Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
03-20-2011, 03:54 PM   #1
Senior Member




Join Date: Mar 2009
Location: Perth - Australia
Photos: Albums
Posts: 214
Sigma 530 DG ST on a K20

Hi Guys

As i am very new to external pttl flashes (by external i mean mounted on the hotshoe) i am looking for a 'bit' of help please!

I have the sigma 530 dg st as it was purchased at a silly aussie price, the super would have been a better choice i know, but the st was only $99, new with warranty from a reputable dealer.

OK if i mount the flash on the hotshoe, set the flash to TTL and the camera (as described in the poor instructions) to P, the camera in a lit room (tungsten and early morning light through the window) will set itself to 1/50 in the shorter reaches and 1/60 in the 60-70mm reaches and F2.8 regardless of what program line has been set to (speed, depth or MTF)

now i can change the aperture to f16+ (i'm testing in a small home office) and it will still expose ok but the shutter is still at 1/50

with the camera in M i can change both but the meter is saying its badly underexposed (i'm assuming because its metering the current light) and i know the flash does a pre flash to set the power output correctly, i'm assuming from the data regarding aperture and shutter from the camera.

i guess the question is that in P is this typical behaviour as 1/50 isnt much of a shutter speed, understanding that the actual flash is running at more than 1/1000th but with ambient light available more flash speed is required, it just seems that the camera in P mode doesnt want to give it, it would rather reduce flash output!

I was trying to find Steve Jacobs flash guide but it seems to have fallen off the internet.. so any pointers at somewhere that would help a 'dummy' with his flash gear would be greatly appreciated!

Steve

03-21-2011, 03:47 PM   #2
Site Supporter
BigDave's Avatar

Join Date: Sep 2010
Location: Hudson Valley, NY
Photos: Gallery | Albums
Posts: 1,443
5:
Even though the flash duration may be 1/1000th of a second or faster, you still have to deal with a flash sync speed for the shutter (focal plane type). Check your manual for the camera, it may have a 1/50th sec sync speed for the shutter.

Also, as the flash duration is shorter than your fastest shutter speed, you only really can change the f stop to control the exposure of the flash. However, if you are blending flash and ambient light (e.g., fill flash) then you will change your shutter speed to get more ambient light in (up to your sync speed).

Does this make sense for you?


Regards,
03-21-2011, 04:03 PM   #3
Pentaxian
twitch's Avatar

Join Date: Nov 2009
Posts: 4,571
The above advice is good advice if you ae shooting in manual flash mode, but does not really apply when shooting in pTTL.

QuoteOriginally posted by 5teve Quote
i guess the question is that in P is this typical behaviour as 1/50 isnt much of a shutter speed, understanding that the actual flash is running at more than 1/1000th but with ambient light available more flash speed is required, it just seems that the camera in P mode doesnt want to give it, it would rather reduce flash output!
Yes that is typical, the camera is exposing for purely ambient light in auto or semi-auto modes, and does not take flash exposure into account in that mode. So, do not shot in auto or semi-auto modes whilst using pTTL on the flash unless you are only doing subtle fill flash. Indoors is not for fill flash.

So, put the camera in manual mode, ISO ~400 to 800, shutter ~1/100 to 1/180 (can't go any faster than this with that flash), aperture to taste. You want the meter to be saying you are under exposing by 1 to 3 stops. The flash should be in pTTL mode. Aim the flash preferably at a wall so light will bounce off that and illuminate your subject. Push the shutter. The camera will then instruct the flash to achieve overall correct exposure. Then chimp and if your subject looks to bright or dim after this then use the FEC compensation on the flash to adjust. Typcially I end up dialing in -0.3 or -0.7 FEC. If ambient is too dark or bright then use ISO, aperture or shutter to adjust.

Remember, in pTTL mode the camera will use the flash output to achieve overall correct exposure. The more negative the meter says the scene is, the more light will have to be dumped by the flash to achieve correct exposure (hence the greater the ratio of flash to ambient).

The best site I've found on using TTL mode on the web is this one http://neilvn.com/tangents/. The think "the storbist" is the best site for off camera manual flash photography.

Good luck and have fun experiementing

Last edited by twitch; 03-21-2011 at 04:18 PM.
04-07-2011, 06:15 PM   #4
Senior Member




Join Date: Mar 2009
Location: Perth - Australia
Photos: Albums
Posts: 214
Original Poster
Thanks Guys apologies for not getting back sooner... i have a busy life and have only just managed to sit down with the camera and flash for 5 minutes....

I have read and digested and read some more .... and then initially chose to ignore the advice above so that i can try and understand myself before looking at the real way of doing it! (its just my quirky way)

Observations...

Camera in P at 70mm on the sigma 70-200 - flash on - default shutter speed is 100, default aperture is 2.8 (in a reasonably lit room) doesnt matter what mode the flash is in (pttl manh manl) it still uses pttl. I was bouncing off the ceiling (white about 3m and angled) to my 'subject' about 3-4m away. The capture was ok although 'underexposed' i use that term carefully as i know its said pttl exposes carefully to avoid blowouts.. anyway up to a point (i think about f5.6 shutter remained at 100) the exposure was consistant.. but then it fell off rapidly.. (at iso100) i also noticed a wierd thing that if i reduced the shutter speed it wouldnt let me up it again? -2 to +1 FEC didnt seem to make any difference?

Camera in AV shutter again seemed focal length dependant.. flash behaved the same as in P (ie no manual available) and behaved very much the same as P with similar exposure.. at least its consistant... FEC again no difference.. but could get brighter by adjusting ISO..

Camera in M, and flash in PTTL with similar settings to P and AV gave same results.. however if i changed the flash to Man H it gives out massively more light... so i get to the right of the histogram centre with the peak, whereas before i was left of by one line (one stop?) which shows the flash can output a lot more light than it is being fed via Pttl..

now i guess one question.. me being a newb to flash is... is this normal behaviour?

Now onto the info given... i havent tried the info yet... but Iso seems to be the key to getting brighter exposure... as i was only testing on iso 100... i promise faithfully to test the methodology out this weekend...

what was meant by You want the meter to be saying you are under exposing by 1 to 3 stops. as in a dark room it will want a really slow speed for this kind of exposure? i think i may be missing the point..

I also did some reading from a pttl flash guide on the UK pentax user forum i think it is (linked on Matts flash site) which was helpful as it now makes me understand i was expecting miracles because i didnt understand the guide number very well! i though 53m was huge... didnt realise that it was at f1.0 and also zoomed in! so when you take into account apreture and distance it becomes a little more realistic!

Any more handy hints or links are very welcome.. especially Pttl orientated ones..

I also hear that the k7 and k5 meter much better with Pttl whereas the k20 was a little quirky...

Thanks again guys.. will report back after trying twitches settings..

Steve


Last edited by 5teve; 04-07-2011 at 06:20 PM.
04-07-2011, 06:48 PM   #5
Pentaxian
twitch's Avatar

Join Date: Nov 2009
Posts: 4,571
Fill flash is to counteract the effect of too much light causing deep shadows; eg racoon eyes on a sunny day, or people standing in dappled shade on a sunny day. For fill flash, using auto or semi auto modes is fine as the camera exposes for the ambient and then adds just a kick of flash to counter the shadows. It's critical you understand this. In auto/semi-auto modes like P, Av, Tv, having a flash on your camera has no influence whatsoever on the exposure settings you camera chooses.

For non-fill flash situations, ie when you are using your flash because there is not enough ambient light for the scene you want to photograph, you do not want to be in auto or semi auto modes as you've already decided there is not enough light on the scene and so the auto modes will give you unfavourable settings (eg too high ISO).

For these situations you should shoot in manual mode on the camera and let the meter indicate you are 1 to 3 stops underexposing. The flash in pTTL mode will then make up the difference and give you enough light to the point where it thinks it has achieved an overall correct exposure (within the limitations of flash power obviously). Overall exposure is controlled by the FEC. If your experiments say otherwsie then you are doing it incorrectly (eg I use FEC on the flash not the body), or there is somethign wrong with your flash.


QuoteQuote:
what was meant by "You want the meter to be saying you are under exposing by 1 to 3 stops". as in a dark room it will want a really slow speed for this kind of exposure? i think i may be missing the point
Have a think about that statement, because your conclusion that "you want a really slow speed for this kind of exposure" is incorrect, actually you get a faster shutter speed.

Say ambient makes your camera choose ISO3200, f2.8, 1/60and you decide that is unacceptable (either too slow shutter speed or too high ISO) Then under exposing by 3 stops in manual mode will give you the latitude to shoot ISO800, f2.8, 1/125. pTTL will then make the flash provide 3 stops worth of light to achieve correct exposure. If you dial down the FEC by 1 stop, it will kick in only 2 stops, if you dial the FEC up by 1 stop it will kick in 4 stops worth of light.

This is very important to understand as the ISO/shutter/aperture setting in pTTL mode make absolutely no difference to overall exposure, those settings only affect how much light the flash kicks in to make up the small or large difference between what the camera meter say, and what the iso/shutter/aperture settings are.

So you conclusion that ISO affects overall exposure in pTTL mode is 100% wrong so long as you are within your limits of your flash. If you don't understand this point then you will be lost in understanding pTTL and how to use it to achieve what you want.

Sorry I sound like a school teacher a bit here, I don't mean too It took a while for the penny to drop for me in understanding all this..

Last edited by twitch; 04-07-2011 at 06:56 PM.
04-07-2011, 07:16 PM   #6
Senior Member




Join Date: Mar 2009
Location: Perth - Australia
Photos: Albums
Posts: 214
Original Poster
I'd rather you did sound like a school teacher.. i may learn something at least...

i appreciate you taking the time to explain it all.. it will sink in eventually...

i'll have a short reply now... try it out and then reply later...

Just to clairfy..

QuoteQuote:
Have a think about that statement, because your conclusion that "you want a really slow speed for this kind of exposure" is incorrect, actually you get a faster shutter speed.
i actually said IT will... meaning the k20 will meter a dull room requiring something like f2.8 and 1/10 shutter.. but with the flash on (in semi auto modes) it meters it at 1/100 f2.8 etc etc.. but then i am taking semi auto... and not manual that you were.. i'l look into this..

FEC - with +1 should i see an appreciable difference in exposure or very slight? as there really wasnt much difference at all.. maybe a very slight increase but not really noticeable.. and does FEC work in all modes, ie P, AV, man?

The main thing that is bothering me is the light falloff with pttl when compared to manual high. High gives a huge wallop of light (which needs tweaking to get correct exposure) but i can get far higher fstops with manual than i can with pttl, which seems strange?

finally for this reply... iso did affect the exposure in av (not sure about p) which kind of incinuates that i was on the power limit of the flash, which looking at manual mode it clearly wasnt?

Now the disclaimer.. all of the above are my observations made while 'farting around' with the camera in 5 minutes i had spare.. so i will go away and make sure i dedicate some time to looking at this logically and using the provided information!

Thanks again...

Steve
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, dg, dg st, flash, light, output, pentax help, photography, shutter, st, steve
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sigma EF-530 DG ST deltoidjohn Flashes, Lighting, and Studio 19 01-21-2011 08:02 PM
How to use Sigma EF-530 DG ST Pietrach Flashes, Lighting, and Studio 2 01-13-2011 02:41 AM
For Sale - Sold: Sigma 530 EF-530 DG ST flash for Pentax (US) letgo12345 Sold Items 2 03-25-2010 08:43 PM
For Sale - Sold: [US] Sigma EF-530 DG ST flash, AF Sigma 28-200mm f3.5-5.6 lens rockmaster1964 Sold Items 2 02-24-2010 10:07 AM
Can Sigma 530 DG GT trigger Sigma 530 DG Super ? eva2000 Flashes, Lighting, and Studio 5 12-07-2008 03:14 PM



All times are GMT -7. The time now is 07:29 AM. | See also: NikonForums.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