Interferometer Mirror Configuration Effects I am building a Michelson style interferometer. I have it on a steel frame that I am reluctant to cut until I gain greater understanding of the mirror configuration effects. I am getting really good concentric fringes, but I can only find them when I move my mirrors about two inches from the beam splitter. But I constructed my frame so the mirrors are about 16 inches from the beam splitter. 
I have attached two images below:


My question is should I persist on trying to find fringes at the 16 inch distance because fringes produced from mirrors father apart produce a better image or does the mirror distance have no effect on the fringe image? Does the offset configuration produce different results than the straight on. I have tried to find these answers online and through actual experiments but without success.
 A: This is an excellent project but obviously requires unwanted movements of the various components of the interferometer to be kept as small as possible.
Longer path length will require more rigid supports for the component parts of the interferometer.
The first question is why do you want the path lengths to be 16 inches; what is wrong with 4 inches or perhaps less although it then might become more difficult to fit in all the component parts between the mirrors.
The mounting of the mirrors, which should be front silvered, is important so that their orientation can be adjusted with some degree of precision.
A fine thread is best for the adjustment screws.
Another thing which is missing from your diagram is a compensation plate.

This should be the same thickness as your beam splinter thus ensuring that each beam of light passes through three thicknesses of glass and so the optical path length of each arm can be relatively easily made the same.
This will enable you to observe white light fringes as shown in the diagram above.
When such fringes are observed you will know that the optical path lengths for each beam will be the same.
In other words you will be observing the zero order fringe and those close to it.
The fringes that you observe depend not just on the difference in distance  of one mirror from the beam splitter and the other mirror from the beam splitter; they also depend on the $orientation$ of one mirror relative to mirror.

If the mirrors are "parallel" as shown in diagram a you will get circular fringes looking similar to the sort of fringes you get in a Newton's rings arrangement.
If the mirrors are equidistant but inclined as in diagram b you will get parallel fringes of the type produced by a wedge fringe demonstration.
It will be informative to "play" with you interferometer and to see, as you move the mirrors both in terms of separation and orientation, how the parallel fringes slowly become curved and the circular.
You should be able to do this with your prototype arrangement.
To observe these fringes it is best to use an extended source although a laser as the source of light might well mean that you do not need to worry about the extended source as the laser beam will have some width (adding a small diverging lens will probably help) and possible not even bother with the compensating plate unless you want to observe white light fringes?
But it all depends on what you are going to use the interferometer for and most of what I have written above is not necessary if you want to just produce some fringes.
As soon as you want to take readings which require the accurate translational measured movement (with a micrometer) of one of the mirrors the task of manufacturing the interferometer becomes harder.  
I found many designs by googling michelson interferometer construction and michelson interferometer making.
Good luck.
A: I ended up moving the mirrors closer to the beam splitter, about 4 inches. As one might expect, the closer the mirrors are, the easier it is to get a good alignment. The image is brighter and more stable too. I have a micrometer on one mirror so the stability factor is important. If you look at the two diagrams that I posted, you'll see one is offset the other is not. I found no difference in the image between the two configurations. If you expand the beam before the beam splitter you will get circular fringes on the screen. Here is the image.
