Saunders/LPL 4500 II - Troubleshooting Light Projection Issue

[Drew Wiley]

My favorite diffusion material is 1/16 inch "Sign White" Acrylite (similar to Plexiglas). This transmits more light than standard translucent white acrylic of the same thickness. If falloff correction is needed, this material can be ground thinner towards the corners, but that's a tricky acquired skill. So just burn in the corners and edges when using a 150, or use a longer enlarging lens like a 180 if you don't want to burn-in. No big deal.

[Sal Santamaura]

My favorite diffusion material is 1/16 inch "Sign White" Acrylite (similar to Plexiglas). This transmits more light than standard translucent white acrylic of the same thickness. If falloff correction is needed, this material can be ground thinner towards the corners, but that's a tricky acquired skill. So just burn in the corners and edges when using a 150, or use a longer enlarging lens like a 180 if you don't want to burn-in. No big deal.

A 180mm enlarging lens will not eliminate the edge falloff resulting from a uniform diffusion plate on that mixing box. The falloff would result from the enlarger's design, not cosine fourth loss of a 150mm lens.

[Michael R]

Yes very good point.

Better to just buy a new 4x5 box I think.

Note that the plastic plate on a 4500 II 4x5 diffusion box is denser in its center than at its edges. In other words, it's a "center filter" designed to even illumination on the negative. Using a uniform material to replace it will result in a center "hot spot."

[Oren Grad]

I've only ever had the 4x5 diffusion box. At least for my printing habits - I've never enlarged a full- or half-frame 35mm negative beyond what will fit on an 8x10 sheet - even the 4x5 box provides ample illumination and short printing times even for the smallest formats. So standardizing on the 4x5 box has been effective and convenient for me.

[ic-racer]

Note that the plastic plate on a 4500 II 4x5 diffusion box is denser in its center than at its edges. In other words, it's a "center filter" designed to even illumination on the negative. Using a uniform material to replace it will result in a center "hot spot."

Good point.

[Drew Wiley]

Lens falloff and uncorrected diffusion chamber falloff are additive. Technically, a different diffuser would have to be ground for each significantly different lens. Longer lenses are in fact a partial solution. So is having a well designed oversized diffusion chamber or mirror box, at the expense of more concentrated light of course. I've also used carefully crafted stainless mesh scrims inside of mirror boxes in lieu of ground diffusers. Industrial sieve mesh comes in quite a variety of very fine wire sizes. Another trick is lenticular linear arrays, a very special kind of fresnel lens. Of course, all these options can hypothetically be combined. Relatively few enlarger heads are ideal in this respect right out of the box.

[Sal Santamaura]

Lens falloff and uncorrected diffusion chamber falloff are additive...

So? The LPL 4x5 mixing box variable-density diffuser is designed to present negatives with even light. It's got nothing to do with lens falloff.

...Technically, a different diffuser would have to be ground for each significantly different lens...

Technically, given that the LPL 4x5 diffuser is a molded part that fits over / wraps around and is screwed to the metal mixing box (as seen in the second image of post #6 above), it's far fetched to think that anyone would be "grinding" any kind of replacement.

...Longer lenses are in fact a partial solution...

An enlarging lens 30mm longer than 150mm would in fact be absolutely valueless in solving the OP's problem.

...So is having a well designed oversized diffusion chamber or mirror box...

This thread is in the Darkroom Equipment category, not LF DIY. The OP's not building an enlarger. No oversized mixing box will fit inside an LPL 4500 II housing. Real world constraints must be dealt with.

...I've also used carefully crafted stainless mesh scrims inside of mirror boxes in lieu of ground diffusers. Industrial sieve mesh comes in quite a variety of very fine wire sizes. Another trick is lenticular linear arrays, a very special kind of fresnel lens. Of course, all these options can hypothetically be combined...

None of those "tricks," singly or in combination, would be of any use. The OP's mixing box is one designed for medium format negatives. There's no way to make it cover 4x5. Period.

...Relatively few enlarger heads are ideal in this respect right out of the box.

The LPL 4500 II's only "shortcomings" are that it illuminates just enough area for 4x5 negatives, frustrating those who embrace the affectation of printing rebate areas, and its 4x5 negative carriers slightly further restrict things by having a openings of only 93.5mm glass / 93.7mm glassless in their short dimension. When equipped with the correct factory mixing box, this enlarger's damn near ideal in terms of 4x5 illumination evenness.

The OP would be well advised to obtain a correct mixing box. While currently out of stock, here's one good source that should be able to provide more information on when it might once again become available:

http://store.khbphotografix.com/4x5-...-LPL55545.html

[PRJ]

I've only ever had the 4x5 diffusion box. At least for my printing habits - I've never enlarged a full- or half-frame 35mm negative beyond what will fit on an 8x10 sheet - even the 4x5 box provides ample illumination and short printing times even for the smallest formats. So standardizing on the 4x5 box has been effective and convenient for me.

Oren if you ever get a chance to buy the 35mm mixing box I'd recommend it. The print quality with the combined diffusion/condenser is great. Probably the best 35mm enlarger I've ever used. Better than my Focomat 1c even.

[Drew Wiley]

I have no intention of responding in detail to any chronic gadfly whose only purpose in commenting seems to be an attempt to maliciously discredit me and undermine anything I post, regardless of what it is. I've actually built high-performance custom colorheads, precision mirror boxes, everything I mentioned. I know what works, and am not guessing about any of this. But for most people, a bit of simple corner and edge burning-in to even out print densities is going to be an acceptable solution. Of course, all this is predicated by a properly sized mixing box to begin with.

[Sal Santamaura]

I have no intention of responding in detail...

Of course not. What can you post other than further arm-waving irrelevancies?

...chronic gadfly whose only purpose in commenting seems to be an attempt to maliciously discredit me and undermine anything I post, regardless of what it is...

I scan and pass by most of the things you post, Drew. My responses to a select few of them are submitted for the sole purpose of correcting erroneous information that new readers might be mislead into believing as a result of your know-everything-about-everything attitude and 15,000+ loquaciousness.

...I've actually built high-performance custom colorheads, precision mirror boxes, everything I mentioned. I know what works, and am not guessing about any of this...

A perfect example of irrelevant arm-waving.

...But for most people, a bit of simple corner and edge burning-in to even out print densities is going to be an acceptable solution...

The OP has a medium format mixing box. No amount of corner and edge burning-in will accomplish anything with a 4x5 negative.

...Of course, all this is predicated by a properly sized mixing box to begin with.

Of course, that's the whole point. Why do you persist waving your arms about building things, longer lenses and edge burning when the OP has a commercially produced enlarger with one incorrect part that simply needs replacing with the correct one?

Gadfly? Pot, meet kettle.