why is Glass ground ?

[brighamr]

Hi

I'm sure there is an obvious answer but why do we use ground glass instead of clear glass
removing my GG and holding my loupe in place gives such a sharp image
why do I want the GG one

thanks

robin

[Vaughn]

1) hard to see the entire image at one time with a loupe.

2)"holding my loupe in one place" -- which place? The actual place is very important...it needs to be the same place that will be occupied by the film (which is the front of the GG -- side closest to lens). having the image thrown onto the ground part of the GG makes sure you are focusing on the proper plane.

[brighamr]

1) hard to see the entire image at one time with a loupe.

2)"holding my loupe in one place" -- which place? The actual place is very important...it needs to be the same place that will be occupied by the film (which is the front of the GG -- side closest to lens). having the image thrown onto the ground part of the GG makes sure you are focusing on the proper plane.

Hi Vaughn
thanks for your quick reply
If I had a glass made with cross hairs on the lens side/film plane
I could focus the loupe first on that and then check focus thru the lens from there
Am I right in thinking that this is how you set up a loupe in the first place

I'm sure I am missing something but can't figure out what

robin Brigham

London

[John T]

For focusing, yes you are correct. However, how can you compose with a clear glass?

[Nathan Potter]

Clear glass is the same as no glass - only what is called an aerial image is produced at the point of focus. The image is there you just can't see it over the field of view so you can't do a global focus or see the effects of camera movements using only the unaided eye. Grinding ie faceting the glass causes the aerial image to scatter giving the eye a real image to look at. I use a couple of Linhof screens which are finely frosted except for a center spot which is clear with a painted cross at dead center within the clear area. With this arrangement I can do a gross focus using the frosted part, then a critical focus at center using a loupe in the clear area.

Nate Potter, Austin TX.

[SaveBears]

Probably the easiest answer, is try it and see how you do!

Experimentation, has been the hallmark since day one in photography...

[John T]

Caroline,

It is not a silly question. Far from it. It is just something you aren't interested in discussing.

brighamr has a point. Aerial image focusing is a well-established focusing method. Nikon and Olympus (and maybe others) have made them for their SLRs, I have a focusing glass for an 11 x 14 copy camera similar to Nathan's, except that it has multiple clear spots to check focus throughout the image. It seems to be primarily used for astro, micro and copy photography. If the clear area has cross hairs to calibrate the human focus, aerial image focusing is much more precise than ground glass focusing. It just isn't practical for traditional photography.

[brighamr]

Where is Brian Ellis when we need him to explain this sort of thing?

Shouldn't we have a silly questions filter on the forum?

And, . . . then people answer it !!!!!!!!!

Caroline

I joined this forum to get help with things I don't understand

why did you join ?

You don't seem to of asked any questions about LF recently,
You just seem to whine about peoples spelling

Robin

[Anupam]

The M screen on the Nikon F3 is an aerial screen. If you have access to an F series camera, you can try it out yourself quite easily.

And Caroline, what we need is a filter for smartass answers.

[sparq]

Search works quite well, too.
http://www.largeformatphotography.in...t=ground+glass