Stacking Low Cost Enlarger Lenses For High-End Image Quality

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rjlittlefield
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Post by rjlittlefield »

RobertOToole wrote:
Does dismantling the lens and reassembling, change the performance ?
The front and cells are sealed like a large format Nikon or Rodenstock lens so I don't think so.
Again a cautionary note...

Unless that's an infinity space between the cells, any decentering or change of spacing will have some effect on the IQ (possibly too small to matter).

And it's not at all likely to be an infinity space, since that would occur at only one specific focus distance, and not the same one that would give infinity space between two stacked lenses.

--Rik

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Post by RobertOToole »

rjlittlefield wrote:
RobertOToole wrote:
Does dismantling the lens and reassembling, change the performance ?
The front and cells are sealed like a large format Nikon or Rodenstock lens so I don't think so.
Again a cautionary note...

Unless that's an infinity space between the cells, any decentering or change of spacing will have some effect on the IQ (possibly too small to matter).

And it's not at all likely to be an infinity space, since that would occur at only one specific focus distance, and not the same one that would give infinity space between two stacked lenses.

--Rik
Thanks for the reminder.

This is the exact reason that I don't expect much out of a lens that you can see where all the retainer rings have been removed/replaced. In my experience the results are always poor to worse especially with high-end lenses like scanner type lenses.

There is a guy on Youtube that removes all the elements out of a Mituyoto 20x M Plan by hand and cleans and then replaces them claiming there is zero effect on IQ. I flinched a little when I watched his video :?

All of the 3 lenses were only hand tightened to be snug, and one was loose but I guess that meets the QA requirements for the componon lens line up as these lenses were sold as new and sealed/bagged with a packet of silicon and boxed when I received them.

Best,

Robert

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Post by ChrisR »

I guess you could check it versus the lens 1/4 turn loose. Better on a vertical setup perhaps, for staying concentric.
I have a couple of lenses with "bits" in them, but I'm wary of un screwing things.
Chris R

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Post by RobertOToole »

ChrisR wrote:I guess you could check it versus the lens 1/4 turn loose. Better on a vertical setup perhaps, for staying concentric.
I have a couple of lenses with "bits" in them, but I'm wary of un screwing things.
Great. Another variable to test?

-Front cell unscrewed 1.4 turn vs tight
-short focus vs infinity
-more and less space between rear and front lens
-CA test using aperture between the lenses vs front lens aperture

Thats only with the 4/28, I still have two more lenses to go :shock:

Robert

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Post by ChrisR »

.....plus some in the post :wink:
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Post by Lou Jost »

No Robert, you should really never be stopping down either of the lenses, just stop down between the lenses with a paper aperture. Use both lenses wide open. Trial and error may be needed to find the best distance to place the aperture behind the front lens.

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Post by RobertOToole »

Lou Jost wrote:No Robert, you should really never be stopping down either of the lenses, just stop down between the lenses with a paper aperture. Use both lenses wide open. Trial and error may be needed to find the best distance to place the aperture behind the front lens.
Hi Lou,

Yes, I agree, you are right of course but the front lens aperture is so much easier. I would like to run both side by side to see the difference. You never know after trying it the right way I might stop using the front lens aperture eventually.

:D


Robert

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Post by Lou Jost »

I don't really know how much difference it makes...

rjlittlefield
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Post by rjlittlefield »

Heh, well, at higher magnifications the optimum location might actually be inside the front lens, at a place closer to its own iris than any place you might reach to add one. No practical way to tell except to test it.

--Rik

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Post by RobertOToole »

Lou Jost wrote:I don't really know how much difference it makes...

Made an 8mm paper disk. Works great. Not difficult to make and the results are fantastic.

So the next question is can a Componon perform as well as a Mitutoyo 5x Objective?

I ran a test at 4.3x with Makro-Symmar+Componon 4/28 vs the Mitutoyo 5x pushed down to 4.3x @ f2.9. I still need to sort through and convert the files.

This is the Makro-Symmar+Componon 4/28 at 100% center crop taken from an embedded jpeg.

Image

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Post by rjlittlefield »

Robert, can you clarify what "f2.3" means in the image?

--Rik

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Post by RobertOToole »

rjlittlefield wrote:Robert, can you clarify what "f2.3" means in the image?

--Rik
Hi Rik,

This was one of a few Jpegs I used for a quick comparison to sneak a look before I had a chance to process the RAW files and I was so enthusiastic about the results I didn't think about the label.

The label is an estimated nominal f-stop since its between the 9,5mm f2 disk and 6,5mm f2.9 disk.

Processed two raw files now and they look super, both the Makro-Componon-28 and the Mitutoyo 5x @ 4.3x.

Robert

Miljenko
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Post by Miljenko »

RobertOToole wrote:...but with the slower old-fashioned manual method I can easily compare files.
Trust me, Robert, it is even easier to compare numerical figures than stare to blocks and traces.
RobertOToole wrote:It would be a different story of course if I had 100 MTF curves on my hard drive already.
I believe that so far you have tested more than 100 lenses. So you actualy could have 100+ MTF curves on your HD. :-)

You have put a huge effort (not to mention investing in all those lenses) to get to very valuable results. However, if you were using MTF measuring methods, results would be universal and comparable over a wider database. After all, lens manufacturers are using MTF method with a good reason. Although visual comparison can be fun, it can sometimes be missleading. Even USAF 1950 comparison method is not 100% proof as it depends on visual assesment. Tried it all since 2004. and ended with MTF method as the most reliable.
All things are number - Pythagoras

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Post by RobertOToole »

Update:

This morning I measured a SK 28/2.8 Componon V-mount that I happen to have on hand.

Measuring the front and rear pupils gives me:

f/2.87 front
f/2.71 reverse

Honestly I thought the f/2.8 label was a little optimistic since the iris is not fully open, the f/2.8 lens is on the right.

Image

This lens was never anything special, it was not as sharp as a few 4/28 componons that I have also owned over the years but the corners were a little more consistent but the image quality was a little below average with this sample. So I swapped out the 4/28 for the 2.8/28 lens for a quick test and this results was a real surprise.

Image



So a lens that is not especially sharp or clean on extension is very sharp and CA-free when stacked with the Makro-symmar.

So looks like I am keeping it, I removed the lens from my Ebay listing this morning. :shock: :D

Robert

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Post by RobertOToole »

Miljenko wrote:
RobertOToole wrote:...but with the slower old-fashioned manual method I can easily compare files.
Trust me, Robert, it is even easier to compare numerical figures than stare to blocks and traces.
I actually prefer to look at images, some of the wafers have interesting patterns, rather than just stare at numbers. I can see an engineer or accountant might prefer the opposite.:D

In my experience some sites, not your tests, but some sites that use MTF are useful to compare lens to lens within that website but when you look at the real world results from that lens there is not much correlation between images and the ratings. For example one lens might place 2nd of all time based on MTF but the lens is almost unusable in the real world due to poor coverage and high CAs.
RobertOToole wrote:It would be a different story of course if I had 100 MTF curves on my hard drive already.
I believe that so far you have tested more than 100 lenses. So you actualy could have 100+ MTF curves on your HD. :-)

You have put a huge effort (not to mention investing in all those lenses) to get to very valuable results. However, if you were using MTF measuring methods, results would be universal and comparable over a wider database.


I disagree with you here Miljenko. I firmly believe you cannot compare MTF data from one source to another, or even within the same site or database sometimes due to test parameters changing.

Some sites sharpen Jpeg images for MTF, some use RAW converted files, Some use razor blades, some sample 10 lenses and spin the lens for 5 readings and average. There are too many variables.

Some MTF test sites us an optical bench without even using a camera body.

After all, lens manufacturers are using MTF method with a good reason.
These are just computer simulations based on an ideal lens design. Only one manufacturer shares tested MTF and that is Zeiss so that is not exactly a endorsement. I would argue the opposite. MTF from manufacturers is one way the marketing department can mislead customers with overly optimistic performance promises so these should never be trusted.


Also as far as I know, no MTF lens test site or manufacturer shares MTF data at close up distances or magnification. 100% as far as I know are at an estimated infinity distance. We all know this is not going to be an accurate way to judge a 1x macro lens.

Testing a production lens at magnification the only real way to know how a lens performs.
Although visual comparison can be fun, it can sometimes be missleading. Even USAF 1950 comparison method is not 100% proof as it depends on visual assesment. Tried it all since 2004. and ended with MTF method as the most reliable.


I agree with you here.

Best,

Robert

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