Canon 20mm f3.5 Macro Bellow Lens

SigmaTog wrote:

I have just purchased a vintage Canon 20mm f3.5 Macro Bellow Lens.

Congratulations. I've used those before: they're sharp, low distortion, flat field, and have excellent contrast.

It is pristine, but it has a terrible flare.

Is there a way to deal with this please ?

That lens is not known for flare. If it's truly pristine, but there's a lot of flare, check your tubes or bellows. Remember, most lenses will happily spray light at least 45° off axis (some might go past 60°) so if it's in a relatively shiny tube, you will get a ton of flare.

Are you on a Canon bellows with the huge, flat Canon FD adapter? Generally, that combo pretty much won’t flare. The stray light doesn’t even hit the first 40-50mm of the bellows, and bellows accordion pleats are pretty good light absorbers.

Now, my conical RMS adapter flared like crazy when I got it. It was fine with microscope objectives, which only illuminate like a +/- 15° cone, but turned to crud with my 25mm Leitz Photar, which sprays light far and wide, like your Canon. I ended up having to really carefully cut flock paper to fit. Wasted three or four pieces before I got it right.

Tubes are easier to add flock paper to, because they’re wider than a conical adapter, and you can baffle them by cutting discs to fit, then cutting appropriate holes in the discs. That's provided you haven’t got flare starting in your RMS adapter.

ken_in_nh wrote:

SigmaTog wrote:

I have just purchased a vintage Canon 20mm f3.5 Macro Bellow Lens.

It is pristine, but it has a terrible flare.

Is there a way to deal with this please ?

What bellows are you using? What adapters?

I have the same lens but don't use it much anymore because there are easier ways to get to high mag while still preserving full automation. Also, lighting is a problem with such a short focal length lens, isn't it?

The magnification range for that lens is roughly 4x to 10x. The working distance at 10x is about 16mm, and that does sound scary for lighting, until you realize how small the MP 20 really is. It's similar to manual lenses of the day in that it has a small front. It even has a chamfered front, like a microscope objective, so it's 24mm in diameter where it faces the subject.

That means your light comes in from arctan((24mm/2)/16mm) = 37° from perpendicular.

At 5x this improves to 31°, while the overhyped MPE-65 can only manage about 48° at 5x. (Although, if you really want to see 5x goodness, the MP-35 can be lit from 20° from perpendicular).

I found a lovely illustration of this on a page about this lens over at Photography in Malaysia (a fantastic resource for photography outside of Malaysia, too).

https://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/fdmacro/2035macro.htm

Unfortunately, they don't allow direct image links.

SigmaTog wrote:

Thank you everybody for your great professional replies, all very much appreciated.
I had the lens on blackened tubes. I can now see that bellows would be better with all those angled pleats inside.

Almost always. The angles in the bellows make them near perpendicular to the light from the lens, and that really helps reduce reflection.

Tubes tend to have light grazing them far from perpendicular (almost parallel sometimes) and that tends to make even the best black paint appear surprisingly reflective.

Over on photomacrography.net there are multiple threads about flare control and the various paints, flocks, etc. that people have tried. Unfortunately, half of them end with "___ is the best I've ever used, but they don't make it any more."

(And why is your post and my reply showing in bold?)

I have tried a baffle inside the tube with a 12mm hole, about 20mm behind the lens & that worked,

Excellent!

I've always been baffled why people don't try this more often. It's simple, easy, and quick. You can get black flocked paper from a scrapbook store that might not be what you want to line a tube, but sure makes great baffles.

I will try a bellow too.
All the good points of the lens mentioned above are true for mine too.
" there are easier ways to get to high mag while still preserving full automation ", what are the choices please ?

I have no idea what that poster meant by "full automation". Autofocus isn't much help at 5x, if you're doing stacking you want to set exposure manually anyway, and letting the lens motor handle the stacking under camera control instead of letting a focusing rail do it with its own controller doesn't strike me as optimum.

Maybe wide-open composing?

I am trying to photograph a luminescent beetle's shell at magnification to see the structure of the surface. The dynamic range is large.
PS I made a mistake with the scale, the interval should be 0.1mm.

SigmaTog wrote:

Thanks very much Joseph

You're quite welcome. Together, we are greater than the sum of our parts.