A ground glass discovery and scotch tape

[Douglas Henderson]

Some years ago, I bought a Cambo 8x10 studio camera from a dealer in the mid-west. Although reasonably well packed, the GG was broken during shipping. I just patched it back together with magic tape/scotch tape and made an unexpected discovery.

Where ever the tape lay on the glass on the inside of the ground glass against the ground surface, the resulting view through the ground glass was as crystal clear as if looking out a window. Focusing became a breeze in any light or through any dark filter. I put a small strip of tape in the center of the ground glass (on the inside) and four other strips near the GG corners (too close to the corners precludes seeing the image with a lupe). Focusing center and corner elements of artwork with a lupe of any kind is now so easy and accurate, I wonder why I haven't heard anyone else mention this trick.

Standard procedure now is to strategically place small patches of tape across the ground glass for studio copywork. All 8x10 copy is done using an Apo-Ronar 360mm--corner to corner sharpness is superb since the focus is much closer than infinity. Tape on the GG of a smaller 4x5 Graphic View using an Apo-Ronar 240mm works fine as well.

[aggibson74]

Interesting. If there are grid lines on the ground glass, can you still see them?

Al

[Douglas Henderson]

Al,

The tape doesn't mask the wider view at all--the grid lines are still visible. The taped portions of the ground glass are strikingly brighter, however.

To focus with lupe on the more corner tape patches, you have to set the lupe flat against the GG, but move it around to view the path of light from the lens--the reason you can't use tape right to the 8x10 edges.

I had questions if this distorted the true focus, but the film results show everything tack sharp.

Doug

[tom thomas]

Doug, wouldn't this be the equivalent of a fresnel lens in front of the GG?

Tonm

[Douglas Henderson]

tom,

I've used fresnel lenses--they brighten the image certainly, along with all the added concentric lines. But the small portion of the ground glass covered with a small strip of magic tape produces something more like a crystal clear viewfinder. I'm not sure how such a clear image is being projected through the GG, but it sure is.

You can contrast the GG image and the GG + tape image by viewing across the boundary between the two. Nothing could be much easier (or as easily reversed) as putting it to the test.

I guess I should mention that the tape is not being used together with a fresnel lens. I don't have fresnel lenses on my copy cameras. I doubt tape on the GG would have much benefit with field cameras, as the available light is so much greater and the image is much easier to see. But focusing with 1000 watt lamps in a studio can be a study in frustration--especially trying to see well enough to square the camera and focus over the whole image.

[Lachlan 717]

Douglas,

Do you apply the tape to the smooth or the ground side?

Thanks.

[kev curry]

Douglas, I just took the back off my Tech V and stuck a 10mm square of scotch tape to the inside of the gg.....Shit thats totally nuts man! The gg is ''crystal clear as if looking out a window''...no shit, you got that right!
BTW that's with a fresnel on top of my gg, the difference is eye popping!

[engl]

Interesting idea, I'm going to try it. The GG on my current camera is very poor. It makes sense to me that a material with better diffusion than the current glass would give better "focus snap" in the center, and should make the areas closer to the edges much brighter when looking at the GG "dead on".

The basic idea of "magic tape" is strong diffusion but very good transmission (it is basically clear once on the paper). I'd not be surprised if it is easier to make very fine patterns for diffusion easier the chemical way.

The thickness will create a focus shift. I read the tape is 2.2mil (I'm not sure if this applies to all their "magic tape"), which is 0.05mm. Film holder tolerances are 0.17mm so the shift is significant but not devastating.

[Tracy Storer]

It's brighter because the texture of the tape is finer than the texture of the glass, finer texture=brighter, but also = less even. (particularly with WA lenses)

[engl]

Also, if you wanted to avoid the tiny focus shift, you could put the same tape along the edges of the ground glass. This would move the GG back the same width as the tape thickness.

Since my current GG (from the 50s) is horrible I've considered making my own, but finding the supplies around here is not very easy. If the tape works out good, I guess I could cover the entire side of a piece of glass in magic tape :) I wonder how it compares to IKEA window frosting film...

[aggibson74]

Here's something interesting I found:

"Before I leave the subject of broken ground glasses I found that a very adequate emergency replacement could be made. Just go to a local hardware store and have a glass cut to the proper size. Tape Scotch brand Magic tape to one surface of the glass. The tape is frosted and will work in a pinch as the ground surface. The image is serviceable but has a streaky nature to it. Make sure that the tape runs all the way to the edge so that the ”ground“ surface is at the proper plane. "

From this article (http://www.dokasphotos.com/techniques/ground_glass/)

I was going to try this to see how well tape on regular glass works.

Al

[Michael Rosenberg]

As Al pointed out Dick Dokas had published the emergency use of tape on glass in PT magazine in the 90's. A few years ago I was with some friends in Bluff photographing. One of us had a light weight camera, and took his hands off the tripod for a moment to get something out of his pack - and a breeze blew up at that moment to catch his camera and take it down. The only thing broken was - you guessed it - the ground glass. He was able to get a piece of glass cut to the right size, and was going to try and grind it. I recalled Dick's article and he was able to photograph the rest of the trip.

Mike

[cowanw]

This effect is well known the finer the grind on a GG the brighter it is but the more there is a hot spot in the centre.
As a result, some will wax ( or laquer or nail polis) a spot in the centre (or any other area you wish) and have a bright easy to focus area and with a coarser grind +/- a fresnel have an area of easy composition. the scotch tape works like this.

[Filmnut]

Neat idea, I'm going to try it out on my Speed Graphic.
Keith

[kev curry]

After trying the tape I thought I'd try some Vaseline on the lens side of the gg...wow! That alone has made the gg significantly finer and brighter and easier to focus!

[Douglas Henderson]

kev,

Your first response viewing through a little strip of tape was pretty close to mine. But Vaseline? Surely, you jest. If not, wouldn't the Vaseline "outgass" some petroleum product that might accumulate on the inside of the camera and the back of the lens? Maybe it doesn't get hot enough in Scotland.

Wonder what a little spray acrylic would do.

Just to mention, it has been about 6 years since I repaired that broken GG on the 8x10. I never used a fresnel with that camera. But I've since forgotten all the experimenting I did and checking today my 4x5 Graphic View, sure enough, I'd put tape strips on the GG's frosted side and replaced the fresnel lens--the tape sandwiched between. Works very well.

Copywork with exposures at F22 probably masks any slight change in the focal plane. The tape thickness is probably less than the normal variance of manually focusing the lens--especially if you are guessing some ideal focus point at a wide aperture. In the future, I'll take the advice to add tape of the same thickness right to the glass edge to shift the GG back in its frame.

[kev curry]

Douglas, aye Vaseline! I rubbed in a spot of the stuff right up to the line of the tape, cleaned off the excess with tissue then had a look. The scotch tape area was brighter but the Vaseline area was still plenty bright. When I then removed the tape it left a sharp line clearly delineating the non treated gg side from the Vaseline treated side and again the difference was/is eye popping.

Focusing with the vaseline treated side of the gg is improved significantly!

The out gassing thing did cross my mind because theres always a lens folded up with the Tech....hmm?

[kev curry]

OK... I just cleaned the Vaseline off the GG with a smidgen of soap and a polyester cloot, thats a cloth not a camels toe;-) then rubbed some butter onto the GG instead...works great!

Will butter attack my lenses or camera...? I'll end up frightened to leave the house!

I'll away and make some tea and butter the rest of the GG!

The things you get up to when the weathers grim and business has died on its arse!

[jp]

I wonder how car/ski wax would do compared to vaseline or butter? That would be more stable than butter or oil. I might try it on an old GG.

[Kevin M Bourque]

I once found the original patent for Brightscreens..basically its a very thin application of some kind of epoxy resin. Permanent Vaseline.

[Kirk Gittings]

I used vaseline once to brighten the image. It worked well but was messy and collected dirt and I gave up on it.

[Douglas Henderson]

Kev,

Mother of God, is scotch tape hard to find in the Old World? Butter will probably oxidize and decompose--and maybe change to something less clear, charged with bacteria. We have bio-defense labs for this here. Really, tape (and love) is all you need.

Any great northern lights the last few days? All overcast of late in Montana.

Doug

[kev curry]

The worlds becoming scarier by the minute...so many hazards lurking around every corner, maybe I should reconsider the anti depressants...it might be cheaper than Whisky;-)

[johnielvis]

I just tried this---I reallyneed a brightener--very long (and dim) lens on a deardorff ground glass---tape did absoluetly nothing except look like there's apiece of tape on the ground glass---I have no fresnel, so maybe there's something to that...OR...maybe the deardorff gg is already as fine as they come--I tried the tape on both sides too...same thing--absolutely no difference in brightness.

stands to reason that nothing can make anything brighter by standing in the way---it's simple physics....did anybody do a test with a light meter and actually get MEASURABLE brightness increase???? maybe this is some kind of contrast increasing effect that only works with shorter lenses where the rays spread out---the lens I'm using was VERY LONG--44"...so all rays are about coming from the same direction---so I'm guessing this has something to do with it...

[Douglas Henderson]

John,

My enthusiasm for the results of putting scotch tape/magic tape on the inside of the GG (the ground/frosted side) had much more to do with the clarity of the image when viewed through a magnifying lupe for the purposes of focusing.

There is the additional element of greater brightness, but this is much more apparent to me when looking through the taped portion of the GG with a lupe. Also my experience is with an 8x10 with a reasonably short 360mm lens (wide open) and a 4x5 with a 240mm lens. Other posters seem to have emphasized the brightness of the whole image projected on the GG when aided by various off-the-cuff, crack corn methods in a pinch (which I'm not above doing in a pinch).

Did you view any small part of the GG image projected through a strip of tape with a magnifying lupe?

[gliderbee]

"Scotch Magic Tape" ... We are talking about the frosted type, not too sticky, right ?

I have some Scotch tape here, but it's completely clear and VERY sticky, in fact, so sticky I hesitate putting it on my gg ..

Thanks,
Stefan.

[Douglas Henderson]

gliderbee,

I think I tried scotch tape and magic tape--if I recall, both worked fine. I think I used the genuine scotch tape, not some off brand version. The adhesive on scotch tape is stronger and removing the tape may take a little time--but rubbing alcohol with remove any adhesive gum left on the GG.

For the sake of a test to see results, just fold over one end of a small strip of tape so you are left with a little tab to grab when comes time to remove the tape from the GG.

The tape I put on my two copy camera GG's is still there after about 6 years. I know the adhesive should decay--but stuck to glass rather than paper, the adhesive can't breath as easily and looks to remain unchanged. I know most tape adhesives on paper over time just go completely crusty.

[dupont07]

Thank you for your idea.

http://farm6.static.flickr.com/5199/5883723290_cac1be11a0_z.jpg

http://farm6.static.flickr.com/5273/5883724952_3d7bd83a0a_z.jpg

I have tried scotch tape on my 5x7 ground glass. I have found only the scotch tape 19mm in width. Is there any wider tape?

[Nathan Potter]

Hey, the principle is simple and very old. Your taking lens forms a real image of the scene at the surface of the GG. You can see the image because the GG scatters the light from that surface forming a physical image that can be seen by the eye or a loupe that is focused at the plane of the GG.

Remove the GG and that image from the taking lens is still there, you just can't see it. It then is referred to in optics as an aerial image.

Now the application of the scotch tape directly onto the frosted side of the GG is equivalent to removing the grinding. The glue on the tape fills in the fractures of the grinding, eliminating the light scattering. For best results the "Scotch" tape should be of the clear variety. The best light transmission will occur when the index of refraction of the tape and glue matches that of the glass. Any other transmissive medium such as vaseline or wax, etc. will accomplish a similar effect, to a lesser or greater degree.

There are Linhof screens around that have partially ground surfaces where sections are left unground that can be used for critical focusing using a loupe. Don't know whether they still offer such new though. The advantage of the Linhof is that the frosted and clear areas are in exactly the same plane so that as the eye is focused on the grind the aerial image as seen simultaneously in the clear area can be focused more critically using a loupe.

Nate Potter, Austin TX.

[neededandwanted]

Normal Scotch Magic tape is 3M product number 810. They also have an 811 tape that is called "repositionable" which is easily removed, just like their Post-It notes. Highly recommended instead of the more permanent Magic tape.

[Corran]

Interesting, I am going to try this for sure! I am having a lot of difficulty focusing 47mm and 58mm SA XL lenses even with a fresnel.

[patrickjames]

Wax works wonders as is mentioned above. Doesn't look like crap either. I use Butcher's wax only because I have it on hand. Any beeswax or Carnauba wax should work. A light coat is all that is needed.