[dizzyfish]

Hello, I'm new to the forum - I'm hoping for some advice from the guys on here.

I am using a Pentax K-70 with the 18-135 WR lens. I have just purchased a Shanny SN600FGZ pentax flash unit. I popped the Shanny on the K-70 and put it into P-TTL mode.

I took a few test indoor pics in auto, aperture and shutter priority modes with the new flash - using average/matrix metering (flash pointing directly at subject - no diffuser - distance to subject approx. 10 feet). All of the shots appear to be over exposed by quite a margin. As soon as I take the flash off and revert to the built in flash instead, the exposure seems to be spot on.

Can someone suggest if this is a possible issue with the Shanny flash unit, or if there is something I am missing in terms of settings on the camera (or flash unit)?

I have manually reduced the power output on the Shanny flash by a few points, and that solves the problem - but surely, I should not have to do this?

[mcgregni]

Hi, welcome! Aperture and ISO play a role here ... If you are using an unnessesarily high ISO and / or a wide aperture, then you can easily exceed the minimum distance to subject limit, causing exposure problems. 10 feet is quite a small distance for anything other than a very low ISO and /or small aperture.

Does your flash display a suitable working range after half pressing the shutter? It it does then that is your ultimate guide and you can make settings adjustments to get a suitable range before even taking a picture.(Note this technique applies only to direct flash, not bounced.)

The fact that your built-in flash is ok suggests that the Shanny is just too powerful for the settings and flash to subject distance you are using. Tell us your aperture and ISO settings for those 10Ft test shots.

[dizzyfish]

Many thanks for the reply mcgregni... I will take some shots with the Shanny and post them up together with the settings used.

In the meantime, I am trying to get my head around how the metering works for P-TTL flash shots, I always thought that the camera knew the flash was on the camera, and compensated for this when you half pressed the shutter release... but after taking a few more shots, I am thinking, I must be wrong. It seems as if the camera just meters the subject exactly as it would when the flash is not connected, then when you take the shot, it controls the output of the flash to provide the correct amount of light for the given aperture and shutter settings. Is this correct?

Apologies, but I am new to TTL flash photography - I bought the flash because I am going to an indoor event in a month or so, and I wanted to take pictures of subjects on stage from a distance using a fairly decent telephoto (Say 100mm), and given the indoor lighting, handheld pictures taken without a flash would not look great.

[mcgregni]

I do recommend some general study and reading up on flash photography before expecting to get good control over things, and to expect consistent results. Certainly for an event this prior knowledge is going to be needed.

The flash has a range of outputs that it can provide .....a minimum and a maximum, plus many steps in between. The actual brightness effect these outputs have on an image, as recorded by the camera sensor, depend on the ISO, Aperture and the distance from the subject. If any of these factors causes the minimum/maximum limits to be exceeded, then the flash is unable to automatically adjust itself any further. The automatic metering is likely to be inconsistent also when the flash is working at these limits.


I always recommend a fixed ISO for flash work. At small distances indoors then ISO 200 should be your maximum ISO, or 100 if you are shooting at very wide apertures. Try again and put this into practice and see the results.


If we are wanting to get more ambient light recorded into the mix by using a higher ISO, then we will likely have to take steps to increase the effective flash to subject distance, such as by bouncing the flash ....this gives nicer looking light also.


You will find plenty of information to help in my “Pentax Flash Guides”, downloadable from my signature below my posts. Even though the focus is on the Pentax flash models, you will find a lot of relevant information about the Pentax flash system and general flash operations that will apply to using your Shanny model.

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Last edited by mcgregni; 03-11-2018 at 09:26 AM.

[dizzyfish]

Apologies for taking so long to reply. Ok, so I have a few pictures taken with the Shanny Flash which will show the issues I am having.

The pictures were shot indoors with the K-70 on a tripod. Distance from the camera to the subject was approx 18 feet with the 18-135 WR lens fixed at approx. 100mm and ISO fixed at 200.

First shot (Attachment IMGP0069.jpg) taken without the flash, camera metering in Av mode f5.6 at 0.8 seconds.

Second shot (Attachment IMGP0070.jpg) taken with the flash in P-TTL and camera in Av f5.6 1/160 sec.

Third shot (Attachment IMGP0072.jpg) taken with flash in P-TTL and camera in Tv f5.6 1/8sec

Fourth shot (Attachment IMGP0073) taken with flash in P-TTL and auto zoom on flash at 80mm and camera in P mode f5.6 1/160sec

Last shot (Attachment IMGP0079.jpg) taken with flash in P-TTL and and Shanny power compensation manually set to -1.7. Camera in Tv f5.6 1/160 sec


So, as you can see, most of the flash pictures appear to be overexposed... when I manually drop the power on the Shanny, then I get a better result.

I would welcome your thoughts on this - do you think there is a problem with the Shanny flash unit? (I also noticed the auto zoom on the flash unit only worked in P, Sv and Tv modes on the Pentax).

[mcgregni]

It’s a limited test, and it shows only that you get overexposure of 1.7 stops with direct flash indoors at a fairly small distance, and that flash compensation of -1.7 fixes it. If you can get consistent results with the compensation set then it is not a problem, at least not a practical one. There are very few real photo situations where that sort of flash shot will look any good anyway.

A better test would be to check also the results if you use ISO 100, and F11 (to see if the working distance is too small) . Also to bounce the light at various settings, to check the metering in a bounce situation. So long as you get fairly reliable and repeatable results in a range of configurations like this, then there is no problem. The key is to practice and develop a sense of in what situations the over exposure is likely to occur. Your test shots seem to be pushing the distance limits to the edge really, so not a good example of real life use.


Almost every flash shot I take with my Pentax AF-540FGZII, when on camera, needs a flash compensation setting, usually within a range of -1.7 to + 1.0.

[dizzyfish]

Thanks - that was exactly the type of information I was after. I really appreciate you spending the time and giving me the benefit of your experience. I am starting to understand that is not an exact science.

Could I ask one further question? Can you give me some advice on the scenario which I will be using the camera and flash set up for. I will be taking some pictures of guys at a competition being presented with various awards on stage indoors. The indoor lighting probably won't be great, and I will only get one chance to capture them on film (no rehearsals). I was planning on using the Pentax 100mm WR lens with the Shanny flash. In terms of the ambient exposure, I don't need too much background or foreground interest. I am only interested in capturing the individual and presenter holding trophies. I will be no closer than 15 feet, and maybe much further back. What would be your recommendations as a start point for exposure modes/settings/metering type for such a scenario?

I will be able to update the compensation on the flash unit because there will be several people receiving prizes, but would appreciate your advice.

[rawr]

I am only interested in capturing the individual and presenter holding trophies. I will be no closer than 15 feet, and maybe much further back. What would be your recommendations as a start point for exposure modes/settings/metering type for such a scenario?

My settings would be along the lines of: set the drive mode to single-frame shooting, set the focus mode to AF-S, set AF active area to Auto 11 or Auto 5 (focus and recompose on the faces, or shoot using LiveView and turn face detection on), set metering to multi-segment, set the flash on, camera to M, check that shutter speed isn't less (or more) than 1/180, set fixed ISO to 200 or 400, set the lens aperture (on a 100mm at 15 feet for shooting people where you want body+face to be in focus) to about f4 or even f5.6, let the P-TTL do it's thing, and just start shooting.

100mm might sometimes be a little long on APS-C though. Typically a 28-75 would work well for this kind of job, or even 50-135.

A couple other suggestions: if possible, visit the venue before the event and walk the scene in advance to rehearse your shooting scenario, understand all the people placements, and get a good feel for how your lens might work on the day. Probably also a good idea to do some flash test shots on the scene just to nail your camera & flash settings before the event.

[mcgregni]

Yes, it’s a good idea to scout out the venue if possible. You should also set up a test subject, a dolls head or soft toy, at the approximate distance you expect for the event. Then practice with different settings until you get consistent good exposures. You can do this at home.

For direct flash you are still pushing the minimum limit with a GN 60 flash, maximum flash head zoom, ISO 200 and F5,6 at 18 ft .....


I think you should look at shooting at ISO 100, and even also F8 if it’s going to be that close. If overexposure still occurs then you also have the option of manually controlling the flash head zoom to a wider setting. This will waste some light by spreading it over the edges of the frame, but cuts the effective GN also. Only if you are shooting from further back, say 25ft or more would I go to ISO 200 and F5.6, at least with maximum flash head zoom.


Remember that the ambient /natural light makes no difference to any of these settings considerations. It makes no difference if you are shooting in pitch black indoors, or daylight outdoors ....the settings and distances referred to have exactly the same brightness effect on the subjects. The only difference is that in daylight the sun will add its light to that of the flash, however the P-TTL metering takes account of it and will reduce the flash output accordingly. So at close distances then overexposure is more likely to occur with flash plus a sunlit subject. Ambient exposure settings should be such as to ensure the sun highlights are well below the right edge of the histogram before adding any flash light.


Back to your event .....it would be even better, both for an exposure point of view as well as quality of lighting, if you could bounce your flash light off a light coloured surface, ideally white or cream coloured. If there was a wall or overhang from a ceiling that you could use fairly close to the subject you will get much nicer looking photos if the light was bouncing off from a side and above the subject. In this case because of the increased flash to subject distance and light loss caused by the bouncing , then you will need to increase the effective guide number by increases in ISO (eg to ISO 800) and wider apertures (eg f4.0).

[mcgregni]

A quick bit of GN maths showed me that for settings of ISO200, f5.6, flash head zoom of 105mm and a GN 60 flash, your effective flash range is about 5m - 40m ....meaning that your flash should be able to correctly expose something placed between 5 and 40 meters from it. Clearly the 5 meter limitation is quite a good distance away in real life situations, hence my thought that you might be overestimating your distance and therefore pushing this limit.

My reckonings were based on a flash model that has a lowest manual output setting of 1/256th (eg Pentax AF-540FGZII)......if your flash does not go this low then its minimum range in P-TTL mode might be an even greater distance with those settings .....eg 6 meters.

[dizzyfish]

Many thanks to the both of you for your replies.

Nigel - May I ask, is there a lookup table or reference I can use for Guide number/ISO/distance/aperture settings? And also, given the lookups, is there any advantage to using the semi auto modes (Av, Tv, P etc) rather than M?

[mcgregni]

The easiest reference point for distance and range relating to aperture / ISO / Flash zoom is often on the flash itself , in the form of it's distance/range indication. This updates automatically each time a change is made to any of those settings....(this pre-supposses a dedicated system flash and the flash head pointing forward, not bounced) . This indication will give an instant correct distance for good flash exposure in Manual mode, and a range of distances (eg 5m-40m) in P-TTL mode. Does the Shanny do this? It should come on the display after focusing and activating the meter circuit with a half press on the shutter button.

If it doesn't have that indication then the Manual should include a table showing distances and ranges at ISO 100 for a number of different apertures and flash zoom settings. Just use interpolation to work out things around this ..... This approach gets you into the ball park. I wonder if someone else knows of a good resource online for this sort of thing?.....a lot of it is way too much maths for my brain !

In any case, you just need to get a feel for the limits and be abie to make quick settings adjustments to correct if needed. The indication on the flash is a handy quick guide to this..... So for example in your overexposure example you might quickly recognise that the subject is a bit close and make a quick adjustment. ..... This could be any one of these things : Lower ISO ..... Smaller aperture ......wider flash zoom ....... Bouncing the light ....standing back more .....or a combination of any of these together.

If there's not enough power available for the flash to subject distance then the corrections are the opposites : Higher ISO .....wider aperture ....narrower (zoomed in) flash zoom .....stand closer.

Note that your camera position does not affect things in a bounced light situation, where it is dependent on the angles and reflective quality of the surfaces on which the light bounces off. But with direct on camera flash then moving closer or further away from the subject has a direct effect on the possible range for good exposure.

[dizzyfish]

Unfortunately, the Shanny flash head provided no range/distance information. I also couldn't find the lookup tables in the manual :-(

Was hoping there might have been an iPhone app where you could enter the ISO, aperture and guide number and it would tell you the operational distances

[rawr]

Was hoping there might have been an iPhone app where you could enter the ISO, aperture and guide number and it would tell you the operational distances

There are lots of web pages around that do this - eg:
Tools: Canon flash power calculator - Canon Professional Network
Understanding Camera Flash Guide Numbers, plus GN Calculator

I'm pretty sure there are many apps that will do this too.

The Shanny is GN 60 at ISO 100 / 200mm. That's all you need to get started with calculating workable distance etc.