First venture into macro with Pentax 67

[Joachim_I]

Just received two rolls of Velvia 50 documenting my first venture into medium format macro photography. I shot backlit cactus flowers in nature at magnifications around 1.5:1. I am more than happy with the results. I will certainly spend more time with macro photography in future. This is a completely new and exciting chapter for me.

I adapted a Schneider-Kreuznach M-Componon 80mm f4 to my Pentax 67II and used the Pentax helicoid extension tube to focus. I obtained two adapters: 1) #0 to M39 (Schneider-Kreuznach adapter ring no. 10711) and 2) M39 to Pentax 67 (from a Chinese seller on *bay). The helicoid extension tube alone is sufficient to yield magnifications up to 1:1.1. In order to reach higher magnifications, I added 6cm of M39 extension tubes (taken from an old Leica BEOON copy stand) which brings me to around 1.6:1.

Does anyone know the optimal aperture of the M-Componon 80mm? I used f11 for my first attempts but plan to play around with this in future.

[Michael W]

I don't have any answers, but it sounds like a great idea. Well done.

[david James lee]

be careful with refraction (sorry,difraction i meant...). when you add extension the actual aperture is less than selected since the lens is actually longer. ( may we see the first photos ? )

[domaz]

I think what david meant was not refraction but what is known as bellows extension factor in the Large Format world. Basically once you have a lens focused to farther than 2/3 more than it's focal length you have to start applying bellows extension factor. The easiest formula is probably (extension/focal length)^2 - convert that number to stops (i.e. 4=2 2=1).

[keithwms]

Does anyone know the optimal aperture of the M-Componon 80mm? I used f11 for my first attempts but plan to play around with this in future.

f/11 may well be optimal, though the with macro there are [at least] two things that may override conventional wisdom: (1) for want of DOF, you may need to stop down considerably past the 'optimal' aperture; (2) at close focus, the corner sharpness can degrade quickly... hence floating element lenses and the process lenses optimized for 1:1. Without floating elements, if you need best corner performance then sometimes you are forced to stop down in a way that degrades centre performance (via diffraction)... but at least then you have consistent performance across the frame.

Bottom line, as always: if you like your results, then keeping doing what you're doing and be happy! Nevertheless, some quick testing can give additional confidence.

P.S. the bellows factor formula I use is (1+m)^2, where m= magnification. E.g. for 1:1, m=1 and you need (1+1)^2 = 4 times longer exposure... or two stops.

[Anscojohn]

I don't have any answers, but it sounds like a great idea. Well done.

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I have done the same kind of lash up with mine, including the helicoid tube. Theoretically, two stops down from wide open is your best aperture. I like F/11, though.

And I always use my mirror lock up; a heavy tripod, with my camera bag hung from the center standard of the tripod.

[Joachim_I]

Thanks a lot everyone. At home, I did some research and came across a formula which yields an optimal aperture setting for macro photography. If I understand correctly, it is optimal in the sense of providing maximum depth of field without sacrificing resolution. The formula is A* = 1000C/(1+M) where C denotes the circle of confusion and M magnification. Hence, with M = 1.5 and C = 0.05 I obtain A* = 20. I could have used 16 or 22 and also would have gained a slight increase in depth of field. I will experiment more with this.

The limited depth of field is very attractive. For example, I can get one layer of leaves of a flower sharp while the rest vanishes out of focus. Or I can have one needle of the cactus sharp (on both counts) while the flowers remain out of focus and provide a nice complement to the sharp needle. I really like these effects.

A large cactus hardly bends with the wind. Therefore I was able to get a large number of sharp pictures. A sturdy tripod and mirror lock up are still necessary of course. For the Pentax I need these anyway.

I am amazed about the M-Componon which is optimized for M>1. The corner sharpness under the magnifier is simply stunning. The out of focus area is very smooth. What a great little lens. Watch out for it, I got mine brand new for less than 60 Euro.

I would love to show pictures but I don't have a scanner. I watch my slides projected on a screen.