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SMC Pentax 100mm F4 Bellows Review RSS Feed

SMC Pentax 100mm F4 Bellows

Reviews Views Date of last review
4 36,312 Thu January 14, 2021
Recommended By Average Price Average User Rating
75% of reviewers $103.75 7.00
SMC Pentax 100mm F4 Bellows

SMC Pentax 100mm F4 Bellows
SMC Pentax 100mm F4 Bellows

This lens has no focusing ring and is intended for use on a Pentax bellows unit.

SMC Pentax 100mm F4 Bellows
©, sharable with attribution
Image Format
Full-frame / 35mm film
Lens Mount
Pentax K
Aperture Ring
Yes (no A setting)
Manual, 6 blades
5 elements, 3 groups
Mount Variant
Check camera compatibility
Max. Aperture
Min. Aperture
Min. Focus
Max. Magnification
Filter Size
52 mm
Internal Focus
Field of View (Diag. / Horiz.)

APS-C: 16 ° / 14 °
Full frame: 24 ° / 20 °
Not needed
Dedicated hard case
Lens Cap
Plastic clip-on
Weather Sealing
Other Features
Diam x Length
60 x 40 mm
185 g
Production Years
1975 to 1998
Engraved Name
SMC PENTAX BELLOWS 1:4/100 (early version), smc PENTAX BELLOWS 1:4 100mm (later version)
Product Code
28240 (early), 28250 (late)
User reviews
No focusing mechanism

Two variants were produced, only differing in the engraved name:
SMC PENTAX BELLOWS 1:4/100 (early variant),
smc PENTAX BELLOWS 1:4 100mm (later variant)

Manual FocusAperture RingFull-Frame SupportDiscontinued
Price History:

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Sort Reviews by: Date | Author | Rating | Recommendation | Likes (Descending) Showing Reviews 1-4 of 4

Registered: April, 2015
Location: USA
Posts: 2,870
Review Date: January 14, 2021 Not Recommended | Price: $75.00 | Rating: 1 

Pros: Well made
Cons: Lens element separation makes it unusable
Camera Used: K10D   

I just purchased a copy of this lens. On the outside it looked new. However, mine has terminal lens separation of the two front elements!

The lens separation looked sort of like haze with some tiny particles in it. But when I took the lens apart and cleaned each element, it because obvious that this "haze" was located between the two cemented front elements. This type of separation is nearly impossible to correct yourself, and I know of no lens repairers who would fix this at an affordable cost. Therefore, my copy of this lens is a functional total loss. I never had the chance to use it as I trashed the lenses after identifying the separation.
Veteran Member

Registered: September, 2017
Location: MedellŪn
Posts: 1,322

2 users found this helpful
Review Date: December 23, 2019 Recommended | Price: $120.00 | Rating: 9 

Pros: Wide open focusing with the Auto Bellows and/or extension tubes.
Cons: Most copies have separation.
Sharpness: 10    Aberrations: 8    Bokeh: 9    Handling: 10    Value: 10    Camera Used: Film cameras, K-5   

It's a nice lens for tabletop photography. Funny thing is, it focuses to infinity on the Auto Bellows. Works just as intended on it. Got everything as a kit from a forum member. I first used it with the original Asahi Pentax double cable release and a Canon T3 threaded cable release adapter and later with a modified Nikon AR-10.
Sadly, all copies I've ever seen suffer from a bit of separation on the edges, but that really doesn't seem to affect it since one rarely shoots wider than f/8 or wide open at infinity. That's not what this lens is for anyway, although there's still the option. I would rather take the 50 mm or 100 mm plus other auto tubes combined to use in the field. Less weight and still wide open focusing. Clip on hood works well. Fits all in the small case.
New Member

Registered: November, 2013
Posts: 14

1 user found this helpful
Review Date: November 11, 2018 Recommended | Price: $100.00 | Rating: 10 

Pros: an excellent cose ups lens
Cons: some very few CA's
Sharpness: 10    Aberrations: 9    Bokeh: 10    Handling: 9    Value: 10    Camera Used: k--5,k-s1, k-x, k200d fuji x-t100+x-e1   

Important tip: Without an additional bellows extension you'll get never sharp images, shan't you ?

a very good performer:

++ very good sharpness (80 LP/mm)

++ high contrast

++ no distorsion (=%)

+/++ very small CAs (sometimes especially in bokeh visble)

for macro shootings you can improve sharpness by using a self made focal reductor of an achromatic top lens element of a binocular 8x30, integrated into an extensions tube 12mm, so you'll get a 2.8/70 or 3.5/85 mm macro lens with extreme sharpness on bellows

for photos taken in this way excellent results !!! approx. 90 LP/mm - a professional value !

Highly recommended !
Site Supporter

Registered: October, 2008
Location: Vancouver, Canada
Posts: 8,068

3 users found this helpful
Review Date: January 18, 2009 Recommended | Price: $120.00 | Rating: 8 

Pros: Size, quality and 100mm focal length.
Cons: Slow f4.0, limited usage as itís dependant on a bellows unit.
Camera Used: K Series film bodies (K1000, KM, KX, K2, K2DMD)   

The K100/4 Bellows definitely falls into the specialty lens category. Itís basically unusable without a bellows unit, as the lens has no focusing ring to control magnification. The K100/4 Bellows has an automatic diaphragm which will be retained when used with the ďautoĒ bellows unit, or it can also be used on the ďregularĒ bellows unit as a manual diaphragm lens. For me this limits the K100/4 Bellows to indoor macro use only. For outdoor use Iíll take my rail kit, extension tubes and regular macro lenses, which are far more durable than a bellows unit.

However, if you donít have a Bellow Unit or donít want to use one outdoors, you could use the K100/4 Bellows lens with Extension Tubes and these two options for focusing:

1) Use a macro focus rail to focus the K100/4 Bellows and use Pentax Auto Extension tubes for magnification. This option will preserve the lenses automatic diaphragm and would require a tripod for the focus rail.

2) Use the Pentax Helicoid (variable) Extension Tube to focus the K100/4 Bellows on its own or add more Pentax Extension (Auto or manual) tubes for higher magnification. As the Helicoid tube does not maintain the full aperture metering mechanism of the K100/4 Bellows lens, you will have to use stop-down metering. This is a good handheld option, as the K100/4 Bellows does not weigh very much and neither do these extension tubes. I tried this option and it worked pretty well, though the Helicoid tube on its own does not give you very much magnification. (About the same as using a Pentax Close-up filter attachment on a regular 100mm lens.)

The K100/4 Bellows is rather slow at f4.0, so you get a darker viewfinder especially if used indoors. I compensate the slow maximum aperture by using two 500-watt portable studio lights when Iím doing indoor macro shooting.

The 100mm focal length gives you a longer distance to subject ratio than the 50mm macro; this is nice when using the bellows unit on a tripod. For extreme magnification in macro photography, the 100mm focal length does not benefit when the lens is reversed. You are better off reversing the 50mm macro or the K28mm f3.5, for magnification greater than 1.0. The K 28mm f3.5 is still the best Pentax lens for this purpose.

Even though the lens element is recessed, you should use the dedicated plastic round clip-on lens hood. This hood is shared with the K85/1.8, K100/4 Macro & the K105/2.8 lenses. (52mm filter diameter)

All in all itís a valuable tool if you are into macro photography and have other macro lenses to compensate for some of its weaknesses.

Sample shots taken with the K100/4.0 Bellows. Photos are medium resolution scans from original negatives.

Camera: K2 Film: Kodak Portra 400VC ISO: 400
With PENTAX Bellows Unit K

Camera: K2 Film: Kodak Portra 400VC ISO: 400
With PENTAX Bellows Unit K

Camera: KX Film: Kodak Pro Image 100 ISO: 100
With PENTAX Helicoid Extension Tube K
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