[cco]

Dear all,

I am considering to use my Pentax SMC DFA 100 mm / 2,8 Macro - Lens with a Teleconverter (Body K5). Currently I try to find answers to the following questions:
- Does it generally speaking make sense to use this lens with a Teleconverter? Will / can it result in (very) good quality?
- What type of Teleconverter (1,4x, 2.0x, etc.) do you recommend to ensure high quality?
- Which concrete Teleconverter can you recommend based on your experience?
- Can you provide URLs to additional readings related to this topic?

Thanks for every help you can provide.

Best, Chris

[Louicio]

What are you trying to achieve?

[Michaelina2]

Dear all,

I am considering to use my Pentax SMC DFA 100 mm / 2,8 Macro - Lens with a Teleconverter (Body K5). Currently I try to find answers to the following questions:
Does it generally speaking make sense to use this lens with a Teleconverter?

No... It can be done, but that's not a good reason to do it.

Will / can it result in (very) good quality?

No to "very", but Yes to "good." If you want "very good" (or better) quality, you will never be pleased.

What's your purpose? If you are you seeking a telephoto on the cheap, forget it. A TC'd 100 will NEVER consistently match the image quality produced by a DA 200, or DA 300, or second-tier third party dedicated FL lens. Don't waste your money on a TC. Get the best lens you can afford that's designed for your desired focal length.

- What type of Teleconverter (1,4x, 2.0x, etc.) do you recommend to ensure high quality?

NONE

- Which concrete Teleconverter can you recommend based on your experience?

Pentax does not make a teleconverter. Third party TC's exist, but I'll be surprised if you are ever completely pleased with the results.

- Can you provide URLs to additional readings related to this topic?

Use the SEARCH function on this and other sites.

Thanks for every help you can provide.

Best, Chris

BTW: I speak from experience using a Pentax 1.7, and/or Kenko 1.7 TC, paired to a 100 WR and K-5.

...my 2 cents... Cheers...

[RioRico]

With certain long fast glass, certain TCs make sense, as more than a few birders will attest. With a 100mm macro lens, a TC does NOT make sense. You will get better image quality by cropping and enlarging than by adding optics that degrade IQ and eat light. If your goal is more reach and adequate speed, are many decent MF and even AF primes and zooms in the 200mm f/3.5-4 range that will cost less than the 'best' TC and will produce better images.

That said, it all depends on intent. WHY do you want to take a macro to 140/4 or 200/5.6? I find a couple sorts of TC handy for specific purposes:

* If I want to fill the frame, and content trumps quality, I'll use a vanilla 2x or even 3x TC. I recommend this for surveillance, blackmail, crime planning, etc -- but you may wish for legal advice.
* If I need reach and *must* stay lightweight (if not exactly unobtrusive), I'll put a 2x TC behind my Enna Tele-Ennalyt 240/4.5; the results are slightly better than with my Sakar 500/8 mirror.
* I like my front-loading Sony VCL-1546A 1.5x tele adapter, which doesn't eat light nor interfere with lens automation. I mount it on my FA50/1.4 to get a 75/1.4 optic, for razor-thin DOF and good IQ.

You may indeed have some purpose that justifies a TC. Please tell us!

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Last edited by RioRico; 06-02-2012 at 08:14 AM.

[normhead]

Tess loves the Pentax 1.7 TC on the Tammy 90 for macros. It increases the magnification. Honestly, while I like the TC for close ups, if you're trying to achieve more range, it's a toss up between using it or not. For birds, if you want feather detail at distance, I don't really like it. For animals with courser hair, then it might be a good thing. But you definitely have to pick and choose when it's going to help you.

[littledrawe]

The more experience I get the more I am content to never own a 2x TC, unless it was given to me for free, I just don't think it is worth the loss in image quality but there are a couple 1.4x TCs that are really good.

[Marc Sabatella]

I'd be willing to wager that a 2X TC on the DFA 100 - which would turn it effectively into a 200/5.6 - would yield IQ no better than the DA50-200 at 200 and f/5.6. Which is to say, better than some give it credit for, but if the DA50-200 does the job more cheaply and easily, what would be the point of the TC? Except, as noted, that it will increase magnification at the macro end, and the DA50-200 would not focus that closely.

[crewl1]

2x TCs are only good for gutting and turning into extension tubes, IMHO.

[RioRico]

Wait! Disregard all of the above! Get a cheap A-type 2x TC. Use it ALWAYS on your new 100 macro. You'll quickly become so disgusted that you'll sell both, cheap. I'll take the lens, OK?

[ultraviolet]

What type of Teleconverter (1,4x, 2.0x, etc.) do you recommend to ensure high quality?

"Pentax rear converter-a 1.4x-s" may be used without loosing significant IQ. I have used it with my A50/2.8 Macro, yet to try with my DFA100.
Rear Converter-A 1.4x-S Reviews - Pentax K-mount Teleconverters and Adapters - Pentax Lens Reviews & Lens Database
A 1.4X-S

http://kmp.bdimitrov.de/teleconverters/A1.4X-S.html

[Danny Delcambre]

Buy +1, +2, and +4 close-up filter better than TC. Try it.

[littledrawe]

DA50-200 at 200 and f/5.6. Which is to say, better than some give it credit for

I totally agree with this this even if it is a bit off topic. I used this one last summer all day at one of my nephews motocross races and I was really surprised how well it performed in this fast paced environment.

[lmd91343]

Chris,

To beat a dead horse, most teleconverters in most situations do not produce good results. A summicron 50mm would have center resolution northwards of 50 line pairs per mm resolution in the center. That is pretty good resolution. It is tough to beat. Put a 2X teleconverter behind it and the resolution will drop by half resulting in 25 lpmm if the teleconverter is perfect. Have you ever seen a perfect lens or teleconverter?. You have just turned a very expensive high quality lens into an ok lens. Start off with an ok lens and halve the resolution and you have... (you get the idea).

If the resultant resolution of the lens teleconveter complex exceeds the recording media, You will be fine. I doubt that happens in most cases. However I do have a Canon 400mm prime lens with a Canon 1.4 teleconveter that produces a wonderful image on film. That is the ONLY combination I have found testing about seven teleconverters with about 40 prime lenses (All Canon brand, not third party. Sometimes the stars line up.

[lmd91343]

~snip~

* I like my front-loading Sony VCL-1546A 1.5x tele adapter, which doesn't eat light

~snip~

That is not the case.

If you increase the effective focal length by adding elements in the front or the back, the result is the same relative to effective f/stop.

The absolute lens opening diameter stays the same, but the focal length increases. Therefore the focal length to lens opening ratio changes. The focal length to absolute lens opening is the definition of f/stop.

Of course a front mounted teleconveter will preserve automation. There is no change in the mechanical or electronic linkages.

[drougge]

That is not the case.

If you increase the effective focal length by adding elements in the front or the back, the result is the same relative to effective f/stop.

The absolute lens opening diameter stays the same, but the focal length increases. Therefore the focal length to lens opening ratio changes. The focal length to absolute lens opening is the definition of f/stop.

The definition is about the front opening actually, and applies to simple lenses. For complex lenses the aperture mechanism usually sits further back, and is smaller than the simplified math would suggest. (The front still has to be at least as big as the corresponding simple lens, but may be bigger.) So assuming the front converter is large enough, it does in fact not cost you any speed. (You'll still lose some light to extra surfaces, and no doubt quality as well.)

And to try to be useful to the OP: I have been happy using a 1.4x converter on my 120mm macro on 645, but I wouldn't do it for reach, just magnification. It's better than a front dioptre in that it doesn't cost you working distance. A good converter is expensive though, and I don't know if your lens has enough resolution to make this better than cropping. A camera with smaller pixels (like the Q) is also an option, and probably not more expensive than a good converter.