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09-23-2011, 08:03 PM   #1
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Purple fringing in macro

Hi again, It's been awhile since I had a question, and that's good! But last week I bought some of those tubes for trying to do macro on the cheap. I thought they worked pretty well--until today. I've been using them with my cheap Promaster 70-300 lens, with which I've been surprisingly satisfied. Anyway it rained and then the sun came out and our juniper bush had drops of water with sunlight on them and they looked like diamonds (or something like that). So I thought I'd play a little more with my tubes. So with all 3 tubes on I took pictures of the sunlit water droplets (of course, from very close). Unfortuantely, in nearly every picture, where the speck of sunshine reflected off the drop there was significant purple fringing. I suppose what I want to know is if that is caused by my cheap lens. Is that characteristic of cheap lenses and would I eliminate this problem with, say, a Limited or * lens? Not that I'm in any position to buy a lens like that, but if my lens is causing the purple, I'll not bother to take any more water droplet pics. Thanks, Jim

09-23-2011, 08:06 PM   #2
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It is a characteristic of some lenses, not necessarily cheap. However, cheaper lenses can be expected to have some sort of purple fringing wide open, or chromatic aberrations. It can be post-processed out, in nearly all cases.
09-23-2011, 08:22 PM   #3
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Cheap tubes might be hurting your image, if they have reflective surfaces inside. Tubes can just not work with some lenses. I tried to turm my FA35 into a macro with tubes, and every image had a giant white spot in the center.

You could try some other apertures next time. A quick blast with the hose on the bushes can recreate the same conditions.
09-23-2011, 08:42 PM   #4
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CA happens most often on out of focus areas, and when shooting macro you have a very very narrow DoF, meaning more of the image, and often some of your subject will be OoF. Lenses that are prone to CA anyway aren't the best choice for macro.

Also, if you have one, a small prime will give much better results with tubes than a big zoom. Most people have a 50mm of some sort, if you do, try that instead. You'll be able to grab more light with it, use a smaller aperture, and increase your DoF. As a very general statement, any prime will be better with tubes than a zoom of similar length.

09-23-2011, 09:48 PM   #5
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As stated above, try to use primes if you can. Even cheap ones do very well, I use an Auto Chinon 50 1.9 which I picked up for some where between $10 - $20 AUD off ebay.
09-24-2011, 01:10 PM   #6
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If the insides of the tubes aren't flat black, spritz them with a can of spray paint. No problem!

The PF is undoubtedly caused by the cheap long tele zoom. Such lenses really aren't suitable for anything like serious macro work -- the design compromises that may be acceptable for casual general work show their shortcomings when working very close, as you see. Many cheap primes will do much better. I have some suggestions:

* Manual prime lenses of 50-55mm and 135mm are cheap and often very good. Those between 55-135mm usually aren't cheap. With a camera prime, to reach 1:1 magnification, you need as much extension as the lens' focal length, and your working distance will be the same. So if you want to work close, a 50mm lens and one set of cheap macro tubes (50mm thick) are right. To work further away, a 135mm lens, and either three sets of tubes or a cheap bellows, will do the trick.

* I really really like using cheap enlarger lenses (ELs) on bellows and tubes. An EL hasn't the body length of a camera lens, so use extension equal to twice the focal length to achieve 1:1. ELs longer than 80mm can usually reach infinity focus on a bellows. I find my 100-105-110mm ELs to be fine for general-purpose and macro shooting on bellows with some tubes as needed.

* Just filter-out the PF in PP.
09-24-2011, 04:31 PM   #7
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QuoteOriginally posted by RioRico Quote
To work further away, a 135mm lens, and either three sets of tubes or a cheap bellows, will do the trick.
Just to add to that, another good, cheap route is to slap a 50mm or shorter prime on the end of your 135mm, reversed. You can get some pretty crazy magnification this way. The other day I experimented with this by reversing a 28mm on the end of my 135mm, and the magnification was just shy of 5:1 (but the DoF was about as thick as a sheet of paper at apertures where you could see much). The only extension with this was caused by the required step down rings and reversal ring between the lenses.

Still, a 50mm on the end of a 135mm is a more moderate approach that works quite well.
09-24-2011, 05:16 PM   #8
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QuoteOriginally posted by Philoslothical Quote
Just to add to that, another good, cheap route is to slap a 50mm or shorter prime on the end of your 135mm, reversed. You can get some pretty crazy magnification this way.
Indeed you can. Reverse-stack a 24mm onto a 200mm and the magnification is 200:24 or over 8x. The downside of reversing any prime is that the working distance is the lens register, which with Pentax glass is about 45.5mm, under 2 inches. Not great for field work nor for subjects that try to escape the intrusion, eh? One trick: Reverse-stack a T-mount lens. T- and T2- and TX-mount have a 55mm register, for slightly more working room. A longer-register MF lens would be even better. But it probably won't be cheap. TANSTAAFL.


Last edited by RioRico; 09-24-2011 at 05:23 PM.
09-24-2011, 05:20 PM   #9
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This is true, everything is a tradeoff. I think that a reversed prime will eat less light than tubes though (it sure seems that way), so if shutter speed is a consideration it might be the better choice, for some things.

For studio stuff with a tripod and rails, I'd assume bellows are the best way to go. I'm only shooting handheld so far, so anything to get more light is a boon to me.
09-24-2011, 07:08 PM   #10
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Thank you all for your replies. The inside of the tubes is threaded black plastic, so I'm not sure if that's shiny or not. And I guess I completely misunderstood the whole thing because I thought you had to use the highest magnification lens you have in order to get any kind of magnifcation. Since that's obviously not the case, I'll try out my other lenses, which will soon include a 50 M 1.7, and see if any of them work better. I just figured for magnification, if I had a choice between 50 or 300, I would obviously go for 300. Unlike riorico, I do not have a mathematical mind and stuff like this doesn't come easily. Actually, nothing seems to come easy.
09-24-2011, 10:23 PM   #11
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A 50mm f/1.7 is ideal, you'll love it. It sounds like the inner surface of the tubes you have is the same as mine - I wouldn't worry about that.
09-25-2011, 12:59 AM   #12
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Me, mathematical? I can barely handle arithmetic and logic; I still cheat at trig and geometry. But I have my bible: FIELD PHOTOGRAPHY, by Alfred Blaker (still an incredible deal at Amazon) with its handy little formulae that I can plug right into a spreadsheet.

I learn from Blaker that there are various ways to get a desired magnification at various working distances. If you don't mind working close and want great magnification, either use a short lens on lots of extension, or reverse-stack a short prime onto a long one. If you want more working distance, use a long lens on LOTS of extension.

Or cheat: use a Raynox or TC, and do a bit of PP cleanup. Do whatever it takes to get a usable image, eh?
09-25-2011, 08:43 AM   #13
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QuoteOriginally posted by jjhenders Quote
Thank you all for your replies. The inside of the tubes is threaded black plastic, so I'm not sure if that's shiny or not. And I guess I completely misunderstood the whole thing because I thought you had to use the highest magnification lens you have in order to get any kind of magnifcation. Since that's obviously not the case, I'll try out my other lenses, which will soon include a 50 M 1.7, and see if any of them work better. I just figured for magnification, if I had a choice between 50 or 300, I would obviously go for 300. Unlike riorico, I do not have a mathematical mind and stuff like this doesn't come easily. Actually, nothing seems to come easy.
It sure doesn't seem logical at first. Here's something I did last year, comparing a 90mm lens with a lens similar to yours:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/98808-300mm-le...ml#post1015299
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