Pentax 6x7 horizontal streak on negatives

[velviamax]

Hi All,

Have bought two Pentax 6x7 camera bodies. Tested them with same subject and same settings to compare them up front.
I found out that one body mostly at times 500 / 1000 will create a "streak" in the top part of the negative (if the camera is oriented horizontally).

I have checked the following:

• clean inside and rolls of film transportation mechanism
• inside reflection of mirror box
• different film types
• scanner (unlikely as streak is on the negative itself)

Will post an example below. The line I am talking about is quite diffuse so if you don't see it I recommend you squint at the top part of the photo.

My thought is that maybe there is some dirt or fiber caught in the slit of the shutter curtain. Does anyone have an idea on how to access that one easily, just to have a look?

Many thanks in advance.

 

[AgX]

My first idea too, is a partially narrowed shutter slit.

But that can be easily checked by setting various shutter times.
As you experienced the artefact only at fast shutter speeds you got proof of that.


(EDIT: at first I overlooked that you actually saw the artefact only at fast shutter speeds.)

 

[Arbitrarium]

Would firing it on bulb help you to look at the edges of the curtains?

 

[D90]

My first idea too, is a partially narrowed shutter slit.
But that can be easily checked by setting various shutter times. As you checked various films, you likely set different times.


So likely we have to think over a different culprit...

Uneven shutter slit was my immediate thought, but ruled it out as this camera presumably has a horizontal shutter......

 

[mrosenlof]

I think the OP's idea of fiber or something in the shutter slit is probably correct. Seeing this at the highest shutter speeds would support this theory because at slower speeds the slit is wider and little bits of cruft have a smaller impact on exposure.

D90: Yes, horizontal shutter for this beast.

Unfortunately, I don't have any idea how to inspect this, or to repair. No experience there...

 

[velviamax]

I think the OP's idea of fiber or something in the shutter slit is probably correct. Seeing this at the highest shutter speeds would support this theory because at slower speeds the slit is wider and little bits of cruft have a smaller impact on exposure.

D90: Yes, horizontal shutter for this beast.

Unfortunately, I don't have any idea how to inspect this, or to repair. No experience there...

Thanks everybody for the good input.
Maybe someone knows how to inspect the shutter curtain slit without completely taking the 6x7 apart?

 

[shutterfinger]

Maybe someone knows how to inspect the shutter curtain slit without completely taking the 6x7 apart?

Lock the shutter open on B, inspect the frame edges. Cocked - first curtain showing; tripped - second curtain showing.

 

[Poisson Du Jour]

You need also to exclude any fault with the roll of film loaded. Perceived "faults" with the camera can often be traced back to the film being the culprit!

I suggest that as a clearer and more revealing experiment, you photograph a white wall over several frames, at various shutter speeds and then examine the results.

Having said that, all of the Pentax 6x7 / 67 bodies have horizontal travel focal plane shutters. The streak can be caused by the tape on the shutter curtain overlap deteriorating and impating sticky residue on one or both of the curtains. That is but on possibility and has been seen in the old (1969-vintage) Pentax 6x7 cameras. The 1989-era Pentax 67 was given a different treatment for the curtain overlap.

Neither of these cameras is designed for dry-firing ('test firing' with the back cover open, without any film actually loaded). However, a well-known technique (and one covered in the original instruction manual) is to insert a shim under the wind-on lever, press the shutter and wind on. It is unlikely however that this trick will reveal the problem of what is causing the streaks because the shutter, when open, is completely within the camera, with just the mirror box exposed. Do not insert any object through an open shutter curtain as it can close without warning in this instance.
Opening the back and inspecting the visible section of the shutter should be the sensible limit of enquiry. Any further and the camera should be seen by a service facility. Certainly, avoid the temptation to apply anything to clean the shutter -- it is very, very fragile.

Parts when required are taken from like-bodies. Doing so may provide a sufficient repair, but still introduces unreliability and redundancy.

 

[AgX]

Thank you for hinting at the curtain edge overlap. I was not aware of that, let alone of the difference to the 2nd model.

 

[velviamax]

I took the advice from shutterfinger and Poisson. I triggered Bulb Mode and then looked right in (see photos below, right side, then left side).

I did not see anything.

Maybe I have broken the camera by doing so - it is incredible how easy one can break it - but I opened up the back gently and had a look into the slit of the curtain. And voilà as predicted some strange artefact (last photo). The same artefact is on the other side of the curtain.

Oh yeah and inside the mirror box coming from the front to the left is a strange tape. Is that supposed to be there?

Any ideas how to proceed?
Poisson du jour?

Again thank you.

 

[shutterfinger]

In situations like this I use a pair of 6 inch tweezers and gently try to pull the gunk off. The edge of the curtain is likely hard plastic and the gunk looks like tape residue. The curtain travels right to left when released. Up-down motion will likely release the second curtain so hold the gunked right edge near center as you try to remove the crud. If you need to wash the edge with a solvent use 90% isopropyl alcohol on a cotton swab then remove any fibers left behind.
This is generic service procedure, I yield to factory experienced service information for this camera.
The patch on the side of the mirror box looks factory.

 

[Poisson Du Jour]

The mirror box and workings look good -- nice and clean.
But that patch is definitely not standard nor factory -- I do not have it in my Pentax 67, nor is it visible in a friend's Pentax 6x7. Is it a modificaiton from the previous user? The markings on the mirror box wall proximal to the patch are evidence of pussy-footing around that area. Yes, I would like to know what is being hidden by that sticky patch inside the mirror box. It may give rise to evidence of modification/service? I am not alluding to this patch being the root cause of anything in particular, but obviously somebody has been down there, possibly even a service tech -- who knows??

Meanwhile, the suggestion that you photograph a white wall to give a much clearer picture in isolation of the fault still holds. The image you posted does not really convince me that it is a fault with the camera (the tape problem I spoke of often results in the tape being ensnared on the shutter curtain and crinkling it), but rather film processing, but we shall see! So run another roll -- preferably two, through the camera, including white wall shots and if possible, clear blue sky shots. It may sound like a damned costly waste, but it will go some way toward eliminating endless speculation and getting straight to the point of either camera fault or film processing fault.

Be aware that these cameras are literally old dinosaurs, but they make up for their archaic vintage and idiosyncracies withh outstanding imaging quality. The older Pentax 6x7 cameras that first appeared in 1969 very often now turn up with any number of faults, chief among these being inaccurate shutter speeds (corrosion of the copper circuit "fingers"), sticking mirror solenoid (preventing the mirror from rising or falling in sync with the shutter firing), winding lever wear/broken return spring, the aforementioned shutter curtain tape and of course the fragility of the aperture coupling chain at the front top of the mirror box (visible with the prism removed). Battery compartment corrosion isn't really as common as often reported.

 

[Poisson Du Jour]

Thank you for hinting at the curtain edge overlap. I was not aware of that, let alone of the difference to the 2nd model.

There were quite a number of small improvements around the shutter area, such as the governor, anti-bounce, inertia controller and the binding tape. The aperture coupling chain was also modified. The original Pentax 6x7 engineering manual contained an addendum (partly in Japanese) about these modifications (including changes to oil weights and component redundancies), but a newer manual is known to have come out around 1991, but I have never seen it. Perhaps Eric at pentaxs.com (pentaxs.com/index.html) has one -- he is also the go-to for involved repairs to these cameras, much better than a DIY job!

 

[velviamax]

Thanks for the advice.

Yes, I am worried about that sticky patch. It is deteriorating and possibly the source of gunk on the curtain. Though taking tweezers and lightly taking that gunk off seems like a really good way to destroy the camera.
Although the service technician would probably be doing the same thing... Any thoughts on this?

To clarify my situation:
I bought two P6x7 bodies with lenses. One - lets call this one "Gunky" - has been described above and has the gunk on the shutter curtain. All films (I am shooting 2 rolls per week and develop in different labs) wether c41 or e6 show horizontal stripe when shot at 500-1000, though never at longer times. The stripe is visible on the negative image itself, never outside of the frame of that negative image.
The other body - lets call this one "Cleany" - is in superb condition, looks new and has reportedly not been used a lot. It had a broken chain, which was replaced by a technician with an "industrial string" and so it can show Exposure in the metered Prisma. This body does not have that sticky patch. Maybe Cleany is a newer version of the 6x7?

 

[Poisson Du Jour]

Derangement of shutter speeds is a known problem with the older Pentax 6x7 bodies from 1969. It is good practice to store the camera with the shutter speed dial set to B when the camera is not in use, even when putting it away in the kit. The Pentax 67 (which is what appears in one of your photos), has a bit more of a modern appearance from 1989, and had improvements in the shutter speed dial circuit area, the shutter curtain, winding mechanism, exposure counter roller and aperture coupling chain among other places.

Gunk on the shutter curtain is usually removed by techies with a very fine atomiser spray of isopropyl alcohol and an extremely fine-spread brush. Touching the shutter curtain with fingers is a no-no because it is under precise tension by the mechanism, quite apart from the curtain picking up whatever residue is on your fingers. The source of gunk otherwise can be myriad, evening the seemingly harmless task of loading and unloading the film can expose the shutter curtain to hazard. Consider the photographers who would do so with a cigarette in the lips, puffing away and giving the fag a flick, the hot ash contacting the shutter curtain. And you know what? They imaginative boys applied black silicone sealant to the resulting holes and then got on with the job!

I cannot shed any light (!) on the sticky patch mentioned in the older camera, other than to my eyes the marks on the mirror box wall around it indicate interference with something there.