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This is the illustration that I had wanted to use for the BrightScreen discussion but I couldn't find the book that it was in. The one that I did use was from a Ciroflex patent drawing.
On the left is a TLR with a plain groundglass, on the right the same TLR with a Fresnel lens added. The length and weight of the colored lines reflects the amount of light that each line represents.
In both cases, light from the lens is scattered as it strikes the focusing surface - this is how the image is formed for focusing. As a result, most of the light passing through continues in a straight line, but a portion of it is scattered off in different directions.
In the case of the plain groundglass, this results in most of the light reaching the eye for the central part of the image, but toward the edges the main portion of the light continues outward and is lost into the sides of the focusing hood - only a small part of the scattered light comes out in the direction of the user's eye.
With the Fresnel lens, the light coming out of the screen is focused toward the eye. Some is still lost to scatter as before, but the main portion is directed toward the eye and only the scattered portion is lost. This is why a Fresnel screen appears brighter and more uniformly illuminated than a plain groundglass.
Another way to increase apparent brightness is to reduce the amount of light that's lost to scatter at the focusing surface: press photographers sometimes smeared a little Vaseline on an area of the groundglass to create a brighter spot, and some bright screens have the surface treated to reduce scatter. HOWEVER, since it's the scatter that forms the focusing image, reducing scatter also reduces focusing precision.... and if done without the Fresnel lens, it makes the light falloff even worse in the outer field than it was with the plain groundglass.
> Note that in the center, the Fresnel lens has little or no effect. The effect increases as you move toward the edge of the image, cancelling the light fall-off of the groundglass.
>> A dim groundglass and a Fresnel bright screen both transmit the SAME amount of light (about 92% - actually, where the brighter screen is in 2 separate parts it transmits slightly less than the plain groundglass, due to the extra reflective surfaces). The difference is entirely in how the light is directed as it exits the screen.
>>> For this reason, changing to a brighter screen may or may not affect a TTL meter reading - it depends on how the meter cells are designed and positioned.
>>>> The Fresnel lens can be placed above or below the screen, it works either way. In many earlier factory installations the Fresnel lens was placed below the existing groundglass; in many later factory installations (and the BrightScreen), the screen is designed as one piece with the focusing surface on the bottom and the Fresnel on the top. The Rolleiflex "Rolleigrid" Fresnel accessory was a separate piece installed above the groundglass.
>>>>> The lens does not have to be a Fresnel, a plano-convex condenser lens works the same way. Exakta 35mm SLRS and Pentacon Six used a glass condenser lens to increase brightness. The thick glass lens tends to introduce distortion into the view, and it's thick and heavy especially in larger formats. In many cases, both a Fresnel and a plano-convex condenser lens are used in the same screen... this is the case in the Mamiya M645, the Kowa Six and the Nikon F. In the OM-1, Olympus made the pentaprism with its bottom face convex rather than flat, obtaining the benefits of the convex lens without the bulk; the interchangeable screen below the convex prism incorporated a Fresnel lens on its bottom surface and the focusing surface on the top.
>>>>>> Typically, the focal length of the Fresnel lens is specified to correspond to the focal length (or the back focus) of the camera lens it is intended to be used with. However, a Fresnel lens can be designed with more than one focal length: because it's broken up into multiple facets, it's possible to have some of them representing one focal length, interspersed with others of a different focal length. Zeiss patented this idea in the 1950s, and the Brightscreen is designed this way.
Tooling has just (FINALLY) been completed for a new, plain all-matte version of the BrightScreen.. The Fresnel side is the same as the MP and MPD screens, and it comes in the same sizes and grid options. Shown here cut for the Mamiya M645 with no grid.
The original groundglass was broken, so I replaced it with a BrightScreen. Installation was a bit easier than I had expected.
(Interesting background bokeh in this phone picture .... overcorrected spherical aberration, I think we'd call that)
I don't do too many large format BrightScreens but they do come along now and then. Maximum size is 103 x 133 mm
I was considering leaving the Dallas News Yashica Mat all original, but decided to put a BrightScreen in it. I've ordered a new mirror too, the one in it is pretty drossy and I'm afraid by the time I got it clean there wouldn't be any silver left. Trying to preserve most of the warts as they are though.
Here's what the screen looks like in a 1951 Rollei. It's a big difference in brightness from the original groundglass......
One corner of a BrightScreen, after it's been scribed and cut out but before removing it from the blank. The cutting process leaves about 1/4mm of material at the bottom to keep the part attached to the blank... the part is then 'unzipped' from the surrounding blank and the edges cleaned up by hand. The milled trench around the edge is about 3mm wide by 1.2mm deep.
I can't engrave numbers as small as the ones on the factory ECTL screen, so my solution is to skip every other speed on the scale. So if a light appears in the space between 1000 and 250, that's 500.
I don't know how much need there is for these little things, but I guess I'll find out. The retaining clips that hold the focusing screen in a Rolleiflex are small, easily lost and occasionally damaged, and scrapping a camera for parts is an expensive way to get a replacement.
So, I've just had several hundred of them made out of stainless steel. They fit and work in Rolleis, I'm still in the process of finding out how well they will work in copies such as Yashica Mats and Autocords.
Just made my first BrightScreen to fit a Pentax 67-II. The recesses for the retaining clips at the edge make this one a little more complex to cut, and the size is right at the limit of what's possible with my molded blanks.
After more than 20 years at rick_oleson.tripod.com, the entire Lycos system went dead for more than 24 hours this week, taking my website with it.
It's come back up now, thankfully, but not before I'd already signed up for 3 years on another host. So now I have 2 websites. The new one is at rickoleson-brightscreen.com .... rough as a cob right now, hopefully over time I'll build up some content on it.
I had a successful molding run yesterday, and as a result there are now two different versions of the BrightScreen: the original microprism style on the left and a new one with a diagonal split image spot inside a microprism collar, shown on the right. This was I think the fourth molding run since the spring of 2018, and we seem to learn something on each run. We're actually getting pretty good at this now......
Makes for a long day, though, as the molding shop is a bit of a drive from home. I left the house at 7:30 yesterday morning and got back home at 9:30 last night. But I have enough screens on hand now that I won't have to do it again for a while.
Installed a bright screen in a Pilot 6. The screen is meant for Kiev 88 SLR, and is 55 x 55 mm. The original Pilot 6 ground glass is 56 x 56 mm, so it's a not a perfect fit. I think the screen has changed the focus very slightly, but will have to test it.
I've had the mold in service for about a year now, starting to get it worked out to kind of a system. It went very smoothly this time, made for about a 13 hour day including travel time. This was the third production molding run since I took over the tool.
I'm the press operator, the QC inspector, the packer, the purchasing agent and the accountant ..... it's very efficient :)=
Testing a new Brightscreen from Rick Oleson to replace my old, foggy original B&J ground glass. The Brightscreen is brighter, clearer, and focused just fine.
Film: CatLabs X-Film 80
Camera: Burke and James 4x5 Commercial View
Lens: Schneider Symmar 180mm/5.6
Aperture: f/22
Shutter: 13s (seems long, but my notes say so)
Developer: Caffenol C-H
I happened to be scrapping out an old Minolta camera body, and thought I'd use the opportunity to show some close-up details of focusing screens.
On the left is the focusing surface of one of my BrightScreens at about 100x magnification - like a groundglass, it's a random texture with no particular pattern to it.
In the center is the "focusing" surface of the screen in the autofocus Minolta, at the same magnification - this isn't exactly a matte surface at all but a pattern of tiny positive lenses. This can be brighter than a random texture because the field of view of these lenses can be matched to the max aperture of typically used kit zoom lenses - about f/5.6 - thereby making the most efficient use possible of the available small lens aperture. The down side is that if you have a faster lens on the camera, this screen only views the central f/5.6 area of the lens aperture, so it's blind to the shallower depth of field at larger apertures. Fine when you have an AF system, but not good for manual focusing older lenses.
On the right is a 1000x magnification view of the Minolta screen.
These were all taken with a cell phone camera through the eyepiece of a suitably antique Carl Zeiss laboratory microscope.
This is a BrightScreen for a Graflex RB Auto 3 1/4 x 4 1/4, with framing lines for that format plus 6x7 and 6x6 cm. Has sort of an art deco look to it.
It had been a rainy, foggy evening, and many people preferred to stay home, rather than wander the streets. But there were a few exceptions--such as this profiled, silhouetted figure, who was leaning against a building just beyond the edge of the scaffolding. Were it not for his phone, there would be no light on his face at all; he would have been entirely absorbed into the penumbra...
Washington Heights, Upper Broadway
Uptown Manhattan, New York City
This is where BrightScreens come from : custom cut in Kentucky from blanks molded in Ohio using material produced in New Jersey.
What's left after cutting out a BrightScreen makes a unique and festive Christmas tree ornament!
or not
This is one I've never been able to make before.
I still can't make the engraved numbers along the left-hand edge.
Trying to sort out the hopeless mess that is Mamiya C-series focusing screens:
... the screen above fits the C330 and C330f
... A different screen, a plain square shape without trans or notches, fits the earlier models C, C2, C3, C22, C33 and C220. I can make those.
... Another different screen fits the later models C330s and C220f. I don't have that one yet but I expect to in the future.
This is a map of sales destinations during 2020 and 2021.
Other random trivia:
CNC machined 67%, hand cut 33%
Camera brands:
- Rollei 45%
- Mamiya 17%
- Yashica 13%
- Bronica 10%
- Hasselblad 5%
- Pentax 3%
Grid pattern styles:
- rule-of-thirds 48%
- 'NONE' 17%
- 6601 checkerboard 10%
- 645 / 4:5 crop 8%
My new year's resolution for 2011 was to learn DIY black and white film developing and things are looking up :)
This is from the 3rd roll that I shot but the first I developed (roll 2 is still waiting).
You can read about my fumbling attempts at learning this craft and the method used here: nhilmy87.tumblr.com/post/2623010615/first-attempts-at-diy...
The camera is a new acquisition a 1960s era Rolleiflex 2.8F twin lens reflex (TLR) camera with the 80mm f/2.8 Schneider Kreuznach Xenotar lens. It exposes 6cmx6cm (actually around 56mmx56mm and therefore around 4 times the area of 35mm full frame) frames on 120 or 220 medium format roll film.
Previously owned by a collector it is in superb mint condition and came with an upgraded brightscreen, optional 35mm adaptor and optional prism finder.
I scanned the film at 3200 dpi getting 50 megapixel files. When technique is good and there is no shake, even the grainy Tri-X film seems to resolve fine detail at that scan resolution (not this particular picture though, slight camera shake here).
Taken with Rolleiflex 2.8F Xenotar
Kodak Tri-X 400 in Kodak HC-110
New Laptop for the office - gives me both a iBook (Mac) and HP (PC) to work from (save money in buying mac versions of everything!
AMD64 - 3500+
1GB Ram
100GB Drive
DualLayer DVD-RW/+RW
15.4 BrightScreen Widescreen Monitor
802.11G/B - Works Awesome!
Continuing the theme, here is a view of the reverse side of each screen - the BrightScreen on the left and the Minolta 400si screen on the right - both at about 100x magnification.
Although the Fresnel lens grooves on the BrightScreen are very fine for medium format use, the grooves on the 35mm format Minolta screen are even finer. This is one reason why I can't just cut down a BrightScreen to fit a 35mm camera and promise a good result - the grooves will appear coarse on that smaller format.
The other reason is that these Fresnel lenses have a focal length, which is designed to correspond to the back focus length of the taking lens. Designed for medium format lenses, my BrightScreens will be better than a plain groundglass but they will not perform optimally with the shorter lens distance in a small format camera.
After having launched the original Nikon FM in 1977, succeeded by the FM2 in 1982, the FM2n followed one year later in 1983 together with the electronic FE2 and Nikon’s first multimode auto exposure FA.
As the Nikkormat accompanied the early F and F2 and the more recent F100 accompanied the F5, the FM/FE/FA cameras were the daily companion of the F3. The Nikon FM2n is one of the longest serving Nikon SLR camera models – from its launch in 1983 untill 2001 when it was replaced by the hybrid FM3A.
Differences between the FM2 and FM2n were minor. Nikon changed the focusing screens to the type II Brightscreen screens and a refinement was made in the sync speed from 1/200 sec to 1/250 sec. The X200 setting was removed. Also, the hot shoe was of a slightly different design, with a squared-off center cutout for the base of the hot shoe. The mirror box was redesigned to add a light trap that flipped up when the mirror flipped down. Around 1989/1990 the honeycomb pattern shutter was replaced with an aluminium blade-type curtain.
The FM2n was available in either black or chrome finish. The camera is fully mechanical; its meter (and only its meter) requires two PX76 batteries or one CR 1/3N lithium battery. There is a 1–1/4000 sec shutter speed range, plus B; and an ISO range of 12–6400. Focusing screens are interchangeable (Type III screens for the FM3A can be used). The MD-12 motordrive was optional. The camera can be used with the older MD-11, however with restrictions.
Testing a new Brightscreen from Rick Oleson to replace my old, foggy original B&J ground glass. The Brightscreen is brighter, clearer, and focused just fine.
Film: CatLabs X-Film 80
Camera: Burke and James 4x5 Commercial View
Lens: Schneider Symmar 180mm/5.6
Aperture: f/11
Shutter: 2 s
Developer: Caffenol C-H
this is my brightscreen split prism focusing screen for the d700, i love it! I got it to help me focus my 50mm 1.2. It works AWESOME!
The tiny little box came in something this big from fedex (to cat scale). At least it was well protected
Here we see a subject which is a little out of focus, using my Minolta 70-210mm F4.0 'beercan' @ 210mm. You can see that there is a disjoint on the 'F' on the inscription where split prism meets due to being out of focus, watch the next slide for the punchline.
That exact same setup as the prrevious slide, but now it is focused, notice how as the writing becomes more out of focus it becomes more pixelated? This is due to the microprism collar doing its thing. The microprism collar comes in much more useful for moving subjects or those without available lines, though the split prism feels quicker and easier on static lines.
READ THESE THOROUGHLY FIRST, particularly the part about replacing your own screen first before trying the new one, I think I probably scratched my G type screen a little, oh well... it's not expensive and it's just a bit of blemish. I didn't photograph it here, but there's a small addendum which specified that the screen may contains imperfections and how to clean it, most noticably don't use a lenspen brush, I might have done this on my first screen and caused a minor scratch, I discovered a rocket blower or similar works pretty well anyway, you'll have dust pretty soon after opening this.
Sony's original 'G' type accu-matte screen, removed from my camera. Hold the tweesers gently but firmly, and have a steady hand, or someone with s steady hand, there's plenty of places to knock the screen coming out of the chasis.
I've lowered the focus screen tray, and removed the original screen, notice the reflection of the AF indicators on the mirror.
Apologies if this looks strange, but I turned up contrast and definition so you can clearly see the differences in this comparison of the birghtscreen #5 (lower) to the sony 'G' (stock) type (upper) focus screen. You should notice how the outer area of the brightscreen looks like the entirety of the Sony's screen, though the sony seems a little more finer and darker, but this could be due to the flash or distance to it, it's hard to tell the difference without looking through the viewfinder which is surprising.