Do I need to DISASSEMBLE the New Sinar 90mm f/4.5?

[Harvey King]

Hi there:
I am new to LF format photography. Recently, I purchased a brand new Sinar 90mm w f/4.5 lens. When I was appreciating this great lens the day before yesterday, I saw a dust under the first front elements of the lens(dust is on the inner surface of the front element). It is near the center(15mm or so) and the dimension is 0.4mmX0.4mm. I am wondering if I need to take out the front element and use a brush to take it off. If yes, how can I do that? Is it a risk to do so? If I leave it as it is, how could a dust with such a size affect my image quality? Can someone give me any suggestions? I will be appreciated for your help. Thank you. :-)

[Doug Dolde]

Are you sure it's not accessable when you unscrew the front lens half? Possibly the optics are tricking you as to the location. If it's really embedded withing the lens I would return it to the dealer as that's certainly unacceptable.

[Mike Lopez]

You can just unscrew the front element and use a soft brush to get the dust off. No harm at all. If the dust is embedded, as Doug asked, send it back.

[Frank Petronio]

It will probably have no effect, but if I bought it new I'd be raising hell...

[Michael S. Briggs]

LF lenses normally consist of two cells that screw into the front and back of the shutter. It is reasonable to unscrew either lens cell from the shutter. On most LF lenses the rear cell must be unscrewed to mount the lens/shutter to a lensboard. Its probably better to unscrew the rear cell. You may find that the dust is on the inside glass surface of a cell. Even if it is on the front cell, you may be able to blow it off by unscrewing the rear cell and opening the shutter blades. Many of these wide-angle lenses have a very thin shim washer between the front cell and shutter -- be very careful not to lose or damage the washer if you unscrew the front cell. On many of these wide-angle lenses, the inner glass projects from the cell, so be careful. When you return the cell to the shutter, be careful not to cross thread the fine threads.





I recommend against disassembling either lens cell to access interior glass surfaces. You are likely to scratch the ring the holds the glass in place and likely will void the warranty. If the dust is unacceptable, I suggest returning the lens, either for replacement or warranty repair.

[Harvey King]

Hi Michael ,Frank, Mike, Doug , Thanks for your replies. Today I looked at the lens again, the dust was still there. I did separate the front and the rear part of the lens, but neither of the surface had any dust. I think the dust is not embedded in the glass. It's actually on the interior surface of the first element of the front part. To Mike, I consider it's possible to uncrew it. But I am really worring to make the things even worse. To Michael, i know that unmounting the lens is at high risk. Since nothing in the world is perfect. We may get the lens cleaned, but the limiting part may not be the lens. We may not control the dust in the air of the bellow and the dust on the film. Even if we could, when enlarging or scanning, there's too many factor that may affect our final quality. So, I decide to take Michael's suggestion, leave it on or return it. Thank you for your all great ideas. This forum is wonderful, I will be with it if it's still accessible. With regards to you all:-)