I use Apo Rodagon N's, excellent for general enlarging. But per fresnels, it ain't that easy to do it right. There are a lot of types.
I use Apo Rodagon N's, excellent for general enlarging. But per fresnels, it ain't that easy to do it right. There are a lot of types.
Drew, by now I've been playing quite with cheap acrylic fresnels in the development of my DIY 1010 enlarger. Now I see fresnels as the way that allows an efficient illumination for a big enlarger.
I agree with you that it ain't that easy to do it right, but IMHO it can be a good bet.
> There are plenty of choices to use it in 45 and 57 enlargers, because size an focal length variety, and also fresnels are easily stacked to get more choices.
> For really big enlargers there are less choices.
If you're trying to even out illumination in rectangular mirror box or light diffusion chamber, you want something called a linear array fresnel. Not cheap and not acrylic, but far better for this kind of purpose.
Drew, thanks for the tip, I've searched and there are also linear acrylic fresnels, don't think that acrylic fresnels are bad, see those used in ground glasses.
Preliminary tests I made points that I can get a a fairly even illumination by using fresnels, some mirrors and a certain degree of diffusion. I was told that a very good enlarger may be made with a modification in a condenser enlarger by including two very slightly frosted glasses in the path. Then the efficiency decreases a bit but eveness is asured. This is the way I was targeting, we'll see...
A true lambertian white diffuser like opal glass takes a terrible toll on brightness. I like a polished stainless steel mirror box with a thin "Sign White" acylic diffuser slightly above the neg carrier, and a clear linear array an inch or two above that. You can use white fome-core board to make inexpensive test mock-ups. Hard to do it perfect the first time.
The Condensor/Diffusion enlarger question has been discussed to death over the past 40 years! All you need to do is google it. Wish we'd discuss something challenging like how many angels can dance on the head of a pin.
Luis, I Googled for quite a bit on this subject, specifically as it related to graded papers. I could not find a direct answer to whether or not the contrast change was exclusive to VC, or universal, as I learned here.
I think sometimes the problem with questions that have been discussed a lot is that this also dilutes the results from Google to the point where you go cross-eyed trying to find the answer to a tangential question in the myriad number of fora and threads. Also, I was interested in learning more about the head types vs. the format, as indicated by the title. I think this has been a valuable thread for multiple reasons, at least to me.
Opal glass isn't a true lambertian diffuser by any stretch.
The closest you can get is a PTFE coated integrating sphere, which will have a 1-4% output variance depending on the port to diameter ratio.
Anything you can do to get close to the design of an integrating sphere will help you, and a piece of opal flashed glass isn't on the path to Lambertian utopia. Hollowed out box flocked flat white on the inside is a good start to a poor man's integrating sphere.
Newly made large format dry plates available! Look:
https://www.pictoriographica.com
Read the Zone VI workshop or the Newsletters. There is a link in a post for Fred’s newsletters on the forum. Sorry sometimes I forget that something that is obvious to me is worthwhile to someone else.Originally Posted by Corran
There were also some very good links and discussion had on the first couple pages before the devolution into semantics of acrylic.
Yes, a lot of "obvious" stuff is not very obvious to us younger folks, and paper costs these days mean I'm not super eager to spend a box to test stuff that's already been tested.
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