Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: I have a Canon Macro Lens EF 100MM 1:28 L IS USM 67MM, I ordered this flash and it wont fit the lens. It Keeps falling off. Any ideas?
Document: Why I am going for it ? After reading the reviews, I learn it is not TTL, out put light is controlled manually, can be lit from left or right half, 4 AA cells, 2 hrs in continuous mode. This suits me. Coz :-Macros need manual focus, Canon manual of L 100mm USM Macro states it.
I admittedly wasnt expecting much from this when I bought it, but I wanted a ring flash for my macro lens and the description said it would work. I was impressed. It was easy to match the correct lens adapter. The rign flash clips on quite easily. This worked with my Canon 5D Mark iii, and on the shoe, you could select flash intensity or simply turn it on for direct lighting. It allowed me to use a quite long lens to get really close and have perfect lighting.
I love this ring lite. It's great for up close macro photography. I deliberately chose this one as it came with the most adapters to fit your SLR lenses. The adapters screw in to the filter threading on your lenses/filters. The ring lite then clips on to the adapters. The range is quite limited, effective between 1 and 3 feet.
Polaroid 48 Macro LED Ring Flash does what it says. I'm using it on Canon T4i with good results. Is it as easy to use as a 500.00 dollar canon macro... (No) but damn doable. Using a FD Canon 70-210 MACRO lens with a adapter for the t4i
I use an ultra-wide lens with my Canon Rebel XT--and when using the built-in flash, there is always a dark spot at the bottom of the frame. For that reason, I've searched high and low for a good ring flash. Only thing is, the one's I've found that worked were brutally expensive. This one, on the other hand, can be purchased for less than a softcover book on photography. In fact, a LOT less. And it works great. Highly recommended.
Because I wanted a unit that would work with my Canon's exposure system, I returned it and bought the &#34;Meike MK-14EXT Macro TTL ring flash for Canon E-TTL TTL with LED AF assist&#34; available from Amazon.
I am definitely NOT a professional photographer, but I needed a ring flash for macro photos of teeth in a dental office setting. After using the luxurious Canon MR-14EX TTL ring flash for my other camera, I thought I'd buy something more economical for the back up camera and this Polaroid 48 LED seemed like a good idea. I think for art photos or for someone who knows a lot about settings and such, this would be an adequate product.
Light can be very tricky with macro photography since you'll probably end up right next to your subject. This will cause your shadow to cast over your subject depending on your angle. You'll also probably stop down a bit so that's another point of light loss. A macro ring flash will help since the flash is attached to the front of your lens.I didn't want to spend hundreds of dollars since I'm not a pro, but I did want something that would work well.
With macro photography light is a tricky aspect of the shot. The ring lites eliminate the shadow cast by the lens if you're using the camera's on board flash or a lower speedlite. You need your flash to get past the lens and onto the subject. This lite works well and is a steal at the price.
The flash worked the first time I tried it. The second time it would not flash. I would rate it lower than 1 star if possible.
Answer: Be sure that you have the 67mm ring and screw onto the lens then be sure to depress both the tabs on the side of the flash ring so that it will easily slip over the 67mm ring.