Extension Tubes Q:

[n30_mkii]

Probably a stupid question. But here goes.

I have an old Sigma 90mm macro which will produce 1/2 lifesize.

I also own a set of Kenko AF Extension tubes.

Can anyone tell me what scale I would be working with if I add each one on, and then finally with all of them on?

12-20-36

I'm not sure how to work it out?

I guess the working distance is going to get incredibly small

 

[RobertP]

Personally I'd do it the easy way. You know how big your sensor is.... so take a picture of a ruler and see how much ruler you get in the picture.

say your sensor is 22.5 mm wide and you see 22mm of ruler in your picture - you are getting about 1:1.
11mm of ruler in the shot would mean you had managed 2:1 etc.

 

[Cobra]

Personally I'd do it the easy way. You know how big your sensor is.... so take a picture of a ruler and see how much ruler you get in the picture.

say your sensor is 22.5 mm wide and you see 22mm of ruler in your picture - you are getting about 1:1.
11mm of ruler in the shot would mean you had managed 2:1 etc.

:bonk:
Oh yeah Thanks Robert

 

[Canon Bob]

I haven't had chance to use this lens but believe you will get the following results;

Tube length Mag
0 .50x
12 .63x
20 .72x
32 .86x
36 .90x
48 1.03x
56 1.12x
68 1.26x

There will be some slight errors in the calculation caused by the native internal extension in the lens and the changes due to reduced minimum focus distance as the tube length increases. It's also possible that the MFD will decrease to the point where the focus becomes inside the lens and hence the stated mag can't be achieved.

Bob

 

[n30_mkii]

Ok the other option would be to use a Ranox MSN-202?

I could pair it with the sigma 90mm Prime, or My tamron 28-75?

What sort of distance would I be working at, with those combinations? Obviously they have less light loss if any than the extension tubes.

Any further advice?