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Old Feb 15, 2007, 10:07 PM   #1
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I'm dinking around with a doubler on my DL with my Tamron 28-300 lens.

I also have an old Vivitar 75-260 screw-mount lens and an M42 adaptor.

The doubler is a Kenko MC4 which supposedly is an autofocus compatible doubler, but I've always had to set the camera to manual to use the Tamron with it. It tries to focus, but it just can't seem to do it and I don't want the motor running long enough to do it if it even can at all.

I do have a lot of trouble focusing at full zoom with the doubler in -- part of it is due to the lower light, and part of it is due to the loss of field depth, I guess. I haven't had a chance to play with it on a bright sunny day and something interesting to focus on. So far I haven't been too impressed -- but then I know that there are limitations and I want to learn to work with them. So far I've had to go to low shutter speeds and high film speeds. And I'm not at all sure what needs to be done with the apature. Do you just ignore what the camera says about it and set it with the manal ring on the lens? And I've also read that you have to bump your f-stop up to a higher minimum to use the lens at all.

As far as the screw mount lens, I've put it on and switched the lens switch to manual, but all I get is a flashing "Av" on the display. I can look through the viewfinder and focus, but even putting the camera in full Manual mode doesn't change the display, and it doesn't change the fact that I can't trip the shutter. I think the fact that the doubler has AF contacts but the actual manual screw mount lens isn't passing information back through it is confusing the camera. I can use the lens without the doubler (just with the M42 adaptor) and the camera works fine.

Is there a way to fool the camera into just ignoring all lens info so I could try it with the doubler? I'm just trying to understand how it works so I'll know what my options are.
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Old Feb 15, 2007, 10:13 PM   #2
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This has been discussed a bit lately if you look back a little....

PERSONALLY 1.4-5 is as far as I would go on any telephoto lens.... a fast short lens OK then 2x perhaps maybe even a 3x.... but for the F/stop loss and other factors... well personal choice, but become big compromises.

Many including me, seem to be quite impressed by the Tamron 1.4x TC (and for the quality very ineaxpensive to boot)
Minimal exposure impact and nearly transparent effect. Works real nice on a SIGMA 70-300mm. (With the imager crop factor brings it from 450 to 630mm and a just under 1 stop loss)
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Old Feb 15, 2007, 10:30 PM   #3
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philmon wrote:
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Is there a way to fool the camera into just ignoring all lens info so I could try it with the doubler? I'm just trying to understand how it works so I'll know what my options are.
Judiciously placed non gooey tape over the TC contacts? (Or beter yet ring cut from some thin plastic)
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Old Feb 16, 2007, 12:46 AM   #4
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Hi philmon,

The only thing I can comment on with any reasonable knowledge would be the 28-300 and the 2x TC. Unfortunately, your lens is a bit too slow to use with a 2x and get AF. At 300mm, your max aperture at 300mm is f6.3. With the 2x TC this max becomes 2 stops slower or f12.6. The only way it might work is in very bright sunlight, and that would be a stretch. The TC will not convert the aperture value for the display or exif, but that doesn't matter as far as metering the shot goes. The meter reads the amount of light reaching the metering sensor, not the aperture value, so just go with what it suggests and make any adjustments that might be needed for the particular scene. The only "problem" is that the exif will reflect the unconverted aperture value and the actual focal length of the lens without the TC, but you can, with the right software, edit these values.

As Hayward suggested, a 1.4x TC would possibly give better AF results, but the max aperture would be f8.8, and many say that the upper limit for consistent AF performance is f8. Since you're talking a borderline situation, I'd see if I could try one and see how it works before purchasing it.

Scott




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Old Feb 16, 2007, 10:19 AM   #5
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So I'm guessing this would be between the camera and the "AF" doubler.

Plastic ring sounds like the way to go.
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Old Feb 16, 2007, 10:25 AM   #6
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I'm not terribly worried about using AF. Matter of fact, I just turn it off when I slap it on in the first place anymore.

I've read that 1.4, maybe 1.7 is about as far as one should go anyway... but I thought I'd try. It wasn't expensive.

So .... F 12.6 using the 1/125 F-16 rule should give me ok results on a sunny day, I would think. I can always dink with the film speed and shutter speed.

But a followup on that... if your maximum apature is 12.6 and you're using manual mode, do you actually set the apature on the apature ring on the lens to 12.6, or does setting it to anything lower actually end up giving you 12.6 ... or does it just give you fuzzy results?
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Old Feb 16, 2007, 10:59 AM   #7
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This is probably not comparable to one of the new teleconverters, but here's my experience with doublers.

Recently I came across a 200mm M42 mount lens. When I tried it out, it turned out to be a great lens. Sharp, no Chromatic Abberiation, smooth bokeh, simply awesome.

When I put the Soligor M42 doubler I got with it between the body and the lens though, the quality decreased massively. Suddenly the picture was dark, soft, and full of ugly CA. And not just a little, every image I shot was not usable.

So basicly what I'm saying is: although there are probably good doublers out there, IF the one you buy is bad quality, the quality of every lens you put on it will decrease a lot.

Judging from photos I've seen with it, the tamron 1,4x doesn't seem to have that problem.
Also read good things about the Pentax 1,7x AF adapter, but it's hard to find. (will give AF to manual focus lenses though :shock
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Old Feb 18, 2007, 12:33 AM   #8
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snostorm wrote:
Quote:

As Hayward suggested, a 1.4x TC would possibly give better AF results, but the max aperture would be f8.8, and many say that the upper limit for consistent AF performance is f8. Since you're talking a borderline situation, I'd see if I could try one and see how it works before purchasing it.

Scott
Yeah well even for the 1.4 Tamron they still say it should be a 2.8 lens for reliabe results yet works pretty flawlessly in low ligh on my K10D (with a 4-5.6 SIGMA 70-300mm)

Where as same SIGMA 70-300 lens on my original C Rebel (300D) would go off to never never land frequently in those condition WITHOUT the TC and not come back.

The K10D for the first time got lost post sunset tonight (w/TC)... but where as I had to zoom out with the Rebel to get it back.... K10Djust hit the shutter again and ZIP right back to sanity.

The other thing to is the K10D doesn't full speed drive/overshoot the AF like the Rebel did... it takes baby incremental back and forth steps in low light

I really have had very little trouble with the Tamron 1.4 with the SIGMA 70-300mm even at ful zoom (f/5.6 actually with the 1.4 TC really f/8 )again tonight the first time ever got lost and well AFTER sunset.

But Tamron still says you should have a 2.8 lens.... but really all depends on how good the AF system is.... the K10D's is rather amazing.

Not having my wide lens for it yet and using the 70-300mm indoors for the first time the Flash strobe assisted even.... and FAR less abnoxiously long as the Rebel almost always did even with a wide lens. When I had the Pentax kit lens it NEVER strobed even in near dark conditions.

So as much as lens speed TC reliability depends on the quality of the AF system involved as much or more. And while it might be slower that the Pentax creep/step focuses in low light... is really a benifit... vs lens just launching into the ozone and never coming back.

OP didn't mention which Pentax they were using it on....
Plus also for whatever X TC quality matter and dispite its low cost the Tamron 1.4 has yet to get a bad review I have seen... yet there is a plethora of BAD 2x's out there.
Again OP never mentioned which.
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Old Feb 19, 2007, 9:07 PM   #9
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The plastic ring did the trick as far as getting the camera to forget all about autofocus. I was able to take a shot with my Vivitar 75-260 and the doubler. And it's way better than the doubler with the Tamron 28-300 @ 300. I was pretty disappointed (but not terribly shocked) at the image quality with the Tamron. I was hoping I'd get something acceptable at ~900mm equiv. Not so.

On the other hand, 260*2*1.5 gives me about a 780 eqiv -- so that's better than the 450 equiv I get with the Tamron at full zoom.

Not that I'm knocking the Tamron. If I'm going to carry just one lens, that'll be the one. It just doesn't work real well with the doubler. Maybe I'll try that 1.4 you were talking about sometime.

I did notice that with either one, focusing ismuch moredifficult than even the Tamron by itself at 300. Is that normal with doublers, or with long telephotos, or both?

Here is a shot of the sign with the TC & the Tamron @ 300from this afternoon:



It MIGHT be a focusing problem, but I'm not too sure about that. I can see some significant CA, and the edges are fuzzy.Here's a shot from this evening of a lamp in my living room with the Vivitar @ 260and the TC:



Much nicer, and no visible CA (hand held, 800 speed, 1/250 F8 ).

Pretty cool!

At any rate... I think I'll hunt for an old fixed500mm m42 lens and see what I can do with it and the doubler. I might be very happy.


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Old Feb 20, 2007, 8:48 AM   #10
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Hmmm... I'm going to take a little of that back.

The Tamron did just as wellas the much heavierVivitar when I set it at 260 instead of the full 300.Maybe even a little better. I should test them with a tripod.But it appears to be the end of the range that really starts the distortion -- plus, you have to get it focused just right -- which, like I mentioned before, is difficult with a long telephoto like this.

Is it less difficult with a larger lens? Say somewhere closer to 80 mm? It LOOKS focused in my viewfinder, but when I dump it off on the compter, not so much.

I can see wherethis might take quite a bit of practice.

One thing I noticed about the Vivitar is that there doesseem to be less light loss.
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