In Av mode, Pentax camers use the FL of the lens to pick the lowest "useable" shutter speed using the 1/FL formula, so when you mount a lens that reports it's FL you'll get the rule of thumb shutter speed, adjusted for the difference in size for the APS-C format vs the 35mm format, (if you mount an A or earlier lens you'll get maximum X sync). I'd assume that you've set the zoom to somewhere between 70 and 100mm based on the shutter speed that the camera is providing.
George Sinos wrote: > Yes, I probably wasn't very clear. As the aperture changes the flash > will compensate. I should probably rephrase that comment and move it > to the intro. > > I shot a series in Av mode, running the aperture from f/2.8 through > f/11. In Av mode, with the flash on, the camera seems to like 1/125 > sec shutter speed. I could clearly see the flash change it's power > output from shot to shot. In this series all of the backgrounds are > about the same, but you can see the depth of field change. > > In Tv mode I ran the series from 1/4 sec to 1/180. At 1/4 sec the > camera chose f/3.5. It chose f/2.8 at all other shutter speeds. The > results were similar to the manual mode series. In the end I used > manual so I could control as many variables as possible. > > GS > <http://georgesphotos.net> > > On Sun, Jun 1, 2008 at 11:45 AM, Bob W <[EMAIL PROTECTED]> wrote: > >> That's quite instructive. In the 3rd picture, though, you write "Flash >> adjusts output to keep the foreground subject correctly light". The >> flash doesn't need to adjust the output - for the same distance and >> aperture the flash output should remain constant, and TTL isn't >> needed. >> >> Bob >> >> >>> -----Original Message----- >>> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On >>> Behalf Of George Sinos >>> Sent: 01 June 2008 17:14 >>> To: Pentax-Discuss Mail List >>> Subject: GESO - Balancing flash with available light >>> >>> Balancing flash with available light. >>> >>> This is a gallery of a few shots put together for a class drill. >>> >> The >> >>> idea is to light the foreground subject with the flash and the >>> background with available light. The lightness/darkness of the >>> background is controlled by changing the shutter speed. The aperture >>> is held constant for all photos. The P-TTL flash keeps the subject >>> >> lit >> >>> at the desired level. >>> >>> For the Pentax folks here's a little additional info. >>> >>> The Flash is a 540 set in the wireless mode. It's set to +1/2 stop >>> flash exposure compensation. It's zoomed in as far as possible to >>> narrow help keep light from spilling onto the background. There are >>> only seven images in the gallery, but I did a lot of experimenting >>> >> and >> >>> fired the shutter just short of 100 times. The flash is very close >>> >> to >> >>> the subject so it probably didn't need to use much energy. Even >>> >> when >> >>> I was experimenting with very small apertures requiring noticeably >>> more powerful flashes the flash recycled almost immediately. The AA >>> alkaline batteries seemed to work OK for this application. >>> >>> The lens is the DA* 50-135mm f/2.8. The focus point is the black >>> queen in the back row. >>> >>> The camera is the K20d, flash set to wireless control mode. Manual >>> mode for this series. Though I had set the white balance to >>> >> daylight, >> >>> it didn't make any difference. I had custom setting at "WB auto >>> >> when >> >>> flash attached." I've since set it to "unchanged" so it will use >>> >> the >> >>> WB as set on the camera. No matter, I was shooting raw files. >>> >>> Here's the link >>> >>> <http://Georges.smugmug.com/gallery/5066768_nv8WE/1/304882093_iUGLx> >>> >>> Oh, the opening image documenting the setup was shot with a Canon >>> >> G9. >> >>> This was time well spent, if only to learn about the custom settings >>> on the camera and flash that interact. I've only had the K20 and >>> >> 540 >> >>> for a short time. >>> >>> GS >>> <http://www.georgesphotos.net> >>> >>> -- >>> PDML Pentax-Discuss Mail List >>> [email protected] >>> http://pdml.net/mailman/listinfo/pdml_pdml.net >>> to UNSUBSCRIBE from the PDML, please visit the link directly >>> above and follow the directions. >>> >>> >>> >> -- >> PDML Pentax-Discuss Mail List >> [email protected] >> http://pdml.net/mailman/listinfo/pdml_pdml.net >> to UNSUBSCRIBE from the PDML, please visit the link directly above and >> follow the directions. >> >> > > -- Vote for Cthulhu. Why settle for a lesser evil... -- Dr. Jerry Pournelle -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
