Test results of Bosscreen vs Fresnel vs Ground Glass only!

I thought some might find this interesting. and I will try and make

it relatively short.

 

I have always been curious about the Bosscreen after reading a two

part review of focusing screens and brightness in older issues of

View Camera Magazine. I never had seen or used one in this area of

the country (Phoenix). I recently purchased a Shen Hao from The

View Camera Store (really great camera) but it came with a very dark

GG. So I decided to experiment (decidedly unscientific) with several

approaches.

 

I purchased a mint Bosscreen on Ebay which I compared to the

original ground glass and a ground glass that I had made myself

(instructions from a recent article in Photo Technique magazine)

with all three being used by themselves AND with a fresnel.

 

I focused on a lamp with my 180mm f5.6 Symmar, removed the screws

holding the springs that held the GG in place and substituted non-

sticky tape to hold the variations so I wouldn't jar the camera as I

changed GG's etc.. I used my spotmeter under the darkcloth to

measure brightness differences and a Peak 4X loupe to test ease of

focusing.

 

The Results:

 

The fresnel helped the original ground glass significantly in

brightness (especially in a more even light distribution) about one

stop. However, you could see the fresnel ring pattern and with the

loupe the GG was very course.

 

The hand-made GG was extemely smooth to focus on and was brighter

than the original GG by about 1/2 or more of a stop without the

fresnel. With the fresnel the entire screen was about a stop

brighter with very even light distribution, however I could still

see the fresnel rings under the loupe. The grain of the glass under

the loupe was very even and smooth.

 

The Bosscreen without the fresnel was about as bright as the hand-

made GG but with an even better smoothness of grain but not by much.

However, the real surprise was that with the fresnel I got the

increased brightness and evenness as I got with the others but you

COULDN"T see the fresnel rings (I have no idea why).

 

Since I live in the Phoenix area I am afraid of using the Bosscreen

outside in the heat or leaving it in the car since it is made with a

wax layer, but in the studio or mild climates I would imagine it

would work fine. I will personally be sticking with the handmade GG

for all outdoor work but probably without the Fresnel. BTW the

fresnel was on the inside of the GG towards the lense.

 

These were my results and your milage may differ but it was an

enjoyable and interesting experiment.

Excellent post Jerry.

that was laso my experience with the bosscreen, and i immediately returned the item because of small bubbles in the wax(?) binder between the two pieces which comprise the bosscreen. i purchased a beattie intenscreen, which i still use, but i still must use a fresnel with the beattie to get the brightness i need.

RE. Beattie Intenscreen : I believe this is an integrated fresnel/ground glass. Why do you need an additional fresnel? I wouldn't expect that to improve things, rather the contrary. BTW, I only have a 6x6 version for a TLR, perhaps the 4x5 version is different (doubtful).

The bosscreen is a 'sandwich' so the fresnel is not in direct contact

with the GG surface: This may explain why you can't see the fresnel

rings. BTW, I would be concerned about the true plane of focus when

you have the fresnel between the GG and the lens..... To simplify the

problem, it should be on the other side of the GG.

 

I've been making my own GG with Carborundum powder for several years.

I use #500 grit and this provides a nice fine texture. They work so

well I never have a thought about upgrading.

Richard, I too use a Beattie Intenscreen, but on a Cambo 45NX. Like yours, the one I purchased (from Calumet) has an integral fresnel.

Richard: The Beattie Intenscreen is a screen only, no fresnel. It is brighter than the Linhof GG by about 1/3 stop and a little finer than old Linhof screens. Worth the extra money?

I replaced the original GG from my Linhof Kardan with a Beattie screen and while the

improvement wasn't mind-blowing, it has made life easier enough over time that I

think it was definitely a worthy purchase. My only complaint is that it has picked up

some scratches and dings on the ground surface from when it was removed to use

certain accessories in the Graflocks, but I'll be the first to admit I haven't exactly

babied the assembly.

I put a Beattie screen on the Linhof Tech III I used to have before I got my Ebony (yeah, I know!). The Beattie is a combination GG and fresnel along with a multicoated cover glass that is mounted on the camera one way or the other depending on how the original screen is mounted. In the case of the T III, the fresnel side of the Beattie was facing the lens with the GG side out facing the photographer. Then the cover glass is placed over the screen to protect it. I found a marked improvement over the Linhof GG, although the one thing about it and this goes for the screen on my Ebony as well, is that it is a little harder to see everything with both eyes at once probably because the light rays are focused straight back instead of spreading out. However, the brightness and ease of focusing definitely makes that worthwhile.

I recently purchased an Ebony camera that comes with a Fresnel. I had Bosscreens on all of my previous cameras except a Tachihara that I owned some years ago. I've had a lot of trouble adjusting to the difficulty of using a loupe with a Fresnel after becoming so accustomed to the Bosscreen, which is much better in that respect. The Fresnel produces a somewhat brighter image than the Bosscreen but I never had any trouble seeing the image with the Bosscreen even in dim light and it was much easier to focus with it than with a Fresnel. I hate to spend any more money on this camera but if there is a Bosscreen made for it I'll probably eventually replace the Fresnel.

 

With respect to using a Bosscreen in Phoenix, I live in Tampa and had no problems. I do have some of the tiny bubbles that someone mentioned on the Bosscreen that's on my Deardorff but they don't interfere with use of the screen. I can't see them except when I'm using a loupe and even then the screen still functions fine.

I replaced on my Technika the original GG into a Bosscreen and combined it with a Linhof Fresnel. With this combination i 've got a more than 1 stop brighter image an a more even light distribution. This helps me especially when i use a wideangle lens with f5.6 max. aperture or lower in dim light.

Linhof, Germany mentioned that it is not necessary to use a bosscreen but everybody who worked with both, know the advantage in focusing at fine structured details. In Austria - i live there - we dont have the problem with extemely hot weather, so i dont know the problem with bubbles in the wax. From my appointment i can only recommend this combination to everybody.