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08-16-2011, 06:33 AM   #1
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Teleconverter on a 500mm mirror lens

Hey all.

Thinking of picking up a cheap used teleconverter for occasional use with my Tair 3M-5CA 500mm f:8 mirror lens & K-x. I'd only be using it in bright sunlight for bird shots. Here's my question:

I can focus the lens as it is easily with my KatzEye Optibrite split-prism screen, but I know if I use a TC, it'll make focusing trickier. But will it be so dark as to make it impossible to focus? I'd like to find a cheap 1.4x TC so I don't lose too much light.

Or would I be better off to just crop & bypass the TC altogether?

I've noticed for some odd reason the 1.4x TCs are more expensive than the 2x. You'd think the 2x TCs would cost more... Go figure.

Cheers,
Bobbo :-)

08-16-2011, 06:54 AM   #2
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I use a Vivitar f8 500mm mirror lense with a 2x converter with no real problems. The focusing of the lens is softened a bit but a bit of PP can help that out a bit. It does not create the best quality images but it will give you a nice long focal length lens to work with. The good thing about this set-up is that for its effectivre length of lens, it is nice and compact to carry around. I would recommend the use of a tripod where using this set-up. A monopod can also be used help keep camera steady. You will need to bump up ISO as well to at least 400 in bright sun light to get a good shutter speed.

If you are looking at getting higher quality images, you will need to look at much more expensive lens options. By starting out by using this less expensive alterative, you can see if the cost of going to higher quality glass worth to you.
08-16-2011, 07:25 AM   #3
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If you find an inexpensive 1.4x TC, please let me know. I've seen (and owned) (and sold) zillions of 2x and a few 3x but I've never encountered a 1.4x. Even the ripoff camera shops in San Francisco's Chinatown and Fisherman's Wharf robbers' rows don't carry them. Seems like 1.4x's are off in another price zone. Why? Supply vs demand, probably. The demand for 1.4x's will be by more discerning toggers who want better quality, which ain't cheap. And I guess 2x's ARE easy and cheap to make. Go figure.

So I've used cheap 2x's on my Sakar 500/8 and I find: 1) CIF is out, except for the absolute brightest targets; 2) just about ditto with my split-screen VF, the subject needs to be VERY bright and contrasty; 3) even Focus Confirmation is iffy except in full light; 4) it's fun to have the extra reach and OK as long as subject|content are more important than image quality, but otherwise cropping (instead of the TC) generally yields better IQ. Maybe a high-quality 1.4x will produce better results, I dunno. Good luck!
08-16-2011, 07:34 AM   #4
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Hi, Stevbike.

Since you're using a 2x TC with no issues, I might pick up a cheap one & give it a go just for kicks. The 3m-5ca is actually a surprisingly sharp lens, with image quality on par with a good conventional telephoto design. It's similar to the Tamron SP (55BB), with just a tad better contrast and sharpness.

I guess if I don't like the result of using a TC with it, I'm out of what... $10? I can live with that.

Cheers,
Bobbo :-)

08-16-2011, 07:45 AM   #5
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QuoteOriginally posted by RioRico Quote
cropping (instead of the TC) generally yields better IQ
Hmmmm.... Now I'm not so sure... :-/
08-16-2011, 08:44 AM   #6
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I've used my Tamron 55BB and the 01F Adaptall 2X TC together a few times. Focusing is possible but even in bright daylight, I get some prism blackout, the microprism collar is unusable and the matte field is pretty dark. It doesn't require a $600 tripod to support the weight. It works for moon photos. I tried to use the combination for eclipse shots and shutter speed fell too low. The moon moves pretty fast at 1000mm. I do have a couple of decent bird photos with it, but shutter speed is also an issue there. My conclusion: with the Tamron, the 2X TC works better than I thought it would. The 01F is often really cheap.

I didn't think the Vivitar/Samyang 500mm f8 mirror was usable with its included 2X TC. The lens itself was not that great. The included TC is light and does not seem to have more than a couple of elements.

The exposure math doesn't really favor the 500/8 + 2X TC combo for birds, even if quality was good. You'll have to raise ISO for reasonable shutter speed.
08-16-2011, 09:51 AM   #7
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I've tried Tamron 55B with AFA 1.7x, Tamron PZ-AF 2x, and 01F 2x. By far, the best image was obtained with AFA 1.7x it's acceptable but no pixel peeping allowed. I think the better option is to buy a Samyang 800/8.0 or it's many rebrand incarnates (one of many on my wish list) than placing a TC before a 500mm mirror lens.

Thanks,
08-16-2011, 11:09 AM   #8
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QuoteOriginally posted by GibbyTheMole Quote
Hi, Stevbike.

Since you're using a 2x TC with no issues, I might pick up a cheap one & give it a go just for kicks. The 3m-5ca is actually a surprisingly sharp lens, with image quality on par with a good conventional telephoto design. It's similar to the Tamron SP (55BB), with just a tad better contrast and sharpness.

I guess if I don't like the result of using a TC with it, I'm out of what... $10? I can live with that.

Cheers,
Bobbo :-)
If you pick up a TC and it does not work on the 500mm, you can still it on shorter lens like the 200mm, longer zooms, etc. They come in handy at times. Good luck in experimenting to see what come up with.

08-16-2011, 06:16 PM   #9
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QuoteOriginally posted by stevbike Quote
If you pick up a TC and it does not work on the 500mm, you can still it on shorter lens like the 200mm, longer zooms, etc. They come in handy at times. Good luck in experimenting to see what come up with.
Yeah, I still might. I wouldn't need to use it on anything else, though. I have everything up to 500mm covered pretty well as it is. Thanks for your input! - Bobbo :-)
08-16-2011, 06:42 PM   #10
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I have to vote for cropping. Unless you have an unusually sharp mirror lens that produces sharp images when viewed at 100% pixel peeping then putting a TC on top will be useless.
08-16-2011, 08:07 PM   #11
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QuoteOriginally posted by kristoffon Quote
Unless you have an unusually sharp mirror lens that produces sharp images when viewed at 100% pixel peeping then putting a TC on top will be useless.
With all due respect to the owners of Vivitar/Opteka/Sakar/Samyang, etc mirror lenses, the 3M is at least in my experience, in a totally different class. I've owned some of the others, and they're worlds apart. The 3M is a mirror lens that doesn't know it's a mirror lens. (Except for the donut bokeh, which I actually don't mind on this lens.) For a mirror lens, it's ridiculously good.

I can get a cheap manual TC for $10, which is all you need for a mirror lens anyway, since it's a fixed aperture. If I do try one, I think I'll try a cheapie & go from there. If it's crap (which I suspect it may be) I'll just flip it on eBay & chalk it up as a lesson learned.

And I really meant no disrespect for the Vivitar/Opteka/Sakar/Samyang mirror lenses. I've seen some good images from those. But at least in my experience, it's just a whole lot easier for me to get good results from the 3M.

Cheers,
Bobbo :-)
08-17-2011, 05:04 AM   #12
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Here is a picture I posted using my 500mm and 2x converter. It was also cropped using the in-camera cropping feature. The result is not the greatest but allowed me get the picture I had in my minds eye.



Here is a sample of a straight 500mm Vivitar mirror lens image of mine.


Last edited by stevbike; 08-17-2011 at 05:12 AM.
08-17-2011, 07:49 AM   #13
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Shots from my 500/8 mirror (Opteka/Samyang) are borderline in regards to sharpness and it's quite difficult to nail focus. Adding a converter certainly won't improve IQ and will likely degrade it, especially one of the "cheap-used" variety. I don't know how sharp your Tair is but if you are going to use a TC, try to find a good one. The IQ on my mirror won't stand up to cropping.
08-17-2011, 10:24 AM   #14
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To echo other forum members: You are just throwing money away if you buy a cheap TC to attach to a mirror lens. Even with the better 7 element TC, the resulting IQ won't stand up to cropping unless you like the dreamy soft focus portrait look. If this is your intent, then by all means get the cheapest TC you can find.

Thanks,
08-17-2011, 10:44 AM   #15
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I have both the Tamron 500 55B and 55BB and the most I will use TC wise is the SP 1.4x matched TC on there. these are a fixed f8 and therein is one issue.
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