norman_valentine Posted March 20, 2010 Share Posted March 20, 2010 <p>I have a Fuji GW690 and wish to replace the front lens group. I bought a brand new front lens group that was advertised for the GW690II but as they are both fitted with an EBC Fujinon 90mm f3.5 lens I thought that it might be worth the chance. I tried a rough and ready test by photographing a newspaper at 6ft. The new lens assembly produced a much less sharp image. Could this just be a matter of shimming the lens or have I got the wrong parts? If it is a matter of shimming how best should I proceed? Thanks for any advice. Norman</p> Link to comment Share on other sites More sharing options...
akocurek Posted March 20, 2010 Share Posted March 20, 2010 <p>Have you tried photographing something at an angle to see where it's focussing to make sure that just the focus is off?<br> Those cameras shipped with a frosted piece of plastic to use as a ground glass with the back open. You might be able to use that to see at what point it's focussing on.<br> Good luck.</p> Link to comment Share on other sites More sharing options...
norman_valentine Posted March 20, 2010 Author Share Posted March 20, 2010 <p>That's a good idea to check whether it focusses at all. Will screwing the lens element in or out affect the focus?</p> Link to comment Share on other sites More sharing options...
akocurek Posted March 20, 2010 Share Posted March 20, 2010 <p>As you focus from infinity to near, the lens moves away from the film plane. I've never taken that camera apart, so I don't know how any adjustments can be made.<br> After looking at your first post again, I realized that maybe you only replaced some of the elements, right? I don't know, then. I think they are supposed to be precisely aligned.</p> Link to comment Share on other sites More sharing options...
norman_valentine Posted March 20, 2010 Author Share Posted March 20, 2010 <p>that's right, I only replaced the lens group in front of the shutter. What I am really asking is the spacing between the front and rear groups critical?</p> Link to comment Share on other sites More sharing options...
david_mcniven Posted March 21, 2010 Share Posted March 21, 2010 <p>Hi Norman, yes, the spacing is critical.<br> Usually one uses a focus screen at the film plane for checking focus settings, setting rangefinder etc.<br> Cut a piece of clear plastic sheet to size - it has to sit on the film rails - sand one surface randomly with around 1200-grit wet-and-dry paper, available anywhere cars are sprayed or from their suppliers.<br> If you have access to a digital caliper gauge you could measure & compare the dimensions of the cell housings.<br> What was wrong with the original front cell? If it's sharper than the new one then I guess it just has a scratched front element or fungus?<br> It may be possible to swap just the front element if scratched, or all if fungus is the problem, into the old cell housing if the new one is different.</p> Link to comment Share on other sites More sharing options...
norman_valentine Posted March 21, 2010 Author Share Posted March 21, 2010 <p>There is nothing wrong with the original front element. There is a filter stuck on it and I fear damaging the front element as I will have to use force to remove it. I found this new front group at a good price and thought that it might be good insurance.<br> I think that I will have to make a ground glass to check the focus.</p> Link to comment Share on other sites More sharing options...
david_mcniven Posted March 21, 2010 Share Posted March 21, 2010 <p>Strap wrenches come in small enough sizes to remove filters from most lenses. You need two, used in opposition - one on the filter, one on the lens. But only on the FRONT of the lens body, right next to the filter, otherwise the lens may be ripped apart. Tiny screws hold lens sections together and are safe enough in normal use but may not withstand the force required to remove a jammed filter.<br> There are dedicated filter wrenches for sizes too small for strap wrenches. I find that they slip - to prevent this I first stick double-sided adhesive tape around the filter and the FRONT part of the lens. Separately of course :-)<br> Never hold a lens in even a soft-jawed or padded vise - the housing would be compressed and the force would be transferred to the glass - an element could easily shatter without warning.<br> A nylon hose clip of the right size (or a Jubilee clip) with double-sided tape on the filter ring may give you enough purchase to remove it by hand. Cheap so worth a try. Or double-sided tape and an old fan belt from a car. Anything that will add grip.</p> Link to comment Share on other sites More sharing options...
norman_valentine Posted March 21, 2010 Author Share Posted March 21, 2010 <p>I've already tried filter wrenches and it is not possible to put enough torque into it. I plan to try to destroy the filter but I fear damaging the front element, hence the new front group.</p> Link to comment Share on other sites More sharing options...
david_mcniven Posted March 21, 2010 Share Posted March 21, 2010 <p>If you have a vise clamp a flat bar horizontally and edge uppermost which is longer than the filter is wide. Or a steel sheet 2mm.+ G-clamped to extend a little over a table's edge. File 2 slots for the bar in the filter frame (at opposite sides) and use the bar as a "lens key" by rotating the lens against it, with a strap wrench if necessary. I've never had to do it this way because strap wrenches have always worked. Sometimes I used lens keys in the vise for stiff locking rings though for safety of the glass.</p> <p>The only lenses from which I ever cut filters were those of such value that their filter threads had to survive with no more damage than had already been caused by the crossed thread, so forcibly unscrewing wasn't an option. Strap wrenches/double-sided tape would have worked but may have marred the finish of the dressed thread. Most people chose the cheaper solution of a permanent filter adapter.</p> <p>First you need to break the filter glass with no possibility of the tool hitting the front element. A simple solution would be a hard nail in a drilled hole through a block of hard-ish wood or thick MDF sitting on the filter's outside frame. The length of the nail should be measured to reach the filter + 0.5mm. and no further when the nail head reaches the wood and stops. The nail should strike the filter glass close to the frame where the lens is furthest away. A light tap should do the job.</p> <p>After removal of the broken filter glass protect the lens. Thick card is better than nothing. Two cuts in the filter frame about 1/4 inch apart and almost reaching the lens thread may let you use snipe-nosed pliers to twist the 1/4 inch tab you've made and thus reduce the frame's diameter enough to remove it. Depends on how thick the ridge/step is that the filter glass sits on. Try turning the filter with the pliers while twisting.</p> <p>If the ridge is too thick to twist the tab (but try the filter wrench/tape again) then it has to be cut or thinned adjacent to both existing cuts. If the tab broke cut another one.</p> <p>A Dremel tool using the side of a 2mm. dia. cylinder burr is best, drills slip easily. Work centre to edge, not front to rear & don't go deeper than necessary to twist the tab you made.</p> <p>These are, with only a little simplification, the methods I used over 20 years ago before I built various special tools and they always worked for me.</p> <p>Good luck.</p> Link to comment Share on other sites More sharing options...
rob_hale1 Posted March 22, 2010 Share Posted March 22, 2010 <p><br /> Hi Norman,</p> <p>First things first. Unless you are like David and have spent a lot of time taking delicate mechanisms to pieces and repairing then trend carefully when following David’s plan. Have you tried one of those arthritis "Boa Constrictor" jar lid removers. They have a rubber strap and handle through which the rubber strap passes so that it can be tightened around the jar top as you unscrew or in your case the filter. These are very similar to one of the many car oil filter remover desgins. You can get them from Lakeland in England, who have a web page. I have never had a filter or LF lens elements that have not responded to this device.</p> <p>Secondly.Adrian's suggestion can be extended by marking out a ruler on the surface and a focal point. Then you will know which way and how much the focus out. You can also use it to check DOF.</p> <p>Regards</p> <p>Rob</p> Link to comment Share on other sites More sharing options...
david_mcniven Posted March 22, 2010 Share Posted March 22, 2010 <p>Hi Rob, my preferred make of strap wrench is in fact the Boa Constrictor - I've given them serious abuse over the years and never had one fail (other makes have).<br> I should have given more detail but my post was becoming tedious even to me.<br> Need to write more clearly & edit more effectively I think.</p> Link to comment Share on other sites More sharing options...
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