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10-04-2011, 12:36 AM   #1
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A400-f/2.8 vs A600-f5.6

In a moment of lens frustration (and only rare buying opportunities), I managed to find a suitable place to get my A600-f5.6 serviced and repaired
so that it works nicely, but before that was accomplished a buying opportunity became available for the A400-f/2.8, and I got a tripod rated
big enough to hold up either one, so now the challenge is to attempt to figure out when I should be using one and when I should use the other.

Both are obviously exotic lenses which can and often are used for similar purposes. I also have most of the converters that Pentax has ever made
including the "Pentax rear converter-A 1.4x-L, the Pentax Rear Converter-A 2x-L, the Pentax Rear Converter-A 2x-S, and the Pentax Adapter 1.7x.
I'm really looking for some wisdom on which of this equipment to use under various conditons.

I've been doing some testing and what I think I'm seeing don't always match up with my expectations.

My latest set of test photos and discussion show up on my website at Using extreme telephoto lenses

I have a punch list of tenative conclusions/thoughts that I welcome challenges to:

1) The AF 1.7x adapter isn't a friend of the 600/f5.6 lens. At f/5.6 the lens doesn't seem to pass enough light to work reliably, but it is very happy
on the f2.8 long lenses.

2) the A400 provides significantly greater depth of field than the A600 in a fairly short range---50-60 feet. even at F3.5 or F4 as compare
to the A600 wide open.

3) Since my goal was to provide an equilivalent image, On the a400, I tried two solutions to make it 'work like a 600. I used the Rear Converter 1.4x-L in some, and in the other test photo I used nothing---but then did a photoshop 'digital crop' and simply trimmed the image in photo shop
down to match the A600.

the Lighting conditions I chose were late afternoon on a dark cloudy day just before it started to rain.
to maximize the camera stability, I used a studio class Bogen/Manfrotto 3046 tripod and a wireless release...I did not lock lock up the mirror.

With a slightly elevated ISO of 400, the f5.6 lens produced 1/60th shutter speed wide open. There was minor movement is some of the leaves.

The A400 F/2.8 produced a picture (on my K5 program mode of F3.5 at 1/125., and when I added the rear converter 1.4x-L, it would have gone
to 'wide open' but I forced it to F/4 based on the old rule that when you add a converter you ought to stop the lens down at least one stop from wide open, and the time came in at 1/40th.

Now what surprised me, is that of the 3 setups---- the A600 f/5.6 wide open, and the A400 digitally cropped to match the 600mm lense, and the A400 with the 1.4x converter (making an effective 560mm) all under fairly weak light as that the A400 which I digitallycropped clearly had the sharpest photo, and although there were some differences, between the A600 and the A400 with the 1.4X rear converter, I think it's far to conclude that the results were very very similar.

Now this isn't the first time that I have observed that an 'digital crop' inphotoshop produced a better result than an optical crop (using a converter)
but It is not what I was expecting and before I put all my converters on EBAY I'm wondering if others have had similar experiences or can define
when one method works better than the other. I'm surmising that strong light will allow the allow the lens to be stopped down more which may produce somepretty major improvements with the converter, and less so for the photoshop digital crop.

I'm a bit takenaback, that the a400 out performed the A600 even after I whacked the a400 photo down to match the field seen by the A600.
Again, though before I put the a600 on EBAY, I'm surmising tht it may shine under stronger lighting conditions or at a longer distance.

I haven't tried that yet. anyone beendown this road?????

10-04-2011, 06:07 AM   #2
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I can only add that after hundreds of test shots at different settings, my A*400/2.8 with the 1.4xL appeared to have no IQ degradation when used in normal outdoor lighting. None. Although I am sure physics dictates there must be some degradation, it was not something I could ever pick out like I could easily do with the 2xL or cheaper 1.4x TCs that I have long since disposed of. Adding the AF 1.7x requires at least strong indirect light to make high IQ. Anything less was better with a crop. The A*400/2.8 with that salad plate front element can really pick up enough light to shine with the 1.4xL and even with the AF1.7x and better light.

So yes, I support your conclusions even though I never touched a 600/5.6.
10-04-2011, 01:56 PM   #3
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A down side to getting rid of the 600 and the teleconverters is that you always have the option of cropping from those as well... at a certain point you just can't crop any more from the 400 for more "zoom". Of course i have no experience with any of these lenses, so that is just a theoretical concern.
10-04-2011, 05:31 PM   #4
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Clinton.......??? Actually He is probably busy playing with his 1200mm!

10-04-2011, 09:42 PM   #5
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QuoteOriginally posted by imtheguy Quote
I can only add that after hundreds of test shots at different settings, my A*400/2.8 with the 1.4xL appeared to have no IQ degradation when used in normal outdoor lighting. None. Although I am sure physics dictates there must be some degradation, it was not something I could ever pick out like I could easily do with the 2xL or cheaper 1.4x TCs that I have long since disposed of. Adding the AF 1.7x requires at least strong indirect light to make high IQ. Anything less was better with a crop. The A*400/2.8 with that salad plate front element can really pick up enough light to shine with the 1.4xL and even with the AF1.7x and better light.

So yes, I support your conclusions even though I never touched a 600/5.6.
I was out again today tryingn to figure out how these things work in real life. I've added a tranche of photos with
the A400 f/2.8 to my web page at Using extreme telephoto lenses. I tried the 1.4x-L TC, the 2x-L TC and then I stacked a 2x-S TC on top of the 2x-L TC. The ambient lighting was
a few stops better than yesterday. I also lengthened my 'test' distance from 50 feet to 500 feet or so.

The main difference I see in the photos all the way to the stacked converters (besides some exposure problems because I suspect the 5 F stops or so of lost light from stacking the converters put things beyond the range of the light meter) was that will all the converters---I can detect some camera shake, which I suspect is mirror induced vibration. Unlike the leaves of yesterday I selected a piece of large machinery which I knew wouldn't move, but I stll see a small amount of astigmatism on all the shots
with any converter combination.

IF we assume I can get the vibration out with improved technique, what I'm seeing is that a) using a converter----even up to stacked ones) with this lense provies very little degradation of the image, but that you can get essentially identical results
with an 'digital crop' in photoshop..

Converters were very important when you needed to fill the color slide frame, but it seems to me that as the megapixel war proceeds the benefits of an optical TC will diminish to the point that it approaches zero, and from a very practical standpoint we may have already arrived at that point.
10-04-2011, 10:01 PM   #6
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QuoteOriginally posted by Nick Siebers Quote
A down side to getting rid of the 600 and the teleconverters is that you always have the option of cropping from those as well... at a certain point you just can't crop any more from the 400 for more "zoom". Of course i have no experience with any of these lenses, so that is just a theoretical concern.
I took another round of investigatory photos today with a slightly higher light level (Cloudy medium to Cloudy bright) and a considerable additional
distance---- 500 feet instead of 50-60 feet. As I had surmised the overall results are very different.

The performance of the the A*400 f/2.8 remained outstanding, but the A*600 f/5.6 came into its own.

I agree with the focal length being valuable. I am begginning to seriously question if the converters are adding value to the mix.
It's been long reported that the recording capablity of the high megapixel sensors is approaching that of the optics.

The converter is simply an optical cropper. It doesn't bring more image or more resolution through the front of the lens. It just bends the light a little so only part of the image that the lens 'sees' gets to the sensor. thus it 'crops' the image before it gets to the sensor. When you use photoshop to crop the image it's obviously after the sensor has seen it. If the sensor is as good as the optic, the lens is limiting factor, and whether you crop the image before or after it goes through the sensor, the result should be about the same----which is about what I think I see.

The 600 clearly has value in a theoretical sense because of its longer focal length. It should 'look harder' and further.

What I think I'm seeing there is that ifyou give it enough light it will......

It's real limiter is the pathetic speed of F5/6..... Like all the inexpensive lenses that max out in this range,
when the sun is out of sight they struggle. Too many of my A600 images failed to really have strong conclusions,
but gatherniglight enough to function is its limitation.

Last edited by rvannatta; 10-04-2011 at 10:19 PM.
10-05-2011, 01:41 PM   #7
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It is an enviable position to be in to have the burden of having to test these 2 subjects!
10-05-2011, 02:12 PM   #8
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QuoteOriginally posted by littledrawe Quote
It is an enviable position to be in to have the burden of having to test these 2 subjects!
It is a symptom of a very serious disease......... LBA (lens Buying adddiction)

What I have been overwhelmed with so far as I work on these things is
the outstanding value of the 400 f/2.8. I've fiddled around with long lenses for over 40 years, but I have never had my hands on anything that has performed
so well.

To be sure at 13.5 lbs it's not one to take hiking, but I don't find anything close
for long shots with bad lighting. Of course, I've never used a 600 f/4, and it may be it with the extra stop gets enough light to be useful under impaired lighting as well. I just don't know.

The problem is that 'smart' little critters don't often expose themselves in the best of lighting, because bigger critters that like to eat smaller critters can see them better if the lighting is good so the smaller critters tend to stay in the shadows.

10-05-2011, 02:21 PM   #9
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Interesting tests rvannatta. I think not locking the shutter up is more realistic of real world use.

I have a new-to-me A*300mm f/4, with a Kenko 1.4 Teleplus and Pentax 2X-S. I haven't had any of this gear long enough to draw solid conclusions, so I'll be watching this thread with interest. I've only had one real outing, shooting small birds with the bare A*300. I was very pleased with the results, but had to do major cropping in post. With a TC on an f/4 lens, I'm going to need lots of light or very high ISO's.

A simple rule (probably too simple) occurred to me from your testing and my limited experience. For computer viewing and internet posting, a digital crop will usually look better. For prints you would benefit from more pixels, so the TC should beat cropping.
10-05-2011, 04:15 PM   #10
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QuoteOriginally posted by audiobomber Quote
Interesting tests rvannatta. I think not locking the shutter up is more realistic of real world use.

I have a new-to-me A*300mm f/4, with a Kenko 1.4 Teleplus and Pentax 2X-S. I haven't had any of this gear long enough to draw solid conclusions, so I'll be watching this thread with interest. I've only had one real outing, shooting small birds with the bare A*300. I was very pleased with the results, but had to do major cropping in post. With a TC on an f/4 lens, I'm going to need lots of light or very high ISO's.

A simple rule (probably too simple) occurred to me from your testing and my limited experience. For computer viewing and internet posting, a digital crop will usually look better. For prints you would benefit from more pixels, so the TC should beat cropping.
That A* 300 f/.4 is a very good lens. I have one and was fiddling with it
yesterday with my 2x-S converter.

Fall has arrived with a vengence here, and I'm not likely to get to play
with a camera on sunny day until next june.

One thing that I think is over rated is the 'fear' and 'bias' against using
fairly high ISO's. a little more noise isn't nearly as destructive of a image
as some camera shake/vibration.

One of the things I would really like to understand better is where the trade off is,
and how high it makes sense to push the ISO to suppress issues related to depth of field, and slow shutter speeds.

Some times you can turn a shallow depth of field into 'art work', but rarely can
you do so with camera shake.---something that I can detect with the heavy long lenses even on a sturdy tripod and a remote release. Ironically enabling
the remote release disables the 'shake reduction' in the camera, but it may not be able to manage vibration anyway.

I think there is some consensus that the K5 in particualar does pretty well and higher ISO settings, But I see camera equipment as like flying a airplane.

Autopilots are fine, but if you want to avoid disaster you need to know when to turn the autopilot off and what to do when you do.

I may be totally egotistical, but I like to think that with some research
I can be smarter than 'program mode' at least is exotic lenses for which presumably program mode was not optimized. (I'm assuming).

Part of the problem I see is that a lot of us 'learned' photography on a film medium, and we have assumed that everything we 'learned' about taking photos with a film medium remains true.

For my part, some of what I've seen, in fiddling with this equipment is a long ways from what I 'expected'.
10-05-2011, 08:43 PM   #11
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I am really surprised that there have not been many people weighing in on this. I realize not everyone has both lenses but there are a lot of forum members that have long lens experience and they could be offering it here. Just out of curiosity what tripod/head setup are you using?
10-05-2011, 10:10 PM   #12
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QuoteOriginally posted by littledrawe Quote
I am really surprised that there have not been many people weighing in on this. I realize not everyone has both lenses but there are a lot of forum members that have long lens experience and they could be offering it here. Just out of curiosity what tripod/head setup are you using?
dunno where those that know are? I've been trying to learn about this stuff and hoping others would kick me when I got off track (or if I didn't)
but not hearing much.
click photo to expand


The tripod is a Bogen/Manfrotto 3046 with a 3047 head. It's rated for the kind of weight that the A400 has---13.5 lbs. It's the heaviest bogen/manrotto that I could find on Ebay. I use a pentax wireless release.

what I have not done is use the mirror lockup feature which isn't too hard to activate but I have until your message been too lazy to RTFM to figure out how to do it. I really liked my old film based K2----It had a button right on the front of it to manually flip up the mirror, but the whole concept
that an optical converter really doesn't do anything that you can't do just as well in photoshop blows my mind.

Similarly the fact that I still get usable images even with converters stacked is mind boggling.
10-06-2011, 09:37 AM   #13
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In the future maybe the 300mm plus long lens club in the lens club section would be a better place to ask questions, it might get a little more traffic from people that are shooting with long focal lengths regularly.
10-09-2011, 12:03 AM   #14
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Well, I have done some more work on the issues and have somemore thoughts.
<photos expand to full screen if clicked on>

Above: A*400 f2.8 lens w/ Pentax rear-converter-A 2x-L.

Above: A*400 f2.8 lens w/ Pentax rear-converter-A 2x-L. cropped to match stacked converter photo below.

Above: A*400 f2.8 lens w/ Pentax rear-converter-A 2x-L stacked with a Pentax rear-converter-A 2x-S.

I do have at least one conclusion. Stacking converters seems to be a pretty definite negative event. Here in the 3rd photo I put a 2X-S on the back of the 2x-L converter. The corner of the photo is completely fuzzed out. the middle photo which is really the first photo optically cropped
in Photoshop to approximately the same size is clearly superior.

Alas, I don't show a photo of the cow with no converter at all not because I didn't take one at the same time, but because the focus is bad.
This, it seems is a downside of not using any converter, is that the target is so small in the photo that you can't see to focus sharply. I've got a Katz eye, but haven't installed it. Even though I know from other work I've done that a photo shop crop produces similar results to that of an optical crop using a converter, there are other issues that are extremely hard to control that impact the final result.

1) accurate focus and accurate exposure become more difficult the if your target is a small part of a large photo
2) Optical cropping with a converter eats a lot of light and is less satisfactory under poor lighting conditions.
3) Extremely long focal lengths are extremetly sensitive to camera vibration, and the longer they are the worse it is.
4) Optical Cropping may lead to longer exposures which is profoundly an issue if the target is moving.
5) Longer exposures driven by Optical cropping may be offset by elevated ISO, because less digital cropping will be possible anyway.
6) Accurage focus and exposure may be difficult with extenders because the viewfinder may 'blackout' because of insufficient light.
7) Accurate composition becomes increasingly difficult with longer effective focal lengths. Indeed one of the reasons the cow isn't centered
in the 'stacked converter photo, was that I couldn'tquite get the tripod swing to settle in with a better compositon.

If you can manage all these extraneous issues, I have in my research on this issue produced photos that are very similar regardless of whether
a converter is used. What you must remember is that there is a substantial reciprocity ----If you pile on the converter power, then your ability to
enlarge/crop in Photo shop is impaired by a simlar amount. The native size of the K-5 image at 240ppi is approximately 13.5x20 inches and the image is usually pretty good at that size --- called the 100% crop, but if you crop it in the camera optically by using a 2x converter expect only
to enlarge the result to 50% or 7x10 inches.

For the most part, if the camera is on a tripod (as compared to a beanbag) use of a remote release and mirror lockup will be required for good results with these long lenses, profoundly if you are using a converter. The Mirror Lockup is actually quite convenient on the K5 with a wireless remote. ---- Ifyou chose that option, you pushthe release button twice. --- the first click locks the exposure and lifts the mirror, and push the remote a second time to actually take the image.

Light leaking in the viewfinder through the eyepiece will impact the exposure, but inlieu of the cover provided by Pentax, you can block the
light with your eye by actually looking through the viewfinder at the time you do the 'first click', or you can put your hand over
the viewfinder for the first click, and then take it away and let the camera/lens stop shaking and then take the photo.

While I am not likely to sell my converters as useless anytime soon, I am not likely to use them very often either.
10-09-2011, 07:44 AM   #15
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In your opinion does optical cropping become less desirable if the image is destined for print? If your printer required a minimum of say 200ppi then a K-5's resolution of 4928 pixels (long edge) would give a print of 24.6 inches. Without resorting to image resampling, a 1.4X crop would only allow a print of 17.6 inches. To get back to the 24.6 inch print, do you think resampling would be better or worse than optical cropping using the full resolution?
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