Meking Corona 250T strobe flash light test & review

I was looking for a couple of inexpensive monolight for my niece. She sells vintage clothing on the net and needed a lighting setup to photograph her items. The Corona 250T sold by Meking Equipment (also listed as Meking Studio) looked like the ideal solution. Unfortunately it does not come close to meet Meking's advertised specifications. Both the wattsecond and guide number listed is more than double what the unit actually puts out.

The 250T is the lowest power monolight in the Corona series. In addition to the 250T there also is the Corona 350T and the Corona 450T. One initial note on this monolight. While the specifications lists that a 120 volt version Meking only sells the 220 volt versions individually. But they do have an Ebay listing for a kit that includes two 450Ts and a 250T for 120 volts. Odd.

Jan 2012 Edit: - The following is the specifications claimed by Meking. From my examination and test on the 250T the power and guide number stated is completely fiction. It is not even remotely close to what the the unit produces. I have repeatedly asked Meking for clarification and they keep stalling.

Corona	250T	350T	450T
Power Range	250ws	350ws	450ws
Power Control	Variable	Variable	Variable
Guide No.	50GN	58GN	66GN
Recycle Time	0.8-1.5s	0.8-1.5s	1-2s
Continues Lamp	100ws	100ws	100ws

The primary thing that attracted me to this flash unit is that the reflector can be removed and it can be operated in bare bulb mode. This is desirable when using a flash/strobe in a softbox. With the bare bulb a lot of the light is reflected off the sides before being reflected into the diffusion layers. So one big plus for the Corona 250T.

Corona 250T with reflelector removed.

The back of the 250T shows all the basic monolight controls. While it does have a switch for turning on and off the modeling lamp the modeling lamp is strictly on and off. It does not have a proportional setting that tracks the flash power output. I don't consider this much of a problem though. It is one of the ways the manufacture was able to reduce the cost of the strobe. 

Another way to cut the cost was in using smaller cheaper switches where they could get away with it. Many studio strobes will use the same style of switch for all the switches. The power switch needs to have a certain rating to switch the power to the strobe. This will dictate the size to a large degree. In order to keep the styling consistant many manufactures will use the same switchs for the remainder of the switch functions. From an electrical point of view this is not necessary. So a higher cost switch is often used more for appearance. The Corona instead uses lower cost switches and this is perfectly adequate.

The mount for the light stand is plastic but it seems adequate. There is a steel nut in the plastic for the tightening screw. The umbrella mount is also plastic and is a part of the rotating joint. There is a spring metal strip to apply pressure to the umbrella shaft when inserted. There is no locking screw. It seems very unsecure to me when I used the light with a 60" (150cm) reflective umbrella. I used a eraser between the end of the shaft and the housing in order to provide more friction to the shaft and to change the shaft angle slightly so the light is directed to the center of the umbrella. While I feel comfortable using a 60" shoot through umbrella with this light I may limit using a reflective umbrella to a 42" size. Shoot through umbrellas are lighter than reflective umbrellas.

The one corner where the manufacture cut costs on this strobe, that I have a problem with, is the size of the photo flash capacitors used. While the specifications imply that this is a 250 watt-seconds flash the capacitors used in this strobe, and the voltage they are charged to, only comes to 108 watt-seconds and not the 250 watt-seconds advertised. The maximum output is less than only 43% of what is claimed.

The trigger input is a standard 1/4" phone jack. The trigger voltage is 5 volts. It also has a sensitive optical trigger with the sensor on the top of the unit. It worked well in my tests. The switch to disable the optical trigger is on the top. When enabled the sensor lens glows red. The optical trigger can trigger the flash on the first or on the second flash selected by a switch on the back panel. I would be surprised if anyone needs this feature. Another addition is a plastic cover that fits over the reflector to protect the flash bulb when stored or packed away. A nice addition.

When initially testing the 250T I was quite disappointed with the measured light output. I had expected much better considering the guide number of 50 listed in the advertisement. Along with flash meter test of the Corona 250T I did a side by side comparisom with two of my Canon Speedlite flashes. I used the Canon 580EX as a reference because it is well known. I also included a comparison with an old Canon 200E that has a guide number of only 20.

The point of including the Canon 200E was to show that the Corona 250T lights up a scene not much better than the 200E with a guide number of only 20. The Corona is claimed to have a guide number of 50. I can't understand how they can make this kind of claim since the results indicates that it is nowhere near that. 

All the shots (next 7 images) in this test were made at full power from the Canon hotshoe flashes and at full power from the Corona 250T. All lights were in the same physical location (about 5 feet hight) and aimed toward the flash merter attached to the light stand.

In the following three shots the camera was set to F4.0 with an ISO of 100. The Canon 200E was used without modification at it's only coverage area equal to a 35mm view on a full frame camera. The Corona 250T in the second shot was with it's supplied reflector. The 250T throws light over a larger coverage area than the 200E with it's 35mm coverage. You can see the difference at the bottom of the frame. But in the center of the coverage area the Corona 250T only puts out as much light as the Canon 200E with a low guide number of 20.

Canon 200E - flash meter reading F4.0 +2/10. Guide number 20 @ 35mm

Corona 250T with reflector - flash meter reading F4.0 +2/10. Guide number claimed as 50. Looks like less than half that.

580EXzoom set for 24mm - flash meter reading F5.6 +7/10. Guide number 28 @ 24mm



In the above frame the 580EX was set on it's 24mm setting. At this setting the 580EX has a guide number of 28. Compare this to the previous frame with the Corona 250T with a claimed guide number of 50. As previously stated the camera settings for the three above shots were the same. The only change was the different lights. As you can clearly see the 580EX lit image is far brighter than the Corona 250T and of course the Canon 200E.

I then tested both the Canon 580EX and the Corona 250T in a 20"x27" softbox. I had set the 580EX to it's 24mm position setting. Set for full power on the flash and the flash meter set for ISO 100 I measured F11 +1/10 at a distance of 1 meter from the front softbox diffuser. With the 250T set for full power I only measured F8 +1/10, one stop less than the 580EX. I had hoped that the 250T would have worked a bit better in the softbox but the differences was much like the first direct flash tests above.

With the same setup as the first test I took a room shot with both the 580EX and the 250T in the softbox. For these two shots I had the camera set for F3.5. With the flash meter 9.5 feet from the softbox I got a measurement of F2.8 +8/10. With the same setup but with the 580EX I measured F4.0 +7/10. Almost a full stop difference which is almost identical to my tests at 1 meter.

Canon 580EX in 20x27 softbox - flash meter reading F4.0 +7/10

Corona in 20x27 softbox - flash meter reading F2.8 +8/10

If you click on any of these images another window will open where you can get a slideshow where you can advance each image and step back and forth to see the differences a bit better. To see larger images for a better comparison go to http://www.mts.net/~wrpa/Corona.html

While I was at it I decided to see what the difference in output was for the Corona 250T with and without it's supplied reflector. This was with the same setup as the first test (not using the softbox). Using the reflector the output was 3/10ths of a stop higher than without the reflector. The reflector really has minimal effect. There is a larger reflector available listed as being a Comet mount that should improve the distribution and on axis output. It sells for about $20.

Corona with reflector - flash meter reading F4.0 +2/10

Corona without reflector (bare bulb) - flash meter reading F4.0 +0/10

All the above tests we done in a relatively small space. Because of this I decided to also do some measurements at work in our warehouse with a large open area. I wanted to measure direct output from the flash and studio strobe without significant reflections adding to the exposure. I took two sets of measurements, one at five feet and one at ten feet. I got the following.

Corona 250T without reflector at 5 feet. F5.6 +3/10

Corona 250T with reflector at 5 feet. F5.6 +6/10

Canon 580EX set to 24mm at 5 feet. F11 +5/10

Canon 580EX set to 28mm at 5 feet. F11 +7/10
Canon 580EX set to 35mm at 5 feet. F16 +0/10

Corona 250T without reflector at 10 feet. F2.8 +6/10
Corona 250T with reflector at 10 feet. F2.8 +9/10
Canon 580EX set to 24mm at 10 feet. F5.6 +7/10
Canon 580EX set to 28mm at 10 feet. F5.6 +8/10
Canon 580EX set to 35mm at 10 feet. F8 +2/10

So this studio flash with a 250 watt-second rating gave such disappointing results I had to take a look inside in case I could determine the problem. Please don't add a comment about the potential for electocution when opening a flash/strobe. I design power electronics for a living and am fully licensed.

I was quite satisfied with the overall construction of the 250T. The design and build is actually pretty good. But when I added up the capacitance values (six at 400uF each) and, with a measured voltage of 300 volts across each capacitor, I calculated that the real watt-second capacity to be only 108 watt-seconds. The calculation is 1/2 C V^2  or  0.5 * 0.0024F*300v*300V= 108ws. This low wattsecond capacity explained one thing that impressed me. The quick charge time. When set for full power it takes one second or less to charge after a pop. But that's no surprise now that I find it is really a 100ws flash.

The 580EX has a 1300uF photoflash capacitor and charged to 330 volts that calculates to about 70 watt-seconds. The Corona 250T has 2400uF of capacitance (6x400uF) charged to 300 volts (each) that calculates to 108 watt-seconds. So why is the 580EX two stops brighter than the Corona 250T? 

There are at least two reasons. The reflector used on the 580EX is more reflective. The reflector is like a mirror. The reflector on the Corona is a somewhat bright white metal that is not even close to the mirror finish used on hotshoe flashes and some studio flash reflectors. Another big factor (maybe bigger) is the distribution of the light generated. Speedlight flashes focus the light to match the view of the camera when the flash is on the camera. Under these conditions the flash is mainly illuminating what the camera is seeing. This is how hotshoe flashes come up with impressive guide numbers. 

Studio flash/strobes tend to have a wider pattern that is circular rather than rectangular like hotshoe flashes. This is often desirable when you are trying to fill an umbrella that happens to be circular.

The following images are from the 250T and the 580EX 24" from a white wall. The black marked points are 24" from the center. Power levels were adjusted to keep the center at about the same brightness and below clipping. The measurements were reflective flash meter reading with the spoot meter attachment to my Minolta Autometer IV F.

So you can see that the Corona has quite a spread even with the reflector in place. The wide distribution reduces the on axis energy. One of the reasons why the 580EX has about 2 stops higher output on axis compared to the 250T with higher power. (70ws to 108ws) I expected a wider distribution and for this reason I compared both the 580EX and the 250T in a softbox. This should have provided an advantage to the 250T compared to direct unmodified output. Unfortunately even in a softbox the 250T was still one stop lower in output compared to the lower power 580EX.

As a result of the above pattern tests I tested the 250T and the 580EX into a 60" reflective white umbrella. Even with the 580EX set for the 17mm coverage setting it still produced one third of a stop more output than the 250T. With the 580EX set for 24mm it had an output two thirds of a stop higher for the same setup.

There is a larger Comet mount reflector available for the Corona. I would have like to see how much better the 250T performs with a better reflector but at this point the low power output really does not meet my needs.

I really wanted to like Corona 250T studio strobe. The build quality is adequate for non-professional use. It operates just fine but unfortunately the output is too low. It doesn't come close to the rated output claimed by the seller. I would really like to hear how they come up with their rated guide number. I'm sure some photographers would be quite happy with this light as long as you keep your ISO up or you didn't need to cover a larger area.

Feb 24/2012 addition

The fractional setting position is not quite what the light puts out. So I marked where the actual positions are for the listed outputs. The half power position was slightly lower than indicated and the quarter power position was slightly higher than indicated. The 1/8th position is about half way between the 1/8th and 1/4 position. The actual power at the listed 1/8th position is about half a stop lower than 1/8th power.