Flash and wide aperture


Link Posted 03/10/2012 - 09:17
What do you guys/girls do when using flashes at wide aperture settings (i.e. f2)? and i dont want to increase shutter speed and already at lowest possible iso (100 on my GX10).

Currently have a pentax 280T flash - which I use in auto mode. But consequently usually somewhere around f8. Is this typical or do I just need a better flash with more power settings? Will something like the pentax 540 allow p-ttl at any aperture and as close as 1M? (I always bounce the flash if poss)

I could perhaps go go to a wider aperture if I put an ND on the flash in manual mode? (I think in auto the flash just increases the output to compensate the ND?)
I could also put an ND on my lens - but sometimes I'll be shooting indoors and could make focusing difficult.

Keen to know what other people do - i.e. avoid auto altogether and just set an ev adjust when using a flash on low power?
Last Edited by lgriffiths on 03/10/2012 - 09:17


Link Posted 03/10/2012 - 10:25
I don't know the 280T
But if you're at 'base' iso and over-exposing at f2 your options are:

1) Dial down the flash power (unless the 280T is one of those silly flashes that shoot at 1/1 in 'M' mode)

2) Close down your aperture - (why is f2 important here? - DoF for a particular shot?)

3) ND flash filters are available - shooting in manual is the only way I know...

By adjusting your shutter-speed you're not actually changing your 'flash-exposure' but instead allowing more/less (dependant) 'natural/ambient' light to effect the exposure as a whole
This can create an 'ethereal' effect but I'm not sure (that's) what you're going for... (?)

Shooting indoors with an ND on your lens is not the way I'd play it... Sounds like a mini-nightmare...

Honestly... If you can't dial down the power with your current flash then look for a Yongnuo (560) so that you can...
Pentax K5- Vivitar 19mm 3.8; FA35mm f2; D-Xenon 100mm macro f2.8; DA50-200mm WR...
Yongnuo YN-560; Vivitar 285HV; Cactus V4 triggers...
Pentax-MX & M50mm f1.4; Spottie & 55mm f1.8; MG & M40mm 2.8...

Last Edited by DaveHolmes on 03/10/2012 - 10:27


Link Posted 03/10/2012 - 10:31
Whilst the AF280T is a very good flash, it uses the older TTL flash technology. You'd have much more control using a modern P-TTL flash. There is a Samsung badged AF540FGZ on here for sale at the moment. It's identical in operation and performance to the Pentax badged version. There are other P-TTL flashes, but this is a Pentax forum and I've no experience of other makes.

With the 540 you can vary the output power in P-TTL mode by -3 to +1 stop on the flash and you can adjust it further on the camera body. You also have Auto, and manual settings of 1/1 to 1/64th power.

Best advice is to visit a dealer and try one out, but I doubt you'll be disappointed if you just bit the bullet and bought a used one.
Peter E Smith

My flickr Photostream
Last Edited by Mannesty on 03/10/2012 - 10:33


Link Posted 03/10/2012 - 10:39
Currently have a pentax 280T flash - which I use in auto mode.

Huh? You must be using it wrong

For a 'dumb' auto flash there's a guide on the back that stipulates the auto range settings. For example, typically it might be f/5.6 at ISO100 (within a specified distance).

Not many auto flashes provide for f/2 settings because they can't dial their power down enough. (Some of the larger Metz, however, allow for 1/256 power)

It's unusual to be using flash with a very wide aperture.

The P-TTL flashes may also not be able to handle wide apertures
It really depends how much ambient light there already is, and how close you are to the subject. Most flashes will go down to 1/32 or 1/64 power - and that may still be too much!

For a manual flash, or a P-TTL flash (but not auto), you can 'slug' the flashes output further by fitting a diffuser of some kind. Even a few layers of tissue paper, or a white handkerchief (clean of course!) can absorb a large amount of power and weaken the overall output.

My recommendation is - if you are shooting shallow DoF portraits in a fixed environment (studio etc) then use fully manual on flash and camera, with the flash at its lowest power setting.

If you're shooting out-and-about and the lighting is exceedingly variable and you have no time to adjust, then think about P-TTL.

But, honestly, try fully manual + diffusers first. It's not that hard

(For gallery, tips and links)


Link Posted 03/10/2012 - 20:12
Cheers for the comments all. Think I'll try something with more manual power variation and... perhaps find a good book on flash photography. (I think my book buying addiction is worse than my lens buying... )

Huh? You must be using it wrong

Quite possible - though I meant the flash is in auto as in using the thyrsitor.

1. Dial down the flash power (unless the 280T is one of those silly flashes that shoot at 1/1 in 'M' mode)

Only has 2 manual modes - though no idea what power the 'low' one is at.

2. Close down your aperture - (why is f2 important here? - DoF for a particular shot?)

yeah it is the DOF (lack there of) I want it for. I dont need much flash at all, just to lighten the face a touch.

By adjusting your shutter-speed you're not actually changing your 'flash-exposure'

Ahhh of course, good point! So ev compensation in my case (changes shutter speed) will do... just about nothing. might explain a lot


Link Posted 04/10/2012 - 08:59
You mention using Auto and the thyresistor which means that at 200ISO, for example, the widest aperture you can use is f5.6 or you will overexpose. The red and green switch settings correspond to the red and green markings on the scale.

If you don't have the manual you can download it from the Pentax USA site.
“We must avoid however, snapping away, shooting quickly and without thought, overloading ourselves with unnecessary images that clutter our memory and diminish the clarity of the whole.” - Henri Cartier-Bresson -


Link Posted 08/11/2012 - 11:01
If you can't reduce the power of the flash could you look at flash modifiers - even a couple of layers of tissue paper over the flash? or bounce it? Or go off camera and move it further away?


Link Posted 08/11/2012 - 13:27
I have the Metz 48 and 58 flashes and both expose correctly at F2.8, I haven't gone for a wider apature.
Bodies: K5IIs, K7, MZ5n, LX, MV
Lenses: DA*16-50, DA18-55WR, DA18-135, DAL35, M50 F2, A50 f1.4, FA50 f1.4, DA*50-135, DA55-300, Tamron 70-300, DFA 100 WR Macro, M135 f3.5, Sigma 120-400 APO DG HSM, Tokina 500 f8.0
Flash: Metz 58, Metz 48
Accessories: BG4, Pentax right angle finder, Pentax mirror adaptor lens, O-ME53 Viewfinder Loupe
Auto 110 System: Auto 110, Winder, 18mm, 24mm, 50mm, 70mm, 20-40mm, AF100P, 1.7x telecon
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