Pentax 50mm SMC-M F4 ?


Link Posted 02/04/2007 - 16:38

I just bought this lens for 40 pounds ( about 70~ usd ) . I want it to use it with my k100d . Is it any good ? I am pretty sure this lens is 1:2 magnification ( not life size ) . This is for film right ? Will the magnification be greater than 1:2 if used with digital ? like 1:1.5 ? Now... if I want to get better macro from this lens .. is it better to use extension tubes or reverse ring.. or ?

I hope I won't regret giving 40 pounds for this lens ..

Thank you!


Link Posted 02/04/2007 - 23:06
I've never used one but I can't imagine a Pentax SMC prime being bad.

see some other users comments here

I always refer to that site when I'm considering a Pentax lens, older ones especially. For some reason that link takes you to the older version of the lens, scroll down just a bit to find the SMC-M version you have

The magnification issue is a little confusing in some ways, but here goes:

In the purest sense, no the macro will still be 1:2. This is because the macro ratio refers to the size of the image vs the size of the object and takes no account of sensor size.

However, since the sensor is smaller you need less magnification to fill the frame, so for most practical purposes it is as if the magnification has increased by 50%.

If you want to get closer still, I'd probably opt for extension tubes. You can always use a reversing ring as well if you really want to get close.

The advantage with the tubes is that the focus control on the lens will still work so you can adjust fine focus that way rather than having to move the camera (the focus does nothing on a reversed prime).


Link Posted 02/04/2007 - 23:40
The SMC Pentax-M 50mm f4 Macro is a very fine macro lens of the highest standards. It comprises 4 elements in three groups. It focuses down to 1:2

I have owned this lens in the past and it will not disappoint you.
Best regards, John


Link Posted 03/04/2007 - 00:47
thank you very much . I am glad it is a good lens . Could you post some pics maybe which were shot with the scm 50mm f4 macro ? Can someone tell me if extension tubes are the best to get some more of the lens ?

thank you

edit : are there any incompatibilities with this lens and digital SLR ? Like chromatic aberrations , ghosting flares etc.. ? I am new to SLRs


Link Posted 03/04/2007 - 11:25
I have the SMC A 2.8 which is also 1:2. I've had no problems with chromatic aberation, ghosting or flare with that lens.

Magnification - at 1:2 you fill the frame on a Pentax DSLR with an image which is about 47x31mm in size. On a 35mm camera (where full frame is 36x24) it would take a lens capable of a magnification of 1:47/36 or approximately 1:1.3 to acheive the same result. So it is like using a lens of that magnification on a 35mm camera (only the depth of field is somewhat improved - by about a stop)

As to larger magnification - tubes or even a bellows is the way to go I would think - macro lenses are designed for this. I think Pentax even used to do a dedicated tube for the 50mm macro to make it 1:1 (the 50mm auto extension tube acheives that I believe)
Tony Milner
Super A, ME Super, MZ6, K5II, Ricoh GR & lenses from 8-500mm
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