Non reversed lens stacking.

austrokiwi1 · Post by **austrokiwi1** » Wed Feb 25, 2015 1:24 am

My list of tasks is getting longer...and I am laid up with the worst dose of gout I have ever had ( teach me for doing a body building programme, as part of a weight loss programme and going on a high protein diet.

I became intrigued by telecentric lenses... my aim I have a very rare medal( 64,5mm in diameter( less than 10 exist). It has a huge amount of fine detail so I want to stack and stitch to get the highest quality images. Telecentric seemed the way to go but the info provided in this forum has sent me back to basics. In attempting to set up a telecentric rig, I serendipitously discovered how to get use out of a Large format Schneider Kreuznach 210 f5.6 enlarging lens. I mounted it in front of a minolta 100 mm F4 bellows lens:

Prior to this the only way I could even get an image was to use two extension ring sets and the bellows at full extension...that let me set the lens at around 900mm from the subject...with a huge loss in image quality due to increased vibration( just think about the A7r shutter and an unstable set up!!!) You can see in the photo how much The working distance was reduced. I also found I could vary the magnification by extending the bellows that the minolta 100 mm was on. As serendipitus as it was for me....what have I actually achieved (ignore telecentric, thats off my map for now)?

I like the results I was seeing, but I have yet to formally test the resolution of this set up and won't be testing for a while until I have got a good handle on the resolution of my lenses on their own.

another immediate question following the first( what have I actually achieved in technical terms) how do I calculate the magnification? Of course I can just photograph a Ruler but I want to understand the theory behind what I have done

austrokiwi1 · Post by **austrokiwi1** » Sat Feb 28, 2015 6:44 am

I think I have an answer: I was achieving almost absolutely nothing in regards to magnification. In the absence of an answer so far I got out a Ruler and checked the magnification of the 100mm Minolta lens on its own. I then tried the the two lenses together with the minolta in the same position. From the measurement I was getting almost exactly the same magnification I will have to try a calibration slide I might be getting a very slight increase in the magnification...but not enough for my purposes. I tried the SK Reversed and there was no difference...suggesting to me that the lens arrangement is symmetrical in the SK( but I could be wrong).

I am not going to give up on that SK just yet I know it has a long working distance so I will try it in the field on some flowers and insects in a few weeks. Even though with my bellows it will only produce 1-2 magnification, with close to a meters working distance it might prove to be useful.

ChrisR · Post by **ChrisR** » Sat Feb 28, 2015 7:47 am

The focal length is the same both ways round, so the magnification would be similar. You may win or lose on working distance. You would expect quality to be best with the lenses working near their designed object & image distances.

1-2 magnification, with close to a meters working distance

Remember again, you'll only be using a tiny angle the lens was designed to cover, so you're asking a lot for high quality where you're interested.

rjlittlefield · Post by **rjlittlefield** » Sat Feb 28, 2015 10:47 am

austrokiwi1 wrote: how do I calculate the magnification? Of course I can just photograph a Ruler but I want to understand the theory behind what I have done

I confess to skepticism, but perhaps an answer to your question lies in the Wikipedia article on "Lens (optics)". The section in "Compound lenses" dealing with lenses that are "separated in air by some distance" contains the formulas that govern your system.

The reason for my skepticism is that except for a few special cases, I find that I never have a good intuitive understanding about lens combinations that have significant gaps between the lenses. I also find them quite difficult to handle by calculation. One bit of useful intuition is that in your situation, if the rear bellows extension is fixed, then adding that extra lens in front will generally give you more magnification than you would have without it, but the increase diminishes in a complicated way with larger spacing between the two lenses.

Rather than trying to make predictions from the formulas, I find it more effective to use the WinLens3D Basic software program (http://www.winlens.de/). This free program definitely has a learning curve, but it's not too bad if you restrict investigations to approximations like thin lenses with just separations between them. The reason I like WinLens3D is that it has a simple user interface that works directly in terms of object distance, image distance, and magnification that are produced by lens focal lengths and separations. The result is consistent with the math formulas when those are properly used, but with WinLens3D it's much harder to misapply or misinterpret the theory. At least that's my experience.

--Rik

austrokiwi1 · Post by **austrokiwi1** » Sat Feb 28, 2015 11:35 am

rjlittlefield===>Thanks I will look at that win lens software. I am still wondering why the magnification is little different while my perception was that there was a marked improvement using the two lenses over just one. I am wondering if that was just me seeing something that wasn't there or there's another factor at play, contrast resolution? I had put the purchase of that Large format SK enlarger lens down to a good investment in experience( euphemism for mistake). BUt it is teaching me a few more things

with macro photography my biggest challenge is the maths. I have to be honest for much of my working life my main mathematical language has been Statistics( up to factor analysis) and in the last 20 years computer software has made me lazy........I doubt I could do a standard deviation calculation by hand now without having to pull out a text book( slight exaggeration) The trigonometry involved with macro photography has thrown me. I am awaiting the arrival of Enrico's book.... I am sure I am going to get a sore head trying to work out Arctan etc.

ChrisR====> yeah it may well be the SK just isn't going to cut it. this time last year I was using a canon FD200mm F4 macro. I loved the working distance...but the CA was shocking. I can recall coins with purple fringing on the high points of the design( not just the edges). What I did love about that lens was the working distance. With insects it was great! Its what prompted me to look at the SK 210 enlarger lens. I am still kicking my self for missing an ebay sale of a Minolta APO 200mm macro that ended at €500.00.

Charles Krebs · Post by **Charles Krebs** » Sat Feb 28, 2015 12:47 pm

I'll leave the lens calculations to others....

But you have my deepest sympathy for your gout attack!

Allopurinal

austrokiwi1 · Post by **austrokiwi1** » Sat Feb 28, 2015 1:24 pm

Charles Krebs wrote:I'll leave the lens calculations to others....

But you have my deepest sympathy for your gout attack!
Allopurinal

Thanks. Allopurinal & dried cherries(too early for fresh ones). I am at the stage of regaining my sense of humour.2days ago removing my right big toe with a shot gun was seeming like a good option

Non reversed lens stacking.

Non reversed lens stacking.

Re: Non reversed lens stacking.