Fresnel screens/brighter ground glass?

[welly]

Hi chaps,

It could well be the case that the fairly thin black tshirt I'm using isn't quite dark/opaque enough but have had a few problems viewing the ground glass on my Sinar F2. Actually, it's a fair bet the tshirt isn't opaque enough. I'll get a decent dark cloth on pay day. But as a bid to get an even brighter ground glass, what are the options? I understand a fresnel screen is something worth considering? Is this something that replaces the ground glass or something additional?

Cheers!

Welly

[anchored]

As far as the black t-shirt not being opaque enough... the down-and-dirty cheap fix to that is simply double up on the shirts... when I first started I wore 2 T-shirts and they worked quite well.

I used to use a fresnel (used in addition to the ground glass), but replaced it with a Maxwell screen. Fairly expensive route to go, but to me worth the cost as it was by far brighter than the standard screen with fresnel. With this replacement, it's now bright enough on most occasions to be able to see the ground glass without a focus cloth.

[welly]

Many thanks for your reply. I've got plenty of black tshirts so will try doubling up!

As for the fresnel, I'm looking at one of these on eBay - http://cgi.ebay.com/NEW-HORSEMAN-4x5-Fresnel-Bright-Screen-4-HORSEMAN-SINAR_W0QQitemZ350298286704QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item518f67aa70#ht_4733wt_941

Would this replace the ground glass entirely on my Sinar or is it attached somehow? Any ideas how it attaches?

[rdenney]

But as a bid to get an even brighter ground glass, what are the options? I understand a fresnel screen is something worth considering? Is this something that replaces the ground glass or something additional?

With Sinar, the accessory Fresnel is mounted in a metal frame that clips into the ground-glass frame behind the ground glass, so it is easy to use it when you want it and not use it when you don't. The Fresnel is good for lenses of 150mm and longer, but it will fail you if you attempt to use it with lenses shorter than 90mm.

I use shorter lenses routinely, so I invested in a Maxwell screen for my Sinar, and it was very much worth the investment ($300). It's a marvel even with lenses in the normal range, but I might not have felt compelled to spend the money with lenses in the 150-180 range and longer. The Sinar Fresnel can often be found used in its metal frame for well under $100, though the plastic might be a bit scratched up.

Rick "noting that Bill Maxwell will tell you how to polish those scratches off the Sinar Fresnel" Denney

[erie patsellis]

Note that while many accessories interchange, that fresnel won't snap into the holders for the fresnel on the Sinar.

[welly]

Cheers erie,

I'm going to hold off that fresnel for now and double/triple up on tshirts until it becomes unbearable. I didn't get into this large format game to be spending money :)

[rdenney]

Note that while many accessories interchange, that fresnel won't snap into the holders for the fresnel on the Sinar.

You're right--I missed the link. The Sinar accessory needs to be a Sinar-branded accessory, though sometimes you can buy the frame and attach your own Fresnel. It's easier and no more expensive, though, to just buy it complete.

Rick "noting that Horseman lens boards and bellows are the only interchanging items" Denney

[Ari]

It might be worthwhile contacting Steve Hopf via his eBay store. He can answer some of your concerns and make you a bright new GG for under $40.
http://stores.ebay.com/Steve-Hopfs-Ground-Glass-Store

[JosephBurke]

I'll second on Steve Hopf...replaced the GG in my Toyo 8x10M...wow...now that is one fine and very bright GG..........and I have a Maxwell on my Linhof 4x5........Try Steves first....dang that great glass..

[welly]

Ordered some glass from Steve so should hopefully get it sometime this week. Looking forward to giving it a go!

[Dave Dawson]

I find the Sinar gg/fresnel to be dissapointing compared with other combinations. Because there are two focusing planes when the fresnel is fitted it makes focusing impossible and you have to focus without the fresnel and compose with. This is due to the fact that the ridges of the fresnel is mounted behind the gg and is in contact with the smooth side of the gg which means there is about 1.5mm space between them.

In other systems I've used in the past, the fresnel is mounted on the lens side of the gg with the ridges in contact with the rough side of the gg so there is only one focusing plane, so focusing can be done easily with the fresnel permenantly in place.

It's also a pain storing the fresnel when off the camera resulting in it getting lost or scratched.

Just my two cents worth!

Cheers Dave

[Arne Croell]

I find the Sinar gg/fresnel to be dissapointing compared with other combinations. Because there are two focusing planes when the fresnel is fitted it makes focusing impossible and you have to focus without the fresnel and compose with. This is due to the fact that the ridges of the fresnel is mounted behind the gg and is in contact with the smooth side of the gg which means there is about 1.5mm space between them.

In other systems I've used in the past, the fresnel is mounted on the lens side of the gg with the ridges in contact with the rough side of the gg so there is only one focusing plane, so focusing can be done easily with the fresnel permenantly in place.

It's also a pain storing the fresnel when off the camera resulting in it getting lost or scratched.

Just my two cents worth!

Cheers Dave
Actually it has to be permanently in place. As discussed in several other threads before (like the Chamonix problem one), the downside is that the fresnel changes the optical path and that has to be corrected by shifting the ground glass position. If one takes the fresnel out, the focus plane of the ground glass and the film plane are no longer the same.

[Dave Dawson]

Actually it has to be permanently in place. As discussed in several other threads before (like the Chamonix problem one), the downside is that the fresnel changes the optical path and that has to be corrected by shifting the ground glass position. If one takes the fresnel out, the focus plane of the ground glass and the film plane are no longer the same.

That makes no sense atall...........You can ONLY focus on the ground glass. If you focus on the fresnel it will not be in the same place as the film:confused: I'll leave it there for now.

Cheers Dave

[Frank Petronio]

What Arne said. It's that way with all cameras using fresnels on the lens side of the ground glass.

I don't care for fresnels, I rather see the image without ridges and such. Try to let your eyes adjust....

[Steve Hamley]

That makes no sense at all...........
Cheers Dave

It makes perfect sense. A fresnel lens is a lens, and when it's in front of the GG it's in the path of image-forming light, but it isn't when the film holder is in place.

So try an experiment with any other lens; tape a weak magnifying glass or spectacle lens behind the taking lens, focus (if you can), then remove the magnifying glass. Would you expect the image to still be in focus? The only difference is that the magnifying glass is behind the lens instead of in front of the GG.

But it's incredibly apparent from the Chamonix threads that people don't understand that lenses affect focus. Maybe because fresnels don't look like a regular lens.

Cheers, Steve

[Dave Dawson]

Steve....Is my posting #11 rubbish then?

Cheers Dave

[Dave Dawson]

I geuss not the ? :D

Cheers Dave