100mm Macro Quandry

Hi Folks,

I have a long distance friend who has come to me for help - silly goose!

He's trying to classify a lens as True Macro or not.

He has a 100mm SMC Macro f4 - f32? K mount lens. He also says the front bezel says 25 to 2. No electrical contact or "A" on the aperture ring so obviously an "M" lens that I would assume to be a very early K.

I thought the 100mm Macros were true 1:1, but this one seems to be 1/2?

Is this possibly a bellows lens? I wouldn't think so as even though it's 100mm like a bellows lens, it says Macro.

Am I missing something? Sorry I have no picture yet, so am going on his observations only for now.

Would the serial # help?

I hope this is dead obvious to someone - JR? Daniel? Galoot?

Thanks in advance for any consideration.

Cheers

Mac,
According to Bojidar Dimitrov, it's one of two:

http://www.bdimitrov.de/kmp/lenses/primes/short-tele/M100f4-Macro.html
http://www.bdimitrov.de/kmp/lenses/primes/short-tele/M100f4-Dental_Macro.html

And yes, both are max mag of 0.5x

(The AF 100mms are 1:1 - SMC-F, SMC-FA, SMC-DFA)

Hope that helps!
Matt

There is no such thing as a "true macro", beause there is no universal agreement on precisely what "macro" means. To Pentax, it means a lens that focuses much closer than normal, and thereby permits macro photography.

So your friend certainly has a macro lens. And a damn good one.

G

Thank you both, SO VERY MUCH!

I'll certainy pass this info along post haste!

Gotta love this forum!

Cheers

As far as I understand it, the term "macro" originally applied to equipement that would let you acheive 1:1 or greater magnification on the film/sensor plane. A lot of lenses with close focusing ability, but not true "maceo" lenses, have been sold as "macro" over the years.

The 100mm f/4 lets you acheive half of life-size on the film plane, so technically it's not a true macro lens. But with an extention tube, you can go macro easily enough. It's also corrected to function best at close distances, so in a sense it's more of a "macro" lens than a regular 100mm lens.

Arthur - I have this lens too and maybe you should tell Pentax about your criteria for macro lenses because the lens is clearly marked SMC Pentax-M MACRO 1:4 100mm and so does the leather case it came in. There is an extra set of numbers marked on the barrel that correspond to the focus distance where the number 2 lines up with 1.48' and 25 lines up with 15'. I always assumed this meant 1/2 to 1/25 life size at those distances but would be open to other interpretations as I do not have the manual for it.

Regards

Drew

PS: Am I right in assuming that it would be a .75 magnification factor when used with my *ist Ds?

The figures on the SMC Pentax-M 100mm f4 Macro do indeed refer to magnification and 2 means 1:2

In practical terms, macro lenses are specifically designed with a flat field and to give superb image quality when used close up. A 1:2 magnification, half life size, is usually referred to a macro, and 1:1 is achieved with a dedicated extension tube.

More modern macro lenses usually focus down to 1:1, which is definitely a bonus.

Vivitar tried to quantify the terms in the 1970s, but with no lasting impact on the use of the word "macro".

Zooms that focus down to 1:4 are very useful, but do not have a flat field at these distances and are not suitable for document copying.

A good macro lens is well worth having.

Drew,

This is an odd one, and depends on how you look at it! Compared to 35mm film, you will apparently have greater magnification. If you have a subject that is 48mm long, on film the image would be 24mm, or 2/3 of the width of the frame (1:2 magnification). On your DSLR, the image would still be 24mm, but that would now be the full width of the frame.

The magnification at the taking stage is no different, it's still 1:2 (half life-size), but at the output stage (ie. if you made a 9x6 print, full frame from both film and digital), the magnification would be greater for the DSLR.

Does that make sense?

Dan

I also have this lens in "M" guise i.e.SMC Pentax-M Macro 1:4 100mm, brilliant lens, whether a true macro or not. It and the 200mm F4 M lens I bought are super lenses.

I'm not sure if it does make sense to me. I just used the 1.5 multiplying factor to come up with the .75 magnification assumption. You made me dig out my dusty old MZ5n and try it on to compare. If using the MZ5n and I focus on a ruler I can see approximately 65 mm width at the closest focus (which is about 45 cm.) When mounted on the *istDs the view is 42mm wide and surprisingly (to me) the same approximate 45cm minimum focusing distance. I'm not sure if there is much difference in the viewfinder coverage between the two cameras but 42 x 1.5 = 63mm so I'm thinking that .5 x 1.5 = .75 magnification was pretty close considering my crude measurements. Or is that basically the same as you said or... am I waaaay out to lunch?

Regards

Drew

My head hurts - I just posted and deleted a reply to this which was quite wrong...

I think someone should get the SMC Pentax-DA 100mm f2.8 Macro, try it on a film and a digital body and see if it is 1:1 on film or digital. On the face of it it can't be both and if it's 1:1 with film it must be greater than life size with digital.

Interesting question that will be easier to work out practically than by thinking about it....

Well, I did say "This is an odd one, and depends on how you look at it!"

Drew, the minimum focusing distance of the lens is not going to change - it's the same lens whatever body it's mounted on, after all.

The reaon you could see 65mm width on your MZ5N, is because that's roughly twice the width of your 35mm film (okay, that would be 72mm, but you'll lose some from the edges of the viewfinder, you don't see the full 100%).

The reason you could see 42mm when you used your istDS, is because that's roughly twice the width of your sensor (okay, that would be 48mm, but you'll lose some from the edges of the viewfinder, you don't see the full 100%).

It's twice the width in both cases because the lens give half life-size reproduction, the magnification ratio is 1:2. Therefore, every 2mm of subject is 1mm wide on your sensor/film.

So your lens, on both bodies, gives 1:2 magnification. But when you then view that (either as a print, or on your screen), the Digital body will show a narrower field of view, and hence the output will be more magnified.

So yes, in effect, you get more magnification with the DSLR. But it's because of the body (the smaller sensor), not the lens.

Is that any clearer? It's always much easier to explain things face to face, I have to admit - you can actually demonstrate things then.


When I got my Sigma 105mm macro, I had a similar thought to you - I'd got so used to this 1.5x factor with DSLR's that I thought "great, this 1:1 lens will be a 1.5:1 lens". When I got it home, I got a ruler out, looked through the viewfinder, expecting to see just 16mm (24mm/1.5), but it was 24mm instead, which was a surprise. But then I thought about it, and realised that the lens still gave 1:1 magnification, but the smaller sensor meant that the subject would fill more of the frame. A 15mm long bug was still 15mm long on the film or the sensor, it's just that there's less background shown on the DSLR.


Hope that helps! Just enjoy your macro work, I know I do.

Dan

Thank you for that.

It made sense?

Dan

That was a very good explanation Daniel. I think all those little faces in your last post helped by simulating a face to face I knew the lens characteristics wouldn't change on a different body but at first it seemed natural to assume that the min. focus distance would be closer if the image appeared closer and that was wrong. So really it still does all boil down to the fact that there is a 1.5 magnification increase using a digital body when you look at the final output. I guess this would be be no different than adding a 1.5 teleconverter or an appropriate length extension tube for 1.5X to a 1:2 macro lens on a film body. The output is the output right?

Regards

Drew