Is 250D closeup filter compatible with Sigma 105mm?

[foxbat]

I've decided I'd like more than 1:1 on my Sigma 105mm macro and one option seems to be a 250D closeup filter. I have a few questions that I can't find the answer to:

Will it work? The 250D is for up 135mm. With the crop factor the 105 is a 168. Can the crop factor be ignored here?

Will it reduce the min focus distance even further? Is there a formula for calculating the distance. The diopter effect is +4 on the 250D.

What will the new magnification factor be? Again, I'd like the formula if possible.

Thanks in advance.
- Andy

[RichardtheSane]

Can't answer the formual questions I'm afraid, but you can use it on the sigma 105mm.

The effective focal lengh for lenses because of crop factor is just that, effective - not optical. So it will be fine :)

[CyberDyneSystems]

Think about extension tubes too....

[foxbat]

Thanks Richard, I thought as much.

Thanks CDS, I did. It was easy to do the calcs for the tubes but I could't work it out for the filter and I like to consider all options.

[gasrocks]

Quality wise, grab extension tubes before you get out the close-up lens. Added bonus - you don't get closer for more "power." Diopters? +1 means waht would normally be inf. focus is 1 meter. +4 means 1/4 meter. Rough guide.

[foxbat]

Thanks for the advice, 1 set of Kenko DG tubes is on its way...

[RichardtheSane]

Thanks for the advice, 1 set of Kenko DG tubes is on its way...

Good tubes, they are what I use :)