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Fun with Teleconverters
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PostPosted: Sat Aug 15, 2015 7:36 pm    Post subject: Fun with Teleconverters Reply with quote

I've been meaning to do this for quite a while and finally got around to doing it yesterday. Plenty of sunlight for this little experiment, but gawd was it hot!

For the lens, I selected my Tamron 300mm f/2.8 LDIF. I chose it for a couple of reasons. 1) It's reasonably well corrected for CA, and 2) it is a fast lens that will not have some ungodly effective aperture by the time I'm done with it.

For the camera I chose my NEX 7, mounted to a sturdy tripod. I set it for a 10-second time delay.

I've amassed quite a few teleconverters over the years, but for this test, I chose to use my Tamron TCs and my Nikon mount TCs. The only Nikon TC I wasn't able to use was the TC-14b because of its protruding front element. So for this test, I used my Tamron 140F 1.4x, both 01F 2x's, my Nikon TC-201, and my Vivitar macro TC 2x in Nikon mount. That's five, count 'em, five teleconverterrs.

This is the way things worked out:

With the Tamron 014F, 420mm f/4 at an indicated f/2.8, f/11 at an indicated f/8
With the above 014F and one 01F 2x, the lens becomes an 840mm f/8 at an indicated f/2.8, f/22 at an indicated f/8
With the above two TCs and the second 01F 2x, the lens become a 1680mm f/16 at an indicated f/2.8, f/45 at an indicated f/8
With the above three TCs and the Nikon TC-201 2x, the lens becomes a 3360mm f/32 at an indicated f/2.8, f/90 at an indicated f/8
With the above four TCs and the Vivitar 2x, the lens becomes a 6720mm f/64 at an indicated f/2.8 and f/180 at an indicated f/8

Living here in Houston and surrounded by tall trees, even from the second storey of my house, I could not find any interesting distant objects, except for a power pole or two. Boring. So I selected instead the tag on a transformer connected to a power pole across the street from my backyard. Probably about 40 meters from where I was standing. Also, even though I shot images with the lens wide open, and then stopped down to an indicated f/8, I'm only going to show the latter images here. Mostly just because they look better. All I did to the images was increase contrast as required. No sharpening was done to any of the images.

With the 014F 1.4x Tamron TC at an effective 420mm:


With the 01F 2x Tamron TC added for an effective 840mm:


With the second 01F Tamron TC added for an effective 1680mm:


With the Nikon TC-201 addedd for an effective 3360mm:


And finally, with the Vivitar 2x added for an effective 6720mm:


Yeah, sure it's blurry at 6 thousand seven hundred twenty mm, but so what? I'm surprised it worked at all!

The above images are full-size, so if you click on them to view in your browser, you'll have a better idea of the resolution.

Now, one thing I'm really curious about is the artifacts that began to appear at 3360mm, and became much more pronounced at 6720mm. They appear as round dots, some darker than others, showing what almost appears to be perhaps dirt on the sensor, but it's clean -- I checked. And a lot of the lighter-colored dots are in rows, which makes me wonder if these are reflections of the pixels on the sensor. If not, what would they be? And why do some appear dirty? Microscopic levels of dirt accumulated on some that isn't apparent even under mild magnification? Any ideas?

Lastly, in case you're wondering the purpose of this "test," there really wasn't much of one. I just wanted to see if it was possible to render decent images. My conclusion is I can probably get away with stacking a couple of TCs, but beyond that, there isn't much point. Comments are welcome.


Last edited by cooltouch on Wed Sep 09, 2015 2:16 am; edited 2 times in total


PostPosted: Sat Aug 15, 2015 7:42 pm    Post subject: Reply with quote

Just add ONE "video converter 2.0X" or something like that and you'll get worse blue fringes.

I think your dirt hypothesis is probably correct, too. With all this convertting you must end up at something like f/82 which means anything is in focus


PostPosted: Sat Aug 15, 2015 7:50 pm    Post subject: Reply with quote

That video converter -- which usually mounts to the front of a lens -- would have to have a thread diameter of 95mm. Not very common, methinks. And as for a final effective aperture, it's more like f/180 than f/82.


PostPosted: Sat Aug 15, 2015 10:29 pm    Post subject: Reply with quote

buerokratiehasser wrote:
Just add ONE "video converter 2.0X" or something like that and you'll get worse blue fringes.

I think your dirt hypothesis is probably correct, too. With all this convertting you must end up at something like f/82 which means anything is in focus



I always the thought the reduction in aperture when using teleconverters only refers to f-stops in terms of light loss, and doesn't really affect the size of the diaphragm, negating any increase in depth of field, but I am not sure.....


P.


PostPosted: Sun Aug 16, 2015 4:45 am    Post subject: Reply with quote

Impressive results!

I have a question, since here specialists of TCs appear.

I've got excellent (as from pictures, still on the way), Tamron Adaptall SP 2x teleconverter. I want to use it with M42 mount lens. I have an adapter, which allows tamron adaptall lens to be mounted in M42, but are there adapters, which will allow M42 lenses to be mounted in adaptall mount?


PostPosted: Sun Aug 16, 2015 5:06 am    Post subject: Reply with quote

The short answer to your question is "no." What you would need in order to mount the Tamron TC, or any Tamron adaptall mount, for that matter, is the face you see at the back of a Tamron lens with the mount removed. And I've never heard of anyone making that face that could be adapted to other lenses.

This is the reason why I couldn't use my Nikon TC-14b. The only way I could mount it at all because of its protruding front element was directly to the back of the Tamron lens, but then I wouldn't have been able to use any of my Tamron TCs because they are dedicated for use only with Tamron lenses. That is, they hook up to the back of a Tamron lens the same way the adaptall-2 mount does.

For a good TC to use with your M42 lens, I recommend you look for the Vivitar macro 2x or the Komura 7-element (maybe 6?) 2x. Both are excellent quality, but they are not very common for M42. There are probably others, but I have no information on them.


Last edited by cooltouch on Sun Aug 16, 2015 8:01 pm; edited 1 time in total


PostPosted: Sun Aug 16, 2015 6:20 am    Post subject: Reply with quote

So, If I understood properly, the problem is purely mechanical?
Because I can make such adapters with ease. I already made such adapter from Petri 2x teleconverter. It was Petri "input" and "output". Now it is Minolta AF "output" and M42 "Input".


PostPosted: Sun Aug 16, 2015 10:38 am    Post subject: Reply with quote

The first two photos appear identical, with the 2nd more contrasty. Assume it's just a cropping matter.

Proves you started with a very good basis and the TCs are of excellent quality. Really surprised me too how good the end photo was, I could read the print!
I may have to try this myself now that I have a 2nd 01F.

This bit of fun reminds me of an article of some guys stacking Canon 2x TCs to a lens to see how many they could mount and shoot at people on top of skyscraper.

I think the circles are magnifications/focused particulates on the elements. As the f/x value drops, they become prominent. I noticed this on a regular lens just stopping down and in bright daylight. Nothing in the pic at f/5.6 but at f/22 f/32...little dots and lens bubbles.


PostPosted: Sun Aug 16, 2015 11:53 am    Post subject: Reply with quote

Well, my stacking tests up to 4000mm FOV have not been bad either: http://forum.mflenses.com/minolta-rf-rokkor-500mm-f8-and-tcon-on-mft-t71740,highlight,%2Brokkor+%2B500.html

Maybe I should add another TC additionally to compare it with your test? Laughing

Practically I could also reach the same 6720mm FOV with my present gear when I use my Tele-Tokina 600mm as the basis on my Lumix M43 camera and adding additionally my Kenko Tele-Plus 1.4x converter which is not bad either. Theoretically I could add the Vivitar Macro-Converter as well which would give me then 13.440mm FOV equivalence (11.200mm if the Minolta RF 500 is used as the basis). Maybe I'll do that sometimes... Wink

Seriously, I didn't encounter similar strange artifacts in my test examples up to 4000mm. So I don't really know where they are coming from.
So at least up to 4000mm FOV I considered the outcome as quite usable.


PostPosted: Sun Aug 16, 2015 8:47 pm    Post subject: Reply with quote

WNG555 wrote:
The first two photos appear identical, with the 2nd more contrasty. Assume it's just a cropping matter.


I'm not so sure. I was taking notes as I shot the photos, but still, I may have made an error. If so, what likely occurred was I started the test with the Tamron 014F mounted. Thinking back on it, I can't recall if I made this slip-up or not. I should have recorded the actual image file numbers associated with each TC, but I didn't do this.

@pdccameras, I agree with your analysis. I've also always thought that it is the actual opening of the lens iris that determines depth of field. TCs just magnify the image. And the appearance of the spots are most likely a result of magnification than any sort of DOF increase.

Well, I'm somewhat glad, I guess, to read that all of your conclusions agree with mine, that is that my NEX 7's sensor is hiding some dirt that doesn't appear at lower magnifications. I've cleaned this camera's sensor before by first using a regular blower brush and then using lens cleaning fluid and a cotton swab. I just googled this topic and came up with a rather comprehensive article over at Adorama's website:

http://www.adorama.com/alc/0013666/article/The-Secret-of-Effectively-and-Safely-Cleaning-Your-Digital-Camera-Sensor-Yourself

I tried the software imaging with limited success. I might not have shot the initial image properly because I was getting dust particles, but only in the very corners, giving the appearance that the image had burned through toward the center, washing out dust detail. So I'll try another image capture. At any rate, it looks like I should probably buy a different cleaning fluid and probably a brush dedicated for this purpose.