Bosscreen or Fresnel?

[daniel_luu_van_lang]

Hi, All

I've no more sharp eyes and my GG seems very dark, so I plan on to change it for a Bosscreen, or add a Fresnel. I'd like to have feedback from the community on the best choice. I use a Gandolfi 4X5.

Does the Bosscreen exist with "cutcorners", so that I can keep on checking the vigneting?

Thank's to all of you for your contribution to improve my knowledge!

Best regards

[thilo_schmid]

<p>Daniel,</p>

<p>depending on the focal length, applied tilt and/or shift, the

light from the

lens hits the ground glass at different angles. Apart from the

refraction within

the GG-Material and more or less scattering, the light is emitted by

the GG in

the same angle on the other side. This is why you see different

bright areas on

the GG depending on how and in  which angle you look at it.<br>

A Fresnell Lens will diffract the light in a certain angle, trying to

compensate

this. Obviously, there cannot be a Fresnell Lens to correct all

possible angles

of incidence. The visual effect on a Fresnell Lens will vary with the

focal

length and the amount of tilt and/or shift you apply. However, the

Fresnell Lens

usually provides some enhancement.</p>

<p>The Bosscreen on the other hand works primarily by scattering the

light in

all directions. Although a Bosscreen still provides maximum

brightness at the

angle of incidence from the lens. But it scatters part of this light

in all

other directions. So you usually can see something on the GG,

regardless of the

the lens and its position. The Bosscreen further provides a structure

less

surface that can be magnified beyond 10x without disturbing the image

and thus

provides the most exact way to focus. A Fresnell Screen is built with

concentric

thin circles of plastic that diffract the light inbounds. Around 8x

magnification

this structure usually starts to disturb the image.</p>

<p>Summing it up, a Fresnell Screen will provide the brightest screen

within

certain limits of focal length and/or applied shift/tilt (there even

do exist

special Fresnell Screens for lenses with shorter focal length) and

the Bosscreen

will make sure, that you can see always something, although not very

bright.</p>

<p>Regards,</p>

[matthew_runde]

Daniel,

 

<p>

 

I've seen posts talking about the high quality of screens/Fresnels

made by Bill Maxwell, though I have no direct experience with the

products. The archives list his contact info as: Bill Maxwell,

phone:(404) 244-0095, address: Maxwell Precision Optics; P.O. Box

33146; Decatur, GA 30033-0146.

 

<p>

 

Good luck.

[tedharris]

I use a Bosscreen with my Phillips 4x5 and have a fresnel on my

Horseman FA. You have an answewr that gives you some of teh

technical differences so I will stick to the emperical. Both seem

equally bright with the same lens and movements. As noted,

there is an appearance of more grainularity with the fresnel

when viewing the image through a loupe.

 

<p>

 

On the Bosscreen specifically I do not know of any with

cutcorners. Keep in mind:

 

<p>

 

The screen is a thin parafin layer in a glass sandwich and as

such requires a teeeny bit of thought and care. In extreme heat

(say extended use over 100 degrees F) it could melt. In extreme

cold (extended use at below 0 degrees F) it could have some

crystallization. I have uesd mine in some very cold conditions

and had no problems.

[frank lahorgue]

After a year's use, I replaced my Bosscreen with a fresnel by Bill

Maxwell. I don't remember ever subjecting the Bosscreen to excessive

temperature, but bubbles appeared in the wax coating in annoying

places. The Maxwell is the brightest fresnel I have ever seen. The

view is excellent even with my G-Clarons. There is a degree of

granularity but it is acceptable IMO.

[nathan_congdon]

I had Maxwell make me a special screen for my 8X10. Though this

screen is VERY positional, it provides the brightest image I have

ever seen on a GG, literally the image on the GG of a darkish corner

of a room will be subjectively brighter than the eye registers it

when looking at it directly. For 4X5, he has some "out of the box"

screens which are excellent, but will make you a custom screen in any

format. As is often the case in LF, his custom work is neither cheap

nor fast, but the results are quite amazing. I have also had

trouble with melting Boss screens, and not from leaving them in a car

in the summer, but just from walking around with them in a pack.

They are nice, but really too fragile for my taste under day to day

use.

 

<p>

 

Good luck,

 

<p>

 

Nathan

[brian_ellis3]

I've had four different Bosscreens and currently use two, one on my

4x5 and the other on my 8x10. I use them regularly in Florida in the

summer when 10 seconds under the dark cloth leaves sweat rolling down

your face. I've never had any problems even in those kind of

temperatures with bubbles or melting or anything else. If they melted

or bubbled even in that heat I doubt that he's continue using them. I

haven't used Maxwell's Fresnel screen but I had a Fresnel screen on

my Tachihara. I liked it very much with lenses 150 mm and longer but

it was terrible with a 90 mm lens. With that lens everything went so

dark in the corners and for an inch or so all around the edges that

it was impossible to compose. If Maxwell's Fresnel screen brightens

the entire image equally regardless of the focal length of the lens

then that would certainly be the way to go I would think. If not,

then I'd go with the Bosscreen.

[alpshiker]

My Bosscreen has cut corners. I use it with a removable Horseman Fresnel on my Technika. I think it's an excellent

combo, main benefits are the possibility to make extremely precise focussing, especially beneficial with darker long

lenses and the other point is that the screen remains bright and contrasty even if it is exposed to ambient light. In

comparison, my Toyo VX-125 combo goes milky white in ambient light and I can't see much. I wish I could fit a

Bosscreen on it, unfortunately it misses precise positioning by a few microns. Some tiny bubbles have appeared after

some years of use in the Bosscreen but it's not really a problem for me.

[andrea_milano3]

Bosscreen, actually Stabilix, the Dutch company which produces

Bosscreen will provide any size required on demand, with or

without cut corners (by the way, the corners are cut precisely to

check if the lens produces any vignetting, if looking trough the

cut you can see the lens opened you have no vignetting ).

Answering another entry

Bubbles can appear if the camera is exposed to extreme heat or

if the GG is mounted very tightly and if you press too hard on it

with your loupe (I can't imagine that I'd do that, but there is

always someone who does strange things), the proble is a

mechanical one the two glasses which make the Bossscreen

will tend to separate if any warping is induced, like any glass GG

or not tight fitting can give problems).

Other than that, fresnel is very annoying if you are looking outside

of the orthogonal axis.

Good luck and be patient when phoning to Stabilix to order and

specifying your product. Speak to mr. Schreuder personally and

quote my name, they know me and it might just help to speed up

the procedures. Stabilix is a somehow very traditional company

and they do not react very promtly at times.

[daniel_luu_van_lang]

Thank's to all of you for your posts, they are very helpfull! It

seems both increase the light for two stops. I think I'll purchase

the fresnel since it is easier to fit on the camera.

Good luck for your photos!