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11-17-2009, 11:11 PM   #1
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Any way to reduce on-board flash output with manual aperture lenses?

I have a bunch of macro extension rings and and my little film canister diffuser, if only the darn flash didn't fire at full power. I dont think +/- Flash EV even effects it, -2 EV would at least be something!

I am thinking of taping a bunch of tissue paper to it. I'd rather not have to carry around my external flash on a bright sunny day and save the space for another lens

11-17-2009, 11:23 PM   #2
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What camera and is the lens an A series or M series? You control flash with aperture. So if the lens is an M or M42, then the flash on most DSLR's will fire at full power. It has no idea what's attached. In that case you stop the lens down to control the light coming back in.

If that doesn't work for creative reasons etc, then you will have to make a darker diffuser or reflect the flash in some way.
11-17-2009, 11:35 PM   #3
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K-x, not A or M series, effectively M series - no information is being transmitted.

That sucks how there is no half power or even +/- Flash EV has no effect! I guess I will try the toilet paper. in the film canister, kinda makes it easy, won't have to use tape. But it will kill my battery life!
11-18-2009, 12:13 AM   #4
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QuoteOriginally posted by Eruditass Quote
I have a bunch of macro extension rings and and my little film canister diffuser, if only the darn flash didn't fire at full power. I dont think +/- Flash EV even effects it, -2 EV would at least be something!

I am thinking of taping a bunch of tissue paper to it. I'd rather not have to carry around my external flash on a bright sunny day and save the space for another lens
Fool the camera into thinking an A lens is mounted. This is done by insuring the "A"pin on the camera is connected to ground.

Place a ball of aluminum foil over it, or alter the extension ring contact, or alter the camera side of the lens mount.

I've altered my lens mount in the following simple way (reversible):

Just unscrewthe mount ring, cover the A pin with a bit of metal foil, and replace the mounting ring. Now the camera thinks all lenses are A type.

This appears to have few downsides and automatic flash metering will function properly. The f-stop indicator in the view finder will work; turn the e-wheel so the displayed f-stop is as low as it will go; now the exposure will be completely controlled by presetting the len's aperture.

11-18-2009, 12:18 AM   #5
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Wow, that is cool - it will do P-TTL with all lenses?

Will this also allow trap-AF with all lenses?? I assume the aperture information will just be plain wrong?

If this isn't in the article section, it should be!
11-18-2009, 12:42 AM   #6
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Yeah, it's a wonder they didn't made it this way by default...
11-18-2009, 05:27 AM   #7
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QuoteOriginally posted by Eruditass Quote
.... it will do P-TTL with all lenses?

Will this also allow trap-AF with all lenses?? I assume the aperture information will just be plain wrong?
.....
Yes, All lenses will do P-TTL.

Aperture info in the EXIF will be unrelated to actual lens aperture.

The reason to set the viewfinder F-stop to the lowest value is to prevent the camera's trying to close the lens' aperture at exposure time. This is important because if the camera thinks it will be closing the aperture when shooting it will calculate the wrong exposure time.

The physical downside of this method is that the viewfinder image dims as the lens is manually closed at composition time. The upside is a huge range of early Pentax and adapted third party lenses can be more easily used (auto exposure& P-TTL flash).

The Green Button can still be used to accommodate SMC, K, & M lens exposures I think.

Dave in Iowa

Last edited by newarts; 11-18-2009 at 05:43 AM.
11-18-2009, 06:12 AM   #8
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This mod can be more easily done by carefully adding a small amount of solder on the camera A contact to make it flush with the mount surface... No need to unscrew the camera mount!

Regarding PK-M lenses, from memory, this mod is not really satisfying because Av mode will not work, and only M mode and Green button will let you meter "on the fly".
For this, another useful mod is to drill a second locking hole in the lens itself, so it locks halfway into the mount... This way, the aperture lever is not kept pushed by the camera aperture actuator, and your PK-M lens now behaves just like a m42 and stops down as you select another aperture...

Greatest point is that you can still use the original locking hole (by rotating the lens fully into the mount) if you want to use it on a film camera...

11-18-2009, 07:10 AM   #9
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QuoteOriginally posted by dlacouture Quote
This mod can be more easily done by carefully adding a small amount of solder on the camera A contact to make it flush with the mount surface... No need to unscrew the camera mount!

Regarding PK-M lenses, from memory, this mod is not really satisfying because Av mode will not work, and only M mode and Green button will let you meter "on the fly".
For this, another useful mod is to drill a second locking hole in the lens itself, so it locks halfway into the mount... This way, the aperture lever is not kept pushed by the camera aperture actuator, and your PK-M lens now behaves just like a m42 and stops down as you select another aperture...

Greatest point is that you can still use the original locking hole (by rotating the lens fully into the mount) if you want to use it on a film camera...
I agree entirely.

Note the mod does not prevent using PK-M lenses with M mode & Green button; in that sense nothing is lost, and if the extra locking pin stop is added to the PK-M lenses base they will function the same as M42's regarding P-TTL etc.

Last edited by newarts; 11-18-2009 at 10:07 AM.
04-08-2010, 10:00 AM   #10
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QuoteOriginally posted by newarts Quote
I agree entirely.

Note the mod does not prevent using PK-M lenses with M mode & Green button; in that sense nothing is lost, and if the extra locking pin stop is added to the PK-M lenses base they will function the same as M42's regarding P-TTL etc.
Tried it today on my K-x with PK-M lenses (fully mounted). The P-TTL is working with aperture wide open. However, in M mode, the camera no longer do stop-down metering when the green button is pressed. In stead, the metering is done with aperture wide open and adjusted based on the F number set in camera --- just like A lenses --- which won't be accurate for M lenses.

Last edited by xjx; 04-08-2010 at 10:10 AM.
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