Filter problems

Fred D Hummel · Sep 25, 2022

Just acquired a computar symmetrigon 150/6.3 to use on 4x5. I've been able to use adapter rings on every other lens I have to mount a Firecrest filter holder I bought years ago for Nikon 850, but not so with the computar. 72mm too small, 74mm too large. The Goldilocks philosophy tells me 73mm is "just right" but for the life of me I can not find a 73mm adapter ring. Need some advice:

Does anyone use a computar 150/6.3 and know the exact size of filter thread and where to find one?

Thanks,
Fred

jeffreyg · Sep 25, 2022

Fred
I can't help with your particular lens but why not consider a Lee filter holder that can hold 4x4 polycarbonate filters. You can use them on a variety of lens sizes and even hand hold them in front of your lens. Some years ago I got one and even made my own graduated yellow and orange filters using Rit dye.

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Nicholas Lindan · Sep 25, 2022

In cases like this (usually old lenses that took series filters) I would permently attach an adapter ring to the lens with a bit of epoxy. I would use a ring that would nest in the lens' threads and then epoxy it in place. One advantage - no more hunting for the adapter ring. I standardize on a few filter sizes and use adapter rings to bring lenses to heel.

Sirius Glass · Sep 25, 2022

Try Series filters with a push on adapter, no epoxy at all!

AnselMortensen · Sep 25, 2022

There are various filter holders that attach to the outside of lens barrels by thumbscrews or springs, as well as slip-on 'Series' types.
My source for filters and filter accessories is Tim at www.filterfind.net
He can most likely help you out.

AgX · Sep 26, 2022

The outer diameter of the lens-shade is given by Computar as 75mm. Then a 74mm thread seems plausible.

Are you sure your that your 74mm filter or adapter is too big, and not the thread in the shade harmed at its start, or the shade slightly bent or distorted (elliptical)?

Fred D Hummel · Sep 26, 2022

Great replies to such a minor but huge PIA issue. Fantastic forum, thanks to all.

At this point I'm likely heading towards gluing the closest sized ring to the front of the lens although it's against my nature. But heh, its not a big $$$ lens.
I am curious where AgX got the info from Computar, I looked hard but couldn't come up with it.

Thanks, Fred

AgX · Sep 26, 2022

Maybe Google was not in the mood that moment...

https://forum.grossformatfotografie.de/attachment/3361-computar-f9-lens-brochure-pdf/

reddesert · Sep 28, 2022

The fact that the brochure doesn't give a filter thread size in the mechanical specs, suggests that they didn't expect people to use thread in filters. These were originally built as process or repro lenses, not primarily intended for field use.

Sometimes what look like filter threads at the front of a lens are either the threads used to hold in the front retaining ring or trim ring, or grooves cut in the metal to aid in light baffling (breaking up stray light reflections), and will not match any standard filter. Push on or snap on filter adapters are a workable solution.

AgX · Sep 29, 2022

reddesert said:
The fact that the brochure doesn't give a filter thread size in the mechanical specs, suggests that they didn't expect people to use thread in filters. These were originally built as process or repro lenses, not primarily intended for field use.

The repro lenses I know have no shade at all.

If those Computar ones originalla actually had one, one could have made them with a shade with a standard filter thread instead, when offering these lenses to the non-repro market. Likely would have cost them practically nothing extra.

grain elevator · Sep 29, 2022

Fred D Hummel said:
Great replies to such a minor but huge PIA issue. Fantastic forum, thanks to all.

At this point I'm likely heading towards gluing the closest sized ring to the front of the lens although it's against my nature. But heh, its not a big $$$ lens.
I am curious where AgX got the info from Computar, I looked hard but couldn't come up with it.

Thanks, Fred

Nicholas Lindan said:
In cases like this (usually old lenses that took series filters) I would permently attach an adapter ring to the lens with a bit of epoxy. I would use a ring that would nest in the lens' threads and then epoxy it in place. One advantage - no more hunting for the adapter ring. I standardize on a few filter sizes and use adapter rings to bring lenses to heel.

But why epoxy, have less permanent solutions like wood glue or double sided tape failed you?

Fred D Hummel · Sep 30, 2022

Good question ! Haven't gotten to the lens yet, day 20 of covid so I'm delayed in everything. I used "epoxy" as it was used in the thread to which I was responding, but thinking about it now I'll most likely try a silicone or latex caulking first. More likely I'll start searching for a higher quality 150mm.

BrianShaw · Sep 30, 2022

Try a hot glue first. Completely reversible if it doesn’t work out.

But a replacement 150 of the plasmat variety should be easy and affordable.

AgX · Sep 30, 2022

grain elevator said:
But why epoxy, have less permanent solutions like wood glue or double sided tape failed you?

As those lenses, to my understanding, are no collectors but users items. As such filter adapting ring greatly improves usability, why not fix it decently?

gone · Sep 30, 2022

I always wrapped the filter threads a little w/ masking tape, you could probably use any sort of tape, maybe even Teflon. The filter will screw in until the tape binds, and will be pushed into the lens threads. Very secure, I've never had one get loose even w/ a big metal hood on the lens.

AgX · Sep 30, 2022

momus, the issue in this case is not the filter becoming lose and thus having to be locked, but that no standard filter thread size fits at all and thus a adapter of some kind must be fixed (temporarily or permanently) to the lens.

weasel · Oct 3, 2022

I have a lens with dented filter ring I couldnt get straight enough to hold a filter, so I bought a cheap filter of the same size, broke the glass out and used Gorilla tape to put it on. It has held up for about ten years like that, and no glue.

Filter problems

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