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01-05-2011, 04:53 PM   #1
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Flash Settings Using M Series Lenses On The K X

Pardon me for being stupid but I just acquired a mint condition 50mm M series f1.7 off Ebay for $60.00 after seeing reviews on here praising the optics. I've set the aperture ring to "allowed" in the custom menu but every shot using the pop-up flash is washed out. Have I forgotten a setting a setting here or there. Sorry, if this has has been asked before.

Barry

01-05-2011, 05:18 PM   #2
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When using a non-"A" lens on a Pentax body, the flash will always fire at full power.

For the built-in flash, the guide number is 13 in meters at ISO 100.

This means, if your subject is 3 meters (10 feet) away, the correct aperture setting is 13 (guide number) / 3 (distance) = 4.33 so set the lens to f/4. If you are at ISO 200, the guide number doubles to 26, so you'd need to set the lens to f/8.

Needless to say, using flash with M lenses is a waste of battery power and quite limiting.
01-05-2011, 06:40 PM   #3
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Manual flashes and auto flashes with their own built in sensor work quite well with manual lenses.

With a manual flash you estimate the distance and select the correct flash power level for the aperture you want to use. There is generally a table printed on the flash to help with the calculation.

With an auto sensor flash you select a sensor setting for the f-stop and ISO you want to use and then set the camera to match the settings you chose on the flash. Again, there will be a table or calculator on the flash that says what distance range each sensor setting will work with.
01-05-2011, 06:51 PM   #4
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QuoteOriginally posted by Steinback Quote
Manual flashes and auto flashes with their own built in sensor work quite well with manual lenses.

With a manual flash you estimate the distance and select the correct flash power level for the aperture you want to use. There is generally a table printed on the flash to help with the calculation.

With an auto sensor flash you select a sensor setting for the f-stop and ISO you want to use and then set the camera to match the settings you chose on the flash. Again, there will be a table or calculator on the flash that says what distance range each sensor setting will work with.

I'm just talking basic pop-up built-in flash here, I assume doing close up macro flash photography is out of the question. LOL I did a test shot from 10 feet away at ISO 200 and the pics are still washed out.

01-05-2011, 07:23 PM   #5
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Here are flash tables for using the built in flash with manual lenses:



Using the middle set of figures it looks like you should be using f/5.6 at 10 feet (around 3 meters) and ISO 200 with the shutter speed set to 1/180 or slower depending on ambient light levels.

Macro work is possible with flash diffusion or ND filters, assuming the lens doesn't block light travelling from the flash to the subject. Even with a lens in the way it is possible to bounce the flash off of a diffuser and towards the subject.
01-05-2011, 08:58 PM   #6
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The flash/aperture table (which is just a bigger version of GN/distance) is all well and good..

The problem is that since the flash is firing at full power all the time, the recharge time (time between shots) is long, and you'll deplete your camera's battery much faster.

To the OP, if you want to take macro shots, buy the $60 Yungnuo YN-460 or YN-560 flash. It has eight (or sixteen) variable power settings. That's what I do.

In fact with a D-FA 100mm Macro, I just use 1/80s shutter, f/11 aperture, ISO 400, and set the Yungnuo at 1/4 power, that's it. At the distances I'm working (close to 1:1) these settings consistently give me what I want in terms of exposure.
01-06-2011, 03:39 PM   #7
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I use the onboard flash now and then, I sometimes have to go all the way to f22 with my M 50's, depends on conditions. I just keep going to smaller apertures on a few test shots, until I get good exposure. You can also increase shutter speed but that gives a minor difference usually.

I have the same 1.7 M 50, nice lens. I've used the onboard flash for macros a few times but prefer an external for that.

You can also fold up a cash register reciept into a small envelope and use it as a diffuser if you're getting too much flash, it works quite well. You need a standard cash register reciept about the length of the camera. Fold it in half lengthwise, then twice in thirds. Open the center so only one sheet of paper is in front of the flash and slip it on. Works great. Make sure you put the printed side out, it's heat sensitive so if it's next to the flash it will develop a black spot.
01-06-2011, 10:49 PM   #8
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QuoteOriginally posted by orly_andico Quote
...
If you are at ISO 200, the guide number doubles to 26, so you'd need to set the lens to f/8.
...
As the table in post #5 shows, it does not double but needs to be multiplied with the square root of 2 (1.4). GN doubles every 2 ISO steps.

01-07-2011, 11:53 AM   #9
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QuoteOriginally posted by shutterpuppy Quote
I did a test shot from 10 feet away at ISO 200 and the pics are still washed out.
You just need to stop down the aperture enough so that the picture is properly exposed.

Flash exposure is governed by flash power, ISO, aperture, and distance from the light source to the subject. Since flash power is fixed to 1/1 with M lenses, you are limited to adjusting the other parameters.
01-07-2011, 12:01 PM   #10
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Nice table up there! Really helped. I also have the M 50 f1.4 and washed everything everytime I used the flash... until I set the aperture a bit high, around f8 or f11 I think (and yeah, the shutter speed wouldn't go faster than 1/180, even at ISO200.... ). Thanks for the tips!

Will try Pete's suggestion above next time. Improvised diffuser
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