Need Advice "Best Manual Teleconverter" For manual Lens

Hello I would like a 2x teleconverter for my Samyang 135mm F2. Obviously I do not need a Canon TC, but I really appreciate the optical quality in the canon TC. I am using this for astrophotgraphy so all I really care about is not having coma or chromatic abberation, and being able to shoot at F4. This lens already performs flawlessly at F2 so I should think that it will have no problems working at F4 with a 2x.

What I really want to know is if a manual non chipped TC exists that can perform optically as well as the canon tc? It seems like I could save some $$ by not getting an autofocus TC.
Does anyone have any recommendations or suggestions?

Tom,

I think you were still in multi-quote mode from another thread. . I just wanted to make you aware that you posted a couple of quotes that have no bearing on this topic.

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Oops.sorry. on phone now. Will repost link tomorrow.

Well, if you NEVER wanted to shoot other than 'wide open', a non-chipped non-contact teleconvertor might suit, but one wonders if anyone would make such a product, since most folks would want to stop down the aperture one or two f/stops for improved optical performance for non-astronomical photos.
Or is your lens an old film camera lens with aperture control ring on the barrel of the lens, and you assume the teleconvertor always causes the lens to stop down to selected aperture size?!

When it comes to finding an inexpensive teleconverter, most 3rd party brands are now chipped/electronic. But if your main concern is budget and optical quality, why should it matter? Yongnuo makes a 2x teleconverter that's a direct knock off of the Canon 2x mkIII:

Yongnuo’s Clone of the Canon 2X Teleconverter Costs $180 Instead of $449

Vivatar makes a 2x Canon mount teleconverter for $110

Vivitar Series 1 Teleconverter For Canon

calypsob wrote in post #18517007
What I really want to know is if a manual non chipped TC exists that can perform optically as well as the canon tc? It seems like I could save some $$ by not getting an autofocus TC.

I am not sure why you are thinking this way. . A teleconverter without AF would be a highly specialized item, because there are hardly any people who would buy one. . When things are very specialized, with low demand, that typically drives the price up, not down.

It's like those people that think a DSLR without video would be cheaper than the same DSLR with video. . WHAT????? . That is not sound logic, because the product that is in the highest demand, and sells the most units, will normally be the cheapest product, regardless of what parts and technology it has or doesn't have.

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As I mentioned the Lens is a Samyang 135mm F2, these are all manual, very similar to a Zeiss 135mm APO. I want to work at an aperture no slower than F4 and the 2x TC will bring the wide open F2 aperture to F4. I do indeed wonder if a good manual TC exists, hopefully someone has an answer.

AF is not a huge deal here, I assumed that there might be an older TC which performed well and did not have a chip, or maybe a new one without a chip, I have seen alot of non chipped extension tubes and lens adapters, there are even a few focal reducers. Heck Samyang doesn't chip its EF lenses. I created this post because I have seen a very small selection of TC's and assumed that I might be missing out on a nice one which is not as common.

davesrose wrote in post #18517426
When it comes to finding an inexpensive teleconverter, most 3rd party brands are now chipped/electronic. But if your main concern is budget and optical quality, why should it matter? Yongnuo makes a 2x teleconverter that's a direct knock off of the Canon 2x mkIII:

Yongnuo’s Clone of the Canon 2X Teleconverter Costs $180 Instead of $449

Vivatar makes a 2x Canon mount teleconverter for $110

Vivitar Series 1 Teleconverter For Canon

Excellent, the Yongnuo sounds like the way to go in terms of optic quality. And I like the price much better, especially considering the fact that I have to buy 3 of them..

IMAGE LINK: https://flic.kr/p/ZuBT​sk

http://www.traumfliege​r.de …r/overview.php#​kenko14dgx

This is the link I posted yesterday with errant quotes. It is not in English, but the numbers speak just fine. It may be a tad off-topic, as it only tests wired TCs; no manual TCs here.