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05-20-2013, 02:25 AM   #1
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Pop-up flash with M-lens?

Hi,
I have been trying in vain to use the K5 pop-up flash with my M-50 f1.7 lens.

I want a shallow dof, so I let the aperture at f1.7 and used M, Av, and P mode. I used
different kind of exposure metering. I focus, press on the green button and shoot.

The result is always extremely over exposed!

I do not want to kill the shallow dof by closing the aperture and that's the only solution
I found in my searches on the web.

Thanks for your help.

05-20-2013, 03:07 AM   #2
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1.7 is a bit too open for the flash. The only way I could see you pulling that off straight is to use an ND filter. Even then, we're talking a 4-Stop filter at best.

I suppose you could always shoot in M, and tape a piece of paper, folded in half(Two layers thick) over your flash. That'd diffuse/disperse some excess light, provide a bit softer of lighting, and possibly bring it within range. With that setup, I think you could push into around 1/180S exposure and get decent results.
05-20-2013, 03:11 AM - 1 Like   #3
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QuoteOriginally posted by Naruto Quote
Hi,
I have been trying in vain to use the K5 pop-up flash with my M-50 f1.7 lens.

I want a shallow dof, so I let the aperture at f1.7 and used M, Av, and P mode. I used
different kind of exposure metering. I focus, press on the green button and shoot.

The result is always extremely over exposed!

I do not want to kill the shallow dof by closing the aperture and that's the only solution
I found in my searches on the web.

Thanks for your help.
With Pentax lenses from the first two K-mount series, generally called K and M lenses, the flash on a K-5 will ALWAYS fire at FULL strength when a K or M lens is mounted. This is covered near the end of Chapter 11, on my copy of the manual it is at the bottom of page 338.

If you want to control flash output, you will need an A, F, FA FA J, DA or D FA lens. Any lens from the A series or later,

Or en external flash which you can use on manual.

Regards

Chris
05-20-2013, 03:18 AM   #4
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Setting the ISO range to something very low like ISO 100 or 200 may also help to minimise over-exposure.

05-20-2013, 03:43 AM   #5
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The built-in flash is a P-TTL flash only, no auto or manual modes. In order to work properly, the flash must know the lens aperture. M series lenses do not communicate aperture data to the camera, therefore you cannot use the built-in flash with M series lenses. You will need a shoe mount flash that works in auto or manual mode.
05-20-2013, 04:40 AM   #6
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All of the above is good advice. My only suggestion is a combination of some of the ideas, pls one other. Is it possible to keep ISO at a minimum, and drop the flash compensation down to minimum and start to get a result??

Im not sure what you are attempting is possible, however.
05-20-2013, 09:51 AM   #7
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Thanks for all of your replies. That is sad but nothing seems to help with this.
I will try with an external flash.
05-20-2013, 11:26 AM   #8
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I used a K85 in manual with no problems with the pop-up and had great exposure. Make sure to use the Histogram.

05-20-2013, 04:21 PM   #9
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The built-in flash is not only P-TTL. It also supports manual mode .... and if you are using a lens without a body controlled aperture (pre A series, like the OP's M series lens), ALL you get is full manual control.

You now have two choices....
Here is a link showing how to non-destructively modify your camera body and M series lens: https://www.pentaxforums.com/forums/pentax-camera-field-accessories/113756-pk...ml#post1965512
Be sure to scroll down a couple posts for the photos - this is a LOT easier to do than the text might lead you to think.

So far as I am concerned, Pentax's attempt to protect users from themselves sadly includes a bunch of artificial limitations.
05-21-2013, 12:13 AM   #10
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QuoteOriginally posted by Naruto Quote
Thanks for all of your replies. That is sad but nothing seems to help with this.
I will try with an external flash.
It seems you do not understand the core of the problem, you're asking for something impossible.
With a M lens the camera does not know about the aperture set. Aperture is essential for flash exposure.
The internal flash is a P-TTL flash only. (You can make a flash exposure correction for the given exposure though.)
05-21-2013, 03:30 AM   #11
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Well the external flash solution will work, if you put it far enough and radio trigger it.

Edit: seriously though, put some paper or tape on the flash head, and stop down the lens just a bit.
05-21-2013, 03:40 AM   #12
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QuoteOriginally posted by dragra Quote
The internal flash is a P-TTL flash only.
Not correct. The internal flash can be P-TTL, but only if you are using a lens with body controlled aperture - meaning A-series or newer. Otherwise the internal flash is fully manual control, and with M, K or M42 lens only manual control. There is a work around as shown in the links in my preceding post.
05-21-2013, 04:20 AM   #13
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QuoteOriginally posted by JimJohnson Quote
Not correct. The internal flash can be P-TTL, but only if you are using a lens with body controlled aperture - meaning A-series or newer. Otherwise the internal flash is fully manual control, and with M, K or M42 lens only manual control. There is a work around as shown in the links in my preceding post.
I don't have a K-5 but I assume the pop-up flash works the same across different Pentax dSLR cameras. This means P-TTL with A-lens and newer, but with M-lens no P-TTL. I know that with M-lens the flash always fires full power.

The OP expected some sorts of control over the flash power while he wants to leave the aperture of his M-lens fully open. He has no manual control option over the pop-up flash. Pop-up flash will always fire full power with M-lens, as we know.

Under manually controlled flash I understand a strobe that has zero automation & no communication with the camera (except sync) yet it has some sort of power control. If it has only one power setting then there is no manual control.
05-21-2013, 05:34 AM   #14
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QuoteOriginally posted by Naruto Quote
Thanks for all of your replies. That is sad but nothing seems to help with this.
I will try with an external flash.
Sorry, you will have the same metering problem with an external flash.

If the external flash has some manual power controls, like 1/2, 1/4, 1/8, 1/6, etc,, then you will have better control. But you still have to do some manual calculations, or trial and error.

If the external flash has an auto thyristor mode, then you might be in more luck. However, few flashes that I know of support a thryristor setting corresponding to an aperture as wide open as f1.7, which you said you were chasing. (In auto thyristor mode, you do have to initially "sync" the camera's aperture with what the flash thinks is being used, and f/1.7 probably won't be within the flash's range.)
05-21-2013, 06:01 AM   #15
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QuoteOriginally posted by Naruto Quote
Hi,
I have been trying in vain to use the K5 pop-up flash with my M-50 f1.7 lens.

I want a shallow dof, so I let the aperture at f1.7 and used M, Av, and P mode. I used
different kind of exposure metering. I focus, press on the green button and shoot.

The result is always extremely over exposed!

I do not want to kill the shallow dof by closing the aperture and that's the only solution
I found in my searches on the web.

Thanks for your help.
I'm sure you've read all the replies outlining the difficulty in trying to do what you want with an M lens. From a different perspective, the pop-up flash is an add-on that's designed for two basic needs: fill-in flash in difficult lighting (such as "harsh") lighting conditions and for snapshots in very dark circumstances. You are trying to use it for a much different purpose, one that really demands a more controllable flash unit.
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