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SMC Pentax 45-125mm F4

Reviews Views Date of last review
16 56,681 Sun May 19, 2019
Recommended By Average Price Average User Rating
94% of reviewers $73.75 8.25
SMC Pentax 45-125mm F4

SMC Pentax 45-125mm F4
SMC Pentax 45-125mm F4

This popular zoom lens has a focal range which is unique to the K series.

SMC Pentax 45-125mm F4
©, sharable with attribution
Image Format
Full-frame / 35mm film
Lens Mount
Pentax K
Aperture Ring
Yes (no A setting)
Automatic, 6 blades
14 elements, 11 groups
Mount Variant
Check camera compatibility
Max. Aperture
Min. Aperture
Min. Focus
150 cm
Max. Magnification
Filter Size
67 mm
Internal Focus
Field of View (Diag. / Horiz.)

APS-C: 36-13 ° / 30-11 °
Full frame: 51-20 ° / 44-16 °
Two variants:
1) in one part
2) in two parts separated by the (optional) filter
Dedicated hard case
Lens Cap
Plastic clip-on
Weather Sealing
Other Features
One-touch Zoom
Diam x Length
69 x 127 mm
612 g
Production Years
1975 to 1984
Engraved Name
SMC PENTAX1:4/45~125 (early version), smc PENTAX 1:4 45~125mm (later version)
Product Code
User reviews
Two variants were produced with different engraved names:
SMC PENTAX1:4/45~125 (early variant),
smc PENTAX 1:4 45~125mm (later variant).

The later variant was supplied with a close-up lens and had a close-focus scale engraved on the focusing ring.
Manual FocusAperture RingFull-Frame SupportDiscontinued
Price History:

Add Review of SMC Pentax 45-125mm F4
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Site Supporter

Registered: June, 2013
Location: Utrecht
Posts: 29
Lens Review Date: May 19, 2019 I can recommend this lens: Yes | Price: $75.00 | Rating: 10 

Pros: Sharp, even full open.
Cons: Some zoom creep.
Sharpness: 9    Aberrations: 9    Bokeh: 10    Handling: 9    Value: 10    Camera Used: K1-II   

This oldie goldie is a big surprise on my K1ii! I bought this lens many years ago and compared this now at 100% with my DFA 28-105 at 45mm, 70mm and 105mm at full frame. This lens shines as never before! There really is nothing in between this one and the DFA Kit Lens! Only at 45mm in the extreme edges in harsh conditions there is some purple fringing. My version is the 1977 one (3th/4), It is in excellent shape with very clean optics. Zooming goes fast and light (be aware for some zoom creep), focusing is nice and easy. Just focus at 120 mm and shift the zoom ring to wider view avoiding turning it. Very easy, fast and precise. At F4 there is some vignetting, but not by much. Top quality more then 40 years old now

Ca. 80 mm at F8

Ca. 120mm F4
New Member

Registered: April, 2017
Posts: 2
Lens Review Date: April 2, 2017 I can recommend this lens: Yes | Price: $30.00 | Rating: 9 

Pros: Sharp, nice Pentax color rendering
Cons: A bit heavy, f4 is a bit small
Sharpness: 10    Aberrations: 8    Bokeh: 7    Handling: 8    Value: 10    Camera Used: SONY A3000   

Just picked up this lens from an old lady. The package include a Pentax SF1 film camera, very solid build. A Pentax-F 50mm f1.7, A pentax smc 28mm f3.5 and this zoom lens.

It is really sharp at f4, which is not expected for a cheap zoom lens. Color is nice, overall, a very good lens for the money.

Some example photos:

Registered: September, 2010
Location: MD
Posts: 936

2 users found this helpful
Lens Review Date: May 28, 2016 I can recommend this lens: Yes | Price: $35.00 | Rating: 9 

Pros: Sharp, nice Pentax color/contrast; unique focal range
Cons: big; not fast; mfd is ~5' / 1.5m; unique focal range
Sharpness: 10    Aberrations: 9    Bokeh: 8    Handling: 7    Value: 9    Camera Used: K-30   

I have version 4 of this lens as identified by gofour3 below. To clarify a couple things:
  • The front filter is really 58mm (not 67mm as indicated in the data form above). One hood option was to use a 58 > 67mm step up ring, and that apparently was the preferred way to attach filters to avoid vignetting. (Personally, mine came with one of those rubber hood things, and that works well and can be adjusted for the zoom length.)
  • It is indicated that there was a close-up attachment available for this lens as there was for the 85-200. After some research, I came across this note from 2002 that indicates no such attachment ever was made. If someone does have one, let us know! UPDATE: gofour3 found one! See his updated post below w/ pics.
As for the lens itself, it's rather large and heavy compared to a modern zoom like the DA 18-135, but it has that wonderful feel of a well-built lens. I prefer the push-pull zoom as this has as compared to the two ring zoom/focus type. It works great on my K-30 with green button metering. For shake reduction, I just set the camera to 85mm.

I find the lens to be very sharp, and I'm not having much issue with aberrations. It's a bit long of a focal range on an APS-C, and I think it would be better suited on a full frame. The minimum focus distance of ~5 feet is also a bit of a limitation.

Overall, another fun old Pentax lens with Pentax quality.
Pics attached were probably taken closer to the 125mm end at f5.6.

Site Supporter

Registered: October, 2014
Posts: 116
Lens Review Date: January 27, 2016 I can recommend this lens: Yes | Price: $35.00 | Rating: 10 

Pros: solid- nuetral renditions- sharp constant F4 slide zoom
Cons: manual focus
Sharpness: 10    Aberrations: 9    Bokeh: 9    Handling: 9    Value: 10    Camera Used: K-3   

on my K-3 this lens does some wonderful things- if you know what you are doing-handheld low light ISO 200 400sec indoors pointed at a ikea lamp and the images are really close almost identical except for color rendition to my sig AF17-50 f2.8 shot at F4 which has warmer tones- the SMC 45-125 can be summed up as 'accurate' and the last pic i took the 45-125 handheld @ f8 ISO 100 125 sec indoors no flash actually beat the sigma which is known for Great IQ - i bought this lens used from a fellow pentaxian-Mahalo for such a choice piece of glass i am going to get more acquainted with this legacy lens and when the FF comes out this lens will work nicely-IQ IQ IQ with a steady hand and using the autofocus confirmation to get you in the ball park for static images makes lens is a great steal!
New Member

Registered: March, 2014
Posts: 2
Lens Review Date: March 11, 2014 I can recommend this lens: Yes | Price: $100.00 | Rating: 10 

Pros: Full open aperture at all focal lengths are terrific optical performance; Feel good zoom and focus; Sophisticated manufacturing process, solid materials; The push-pull zoom reverse design, real constant aperture
Cons: Relatively bulky and not easy to carry 45mm focal length is not wide enough
Sharpness: 9    Aberrations: 9    Bokeh: 8    Handling: 10    Value: 10    Camera Used: K100DS   

This is a very good value old lenses, It's very suitable for shooting portraits on APS format.
Junior Member

Registered: January, 2012
Posts: 36
Lens Review Date: December 15, 2012 I can recommend this lens: Yes | Price: N/A | Rating: 9 

Pros: Sturdy built, impressive at 135 even wide open and in low light
Cons: A bit weak at 45mm
Sharpness: 9    Aberrations: 7    Bokeh: 8    Handling: 8    Value: 10    Camera Used: Pentax K-x   

This is my most recent chunk of glass.

Sturdy built. I took some really sharp shots letting me read in 100% crops some printed text I could not even devise at naked eye at 135mm and wide open.

Easy to focus even on standard k-x screen!

Still to compare to other 135, but so far so good.

Forum Member

Registered: November, 2012
Posts: 64
Lens Review Date: November 27, 2012 I can recommend this lens: No | Price: $20.00 | Rating: 2 

Pros: Excellent built, nice handling, nice colors
Cons: Too soft, CA, barrel distortions, front focusing, heavy
Sharpness: 3    Aberrations: 3    Bokeh: 5    Handling: 8    Value: 2    Camera Used: K5   

I was excited when I bought this lens on ebay. It had a good reputation and felt very nice in my hands, built like a tank. But, I felt very deceived when I tried it on my K5 .

The first trial gave very soft pictures because I used view finder with confirmation signal. I put it on a tripod and used the live-view for focusing. The result looked good for small size 4" 6" pictures. Unfortunately, it is too soft for a 8" 12". It gets barely sharp enough in the center and it is very soft in the corners, improving to its insufficient best at f8.

It also shows an important amount of lateral chromatic aberration which can be corrected in post-processing, as well as purple fringes in out of focus area and around the bokeh spots.

There might be some sample variation, but there are so many nicer old and new Pentax lenses out there, waiting to help us get nice pictures. This is why I do not recommend it.

Registered: September, 2006
Location: Bamaga, QLD
Posts: 3,757
Lens Review Date: August 1, 2012 I can recommend this lens: Yes | Price: $90.00 | Rating: 9 

Pros: IQ - rendition colour and contrast
Cons: Heavy
Sharpness: 9    Aberrations: 9    Bokeh: 10    Handling: 9    Value: 10    Camera Used: K20D   

Have to agree with others above on many points.

Below is a comparison with DA50-200ED zoom at same focal length 125mm and f stop of 1/5.6. Bothe lenses were used with out hoods in mid morning sunshine.

I prefer the K mount as it is handling the sunny highlights better and the image has a cooler feel overall. The lens at this stage seems sharper in the focused area - near the end of the railing and seems to have a longer depth of field.

I look forward to using this lens more.
New Member

Registered: July, 2012
Location: Perth, Australia
Posts: 17
Lens Review Date: July 24, 2012 I can recommend this lens: Yes | Price: $70.00 | Rating: 7 

Pros: solid build, fairly sharp
Cons: old style lens movement
Sharpness: 7    Aberrations: 7    Bokeh: 8    Handling: 6    Value: 7    Camera Used: Pentax KX digital   

I bought this because it was going cheap on ebay. I wanted some old film lenses and one day if Pentax ever went FF, I have something to put on it straight away.

Unusual focal length and my copy has a slightly sticky zoom movement.

Reasonably sharp in the centre, which of course works extremely well on an APS-C sensor camera. I would rate it way sharper than the 18-55 kit and almost as good as the 55-300.

Nice solidly built lens reminiscent of the old film day, sturdy stuff.

Worthwhile purchase at a cheap price (which it normally sells for) because its an odd ball focal length.
Site Supporter

Registered: October, 2008
Location: Vancouver, Canada
Posts: 6,512

3 users found this helpful
Lens Review Date: August 14, 2011 I can recommend this lens: Yes | Price: $225.00 | Rating: 8 

Pros: One touch zoom, constant aperture, focal range on film, build.
Cons: Slow & two-part hood design.
Camera Used: K Series film bodies (K1000, KM, KX, K2, K2DMD)   

The K45-125/4 is one of the original three Pentax K series zooms released in mid 1975. (The others being the K85-210/4.5 and the K135-600/6.7.)

Four versions of this lens exist, all have the same optics the differences are just the lens mount and cosmetic. I have the 3rd version.

1) Super-Multi-Coated TAKUMAR-ZOOM 1:4/45~125 (No additional distance scale for close-up lens) 1975
2) SMC PENTAX ZOOM 1:4/45~125 (No additional distance scale for close-up lens) 1975-1976
3) SMC PENTAX ZOOM 1:4/45~125 (Additional distance scale for close-up lens) 1976-1977
4) smc PENTAX ZOOM 1:4 45~125mm (Additional distance scale for close-up lens) 1977-1984

Note: A close-up lens attachment was made available for this lens in 1976 and was an optional extra and not included with the lens. It reduced the minimum focusing distance from 1.5 to 0.9 meters.

Pretty sharp with a decent bokeh and minor distortion, all in all not bad for a zoom lens of this age. Pentax summed it up well in their 1975 SMC Lens Guide; By nature, zoom lenses give rise to slightly greater distortion (alterations in the shape or proportion of objects) than normal lenses. This distortion varies according to the focal length of the lens. The zoom lens is, therefore, not recommended for situations where proportional accuracy is crucial.

Focal length:
On film 45mm-125mm is quite a useful range and covers the standard/normal to short telephoto/portrait focal lengths. On APS-C its just a short telephoto/portrait lens.

Superb K Series build, with a decent size and weight. The K45-125 has a dedicated two part screw-on metal lens hood, with the first part being a 58mm 67mm step-up ring. I leave the step-up ring and a 67mm filter on the lens all the time and bought a 67mm lens cap to replace the original 58mm one. I just remove the cap and screw on the second part of the hood when Im ready to shoot. The zoom is a one touch design which I prefer over the two touch type zooms.

Better than some newer kit zooms but way slower than the primes the focal range covers. The K45-125/4 is best used for daylight scenic shooting; use your fast primes for indoor portraiture, action or low light shooting. This is a constant aperture zoom, which I like much better than the variable ones.

As a film only shooter Ill use this lens as a short telephoto for walking around town, I always will carry a standard prime to cover the 43-55mm focal range. A pretty decent performer for an old zoom, but due to its speed and optics the K45-125 will never replace the great K series primes in the focal range it covers.

Note: The high price I paid for this lens is due to it being basically new. It came in its original box with all packing. 100% mint condition.

October 2017 Update:
After years of searching I have located the allusive K45-125/4 close-up attachment lens. The attachment lens has a 58mm filter thread on the bottom to mount on the K45-125/4. The top of the attachment lens has a step-up filter thread of 67mm, so you can screw on the top part of the K45-125/4 lens hood.

Here is a picture of the K45-125/4 close-up attachment lens:

And one of the close-up attachment lens and hood mounted on my K45-125/4:

Note with the close-up attachment lens mounted, the K45-125/4 will only focus from 1.5 to 0.9 meters and there is no increase in magnification like when using a regular close-up "filter". It's cumbersome to use, but never the less it does reduce the K45-125's minimum focusing distance quite a bit.

Sample shots taken with the K45-125/4. Photos are medium resolution scans from original negatives.

Camera: KX Film: Fuji Superia 200 ISO: 200

Camera: KX Film: Ferrania P30 ISO: 80 (With Pentax 45-125/4 attachment lens)


Registered: September, 2010
Location: Somewhere in the Southern US
Posts: 12,244

1 user found this helpful
Lens Review Date: June 24, 2011 I can recommend this lens: Yes | Price: $90.00 | Rating: 9 

Pros: Smooth, Sharp, Well built, Constant f
Cons: front heavy
Sharpness: 9    Aberrations: 7    Bokeh: 8    Handling: 8    Value: 9   

I became fascinated with this lens while reading the 1981 SMC Pentax Lenses Catalog/Manual that I got with my 3 gift M lenses. It's used as an illustration in quite a number of places within the little book. Its quite an unusual lens in my opinion but its sort of like having a bag full of primes. I wanted a slide zoom lens when I was in HS but they were prohibitively expensive for me at that time so I never got to use one. When one came up for sale at eBay with a good price and a 100% rated seller of camera equipment I just had to get it (LBA?) .

Anyway, its in beautiful shape and is incredibly sharp across the focal range as far as I can tell at this point. I've taken some of the sharpest pictures with my K-x of any lens I own. The constant f across the zoom range is terrific and really makes using it in full manual mode easier.

As Dana G said in his review "The lens itself has 58mm threads, but the inner part of the hood (which is a step-up ring) screws onto these threads and the outer part, where the words "SMC Pentax Zoom 1:4 45-125mm" are inscribed, screws onto the 67mm threads of the inner part." The 1981 Pentax SMC Lenses catalog says "Note: There is slight vignetting if 58mm filters are used with the 45-125mm zoom lens when it is focused at 1.5m and set to the 60-70mm focal length" They recommend 67mm filters for that reason. So, Dana G was right. However, on the smaller sensors used in the K series dSLRs I don't believe this is a problem. But that is why the original hoods from Pentax had a step-up inner part to prevent problems with the hood or with filters.

I agree with Freewheeler - this is a stunningly sharp lens which brings some real beauty to photos. On top of all that, its the easiest of my manual focus lenses to actually focus
Senior Member

Registered: October, 2009
Location: amsterdam
Posts: 130
Lens Review Date: May 1, 2010 I can recommend this lens: Yes | Price: $70.00 | Rating: 9 

Pros: sharp and contrasty
Cons: bulky

Bought this lens because I like comparing m- and K-lenses against modern ones.
It's a quite rare lens with a good reputation. When I had the opportunity to buy one for only euro 50 I did.
After seeing the results of this lens my DA50-200 had to leave instandly.
This time I even did not side to side comparisons in terms of sharpness or contrast. Maybe its about micro contrast, I don't know but I do know that not all qualities of a lens are measurable, at least not for me.
Just a stunning oldy that gives you technically speaking good results but also adds some pixi dust that until now I never experienced in zooms
Senior Member

Registered: January, 2009
Location: University of Waterloo, ON
Posts: 239
Lens Review Date: March 16, 2009 I can recommend this lens: Yes | Price: N/A | Rating: 8 

Pros: sharp, one-touch zoom/focus, constant aperture, all-metal construction
Cons: heavy, zoom-creep, front element rotation

I have the model with the close-focus scale but, alas, I haven't the close-focus filter so I can't attest for that feature. My copy survived a flood and many years of storage in its leather case thereafter and, despite having acquired what appear to be oil spots on the next-to-front element, still outperforms my DA 50-200 in terms of contrast and sharpness. The one-touch design and constant aperture are nice touches, keeping set-up time down.

The only real disadvantages I can think of are the weight (though I don't mind it) and the slight amount of zoom creep (worse pointed down than up), but seeing as it's MF, your hand should be on the barrel anyways. Oh, the front element rotates when focusing too. As mentioned before, there is noticeable distortion at either end, but I wouldn't worry about this for typical use.

Overall, I'm certainly not disappointed to have this lens in my kit and I imagine most people wouldn't mind it either.
Senior Member

Registered: October, 2006
Location: Masachusetts
Posts: 245
Lens Review Date: March 1, 2007 I can recommend this lens: Yes | Price: N/A | Rating: 8 

Pros: Good, simple sharp lens. Constant aperture
Cons: Strange two-peice lens hood.

I got one of these lenses to go with my *st D, since it replaces my 70-200 zoom that I used on the film cameras.

It may be old, but it seems to be sharp and contrasty (I haven't done any formal testing).

The lens hood for this lens requires a step-up ring, thus you have a choice of two filter sizes to use for the lens.

The lens itself has 58mm threads, but the inner part of the hood (which is a step-up ring) screws onto these threads and the outer part, where the words "SMC Pentax Zoom 1:4 45-125mm" are inscribed, screws onto the 67mm threads of the inner part. I suppose that the idea was to prevent vignetting, but unless I'm using it on the MX, the reduced sensor size of the digitals makes the point moot.

It's light, my copy has a fairly firm zoom push-pull action, and it works just fine in Manual mode.
Site Supporter

Registered: September, 2006
Location: Pennsylvania
Posts: 1,432

1 user found this helpful
Lens Review Date: February 12, 2007 I can recommend this lens: Yes | Price: N/A | Rating: 8 

Pros: Optics are outstanding, Extremely sharp lens. Good zoom range for film.
Cons: While my version does not drift, some of these lenses might .

This report is on the SMCP K mount version of this lens and not the screwmount.

This lens languished nearly forgotten in my studio for nearly 20 years. What a mistake! I had always favored the SMC A 70-210/4 Macro as my zoom of choice for film. It was sharp, had great bokeh and a fantastic range. Unfortunately, I found it DOA one morning while going on an assignment and decided to see what might fill the bill. Tucked away I found the SMC K 45~125/4. It is quite an unassuming looking lens as zooms go.

I mounted it to a Pentax DL last summer and was really astonished at the color rendition and the ability to handle contra light without any abuse from CA or PF. The contrast is outstanding, and flare is well controlled. I found sharpness to be within acceptable margins across the digital image and even at the longer end the image did not suffer from a loss of contrast or saturation.

The lens is pretty rare and worth getting if you can use a lens = to roughly 70~190 on the small sensor and can't afford something more. You need to work it manually but the reults should be worth th effort. It functions quite well wide open and only gets better as you add a stop or two.

Overall I would really give this lens a rating of about 8.5 or more but you can't do that so I had to come down a little bit on the above scale.

Looks and zoom style 7 (it takes high end images but is technologically outdated by contmporary technology
Build 9
Contrast 9
Color rendition 10
Sharpness 8.5 +
Image quality 8.5-9
Bokeh 9

Very nice lens,
Add Review of SMC Pentax 45-125mm F4

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