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05-26-2010, 12:22 AM   #1
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Are my 1.7x TC expectations to high?...

I purchased a Pentax AF 1.7x TC a few months back and I just love how it enables AF on my old manual lenses. But more importantly, I was after the highest quality TC money could buy. And though this would qualify as the best TC I've ever owned, I wanted to know if I was being realistic about an issue that's been bothering me...

Today I decided to do a test with a 200mm lens(340mm) and though resolution seemed very good:

Pentax K20D, M42 Telear-N 200mm, Pentax AF 1.7X TC, f/3.5(wide open)


I'm finding pretty strong purple fringing at the edges of the scene which I have not been successful in removing in RAW development(seems unaffected).

So I wanted to run this past others here and ask if you think I'm being unrealistic about the results I'm getting now. I only payed 100 dollars for the lens so Its not like I'm at a huge loss or anything. I guess if I had to summarize, I'd say, I'm just a little disappointed with this type of side effects TC's have on lenses.

PS. The PF is not apparent on this scene as it only seems to occur at the vertical extremities of the image(left and right edges).

05-26-2010, 01:43 AM   #2
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QuoteOriginally posted by JohnBee Quote
So I wanted to run this past others here and ask if you think I'm being unrealistic about the results I'm getting now. I only payed 100 dollars for the lens so Its not like I'm at a huge loss or anything. I guess if I had to summarize, I'd say, I'm just a little disappointed with this type of side effects TC's have on lenses.
My guess, and it's only a guess, is that the the CA you are seeing is not primarily the result of the TC but the prime it's connected to.

You are pushing the hell out of a old film camera lens that was never very well corrected for CA in the first place. CA wasn't a big deal in film days but sensors are much more sensitive to CA than film.

Try the TC on a modern APO lens before you get too bent out of shape about CA in your TC.

BTW the way your pic is not a very good example for seeing CA it's too small and complex.
05-26-2010, 01:58 AM   #3
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IMO, I believe the CA you are seeing is from the lens itself. The lens is from an old film camera lens that was never very well corrected for CA in a dSLR. I agree with wildman assessment that CA wasn't a big deal in film days but in today's digital technology, sensors are much more sensitive to CA than film. So I think it is not the TC's fault, more from the lens.

Like wildman's suggestion, try the TC on a lens made for dSLR and see the difference (if any). Also try to take a different picture to explore the CA as the current picture shows a very small CA only.

Cheers.
05-26-2010, 02:35 AM   #4
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Thanks guys... I agree with the usefullness of the image, and I will take more photo's today and post them here to reproduce the issue I mentioned(in aprox. 2 hours).

05-26-2010, 07:59 AM   #5
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Most of the CA may be due to the lens itself and not the TC but don't TCs add some extra/exaggerate the amount of CA to any lens that is already susceptible to CA?
05-26-2010, 08:24 AM   #6
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Hi John,

If you are out taking pictures, I wonder if you would take one more for me as a test: Take a picture of the exact same subject but without the TC. Then crop just 40% and compare with the image using the TC.

Sometimes I really wonder if TC's are worth the hit in max aperture, and the reduction in sharpness, in this age of high resolution cameras like the k-7, and excellent optics. A 40% crop is not really a big crop for a k20d or k-7 unless you are planning to print poster sized.
05-26-2010, 08:38 AM   #7
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here is an example of the smc pentax 300mmF4 and the 1.7x AF TC.

The old SMC tele's are known for generating purple fringing, or more appropriately Chromeric Aborations (CA)

this can be removed in PP using PSP X3 (pr any corel PSP product for that matter)



this is a 100% crop out of a much larger image with the K7. The heron filled the entire frame.

While it was shot to show the quality of shake reduction (shot at 500mm, 1/40 second) it also shows the quality of the image with respect to sharpness.

I might object to cropping this from an image shot at 300mm,

As far as I am concerned a good TC, and the SMC-F 1.7x AF is one of them, is worth the money and resulting image. A cheap one is a waste of time.
05-26-2010, 09:26 AM   #8
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QuoteOriginally posted by KxBlaze Quote
Most of the CA may be due to the lens itself and not the TC but don't TCs add some extra/exaggerate the amount of CA to any lens that is already susceptible to CA?
I just got in from taking some shots, and I did many with and without so... I'm hoping to find the answer to this too(shortly).

QuoteOriginally posted by PentaxPoke Quote
Hi John,

If you are out taking pictures, I wonder if you would take one more for me as a test: Take a picture of the exact same subject but without the TC. Then crop just 40% and compare with the image using the TC.

Sometimes I really wonder if TC's are worth the hit in max aperture, and the reduction in sharpness, in this age of high resolution cameras like the k-7, and excellent optics. A 40% crop is not really a big crop for a k20d or k-7 unless you are planning to print poster sized.
That's a great idea actually! - I just got in(back yard) so I'm going to go back out and shoot some similar frames to test out this theory also. The only advantage I could see beyond this point would be the AF factor.. however, if it comes at the expense of CA, then I think you may have a very good argument against using a TC


QuoteOriginally posted by Lowell Goudge Quote
here is an example of the smc pentax 300mmF4 and the 1.7x AF TC.

The old SMC tele's are known for generating purple fringing, or more appropriately Chromeric Aborations (CA)

While it was shot to show the quality of shake reduction (shot at 500mm, 1/40 second) it also shows the quality of the image with respect to sharpness.

I might object to cropping this from an image shot at 300mm,

As far as I am concerned a good TC, and the SMC-F 1.7x AF is one of them, is worth the money and resulting image. A cheap one is a waste of time.
Wow the sharpness is good there too!
And I see pretty much the same type of rendering I'm getting from my own lenses here, especially in the OFF regions.

Here's a shot I took this morning using the same lens. Except this time I held back a bit on the exposure in hopes that it would help reduce the effects. It was overcast also, and so that didn't help as contrast and saturation adjustments both contribute(amplify) the effects of CA.



UNPROCESSED, K20D, ISO1600, TELEAR-N 200mm, AF 1.7x TC


And crops of the areas where the CA seems problematic:







And the result after using Helicon Filter 5 for CA corrections and some quick CS5 adjustments(sloppy masking):

PROCESSED, K20D, ISO1600, TELEAR-N 200mm, AF 1.7x TC



I'm off to take more shots and find some answers...
PS. I payed 90USD for the lens btw.


Last edited by JohnBee; 05-26-2010 at 09:34 AM.
05-26-2010, 09:37 AM   #9
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the images you have are great.

there is nothing wrong with the TC and you would see the same issues without the TC and a tighter crop.

What you see is simply a result of the CA present in the lens and the marginal DOF of a long tele lens.

You may be too critical of the results, after all, who looks at a bird at 2-20x life size.
05-26-2010, 11:05 PM   #10
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Yes you have a bit of CA in your pics but I've seen much worse:

What a virtually perfect color corrected lens looks like. This is a 600mm glass cost about $4000. Not mine BTW...

Last edited by wildman; 06-08-2010 at 05:57 AM.
05-27-2010, 05:35 AM   #11
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wildman

you can get images like that without spending $4K, just control the lighting situation.

here is the same smc 300 F4 with 1.7x AF TC, using a flash and stopping down a bit. This has been posted before, but it is one of my best shots and shows what the 300F4 can do when used with the TC.

05-27-2010, 09:33 AM   #12
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QuoteOriginally posted by wildman Quote
Yes you have a bit of CA in your pics but I've seen much worse:

What a virtually perfect color corrected lens looks like. This is a 600mm glass cost about $4000. Not mine BTW...
Just gorgeous...
05-27-2010, 11:11 AM   #13
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Hi John,

I'll add my 2 here, but with the caveat that I'm an extensive user and supporter of the 1.7x AFA, so keep that in mind. The best lens I have for CA/PF control is a newly acquired Sigma EX 180 f3.5 Macro APO DG. The only times I've seen any color aberrations with the lens alone have been with PF on pinpoint highlights that are blown out, and the same is true with the AFA mounted, but it's no worse, and since the areas effected are so small, it's not really an issue. I'm a novice at macro shooting, and am just getting my head around using flash with this setup (so I can shoot it handheld), so exposure mistakes with some very high contrast areas are inevitable, and I've made my share, but I've yet to see any instances even in very extreme examples where the AFA has added any color aberrations.

I've also used the AFA extensively with FA*300's, both the f4.5 and f2.8. Both of these lenses control CA/PF very well, but are not perfect, nor as good as the Sigma 180 in this respect. IMO, the AFA magnifies the existing color aberrations, but does not add to it. This is, for me, an expected result -- and is not a matter of concern.

Scott
05-27-2010, 01:59 PM   #14
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QuoteOriginally posted by Nachodog Quote
Just gorgeous...
Maybe you will like this one too...

... same lens with 2x TC in low light deep woods situation.

Last edited by wildman; 06-08-2010 at 05:57 AM.
05-28-2010, 01:47 AM   #15
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I just wanted to post that I still plan on posting my before and after TC results here shortly. It's been nothing but rain these past few days here(arg!) and so I'm waiting for thins to clear-up. It looks like today might be the day though(cloud breaks and singing birds at 5am). I have 7 200mm lenses to run some tests with, so it should be interesting

OH and that's one hell of a shot for the Cardinal(that is a cardinal right?).
But at $4000, it makes me quite content to sit on the sidelines with my budget lenses

Thanks to all who have been helping out btw.
I love this community!
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