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05-06-2015, 07:58 AM   #1
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New 1.4 HD Converter

Hi everyone
My dilema must be shared by others in the world of Pentax. I have a Pentax Kr and do most of my nature photography with the well regarded 55-300HD zoom lens, mostly at 300 f8. Due to the limitations of my set up I avoid low light situations and prefer to plan my trips around bright sunny days to maximise shutter speed and aperture. I am thinking of buying the new Pentax 1.4 HD converter to use with both my zoom and a Tamron 90mm macro. Realising the problems I might face in loss of performance with the converter it would be my intention to shoot at at least f11 with shutter speeds over 300. I will be photographing mostly small birds and therefore only using the centre and sharpest part of the lens.
Does anyone have any experience of shooting with this combination. I know its not ideal, but can not afford the big fast lenses and in any case don't like the weight and bulkiness of these. All my photography is hand held, usually on the move.
I normally have to crop rather massively, which is why I am considering the rather pricey Pentax Converter.
Dave

05-06-2015, 08:25 AM - 1 Like   #2
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The only example I have is a shot I took a few weeks ago when I bought a 55-300mm WR to go in a bag alongside my 18-135mm for when I want to travel reasonably light. This was taken on my K-5IIs with the 1.4x attached.

420mm, ISO 500, 1/400th, f8, handheld and cropped.

05-06-2015, 08:46 AM   #3
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The PF review of the 1.4x teleconverter at Pentax-DA 1.4x AW AF Rear Converter Review - Specifications | PentaxForums.com Reviews highlights an autofocus issue with the 55-800 lens: "SMC and HD Pentax-DA 55-300mm F4-5.8: phase detect autofocus may be unreliable when zoomed in, use contrast detect".
05-06-2015, 09:52 AM   #4
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Remember with the TC you lose one stop of light from wide open when focusing, not from the aperture set in the camera. Focusing is done wide open and the camera stops the lens down only to take the picture.

So the 55-300 @ 300mm will be f/5.8 and with the TC just a bit over f/8. In good light this should be fine, in bad light YMMV. I think f/8 is the line Ricoh drew and since the 55-300 will be just over they put a warning on the label. There are several people on forum that use a 55-300 with a TC (not Pentax) and it works.

05-06-2015, 01:12 PM   #5
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QuoteOriginally posted by jatrax Quote
In good light this should be fine, in bad light YMMV. I think f/8 is the line Ricoh drew and since the 55-300 will be just over they put a warning on the label.
It has been my understanding that the f/8 "line" is not related to the amount of light, but instead is because of physical "blackout"* of the PDAF prism at narrower apertures. I believe there is another thread on this site where this is discussed.


Steve

* Similar to the blackout of a split image prism in some viewfinders.
05-06-2015, 01:23 PM - 1 Like   #6
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QuoteOriginally posted by stevebrot Quote
I believe there is another thread on this site where this is discussed.
I could not find the thread here, but did find a discussion at the "Cambridge In Color" Web site. Below is a post containing a concise explanation:

Autofocus and aperture

The other comments on the thread address the issue with specific lenses.

Edit: I just found the thread on this site. It has links to numerous resources where PDAF is explained along with the aperture-related limits.

https://www.pentaxforums.com/forums/173-general-photography/294117-comparing-...-af-stuff.html


Steve
05-08-2015, 02:38 AM   #7
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QuoteOriginally posted by Mike.P Quote
The only example I have is a shot I took a few weeks ago when I bought a 55-300mm WR to go in a bag alongside my 18-135mm for when I want to travel reasonably light. This was taken on my K-5IIs with the 1.4x attached.

420mm, ISO 500, 1/400th, f8, handheld and cropped.
What a fabulous picture, was this taken with 55-300 and 1.4 converter.
Dave
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