ACML CRT King 75 mm f/3.5 lens in Copal Press-No.0 and some questions

I have this kinda unusual lens, which - as far as I know - was originally mounted onto a Polaroid camera. If memory serves me right, the CRT in its name might indicate that it was used to inspect CRT screens originally, which probably gives an indication that it's optimized for close distance work. The thing on the bottom is a helicoid used for focusing and the lens is mounted in a Copal Press-No.0 shutter, which I was unfamiliar with when I got the lens.

I'm aware this is not a lens many might have used or seen, but if someone is able and willing to help me find some answers, I would really appreciate it, as I'm always interested to find out some more about unusual lenses like that:

1.) Do you think my assumption is right and it might have been used for close-up work? Here is another listing I found, which features a slightly different lens + the camera: https://www.etsy.com/at/listing/558...how_sold_out_detail=1&ref=nla_listing_details

2.) Is there any way of keeping a Shutter like that open permanently? The shutter seems to work, but I have no realease cable and as I've mentioned I've never used a shutter like that before.

3.) Does anyone know the manufacturer ACML? I've never heard that name before.

Thank you very much!

since the shutter doesn't have a "T" setting, using the "B" settng along with a release cable with a lock can be used to hold the shutter open for extended amounts of time. (This is common on 90mm Angulons which all seemed to come in shutters with B but no T.)

I would expect that lens to cover Polaroid 3x4 at close distance with no movements, and to have poor performance at infinity.

abruzzi said:

since the shutter doesn't have a "T" setting, using the "B" settng along with a release cable with a lock can be used to hold the shutter open for extended amounts of time. (This is common on 90mm Angulons which all seemed to come in shutters with B but no T.)

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Many thanks! Do I need a specific kind of shutter cable apart from the lock-function?

AnselMortensen said:

I would expect that lens to cover Polaroid 3x4 at close distance with no movements, and to have poor performance at infinity.

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Thanks a lot - that‘s good to know. I‘m mostly interested in close distance performance anyway.

Honestly I’ve never used a “press shutter”. They are more automated than common LF shutters—they cock the shutter, stop down and fire the shutter all in one press. They should use standard release cables, but may have issues with ones with shorter throws..not sure. There is a bit of info on press shutters here:

I have a Copal polaroid shutter. Those press-type shutter need a cable release to operate and they are self-cocking. Practical when shooting a fixed subject like a CRT screen (or for multiple exposure) since you won't disturb the position by manually cocking. They won't work with all releases, only those with a long enough plunger.

I used a Oscillo-Raptar (used to photograph oscilloscope traces for scientific documents before computers, sort of an ancestor to a CRT lens I guess?) and even though it would cover 6x6, performance was pretty weird on full-frame digital. Since CRT screens are curved it might also make weird photos.

OAPOli said:

only those with a long enough plunger.

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Thanks for confirming--I thought I had heard something like that, but I've never encountered a press shutter myself.

Hmm. There's what looks like a cable release socket under the aperture scale. If it will accept a cable release, attach one and press. The diaphragm might open.

abruzzi said:

Honestly I’ve never used a “press shutter”. They are more automated than common LF shutters—they cock the shutter, stop down and fire the shutter all in one press. They should use standard release cables, but may have issues with ones with shorter throws..not sure. There is a bit of info on press shutters here:

Copal Shutters - The Photographers Machinist

skgrimes.com

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OAPOli said:

I have a Copal polaroid shutter. Those press-type shutter need a cable release to operate and they are self-cocking. Practical when shooting a fixed subject like a CRT screen (or for multiple exposure) since you won't disturb the position by manually cocking. They won't work with all releases, only those with a long enough plunger.

I used a Oscillo-Raptar (used to photograph oscilloscope traces for scientific documents before computers, sort of an ancestor to a CRT lens I guess?) and even though it would cover 6x6, performance was pretty weird on full-frame digital. Since CRT screens are curved it might also make weird photos.

Click to expand...

Thank you both for the helpful information!

I'm sure you're right, it probably will make weird photos. But I have a couple of Oscillo-Lenses already, one being a Steinheil Oscillo-Quinon 75 mm f/1.9 and I feel like it makes very nice close-up images. I could show you a couple of examples, but I guess it would be misplaced here in the analog part, given that they were made on full frame digital... I also have a Mamiya lens from such an application and I find it quite impressive as well.

Dan Fromm said:

Hmm. There's what looks like a cable release socket under the aperture scale. If it will accept a cable release, attach one and press. The diaphragm might open.

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Thank you very much! I will get one and give it a try. Everything is better than those Copal electronic shutters which need a specific voltage to open. I have one of those on the Mamiya lens mentioned above unfortunately...