Mamiya RB-SD 6x8 top of frame does not have a crisp edge

[tkamiya]

I seem to have found a bit of an odd behavior on new-to-me Mamiya RB-SD with 6x8 power back.

I took several test shots with this setup with back in PORTRAIT position. As you know, 6x8 is only supposed to be usable in portrait position, and not landscape. As this is an SD model, all of the bodies in market are supposed to be 6x8 capable. The light buffle does NOT have "8" on it but it was confirmed with Mamiya itself (I called) that it isn't supposed to be labeled as such and all SDs are already equipped with light baffles capable of this format.

Looking at negative, all frames have one problem in common. All edges have the crisp border EXCEPT for the top of the image - which is bottom of the camera. The top edge has soft of a soft border. Thinking something may be lose and obscuring the light path, I looked inside. Nothing is obviously lose, misaligned or missing. This top edge of the image sort of look like when (printing on enlarger) you get too close to the image edge that border created by neg carrier falls inside the blade of easels. When this happens, it creates not crisply defined border. Images look just like that.

I know this 6x8 capability on RB is sort of an after-thought by Mamiya. Is this how this was implemented and it's the way it is? Or do I have a problem?

I know we have people on this board who uses 6x8 back... If you do, I'd like to hear from you.

 

[tkamiya]

Here's a sample image. Please note, top of the image (left side) has a border that is not sharply defined. This image is EXACTLY 7.5cm long.

 

[Oren Grad]

I don't have the RB 6x8 back, but I did spot this discussion:

http://www.flickr.com/groups/mamiyarb/discuss/72157594268266797/

About halfway down the page, poster Mark Colman raises the fuzzy edges question.

 

[tkamiya]

Yes, I've seen that thread. I know this is a common issue when one adopts non 6x8 ready body to a 6x8 back. In my case, SD is already capable of this back.

I'm looking for someone who has this combination.

 

[Andre Noble]

tkamiya,

I have that combination too. I believe it (soft edges with 6x8 back) is normal. There is an chart that comes with said Mamiya RB 6x8 back showing the long dimension of the image area VARIES according to actual lens in use and focal distance...

Sometimes with 6x9 back you will also get dark, round corners. This is due to filter vignetting.

 

[Marc B.]

Another thought. Correct me if I'm wrong.
Does the fuzzy edge correspond with the slot for the dark-slide edge...yes?
Could this be a very uniform, and ever so slight, light leak from the dark-slide slot?

Marc

 

[tkamiya]

Andre,

Thank you. I don't have that chart you mention but I have found (today) RB-SD brochure that basically said the same thing. You have a 6x9 back? Thanks!

Marc B,

Yes, it does correspond for the dark-slide side. No, it's not a leak as the "fuzzy" fades to clear, not black. Clearly an obstruction of some sort.

 

[paul ron]

I'm just taking a shot in the dark... but can it be the tension of the film or the roller is not properly adjusted at that point?

Have you looked at the film mask n gate to see if the film is laying flat or falling off as it seems to look in your picture?

.

 

[tkamiya]

Have you looked at the film mask n gate to see if the film is laying flat or falling off as it seems to look in your picture?

I just tested with my test film. YES, it is flat viewed from the film gate.

 

[paul ron]

ummmmm.... well how about exposing one frame without a lens... or even takle the back off the camera? If the fuzzy edge is gone, then it is the baffle interfearing.

 

[Andre Noble]

I should have wrote: Sometimes with 6x8 back you will also get dark, round corners. This is due to filter vignetting. not 6x9 back

 

[tkamiya]

I feel better now that I've seen the notation in Mamiya literature you've pointed out. Kind of a poor implementation I think. I just ordered a 6x7 back.