|
Post by belgiumreporter on Jul 15, 2015 14:10:18 GMT -5
I,ve been buying a lot of pentaxes lately and it became a bit unclear what i had or had not. So i went through some boxes to look for what i already had, as in the past i've been a bit careless with the pentaxes. In one of the boxes i re- discovered this black spotmatic wich i've forgotten about. It is well worn, but everything still works fine (there's a slight yellowish cast in the viewfinder, could it be the pentarism is deteriorating ?).Now i know most collectors like their cameras to be in pristine condition and as a general rule so do i. But with the old black on brass cameras i must admit that a well worn one does has it's charm. After all it is showing that is used for what is was made for and probably gave it's owner(s) a lot of fun, good pictures or maybe even an income. What do you think? can a camera like this find a place in your collection and would you put it on display, or won't you give these old junkers a second glance?
|
|
|
Post by Peltigera on Jul 15, 2015 14:34:41 GMT -5
I have always preferred cameras with the 'patina' of use. Very few of my collection are in showroom condition - those are mostly newer Zeiss Ikon cameras - so long as they actually work, 'much loved' = still loved.
|
|
|
Post by John Farrell on Jul 15, 2015 23:52:30 GMT -5
The yellowish cast is most likely the lens - the F1.4 Pentax lens is known for this.
|
|
|
Post by philbirch on Jul 16, 2015 2:31:57 GMT -5
I had a Nikkormat in much the same condition as this. I didn't mind the brass but the scratched paintwork irritated me a little. So I polished it with Brasso wadding all over. This had the effect of smoothing out the paintwork and shining up the brass. Worn but nice.
|
|
Stephen
Lifetime Member
Still collecting.......
Posts: 2,718
|
Post by Stephen on Jul 16, 2015 5:33:40 GMT -5
Personally I would not say the Pentax 1.4 has a colour "cast", it has warm colour balance, not really noticeable till side by side shots are compared, when it is easy to sort out slides taken on a Pentax from Nikon. Pentax made several versions, trying to keep costs down, reducing the element count from 8 to 6, I think. If the cast is visible in the viewfinder, then the mirror may be the culprit, although silvering can go on the prism as well.
|
|
|
Post by John Farrell on Jul 16, 2015 14:21:50 GMT -5
|
|
Stephen
Lifetime Member
Still collecting.......
Posts: 2,718
|
Post by Stephen on Jul 16, 2015 15:27:30 GMT -5
Humm... sounds on the face of it to be true, (not accusing anybody!!!), but if the source was rare earth radioactivity, then why were only some lenses affected. Lanthanum was widely added to glass to alter the refractive values, but most do not go yellow. The company I worked for made lenses from scratch, and used several types of mildly radioactive glass. I checked with the owner and we got no yellowing. The suggestion it reverses with UV seems a bit unlikely, it may alter the coatings, but the base glass? It might be the Canada Balsam, (real or substitute), used as glue between the elements that goes yellow. UV at strong levels may well bleach the yellowing balsam.
Some of the links quoted are unfortunately lapsed, pity as this seems an interesting problem.
Stephen.
|
|
Stephen
Lifetime Member
Still collecting.......
Posts: 2,718
|
Post by Stephen on Jul 16, 2015 15:40:31 GMT -5
It appears the rear element of the Takumar is doped with Thorium, and is a cemented pair, and in my old bosses opinion, it is the glue that has yellowed. One reference on the net refers to the yellowing being patchy, and this must be the glue, as the glass rare earth mix is throughout the molten glass, and added early in the process.
Yellowing of Canada Balsam is well known, it occurs on old prepared microscope glasses, and old microscope lenses.
The best guess is that the mild radioactivity accelerates the ageing, but UV light bleaches the balsam.
Stephen.
|
|
Stephen
Lifetime Member
Still collecting.......
Posts: 2,718
|
Post by Stephen on Jul 16, 2015 15:54:06 GMT -5
Further delve around the net shows Leica had the same problem with Canada Balsam yellowing in some designs, which they connected with the rare earth radioactive doping of the glass. These days substitutes and improved glues are used, and the issue vanished.
Stephen.
|
|
|
Post by Randy on Jul 16, 2015 18:53:02 GMT -5
|
|
|
Post by belgiumreporter on Jul 17, 2015 3:45:53 GMT -5
Hey guys, thanks once more for your input. After checking John Farell's link it became clear to me the problem was indeed the lens itselve. now this made me worry about my other pentax gear but an older spotmatic with a 1.4 50mm was OK and didn't had any yellowing problems. The yellowing issue didn't at first occured to me as i thought the "old" 1.4's had a yellow-gold coating, with the camera's on the shelve you won't see the diffrence between a good and a bad one. Now i know you can see the actual yellowing when looking through the (detached) lens at a white surface.I'm gonna try the sun and aluminum foil trick to cure it, sadly we don't have any californian sun in Belgium i'll have to see if it works over here. The good and the bad, age dosn't seem to matter on the yellowing issue as the good one is older than the bad one. BTW, Randy, your nice spotmatic is an sp and not an sp II ( wich has an hotshoe)
|
|
Stephen
Lifetime Member
Still collecting.......
Posts: 2,718
|
Post by Stephen on Jul 17, 2015 6:19:05 GMT -5
To replace the sunlight any UV lamp will do, you could use about 10 UV LED bulbs in a pattern about 30mm diameter, feed from 12 volts via a dropper resistor for each bulb. These "black Light" bulbs are quite safe output, and dead cheap! They make little heat in operation so no need for foil wrapping, just aim the beam of UV into the lens, preferably via the back, as it is the Canada Balsam in the rear that yellows. With the UV LEDS it should take less than a week to cure it. The LEDS and the resistors are available from several Ebay suppliers.
I use a plate of 8x10 with 100 of the LED UV lamps wired to 12 volts to provide a UV source for Bichromate Printing of Black and White Negatives. The sunlight takes an exposure of 20 minutes, but the lamps do the same in about 3-5 minutes, so plenty of UV light.
Stephen.
|
|
|
Post by belgiumreporter on Jul 17, 2015 8:58:16 GMT -5
To replace the sunlight any UV lamp will do, you could use about 10 UV LED bulbs in a pattern about 30mm diameter, feed from 12 volts via a dropper resistor for each bulb. These "black Light" bulbs are quite safe output, and dead cheap! They make little heat in operation so no need for foil wrapping, just aim the beam of UV into the lens, preferably via the back, as it is the Canada Balsam in the rear that yellows. With the UV LEDS it should take less than a week to cure it. The LEDS and the resistors are available from several Ebay suppliers. I use a plate of 8x10 with 100 of the LED UV lamps wired to 12 volts to provide a UV source for Bichromate Printing of Black and White Negatives. The sunlight takes an exposure of 20 minutes, but the lamps do the same in about 3-5 minutes, so plenty of UV light. Stephen. I think i'm going to get me a facial tanning lamp, they can be had for next to nothing in the thrift shops and most likely will put out enough UV to cure the lens. I've heard they are good as well to expose bichromates, but maybe they consume some more electricity than the led solution.
|
|
|
Post by Randy on Jul 18, 2015 21:13:30 GMT -5
|
|
|
Post by belgiumreporter on Jul 30, 2015 5:38:13 GMT -5
I had a Nikkormat in much the same condition as this. I didn't mind the brass but the scratched paintwork irritated me a little. So I polished it with Brasso wadding all over. This had the effect of smoothing out the paintwork and shining up the brass. Worn but nice. Phill, i took your advice on the brass polish, the stuff we use over here is called sidol. It can give brass or copper a mirror like polish. After using it on the spotmatic the camera looked a lot better. This made me remember that once i was in a music shop in wich i've seen a vintage "surf" green fender stratocaster, in my opinion it was a pity it was so worn, the wood structure showed trough the green laquer, the scratch plate was, well "scratched" and the fret boards had definate signs of intensive use. it was cheap though, considdering how expensive vintage guitars can be. When i asked the shop owner what was wrong with that guitar, he said nothing was wrong as it was a new guitar made that way to look vintage.Some guitarist seemd to like 'em that way so they would look by the sight of their instrument like skilled players...Now i was wondering if i would go out with the spotlmatic if that would make me look like a skilled photographer ? LOL ! The scratches in the black paint are so deep i don't think i'll be able to polish them out The bottom now looks like a box of John Player Specials :-)
|
|