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| 10-04-2011, 12:36 AM | #1 |
| A400-f/2.8 vs A600-f5.6 | |
| 10-04-2011, 06:07 AM | #2 |
| 10-04-2011, 01:56 PM | #3 |
| 10-04-2011, 05:31 PM | #4 |
| 10-04-2011, 09:42 PM | #5 |
 Originally posted by imtheguy  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. 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 |
| Originally posted by Nick Siebers 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. 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 |
| 10-05-2011, 02:12 PM | #8 |
| Originally posted by littledrawe It is an enviable position to be in to have the burden of having to test these 2 subjects!  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 |
| 10-05-2011, 04:15 PM | #10 |
| Originally posted by audiobomber 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. 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 |
| 10-05-2011, 10:10 PM | #12 |
| Originally posted by littledrawe 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? 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 |
| 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. | |
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