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04-01-2008, 02:35 PM   #1
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Built-In Flash + Old Lenses

is there any way of getting this to work in a simple manner? and can any Pentax DSLRs get it to work?

04-01-2008, 02:41 PM   #2
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What exactly isn't working?
04-01-2008, 02:58 PM   #3
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total whiteout ... because i think the camera doesn't know what the exposure is or how to compensate the exposure for the flash?
04-01-2008, 03:15 PM   #4
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Aaah. Yes, with non 'A' lenses there's no electronic communication between the lens and body, so you have to shoot fully manual. I can't find the Guide # for the built in flash for my K10D, but I just did a quick test and up to about 10ft at ISO 100 I'm getting "in the ballpark" exposures at f4.

Hope that helps.

04-01-2008, 03:27 PM   #5
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I think the problem is the flash is going to fire at full power when an older manual lens is attached (non A lens). I have gotten the exposures to work fine by trial and error, but this is definitely a pain to do and not very consistent. If you are going to do much flash photography with your old lenses I would suggest picking up an old automatic or manual flash unit. This way you can follow a guide for the distance and f stop range for what ISO you are shooting. You should be able to get good results that way. And old flashes are cheap, just watch the trigger voltage.
04-01-2008, 03:30 PM   #6
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QuoteOriginally posted by Groundloop Quote
Aaah. Yes, with non 'A' lenses there's no electronic communication between the lens and body, so you have to shoot fully manual. I can't find the Guide # for the built in flash for my K10D, but I just did a quick test and up to about 10ft at ISO 100 I'm getting "in the ballpark" exposures at f4.

Hope that helps.
That sounds about right to me too from what I remember. 10-12 ft, ISO 200, f5.6 should get pretty close. Then fine tune from there.

edit: actually from doing the calculations, it must have been closer to 8ft, iso 200, f5.6.

Last edited by Fritz; 04-01-2008 at 05:25 PM. Reason: correcting facts from my feble memory.
04-01-2008, 04:23 PM   #7
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how do i use the Guide number? poking around i found it to be:
Guide number: 15.6 (at ISO200/m) from Steve's Digicam

have you been using the flash at full power?
04-01-2008, 05:33 PM   #8
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I did a quick google for "flash guide number" and found some good information. But basically the formula is this:

f stop=guide number / flash to subject distance

That's a pretty handy formula. If I had known that one before, I wouldn't need to do so much guessing! Obviously I don't know much about flash photography.

04-01-2008, 06:17 PM   #9
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thanks again fritz ... i was just playing around now
i determine the distance i want to shoot and then from use 15.6 / distance to get the f number
shutter speed doesn't matter (as i've tested) and it goes up to 1/180 so i just use that
04-01-2008, 06:24 PM   #10
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QuoteOriginally posted by k100d Quote
how do i use the Guide number? poking around i found it to be:
Guide number: 15.6 (at ISO200/m) from Steve's Digicam

have you been using the flash at full power?
The formula that Fritz posted is correct. Just make sure that you're using the same units (meters or feet) for the guide number and flash to subject distance

When using non 'A' lenses the built in flash always fires at full power. This isn't really a problem for my way of working since 99% of the time I only use the built in flash to trigger my 540FGZ, which in turn triggers other outboard flashes.

As a side note, you can convert the guide number you found to whatever ISO you want to work at by multiplying or dividing by 1.4. So at ISO 100 the guide number would be roughly 11.2, and at ISO 400 the guide number would be 21.8 etc. Also, keep in mind that it's called a guide number for a reason. Using it will get you very close most of the time, but experience and a little chimping will help along the way.
04-01-2008, 06:45 PM   #11
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thanks Groundloop!
i actually was poking around in the manual and they actually explained all this! maybe i should read the manual more often

from the manual:
Sensitivity Built-in flash guide number
ISO 200 15.6
ISO 400 22
ISO 800 31
ISO 1600 44
ISO 3200 62

Maximum flash distance L1 = Guide number Selected aperture
Minimum flash distance L2 = Maximum flash distance 5*
* The value 5 used in the formula above is a fixed value which applies only when using the built-in flash alone.
04-01-2008, 09:18 PM   #12
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QuoteOriginally posted by k100d Quote
thanks Groundloop!
i actually was poking around in the manual and they actually explained all this! maybe i should read the manual more often

from the manual:
Sensitivity Built-in flash guide number
ISO 200 15.6
ISO 400 22
ISO 800 31
ISO 1600 44
ISO 3200 62

Maximum flash distance L1 = Guide number Selected aperture
Minimum flash distance L2 = Maximum flash distance 5*
* The value 5 used in the formula above is a fixed value which applies only when using the built-in flash alone.
These distance ratings are the range when using P-TTL auto flash. With a manual lens, the exposure does not have a range, but rather a single distance.
04-03-2008, 04:48 PM   #13
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Old Lenses and plastic mounts

I recently bought a chaep but good f1.7 50mm prime Pentax lens off Ebay. The intention is to sue it on my new Pentax K100D. Fisrt off it wouldn't work, I wondered if the lens was faulty, so I slipped on an old Cosina 70-200 and that worked fine in manual mode. I went back to the Pentax 50mm, and the camera just locked up on me.

The only difference between the two lenses appeared to be the mounting ring, metal for thePentax, plastic for the Cosina. So I figured that the electrical contact on the body of the camera couldn't make a circuit on the plastic mount and that is why I had no problems using it
fully manual.

Next step was to test the idea and stick some sellotape on the metal lens flange, Hey presto as soon as it went on I got fully manual up and working.

Next flash of inspiration is that the conct on the body needed to be switched off for the metal manual lens to work properly. So I hunted through the manual and a flicked over to the custom menu where I find there's an option to allow me to sue a manual lens with an f ring.

Works like a dream but as previous posters have hinted the in built flash settings are just too high and the pix with flash get burnt out.. is there a menu somewhere where I can reduce the output from the flash?


Cheers
Tipptoggy
04-03-2008, 05:08 PM   #14
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QuoteOriginally posted by Tipptoggy Quote
Works like a dream but as previous posters have hinted the in built flash settings are just too high and the pix with flash get burnt out.. is there a menu somewhere where I can reduce the output from the flash?
The short answer is "NO". The long answer is "No, but you can reduce the amount coming through the lens." Look up toward the beginning of this thread, and you will see that the flash exposure can be controlled with the aperture.
04-03-2008, 05:21 PM   #15
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QuoteOriginally posted by Canada_Rockies Quote
The short answer is "NO". The long answer is "No, but you can reduce the amount coming through the lens." Look up toward the beginning of this thread, and you will see that the flash exposure can be controlled with the aperture.
Agreed...it's unfortunate but true. The pop up sucks anyway

Time to look for a used Nikon SB flash
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