I have a Darlot lens, no other markings. It measures about 5 inches at about F4 and will cover 5x7 format. The front one piece lens was not a problem to remove, but the back lens I have found impossible. The lens has rack and pinion focus and the rear lens is recessed in the housing.
Any suggestions would be a great help.
Jack
The rear lenses are in a short threaded tube, there should be knurling on the edge
I've taken the rear lens off by covering the lens with my palm wearing a latex glove
and with slight pressure or more and twisting it.
Are there dents or is the barrel out of round ? That could make it next to impossible to remove
the rear lens.
Penetrating oil used sparingly and heat can break it loose, but patience is required
it took 2 days of heating and applying penetrating oil to get the lens hood ring off mine.
Or are you talking about the short threaded tube that holds the rear elements ?
How would be the best way to heat. I do not want to cause damage to the glass.
I've used a hair dryer set on high and heating the outer barrel area evenly till it's warm, working it with a latex gloved
palm and adding penetrating oil using a pin. Then let it cool by it self, repeat.
It's not a quick process, if it's really seized in there via age, it will take a few tries, and sometimes just letting it sit
overnight after applying heat and penetrating oil does it. If you're uncomfortable about applying heat, just use the penetrating
oil, apply it where the threaded lens tube butts against the barrel with a pin and let it wick into the tiny gap. PB Blaster seems to work for me.
Patience is the key.
The glass should be fine as long you you don't douse it with water to cool, the thermal shock might
crack the elements. Just set it aside and walk away.
Thanks, I have applied penetrating oil, and will try heat tomorrow. Have my son and grandson here this PM.
Will post after my try.
Threads on barrels and lens cells can be very tricky. I have eventually unscrewed some where there was no apparent damage, corrosion or dust.
One cause is that the barrel can be distorted. It may look perfectly round when the cell is still there - but, in reality, when the cell is removed it can well out of round! The barrel had been "squeezed round" to get the cell in.
I have found that, apart from following the advice above, that an impact torque, rather than a continuous torque, can do the trick.
This is easy with flanges as there are holes to allow screwing into a length of wood. Hold the brass and give the end of the wood a bash. Anti-clockwise of course!
It can be done at the edge of the lens cell as well. Most petzval rear cells have a reasonably wide edge and many have a raised ridge which gives more stability. You have to invent or modified a tool that will hold the circumferance at many places. Some of my solutions have involved adjustable oil filter wrenches, piston ring compressors and automotive hose clips! The most important things are: no localised pressure points and rubber strip(s) over the whole contact area. A lever device has to included or a place to give an impact.
I agree with Steven's solution of using hose clips (+ rubber strips). Screw tightening clips can be tightened reasonably precisely and give a solid grip when there's not much real estate to grab hold of. I recently also tried a rubber strap friction wrench, but with less success when there's not much of the housing to grab. Penetrating oil and patience worked in that case.
Cut some "grips" from an old piece of inner tube. 6X6" or so. Put a piece of 2X6 on the floor with one end anchored against something. Put one grip on the 2X6. Put the lens, glass down on top of the grip. Put the other grip on top of the barrel where the front group used to be. Now, gingerly hector, use your foot to apply a down pressure while you also torque in counter clockwise direction to get it to break loose. The rest is easy.
Thanks for all above, still no success, will let it rest for a while, then post later.
Jack
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