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Wow, this is more complicated than i thought. Thanks for your replies. btw, do you know why on the sigma 610 super, P-TTL just comes and goes. The letter P on the flash lcd is not staying. Once in a while it disappears...
07-03-2012, 05:03 AM   #14
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baby007 - Either your flash is not propery seated, or you are only intermittently shorting the 'A' pin. My money is on the flash.

diacoulture - I'm waiting for a friend to find his old K1000 kit and lend me a couple Pentax-M lens. It is not that I doubt what you say, but you aren't providing specifics as to the level or consistency of overexposure. I will run some tests and report here.
07-03-2012, 08:16 PM   #15
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Yup, you are right. It is not seated all the way. Cant wait for your report!!
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