Medium Format Family

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CF 350 extension tube


New Member
Hi, I went out today again for the second time with my CF 350 lens. Looking through the vieuwfinder, the image looks excellent. I took some slides which will be ready next tuesday.

Now the question. I would like to focus closer with this lens than the standard 4.75 meters. A meter, maybe 1.5 meters closer would be great. Can this be achieved with an extension tube and if so, which one? I would think the 55/56mm tube. If so, does anyone know how much I would have to compensate the shutterspeed? I know Mr De Bakker has a formula for this but I am very bad at maths.

Thanks for all help, Frank


Active Member
Yes, closer focus can be achieved. I have a 8mm tube I keep with the 350 all the time. 55/56 will move you in pretty close. What do you shoot with a 350 so close? DOF is effected at that range and remember, you loose infinity focusing. The instructions tell you what compensation to use with each tube.


New Member
Thanks, this time I shot frogs at a waterlilly pond. Got some nice shots I think but more frame filling would be nice. How much closer do you get with the 8mm tube?


Active Member
Enough for a head and shoulders shot with an 8mm. There's a 10mm also ... then all the others. 56 is going to cut the light quite a bit if I recall correctly.

For your application a 32 or 56 is probably what you want.


CF 350 mm lens
minimum field of view - focussing distance - compensation required (stops)

8 mm tube + no lens extension:
241 cm - 15.2 m - 0.2

8 mm tube + full lens extension:
41 cm - 3.2 m - 0.8

16 mm tube + no lens extension
120 cm - 8 m - 0.3

16 mm tube + full lens extension
35 cm - 2.9 m - 1

32 mm tube + no lens extension
60 cm - 4.4 m - 0.6

32 mm tube + full lens extension
27 cm - 2.4 m - 1.2

56 mm tube + no lens extension
34 cm - 2.8 m - 1

56 mm tube + full lens extension
20 cm - 2 m - 1.5


New Member
Mr De Bakker, thank you so mach for your help. Seeing this, I think a 16mm would be the one to go for. Also excellent in combination with my 150mm.