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Sapata
Tinkerer
Username: Sapata
Post Number: 10
Registered: 12-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 04, 2011 - 06:28 pm: | 
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Hello,
I have a nice Rolleicord and I noticed that when focusing at the infinity the image on the viewscreen isn't really sharp so I decided to open the front panel to get access to the viewing lens.
The way I'm doing is by setting a laptop on the floor with the room in low light, open a website where I can see texts like a online newspaper for example, (control + and you zoom in the caracters at desired size) I then put a measure tape on the floor starting from the laptop screen and place the camera on the top of the tape at a certain distance, let's say 1.0 m to start.
I turn the knob at 1.0m and focus the image by rotating the viewing lens and looking through the viewfinder until Iget the image focused, In that way I have the image sharp at 1.0m exactly as shown on the knob.
I do this at different distances to make sure everything is alright and that's pretty much the way I fixed my Yashica and my Lubitel, but I'm struggling to fix my Rolleicord!
I set the focus at the minimum distance and get the correct focus but as I go further with the camera and try different distances the knob scale won't match ! let's say I measured 1.20m, the knob will show 1.50m. At 2.30m measured with the tape the knob will show me 5.0m and I haven't got a clue why... any suggestions would be much appreciated ! |
Scott
Tinkerer
Username: Scott
Post Number: 158
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 04, 2011 - 07:14 pm: |
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Not sure why the knob markings seem to be off, but how often do you really check your knob when you are focusing on a subject?
Anyway, what's important is that the image on the ground glass is focusing at the same distance (from the subject) as the image at the film plane. What distance is indicated on the knob is not all that consequential.
The way I do it is to use a long table, set up a target about 6 feet away (like a laptop), focus the camera by checking the image at the film plane with a loupe, then turning the viewing lens for maximum sharpness on the ground glass. |
John_s
Tinkerer
Username: John_s
Post Number: 56
Registered: 07-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 05, 2011 - 08:02 am: |
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What Scott said, you do need to make sure the taking lens is set correctly as well as the viewing lens. I usually tape a piece of white plastic bag or similar in the film plane to see the image.
Also you should be measuring the distance from the film plane. If not, for example if you measure distance from the lens, as you have started from a short distance of 1.0 M there could be errors which increase as you focus to longer distances. It might be better to start with an intermediate distance say 3.0 M and work back towards the shorter and longer distances. |
Mareklew
Tinkerer
Username: Mareklew
Post Number: 232
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 05, 2011 - 11:43 am: |
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Now, just to add to this...
Every precision instrument is made to be adjusted in some way, as there are no absolutely precise manufacturing methods and it is usually cheaper to make something roughly right and adjust it afterwards to a higher standard. 'Roughly' might mean finish tolerances of 0.1mm (0.005"), in optical terms it's rough, but for machining die-cast body it is rather precise already.
Since adjustments are also costly, most devices is designed so, that a chain of operations has to be followed or else later adjustments will throw earlier adjustments off and you end up chasing your tolerances around ad mortum defecatum.
Now, for a twin lens camera there are several critical tolerances that need to be somehow brought together:
1) taking and viewing lenses should have identical focal length (and that, at all apertures of the taking lens).
2) The focus distance should agree with the focusing scale indication
3) The focus on the focusing screen should agree with the focus on film
4) Preferably the camera should not focus past infinity.
The normal sequence that is to be followed is described below.
Point #1 is a disaster for a repairman, because you can't really adjust focal length after the lenses are cut, so only the manufacturer can select matched pairs out of manufacturing batches. Hence, if you buy a camera with mis-matched taking and viewing lens, you are in.
But let's assume your taking and viewing lens are original pair, matched as good as it gets, you still have the focus shift related to aperture that makes absolute adjustment impossible. Keep this in mind and do adjustments with the taking lens slightly stopped. From own observations, f:4 should do for a nominally f:3.5 lens.
There's the balance between focus shift and increasing depth of field that will hide it, so you want to get the first step off the curve.
Okay, but this is a rant, as optical elements cannot be adjusted at home. Now, the mechanical part can.
These cameras are not built randomly, there's an idea how to adjust them behind it.
Step 1: let's hope you don't need it:
Make sure the lens plate is parallel to film rails. This should never need to be corrected, as either the plate is shimmed or the supports - ground at the factory. Unless the camera fell face down on a pavement or somebody disassembled it carelessly this should never need attention.
Step 2: With the shutter assembled and the taking lens installed the infinity stop on focusing knob is adjusted so, that taking lens at f:4.0 or so focuses infinitely distant target sharply onto the film plane. Use a (preferably glass) ground matte screen for this. Don't use soft plastic items as roughed plastic ruler etc. The exact planar surface is critical for accurate focus.
On some cameras the distance scale can be adjusted separately from the infinity stop, the scale gets adjusted for a target 2m away from the focusing plane (or at a distance closest to and greater than 2m that is precisely marked on the distance scale). Why 2m? For a camera with about 80mm taking lens and minimum focus distance of about 1m the 2m setting is close to the middle of the focusing scale, so the error will be least across the distances. Remember, that distances are counted from the film plane (close to the back wall of the camera) and not from the lens.
Step 3: AFTER the taking lens and focusing knob were made to behave, the viewing lens is adjusted for a target at 2m distance. Reason same as above. Then focus for close and distant objects should be checked, focusing screen and film plane should match. If not, something went wrong in the process of adjustment.
Readjust the viewing lens at infinity and check 2m and 1m distances. If they are still off, your optics may have a problem (e.g.: your taking lens halves are not seated properly in the shutter assembly).
Marek |
Sapata
Tinkerer
Username: Sapata
Post Number: 11
Registered: 12-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 05, 2011 - 05:27 pm: |
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Thanks Scott and John for your feedback...
Marek, that's quite a lot information and I really appreciate. I'll make sure I'll follow the 3 steps as soon as I have some time off again and post the results.
Many thanks!
Mauricio |
Sapata
Tinkerer
Username: Sapata
Post Number: 12
Registered: 12-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 11, 2011 - 06:22 pm: |
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I got the first results from my Rolleicord after adjusting the view lens, the taking lens is spot on when I checked so I didn't have to do anything.
I'm still not 100% about it and I'll probably do another test but there's something that I wanted to ask and hope is not a stupid question. I have taken two identic shots ( landscape at infinity) and one them is sharper than the other, the sharpest were taken at F32 and that obviously explains, but the one at F3.5 is very soft focus in the WHOLE of the frame, I've always thought that the soft area would be around the edges and pin sharp in the midle like the results I get from my Yashica635 for example. Is this a common effect on lens from the 30's? |
Sapata
Tinkerer
Username: Sapata
Post Number: 13
Registered: 12-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 11, 2011 - 06:35 pm: |
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hope they can be seen on this examples...
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Scott
Tinkerer
Username: Scott
Post Number: 162
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 11, 2011 - 08:11 pm: |
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"...the taking lens is spot on when I checked so I didn't have to do anything."
I'm curious what you mean here. Is there some other way to adjust the position of the taking lens vis-a-vis the lens board besides using shims?
Correct me if I'm wrong, but I think only the viewing lens can be conveniently adjusted on this camera. The taking lens would not need any adjustment, as long as the viewing lens can be adjusted easily to match the taking lens.
Also, consider that the only way to make sure that the image on the ground glass is focusing at the same plane as the image on the film plane is to look at both images at the same time. |
Mareklew
Tinkerer
Username: Mareklew
Post Number: 234
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 12, 2011 - 12:42 pm: |
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Scott, if you read my post above, you will know, that although the taking lens is bolted to the lens board the infinity stop is defined usually by the focusing knob... So yes, there's a way to adjust the taking lens, but it might require you to readjust the viewing lens afterwards (not if the infinity stop was the only thing off in the system)
Sapata: yes, it is normal that the whole image gets softer. The improvement when stopping down will be most pronounced in the corners, but the center is going to be affected too.
Marek |
Scott
Tinkerer
Username: Scott
Post Number: 164
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 12, 2011 - 03:34 pm: |
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OK, different strokes, etc. I guess some people just prefer giving complex answers to simple problems.
But unless a TLR has obvious damage (like having been dropped on the street), or if it is for some reason not focusing an image across the specified range (3.5 feet to infinity), or there is evidence it has been taken apart by an amateur... then there is no reason to do anything at all to the taking lens.
Re. focus, the only thing that needs to be checked (and the only adjustment that may need to be made) is to calibrate the viewing lens to correspond to the taking lens.
Most TLRs have a simple way to make this adjustment with a set-screw or a threaded ring/collar. |
Sapata
Tinkerer
Username: Sapata
Post Number: 14
Registered: 12-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 12, 2011 - 06:34 pm: |
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"Sapata: yes, it is normal that the whole image gets softer. The improvement when stopping down will be most pronounced in the corners, but the center is going to be affected too."
Thanks Marek... one thing less to be worried, but even so I'm going to do another test, it seems that I got the infinity shots correct but the ones I took at a close distance seems slightly out of focus, but then I might even be my mistake when focusing as my first impression is that old Rolleicords are really hard to find the focus on the view glass,(the center on the viewglass is sharp and then gets blurry on the edge) different than the 60's Rolliflex or Yashica...
Thanks Scott, I just mentioned that the taking lens was ok because I had to adjust the taking lens on my Yashica, but obviously a different situation... |
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