Some lens tests at 0.7x with an ancient coin

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ray_parkhurst
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Post by ray_parkhurst »

kaleun96 wrote: Out of interest, has anyone here tested a Computar/Kowa 1.9/55?
That one has been on my watch list for a very long time. Have never seen one for sale.

kaleun96
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Post by kaleun96 »

ray_parkhurst wrote:
kaleun96 wrote: Out of interest, has anyone here tested a Computar/Kowa 1.9/55?
That one has been on my watch list for a very long time. Have never seen one for sale.
Only €1500 and from Prague!
https://www.ebay.de/itm/Kowa-Computar-D ... 3268315408

ray_parkhurst
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Post by ray_parkhurst »

kaleun96 wrote:
ray_parkhurst wrote:
kaleun96 wrote: Out of interest, has anyone here tested a Computar/Kowa 1.9/55?
That one has been on my watch list for a very long time. Have never seen one for sale.
Only €1500 and from Prague!
https://www.ebay.de/itm/Kowa-Computar-D ... 3268315408
Hah! You made me realize I had deleted my search, and missed the lenses from that seller. That's a bit pricey but it's still nice to see that the lens is not another unicorn.

My understanding is the lens is good at f2.8. It also has a magnification adjustment ring like the MacroVaron / 150 Printing Nikkor. Looks like a nice lens.

I have the Apo version of the Computar 50mm enlarging lens (Apo-Computar). Picked it up thinking it would be a good lens to stack, but like most of my lens stacking experiences, no luck.

kaleun96
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Post by kaleun96 »

You made me realize I had deleted my search
On that note, I assume saved eBay searches are considered to be private affairs that don't get shared around here? At least that's my thinking considering it's what gives one member the edge over another in finding a bargain.
Picked it up thinking it would be a good lens to stack, but like most of my lens stacking experiences, no luck.
Robert seems to have all the luck there!

How do you know whether a particular lens might be worth stacking? Something I haven't explored too much yet.

RobertOToole
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Post by RobertOToole »

kaleun96 wrote:
RobertOToole wrote: I was looking at that lens, the price is ok, but that damage scared me away. Looks like someone dropped it and tried to 'fix' it.


Hope the Bogen is a decent performer, give us a short report after you test it, ok?
Yeah exactly, the ding on the filter thread doesn't bode well. I was thinking of offering a fair amount less for that lens before the Bogen popped up.

I will be away later this month so lens tests will likely have to wait until May but it will be the first thing I do when I return!

Out of interest, has anyone here tested a Computar/Kowa 1.9/55?
I do know that John J. on the forum has two, just a guess, but Ray probably has one. The issue is every copy I have seen has element de-lamination so most you find or see for sale have been 'serviced' at some point. I don't know if its even possible to get a clean factory calibrated sample.

Years ago one of the Computar dL designers was selling his personal stash of lenses on eBay including a 1.9/55. By the time I found the auctions using eBay search all the lenses were sold but that would have been the auction to get a hold of a clean copy. It might be impossible now but you never know with eBay, stranger things have happened.

Best,

Robert

ray_parkhurst
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Post by ray_parkhurst »

RobertOToole wrote:
kaleun96 wrote: Out of interest, has anyone here tested a Computar/Kowa 1.9/55?
I do know that John J. on the forum has two, just a guess, but Ray probably has one. The issue is every copy I have seen has element de-lamination so most you find or see for sale have been 'serviced' at some point. I don't know if its even possible to get a clean factory calibrated sample.

Years ago one of the Computar dL designers was selling his personal stash of lenses on eBay including a 1.9/55. By the time I found the auctions using eBay search all the lenses were sold but that would have been the auction to get a hold of a clean copy. It might be impossible now but you never know with eBay, stranger things have happened.
I don't have one, but it seems I'm not alone in the search. It's good to know about their proclivity toward delam. The ones listed from Czech Republic are described as "beginning haze", which may mean delam and is a definite red flag either way.

Regarding eBay searches, I don't generally mind folks knowing what I am searching for. Others are probably searching for same things, but oh well. I score sometimes, and am happy about it, and others score, and I'm happy for them.

Lou Jost
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Post by Lou Jost »

This is the first I've heard of this lens, and I can't find any test results for it. Is there a reason why it is so expensive?

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Post by ray_parkhurst »

Lou Jost wrote:This is the first I've heard of this lens, and I can't find any test results for it. Is there a reason why it is so expensive?
I'll try to dig up the test results and docs and publish them here. There is a great brochure for Computar lenses which has some very interesting test methods and perspectives not seen in other documentation. Recommended reading.

Computar claimed this lens is optimum at f2.8, which makes it the fastest enlarging lens ever made. There are other f2.8 (wide open) lenses out there, but none are diffraction-limited at f2.8. All require to be stopped-down. It also has a "CAS-style" magnification adjustment ring, so can be optimized over a wide mag range. All in all the price is justified if the particular copy lives up to its hype, which I've never been able to verify. I have seen some images showing poor LoCA control, but it may be that the lens was not a good copy, or it might not have been optimized properly using the mag ring. Just not sure until I see results myself or from a trustworthy source.

Lou Jost
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Post by Lou Jost »

Thanks Ray. The bad LoCA might be due to its design as an enlarger lens, working with absolutely flat subjects. The designers may have prioritized correction of other aberrations.

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Post by RobertOToole »

Lou Jost wrote:This is the first I've heard of this lens, and I can't find any test results for it. Is there a reason why it is so expensive?
All the DL Computars were said to be diffraction limited "DL" and the 1.9/55 was the only one with a compensation ring for magnification.

There is one test that I know of, it's a good read when you have some spare time:

http://ctein.com/PostExposure2ndIllustrated.pdf

The APO-EL Nikkor 105 was rated highest in the test in the notes.

Short excerpt:

Image

Lou Jost
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Post by Lou Jost »

Thanks Robert. I had seen those tests before but didn't notice the Computar had a beta ring. I see the test shows best aperture is f/4, no different from most of the other lenses there, so not offering much escape from diffraction. But the beta ring is an important advantage.

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Post by Lou Jost »

I see that ctein, in his book, elaborates a bit on his Computar test results:
"For instance, my 55mmComputar shows so little contrast at f/1.9 that it is unusable at that aperture. Its sharpest aperture is f/2.8, but f/4 is the optimum aperture when one takes into account contrast and light falloff."
"Pick a lens that matches the range you normally work within. A lens that performs superbly at 10X will probably look very bad at 3X or 40X. As an example, my 55mm f/1.9 Computar is unsurpassed in sharpness when used within its wide magnification range of 4X to 20X. It has an adjustable front element for optimizing its performance at each magnification. Outside that range, performance drops off rapidly. The extreme-enlargement illustrations in most of my articles are made with an ancient 28mm f/4 Componon. That lens was designed for subminiature format and much greater mag-nifications. It can’t hold a candle to the Computar over the Computar’s working range, but at 40X it’s markedly sharper. At the low magnifications, the Computar’s color correction deteriorates. I can make great separations with it from 35mm on 8” x 10” film,but it’s useless for making seps on 4” x 5” film: the resolution is fine, but the color fringing is horrible."

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Post by ray_parkhurst »

The marketing doc and spec sheet are on John Jovic's photocornucopia page:

http://photocornucopia.com/1057.html

Lou Jost
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Post by Lou Jost »

I had just found those as well. What a nice set of documents! I wish more lens marketing info was as detailed and technical as those are. Nowadays it all seems to be hype.

However, I lost some confidence in the writer when he started talking about Fourier analysis in terms of the "sign function"!!

ray_parkhurst
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Post by ray_parkhurst »

Lou Jost wrote:I had just found those as well. What a nice set of documents! I wish more lens marketing info was as detailed and technical as those are. Nowadays it all seems to be hype.

However, I lost some confidence in the writer when he started talking about Fourier analysis in terms of the "sign function"!!
I missed that...not a good sine.

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