Someone make me a wax screen?

[Ben Winter]

I would pay someone $30 for a well-made wax focusing screen on glass with a minimum diameter of 50mm. Any takers?

[Mikko Parttimaa]

Hehe, Ben is desperate to get that good Bokeh.

The whole bokeh thing seems to be the new hot thing with these adapters now. Year ago nobody seemed to think about it, all they wanted was just DOF no matter what it looked like.

Wonder what we want next year? I place my bet on auto exposure and focus! (Can I hear every adapter designer say "oh my god he is right! Back to the drawing board then..."?)

[Andy Gordon]

From my own experimenting I think wax is not a good solution. It loses more light than you need to to get the bokeh. 1 tape layer of wax lost more light than two optosigma 1500s face to face, which lost more light than a 350 grit. Oscillating 350 grit is the way to go IMO. You may need more amplitude to hide the grain, my glass is 3mm thick so the extra weight takes care of that.

[Ben Winter]

Bokeh was always a critereon of mine, I just didn't realize how crucial it was until I realized how much I didn't like the Beattie bokeh. I think most people have, by this time, perfected their adapter and said to themselves, "how can I improve this more?" Naturally the only unconquered aspect of this quest is bokeh.

About that 350 grit, do you have a source for that Andy? Optosigma has something like 120 and then 400, and Thorlabs jumps from 220 to 600 grit. Do you think I can go with the 400 grit Optosigma?

[Andy Gordon]

I wanted a 400 opto but they were out of stock so I tried a 600. Grain on the opto 600 was worse (think due to lighter weight, smaller amplitude) but the bokeh looked about the same as the 40micron knight optical I'm now using. Here's the link:

http://www.knightoptical.co.uk/acata...GBDiameter.htm

The DGP5000.

I think 40micron is equal to 350 or 400 grit, but it seems to vary from one supplier to the next. The thorlabs 600 grit looked more like an opto 1500 bokeh (i.e. terrible).

Opto's are 2mm thick, the knight one is 3mm thick (says 3 on the package not 3.75 as on the site) so depending on your adapter you may or may not be able to hide the grain. With mine the grain is just barely visible in the bokeh if you're really looking for it. But no normal human would notice it :)

[Ben Winter]

Hows the bokeh on the 600 opto? Do the out-of-focus bright points show the aperture blades (ie a distant streetlight out of focus looks like a tiny octagon)? I might consider it if it diffuses properly.

[Andy Gordon]

Yes it varies depending on aperture. So with an f1.2 or f1.4 open you have an edge to the highlight but with a brighter area in the middle, as you stop down to f2 the blades pull in the edge as the highlight gets smaller, the edge is more distinct and the brightness of the disc is more even. Also if the highlight is infront of the focal plane it can be fuzzier than if it's behind the focal plane. Generally speaking the bokeh looks a bit fuzzy at f1.2 or 1.4, better at f2. Same goes for the 40 micron.

Your grain gets wore once you start stopping down, but mine looks ok at f5.6 and I wouldn't go past that anyway.

[Andrew Todd]

ben, i know you sold your pimped out letus, what are you working with right now?

[Frank Hool]

Bokeh is characteristic of lens. Focusing screen bokeh problem actually reduces to diffusing problem. It means You'll achieve better bokeh with better diffusing focusing screen. Just because You'll see natural lens created bokeh more clearly. Clearly - it means projected image is as little as possible mixed with lightrays going right through. Those rays are cause of hotspot and ghosting effect.
So unless you're not about breaking some basic optical rules you have to accept that fact: better bokeh(more natural - lens created) is nothing more than better diffusion and better diffusion takes more light(bigger lightloss).

[Andy Gordon]

The problem is you can't achieve full diffusion cos the gg would be opaque. With my setup the hotspot got worse as I increased diffusion, and the lens has a certain amount of light fall off you can see if you take some slr shots, so the hotspot is not just a function of gg diffusion.

[Jim Lafferty]

Just a note on what you're willing to pay: two pieces of UV grade glass costs nearly $25 alone (two UV filters); then the wax is either a request a sample situation or bought by the pound (another $15-50); then there is the cost of labor -- they're very difficult to get right, without hairs or dust suspended in the emulsion. I make a decent living at about $25 per hour at my "real" job, and you can bet making a decent screen of any kind -- wax or ground glass -- will take the better part of one hour, and maybe two (assuming you're not including research time..)

So, $30 is very low.

I can offer you a custom static screen that will give you what I think are the best results currently possible, at the moment it is fitted to 50mm tubing and is not a full frame image (the optical window is 37mm instead of 43mm), but I would offer you a trade-up as a new (full frame) model becomes available.

My asking price is $120.

[Frank Hool]

Originally Posted by Andy Gordon

The problem is you can't achieve full diffusion cos the gg would be opaque. With my setup the hotspot got worse as I increased diffusion, and the lens has a certain amount of light fall off you can see if you take some slr shots, so the hotspot is not just a function of gg diffusion.

Andy, are You talking about hotspot or vignetting. I am asking because hotspot means(for me) trace that is created from rays which going directly through gg and it's not part of the image on gg. In other words you see your photolens backglow which is round shaped. So if those rays were diffused you wouldn't see any hotspot. But vignetting part of the image on gg and caused of (too small)angle of the rays which are falling to gg.

[Andy Gordon]

I've been using the terms hotspot and vignetting interchangeably, I meant dark corners which I guess I should be referring to as vignetting.

[Ben Winter]

Originally Posted by Andrew Todd

ben, i know you sold your pimped out letus, what are you working with right now?

I have a Letus35 with rubber stoppers on the vibrating unit that have been pushed out to allow more vibration. The focusing screen is a Beattie Contax II. The achromat is a Century Optics 7+ diopter.

[Andrew Todd]

i thought you sold that thing?