Picking ideal lens and fl, for flat copy work

[bglick]

> Why bother asking if you've already made up your mind..?

I don't have my mind made up, hence why I am asking. I just can't find any lenses that seem to out perform the digitar.

I agree with the film recorder concept, but only a CSI film recorder can acheive 40 lp/mm on 4x5, the others perform very inferior, and sharpness is of the upmost criteria, hence why re photographing a back lit trannie will provide the sharpest 4x5 film. CSI film recorders have been discontinued for several years, and no parts are made, so not a good long term solution. In addition, this procedure will be done often, so I need a reliable and consistent method. The only 4x5 film recorders made today, CCG, write at 30 lp/mm to the film, which again, is much inferior to what a sharp lens can deliver to film.

[Jack Flesher]

You won't find any lenses that outperform the digitars... As I said above they are exceedingly sharp.

The real question is do you need that resolution and are the IC's capable of allowing you to generate the image you desire? You seem to believe that the 150 will cover 4x5, and it may, but I suspect you will be left with little to zero avaialble extra IC for movements -- movements that are often critical in copy work to get everything lined up perfectly.

Of course you can back off and crop, but now you are giving up some of the gross resolution you gained by going with the digitar to begin with.

FWIW, I tested a bunch of LF lenses recently using my friend's scanning back. One of the best lenses we tested was a 90mm Digitar -- it made just over 65 LPMM at the center, but fell off significantly 2/3rds the way out. Interestingly, my Rodenstock 150 APO S also made just over 65 LPMM in the center and its resolution also falls off significantly 2/3rds the way out -- but 2/3rds the way out on the APO S is already way beyond the edge of a sheet of 4x5 film. This is what Bill was trying to explain to you above.

It really does sound like your mind is made up, as Tadge said, so why not buy the Digitar and then get back to us with how it works out -- IOW is the IC really big enough and is the MTF really accurate?

,

[bglick]

Jack, thanks for the post....

My only hesitation on the digitars is the Image circle and light fall off.... and of course, what you mention, just how accurate are the MTF's are to begin with? I appreciate you sharing the tests you performed.

After further investigations, I found the digitar information to be misleading, as the Schneider USA site uses the same MTF charts as the German site, however, the German states the MTF charts are for 80mm image circle, whereas the USA site states its for a 150mm image circle. Buried deep in a Schneider brochure, it states the image circles are quoted at max. resolving areas, not the max size image circle the lens can produce. I think the USA site got this information crossed, not surprising. Based on this, and your findings, maybe the Rodenstock APO S is a better choice, as this also has demonstrated some excellent capabilities.

[Jack Flesher]

WG: The APO S is probably not going to perform as well at copy distances -- under 1:10 -- as some of the lenses already mention specifically designed for copy work, like the G-Clarons.

The fact is, a lens is generally designed to generate best performance at over 1:10, between 1:2 and 1:10, 1: 1 and 1:2 or 4:1 through 1:1. Some Rodenstock and Schneider copy lenses are labeled 1x or 2x corresponding to the latter two ranges above. Most of the modern plasmats are better from 1:10 through infinity, and are not true flat-field lenses. Other lenses are optimized for copy work in the 1:2 through 1:10 range -- like the Schneider G-Clarons and Rodenstock Rodagons.

Paul has been doing copy work for several years and can probably tell you more about this than I can since I don't do it for a living. Suffice it to say, there is more to selecting a copy lens than its MTF or image circle -- and it may save you a lot of grief to listen to what folks that do this for a living have to say...

Cheers,

[Jack Flesher]

I should add that I chose a G-Claron as my 210 landscape lens: It is not as hyper sharp in the center as my 150 APO S, but I don't need a 210 often for the way I see landscapes and the G-Claron is relatively light and compact -- especially compared to the 210 plasmats! So it is adequate as a "normal" lens (especially stopped down), but then serves beautifully as my "macro" lens when I want to capture rock patterns or other naturally-ocurring detail with my 4x5 in that sub 1:10 zone...

[bglick]

> Other lenses are optimized for copy work in the 1:2 through 1:10 range -- like the Schneider G-Clarons and Rodenstock Rodagons.

Jack, I agree with this premise, hence why I started this thread. I would have suspected the "copy" lenses would have been better suited for this task, but the MTF data of the digitars clearly pointed me in the opposite direction, which baffled me. Trust me, if the MTF data was even close, I would go with the lens that was designed specifically for this task. Remember, the MTF data I am reading for the digitars is in the same magnfication ratio I plan to use them for, 1:8. (some listed 1:10, some 1:5)

I just checked the Rodagons MTF values at 150mm fl, and even they are much inferior to the Digitars. Either I am missing something, or the new digitar lens design have really trumped older lens designs....or, the MTF data is not reality, but rather a marketing aide. Although, when you look at the lenses with excellent MTF values, they are typically the ones people rave about.

I am not discounting any contributions from people who do copy work. The problem is, unless someone is comparing one lens vs. another, its hard to evaluate their comments. I used to think the SS XL lenses are the sharpest lenses made, till I saw the Mamiya 7 lenses.....then, I saw the digitar 80mm lens and it slightly trumped the M7 lenses. Get my drift? Now copy is a bit of a different animal, but at 1:8, its not too far removed from normal, or non copy lenses... at least that is how I am seeing it......

[Jack Flesher]

Then get the Digitar. Just be sure to report back to us after use it the first time.

,

[paulr]

"unless the entire MTF principle is bunk, the digitar MTF's out perform the G Claron MTF's by a factor of about 3x,"

I don't know how these would compare in real life, but remember that the G Claron is optimised for 1:1 reproduction (with an acceptable range of 1:5 to 5:1). The digitar is an all purpose lens. Those MTF curves don't reflect its performance way outside it's intended magnification range.

it's an interesting question, because the digitar is a much more modern design, but you're also asking it to do something it wasn't designed for.

I'd suggest you call Schneider USA and ask a tech rep. It's been a while since I've done this, but years ago, I got hour long lectures on the phone about optics (and these weren't sales pitches ... it was real information).

If there's no one that helpful there now, shoot me an email and i'll pass along the email address of a product specialist I know at Schneider in Germany.

[bglick]

Paul, I agree that one of the weakness of MTF data is, it is often not supplied at the magnfication ratios you plan to use the lens for, which in most cases, those magnifications would represent an inferior MTF vs. what they offer you. (remember, they are trying to sell lenses) However, I disagree with your comments on the digitars, as the MTF's listed are at the image magnfication I plan to use them for, so therefore, I don't think I will be using it for a task they were not designed for?

I did shoot an email off to Schneider Germany, i will keep you posted.

[paulr]

the other question is what is the final use of these negatives ... how many times will they be enlarged. the digitar lenses, showing mtf values for up to 60 lp/mm, are clearly designed for high multiples, like 4X to 12X enlargements. it's likely that they're great at smaller enlargements too, but they may not be the best. i'd definitely be interested to hear what the schneider people have to say about this.