As I understand it, first surface mirrors afford less light loss and eliminate the possibility of ghost reflections, but require more care. Is it worth going with first surface, or are second surface mirrors (the ones we usually see) good enough for an image flipper?

Assuming the assembly would be completely enclosed I don't see why you wouldn't want to use first surface mirrors.

Ghosting image is not very visible when looking at the mirror at 90 degree, however, 45 degree will give a lot of ghosting and 4 of them will be enough during all lighting conditions. Why bother using regular mirrors when you can afford FS mirrors. I am working on an addon that will flip the image on current letus35(A). This one will be on the Letus35HD also. It will improve the image quality, barrel distortion and color aberration at the same time. Since this one is long and add more weight, I suggest using rod support. I am also working with local machine shop now for Letus35 support as well, hope to have everything done before Christmas, thanks.

Quyen

I got a first surface mirror from an old reflex-photo camera. Normally they are about the size of the 35mm negative, but there are bigger ones in Polaroid camera's. They are indeed butter than normal mirrors, but keep in mind that you will loose light anyway. If you don't have the mirror in a perfect 45 deg. you'll loose more light. In my experience/tests, two mirrors where absorbing too much light to be usable. Maybe an extra condenser in between?

Ok, thanks... that confirms what I was thinking. And yep, I had weight in mind, I'm working on a rail support now. I found 51mm square first surface mirrors for around $5.00 each... which is just over 35mm when viewed at 45 degrees. I'm starting the relay lens before the mirror array, though, so the reflected image will already be approaching 1/3" by the last mirror and (focusing) lens.

I found 51mm square first surface mirrors for around $5.00 each... which is just over 35mm when viewed at 45 degrees.

Would you mind telling us where you sourced the FS mirrors?

http://scientificsonline.com/product.asp?pn=3052324&bhcd2=1133062886

They might not be top of the line mirrors, but they should work for image flipping.