Extension Tubes, Bellows and Macro Lenses


Anonymous

Link Posted 20/10/2005 - 14:56
Kim C.'s manuals have provuded extensive information on the use of Extension Tubes and Bellows with M42 bodies and the Takumar family of "Normal" lenses. He was trying to head off my usual silly questions, but here's a few that slipped through Kim's excellent defence perimeter.

I've had no experience with Pentax's Marco Lenses yet - have to win a major lottery first. Other than the obvious advantage of being able to focus anywhere from really close to infinity, are the Macro lens superior to say a 1:1.4 50mm Super Multi on tubes or bellows for really tight work?

I guess image clarity and the ever-diminishing DOF would be the factors I'd like to compare.

I've seen close-up pictures of items offered for sale on eBay which were taken with a 50mm macro, and the clarity was stunning (I'm referring to wideangleman). Now, while these are close focus, I personnaly don't consider them to be macro. Is there a narrow definition?

I've seen close-up lenses for sale which screw on like a filter and, I suppose, allow for closer focusing of normal lenses. Does this approach Macro?

There's gotta be a glossary somewhere?

Halp!!

Kim C

Link Posted 20/10/2005 - 16:49
Hi Mac,
the true definition of macro is 1x - 10x lifsize on the film. Up to 1x is closeup. However, many lens makers will call their lenses macro if a normal print is lifesize rather than the neg. this equates to 1/4 - 1/5 lifesize but in reality it is close focus. the lenses themselves, normally zoom are optimised fo normal work and not macro so quality is workable but not good. A true macro lens is optimised for good flat field performance and close range work although many will focus to infinity and be perfectly workable. A bellows lens is designed for bellows work and because the focus is down with the bellows, they have no focus mechanism so can't be used like a normal lens.

Early MF macros generally focus to half life size on their own or to lifesize with a tube. They do perform slightly better than the std lenses but it will depend how much macro work you do. As a general rule and according to Pentax's advice, the 1.7/1.8s are much better for macro than the 1.4. they are designed differently. The 1.8's have better flat field performance and appear sharper whereas the 1.4 are designed to give a better 3D modeling effect.

The supplementary close up lens don't go anywhere near macro and are cheap which might give yo an idea of their performance!! You have bellows and a tube so there is absolutely no need for them. Once you get to true lifesize, you will get better results if you reverse the lens. Normal lenses are designed to work best when the angle of light entering the lebs is much narrower than the light leaving (less so for macros but still true) at life size both angles are the same and larger than lifesize it reverses hence the need for reversing the lens to restore the staus quo

Kim

Anonymous

Link Posted 20/10/2005 - 20:25
Thank's, Kim!

I'm using a stuck-in-manual, but otherwise perfect 55mm f1.8 Super Takumar on my bellows and find that it is clearer with a reversing ring as you mentioned. I'm able to achieve up to 2.4 magnification, so it will beat a Macro lens in that respect.

1 to 1, or lifesize, can be achieved with a 135mm f3.5 on a bellows which is the same as a 100mm macro? I'll try this lens reversed as well.

The hairy experiment seems to be with my 28mm f3.5 which, the charts say, can achieve 4.8 magnification. I'm having major problems focusing - maybe I'll try reversing it as well.

Thank's for the heads-up regarding those add-on close-up lenses (too good to be true).

I have a couple of old 8mm projector lenses by Bell & Howell which I've heard can be reverse mounted to the bellows for getting crazy close. Once I figure out how to mount them I'll let you know what I discover.

Cheers!

George Lazarette

Link Posted 20/10/2005 - 21:14
Mac,

The proper Pentax macro lenses are considerably sharper than standard lenses; in fact, breathtakingly sharp.

George

Anonymous

Link Posted 20/10/2005 - 21:37
Hi, George!

Yeah, one day my ship will come in and I'll get one - heck, I'll get both!

Not only are they sharp, they have amazing depth. I would assume that most good catalogue photographers use them. It seems like you get wide angle DOF at 50 or 100mm.

Have you ever tried one on a bellows?

Cheers

Kim C

Link Posted 20/10/2005 - 21:51
Hi Mac,
A 50mm macro can have no greater DOF than a standard 50mm at the same aperture setting because it depends on a mathmatical equation not in the way they are made. And yes they work a treat on bellows but they still need to be reversed at magnifications greater than life size

Kim

johnriley

Link Posted 20/10/2005 - 22:44
And following Kim's comment up, don't forget that the 100mm macro will also have the same DOF as the 50mm for a given magnification.

So, if you want to take a picture of a chess piece that fills the frame, it doesn't matter for DOF whether you use the 50mm or the 100mm as the DOF will be the same. The 100mm will of course be twice as far away from the subject, so perspective will change.
Best regards, John

Anonymous

Link Posted 20/10/2005 - 23:07
John,

Soo, in essence the 50mm would be roughly twice as far away as a 28mm? Is DOF at a given magnification the same as for the 50 and 100?

Gee, I hope so, 'cause it would mean I'm actually starting to understand this.

johnriley

Link Posted 20/10/2005 - 23:24
You've got it. Your example would be closer to being exact with the 24mm though.

The DOF would indeed be the same, but you would be very close and the perspective would again be different.
Best regards, John
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