As a broad generality, all lenses will fit all bodies. But early bodies will not have focus, parallax, and exposure compensation scales for the focal lengths introduced later. The original 1/400th Seikosha-MX shuttered lenses and some Seikosha-S shuttered 180mm lenses will not fit C33 and later auto-cocking bodies. The problem with the MX series is that the lens cocking arm is located higher than on the later lenses, and the auto-cocking lever will not engage. It also fouls the lens lever for manual cocking..
Some lenses are known to fail to cock properly on later bodies. This appears to be due to the auto-cocking lever not moving the lens cocking lever quite far enough. At least one case has been recorded of the body cocking arm needing more travel than the lens shutter arm permits.
Lenses of different focal length have different back focus distances. In practice this means that the bellows extension required for infinity focus is different. This is common with bellows focusing systems, and does have the benefit of giving the optical designer more freedom.
The lens hood diameter refers to the square clamp-fit Mamiya hoods. They will only fit over slimline filters. Conventional screw-fit hoods of suitable dimensions may be used in the filter thread. The Mamiya hoods are of two basic designs. The first design, used for the 55mm, 65mm, 180mm, and 250mm were square with the upper flap hinged at the front. This permitted the angle of the top flap to be set so that glare from the top of the hood was invisible in the finder. The hoods for the 80mm, 105mm, and 135mm lenses were of a circular changing to square aperture rigid type. The 80mm and 105mm chrome lenses used 42mm hoods, the 80mm and 105mm black, and both 135mm lenses used the 48mm hood. All the 180mm and the 250mm lenses used the same hood. These hoods are generally metal. There is also a telephoto lens hood for the chrome series that consists of two rigid square shades in a single plastic unit. (Compiler’s Note: This item is huge!)
There was a change in physical and optical design between the chrome and black series lenses. One known effect is that the 105mm D and DS lenses have a different back focus from the 105mm chrome and the early 105mm black. This means that the scale on the C330 and earlier bodies is incorrect for the later lenses. The C330s (and probably most C330f) have scales for both 105mm lenses. It should also be noted that earlier bodies do not have scales for the focal lengths introduced later. The lenses will function, however. The 180mm (black) and 180mm Super (black) are different optical designs, but appear to share the same back focus.
This is a contentious issue, probably stemming from a lack of understanding of lens coating in general. Lens coating has been common since the Second World War, initially as general single coating, then as single coating tailored to individual lens performance, and most recently coating of internal elements and multiple coating for optimum corrections. Coating is used to reduce reflection from the surface that contributes to flare and lack of contrast. It also helps compensate for minor variations in glass batches, and in multi-coating the performance over a range of wavelengths is made more consistent.
The chrome lenses were single coated, and the black series had single coatings which may have extended to various lens elements. Some late black series lenses have had multi-coating, but there is a lack of substantive evidence as to when it was introduced, and on which lenses. The 55mm, 80mm S, 105mm DS, and 180mm Super are the most likely candidates, as these were later or more extreme designs.
Even the best of these lenses won’t have the class of coatings that appeared in the 1990’s.
The original chrome lenses were fitted with shutters having a maximum speed of 1/400 second (Seikosha-MX). Later chrome lenses were improved to a 1/500 second top speed, giving a conventional range from 1 second to 1/500, plus B (Seikosha-S). The changeover seems to have occurred during the production life of the C2. The final black series lenses used a Seiko shutter with 1 second to 1/500th second plus B settings. Some shutters exhibit a leaf with a raised tip. This ‘anti-crash’ feature is intended to reduce the chance of the shutter blades locking when closing. It usually indicates a newer shutter, often with a blue insert in the shutter cocking arm. The 80mm f3.7 black lens had a Copal shutter. At least one Seikosha-MX shuttered 80mm lens was labelled ‘f=8cm’.
The lenses all have integral leaf shutters, providing X and M synchronisation at all speeds. Connection is via a standard 3mm co-axial PC cord on each lens. Lenses which have been in professional hands sometimes have the flash synchronisation levers fixed in the ‘X’ setting. This is usually achieved by cementing a small stop to the lens barrel. Obviously the inadvertent shift to ‘M’ with electronic flash had happened once too often! There is around 200 milliseconds delay between releasing the shutter (and closing the flash contacts) and the shutter opening on the ‘M’ setting. This delay was to allow flash bulbs time to reach full illumination. Since the delay is a mechanical process, and the M setting is rarely used, longer delays are quite common and the shutter may stick.
The PC connection on most lenses consists of a hollow stud. The centre hole is one side of the flash contact, and connects to a wire running to the shutter assembly. The outer portion of the stud is the other contact, and connects to the lens mounting through its mounting screws. Intermittent flash problems may be caused by the mounting or wire becoming loose. This can be tested using a resistance (Ohm) meter. (A resistance meter applies a negligible current and voltage across its probes. Higher voltages or currents may result in damage.) Set the lens to a slow speed (say 1 second), and cock it. Insert the PC cord, and hold the resistance meter probes to the terminals at the other end of the cord. When the shutter is fired, the meter will register if the flash circuit is made. A slow speed is necessary to be sure the meter has time to react.
Some later lenses, such as the 105mm DS, have a shrouded PC socket that appears less vulnerable to accidental damage or loosening.
At the risk of stating the obvious, these shutters work in fixed steps. Intermediate speeds should not be set. Intermediate apertures can be set.
The most frequent sign of damage with lenses is a dented filter ring. The lens locking wire can scratch the top of the viewing lens barrel.
Weights, where quoted, may include front and rear caps.
Mamiya claim not to have any dating information based on serial numbers.
It has been suggested that lenses can be dated (for black models at least) by the gold two-letter stickers that sometimes survive. These are not the ‘JCxxx’ series stickers that are found on all new Japanese exported equipment. The two-letter stickers do not appear to have been used on chrome series lenses. New information suggests that letter code series apply to individual items. So code ‘AA’ would mean a different year/month on a C330 and a C220, for example. Since this equipment isn’t new, the amount of wear and tear is probably more important than chronological age so far as practical use is concerned. For the curious:
Example two-letter codes carried by black series lenses, cameras, and accessories
| Item | Codes | Body / lens serial prefixes | Production (see note) |
| C330s | KH | None, or ‘l’, W | |
| C330f | BC, GC, GJ, ID, EK, FA | D, none | FA=0107xxx BC=D150xxx D140xxx |
| C220f | BD, BE, CD | W | |
| C330 | AA, AG, BG, BJ, CC, JK, JB (1982) (sticker inside film chamber), IL, IK | D | JB=Late? 1974/5 serials=D457xx & D267xx , BJ D635xx, AG=?47xxx, CC=0718xx,70’s |
| C220 | HK, DG, DI, HF, IB | B | HF=B964xx IB=B222xx |
| C33 | EI, EK, FA, FC, GC, GF, GJ | H (some with R suffix) | FA seen in body purchased c. May 1966 FC=261xxx |
| C22 (220 capable) | DI, DK | S 2036xx, or none | Probably 1966 or later |
| Pentaprism | BL, DI, IJ, CL | ||
| CdS Magnifying Hood | AH, AE | ||
| CdS Porrofinder | GC | ||
| 55mm | AA (round), AG, AI, AK, FH, DC, DH, DL, IK, JA, CA, CF, CH, CI, CL, CK, ED, EG, HB, GE, HC, EK, FD, JE, JF, JK (round) | 501xx, 519xx | FH=Late, CF=1985, AA=439xx, AK=1974/5? serials 501xx & 519xx, CI=non-blue (early 80’s) DH=non-blue 735xx, JA=355xx, CA=non-blue,103xxx CK=66xxx, JK=422xx,425xx JE=377xx,378xx, no insert, no click stops, CH=634xx,631xx FD=803xx,805xx |
| 65mm | AI, BG, BI, CA, CF, CK, EA, EC, JG, HC, HI, ?K, DJ, FF | 57892xx | BG=57892xx , FF=not blue, has click-stops, AI=5789xxx |
| 80mm | AC, AD, AI, BC, BD, BF, BJ, BK, JL, EB, EL, FD, HA, HI, ID, IE, IG, JE, FC, DB, DC, DI, CB, CE, CH, CI, CF, IF, II, GI | 7524xx, 6605xx 6613xx | AC=943000,late BC=105xx, BD=121xx, BF=Middle, AI=Late, JL Unexamined, AD=1969, EL=Late, CE=7524xx, 80mm 1974/5? serials=6605xx & 6613xx, HI (9200xx), CB=blue insert, CI=blue insert, JE=662xxx,663xxx, DB=778xxx,779xxx, BJ=733xxx, CB=7465xx,7445xx FD=827xxx,806xxx, GI=862xxx IG=639xxx,638xxx |
| 80mm ‘S’ | BE, BF, BH, CH, DA, HI, IA (on C220f), IB | Unexamined | |
| 105mm | DA | Unexamined | |
| 105mm D | CD,CG, BF, CI, IK | CD=plain insert,Late | |
| 105mm DS | AE, CJ, EC, JF, JK | AE=Late | |
| 135mm | AL, FC, FF, IJ , CD, CH, CI, BG, IG, JA, JE, DA, ED, EF, EH, HG, JJ, JL (round), BI (or J) round | 6253xx | FF= Late, IJ=1982, Late?, BG=1972, AL=1974/5? Serials 6253xx, FC=blue insert, ED 6476xx, EF=Blue insert, IG=661xxx, CD=blue insert, CI=6365xx,6364xx,blue insert, HG=6595xx,6599xx,blue, 46xxx |
| 180mm | IJ | IJ=112xxx | |
| 180mm Super | AF, AG, AJ, AL, IA, BF, IB, CB, CG, JJ, EA, EF, FC, CI, GD, HB,HH, DE, DK | 267xx | IA=Late, DK – no blue insert on shutter cocking lever, AG=267xx, CG=no blue insert, AJ=299xx, HH=655xx, AL=305xx296xx, HB=620xx, DE=511xx EA=53xxx |
| 250mm | CG, CI, DH, HC, HE, IF, JF | CG=Middle, CI=46xxx, DH, JF and HC Unexamined, HE no blue shutter insert, IF=218xx & 213xx |
The Chrome series lenses do not appear to have carried two letter codes.
The BG C330 and the BF 80mm are believed to be the pairing as originally sold.
The FA in the C33 is known to be no later than May 1966.
The DI C22 is 1966 or later.
Using the barrel focal length marking and aperture click stop as a guide (see section 4) gives the ‘Early’, ‘Middle’ (1970’s), and ‘Late’ (1980’s) production groupings for the black lenses.
The current known ranges are: First letter A – L, Second letter A – L.
For comparison: An early Mamiya 6 rangefinder has a body tag of ‘II’.
Tabulation of example serial numbers
| Item | Serial |
| 135mm | 6253xx |
| 135mm | 6364xx |
| 135mm | 6365xx |
| 135mm | 6476xx |
| 135mm | 6595xx |
| 135mm | 6599xx |
| 135mm | 661xxx |
| 180mm | 112xxx |
| 180mm Super | 267xx |
| 180mm Super | 296xx |
| 180mm Super | 299xx |
180mm Super 180mm Super |
305xx 46xxx |
| 180mm Super | 511xx |
| 180mm Super | 532xx |
| 180mm Super | 535xx |
| 180mm Super | 564xx |
| 180mm Super | 620xx |
180mm Super 105mm D |
655xx 241xx |
| 250mm | 213xx |
| 250mm | 218xx |
| 55mm | 103xx |
| 55mm | 355xx |
| 55mm | 377xx |
| 55mm | 378xx |
| 55mm | 422xx |
| 55mm | 425xx |
| 55mm | 439xx |
| 55mm | 501xx |
| 55mm | 519xx |
| 55mm | 631xx |
| 55mm | 634xx |
| 55mm | 66xxx |
| 55mm | 735xx |
| 55mm | 803xx |
| 55mm | 805xx |
| 65mm | 57892xx |
| 65mm | 5789xxx |
| 80mm | 105xx |
80mm 80mm (MX) |
121xx 1973xx |
| 80mm | 6605xx |
| 80mm | 6613xx |
| 80mm | 662xxx |
80mm 80mm 80mm |
663xxx 638xxx 639xxx |
| 80mm | 733xxx |
| 80mm | 7445xx |
| 80mm | 7465xx |
| 80mm | 7524xx |
| 80mm | 778xxx |
| 80mm | 779xxx |
| 80mm | 806xxx |
80mm 80mm |
827xxx 862xxx |
| 80mm | 9200xx |
| 80mm | 943xxx |
| 80mm | 949xxx |
| 80mm | 950xxx |
| Mamiyaflex C | 590xx |
| C22 | S2036xx |
| C33 | 261xxx |
| C220 | B964xx B222xx |
| C330 | D267xx |
| C330 | D457xx |
| C330 | D47xxx |
| C330 | D635xx |
| C330 | D718xx |
| C330f | D140xxx |
| C330f | D150xxx |
| C330s | W1124xx |
Although there are some exceptions, which may be due to inaccurate or sparse data, it appears that serial number sequences were issued by item type. It is reasonable to expect that numbers were issued sequentially within a block, though there is no evidence to support this supposition. There are 5, 6, and 7 digit numbers, as well as letter prefixes for bodies. Since the letter prefix used on the C33 was ‘H’, even those are not in chronological sequence.
Tabulation of known letter codes and equipment (all lenses cited are black series)
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| AA | * | ||
| AC | |||
| AD | |||
| AE | |||
| AF | |||
| AG | * | ||
| AH | |||
| AI | |||
| AJ | |||
| AK | |||
| AL |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| BA | |||
| BB | |||
| BC | * | ||
| BD | |||
| BE | |||
| BF | |||
| BG | * | ||
| BH | * | ||
| BI | |||
| BJ | * | ||
| BK | |||
| BL |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| CA | |||
| CB | |||
| CC | * | ||
| CD | |||
| CE | |||
| CF | |||
| CG | |||
| CH | |||
| CI | |||
| CJ | |||
| CK | |||
| CL |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| DA | |||
| DB | |||
| DC | |||
| DD | |||
| DE | |||
| DF | |||
| DG | |||
| DH | |||
| DI | |||
| DJ | |||
| DK | |||
| DL |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| EA | |||
| EB | |||
| EC | |||
| ED | |||
| EE | |||
| EF | |||
| EG | |||
| EH | |||
| EI | |||
| EK | * | ||
| EL |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| FA | * | ||
| FC | |||
| FD | |||
| FF | |||
| FH |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| GC | * | ||
| GD | |||
| GE | |||
| GF | |||
| GI | |||
| GJ | * |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| HA | |||
| HB | |||
| HC | |||
| HE | |||
| HF | * | ||
| HG | |||
| HH | |||
| HI | |||
| HK |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| IA | |||
| IB | |||
| ID | * | ||
| IE | |||
| IF | |||
| IG | |||
| IH | |||
| II | |||
| IJ | |||
| IK | * | ||
| IL | * |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| JA | |||
| JB | * | ||
| JC | |||
| JD | |||
| JE | |||
| JF | |||
| JG | |||
| JH | |||
| JI | |||
| JJ | |||
| JK | * | ||
| JL |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| KH | * |
| Bodies | Finders | Black series lenses | |
| Code | C330s | C330f | C330 |
| LD |
Utter speculation (!)
So far I have yet to hear of a letter pair with the second letter greater / later than ‘L’. So this could be a month indicator. That would suggest that the first letter is a year indicator. Given the known chronology (C33 to C330 to C330f, for example) it is obvious that the first letter cannot be a year code, unless it represents the year from start of manufacture of that item. But that implies, just from the codes cited, there is a two year overlap between the C33 and the C330, and a three year overlap between the C330 and the C330f. I find this hard to believe. Then we have the KH for a C330s body and LD for an 80mm ‘S’ lens. This makes some sense, as they are late items. But there are a couple of 80 ‘S’ lenses in the Bx group, implying that these were manufactured for 12 years.
Then we have the letter prefix on the body serial number. This cannot be a year designation, since I know of a C33 with an ‘H’ prefix, several C220s with ‘B’ prefixes, and a C330 with a ‘D’ prefix, and C220fs with ‘W’ prefix. It may indicate production groups (not years, since the C33 was not produced concurrently with the C330 to my knowledge).
This leads me to further speculate that production wasn’t annual, but batched. In which case we lose any direct correlation with age. We also have the problem that any lenses that were re-shuttered during repair could have the late click-stop type installed, thus invalidating that as a guide to the age of the code.
At the moment we have insufficient data to draw any firm conclusions. More letter codes would be useful, especially if the original purchase year is known.
Interpretation
Some new information has come to light from a service manual for the C33. It appears that the letters are year/month pairs, but for the bodies at least these start counting from the year of development or sale. Prior to public sale there may have been more than one development iteration in a year. So an ‘Ax’ tag on a C33 would be unusual, though not impossible. Since these cameras are rarely in the hands of original owners it is very difficult to get accurate purchase date information. And the date of purchase could be significantly later than the date of manufacture.
Mapping of letter codes to production years. This is very preliminary data, and is subject to revision
First-letter year codes from C33 repair manual data. Italicized values are inferred pre-production codes; bold values are known examples. It is very likely that the less popular items were not in continuous production. ‘?’ indicates known examples but uncertain dates.
| Camera | Initial Year | A | B | C | D | E | F | G | H | I | J | K | L |
| C33 | Pre-production period | Pre-production period | Pre-production period | Pre-production period | 1965 | 1966 | 1967 | End of production? | |||||
| C22 | 1965 | 1966 | 1967 | 1968 | |||||||||
| C330 | 1968 | 1969 | 1970 | 1971 | 1972 | 1973 | 1974 End of production? | 1975 | 1976 | 1977 | |||
| C220 | 1968 | 1969 | 1970 | 1971 | 1972 | 1973 | 1974 | 1975 | 1976 | 1977 | 1978 | 1979 | |
| C330f | 1972 | 1973 | 1974 | 1975 | 1976 | 1977 | 1978 | 1979 | 1980 | 1981 | 1982 | ||
| C220f | 1982 | 1983 | 1984 | 1985 | 1986 | 1987 | 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | |
| C330s | 1983 | 1984 | 1985 | 1986 | 1987 | 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | 1994 | |
| 55mm | 1967 | 1968 | 1969 | 1970 | 1971 | 1972 | 1973 | 1974 | 1975 | 1976 | 1977 | 1978 | |
| 65mm | 1967 | 1968 | 1969 | 1970 | 1971 | 1972 | 1973 | 1974 | 1975 | 1976 | |||
| 80mm | 1968 | 1969 | 1970 | 1971 | 1972 | 1973 | 1974 | 1975 | 1976 | 1977 | |||
| 80mm S | |||||||||||||
| 105mm | |||||||||||||
| 105mm D | ? | ||||||||||||
| 105mm DS | ? | ? | ? | ? | |||||||||
| 135mm | 1970? | ? | ? | ||||||||||
| 180mm | |||||||||||||
| 180mm Super | ? | ? | ? | ? | ? | ? | ? | ? | ? | ||||
| 250mm | 1967 | 1968 | 1969 | 1970 | 1971 | 1972 | 1973 | 1974 | 1975 | 1976 | 1977 | 1978 |
Table of 35mm format equivalent focal lengths for the lenses in the TLR range (after Scott, with permission)
| 6x6 cm | Largest Square | Largest 5x4 (10x8) | Largest 11x14 | Largest 2x3 (35mm) |
| 55 | 24 | 30 | 30 | 36 |
| 65 | 28 | 35 | 36 | 42 |
| 80 | 35 | 43 | 44 | 52 |
| 105 | 45 | 57 | 58 | 68 |
| 135 | 58 | 73 | 74 | 88 |
| 180 | 78 | 97 | 99 | 117 |
| 250 | 108 | 135 | 138 | 163 |
The focal lengths in the body of the table are the 35mm lenses required to produce an identical image in a given final format with minimum cropping. In other words, to get a square print covering the same area as the 55mm Mamiya lens you would need a 24mm on 35mm format, while cropping a 2x3 area from the Mamiya negative would give the same rendition as a 36mm lens on 35mm format. This table is derived from original work by Ed Scott for ‘photo.net’ ( http://photo.net/). Please see this link for a more general table and an explanation of the method used to derive these values.
Standard screw fit filters may be used, but the 49mm threaded lenses are very close together, which may make it impossible to fit filters on both lenses. Mamiya made special slim-mount filters for this purpose, but they do not seem to be readily available short of special order. The local Mamiya distributor may be able to help. Standard filters may also cause problems with the Mamiya clamp-fit lens hoods.
It is possible to file a flat on a UV or haze filter to improve clearance if it is going to be a permanent fitting on the viewing lens. Obviously the filter mount should be marked and then de-mounted from the lens before filing it!
An alternative for the viewing lens is to use one of the chrome protective rings to retain a bare UV or skylight filter directly on the lens. This requires dismantling a standard filter unless you can obtain an unmounted glass.
Some users have found that filters can be mounted inside the larger square Mamiya lens hoods. This is done by cementing an old filter mount to the inside (usually after the original mounting thread has been filed flat and the old glass removed) and using it as a threaded mount. Since old or scratched filters can be utilised for the mount this is an economic approach. In use the filter of choice is screwed to the new mount inside the hood. Obviously the maximum filter size that can be used in this manner depends on the hood size and the slimness of one’s fingers!
Most of the same restrictions about fitting plain filters applies to polarising filters. Perhaps more so, since these tend to have physically larger mounts. The common method is to preview the effect by eye, or on the viewing lens, and note the position of the mount (You need a mount marked in increments to do this - you can add your own). The filter is then installed on the taking lens and set to the same orientation.
In theory, you could mount two identical polarisers in common alignment and wrap an elastic band around the rotating rims. Rotating one would move the other in synchonisation. But the physical proximity of the lenses means you’d have to use 46mm polarisers. And a circular lens hood!
Linear polarisers are perfectly adequate for these cameras. The circular versions are intended for cameras with through the lens metering which use an optical system that is itself polarising.
It is difficult to preview the effect on the viewing lens and then transfer it to the taking lens, but possible. Unless you are using a 105mm D/DS lens you cannot preview the effect of stopping down. There was a sliding mount designed for the Cokin ‘P’ series, but this does not appear to be still available. See section 9.2 for the reference.
None of the Mamiya TLR cameras have self-timers on the body. Only the 105mm DS lens has a ‘V’ setting for delayed release. The only other options are to use an air release, or to try and track down a cable release mount accessory timer (usually clockwork).
These cameras do not include infra-red focusing scales. Just how crucial this is will depend on your application. Infra-red film varies in it’s degree of sensitivity. Certainly Konica 750 and Ilford SFX have a closer sensitivity to visible light than Kodak’s (35mm) offering. False colour infra-red film has to include some visible light, otherwise you do not get a full range of colours.
The focus scales are comparatively crude, so a precise adjustment is not practical, or at least hardly repeatable. Unless working at close distances or at wide apertures the correction can probably be ignored. Should highly infra-red sensitive emulsions become available (see below), then experimentation with each lens would be advisable.
The cameras are probably infra-red safe with current emulsions. The biggest risk would come from an extended bellows, so it might be wise to retract the bellows (or close the internal baffle) when not actively photographing.
The new MACO 820c infra-red emulsion falls between the Kodak HIE and Konica 750 offerings. This is a true infra-red film (development should be in a metal or foil-shielded tank, for example), and should be treated with caution. The recommended focus adjustment is an increased extension of 1/100th of the focal length of the lens, or about 0.5mm for the 55mm, and 2.5mm for the 250mm lenses. This sort of correction is actually easier to implement on the rack and pinion bellows focusing of the Mamiyas than on helical mount lenses.
Compiler’s Note: If any reader has practical experience of infra-red with these cameras, I’d be pleased to include it here.
There are reports of lenses that do not provide sharp images on the film, even though carefully focused. This may mean that the lens pair is out of adjustment, but there are several alternative explanations. These are, in approximate order of increasing severity:
Using 220 film in a camera configured for 120 will cause focus errors, as the pressure plate is set for a thicker film and backing paper combination. You will probably have a strange starting position for the first frame, as the leader length on the two types is different.
The backs on these cameras are quite flexible, and must be closed using even pressure on both top corners. Otherwise the back may not latch correctly on both sides. This prevents the pressure plate from applying even pressure across the whole frame.
Some screens can be disassembled when removed. If they are reassembled with the ‘glass’ upside down, the focus is wrong. De-mountable screens should be correctly fitted, though this is a gross error that should be easily spotted. Fixed screens are sometimes shimmed to adjust their height. Remove them only if necessary and with extreme care. The C330, f, and s are designed with replaceable screens.
The flip-up magnifiers and eyepiece correction lenses should be a reasonable match for your eye (with or without correction as applicable).
It is just possible to mount the lens unevenly on the lens panel, but it is unlikely that the auto-cocking feature on later models would work.
If the lens panel isn’t parallel to the film plane and at right angles to the focus screen, then an error will occur. These are tough cameras, so you’d probably need to drop it to cause this fault. (Not advised.)
It does happen, often because the retaining rings are loosened and spacing shims drop out. This is a pain to adjust, so touch the lens as a last resort.