Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-18-2012, 04:33 PM   #1
Veteran Member
ChooseAName's Avatar

Join Date: Aug 2009
Location: Southeast USA
Photos: Gallery | Albums
Posts: 390
Overexposing with external flash and manual lenses

Today I was taking pictures in a small bedroom (about 15ft x 15ft, with 8 ft ceiling) with K-x, M 85/2, and Metz 48 flash. The ISO was down as far as it could go (100), and the shutter speed was as high as it could go, 180. The lens was at 2.8 or 3.5. The flash was set to -3 EV and P, TTL, and HSS (but as I understand it, P-TTL doesn't work on manual lenses...?) I was still getting a large amount of blown highlights, as shown in the sample photo.

I guess technically the highlights might not be completely blown though, as I can recover a lot of the image in Lightroom, as seen in the not-so-overexposed attachment. To achieve that, I set the exposure slider to -4.0 and the Blacks to 45. The recovered version still looks a bit strange to my eyes, definitely not the way I saw the scene.

Is there some magical setting that I am totally missing, or is this something I'll just have to live with? i.e. recovering in LR and/or stopping down the lens (which I'd prefer not to do because I like a thin DOF most of the time)

Attached Images
View Picture EXIF
PENTAX K-x  Photo   
09-18-2012, 04:50 PM   #2
Pentaxian




Join Date: Feb 2009
Location: Alameda, CA
Posts: 3,198
P-TTL does NOT work with manual lenses. Unless you're using the flash's auto mode (using the flash's own light sensor), the flash will fire at full power (or whatever power ratio it happens to be set to).

You'll have to use the manual flash mode: adjust ISO and aperture settings (and the flash's power ratio setting, if available) depending on the distance from the flash to the subject being photographed. It's not the end of the world, but it's clumsy, especially when you bounce the flash.

For this reason, I don't buy ANY flash that does not have auto mode.
09-18-2012, 05:04 PM   #3
Veteran Member
ChooseAName's Avatar

Join Date: Aug 2009
Location: Southeast USA
Photos: Gallery | Albums
Posts: 390
Original Poster
QuoteOriginally posted by SOldBear Quote
P-TTL does NOT work with manual lenses. Unless you're using the flash's auto mode (using the flash's own light sensor), the flash will fire at full power (or whatever power ratio it happens to be set to).

You'll have to use the manual flash mode: adjust ISO and aperture settings (and the flash's power ratio setting, if available) depending on the distance from the flash to the subject being photographed. It's not the end of the world, but it's clumsy, especially when you bounce the flash.

For this reason, I don't buy ANY flash that does not have auto mode.
Ah, well, that would definitely be the problem then. According to to Matt's Pentax flash site (Feature Tables - Pentax P-TTL Flash Comparison), the Metz-48 doesn't have auto mode. Any flashes that do are way out of my price range right now, so I'll just have to live with it. I do have an A 50/1.7 on the way though, so I believe P-TTL should work with that? Thanks for the answer, BTW.
09-18-2012, 05:15 PM   #4
Inactive Account




Join Date: Dec 2008
Location: North Carolina
Photos: Albums
Posts: 1,720
QuoteOriginally posted by ChooseAName Quote
I do have an A 50/1.7 on the way though, so I believe P-TTL should work with that?
Yes it will.

09-18-2012, 06:21 PM   #5
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,862
You could use the manual power settings, 25 steps. A good starting point would be 1/16, since that's four stops down from the full setting.
09-18-2012, 08:06 PM   #6
Pentaxian
aleonx3's Avatar

Join Date: Jul 2007
Location: Brampton, Ontario
Photos: Gallery | Albums
Posts: 3,888
As expected since it will flash with full power, try M mode on the flash and start lowest setting.
09-18-2012, 11:12 PM   #7
Site Supporter




Join Date: May 2012
Location: Adelaide
Photos: Gallery | Albums
Posts: 1,104
As others has mentioned, reducing power from full to a lower setting would be required for close-ups like your sample picture. This should be done in conjunction with reading up in your manual the Guide Numbers for the flash (and making adjustments to this for the zoom setting of the flash if it has one).

Guideline numbers are a simple means of relating flash output to distance, aperture and ISO settings and a basic understanding of this is needed when going fully manual with flash use. As zoom settings on a flash either concentrate light or disperse it more widely, an appendix to your flash manual will probably have different guide number tables for each zoom setting. You would need to make your own adjustment to the Guide Number for any manually lowered power output eg halving, quartering the Guide Number as appropriate for the lowered power level. And Guide Numbers change for different ISO, so make sure the Guide Number used is appropriate for the ISO setting you're using on the camera.

This will allow you to determine the correct aperture setting for the combination of distance and power output. Required aperture equals Guide Number divided by distance (making sure distance is measured in units consistent with the Guideline Number (ie both either in metres or feet, not a mix!). Sounds a little complicated initially but isn't really once you get your head around it.

Note though that bounce flash or using clip on diffusers will lower what flash output reaches the subject. Use the manual's relevant guide number as a start and then experiment with how much you need to open up the lens aperture or increase ISO sensitivity to get correct exposure.

Shutter speed does not influence exposure levels with flash photography (unless you get slow enough that ambient light starts to dominate).

Unless you reduce power by quite some margin for the supplied sample shot, you will most likely need an aperture setting much smaller that F2.8 or 3.5. My rough guess is that your image would have been a lot better around f8 plus or minus.

Last edited by southlander; 09-18-2012 at 11:20 PM. Reason: Refined the response
09-19-2012, 05:25 AM   #8
Veteran Member
ChooseAName's Avatar

Join Date: Aug 2009
Location: Southeast USA
Photos: Gallery | Albums
Posts: 390
Original Poster
Thanks for the advice, everyone. I thought that adjusting the EV values on the flash while in P-TTL would tone the flash power down even with a manual lens, but I take it that's not the case. I'll put the flash in M mode, adjust power down, and see what I get.

09-19-2012, 03:31 PM   #9
Veteran Member
DaveHolmes's Avatar

Join Date: Jul 2010
Location: Yorkshire
Posts: 1,501
Check out Zack Arias OneLight on youtube
Skip to 1:25... He clearly explains how to get proper exposure using manual flash in the full video... This is unfortunately is just a montage...

But essentially: Shutter controls Ambient light... Aperture controls Flash-Exposure - if you need to keep a specific aperture for DoF you need to mess with either your flash-power or your ISO or both...
09-20-2012, 05:43 AM   #10
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
it is unfortunate here no one has yet offered the calculation for manual flash.

your flash is given a guide number, usually expressed in meters for ISO 100.

Guide Number (GN) = Distance (D) x Aperture (A)

the on board flash , for example has a GN of typically between 13 and 16.

to make more use of the formula, consider the following modification and re-orginization of the formula

Aperture = Guide Number / Distance x Square root (ISO/100)

if you are for example at ISO 200 your guide number increases by 40% and at ISO 400 by a factor of 2.

With this formula, you can easily do manual flash calculations, and get within a half stop of perfect exposure,

consider a simple example, shooting at ISO 400 with the on board flash and a kit lens, and a subject at 3 meters (10 feet). The GN is between 26 and 32 (depending on camera model) for ISO 400 and with a distance of 3 meters(10 feet) your aperture would be roughly 30 / 3 = F10

pretty simple.change to ISO 100 and cut the guide number by 2 and you are now shooting at F5 or basically wide open. move in from 20 feet to 5 feet, while at ISO 100 and you are back to F10.

keep the formula handy it is simple to use and you can do the calculations in your head with just a little practice.
09-20-2012, 07:10 AM   #11
Site Supporter




Join Date: May 2012
Location: Adelaide
Photos: Gallery | Albums
Posts: 1,104
Actually I had. Third paragraph after I had first described where and what ChooseAName should look for to find the right Guide Numbers for his Metz flash.
09-20-2012, 09:03 AM   #12
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
QuoteOriginally posted by southlander Quote
Actually I had. Third paragraph after I had first described where and what ChooseAName should look for to find the right Guide Numbers for his Metz flash.
except that you left out the compensation for ISO, as a general formula
09-20-2012, 06:53 PM   #13
Site Supporter




Join Date: May 2012
Location: Adelaide
Photos: Gallery | Albums
Posts: 1,104
True. But my intent was to guide ChooseAName towards his flash manual to look up GN's for different ISOs as a starting point for his exporation of manual flash usage. I normally fail miserably in following the KISS principle but on this occasion had decided to keep away from the maths involving squares and square roots. Also going to the manual would lead him to GN's for the zoom (lens focal length) settings available on his flash (if it has this feature) as ignoring the effect of zooming the flash output would lead to incorrect results.
09-24-2012, 09:00 AM   #14
Site Supporter
JimJohnson's Avatar

Join Date: Jan 2012
Location: Lake Superior - Michigan
Photos: Gallery
Posts: 2,271
QuoteOriginally posted by ChooseAName Quote
Today I was taking pictures in a small bedroom (about 15ft x 15ft, with 8 ft ceiling) with K-x, M 85/2, and Metz 48 flash. The ISO was down as far as it could go (100), and the shutter speed was as high as it could go, 180. The lens was at 2.8 or 3.5. The flash was set to -3 EV and P, TTL, and HSS (but as I understand it, P-TTL doesn't work on manual lenses...?) I was still getting a large amount of blown highlights, as shown in the sample photo.
See this post on how to shoot P-TTL with an M-series lens. It can be done. It may not be worth your effort, but it can be done.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, flash, lens, pentax help, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Definitive manual external flash guidance devorama Pentax Q 11 03-18-2017 06:21 PM
I cant get my external flash to fire in manual mode dmbaile2 Pentax K-r 6 05-20-2012 02:29 AM
Flash with new manual lenses Urmas R. Flashes, Lighting, and Studio 4 04-28-2011 06:43 AM
vivitar flash with kr overexposing Classico Pentax K-r 23 04-28-2011 02:20 AM
K7 overexposing w/ Manual lenses??? JeremeyN Pentax DSLR Discussion 6 04-19-2010 06:22 PM



All times are GMT -7. The time now is 01:13 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top