[mattb123]

I got a Pentax A 645 2x TC pretty cheap from KEH. I bought it on impulse figuring it's a good way to expand my options while my 645 lens collection is pretty limited.
I used it a couple of times while driving home from Taos last week and have to say I'm not super impressed. As I suspected (yet hoped otherwise) the extra reach takes a big chunk out of the IQ.
I tried it on a A 200/4 so maybe other lenses are better but my conclusion was it's not worth using unless I'm valuing reach over IQ in which case I could do a lot better with my K-3.
Here are a couple of examples with 100% screen grabs.

My conclusion is I should look for a 1.4x and/or spend more on lenses to get the reach I want.

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Last edited by mattb123; 12-07-2015 at 12:49 PM.

[promacjoe]

There is a lot of haze/fog in that picture. Regardless of the lens/lens combination, You are not going to be able to cut through the haze/fog. even if you do not see the haze/fog, the camera may see it. And the effect is only amplified by the focal length of the lens. you first need to shorten the distance to eliminate the effect of this haze/fog, 100 yards or less. take a picture of a stationary object using both the standard lens and with the tele-converter. Compare the two images at equal size. Only then will you git a good estimate of how good your tele-converter is. But don't expect it to cut through haze/fog. Also heat from the road will amplify any problems. You just did not pick a good subject at a good distance to make a good comparison.

[WPRESTO]

I've maintained that teleconverters, including the much vaunted 1.4X for the K3, can at the very best maintain the IQ of the lens, but no telecoverter is at the very best. They all degrade IQ slightly compared to a crop from the lens without the TC attached. Converters are really a leftover from the chrome era originally designed and sold to provide at-the-exposure cropping to fill the frame of a chrome, especially when photographing wildlife. During the chrome era I used a 2XL converter on both a 200 SMCA ED Macro and a Tamron 400 f4 with good results ON A CHROME. Although I still have all three of those lens units, I've not used the 2XL since converting to digital.

[mattb123]

I agree conditions weren't optimal but here are (basically) the same scenes at 200mm without the TC. I don't have crops handy but Contrast and pixel peeping looked noticeably better to me in these.

[donesteban]

I really like the 2x converter. But the 200/4 (A and FA) are not really the lenses one would use it with. I had trouble getting sharp images, too.
But there are some lenses it works very well with.. My 300/4* A, for example (so it is not a problem of the 400mm, if I am ale to handle 600mm). The 150/3.5 i a good candidate, too. And, the 55mm/2.8 Kit lens delivered with the 645D. In combination with the converter it is even almost a macro!
The 75/4 and 55/4 (latest version) of the 6x7 line deliver very nice results, too, in combination with the 2x converter.
I use it for the set I carry around every day on my way to work. 645D, 6x7 55 and 75mm, and the 150/3.5 645, plus the 645 2x converter, to get the 110mm I really like, and off course, 300mm when attaching it to the 150/3.5. Could most likely also use my small lens kit (45-85 and 150-300). But knowing the prices of those three lenses, I'll never ever sell them, and I don't just put them in my cupboard.

The 200/4 A 645 works wellin combination with the 1.4x conerter. The 200/4 FA is not really optimal for distant objects, at least the cop I have. It is great for portrait work, razor shark even wide open, just as long as the distnace is not too long.

[mattb123]

I've seen mixed reviews for the A 200/4 but I have been enjoying mine for long landscapes as well as portraits.
I'll hang on to the TC (not much invested in it anyway) and maybe save up for a 300/4. I also like the looks of the 150-300 but I imagine a zoom on that TC would not be optimal either.

Here's a shot with the A 200/4 (no TC) I thought came out well. When printed the detail in the distant snowy peaks really impressed me.

[Alex645]

I noticed that on the EXIF, you shot at 1/5s at f/16....correct? The 645 has a huge mirror that creates quite a lot of internal vibration unless shot in LiveView or mirror lockup. The effective 400mm focal length will just magnify that even more, so perhaps we are seeing not just lack of resolution (diffraction at f/16) but also a bit of blur. I'd run another test with a larger aperture, higher ISO, and faster shutter speed using LiveView.

The free lunch is the huge medium format sensor that allows you to crop your 200mm to get a 400mm angle of view.

[mattb123]

I noticed that on the EXIF, you shot at 1/5s at f/16....correct? The 645 has a huge mirror that creates quite a lot of internal vibration unless shot in LiveView or mirror lockup. The effective 400mm focal length will just magnify that even more, so perhaps we are seeing not just lack of resolution (diffraction at f/16) but also a bit of blur. I'd run another test with a larger aperture, higher ISO, and faster shutter speed using LiveView.

The free lunch is the huge medium format sensor that allows you to crop your 200mm to get a 400mm angle of view.

Yes, I used the 2s timer. I stopped down for DOF but I'll try again when a situation presents its self.
Cropping is just a discounted lunch because I like the compression as much or more than the FOV with longer lenses.

I also won't be able to try live view on my 645D but I'll give the TC another whirl sometime and see how it does under better circumstances.

[itshimitis]

The OP has a 645D which doesn't have live view. Anecdotally, I don't use Live View on the Z on a slower exposure if there is a danger of shutter shock as I find it more pronounced in LV. I shoot with mirror lock up and use LV for focussing only.

I have similar experience with the OP on the 2 x TC. I have always found it softens images with the A 200

[Alex645]

Yes, I used the 2s timer. I stopped down for DOF but I'll try again when a situation presents its self.
Cropping is just a discounted lunch because I like the compression as much or more than the FOV with longer lenses.

I also won't be able to try live view on my 645D but I'll give the TC another whirl sometime and see how it does under better circumstances.

The 2s timer delay will help eliminate you causing any movement hitting the shutter release, but it doesn't stop the reflex mirror shock. I assume you've got a fairly heavy duty tripod, the quick release shoe is tightly secured, and IF the tripod is on the medium to light side, I'd use a decent counterweight. Make sure height is achieved with the legs only, and not the center post which easily vibrates. None of these are issues until you inspect the details.

Is it possible the lens is back or front focusing? Perhaps AF fine tuning would help with the 200mm and 2x TC.

[mattb123]

The 2s timer delay will help eliminate you causing any movement hitting the shutter release, but it doesn't stop the reflex mirror shock. I assume you've got a fairly heavy duty tripod, the quick release shoe is tightly secured, and IF the tripod is on the medium to light side, I'd use a decent counterweight. Make sure height is achieved with the legs only, and not the center post which easily vibrates. None of these are issues until you inspect the details.

Is it possible the lens is back or front focusing? Perhaps AF fine tuning would help with the 200mm and 2x TC.

It would be me front or back focusing because it's the A version, manual focus. Definitely a possibility and I do rely on the focus confirmation but it seems spot on without the TC.
The tripod probably isn't as big as it should be. I'd like a bigger one as funds allow. I never use the center column unless that is the only way to get the shot.

I thought the 2s timer did a mirror lockup when you hit the button which gives the vibrations 2s to dissipate before the shutter fires. Am I mistaken about that?

I'll keep experimenting and report back any significant observations.

Thanks!

[itshimitis]

You can use mirror lock up in addition to the 2 second timer.

[Alex645]

It would be me front or back focusing because it's the A version, manual focus. Definitely a possibility and I do rely on the focus confirmation but it seems spot on without the TC.
The tripod probably isn't as big as it should be. I'd like a bigger one as funds allow. I never use the center column unless that is the only way to get the shot.

I thought the 2s timer did a mirror lockup when you hit the button which gives the vibrations 2s to dissipate before the shutter fires. Am I mistaken about that?

I'll keep experimenting and report back any significant observations.

Thanks!

I thought that even with MF lenses, AF fine tuning would help with focus confirmation with that lens, but I'm not sure. If it seems spot on w/o TC, then it probably is, but the TC essentially creates a new lens with more elements and groups.

In terms of tripods, another advantage of carbon fiber over metal is that it transmits less vibration. Wood is the ultimate, but impractical without a sherpa.

The 2s mode on the 645D self-timer raises the mirror and activates the shutter at the same time.

The reality of your situation could be simply, as you put it, the inherent loss of IQ with a 2x TC. It is essentially cropping optically to the center of your lens. With a loss of two stops, resulting in slower shutter speeds or higher ISO, I question whether it is worth
the compromise. Yes, cropping your medium format sensor reduces it to a FF, but does that loss of pixels worth the loss of resolution from the lens or increased diffraction?

Hopefully this is all just speculation and it's more of a vibration issue and not resolution. I would try ISO 800 and get the shutter speed as fast as possible with the lens only stopped down 2 EV.

[donesteban]

The 200/4 A is a very good lens at distant objects and stopped down a bit, also for objects closer to the camera. The 200/4 FA is vice versa (stop down at least to f/8 for distant objects very good from f/4 for portrait).
Te 200/4 A even works pretty well with the 1.4x converter at long distances. It clearly shows more detail than just a crop. But the 2x converter is just too much, while it is a good les it is not one of the master pieces being able to drive the 2x converter at 40 MP and the quit small sensor compared to the full 645 format.

Did you put the lens itself to f/16? My 645D doesn't translate the apperture when adding the converter, I still can put the 20/4 to f/4 according to the camera. But in combination with the 2x convter that's f/8 wide open. So if my camera shows f/16 in combination with the 2x converter, there is f/32 in fact. This will soften the image, too, don't stop the lens further down than f/8 when usng the 2x converter! If a lens is not sharp enough at f/8 in combination with the converter, don't use it with the converter, as stopping further down will kill sharpness anyway. Just try your 200/4 at f/32 without converter.
The 1.4x converter allows to stop down the lens up to f/11, making it a bit easier for the lens.

[gha128]

I always use live view, 12second &amp; MU timer (does the D have this?) with the my z and the 200fa plus 1.4. Essential. The 2sec doesn't cut it<br />
<br />
I have no real world experience of the 2X but everything I have read suggests it's one to miss...