killes wrote:I don't think this will work in my case. I usually use the macro lense near its 1:1 setting and when I focus by ring, I'll also change magnification. It is also not focussing internally, so the position of the front element changes as well.
Change of magnification by itself is no problem -- any of the stacking programs can compensate perfectly for that.
I have to admit: I didn't know that.
Movement of the front element is definitely an issue. I have one macro lens with similar characteristics (a Sigma 105, old model). Around 1:1 with that lens, both methods of focusing are far from perfect.
That's just the lense I have, too!
However, that lens has one very nice feature: the entrance pupil maintains a constant distance from the front of the lens as focus changes. This simplifies the added-lens approach because no change in separation is required as the lens ring is turned to change magnification/focus.
This is exactly the reason why I did not want the "lens in front" approach, I thought the changing distance would be a problem.
Using the Raynox DCR-250 in combination with the Sigma 105, the combo becomes telecentric with about 45 mm of rings between the Sigma and the Raynox. The useful magnification on APS-C varies from about 1.05:1 to 1.85:1 (field width 21 mm down to 12 mm). Image quality is good corner to corner, with some correctable red/cyan CA.
Fully automatic operation is retained, including auto diaphragm, auto focus and shooting stacks under software control using the A/F motor. The setup can be reproduced by simply screwing together new manufacture parts easily purchased on eBay at any time. I mention these points because they are some of the reasons why I have come to prefer the added lens approach, and I think it's important for other readers to understand the issues.
Thank you for prompting me to check the Sigma+Raynox combination.
Thank you for doing that!
Some findings from my setup:
- when using a 50mm normal lens, I do not need to add extra extensions, the remaining part of the teleconverter acts as a 15mm extension tube. The image does not have vignetting.
- when I use it like that, the magnification is about 1:1
- When stacking, I can't change the magnification at the front lense, since it needs to be at infinity, but I can change the extension of the rear ex-teleconverter. Only 8mm, though.