Weird Effect with Beattie 8*10 Screen

[Bill Hume]

I wonder if anyone has come across the strange problem I have found when I installed (correctly) a Beattie Intensescreen on my Shen Hao 8*10?

The screen is very bright and is on the film plane. However I have to move my head around a lot to see the image in all areas of the screen. If I close one eye, half the screen goes dark and the other half if I close the other eye. It is more difficult to fine focus probably because of the obvious concentric rings on the fresnel side of the glass. Once the lens is stopped down to the taking aperture, moving my head around to check focus produces a line of light radiating from the centre towards the edge of the ground glass, resebling the lines on an aircraft radar screen.

This phenomenon makes it difficult to use the Intensescreen. I have seen other 5*4 cameras with Beattie Screens and they do not show this effect.

Anyone out there with an Intensescreen on 8*10? I'd love to hear if you have a similar problem.

I do not know if I need to return the screen to the distributor or if this odd effect is because the screen is larger than 5*4.

Thanks

Bill

[Gary Beasley]

You didn't say what lens you were using. These fresnels generally need to be matched to the range of lenses you will shoot. A WA will give results like you describe with a fresnel intended for a more normal focal length lens. It's a little like the way you need to match condensors and lenses in an enlarger.

[Bill Hume]

Gary

I only used a 300 mm lens during the time I noticed the problem.

I'll try my 150 lens to see if there is the same effect. However, that does not explain why my 5*4 camera with a Beattie screen does not show this effect with any of its lenses.

I do notice that the 10*8 Beatie scren has very obviouds concentric (fresnel?) rings visible to the naked eye.

Before I contact the UK distibutor, Morco, I thought I'd see what experience others had.

Bill

[Jim Noel]

I fought with one of these a good many years ago. I finally gave up the little bit of extra brightness for a good finely ground glass.

I do carry an 8x10 "page magnifier" which I use occasionally in very dim light by holding it up to the back of the camera. This a is a much better solution for me. Perhaps the same idea occurred to Sinar and caused them to sell a snap-on magnifier rather than an imbedded one.

[Brian Ellis]

"The screen is very bright and is on the film plane. However I have to move my head around a lot to see the image in all areas of the screen"

This is a fairly typical characteristic of Fresnel lenses, especially if not matched well to the lens in use, and is one of ther disadvantages (I don't know why you don't see it with the 4x5, maybe the screen and lens you're using are better matched). However, some Fresnels seem to be better in this respect than others. For example, the Maxwell I used didn't exhibit this characteristic at all even with an 80mm lens unless I moved my head to the left or right an extreme amount. I briefly had a Beattie on a Technika and thought it was the worst of the Fresnels I've seen (which in addition to the Maxwell include OE Fresnels on Tachihara and Ebony cameras). If it were me I'd probably return the Beattie and get a very good ground glass or if you have the money a Maxwell or a BosScreen.

[Bill Hume]

Thanks to all who replied.

Following your comments I traced on the internet an article by Ron Wisner which seemed to identify the problem I noticed.

Having done some tests I think the effect is worse with increased bellows extension and camera movements. It is present with my 150 mm lens as well but the depth of field is not so much of a problem here so the focussing problem is less.

So it looks like the effect is "normal" for a 10*8 (? because moving the loupe to the edges is a much greater distance that in 5*4).

I have contacted the UK distributor asking for their observations

Bill