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Evisc
Tinkerer
Username: Evisc
Post Number: 18
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 30, 2008 - 10:31 am: | 
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I recently exchanged the original focus screen on my rolleiflex 2.8e for a mamiya rb67, with split screen. I've heard that you can do this without focus issues, but I've gotten back a film now with bad focus... I have to teories as to why:
1)I mounted the screen upside down (I mounted it with the wedge protruding upwards).
2)The mamiya screen is thicker and I'm told the focus plane should be at the bottom of the screen.
What do you think?
I've heard you can adjust the focus by screwing the viewing lens. Is this hard? Can it be done with reasonably accuracy? |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 492
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 30, 2008 - 05:04 pm: |
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You mounted the screen upside down. The focusing surface, both on your original screen and on the replacement screen (which is the surface with the RF wedges) goes on the bottom.
If you have a Rolleiflex 2.8E (first series) with the hood attached by 4 screws, thickness is also a possible issue, as the screen is registered from the top surface and you focus on the bottom. However, the depth of focus of the viewing lens is about 0.2mm, and the difference in thickness between the 2 screens is probably less than that, so chances are that there is not enough focus error for you to be able to detect or adjust out.
If you have the 2.8E2 or E3, with the snap-off hood, there is NO focus error as the screen registers directly on the focusing surface and thickness has no effect. |
Evisc
Tinkerer
Username: Evisc
Post Number: 19
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 31, 2008 - 03:36 pm: |
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It appears i didn't mount the screen upside down. The wedges protrude on both sides of the sides,and the side with the fresnel lens was facing downward.
I did a backsighting of the viewing lens set to infinity. The wedge and the surrounding frensnel-free matt screen appeared to be out of focus. I guess this means I will have to do a adjustment of the focus of the viewing lens.
Is it enough to test focus at infinity? |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 495
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 31, 2008 - 08:04 pm: |
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I repeat: If the Fresnel side of the Mamiya screen is facing downward, you have installed it upside down. The Matte focusing surface (which also has the split-image rangefinder prisms) goes on the bottom, the Fresnel rings go on top.
It is enough to test focus at infinity. If you really prefer having the screen upside down, you can adjust the viewing lens to permit it. But you will save yourself a substantial amount of trouble if you will just flip the screen right side up and put it back in. |
Evisc
Tinkerer
Username: Evisc
Post Number: 20
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 01, 2008 - 01:30 pm: |
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Of course you are right. Flipped the focus screen, but still did some adjustment.
Did a comparative backsighting of both lenses and they seem to match up.
There still is a problem with the focus at infinity. I'm thinking maybe the focus knob may be in the wrong position.
How do I go about fixing this? How can I release the focus knob to get access?
Thanks! |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 497
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 01, 2008 - 04:42 pm: |
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I've never done that adjustment on an E model - in many cases, the end face of the focus knob unscrews and you find a nut underneath, which when loosened will permit the outer shell to be relocated to set the infinity stop. If you look at the "Repair Manuals" section on this site, you will find a set of Rolleiflex service manuals which should at least have an exploded view drawing to show you how the knob is constructed. I've downloaded them but don't have them handy at the moment. |
