Enlarger Lens

I have just recently got a 23CIIXL enlarger and it was set up for 35mm with 50mm El Nikkor lens and neg carrier. I am trying to get set up for 6x4.5 for my Bronica ETRSi and I am finding 6x6 negative carriers that I can use and looking for a lens. I have found lens boards that have different mounting holes and wonder if 39mm might be the standard one. Freestyle has lens boards with 39mm hole and also some on ebay. I have seen several lenses on ebay and just wondering which ones are good and if there are any to stay away from. There are some lenses that are 75mm and some 80mm and I guess that range is OK for medium format.
Marvin

39mm is the most common modern size for lenses in the focal length range you are considering.

As to lens recommendations, I'd suggest using the Google Search function on APUG to search "Good Enlarger Lenses" to see how this question has been considered in the past.

After reviewing those threads, you may still have questions, so feel free to ask.

75mm is optimal for 6x4.5, but 80mm works fine, and 90mm would probably be fine too with an XL column. A 105mm lens would cover 6x9 (if you should ever go that way) but would yield small prints from a 6x4.5 negative.

Matt

75mm should work fine for 6x4.5. Our 75mm and 80mm lenses all fit in the same mount as our 50mm lenses. (Nikors, Scheiders and Rodenstocks).

Vaughn

PS...if you think you might go 6x6 or 6x7 eventually, then perhaps an 80mm would be better.