CF 350 extension tube

[frank]

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

 

[fotografz]

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.

 

[frank]

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?

 

[fotografz]

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.

 

[qnu]

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

 

[frank]

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.