Fresnel Lens for TLR

If yo have an old TLR with ground glass screen, you may be

interested in this. Yesterday my wife brought home three magnifying

lenses which were being given away at the local library. They are

fresnel lenses in the shape of a six inch ruler, around three inches

wide and with centimetres marked on one side and inches on the other.

 

I immediately though about using one to brighten up my TLR screen

(New Standard Rolleiflex). They can be cut with scissors to the

appropriate size, and the markings removed with methylated spirit.

When placed on top of the ground glass (fresnel grooves downward),

they make the image significantly brighter. Not , I am sure, in the

Maxwell / Beattie class, but better than nothing.

 

There are some larger fresnel magnifiers available, but these ruler

types seem to have much finer lines. They are marked Handi Lens by

UltraOptix, made in Taiwan.

 

I would say that they will not improve a camera which already has a

fresnel screen of any kind, only one with plain ground glass. You

need to make sure the centre of the concentric grooves is centred in

the screen, and that you don't make it so big that it gets stuck.

Focussing does not seem to be affected, although they do not have

the clear centre of the proper screens - it might be possible to

make a hole in the centre if you wanted a clear spot.

If you want to do it in a more professional way, you can use the fresnel lens of a Hasselblad focussing screen. This might seem expensive but I managed to get some for a few EUR/USD since the Hassi fans don't like them any more as soon as they have the slightest scratch which will be hardly visible in practical use.

 

The Hasselblad screens are two-part, held together by a stamped metal frame which is also two-part - you can easily separate the top and bottom frame, and then you have a ground glass and a fresnel screen. These fresnel lenses are probably with finer grooves than the ones used as loupes. They are also made from plastic. Their dimension is 54x56mm approx which will fit most TLR focussing screens.

 

Depending on the way the orignal screen is mounted your TLR viewing lens will need readjustment. If the original screen lies flat on a frame under it and you can mount the fresnel screen above it without lifting the original screen this will not be necessary. On the east german Reflekta II TLRs the original screen is mounted with four brackets UNDERNEATH its frame. The brackets are just long enough to hold a fresnel lens, too, but of course the original screen will be in a somewhat lower position.

Would sure make an old Argoflex more fun to use. Thanks for the good tip.

I too have one of those rulers and have been brainstorming uses for Fresnel screens in cameras. I understand that Leica is using something similar to make the entry rays parallel in digitals. Anyone have ideas? Why not part of a lens systerm?

In the 1950s, places like Spiratone sold these things just for that purpose, to be dropped in on top of the screen in whatever TLR you had (Rollei was particularly slow in adopting the Fresnel screen in production). They were made in the standard 6x6 size, and the one that I had had about a 1/2" hole in the center for critical focusing. The flat magnifiers do this job pretty well, though the pitch of the grooves is coarser.... use the smallest size you can, as the larger ones have a longer focal length and so are less efficient at brightening the edges of the screen.

"I too have one of those rulers and have been brainstorming uses for Fresnel screens in cameras. I understand that Leica is using something similar to make the entry rays parallel in digitals. Anyone have ideas? Why not part of a lens systerm?"

 

Fresnel lenses are not used for photographic optics because the grooves will cause additional diffraction and - depending on the placement of the Fresnel element - will be more or less visible on the image. The thing Leica is using is probably some kind of 'field lens'. On some older TLRs you find similar - a big plano-convex lens over the ground glass (or sometimes made from the same block of glass as the ground glass) but this does not seem to be very effective on TLR finders. At least the viewfinder image of my two Semflex cameras (which use this type of field lens) became incredibly bright after replacing the ground glass and adding a Hasselblad fresnel lens.

I just got my Rolleicord III with Xenar lens back from a CLA (which cost twice as much as I paid for the camera by the way) and I've been looking for a way to brighten up the focus screen without spending twice as much again for a Maxwell or Beatie screen. I removed the focus screen from a Yashica D parts camera and found a fresnel lens beneath the ground glass screen in it. These pieces I got to fit straight into the Rollei using the spring clips from the Rollei. (A bit tight but it fit) The result was great! The view was 1 to 2 stops brighter. In addition, I now had a screen with a grid pattern to help in aligning horizons, vertical objects, and to frame for a rectagular print. A problem became evident however when I tried to focus the camera. The plastic fresnel lens sat too low and interfered with the Rollei's moving paralax compensating blades. I removed the fresnel screen, clipped off the tabs near the corners and placed the fresnel lens on top of the ground glass and the result is still very good. I can use this dear little Rollei now! My experience supports the previous post suggesting the use of a fresnel lens to brighten the dim focussing screens of the older Rolleis.