F-stop printing

[Pieter12]

I'll take a wild guess. In a projection system, the light source is at a relatively fixed distance from the lens, the projected image distance can vary much more. In a camera, the opposite is true. Maybe.

 

[mshchem]

We aim to please .
I expect that there may be some additional losses due to the fact that there is a greater chance of flare outside of that portion of the lens' imaging circle that is in the frame, but that is probably trivial in amount.

Do you have to factor in bellows extension with projection??? I have no idea.

I have a application on my Android phone that I use to calculate f-stop times. I also have F-stop timers on some of my equipment.

Of course with the old wonderful Cibachrome, Ciba recommended using a constant time and changing the aperture, the ultimate in f-stop control

 

[MattKing]

Do you have to factor in bellows extension with projection???

The bellows extension calculations can actually be re-configured so that magnification is the variable that determines what bellows extension exposure compensation is required.
As the magnification is the same in the two examples - full frame with a 50mm lens, and full frame with an 80mm lens at a higher elevation - there is no change.

 

[mshchem]

The bellows extension calculations can actually be re-configured so that magnification is the variable that determines what bellows extension exposure compensation is required.
As the magnification is the same in the two examples - full frame with a 50mm lens, and full frame with an 80mm lens at a higher elevation - there is no change.

I use longer than normal lenses when making small prints from medium format negatives just to get some room to work the easel. Easier.

 

[redbandit]

Do you have to factor in bellows extension with projection??? I have no idea.

I have a application on my Android phone that I use to calculate f-stop times. I also have F-stop timers on some of my equipment.

Of course with the old wonderful Cibachrome, Ciba recommended using a constant time and changing the aperture, the ultimate in f-stop control

Thats how i thought f stop printing worked...

 

[Pieter12]

Thats how i thought f stop printing worked...

Changing f-stops can change focus.

 

[redbandit]

Changing f-stops can change focus.

TRUE, but the focus knob is really easy to use,, but getting the image resized can be a pain in the cheeks..

 

[redbandit]

Changing f-stops can change focus.

and originally i thought that Fstop printing was a theory to regulate aperture size and "light exposure time" via timer settings... as a means to figure out a way to save paper and scale an enlargement between paper sizes

 

[mshchem]

Changing f-stops can change focus.

I suppose so, but I usually focus wide open the stop down. El Nikkors, Rodagons and Companons.

What you say is true, but I've never had any issues.

 

[mshchem]

and originally i thought that Fstop printing was a theory to regulate aperture size and "light exposure time" via timer settings... as a means to figure out a way to save paper and scale an enlargement between paper sizes

True kind of. F-stop printing is a way to not take a non-scientific wild ass guess as to exposure times to lighten and darken a print. Time adjustments are not intuitively obvious to the human thinking organs.

 

[mshchem]

TRUE, but the focus knob is really easy to use,, but getting the image resized can be a pain in the cheeks..

Changing focus will change the size, tiny adjustments go unnoticed

 

[mshchem]

Changing f-stops can change focus.

Changing f-stop was recommended by Ciba and later Ilford with Ilfochrome because of the reciprocity characteristics of the print material. Color shifts, unpredictable density etc.

 

[Pieter12]

Changing f-stops on the lens doesn't give you the ability to make small adjustments to exposure like changing the time. The RH timer can work in 1/12 stop increments.

 

[Vaughn]

Changing f-stop was recommended by Ciba and later Ilford with Ilfochrome because of the reciprocity characteristics of the print material. Color shifts, unpredictable density etc.

Holds true for RA4 processing, also. At least for the color shifts, which I experienced trying to do a simple burn in a corner of the sky.

 

[mshchem]

Holds true for RA4 processing, also. At least for the color shifts, which I experienced trying to do a simple burn in a corner of the sky.

I guess no different from color film. I managed to dodge and burn with Cibachrome, didn't mess with aperture.

I remember printing Ektachrome paper from slides, mid 70's, I had a humble little Vivitar enlarger, I put a photoflood in it, used my Mom's hairdryer as a cooling blower.
I have a little melted 34.5mm Nikkor lens cap somewhere. Don't leave the lens cap on when you turn on the enlarger.

 

[MattKing]

As you have probably gathered, f-stop printing should probably be called "stop" printing, because exposure adjustments are done in increments of stops and fractions of stops, rather than in linear increments.
But calling something "stop printing" would just confuse everyone!
If one had the ability to repeatedly and reliably adjust the lens aperture in 1/2, 1/3, 1/4 or 1/6 stops, one could approach f-stop printing that way.
In contrast, it is quite easy to make those sorts of adjustments in the exposure time, if one has the appropriate enlarging timer.

 

[redbandit]

As you have probably gathered, f-stop printing should probably be called "stop" printing, because exposure adjustments are done in increments of stops and fractions of stops, rather than in linear increments.
But calling something "stop printing" would just confuse everyone!
If one had the ability to repeatedly and reliably adjust the lens aperture in 1/2, 1/3, 1/4 or 1/6 stops, one could approach f-stop printing that way.
In contrast, it is quite easy to make those sorts of adjustments in the exposure time, if one has the appropriate enlarging timer.

In theory such an enlarging lens COULD be designed and built... but i have a fear it would make the MSRP of a brand new Lieca M6 seem REASONABLE and possibly AFFORDABLE

 

[koraks]

In theory such an enlarging lens COULD be designed and built...

It would be no different from building any contemporary camera lens with an electronically controlled aperture. The reason it doesn't exist is that there's just no market for it.

 

[L Gebhardt]

and originally i thought that Fstop printing was a theory to regulate aperture size and "light exposure time" via timer settings... as a means to figure out a way to save paper and scale an enlargement between paper sizes

Glad you have it figured out now. It’s really a useful way of thinking that you can apply as it makes sense. Thinking about it the name does have a lot of room for confusion. I must have read a good description of it first and avoided the issue. The time aspect is really no different than fractional shutter speeds on a camera, but those at best go to third stop values on modern cameras, and the display of those is all rounded (why do we go from 1/8 to 1/15 - easier and it doesn’t matter?).

 

[Ian C]

In answer to the question posed at the end of post #44

The actual shutter times in seconds are: 1, 1/2 , 1/4 , 1/8 , 1/16 , 1/32, 1/64, 1/128, 1/256, . . . consistent with the law of reciprocity.

These are the reciprocals of 2 to the integer powers 0, 1, 2, 3, etc.

The apparent “jump” after 1/8 second is simply the result of the convention used by camera and shutter makers to give a sequence of denominators that end in 0 or 5.

There are no shutter times of 1/15, 1/30, 1/60, 1/125, . . It’s merely a convenient fiction. It does no harm. Likewise, the familiar aperture number sequence 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, . . . is a result of convention.

The even powers of 2 give exact values 1, 2, 4, 8, . . . The odd powers of two rounded to 1 decimal place give 1.4, 2.8, 5.7, 11.3, 22.6, 45.3, 90.5, and so forth.

By convention, the value of f/5.7 is truncated to f/5.6 while the remaining values of the odd powers are truncated to integer values 11, 22, 45, 90, etc.

 

[redbandit]

In answer to the question posed at the end of post #44

The actual shutter times in seconds are: 1, 1/2 , 1/4 , 1/8 , 1/16 , 1/32, 1/64, 1/128, 1/256, . . . consistent with the law of reciprocity.

These are the reciprocals of 2 to the integer powers 0, 1, 2, 3, etc.

The apparent “jump” after 1/8 second is simply the result of the convention used by camera and shutter makers to give a sequence of denominators that end in 0 or 5.

There are no shutter times of 1/15, 1/30, 1/60, 1/125, . . It’s merely a convenient fiction. It does no harm. Likewise, the familiar aperture number sequence 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, . . . is a result of convention.

The even powers of 2 give exact values 1, 2, 4, 8, . . . The odd powers of two rounded to 1 decimal place give 1.4, 2.8, 5.7, 11.3, 22.6, 45.3, 90.5, and so forth.

By convention, the value of f/5.7 is truncated to f/5.6 while the remaining values of the odd powers are truncated to integer values 11, 22, 45, 90, etc.

and if you figure in that most manual control apertures have a little wiggle room on each stop setting...

Or wonder how long it takes for the electric powered aperture to get out of sync due to wear and tear...
Seriously, with my nikon digital, the thing can take 2 minutes to focus if im trying to take a photo of a bush or tree on a slightly breezy day...

 

[koraks]

Or wonder how long it takes for the electric powered aperture to get out of sync due to wear and tear...

Surprisingly long. If you look at how common such apertures are on lenses that have been in common use since the late 1980s, many of which have seen heavy abuse, it's really remarkable how incredibly few have failed or drifted in such a way to become problematic.

 

[redbandit]

Surprisingly long. If you look at how common such apertures are on lenses that have been in common use since the late 1980s, many of which have seen heavy abuse, it's really remarkable how incredibly few have failed or drifted in such a way to become problematic.

then if one looks at the 50mm flat field corrected enlarging lens with electric aperture.. one asks...

How do i hack the aperture control system to leave the shutter open non stop.... or is it possible to PROGRAM the shutter to stay open for for seconds at a time

 

[koraks]

How do i hack the aperture control system to leave the shutter open non stop...

The aperture is not the shutter, so why would it help to try hacking the aperture control system to do something with an unrelated shutter that's not present on the majority of enlargers anyway? On a non-existent electronically controlled aperture enlarger lens, no less?

Edit: but perhaps I misunderstood your question, and what you intended to ask was "how would one get a suitable 50mm camera lens with electronic aperture to stop down to the desired aperture when bolted onto an enlarger?"

One possible way is by starting with a Canon EF lens, since the EF mount uses an industry-standard SPI interface and the aperture control commands have been reverse engineered an published years ago. One could hook up a microcontroller and any desired user interface to the lens and writing a program that controls the aperture. Aperture control in these lenses consists of a tiny electromotor that can run in opposite directions - one direction for opening up the aperture, and one for stopping down. Control is done by running that motor for a set number of microseconds to get the desired aperture. This is not too difficult to manage for someone with some experience with embedded systems. I.e., someone with moderate Arduino capabilities could hack something together that will work.

With non-Canon lenses, the same mechanism can likely be exploited, but you'd either have to reverse engineer the brand's proprietary mount communication protocol. But personally, I'd just hack the lens a little further and directly drive the aperture motor instead.

 

[redbandit]

The aperture is not the shutter, so why would it help to try hacking the aperture control system to do something with an unrelated shutter that's not present on the majority of enlargers anyway? On a non-existent electronically controlled aperture enlarger lens, no less?

Edit: but perhaps I misunderstood your question, and what you intended to ask was "how would one get a suitable 50mm camera lens with electronic aperture to stop down to the desired aperture when bolted onto an enlarger?"

One possible way is by starting with a Canon EF lens, since the EF mount uses an industry-standard SPI interface and the aperture control commands have been reverse engineered an published years ago. One could hook up a microcontroller and any desired user interface to the lens and writing a program that controls the aperture. Aperture control in these lenses consists of a tiny electromotor that can run in opposite directions - one direction for opening up the aperture, and one for stopping down. Control is done by running that motor for a set number of microseconds to get the desired aperture. This is not too difficult to manage for someone with some experience with embedded systems. I.e., someone with moderate Arduino capabilities could hack something together that will work.

With non-Canon lenses, the same mechanism can likely be exploited, but you'd either have to reverse engineer the brand's proprietary mount communication protocol. But personally, I'd just hack the lens a little further and directly drive the aperture motor instead.

now you understand... but one could go even further..

i remember seeing a few online articles on how folks used old film cameras to build an enlarger.. COuldnt one simply hack saw the back off an old EF film camera, or even an early digital.. and attach that under a nice light source.. like say one of those intrepid enlargers?