Instruction: Given a question and the related document, and generate the answer to the question based on the information provided in the document.

Input:
Question: Can it work on a Nikon D7100? Can I place the trigger on the camera and a another flash on top of it? I have a Sunpack digiflash 3000 for Nikon.
Document: First, the on/off switches are located under where the flash goes, so you need to turn the units on before you mount the flash. And second, the unit being used on your camera doesn't lock in place on the hot shoe, so if you include a flash unit on the camera on top of the 603, the excess weight can cause the flash-plus-trigger to slide off the camera body.
These triggers work fine with my nikon camera and my nikon flash + the 2d Yongnuo flash I have which has a built-in trigger receiver. They are easy to setup, and seem well built. The on off button is in an odd place but that is a minor work around. I haven't put them to any sort of extreme test, either in weather or distance but for outdoor location shooting they seem to work fine.
I have accidentally loosened the trigger on top of the camera while moving the camera around for a shot. But, I'd say that's a minor issue, not a major problem.2. Another minor issue is that the on/off button could be better placed for easier accessibility when a speedlight is attached.3. The biggest issue I've had with it is that the connector on the wire bent very easily within the first couple of uses.
I had purchased this for my Nikon because of the ratings i had seen from others. This product does work for the D3100. Cost a lot less then other wireless triggers! I purchased two speedlights and decided i need another wireless flash trigger so i ordered two more. I am now able to utalize the two speedlights and set them off remotely with this trigger/shutter release. The reason I gave it a four star is becasue it does not work 100% of the time. Sometimes i get missfires.
I use these with my D7100 and D3100. I use it with studio flash and out door flash and remote shutter release. During Thanksgiving , I used these to take candid family photos without the &#34;forced&#34; posed look. They work on 1 set of batteries for weeks! They work from any direction, even from withing a pocket. They even trigger the auto focus.
I'm sorry, but I don't like to read instructions. I opened the box on this product, found the place to plug it in, which is on the side of my Nikon, and did so. I stuck one of the units on the flash receiver (I forget the technical names) and then I plugged the other end of the cable to it. I turned on both units, and then pushed the button down partially, and the camera auto-focused.
Excellect addition to my camera bag! I really like the fact that I can trigger my camera from the remote attached to my flash so I can place my camera on a tripod and move the light around.
Triple yay.In fact these have revolutionized how I photograph an interior room .. sender on top of the camera and TWO remote flashes. Wow. I asked my girlfriend to go to rear bathroom in the house, close the door, and wait. Flash fired through 3 walls and 3 rooms away. So the old-style Nikon IR line of sight sympathy flash is a thing of the PAST in my opinion. Yongnuo's Commander Mode is true commander, not based on line of sight or a 30 foot range.
One of the great things about these is that they work both as a trigger and a receiver. On top of that, they also can be used as a remote shitter release for my D7000. It works amazingly in this capacity. The you can press the button halfway down to focus just like the shutter release on the camera itself.These set up SUPER easily. Just flip the switch and slide it on. No fuss, no muss. Whatever muss is.
Just pass through all the iTTL signals from the D7000 to the hot shoe on top of the RF-603.The RF-603 has decent construction and some nice features, but like another set of Chinese radio triggers I bought, it shows a serious lack of marketing research by Yongnuo. The user manual is a similar embarrassment.Wedding photography is ready for an affordable alternative to Pocket Wizards, and doesn't need iTTL control of every remote flash. A Vivitar 283 can handle that chore nicely, thank you.
Answer: Yes, your flash will work on top, but it will not work in TTL mode. You will have to run it in manual. Which for my purposes is all I need. Hope this helps!