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View Full Version : Ross Xpres f4.5 305mm Coverage?



Colin D
23-Jan-2015, 04:25
Would the Ross Xpres f4.5 305mm (12in) cover 8x10?

Regards

IanG
23-Jan-2015, 11:29
The 305mm / 12" F4.5 Xpres covers 8x6 (whole plate) according to Ross themselves. That includes room for movements.

Ian

Louis Pacilla
23-Jan-2015, 11:42
The catalog claim is WP 6 1/2 x 8 1/2 but would certainly cover the next size so 8x10. If your using it for full length portrait or say H&S portraits it will cover fine but that FL is a little wide for H&S portraits on 8x10. @ infinity focus you can cover up to a 10x12 stopped down but only head on w/ no movements so around 60 degrees @ small stops.This is a Tessar clone w/ three elements in the rear cell instead of two like original formula. They & Gundlach claimed better corrections but this is not proven.

IanG
23-Jan-2015, 11:53
The catalog claim is WP 6 1/2 x 8 1/2 but would certainly cover the next size so 8x10. If your using it for full length portrait or say H&S portraits it will cover fine but that FL is a little wide for H&S portraits on 8x10. @ infinity focus you can cover up to a 10x12 stopped down but only head on w/ no movements so around 60 degrees @ small stops.This is a Tessar clone w/ three elements in the rear cell instead of two like original formula. They & Gundlach claimed better corrections but this is not proven.

It's not a Tessar clone, the Xpres was a Patented design which claimed improved definition across the whole aperture range particularly wider open compared to a Tessar.

However your right we know assume the 200mm Tessars cover 10x8 but before WWII CZJ claimed they covered 8x6.

Ian

Dan Fromm
23-Jan-2015, 13:23
It's not a Tessar clone, the Xpres was a Patented design which claimed improved definition across the whole aperture range particularly wider open compared to a Tessar.

However your right we know assume the 200mm Tessars cover 10x8 but before WWII CZJ claimed they covered 8x6.

Ian

Stuff and nonsense. Whether an Xpres has a cemented doublet (like a Tessar) or a cemented triplet (as in an attempt to avoid infringing the Tessar patent) depends on when it was made.

Stuff and more nonsense. A Tessar's coverage depends on its maximum aperture and when it was made. F/6.3ers have the most coverage, f/4.5ers' coverage grew with redesigns.

Louis Pacilla
23-Jan-2015, 14:11
Stuff and nonsense. Whether an Xpres has a cemented doublet (like a Tessar) or a cemented triplet (as in an attempt to avoid infringing the Tessar patent) depends on when it was made.

Stuff and more nonsense. A Tessar's coverage depends on its maximum aperture and when it was made. F/6.3ers have the most coverage, f/4.5ers' coverage grew with redesigns.

Thanks Dan.;)

IanG
23-Jan-2015, 14:41
I can only comment from experience of using Xpres lenses as well as Tessars (not hype or theory), I always use Tessars carefully and get excellent images, my Xpres lenses are slightly sharper though.

I accept your comment on Tessar series F3.5 & faster, f4.5 and f6.3, I've not yet tested my f5.3 165mm CZJ Tessar (quite rare) but expect it to be very sharp.

Ian

Colin D
26-Jan-2015, 13:07
Long weekend away, just back to this.

Thanks to all for your insights.

Colin D
26-Jan-2015, 13:11
A Tessar's coverage depends on its maximum aperture and when it was made. F/6.3ers have the most coverage, f/4.5ers' coverage grew with redesigns.

Hi Dan, My Xpres is apparently a later build, 1950's or 60's, Serial Number 244752, would that make any difference?

Dan Fromm
26-Jan-2015, 15:24
Colin, I can't be sure. Simple stupid rule of thumb is that early f/4.5ers cover around 90% of focal length, late ones (yours is probably late) around 110%. But this is a simple stupid rule of thumb and ain't exact or even always right.