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Tim Povlick
12-Nov-2012, 22:04
Some questions on brass lenses.

1) If one has a lens with rear element that is 75mm diameter but the largest Packard shutter that can be used has a 2.5" (63.5mm) opening, how 'bad' is it to lose about 15mm of aperture. It seems reasonable to consider the lens has been stopped down from an f/8 to a bit more (f/10?), so not a major deal. I realize the shutter is acting as an Exit Pupil and not a conventional stop. Front mounting the shutter is out of the question due to aesthetics.

2) I assume a bare brass lens should never be polished clean as new as this ruins the patina

3) For a lacquered brass lens if there are 'many' areas of exposed brass turning dark would stripping / cleaning and re-lacquering be reasonable approach.

4) Should the Iris have a small quantity of graphite dry lube applied?

Regards,

Tim

Dan Fromm
13-Nov-2012, 08:33
1) the shutter will mechanically vignette the cone of rays the lens projects. if the shutter's opening is smaller than the cone of rays at the shutter's position, the lens' diaphragm will have no effect -- from the film's position, the lens will be wide open -- until the cone of ray's at the shutter's position is smaller than the shutter's opening.

2) don't know

3) don't know

4) never never never lubricate the iris. if the iris is tight or stuck, dismantle and clean the lens' barrel.

IanG
13-Nov-2012, 11:11
2) and 30 are a matter of judgement and the degree of tarnish or corrosion.

I've only bothered with one lens so far where the condition was terrible to begin with, and I cleaned the brass well and polished it, at some stage I'll lacquer but properly with shellac and I'll get some advice from a member here who used to do it this way professionally. At the same time I've two other lenses I'll re-lacquer as well but they need little work.

This was the optics, the brass wasn't musch but I've deliberately not over-polished the lens to make it look new:

http://www.lostlabours.co.uk/photography/cameras/images/petzval04sm.jpg

http://www.lostlabours.co.uk/photography/cameras/images/petzval07sm.jpg

http://www.lostlabours.co.uk/photography/cameras/images/petzval08sm.jpg

The only reason for re-lacquering will be to preserve the status quo. In this case the value of the lens went from the 20 ($32) I paid for it to a more respectable 200 ($320) which I've been offered but it's not for sale.

4) I have used graphite but mainly to help get rid of slight rust then it's been claeaned off only leaving a trace.

Ian

Ramiro Elena
13-Nov-2012, 11:44
In this case the value of the lens went from the 20 ($32) I paid for it to a more respectable 200 ($320) which I've been offered but it's not for sale.
Ian

25, my last offer!

:D:D:D

DKirk
13-Nov-2012, 11:50
4) never never never lubricate the iris. if the iris is tight or stuck, dismantle and clean the lens' barrel.

I've found lubrication does help, dismantle as Dan says then lubricate ONLY AT THE PINS AROUND THE CIRCUMFERENCE. Use graphite, or one of the automotive 'dry' lubricants, apply with a cotton bud or tooth pick and AVOID THE BLADES

Tim Povlick
13-Nov-2012, 21:53
Thanks for the expert advice:

Dan: I'll go for it with the shutter and live with the vignetting.

Ian: Wow! The lens sure found a good home. What a difference.
So it's a judgement between a heavy cleaning versus a full
restoration. I think you made the obvious / right choice
and the lacquer will look good. My lenses need only a mild
cleaning (comparatively).

DKirk: I was talking with Adam at S.K. Grimes about some work
and broached the subject of the iris / lubrication. His
response matches your expert opinion. Other work on
the lens is required so I will have them handle it all.
I am afraid of shearing a pin or something else bad.

Many thanks for your time and advice,

Best Regards,

Tim