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#11
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Lens Cell Cleaning
Cheesehead wrote:
Cheesehead wrote: On Feb 9, 11:41 pm, "Richard Knoppow" wrote: If its a standard Triplet the back cell will be a single lens so there is no need to remove the glass. The front cell will have two elements. Usually in larger lenses there is a threaded back cap on the cell but it may have a retaining ring on the front which is more common for smaller lenses. If a back cap its easy to remove. The elements are clamped between concentric edges in the cell so are automatically centered. If the cap is too tight for removal with simple finger grip use one of those rubber jar grippers. It won't mar the surface. If you grip too tightly it will clamp it and make it even harder to remove. I agree with the others about cleaning but if the lens is oily the standard optical cleaner is pure acetone followed by dry isopropyl alcohol. Window cleaner like Windex may streak the lens if not followed by alcohol. The newer butyl alcohol "streak-free" cleaners are better. While ammonia is alkaline and strong alkalies can dissolve some kinds of glass there is no real danger from the very dilte ammonia in Windex and similar cleaners. If you use acetone be careful of the edge paint, if any, and of the paint on the cell because it will dissolve both. I do not recommend cleaning inside elements when in a shutter because there is too much danger of getting the cleaning fluid into the shutter, take the cell out. -- -- Richard Knoppow Los Angeles, CA, USA I'm not absolutely certain about the Geronar formula. It is reported to be a Tessar. That said, the rear should be a single piece of glass. But it is not. If it is a cemented piece, then it is not a true Tessar and the fogging may be in the cement. That would be bad. I've not found the formula out there to describe the lens. In the mean time I've been searching for a replacement rear cell. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 12:20:01 up 24 days, 20:55, 3 users, load average: 4.74, 4.81, 4.76 On Feb 9, 11:41 pm, "Richard Knoppow" wrote: If its a standard Triplet the back cell will be a single lens so there is no need to remove the glass. The front cell will have two elements. Usually in larger lenses there is a threaded back cap on the cell but it may have a retaining ring on the front which is more common for smaller lenses. If a back cap its easy to remove. The elements are clamped between concentric edges in the cell so are automatically centered. If the cap is too tight for removal with simple finger grip use one of those rubber jar grippers. It won't mar the surface. If you grip too tightly it will clamp it and make it even harder to remove. I agree with the others about cleaning but if the lens is oily the standard optical cleaner is pure acetone followed by dry isopropyl alcohol. Window cleaner like Windex may streak the lens if not followed by alcohol. The newer butyl alcohol "streak-free" cleaners are better. While ammonia is alkaline and strong alkalies can dissolve some kinds of glass there is no real danger from the very dilte ammonia in Windex and similar cleaners. If you use acetone be careful of the edge paint, if any, and of the paint on the cell because it will dissolve both. I do not recommend cleaning inside elements when in a shutter because there is too much danger of getting the cleaning fluid into the shutter, take the cell out. -- -- Richard Knoppow Los Angeles, CA, USA I'm not absolutely certain about the Geronar formula. It is reported to be a Tessar. That said, the rear should be a single piece of glass. But it is not. If it is a cemented piece, then it is not a true Tessar and the fogging may be in the cement. That would be bad. I've not found the formula out there to describe the lens. In the mean time I've been searching for a replacement rear cell. I thought a Tessar had four elements, the rearmost was a cemented doublet. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 12:20:01 up 24 days, 20:55, 3 users, load average: 4.74, 4.81, 4.76 |
#12
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Lens Cell Cleaning
On 2/12/2011 12:33 PM, Jean-David Beyer wrote:
Cheesehead wrote: I'm not absolutely certain about the Geronar formula. It is reported to be a Tessar. That said, the rear should be a single piece of glass. But it is not. If it is a cemented piece, then it is not a true Tessar and the fogging may be in the cement. That would be bad. I've not found the formula out there to describe the lens. In the mean time I've been searching for a replacement rear cell. I thought a Tessar had four elements, the rearmost was a cemented doublet. Lot of confusion in this thread.. A 210mm f6.8 Geronar -IS- a triplet. The rodenstock sales booklet at the time these were sold stated this. http://www.bhphotovideo.com/c/produc...nar_Copal.html A tessar has a cemented doublet but this lens isn't a tessar. http://en.wikipedia.org/wiki/Tessar Someone along the way may have swapped out the rear cell from some other lens into the sample he has or something odd, I have no idea. Maybe he is confusing a coating problem with fogging inside the cell? I have no idea on that either.. But the rear cell on a normal 210mm f6.8 geronar is a single piece of glass. Stephey |
#13
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Lens Cell Cleaning
Lots of snipping here................................
"Jean-David Beyer" wrote in message ... Cheesehead wrote: Cheesehead wrote: On Feb 9, 11:41 pm, "Richard Knoppow" wrote: I'm not absolutely certain about the Geronar formula. It is reported to be a Tessar. That said, the rear should be a single piece of glass. But it is not. If it is a cemented piece, then it is not a true Tessar and the fogging may be in the cement. That would be bad. I've not found the formula out there to describe the lens. In the mean time I've been searching for a replacement rear cell. I thought a Tessar had four elements, the rearmost was a cemented doublet. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 12:20:01 up 24 days, 20:55, 3 users, load average: 4.74, 4.81, 4.76 That is correct except that it is possible to have a "reversed" Tessar with the cemented component in the front. Also, some Tessar types have the iris in the front air space instead of the rear even though the cemented component is in the back. However, the Geronar is a Cooke Triplet, a three-element, air-apaced lens with no cemented surfaces. Its of high quality and such lenses are capable of good performance at moderate stops. -- -- Richard Knoppow Los Angeles, CA, USA |
#14
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Lens Cell Cleaning
On 2/13/2011 3:22 PM, Richard Knoppow wrote:
However, the Geronar is a Cooke Triplet, a three-element, air-apaced lens with no cemented surfaces. Its of high quality and such lenses are capable of good performance at moderate stops. From my use, it's a very nice lens given a bad rap mainly because it was sold at a low price as a "novice lens". Who wants that when you can buy a pro lens? :P It's multicoated, comes in a modern, reliable shutter and is small/lightweight. It actually folds up in my super graphic. Given most LF lenses are used around f22, the wide open edge performance isn't an issue for most people. I've actually done some portraits with mine on 4X5 at f11 and they look great. The only disadvantage I see with this lens is the smaller image circle compared to the much Larger/heavier/more expensive plasmat types. If I had to choose this over some vintage lens that has questionable coatings and flaky/ancient shutter, I would get this one in a heartbeat. Stephey |
#15
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Lens Cell Cleaning
On 2/14/2011 8:37 AM, Cheesehead wrote:
Thanks all. It looks like my understanding of this lens is in error and that the rear cell needs to be replaced. Bummer. Honestly, you're probably better off just getting another lens. From what I've seen these don't sell for a lot of money and I'm not sure where you would even find a replacement rear cell. Maybe find one with a smashed filter ring or damaged front element (so you can use the one you have) if you are looking for a cheap way out? Stephey |
#17
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Lens Cell Cleaning
On 2/14/2011 5:37 AM Cheesehead spake thus:
Thanks all. It looks like my understanding of this lens is in error and that the rear cell needs to be replaced. Bummer. Whoa just one second. Before you toss the lens, let me bug you just one more time. It seems to have been established that that rear cell is a single element, not a cemented doublet. In which case any fogging would actually be on the surfaces(s) of the cell, not internal. What did you use to clean the lens? Maybe you need to try something stronger, like acetone, which can dissolve just about any kind of crud. Might be worthwhile, even if, as others have pointed out, the lens is not that great: at least you'd have something to shoot with in the meantime. -- The phrase "jump the shark" itself jumped the shark about a decade ago. - Usenet |
#18
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Lens Cell Cleaning
On 2/14/2011 2:32 PM, Thor Lancelot Simon wrote:
In , wrote: From my use, it's a very nice lens given a bad rap mainly because it was sold at a low price as a "novice lens". Who wants that when you can buy a pro lens? :P Well, at least in the 1990s when the question arose for me, it was more like "who wants that when you can buy a nice clean used Commercial Ektar"? I actually replaced a "nice clean" commercial ektar of the same length with this lens and got much better results at my shooting apertures of f16-f22. Maybe my sample was a bad one but the geronar has much higher contrast and "snappyness" to the pictures, especially in difficult lighting. Add to that a much better shutter, I don't think I'd want 50 year old lens with marginal coatings in one of those old supermatic shutters over this one. Like I said, this lens gets a bad rap and I suspect most of the people saying this have never tested or even used one.. |
#19
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Lens Cell Cleaning
On 2/14/2011 3:57 PM spake thus:
On 2/14/2011 2:32 PM, Thor Lancelot Simon wrote: In , wrote: From my use, it's a very nice lens given a bad rap mainly because it was sold at a low price as a "novice lens". Who wants that when you can buy a pro lens? :P Well, at least in the 1990s when the question arose for me, it was more like "who wants that when you can buy a nice clean used Commercial Ektar"? I actually replaced a "nice clean" commercial ektar of the same length with this lens and got much better results at my shooting apertures of f16-f22. Maybe my sample was a bad one but the geronar has much higher contrast and "snappyness" to the pictures, especially in difficult lighting. Add to that a much better shutter, I don't think I'd want 50 year old lens with marginal coatings in one of those old supermatic shutters over this one. What do you mean, "marginal coatings"? Do you think they flake off or something? Sorry, but it sounds to me as if you've bought the marketing hype hook, line and sinker when it comes to "advanced, space-age" coatings. The only "marginal" here is that modren coatings are marginally better than the old ones. Hell, even *uncoated* lenses (horrors!) can perform extremely well (under certain conditions). -- The phrase "jump the shark" itself jumped the shark about a decade ago. - Usenet |
#20
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Lens Cell Cleaning
On 2/14/2011 8:52 PM, David Nebenzahl wrote:
On 2/14/2011 3:57 PM spake thus: On 2/14/2011 2:32 PM, Thor Lancelot Simon wrote: In , wrote: From my use, it's a very nice lens given a bad rap mainly because it was sold at a low price as a "novice lens". Who wants that when you can buy a pro lens? :P Well, at least in the 1990s when the question arose for me, it was more like "who wants that when you can buy a nice clean used Commercial Ektar"? I actually replaced a "nice clean" commercial ektar of the same length with this lens and got much better results at my shooting apertures of f16-f22. Maybe my sample was a bad one but the geronar has much higher contrast and "snappyness" to the pictures, especially in difficult lighting. Add to that a much better shutter, I don't think I'd want 50 year old lens with marginal coatings in one of those old supermatic shutters over this one. What do you mean, "marginal coatings"? Do you think they flake off or something? Sorry, but it sounds to me as if you've bought the marketing hype hook, line and sinker when it comes to "advanced, space-age" coatings. The only "marginal" here is that modren coatings are marginally better than the old ones. Hell, even *uncoated* lenses (horrors!) can perform extremely well (under certain conditions). I guess you missed the "difficult lighting? And yes those early coatings were good, just not as good as later ones. And yes I do use uncoated lenses too so understand your point here. In tough lighting the ektar created low contrast chromes. I didn't make this judgment based on marketing. I wouldn't have bought a geronar at all if I wasn't having issues with the commercial ektar of the same length. I have a 135mm WF ektar and the images it makes are nice and crisp compared to the ones I was getting with the comm ektar, hence I looked for a replacement. I have never considered replacing the 135mm WF ektar, it works just fine so don't thing older coating are rubbish. Sorry if posting that -in my experience- this "novice" lens performs much better that my old commercial ektar did- rocks the boat of people who are sold on those old lenses are somehow some sort of religious experience. I could see nothing wrong looking at the commercial ektar, maybe it was a bad one? I can only base this on my experience. It was a -sharp- lens but didn't have the contrast/snappyness this geronar has. So to say "-Blank- old lens is a better choice" didn't work out for me. Stephey |
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