Apertures for Zeiss Triple Convertible

[Edison]

Hi. I've searched the forum quite a bit and I haven't seen this exact question discussed. Please let me know if this has been discussed already.

I recently received a field camera that came with a Zeiss lens. It is a 285mm in the front and 224mm in the rear and both are protarlinse. From what I have researched, this is a triple convertible which I'm pretty excited about. I'd like to take some portraits using the 224mm lens in a few days. The aperture is marked in mm. The largest is 25mm and the smallest is 3mm. I understand it's marked this way because it's a convertible lens and relative aperture changes as you change focal length. Common sense tell me to take the focal length and divide it by the aperture diameter and that will give my f-stop. For examples 143mm (it's a 143mm when both lenses are in place) divided by 14mm would give an f-stop of f/10.2. I did read another thread where "apparent" aperture is discussed and how removing a front lens for example may change the apparent aperture, so I'm not sure how this plays into the situation exactly. If this is the case with this lens, and I want to use the 224mm in the rear only, is the aperture still 224mm/14mm= f/16? Or does the apparent aperture change this?

Furthermore, I've found this pdf (i can't read German so I'm not 100% sure this even applies to my particular lens, but it seems like it should) and I'm trying to piece together the info. The bottom image is marked with notes to help. So for example the 224mm+285mm (7 o'clock) at 14mm yields 1:9. Is this f/9? I don't think so because the math is wrong (should be over 10). Another example is the 11 o'clock 224mm/18mm yields 1:6.3. If this is f stops, it should be f/12.4, no?

Then an additional question is the 12oclcok to 6 o'clock side. These have the "diaphragm in mm" sections for the single lenses as x:2. For example at 3 o'clock it says 285mm/11:2. There's a handwritten note that says 10:2=5mm. So if that's true 1. Write it this way? and 2. 285mm/5.5mm (which is 11:2 I assume) would equal f/52. But 285/11 does equal just over 25 as the 1:25 would suggest.

So I'm trying to figure out the pattern and sense here. It is a nice lens, I did take several shots with it and it works. I didn't have a lens longer than 150mm until now, so I'm excited to use this one.

I also read in another thread that it's probably the same as a Bausch and Lomb lens, but I haven't found any info on that.

Unimportant info probably: this came with a 4x5 Korona View (II) and has a Packard shutter. Amazingly everything works. I do need a new bellows but throwing the dark cloth over it worked temporarily and I tried out patching with liquid electrical tape too seems to have worked and I'll replace the bellows when I know I'm going to use the camera enough. Is Custom Bellows in the UK the best place to go? I live in Michigan. Also a small complaint about the rear standard is that it tends to slightly lean back when tightened down. Not sure if this is normal, but I can always compensate with tilt.

Thanks in advance,

Alan

[Kevin Crisp]

I have all this worked out in a notebook I carry. Send me a personal email address and I'll scan the table and send it to you.

You must (especially with the Zeiss singles) check and correct your focus on single cells when you've stopped down. Focus shifts.

[Dugan]

Custom Bellows does top-notch work.
Apparent aperture is the measured size as viewed from the front, whether there's a front element in place or not.

[Edison]

I have all this worked out in a notebook I carry. Send me a personal email address and I'll scan the table and send it to you.

You must (especially with the Zeiss singles) check and correct your focus on single cells when you've stopped down. Focus shifts.

Thanks! Doing now.

[Edison]

Thanks! I’ll go with them as long as the price is in my budget. What do you measure it with?

[Dugan]

I use a micrometer, and measure in mm's. Fractions of inches are a pain.

[Mark Sawyer]

Remember that the aperture size will change when you change front elements.

[Edison]

So are the markings on it currently the size in mm as the combined focal length. I see thanks.

[j.e.simmons]

Isn’t the aperture change the reason you use the single element behind the aperture.
OP, B&L licensed the Protar from Zeiss so for the Protar V and Vii, the lenses are the same. For the most part Series IV lenses were very different. I believe yours is a Series VII.
You can find lots of old manuals at
https://www.cameraeccentric.com/

He has some problems that might cause your browser to show a warning, but just ignore the warning.

BTW, all of the Protar I’ve received have had the lower focal length on the front and the longer on the back. All of the Zeiss and B&L manuals above have the longer listed as the front lens. In use, I haven’t seen any difference.

[David Lindquist]

j.e. simmons has beat me to it to some extent. If you look at the early 20th century B&L catalogues on the camera eccentric website you'll see Bausch & Lomb's equivalents to your two lenses had focal lengths of 8 3/4 and 11 3/16 inches respectively. Combined they made a 5 5/8 inch focal length objective.

Circa 1910 Carl Zeiss Jena changed the labeling of their lens focal lengths from millimeters to centimeters. The 224 mm lens became a 22 cm lens and the 285 mm lens became a 29 cm lens; in combination they made up a 14.5 cm lens.

David