Sunday, February 28, 2010

Flash : Diffuser dome and "spread" tests

I decided to do some comparisons between normal direct flash , then with the diffuser dome and with the wide angle diffuser .
When I set the lens to 50mm and set iso 200 , 1/200th sec and F11 [ A good 'average' setting for a sunny day with a bit of haze ] the flash tells me I have 5.7m working distance which is actually the maximum distance it could fully light the subject , just as fill flash you could probably double that distance .

This is the flash pattern at 50mm zoom and 1/16th power .

With the diffuser dome fitted the camera tells me I now have 2m working distance which equates to 1/8th of the original flash power actually hitting the subject . This is its pattern .

Then with the wide angle diffuser out we have 2.5m or 1/5th of the original power which is a bit better than the diffuser dome - and this is its pattern .

In my mind it would be better to use the wide diffuser when firing into an umbrella .
With indoor flash you would be working with wider apertures and letting in more light so I suppose the diffuser dome would have its uses there since the light going sideways will add to the exposure when it bounces .
I don't see much use in having the diffuser dome on outdoors since just about everything that hits the subject will be direct light anyway so direct flash when using fill makes more sense to me - and the diffuser dome will use 8X the battery power for the same lighting .

Now have a look at this comparison . This afternoon I decided to see how much of the flash power is wasted outdoors with nothing to bounce off . I fired the flash at 1/500th and F14 with my D50 and the Yongnuo 602 kit mounted on my D90 - the second shot was at F25 .
I had the lens on the test camera fully framing the sideways calendar - anything outside the calendar is wasted flash .
It would appear that making the flash head rectangular has worked out to be counter-productive in that it creates a diamond pattern at a 45 degree angle to the subject !
I would also imagine that by making a reflective 'snoot' around the flash head that bounces this wasted pattern back to the subject we would get a much better diffusion effect than by putting on the diffuser dome which has almost exactly the same area as the flash head itself anyway - I reckon we could also have close to twice the flash power hitting the subject considering how much falls outside the frame .


Monday, February 22, 2010

Videos : Flash studies .

How TTL/BL works

TTL/BL and wireless flash compared ...

TTL/BL and metering modes

TL/BL flash and the focus point diamond .

Flash basics : TTL flash

Flash basics : Two exposures in one .

On camera flash comparisons ;

How high-fp or auto-fp flash works :

Sound activated flash trigger :

Motion detecting camera trigger ...

Tests with the bounce card and diffuser dome .

Rear curtain flash .

Thursday, February 18, 2010

Is E-TTL the same as TTL/BL now ?!

After doing my own research to work through the confusion of the change of Nikon TTL/BL from "back-lit " mode to "balanced fill flash " I published a blog on it called "Nikon's "new" TTL/BL" to help others understand how it works .
Due to the fact that Nikon had changed the system without really explaining much it has taken a while to convince many of those who thought they knew how it worked .
I recently decided to start reading up on Canon E-TTLii and found that it is almost the same system - so now many of you Canon users could probably learn about E-TTLii from my blog on TTL/BL !
While reading up on it [ I have not done my own tests but Canon seems to hand out the information more freely than Nikon !] the similarities are the fact that
1.) E-TTLii now uses distance information as does BL mode .
2.) E-TTLii now takes the ambient into account [ based on my understanding of the description of how it works ] so should need less exposure compensation when the ambient is correctly exposed
3.) E-TTLii can analyze a pattern and determine that a bright spot is a reflection based on its pre-flash reading compared to the ambient reading of the subject . I would imagine that Nikon has a slight advantage here with its greater number of metering segments - Nikon also advertises that TTL/BL is good for reflective surfaces and I am assuming that it is for a similar reason to the Canon description.
I see that E-TTL has also gone through a few changes but at least Canon changed the name accordingly and explained those changes .

Perhaps a diligent Canon user could duplicate some of my tests on my blog and confirm 1.) the change in exposure with a change in focus distance ...
2.) and then perhaps the most important test of all is the one to see if the flash output changes with a change in the meter reading .
Set the camera up on a tripod with a subject to the side . Set the metering mode to CW or pattern and find a point where the exposure registers a one stop difference between the two modes without changing any other settings . If E-TTLii changes its output based on a simple change in the position of the meter then it is the same as TTL/Bl mode .

Friday, February 12, 2010

A failed attempt at extending the SU800's range

Today I went into Jaycar electronics  and asked if I could try something out with their IR remote control extenders . We used the newer model than this picture but the principle is the same .
My idea was to be able to extend the working distance of wireless TTL using an infra-red repeater system as used to extend the working distance of the TV remote . 
My thoughts were that if this system could receive the IR signal from the SU800  , transmit it to the receiver , and change it back to IR then perhaps reliable wireless TTL could be achieved at up to 100 metres .
The shop assistant was very knowledgeable and spoke about frequencies and wavelengths and said it sounded quite feasible .
We set the SB800 up on remote mode at one end of the store , I triggered it a few times with the SU800 on my D90 and then walked to the front of the store and made sure it couldn't trigger directly from the SU800 , connected up the remote extender modules - but had no success . Then we decided to tell the trainee assistant to actually turn the receiver on and tried again with no success . Finally we convinced the trainee assistant to push the power supply plug all the way in and actually make the lights come on ..... but still no success . I never even got a pre-flash out of the remote .
There were various measuring devices in the store and with one of the CCTV systems we could switch it into a mode that actually made the SU800 signal look like a flash burst . Then we tried to save the signal into a programmable remote and it froze the remote up - twice ! The batteries had to be taken out to reset the system on the fancy remote .
We tried getting real close to the transmitter - every possible variable was excluded [ I think ? ] and the conclusion was that the Nikon trigger signal was too advanced for any of the systems in the shop .
Now I have the shop assistant thinking and perhaps he will come up with something :) .
I would appreciate any suggestions in this regard .

23 February 2010 : Duncan from 
donated a set of AR 1830 remote extenders " to the cause " and I set them up also with no results .
I may have to 'dissect' the controllers .


Thursday, February 4, 2010

Yongnuo RF 602 wireless flash trigger .

Today I tested my new Yongnuo RF602 wireless flash transmitter , this is what you get in the package .

When you look at the instructions you feel like contacting the manufacturers and asking them " Who learned you to spoke english so deliciously ? "

This is a close up view of the transmitter and receiver

Apparently the two back contacts aren't connected to anything inside which either means they are only there to make it look more 'functional'  or perhaps they are there because the next model [maybe the "903's"] will have TTL functionality !
It was also suggested that they may just be for other cameras and the wiring gets connected for the brand you choose .
There are contacts so you can use them to trigger the shutter release of some cameras at 100m .  

 Then I set up the tripod with my old SB24 so I could test the fastest trigger time    
[ which they advertise as being 1/250th sec - mainly because that's the fastest time most cameras can synch flash ] , and the furthest distance it could work at .

I used the D50 because it has an electronically switched sensor/shutter so it can synch flash at 1/500th sec normally and if it doesn't know there is a flash connected - as with a wireless trigger - there is no limit to the shutter speed you can use with flash .
I explain this in my blog on realsynch flash
Standing next to the flash I managed to trigger it at 1/800th second .


Then I took a walk across the farm and managed to trigger that flash from positions 1 , 2  and 3 . With position 3 I had gone out of range and had to walk back to that point to trigger the flash again ..... BUT : I could trigger the flash wirelessly at 1/800th sec from each of these positions .


And these are the results from those positions , all at 1/800th sec !
Tamron 17-50mm lens at 50mm .

I ran and took 96 large strides to get back so perhaps it is more than 100m .
As another test I took I went to the milking shed and placed the tripod with the flash on it behind a metal door and between two large metal tanks to make it as difficult as possible . The flash still fired ! I think that's covered every possibility that I could come up against at any distance I could need it to work at .

As a side issue we were discussing the possibility of transmitting wireless TTL on nikoncafe . This has been done with the radiopoppers but we  also spoke about the fact that the RF 602's wake up the SB800 flash from standby  mode with a half press of the button but can't wake the SB600's and won't let the SB900's go into sleep mode so we did some measuring and this is what mike66 of nikoncafe came up with ....

" Here is what I found on the left rear contact of the speedlights. When active, each contact had a DC component with a negative going square wave pulse. When in standby, the contact was zero Volts.
3.75V DC with a negative pulse of 40mV. The pulse width is 8ms and the period is 130ms.
4.00V DC with a negative pulse of 100mV. The pulse width is 8ms and the period is 250ms.

4.00V DC with a negative pulse of 80mV. The pulse width is 60ms and the period is 260ms.

The SB-800 had another interesting surprise on the front right contact, which neither of the other speedlights shared. When the speedlight was active, this contact had a positive going square wave pulse train of 2.5V. The pulse width is 2.5ms and the period is 250ms. When the SB-800 went into standby, the voltage on this contact was zero with no pulse train. "
As we learn more about the RF 602 wireless flash triggers perhaps we will find a way to make them work properly with the SB600 and SB900 . Perhaps Yongnuo will just make the next product work properly ? They probably took a D200 and SB800 and reverse engineered the contacts thinking that it would work with any flash .  For now anyway they are still a pretty powerful product considering what they can do compared to other cheaper flash triggers .