Beattie screen on Arca 69

[James Winspear]

Hello,

Has anyone had any experience using a Beattie intenscreen on an Arca Swiss F-Line Metric camera, say with wide angle lenses? As I'm looking at possibly buying one, but at £270 inc vat I need to find out if they are worth the cost. On Morco's site in the Uk they say that the screens can give you up to 5 stops extra brightness.....?

(http://www.morco.uk.com/latest/beattie.htm)

Thanks,

James:

[jotloob]

James

That sounds very interesting .
I work with an ARCASWISS 6x9 METRIC (+ORBIX) and always found the ARCA screen very dark .
Who would be able to mount the screen ? ?

Jürgen

[Emmanuel BIGLER]

5 stops extra brightness.
5 stops, 32 times more brigthness, and without any electronic image intensifier ?
Well I wish I could measure such a gain of 5 f-stops by simply changing a ground glass, but I doubt !

[jotloob]

Emmanuel

Could you think of any other way of improvement ? ? ?
I doubt 5 stops as well .

Jürgen

[Brian Ellis]

I've used a lot of screens including a Beattie. It did brighten things up though I don't think by 5 stops. They must get that number by starting in a dark room and then turning on the lights. I thought the Beattie shared the faults, in varying degrees, of most Fresnels - brighter but grainy and somewhat difficult to focus, plus darker especially around the edges when you move your head from dead center.

If you're going to spend that kind of money check into a Maxwell. I don't know what they'd cost where you're located but they do an outstanding job. I think it's generally agreed by those who have used them that they're pricey but the best on the market. Certainly that's what I thought. Another alternative that IMHO is better than the Beattie is the BosScreen, made in the Netherlands.

There have been a lot of discussions here about various "bright screens." Sarch using the names Beattie, BosScreen, Maxwell, and Fresnel and you should find a lot of information.

[James Winspear]

I think that the claims made on their website may be a little over-egged, but possibly around 2 stops which is still quite a lot. I shoot (when I'm working) quite a lot of interiors for retail design clients and using the Shneider 38mm xl find the image on the ground glass always very dark. I wish there was away to try out the Beattie screen before spending £270 on it........?!! : )

[James Winspear]

Thanks Brian,

I'll try that.

Cheers,

James

[Dave Parker]

I would say, 5 stops is a pretty optimistic claim, I have used Betties in some of my medium format cameras and I would say 2 stops maximum increase.

Dave

[Emmanuel BIGLER]

Could you think of any other way of improvement ? ? ?

Well, there are several non-trivial but fascinating intricate issues in the question of the best possible ground glass for view camera use. I hope the group will forgive me for a very long technical message.

The first issue is the brightness of the image. Well, ideally, the brightest "screen" would be a plain transparent glass with a reticle ; in other words looking at the aerial image with no diffuser of any kind. Cannot be brighter.
Except, (and now I am not kidding) if you abandon the direct optical focusing method and use a digital back in live-video mode. Then the screen of your laptop combined with the sensor & electronic system is equivalent to an image intensifier. You could even imagine an automatic correction of light fall-off in the corners, etc.. "Focusing" only on a computer screen is now a method used routinely for studio work. However, many architecture photographers working outdoors (as far as I have discussed with some of them in France) seem to be still reluctant to abandon direct optical focusing & framing at the expense of being dependant on batteries & bulky equipment.

The kind of plain glass screen for aerial image framing was supplied as an accessory for medium format camera systems, mostly for macro use, but was also routinely in use in some optical instruments or process cameras where no tilts & shifts were ever needed.
Focusing on a plain glass with a reticle is a challenge, it can be achieved by the so-called parallax method where you move your eye and look how the aerial image moves with respect to the reticle engraved on the (non-ground !) glass...
For this you need a loupe: the problem with the aerial image is that you cannot prevent your eye to accommodate on the exit pupil of the lens i.e. the image of the iris seen from the back of the camera, a very bright circle. So your eyes switch to this bright object and cannot see the (relatively faint) aerial image except through a loupe where the exit pupil is "off-limits" with respect to where the eye can accommodate. Also, even if you can look at the aerial image, you'll only see a small section of it defined by the cone of rays between the exit pupil and your own pupil. So you loose the interest of the global image view, one of the most interesting feature in photography, in all formats !!

[OFF-TOPIC]
However, plain glass screens combined to a Fresnel lens were in use in the fifties and sixties in certain 35mm reflex cameras like the Zeiss Ikon Contaflex and the Voigtländer Bessamatic. You had to use either the split-image rangefinder or a micro-prism ring to properly focus, at the centre of the image. But the image was examined only through an fixed eyepiece and of course there was no possibility of shifts+tilts. So this is not practical for view camera use.
[/OFF-TOPIC]

The second issue, if you abandon the idea of looking at the aerial image is how a sharp image will "jump" into focus when you manipulate the focusing knobs or some kind of helical rings.
Improved modern bright screens are supposed to deliver a better trade-off between general brightness and how easily you find the proper focus. On this aspect, some old-timers using the Rollei 6x6 TLR and well trained to the old (and dark) ground glass find some bright screens not so easy to use since the proper plane of sharpness might not "jump" so easily. There comes some personal preferences, since we are entering into physiological issues. People with an excellent eyesight focusing a modern & sharp view camera lens will no be annoyed by a darker image if the image has a good contrast. The key point here is to protect your eyes against stray light, several solutions exist besides the traditional dark cloth. Personally I'm happy with a binocular viewer, hence so far I've not found the need for brighter screen.

The third issue, somewhat de-correlated from the previous, is the uniformity of brightness from the centre to the corners, the problem being exaggerated by short focal lengths. In a visual optical instrument like a microscope or a pair of binoculars, you are not allowed to move you eye in front of the eyepiece so the designers will send a maximum of usable rays into your pupil. They achieve this by a so-called "conjugation of pupils" i.e. the exit pupil of the instrument should be located exactly where you place your own human entrance pupil. Place a piece of paper a few mm behind the eyepiece of your binoculars and you'll see a small illuminated circle, this is the exit pupil of the instrument, actually this is also the image of the entrance lens diameter seen through the eyepiece, this is where you should place your eye. The final image is sent far away, i.e. at a distance where you can see it sharp without accommodating too much.

For a view camera the issue is different since we want to switch from a global view to a detail view and we need to move the eye all over the ground glass.
So it is not possible to make the image of the exit pupil of the lens exactly inside our own pupil.
The optical arrangement which is the most common in many view cameras is to add a Fresnel lens for which the focal length is close to the focal length of the view camera lens. In view camera lenses the exit pupil is located at the exit principal plane (only retrofocus and telephoto designs do not obey this rule)
Doing so, the exit pupil of the camera lens, i.e. the image of the iris as seen from the back, is sent very far in front of the camera and appears as a wide illuminated circle, much larger in diameter than the exit pupil itself when no Fresnel is used. This is another means to understand the fact that rays in the corner are bent by the Fresnel toward our eye.
Ideally you would need one Fresnel per lens, focal lengths should be matched ! At least for view camera lenses which, except the telephotos, are of quasi-symmetric design, the exit pupil being located close to the exit prioncipal plane i.e. one focal lengths ahead in front of the focal plane.
Retrofocus wide-angle lenses used in reflex cameras keep by design the exit pupil at a comfortable distance, about the same as the standard lens, hence the question of light fall-off in the corners is not as critical with retrofocus lenses.
This is an interesting issue in the present battle between medium format high-end digital cameras and precision view cameras fitted with a digital back, but let us keep to the initial subject.

In fact usual Fresnel lenses have a focal length equal to the diagonal of the ground glass, their numerical aperture is f/1 which is already a challenge, f/0.7 might be possible but here we understand why there is a problem with lenses of focal lengths significantly shorter than the diagonal of the image, it is not possible to get a Fresnel that would allow a uniform illumination.
Some manufacturers have on catalogue an Fresnel lens that you add in front of the first one when you use short focal lengths. In principle stacking two Fresnel of same focal length gives you a Fresnel with half the focal length, twice the power. I do not know if this is really practical or not. I would be scared by moiré patterns between the two Fresnel ring systems !

So the Fresnel is another optical element, de-correlated from the choice of the diffusing ground glass, sure a Fresnel actually increases brightness but mostly in the corners.

Combining the Fresnel with a bright screen delivers in principle all what you need, a maximum of brightness, uniformly across the screen and a very easy way to see the proper sharpness jump.

Except for short focal lengths.

---

Well after this long discussion I have no advice or recommendation in favour of any brand of brighter screens. The most important thing in my opinion and base on my own experience is that the photographer should be comfortable focusing and should be able to find the proper focus as quickly as possible. If you have to adjust your focusing knobs back & forth for minutes, eventually your eyes get strained and things become worse.

So definitely the ideal situation would be to experiment with various configurations, with or without Fresnel (Fresnel rings can be disturbing for composition), bright or not bright, the important think to take in into account (not taking into account the comfort of your bank account ;-) ) being to be comfortable when focusing in order to find the proper adjustment as quickly as possible.

[Mattg]

Nice explanation Emmanuel!

My experience of 6x9cm screens over the last 4 years includes Ebony's standard screen w/fesnel, Linhof's newer screen w/fresnel, Arca's screen w/fresnel and a Maxwell medium format screen w/fresnel.

The Maxwell that I had on an Ebony was by far the brightest which is important to me because I do a lot of stuff at night. It was also very easy to focus.

At the moment I have the standard Arca screen and have been able to use it under all sorts of conditions but would still prefer something brighter at night. If I get anything it will be another Maxwell screen, Bill can talk to you about the lenses you use and get the correct fesnel incorporated into the back of one of his screens. He can also advise on how to fit the screen to ensure proper alignment and even fit it for you if you'd prefer.