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07-15-2011, 09:41 PM   #1
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Teleconvertor for Pentax

Hi everyone,
Do Pentax make a teleconvertor (2x or ) to suit the DA 55-300 F4-5.8 Lens.
If not which brand could I use.
I realise I may lose auto functions with other brands.
Thanks for your help.
Cheers Darren

07-15-2011, 11:16 PM   #2
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All Pentax teleconverters are discountinued, but you can probably find them second hand. You should look for the "A" types so as to retain all exposure modes:

Pentax Teleconverters

Here is an overview of third party converters:

Third Party Teleconverters

I have had good experience with this 1.4x Tamron converter which even provides autofocus:

Tamron-F 1.4X Pz AF MC4

Note that you lose two f-stops with a 2x converter. That would make your lens an f/8 to f/11.5 lens and autofocus will probably not work and the viewfinder will be very dark. With the lens you have you should probably stay with a 1.4x converter and even that combination will be challenging to focus.

Last edited by Ole; 07-15-2011 at 11:21 PM.
07-16-2011, 12:51 AM   #3
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I have a feeling that the 55-600 won't play nicely with teleconverters because of the movement of the element groups potentially interfering with the elements on tele converters. I'm open to being corrected though..
07-16-2011, 04:13 AM   #4
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I think that with a 2x TC you will cry your eyes out for the poor image quality at 600mm. A 1.4x or 1.5x TC would be usable.

07-16-2011, 07:46 AM - 1 Like   #5
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Last year I tested the DA 55-300 with 3 different TCs.

1. w/Kenko 1.5x MC4 - the 55-300 would AF in decent light. When used on a tripod with the same ISO, images from the Kenko 1.5x TC were slightly better than the DA 55-300 cropped to the same view. In the field, though, if you aren't using a tripod, you'll have to boost ISO in order to have a fast enough shutter to handhold. So, you are losing 2/3 stop in light gathering and you'll (most likely) need to jump another 2/3 stop to control camera shake. Instead of shooting at ISO 400, for instance, you might be shooting at ISO 1000.

2. w/Kenko 2x MC4 - the 55-300 would AF in very good light. When used on a tripod with the same ISO, images from the Kenko 2x were noticeably, although not drastically, better than the DA 55-300 cropped to the same view. Again, though, in the field, if you are not using a tripod you'll have to boost the ISO to compensate for the diminished light gathering and camera shake. You lose 1.5 stops with the Kenko 2x TC, and you'll have to jump another stop or more to control camera shake.

3. w/Tamron 2x MC7. In theory, this should produce the best results as it has 7 elements compared with the 4 in the Kenkos. In actuality this did not work out. The Tamron lost a full 2 stops in light gathering, never AF'd, and images were noticeably worse than if I simply cropped an image from the DA 55-300.

One interesting aspect of TC's is that you can getting smaller DOF. This is a blessing and a curse for obvious reasons. Of the 3 TC's I used, the Kenko 2x was the most fun.

Last edited by luftfluss; 06-08-2016 at 08:25 AM.
07-16-2011, 08:10 AM   #6
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QuoteOriginally posted by luftfluss Quote
Last year I tested the DA 55-300 with 3 different TCs.

1. w/Kenko 1.5x MC4 - the 55-300 would AF in decent light. When used on a tripod with the same ISO, images from the Kenko 1.5x TC were slightly better than the DA 55-300 cropped to the same view. In the field, though, if you aren't using a tripod, you'll have to boost ISO in order to have a fast enough shutter to handhold. So, you are losing 2/3 stop in light gathering and you'll (most likely) need to jump another 2/3 stop to control camera shake. Instead of shooting at ISO 400, for instance, you might be shooting at ISO 1000.

2. w/Kenko 2x MC4 - the 55-300 would AF in very good light. When used on a tripod with the same ISO, images from the Kenko 2x were noticeably, although not drastically, better than the DA 55-300 cropped to the same view. Again, though, in the field, if you are not using a tripod you'll have to boost the ISO to compensate for the diminished light gathering and camera shake. You lose 1.5 stops with the Kenko 2x TC, and you'll have to jump another stop or more to control camera shake.

3. w/Tamron 2x MC7. In theory, this should produce the best results as it has 7 elements compared with the 4 in the Kenkos. In actuality this did not work out. The Tamron lost a full 2 stops in light gathering, never AF'd, and images were noticeably worse than if I simply cropped an image from the DA 55-300.

One interesting aspect of TC's is that you can getting smaller DOF. This is a blessing and a curse for obvious reasons. Of the 3 TC's I used, the Kenko 2x was the most fun.
Great report! Repeats my experience with the Kenko 1.5x on the da 55-300. Little or no gain in IQ compared to enlargement.

+1
07-16-2011, 08:46 AM   #7
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QuoteOriginally posted by RonHendriks1966 Quote
I think that with a 2x TC you will cry your eyes out for the poor image quality at 600mm. A 1.4x or 1.5x TC would be usable.
I agree about 2X but to get usable w/1.4 everything (conditions, body, technique) has to be right--no room for error or a weak link.
The DA 55-300m is a very good and versatile lens in its native FL but using it with a TC is pushing it beyond its reliable capabilities.
07-16-2011, 09:38 AM   #8
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I've been using a Pentax A 2x converter on an M300/4 and the IQ isn't bad IF I can stop the lens down and keep it steady. The M300 doesn't have a tripod bracket and with the 2x on it, that's a lot of weight out front. The CA is pretty bad wide open with the TC. I get an orange fringe around the subject that is very difficult to remove in PP. Stopping down to f/8 cures it but then you are at f/16 and will probably have to boost the ISO up to 800 or 1600 if I want a fast shutter speed and that brings up noise in my K10D. I recently shot some nesting herons and I think the crops are better than most of the TC shots. I say most because I did get a couple of really fine shots at 600mm. Focus isn't easy either. How a 2x TC will work on the zoom I can't really say but I have seen a few shot posted from time to time that looked decent. Shooting long takes practice no matter what, even using a longer lens. A shot with the TC.


Last edited by reeftool; 12-29-2016 at 04:44 PM.
07-16-2011, 01:29 PM   #9
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one thing to keep in mind is that the lower the resolution of your camera's sensor is and the sharper you lens is, the more benefit there is to using a teleconvertor.
07-16-2011, 05:39 PM   #10
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Thankyou for all the info, I have been having a look around for the TC's you have all mentioned and it seems that they are a little harder to find than I thought as far as fitting Pentax's goes. I will digest all this info and keep looking. Great report luftfluss, thanks.
Cheers Darren
07-16-2011, 10:49 PM   #11
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I have not been able to do any "real world" shoots with it yet but I can confirm that the Pentax 1.7x tele will AF with the 55-300. I believe the 1.7x is still available in Japan but your best bet is picking one up in the marketplace like I finally did. I think the average price is around $330. Here's the link in the review database:

https://www.pentaxforums.com/lensreviews/Pentax-Rear-Teleconverter-F-1.7x-Autofocus-Adapter.html
07-17-2011, 05:31 AM   #12
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QuoteOriginally posted by scole Quote
I have not been able to do any "real world" shoots with it yet but I can confirm that the Pentax 1.7x tele will AF with the 55-300. I believe the 1.7x is still available in Japan but your best bet is picking one up in the marketplace like I finally did. I think the average price is around $330. Here's the link in the review database:

Pentax-F 1.7x AF Adapter Reviews - Pentax K-mount Teleconverters and Adapters - Pentax Lens Reviews & Comprehensive Database
I hope you will post some test photos that compare shots with the TC and without the TC enlarged to the same size!
07-17-2011, 01:11 PM   #13
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The important thing to take from these comments - and others in the many similar threads - is that in most cases, a TC will be a waste of money. IQ will be worse, or at best only very slightly better than, simply cropping. And you have to give up a stop or more of light, and some AF performance, which either exacerbates the degradation you usually get,, or nullifies the very slight gain you might have got in the best case.
07-19-2011, 09:13 AM   #14
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using a tamron 1.4x teleconverter on a 55-300.





07-19-2011, 09:59 AM   #15
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QuoteOriginally posted by fishnuts Quote
Hi everyone,
Do Pentax make a teleconvertor (2x or ) to suit the DA 55-300 F4-5.8 Lens.
If not which brand could I use.
I realise I may lose auto functions with other brands.
Thanks for your help.
Cheers Darren
couple of points here.

first of all, regardless of brand, F5.8 is too slow, even for a 1.4x to retain AF functionality.

as a result any TC can be used for MF only but what you need to look out for are the following points

1) sigma TCs, while very very good optically are designed to protrude into the rear of the lens, and require a rear element recessed 12mm minimum and a bore of 35mm at the end of the lens to fit. they are onlky for a few select lenses, and your;'s is not one of them

2) look for a TC with aperture contacts so at least you retain program modes aperture control and P-TTL flash capability, but note that there may be exposure errors, as most TCs do not correct for aperture.

stay away from cheap 4 element ones, as the preformance is somewhat wanting.
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