flare/fog from DaYi 6x12 back

[johndc]

I am having a flare problem with my DaYi 6x12 back. More accurately, it would

described as a fog problem. But whatever you call it, it's a PITA. When using

the back without a mask (i.e. the full 6x12 opening), I get fog clouds on the

short edges of the image.

<P>For the most part, this fogging only extends about 1/4 in from the edge of

the frame, but with brighter subjects and more generous exposures it can creep

in quite a bit. There is also fogging in the empty area between the exposures,

though it appears to be from the same source/location as the in-frame stuff.

Here's a typical example (scanned on a 4990). Please ignore the atrocious color

balance.

<P>

<img src="http://www.baseplusfog.net/images/misc/img011.jpg"></img>

<P>

My best guess: when using a wide-angle lens, or with certain movements, light

passes through the 6x12 aperture of the back and strikes the stainless steel

roller, which reflects light back onto the film and causes the fog cloud at the

edge of the image.

<P>

Has anyone else experienced this, and if so, how did you solve the problem?

Anyone have any suggestions? I would really appreciate some help, because right

now, I'm just wasting film shooting 6x12 if the image edges are going to be

ruined every time. Thanks!

[brettdeacon]

I'm sorry you're having such an annoying problem John. I have the DAYI 6x17 back which is as I understand it essentially the same in construction and structure as your 6x12 back. I have a few questions/comments that will likely not solve the problem, but it never hurts to rule out the most obvious explanations first.

 

First, am I correct in assuming from your post that you notice this flare on *every* exposed frame and not just the first or last shot on the roll? I ask this because I've only ever had one fogging problem and this was due to operator error (accidentally exposing the as yet unrolled film at home when removing it from the back). In this case, only one image (of course, the best shot by far) was fogged. I'm sure this isn't the problem you're having, but...

 

Second, can you please elaborate on which specific portion of this device you're referring to as the "6x12 aperture of the back?" On my back there are only four places where light could conceivably expose the film: (a) through the lens when the darkslide is pulled, (b) through the small side slot occupied by the darkslide, © through the small frame counter holes on the rear, and (d) the connection between the 6x12 back and the view camera. Barring some construction defect or additional pathway to the film on your back, I would expect that the following problems could cause a fogging problem: (a) a light leak in your bellows or other part of your view camera, which if present would cause fogging on 4x5 film as well, (b) not fully inserting the darkslide or not leaving it in place throughout the duration of the exposure, © a light leak in the exposure counter holes on the rear of the back, or (d) an insufficiently light-tight connection between the back and the rear standard of your view camera. Do any of these seem possible, or is there some other means of light reaching the film on your back?

 

If the problem involves light striking the stainless steel roller inside the back, you could always paint it with a matte black finish and observe the effect.

[allen_whittier]

Since it gets worse with bright images I would vote for reflections off smooth surfaces between the film and the lens for the small flairs along the edges. I've even had problems like this with light reflecting off the film, hitting a smooth surface and reflecting back to the film. The lower left hand flair that intrudes deeply into the image looks like outside light. But everything else looks like reflections.

 

The last step of any DIY project is cleaning up the little problems. Check for light leaks. Check for reflections. Black paint reflects very well if it isn't textured. Put some felt around the areas that have problems to see if it helps. It can be hard to find light leeks, but to test for them take two photos in bright light; one with a dark cloth covering the back and one without. Take a photo then advance the film without taking a photo (with the dark slide removed.) Any flair on the blank image will be from the outside. Any flair on the exposed image that is missing from the blank one is from reflection. Figure out ways to test for potential problems to narrow them down to a few that offer potential for results. Test Test Test! Then enjoy the results.

[johndc]

Brett- Your assumption is correct. The problem occurs on just about every frame on every roll, in different conditions, and regardless of the orientation of the back.

 

To answer your second question: when I get a chance I'll snap a shot of the part of the back that I'm referring to, as well as the roller, to show you what I mean.

 

Allen, you've given me a few ideas about how to test. I think tomorrow I'll go out and put them into action. Particularly the idea about making an exposure with the dark-cloth over the back. I will try that first.

 

Thanks!

[thirteenthumbs]

Based on general knowledge of roll film backs and your picture, the light seals at the ends of the opening part of the back are bad and or the latch is weak. The darkslide light trap usually only causes leaks on one side. Check the top and bottom cover plates for weak light seals especially on the film gate side, Mamiya RB backs have this problem.

In a darkroom, lens and lens board removed, roll film back attached, turn off the lights and put a 40 watt appliance light inside the camera and look at the back for light leaks. Be careful not to burn the bellows by touching them with the light bulb. (Other sources of bright light can be used, point the light source at the back.)

[buje]

I had similar problems with RB67 backs. I tightened the little screws holding the aperture plate and fixed all the flare problems. Perhaps this is the same problem with your back.

[vinny_walsh]

I had the original shen hao back which looks the same as the day yi. The light trap was

bad on that one as well. I took it apart and brushed the material back into place and that

took care of the problem. I eventually sent it back for a replacement. I had problems just

like you've got.

[w_t1]

Allen, this is not a diy project, or is that what Dayi stands for? lol I haven't noticed anything like this with my 6x12 horseman back with a 90mm, but i paid extra for the engineering and QC when I bought the horseman over the chinese.

[johndc]

"I haven't noticed anything like this with my 6x12 horseman back with a 90mm, but i paid extra for the engineering and QC when I bought the horseman over the chinese."

 

That must be nice. Unfortunately, I didn't have enough foodstamps to buy the horseman.

[gerald_costello]

I have the Shen Hao 6 x 12cm back and had the same problem, a vertical line of flare just on the edges of the 6 x 12cm frame. I managed to solve it by painting the rather glossy black interior eges of the 6 x 12cm aperture with matt black enamel paint. Problem solved! These backs are inexpensive but do the job, however some of the finish leaves a bit to be desired and the flare problem is caused by the light striking off the gloss finish on the inner edges of the aperture. I also painted the edges of the masks supplied with my back and have had no further problems with flare.

[johndc]

I figured out it was the felt inside the darkslide slot. I opened it up, gave it a thorough brush-up and it's as good as new. Shot all weekend with it and no leaks. I just checked the felt again and it's okay. From now on I'll include checking the darkslide slot as a part of my monthly equipment cleaning routine.

 

Thanks to those who provided assistance!