blopin

If I have a light source that illuminates a subject giving me an EV value of 8 in-camera with zero ambient light, but have an environment that will for instance give me 8 EV without my light source, how many EV would my subject be? 

3 hours ago, rodeo_joe1 said:

I think you might have your answer right there. 

I guess sometimes the most pragmatic solutions are the best ones. Will use sparingly.

So far I've removed the faceplate and attempted to locate a retaining ring/screw, but there doesn't appear to be one. Other than a bead of hot glue how do I ensure that the viewing lens doesn't come loose from the body? 

I'm aware that there are multiple linkages involved when reattaching the faceplate, and will take that into careful consideration. 

4 minutes ago, Dustin McAmera said:

 

That ship sailed! 😜

I’m young with an affinity for 80s riffs, I must have been a bohemian in the last life 🫠 

I just got the digitized scans back and wow, are they soft. I must have missed focus on every single image except those racked to infinity. 

Albeit a low resolution scan, here’s an image of a vinyl record sleeve for The Cars that I used as a makeshift test chart. I used a 7x loupe and spent a gross amount  of time and concentration on attaining the most precise focus possible (not willing to disclose my age but I have a very young pair of eyes). Then shot at 1/125, f/2.8 on Portra 160. The point of focus was on Ric Ocasek’s name. 

I don’t have the negatives right now but I plan to go over them thoroughly under the loupe. But from viewing the scans there appears to be no perceptible blur or indistinctness. 

3 hours ago, kmac said:

A simple answer could be to make sure the film is within the short depth of field of f2.8 ... this, I take it, is what the OP is going to do by using the the ground glass. The image on the ground glass can be checked for sharpness over the whole frame. If any blurriness is picked up on any part of the image, then the bow in the film will be too much for that short depth of field, and f4 will fix it with it's slightly longer depth of field. 

Hi kmac, I just wish to verify center sharpness. But loss in sharpness at the corners arising from lens alignment issues puts me at the deep end of amateur camera repair, and I’ll need to get it professionally serviced instead. 

3 hours ago, kmac said:

But this won't happen in the case of a Rolleiflex if it's in good condition, let's be honest about it. Do they get that bad that the film bows excessively and f2.8 is no longer of use ?

I wasn’t saying that film-bow results in overt loss of sharpness and an unusable image, just that this effect may be more pronounced on enlargements. Rodeo did bring up the hasselblad flatness issue, another thread on this website ceded into mudslinging between impassioned hassy loyalists and those too poor to afford one (just joking, no offence intended) 

Moving the faceplate of my Rollei 1mm takes about a 17mm circumference rotation of the focusing knob. Cut to the focal plane distance tolerance of around +/- 0.15mm at f/2.8 as rodeo mentioned regarding circle-of-confusion, which is a generous 2.55mm of focusing knob movement. A paper shim or two might not seem like a lot, but at 1/10 a millimetre thick this would mean a disparity of 1.7-3.4mm on the focusing knob! That could be the difference between infinity and 20 meters. 

Thanks for clearing up any dissonance from my intended reasoning rodeo, not to discredit kmac for that matter. I meant the bend along the axis that curls around the spool.

If the silver acetate sits firmly on the guide rails, it will rub on the sharp corners on the ends of the rails and may induce friction/scratching/or even tearing. Though the rails are above the rollers and may exacerbate the likelihood of this possible thesis, I don’t think this is the case. I simply think that the natural curve of the film helps it shy away from the sharp edge of the guide rails. This same leaf-spring tension also allows it to rest on the locating plate. 

23 hours ago, rodeo_joe1 said:

As you say, the tolerable blur is given by the f-number * whatever acceptable circle-of-confusion is chosen. Conventionally it's about 0.053mm for the 6x6cm format. Which gives a film-plane tolerance of +/- 0.148 mm @ f/2.8, well less than the (at least) 0.2mm of slop that many cameras are machined to!

However I need help understanding the last sentence of this paragraph. What’s the method to deduce film plane tolerance from circle of confusion? 

6 hours ago, rodeo_joe1 said:

Probably not. As I said, even processed film still has the same tendency to curve inwards to its emulsion side. It takes quite long storage inside a negative sleeve in a folder to flatten it, but as soon as it's released from its prison it starts to acquire a curl again. 

Thanks rodeo, your explanation was not lost on me there. By relax I meant curl. As the film loses longitudinal tension it will start to curve, possibly causing the middle to contact and flatten itself on the locating plate as the outer edges push on the rollers. 

20 hours ago, rodeo_joe1 said:

No. On the Yashica-mat both the rollers are definitely below the level of the rails, as can be seen in my 2nd picture.

Good grief, same for the Rolleiflex. My guess is that when the film runs off the rollers it continues to curve slightly instead of having a perfectly straight tangent. Like when you bend a piece of paper over the edge of a table and it curves at the corner instead of assuming a right angle. That is my only theory as to how the film floats between the guide rails and pressure plate. Will this mean that the film will rest against the pressure plate given time to “relax”? 
 

15 hours ago, kmac said:

But remember this is for very shallow depth of field stuff with the aperture as wide open as it can be. Otherwise, at f8 or even f5.6, it doesn't really matter all that much, but I would use the paper spacer anyway.

If I paid for f/2.8 I’ll use it at f/2.8 😉 

14 hours ago, rodeo_joe1 said:

Ermm, that's out by a factor of 1000! There are 1000 nanometres in a micron (= 1/1000th of a mm, 10^-6 metres or 1 um). A nanometre is 10^-9 metres) - blue light has a wavelength of 450 nm for comparison. 

Oops I used the wrong unit notation for micrometers. It should be μm, but the same principle stands. 

13 hours ago, rodeo_joe1 said:

Yes. 

No. On the Yashica-mat both the rollers are definitely below the level of the rails, as can be seen in my 2nd picture.

I could have sworn the Rolleiflex rollers were above the guide rails, it even depicts it in a cross section diagram of the user manual. But this could be idiosyncratic to Rollei. I don’t have the camera with me now as I’m only home on weekends, I’ll be sure to check then. 

To kmac and rodeo, both these answers have satiated my curiosity. Thank you so much for the very ample write up! 

I found out prior to your responses that the film indeed “floats” between the pressure plate and guide rails at 450 microns of allowance for Rolleiflex, and I was researching a definitive answer for the thickness of the emulsion + backing paper until your replies. 450 nm of gap - 250 nm of film = 200 nm divided by 2 gives us 100 nm of lateral play on both sides, and a sheet of printer paper comes in at 100 nm. The silver/gelatin composites are usually the top layer of C41 stock making calculations easier for us, no need to factor in depth. Hence, only a sheet of paper is needed to act as a shim between the guide rails and ground glass. Correct me on this if I’m wrong. 

24 minutes ago, rodeo_joe1 said:

I measured the relative height of the guide rails with a digital depth gauge, as well as I could, and there's approximately 0.5mm difference in their height. 

Is this between the “pips” and the guide rails? 

26 minutes ago, rodeo_joe1 said:

The rollers either side of the film gate are lower than the film rails, and serve no part in tensioning or positioning the film, apart from preventing it from scraping on the rails and film gate. 

And don’t you mean that the rollers are higher than the guide rails? I’m confused as to what you meant, because the rest of your reply was under the pretence of the rollers positioning the film between guide rails and pressure plate. There also needs to be tension for that to happen. 

Thanks everyone, 

I guess common consensus is that even if the emulsion does not lie perfectly flat on the focal plane, the effects are negligible(?) and less so with a quality Rollei. 

4 hours ago, Dustin McAmera said:

You're talking about a problem that might occur, sometimes, and to a variable extent. If you offset your focus by a fixed amount based on some estimate of how big the problem might be, it will be out by a little every time the film sits correctly.

I have heard people talk about the roll fim backs for Graflex cameras, saying that some hold the film more reliably flat than others - different rollers or something. That's with a 2¼x3¼ inch frame, with more length for the problem to occur. Also a detachable back, with a removable insert, and with the film wrapping 'inside out' round that insert.

There is a back for 70mm film for the Rolleiflex 6006 SLR with a tiny vacuum pump to hold the film against the plate. I guess that wouldn't work on film with a backing paper.

Overall, I think if what you have is a Rolleiflex, it's probably good enough. People have taken quite good pictures with them, I understand! 😁

You make a good point with the variability of this theoretical issue. However, I’m sure there’s a zero point every time the film is freshly wound on, such that the film may jut slightly even under tension from the spools and pressure plate. After all, film curls like a watch mainspring in its natural state. 

2 hours ago, kmac said:

Actually it's not a "pressure" plate as such, it's a "locating" plate. It's there to stop the film from moving too far away from the body of the camera (film plane). There's a gap of a few thou between the film and the body, and a similarly small gap between the film and the plate, and those gaps are to allow the film to travel freely between the two without getting damaged. That's common knowledge, we all know that, but generally we fail to check how much tension the film is under to allow it to miss both the body and plate. Theoretically the correct plane for the film is halfway between the two, or if the camera has rollers, along the top of the rollers. If the tension on the film is not strong enough, the longitudinal curve in the film will come into play, and therefore throw the focus out a bit. 

Longitudinal curve is inherent in roll films, they want to go back to being rolled up again, it's the camera's job to straighten them and keep them straight while the shutter button is being pressed. The secret is to have adequate tension on the film so that it doesn't slacken off after you've wound to the next frame. In a quality camera like the Rollei, all this should be sorted out, but if you still suspect the film is too loose, then it'll need tensioning more. It's up to you how you tension it, I can't tell you what to to with your Rollei, but the film must be tensioned at both ends, the supply end, and the take-up end, from frame 1 to frame 12 (or the last frame)

I use translucent grease proof paper for checking focus, and in the beginning, silly me used to tape it tightly across the film plane and I wondered why my images were always out of focus a bit. Of course it had to be two or three thou (the thickness of a piece of paper) off the film plane, or across the rollers, if there were rollers in the camera. With the aperture opened right up to f1.4, f2, or whatever the camera has, I poke the grease proof paper to see how far it will go before the focus goes blurry, and that would give me an idea of how far the the film would have to move forward or backward before it too would be out of focus. At the full opening of the aperture, it didn't take much of a poke to make the translucent paper blurry, but it usually depressed in further than a film could move. All I was doing was checking that the film was within the depth of field at the widest opening of the aperture, but the film must be straight to start with when you eventually load the camera. 

Using frosted glass, it must be across the rollers in your Rollei, with the frosted side in towards the camera, because as you know, the film emulsion runs over those rollers, but if the film is slack, it can be slightly off the rollers and give you false focus, so again, the film needs to be adequately tensioned, at both ends, but not tensioned so much that the film will get marked. Fresh film is best for testing focus after any adjustments, fresh film won't have the strong curl in it that expired film acquires over years of standing around doing nothing. 

I did not know that the emulsion and backing paper does not touch the locating plate and guide rails. Is this true? When I close the Rolleiflex there is a spring-like force exerted, similar to that of film being sandwiched between the pressure plate and guide rails of a conventional 35mm camera. 

Hi strangers, 

I recently ordered some ground glass and a 7x loupe to calibrate the infinity focus on my Rolleiflex. In the past I discerned rumours that 120 film does not always lay flat on the pressure plate, and may bow outwards slightly. 

By how far does the film curve outwards? I wish to compensate for this to achieve the sharpest possible image. All replies are welcome. 

Well, impulsivity took a turn and I managed to correct the issue within an hour of posting this thread. There is a slotted nut once you undo the three grub screws and remove the ASA reminder dial. Use a spanner wrench to loosen said nut, move the now uncoupled focusing ring a desired amount, then tighten. The faceplate should now be almost in contact with the camera body. 

Hope this serves as posterity for anyone experiencing the same issue. 

My newly acquired Rollei refuses to focus to infinity by a smidge and caps at a distance of around 20m, as the infinity hard stop prevents me from turning the focusing knob further. Prognosis is that the focusing knob is offset, as a flat object in focus is 3 feet 10 inches away from the focal plane when the focus scale reads 4 feet. Photos closer than 20m appear to be in focus so I can rule out lens board or ground glass misalignment. 

The question is how do I loosen the focusing knob so I can adjust it? A user in another discussion by the name of ic-racer mentioned that this was possible, but I've yet to find any online resources. My Rollei is the meterless variant by the way. 

URL to the previous thread: https://www.photrio.com/forum/threads/can-a-rolleiflex-be-out-of-focus-calibration.156372/