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03-16-2011, 09:12 AM   #1
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645 tele converters on 645D - any one tried?

Anybody tried the Pentax 1.4x and 2x tele converters on the 645D?

I tried the Pentax 67 extenders with the 67 300mm/f4 M* ED IF lens. The results are usable with the 1.4x, but not stallar, and the contrast is low. Together it is not in the ball park of the 645 400mm/f5.6 FA performance level. The 2x results are not good.

I wonder if, for some reasons, the 645 converters may do better? If the 200mm/f4 and the 1.4x can approximate the 300mm 67 lens level, I can save quite some weight and space (although it would be only a 280mm/f5.6).

03-16-2011, 12:55 PM   #2
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Hi Leping:

I had a 645 2x which I have only used with film. I sold it years ago; it wasn't worth using. I have the 67 2x and 1.4x; the 1.4x is ok, but again, the 2x really degrades the image for most uses. Honestly I think I'd be better off with a K5 and an equivalent APS-C focal length.
03-23-2011, 08:47 AM   #3
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I had wondered about 645 converters myself. All converters will degrade the image a little but are the 645 converters any worse in this respect that other converters? Do they make the image barely acceptable? I hadn't for instance heard that Nikon converters for 35mm are close to unacceptable and yet any image deterioration should show up more in 35mm than 645.

On the rare occasion that a longer focal length is needed a converter to achieve this may be much cheaper and easier to carry and a lot cheaper than the longer length.

asahijock
03-23-2011, 12:36 PM   #4
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All extenders are not built equal

For example if you follow Lloyd's blogs, he recently found the Canon's new III iterations vastly better than the II.

diglloyd - Lloyd Chambers Blog

diglloyd - Lloyd Chambers Blog

03-23-2011, 10:19 PM   #5
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I found the answers myself

1. As predicted, the 2x basically does not do any good. However,

2. Surprisingly, with my 400mm/f5.6 ED IF lens, which is sharp by itself (see Lloyd's reviews), the Pentax 645 1.4x extender did really well -- one has been sitting on KEH for days, which I put to my card only because I was ordering something else, just wanted to try out for fun, and fully expected to return.

Here is a 100% crop off my resolution target at ( f/10 - one stop ) = f/14. Of course, together it makes a 560mm/f8. I compared the 400mm alone results upsampled to the same size, and found the 1.4x gave much more real details. Some yellow fringes, but livable with natural subjects, and probably correctable if I elaborate, so far only used the default Lightroom 400mm lens profile. I did test a Pentax 67 1.4x with my 300mm/f4 P67 ED IF M*, but I did not see results this good.

No wonder I am keeping the little thing for now. Notice the forum server compresses uploaded JPEG files, both size and quality, so it does not look 100% and as sharp as it has been, but I put a Photoshop level 10 JPEG zip file for downloading viewing.
Attached Images
 
Attached Files
File Type: zip _LZH3025-LR_Crop1.jpg.zip (1.66 MB, 60 views)

Last edited by leping; 03-23-2011 at 11:14 PM.
03-24-2011, 08:59 AM   #6
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Unfortunately my computer says that that attached file is invalid or corrupt so can't open it. I have no knowledge of scanning etc so forgive my ignorance but is the West coast Imaging attachment a crop and in print terms what size of a print woud it represent?

Finally I wonder why the 2x converter is so much worse? Thanks

ashahijock
03-24-2011, 11:38 AM   #7
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QuoteOriginally posted by asahijock Quote
Unfortunately my computer says that that attached file is invalid or corrupt so can't open it. I have no knowledge of scanning etc so forgive my ignorance but is the West coast Imaging attachment a crop and in print terms what size of a print woud it represent?

Finally I wonder why the 2x converter is so much worse? Thanks

ashahijock
It is a 100% original pixel crop of a Pentax 645D digital camera test shot of a flat target, made from different pieces of cards and resolution patterns pasted on the board, nothing related to scanning of any kind, or printing size. The West Coast Imaging advertising card is just happened to be one of the contents used to fill the space, has nothing to do with scanning or printing.

I tested on a Mac, and the zipped JPEG file unzip and openned normally. Anyone else had trouble?

All the 2x converters are worse than the 1.4x, since they "split" the original resolution more. If a lens by itself can resolve 80lpr/mm, simply speaking but not entirely correct, even a perfect 2x would make it 40lpr/mm, while a perfect 1.4x can do 57lpr/mm, in theory.

Last edited by leping; 03-24-2011 at 12:00 PM.
03-24-2011, 01:40 PM   #8
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Leping,

Is AF maintained using the 645 1.4x converter?

03-24-2011, 03:20 PM   #9
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leping, it will download to about 1.6MB and then says corrupt or invalid file. I have a PC with Windows XP and am using IE8 if this makes any difference.

As I understand a crop in pixel terms it is a part of a bigger picture to show the resolution obtained under the equivalent of an enlargement . I has assumed that a 100% crop could be translated into a print size. A bit like me blowing up a print in an enlarger but showing only part of that print. The resolution of the cropped print( let's say the crop was 5x4 inches ) will look much grainier than a full neg enlarged to 5x4 but in effect that crop at 5x4 becomes part of say a 24 x36 print.

So the crop is used to show loss of resolution but needs to be considered against the fact that it is now really part of a 24 x 36 print. That was why I was referring to print size.

Turning to surfotog's Q, I have been told that with all converters you lose AF but I wonder why.

In 35mm cameras provided the max aperture of the lens is f4 or better then AF will still work with even 2x converters as AF is operational at up to f8. The crucial thing I think is loss of light preventing the AF from working

Maybe 645's need a stop better than 35mm but even so with a 75mm f2.8 then a two stop reduction is only f5.6

There may be a flaw in my reasoning above but what is it?

Thanks

asahijock
03-24-2011, 06:01 PM   #10
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QuoteOriginally posted by surfotog Quote
Leping,

Is AF maintained using the 645 1.4x converter?
No. I don't even think there are electronic contacts on the extender.
03-24-2011, 09:15 PM   #11
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OK, I do not use PCs but I clicked the zip file link above again on my Mac. It downloaded and opened the JPEG image in Photoshop without a glitch.

Following the posted 700x1024 pixel dimension limit, as well as 700KB for JPEGs, I have to make only small crops at 100% pixels, plus a reduced size full 645D frame to show the relative scale.
Attached Images
View Picture EXIF
PENTAX 645D  Photo 
View Picture EXIF
PENTAX 645D  Photo 
View Picture EXIF
PENTAX 645D  Photo 

Last edited by leping; 03-24-2011 at 09:51 PM.
03-25-2011, 03:45 PM   #12
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I have just read the Ken Rockwell review of both the P645N and a few of the primes. Worth a read if anyone hasn't done so. Interestingly he says that Pentax recommends the 2x rather than the 1.4. He simply passes this on without commenting except to say that he isn't a user of converters.

I wonder why Pentax favours its 2x over its1.4x when the experience of a number of converter users here suggests that the 1.4 is better.

Unfortunately Ken makes no reference to Pentax reasons for its recommendation.

Anyone know of the Pentax publication/statement to which Ken Rockwell refers? It would clearly be worth a read.

Thanks

asahijock
04-09-2011, 09:22 AM   #13
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There are aperture mechanism only in the converters. There is no AF drive shaft.
Therefore you can get all aperture functions but no AF. This is probably in part due to the converters were released before the Pentax 645 went AF in 1997 and the market demand does not justify the R&D/engineering work required to make these in AF version.

The 2X was released first. The 1.4X was released at the same time as the 300 and the official word was the 1.4 was designed/optimized to work with the 300.

My experience was the 1.4 was a better converter probably due to not needing to work as hard as the 2X optically. This applies not only to the P645 AF300/4EDIF but also the P67 400/4EDIF.

I still have both of them and when you need the reach beyond 400 then they are handy to have around. It also give me the options of how much to I need carry when I am out and need to carry my own gear myself. The 600/5.6 or P67 800/6.7 are nice to have but too costly and heavy so the converters are a lower cost alternative if you can settle for less in image quality.
04-10-2011, 11:05 AM   #14
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I am using the 2x-645-Converter with an A200/4 on a K7 and on an analog 645.
In both cases I am quite satisfied with the preformance and assume that it should be similar on the 645d
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