Measuring for close focusing with folders.

pbromaghin · Aug 6, 2021

Yesterday I watched a video on the "Analogue Insights" Youtube channel. They were trying out a Voigtlander Perkeo 1 (zone focusing) and did some pretty close up shots using a tape measure to get the exact distance. Having used folders for several years, I've never tried any close ups, but it looked fun to try.

My question is, where on the camera is the distance measured from? I would assume it would be at the shutter plane. On my Bessa 1 with 105mm lens the minimum distance setting is 5 ft where the depth of field scale shows the acceptable depth is only 6 inches at f/3.5, so this could significantly affect the photo.

Nicholas Lindan · Aug 6, 2021

Focusing distance is measured from the film plane. Many cameras have a "-o-" symbol on them to show the location of the film plane.

AgX · Aug 6, 2021

Yes, typically at the film plane. Though a shutter scale may be referencing to any plane the manufacturer found useful.

But if you attach a close-up lens the metering reference is this very lens!
(Unless stated differently in a manual of a proprietary close-up system.)

bernard_L · Aug 6, 2021

Nicholas Lindan said:
Focusing distance is measured from the film plane. Many cameras have a "-o-" symbol on them to show the location of the film plane.

This is true for "recent" cameras. For folders, the distance is measured from the lens. This has been discussed before on photrio, with original documentation supplied as evidence. Other than stating what I believe to be correct information, I won't argue, as there is likely to be someone who will shout louder.

AgX · Aug 6, 2021

Bernard, it is not as simple as you say...

I just looked into the first manual at hand of a MF folding-camera: the Agfa Isolette II, a once popular and still wellknown camera.

It says that

-) for the Apotar lens the focusing scale refers to the aperture plane

-) for the Solitar lens the focusing scale refers to the film plane

So if one manufacturer even for one camera in its two lens versions cannot decide...

Dan Daniel · Aug 6, 2021

Focus scales are not always reliable. Best to put ground glass in the film plane and do some precise measuring. A few spot points should give you enough to interpolate other distances.

Nicholas Lindan · Aug 6, 2021

Dan Daniel said:
Best to put ground glass in the film plane and do some precise measuring. A few spot points should give you enough to interpolate other distances.

You can then keep a table of corrections showing indicated focusing distance and actual focusing distance. For subsequent shots you can then set the lens at, say, 3ft. and set the camera 39" from the subject if you found there was a 3" error.

And you will soon find out if your camera measures from the front of the lens, the aperture position or the film plane.

I have found the focusing distances on front focusing Zeiss and Agfa cameras to be quite accurate. I guess I got rather good at distance estimation because I rarely get out of focus shots with either camera and I gave up needing an auxiliary rangefinder (and besides I have lost every one I ever had). I pay a lot of attention to the DOF scale on the lens. In my youth I used close-up lenses on an Agfa Silette; I set the lens with the table supplied by Tiffen and measured out the distance with a tape measure and never had any problems.

AgX · Aug 6, 2021

Dan Daniel said:
Focus scales are not always reliable. Best to put ground glass in the film plane and do some precise measuring. A few spot points should give you enough to interpolate other distances.

Or set the camera at infinity, mount a close-up lens, and bring this at a distance of its focal length.

pbromaghin · Aug 7, 2021

Will wax paper substitute for a ground glass for testing?

gone · Aug 8, 2021

It may if you have a loupe, good eyes, good light, and stretch the paper taut. I've used Scotch Magic Tape before. It would be a lot easier if you tried a piece of ground glass though. I don't have a big piece, just some small pieces that were saved from a broken one, but that's OK. You're only concerned about the center, so you just need enough to lay across the film rails in the middle.

grat · Aug 8, 2021

Wax paper was too fiddly. I used a piece of translucent scotch tape on the horizontal, and the vertical, forming a cross, and used the square where they overlapped for testing focus on my Bessa I. I also used a loupe. Rapidly came to the conclusion that the lens and my rangefinder accessory were in agreement, and shot a whole roll, with no focus issues.

takilmaboxer · Aug 9, 2021

My approach is entirely empirical. Take a focusing target and use a tape measure to place it exactly 10 feet or 3 meters from the film plane - use a tripod. Take a series of shots with the distance scale on the lens (and the rangefinder if it's there) set at close intervals near the corresponding mark on the lens ring, being careful to note exactly where those points are. Develop the film and examine the negatives under a magnifier. The best image will be obvious. Note where the focus ring was set - that's your real 10 foot focal distance regardless of what the ring says. The rangefinder can be off too!
My Ikonta 521/2 with a 105 Novar is a good example. The real 3 meter setting is at 4 meters on the focus ring, in spite of the infinity setting being spot on.

Donald Qualls · Aug 9, 2021

takilmaboxer said:
My Ikonta 521/2 with a 105 Novar is a good example. The real 3 meter setting is at 4 meters on the focus ring, in spite of the infinity setting being spot on.

The most likely reason for this is that at some point the front element was removed (likely for cleaning or lubrication of the focus threads) and reinstalled on the wrong thread start (most front focusing triplets I've seen have either three or four start threads), then the infinity adjusted via shims behind the shutter. End result is that the front element spacing isn't what it was when it left the factory, and there's more or less change in focal length with front element movement than was originally the case.

If you've got a relatively easy way to work around it, as it seems you do, I'd probably leave it as it. If you want to fix it, there are two or three (three on Zeiss lenses, as I recall) alternative starts; one of them will give correct focus at 3m and still have correct infinity (though you may need to add or remove shims behind the shutter to correct infinity again). It's rather a drawn-out process to get both correct if the original shim setting has been altered, so it's likely more sensible at this point to leave it as is and use a correction table ("lens 3m actual 4m" and multiple additional rows) to get correct focus.

AgX · Aug 9, 2021

But someone who is able to shim that thing again, would not have lost threads from the start... or?

takilmaboxer · Aug 9, 2021

Donald Qualls said:
The most likely reason for this is that at some point the front element was removed (likely for cleaning or lubrication of the focus threads) and reinstalled on the wrong thread start (most front focusing triplets I've seen have either three or four start threads), then the infinity adjusted via shims behind the shutter. End result is that the front element spacing isn't what it was when it left the factory, and there's more or less change in focal length with front element movement than was originally the case.

If you've got a relatively easy way to work around it, as it seems you do, I'd probably leave it as it. If you want to fix it, there are two or three (three on Zeiss lenses, as I recall) alternative starts; one of them will give correct focus at 3m and still have correct infinity (though you may need to add or remove shims behind the shutter to correct infinity again). It's rather a drawn-out process to get both correct if the original shim setting has been altered, so it's likely more sensible at this point to leave it as is and use a correction table ("lens 3m actual 4m" and multiple additional rows) to get correct focus.

Thanks for the explanation and advice. I'll leave it alone, as it is a great landscape camera. I learned about the multiple thread starts the hard way, by making mistakes. Readers take note: if you succumb to the temptation to remove the front element for cleaning, take careful note of where the threads come free and replace the ring exactly there!
I also have a 521/2 with a Tessar that I bought from its original owner, in mint condition. Its distance markings work fine. He said he'd run maybe 10 rolls through it in its lifetime.

pbromaghin · Aug 9, 2021

Oh, all very nice solutions. Thank you Momus, Grat and Takilmaboxer. I don't really have time to shoot and develop a roll before I plan to use the camera on a short vacation, so I think I will try the scotch tape route for now and then do a more complete job later.

I have in the past tested a Mamiya C33 with a similar method, setting it at 45degree angle to a wall, marking distances on it and found the actual focusing points. Dusting off my 50-yr-old algebra, and with the help of Mr Pythagoras and some really complicated lens focus point formulas, it was shown that the focusing screen was 1mm closer than the film plane. This was consistent across 3 lenses and so it was soon sent off for new shims.

Dan Daniel · Aug 9, 2021

takilmaboxer said:
. Readers take note: if you succumb to the temptation to remove the front element for cleaning, take careful note of where the threads come free and replace the ring exactly there!

(another way to check if you get a lens element threaded back properly is to move the lens as far IN as possible and note something like where a letter on its ring aligns with a mark or object on the lens. Given the fineness and subtlety of catching threads when reinstalling a lens group, using the fully screwed in approach can save a little sanity. Note that on most any front element focusing lens like on folders, the lens at infinity will NOT be the lens screwed all the way down. You'll need to note things like this.)

takilmaboxer · Aug 9, 2021

If you remove the front ring scale with the lens set at infinity, there is often a scratched line marking infinity alignment between the front and center elements, that was marked at the factory. If not, I mark it myself. Before I remove the front element, I screw it inwards until it stops, noting exactly how many turns it takes. These actions will help reassemble it correctly. But if a previous cleaner has removed any shims...good luck. You'll have the best luck with a folder that has never been dis-assembled, or was CLA'd by an expert. My 521/2 Novar came off the Bay. The 521/2 Tessar, from an old man here in town. My 524/2, from Certo6.
Have fun! Folders are addicting!

Helge · Aug 9, 2021

It’s surprisingly quite hard to determine exactly when the treads disengage.
It’s a far better strategy to measure the distance between the front of the shutter and the moving focusing lens. And then count roughly how many turns it takes from infinity stop to a lose front element.
If you use the wrong thread start the distance will be noticeably off with the right number of turns.

Ground glass or tape is incredibly fiddly and can never be more than a very rough ballpark estimate.
The only way to really be sure and make critical measurements is to use film.
Film is never really super flat in a folder. That’s why it’s important to stop down.
It compensates a bit for field curvature though.
If you are stingy and dexterous enough you can cut part of film and backing paper, and get a “good enough” simulation of real film (no tension tugging from the sides).

AgX · Aug 9, 2021

Measuring the extension with a caliper at min. foc. distance or at a certain coincidence of marking points is one method.
The other is pulling the barrel slightly at very slowly unscrewing it and marking the position the moment it comes loose.
Best use both methods...

ciniframe · Aug 9, 2021

I was gifted a Kodak Tourist with the lowest spec lens, a 100mm f8.8 triplet. It’s too slow to precisely focus on a ground glass, even at 3.5 ft. The bellows have pinholes so it’s stuck on a homemade 4x5 and will cover, (sort of) 95x95mm, so it’s framed for that. I’m only using photo paper for negatives anyway so it’s tripod work all the way. Stopped down to f22 to f32 and with no more than 2X enlargement it’s hard to not get everything in focus.

Danielle_B · Aug 10, 2021

I have one of those in my collection of Tourist cameras. There is actually a lower spec lens than the 100 f8.8 on those cameras. With patience and practice it can actually produce a nice negative. Even though I shoot more with my Tourist that has the 105 f4.5 I still use my f8.8 from time to time.

ciniframe said:
I was gifted a Kodak Tourist with the lowest spec lens, a 100mm f8.8 triplet. It’s too slow to precisely focus on a ground glass, even at 3.5 ft. The bellows have pinholes so it’s stuck on a homemade 4x5 and will cover, (sort of) 95x95mm, so it’s framed for that. I’m only using photo paper for negatives anyway so it’s tripod work all the way. Stopped down to f22 to f32 and with no more than 2X enlargement it’s hard to not get everything in focus.

Helge · Aug 10, 2021

Danielle_B said:
I have one of those in my collection of Tourist cameras. There is actually a lower spec lens than the 100 f8.8 on those cameras. With patience and practice it can actually produce a nice negative. Even though I shoot more with my Tourist that has the 105 f4.5 I still use my f8.8 from time to time.

Slow triplets can often actually be better than larger ones at the same apertures. Don't know if its some fundamental optical property or just manufacturing tolerances and vagaries.
My 105 6.3 Novar beats my two 4.5 Novars at 8 and up. The shutter is also more reliable because the blades have to travel less and less fast. The accessory grove in the lens also take more common filters and shades.

Danielle_B · Aug 10, 2021

Helge said:
Slow triplets can often actually be better than larger ones at the same apertures. Don't know if its some fundamental optical property or just manufacturing tolerances and vagaries.
My 105 6.3 Novar beats my two 4.5 Novars at 8 and up. The shutter is also more reliable because the blades have to travel less and less fast. The accessory grove in the lens also take more common filters and shades.

I've noticed that as well. I always chalk it up to "magic" lol.
Seriously though the Kodak 100mm f8.8 at f11 or 16 produces some really nice 6x9 negatives.

ciniframe · Aug 10, 2021

Danielle_B said:
I have one of those in my collection of Tourist cameras. There is actually a lower spec lens than the 100 f8.8 on those cameras. With patience and practice it can actually produce a nice negative. Even though I shoot more with my Tourist that has the 105 f4.5 I still use my f8.8 from time to time.

Yes, they had a fixed focus model Tourist with a single element meniscus lens, 86mm working at f12.5 and a front mounted aperture that will stop down to f32, all mounted in a single speed 1/50sec shutter with T and B settings also.
The interesting thing about the Tourist was that the flange where the lens clipped on has been the same distance to the film in every one I’ve measured so that you can clip on a lens from a different model, although the shutter linkage won’t align so you usually have to use a cable release.

Measuring for close focusing with folders.

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Measuring for close focusing with folders.

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