Mamiya c330F issue with viewfinder

[emmanuel_b1]

<p>Hi there,<br /> I just purchased a C330F almost like new.<br /> In the same time seller provided 80mm, 135mm and 180mm plus filters caps, belt, and prism like this one http://arukucamera.net/selling/MamiyaPrism02.jpg<br /> I tried my first shot with the prism, unfortunately view was fuzzy and I heard some bad noise coming from it.<br /> After disassembly I discovered a glass part moving freely inside, the visor lens.<br /> I'm not sure of the direction to reassemble it as it is convex/concave.<br /> I found that convex side on eye side should be good by comparison of accuracy with standard viewfinder.<br />But in both directions result seems almost the same.<br /> Can anybody confirm the direction of assembly?<br /> Thank you.</p>

[dhbebb]

<p>Hi Emmanuel!<br>

I have the same prism. At the rear of the prism is a rubber eyecup, which pulls off quite easily. Take this off and you can then grip the screw-thread ring with the milled edge (little teeth) and remove this. Is your problem that there is a loose round glass lens under this ring? If so, this is an eyesight correction lens which you probably don't need. Check like this - remove any correction lens and look through the back of the prism (off the camera). If you can see the edge of the picture area sharply (hold the prism up to a window light), you don't need a correction lens. Verify this by focusing the camera on something (with the prism removed). If the image on the focusing screen is sharp, it should still be sharp when you fit the prism and view through this. Even if you wear eyeglasses, it's probably better to leave out the correction lens and just wear your glasses to focus.</p>

 

[q.g._de_bakker]

David,<br>I believe the question is what side of the eyepiece lens goes up, the convex or the concave one.<br>Could you check in your prism and report back?

[dhbebb]

<p>QG, it is true that the OP is asking which way round the correction lens goes, but the answer is that he almost certainly doesn’t need it and should use the prism without it. Even he does need a correction lens, it’s most unlikely that the one that comes with a secondhand prism and that was right for the previous owner’s eyes will be right for his eyes too.<br>

The OP complains that the view through the prism with the correction lens is fuzzy, so step one is to take the correction lens out as I said and see if the view is now clear. Assuming the correction lens is necessary and is plano-convex (flat on one side, curving outward on the other), I would intuitively insert it with the flat side pointing to the rear – the only effect of inserting it the “wrong” way round would be worse edge definition, the center would be the same with the lens either way, so finding out which way to insert can be done empirically. I can’t check this on my prism because it has no correction lens in it, I simply focus wearing glasses.</p>

[emmanuel_b1]

<p>Thanks for the answers.<br>

Without anything, meaning only a hole, it was fuzzy as I explained before.<br />Without the prism, the picture is sharp.<br>

I'm a bit confused, not sure to understand that "as new" there is nothing to fullfill the hole of the eyecup.<br>

You are probably talking about a lens inserted after disassembly of the outer ring.<br>

In my case there is nothing here.<br>

I'm talking about the lens inserted INSIDE the prism after removal of the lid (4 bolts).</p>

 

[dhbebb]

<p>Emmanuel, I now understand the problem. Does your prism have any signs on the outside of being dropped (dents)? I have owned several of these prisms over the years, obviously they came from the factory as sealed units and in almost all cases stayed that way – I have a horrible feeling that yours has accident damage and has been opened by an amateur repairman, who failed to repair it and missed out some of the parts (possibly including a glass element). I have never opened up a prism and don’t propose to, but I could imagine the rear eyepiece lens was either cemented to the prism or installed in a plastic mount glued to the inside of the casing. If it’s not immediately obvious what holds the lens in place and it gives fuzzy results either way round, I would conclude parts are missing. As these will not be available except cannibalized from another prism, and as prisms seem to sell for about $55 to 60<br>

<a href="http://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=mamiya+TLR+prism&_in_kw=1&_ex_kw=&_sacat=0&_okw=&_oexkw=&_adv=1&LH_Complete=1&_udlo=&_udhi=&_samilow=&_samihi=&_sadis=200&_fpos=&LH_SALE_CURRENCY=0&_sop=12&_dmd=1&_ipg=50">http://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=mamiya+TLR+prism&_in_kw=1&_ex_kw=&_sacat=0&_okw=&_oexkw=&_adv=1&LH_Complete=1&_udlo=&_udhi=&_samilow=&_samihi=&_sadis=200&_fpos=&LH_SALE_CURRENCY=0&_sop=12&_dmd=1&_ipg=50</a><br>

(less than a repairman would charge to fix yours), I would say – buy another one!</p>

[emmanuel_b1]

<p>It is very easy to disassemble this prism, just need small screwdriver.<br>

Coming back to initial question, it was fuzzy because this small lens was uncemented and was moving freely inside the prism body.<br>

After gluing it, picture is not fuzzy, it seems workable.<br>

The only thing is the direction I have to take into account for positionning this small lens, as it is not symetrical.<br>

I decided to stick it convex side on the eye side because sharpness result on the screen was quite similar at the same distance for the same target, to the traditional view finder.<br>

If an exploded view exists somewhere, sure it will help.</p>