Newbie to LF Crown Graphic GG question

[nbagno]

I did search but couldn't find an answer to my specific question.

I purchased this "drop in" GG replacement from ebay http://www.ebay.com/itm/230694924360...%3AMEBIDX%3AIT

It has a smooth side and a rough side and from what I read the smooth side goes towards the lens. I also have a frosted piece of glass with the frosted side towards the lens. So far so good?

My question:

Here is a picture of the frosted glass, you can see it has circular wear patterns in it that bug me.


In addition, my new "drop in GG" has a circular pattern that seems to be developing ( a little hard to tell from the cell phone pic).


Where would this circular pattern come from? And if I wanted to replace this set, would this be it? http://www.ebay.com/itm/221527379069...%3AMEBIDX%3AIT

I don't see any mention of frosted glass.

Thanks in advance.

[BradS]

It sounds like you have a Fresnel lens and a ground glass...sandwiched together. if that is the case, the fresel lens goes in first and the ground glass goes in second. The Fresnel is closer to the lens. The rough side of the ground glass (the side that is ground) goes toward the lens. I cannot remember for sure which way of the Fresnel goes...I think the side with the 'ridges' goes toward the back of the ground glass.

[nbagno]

It sounds like you have a Fresnel lens and a ground glass...sandwiched together. if that is the case, the fresel lens goes in first and the ground glass goes in second. The Fresnel is closer to the lens. The rough side of the ground glass (the side that is ground) goes toward the lens. I cannot remember for sure which way of the Fresnel goes...I think the side with the 'ridges' goes toward the back of the ground glass.

I suspect that it is a Fresnel lens, but it's advertised as a drop in gg replacement :-O

[Jon Shiu]

Actually, it looks like you may have the two items mixed up. The piece with circular grooves is called the Fresnel screen, and the piece with the dull frosted side is called the ground glass. BradS instructions are correct.

Jon

[nbagno]

Actually, it looks like you may have the two items mixed up. The piece with circular grooves is called the Fresnel screen, and the piece with the dull frosted side is called the ground glass. BradS instructions are correct.

Jon

The frosted piece is glass, so it looks like what I bought on ebay that was advertised as ground glass is actually a Fresnel lens? Sure seems like one to me.

[BradS]

The frosted piece is glass, so it looks like what I bought on ebay that was advertised as ground glass is actually a Fresnel lens? Sure seems like one to me.

if it is frosted then it is a ground glass. A Fresnel lens will have circular grooves in one surface. They'll be small but you should be able to see them on one side if you look closely. Try looking at both surfaces of both items with a loupe or strong reading glasses. Both the GG and the Fresnel lens will have a smooth side. Usually, the Fresnel lens will be made of plastic...and the GG is made of glass. The ground glass is literally ground on one side...that's what appears to be rough. It is as if somebody took very fine sand papper to one side of a piece of glass (in fact, you can make a GG this way). The Fresnel has groves...lots of them and they are in a circular pattern.

[Kevin Crisp]

What confuses people about these cameras is that the Fresnel install is backwards from what is typical. Normally the side with the concentric grooves faces the lens (forward). But on these, the smooth side faces forward.

[BradS]

What confuses people about these cameras is that the Fresnel install is backwards from what is typical. Normally the side with the concentric grooves faces the lens (forward). But on these, the smooth side faces forward.

But still, the Fresnel lens goes in first - and then the ground glass goes on top.

The other thing that is very important is that the Fresnel has a thickness and that thickness turns out to be very important. If you omit the Fresnel, then the Ground Glass will be too close to the lens and focus will be off. Spacers must be used in in place of the Fresnel in this case.

[Kevin Crisp]

Yes, the Fresnel goes in first.

And there is an issue with some aftermarket gg units not indexing properly, so that what looks in focus on the gg is in focus on the film.

[Dan Fromm]

Hmm. The wear pattern on the glass is wrong, send it back.

nbagno, your camera has a Graflok back. Graflex Inc. made two versions of focusing panels for Graflok backs, the original that uses only a ground glass and a later version that a fresnel lens in front of the GG. The two types have the same casting number, can be told apart only by looking at the bosses on which the GG (or fresnel-GG sandwich) rides. The original has higher bosses, the later version for fresnel has lower bosses. I know this is vague.

If you have the original version with high bosses the fresnel should go behind the GG (between photographer and GG). If the later with low bosses the fresnel goes in front of the GG (between it and the lens). The frosted side of the GG always faces the lens.