Do lens adapters effect focus?

[colfaxrev]

I bought a C-Mount to Canon EF Mount adapter so I could use my DSLR lenses on my 16mm bolex. I'm wondering if this will change focus values. I would think prime lenses would be fine, maybe the distance reading may be off a little? But for a zoom lens maybe it will mess up back focus?

Any advice / info would be great, so thanks in advance!

 

[Samuel H]

I've used lots of dumb adapters (with no glass), most going from Leica-R to Canon, Nikon and Sony-NEX. All of them sub-$50, bought on ebay. I think all of them affect focus marks, some a lot, some so little that nobody would notice... on most lenses. The focus in my Samyang 8mm fisheye moves the glass forward and backwards so little (much less than 1mm in total, from infinity to closest possible focus) that I had to try several nikon-to-canon adapters just to have the lens focus at infinity. I would think that no adapter is going to keep focus marks accurate on that lens. On my 90mm, it's not a big deal at all.

 

[optitek]

Lets put it this way:
When they are made correctly they will not affect the focus.
When not they will affect the focus.

 

[colfaxrev]

Lets put it this way:
When they are made correctly they will not affect the focus.
When not they will affect the focus.

thanks both of you for response.

Its made by vello and it claims to maintain focus to infinity.

http://www.bhphotovideo.com/c/product/843890-REG/vello_la_c_cef_lens_mount_adapter.html

I guess I'm just curious, if it maintains infinity, does 5 feet distance still mean 5 feet?



Here are photos with the adapter no lens, and then the lens on. The adapter is a little far out, it has to be to fit the canon lens on the bolex. The adapter seems well made and when I look through the eyepiece for focus it seems like I can focus to infinity. That is the crappy canon starter lens, but when my film arrives I'll be borrowing a Zeiss CP2 lens to test the marks with.

 

[Samuel H]

The easiest way to know is my testing it. In any case, I doubt that lens had accurate focus marks to start with.

 

[Ryan Patrick O'Hara]

thanks both of you for response.

Its made by vello and it claims to maintain focus to infinity.

Often cheap adapters that don't want to invest in high-accuracy/tolerance machining/QC, will simply make their adapters off on purpose, but just slightly off, so that they pass infinity. You can either make the flange depth too far or too short. I can't remember which, but they will purposefully make the adapter at specs different from exactly where it should be so you can reach, and actually pass infinity, but you are giving up some room on the CF.

It's a way for them to stay safe, making sure all their adapters hit infinity (or pass it).

This is not all adapter makers but many of the mass producing cheap ones that don't have as strict of tolerances. They make it a little off because that way you can always get to infinity.

Lucky for them, photography lenses have horrible witness marks so it won't matter that they are off. The only goal is to hit infinity, and they don't care if you pass it a little and give up a little on the close end.

 

[visugeek]

I haven't had a lens adapter yet that worked correctly with the focus marks on either my still or cine lenses. I would recommend setting up a focus chart and getting out a tape measure to test before you have a real shoot day. With the Bolex tiny viewfinder, you don't want to have to be hunting for focus on set, especially in a low light situation. You might want to throw a strip of tape on the lenses with new witness marks for this adapter so that you are dialed in and ready to go when you want to shoot.