jon_savage

<p>It didn’t pass close to the moon. I’m not sure when or if ever it crosses the moon from viewing in the UK but to get a better sense of scale I cropped two together. I printed it up at 36x24 cm and it came out much better than I expected as on screen it looks a bit soft and grainy.</p> <p>If you are interested I found 1/1250^th sec and ISO 400-800 best at f6.3. Upping the ISO appeared worse as the grain started to impact on your 30 pixels. The auto colour balanced looked fine.</p> <p> I didn’t see Tim wave but I guess he’s busy</p><div></div>

<p>Some examples of how it changes angle and appearance in the couple of minutes it passed</p><div></div>

<p>Camera view of the ISS – It moves quickly but it is OK to track once you found it in the viewfinder. It’s an unsharpened 100% crop in the corner</p><div></div>

<p>Hi all, thought you might be interested in a shot of Tim Peake - OK, might be a slight exaggeration! (for non-UK based people he’s the first International Space Station visitor we’ve just sent so there’s currently quite a bit of media interest in him over here).</p> <p>The ISS has spent that last couple of weeks passing the UK early evening and so making good opportunities to photograph. But the weather has not been good. Last Monday when I got home from work for once it was clear so I dashed out to watch it pass.</p> <p>I had a D7100 and a Sigma 150-600. I focused on the moon manually through the eyepiece as live view was too wobbly and not that clear to see. I also set the exposure on the moon. Then waited and as predicted it came into view and passed quickly. In the couple of minutes it was in view I took a few images at different ISO and shutter speeds.</p> <p>To my surprise you could recognise the ISS. It was small in the picture, probably not even 30 pixels across. In the sequence you can see it is rotating and as it rotated it picked the light off the sun differently and some shots looked clearer than others. I guess the atmosphere also plays a significant part in clarity.</p> <p>Anyway, following are some images….</p><div></div>

<p>I thought these links might be of interest to anyone considering a super telephoto zoom. The first talks about the usefulness of a wide zoom range on safari so it’s applicable to all and the other two are just specific to a Sigma with one about it with its dedicated teleconverter.</p> <p>I agonised over getting one and in the end I got the Sigma Sport a while back. One reason was because the Nikon 80-400 and new 300f4 (to use with a TC) just felt too expensive in the UK. The other was that I am used to 400mm on DX and when I go to FX I’d miss the reach.</p> <p>I could imagine I would have stuck with Nikon if it had been around at the time as I would have been hessitant to spend that much on a non Nikon lens. But having got the Sigma and used it I appreciate the build quality so I’ve no regrets. In fact I think I could happily try any of their other Sport or Art range lenses based on my experiance of this one and it's USB dock.</p> <p>I don’t get how the 200-500 it’s so reasonably priced compared to Nikons other new lenses. I guess that Nikon gold ring uses some expensive paint!</p> <p>http://www.weblogtheworld.com/countries/africa-africa/shooting-wildlife-with-the-sigma-150-600-mm-f5-6-3-dg-os-hsm-sports-lens/</p> <p>http://dustinabbott.net/2015/05/sigma-150-600mm-f5-6-3-dg-os-hsm-sport-review/</p> <p>http://georghofmeyr.com/blog/sigma-tc1401-teleconverter-review/</p>

<p>Andrew, I was really only pointing out that larger format doesn't appear to fix the diffraction problems.</p> <p>I agree that for the shallowest DOF large format may be easier but obviously there are plenty of other considerations when choosing a system especially if going to the extremes of the focal lengths and apertures on a system (size, weight, cost, build quality, plus the modern additions like auto focus systems, VR etc).</p> <p>I don't know much about large format but it looks like 150mm large format lenses are often f5.6 (so a 50/1.4 in FX?) and a 2.8 one not so common. The only one I came across (not that I looked hard!) was a 150mm Xenotar f2.8, "It weighs seven times as much as the Fujinon-W (f5.6), and if you work with it on your camera you get the feeling that you are budging a spacecraft through a swamp"!</p> <p>I guess there is always a compromise needed somewhere depending on your own priorities.</p>

<p>Shun,<br> <br />“If you indeed need more pixels, you cannot keep squeezing them into 24x36mm. That is why you need larger format so that you can once again use f8, f11 without diffraction problems”<br> <br />If you are having the following scenario:<br> <br />Someone wants f8 on 50MP FX camera but doesn’t like the amount of diffraction softening at pixel level (because f8 airy disc is 10.7 microns and the pixel size is 4.2).<br> <br />Are you proposing they should switch to a larger format for larger pixels so they can take their photo at f8 and reduce the f8 diffraction impact as pixel size is bigger (for example MF 54mm x 40mm pixel size would be of 6.6 microns for 50MP)?<br> <br />But this f8 on a larger format has less depth of field (assuming the same field of view in the final photo) so more out of focus blur in your final photo.<br> <br />So you stop down to get your DoF back. You would need f12.3 on the medium format example. That gives you an airy disc of 16.6 vs pixel size of 6.6, that’s the same ratio as airy disc of 10.7 vs pixel size of 4.2.<br> <br />If you want the same final photo it looks like you have gained nothing in terms of the diffraction softening artefact. So I’m not sure going to a larger format will get you round the diffraction problem</p><div></div>

<p>Even the link I posted earlier stated “We just couldn't achieve the same sort of dramatically shallow depth-of-field with a 35mm camera” and “that advantage holds true for this new Pentax 645Z. Its draw for the creative photographer isn't so much that it has 54 million pixels with a pitch of 5.3 microns, but that its 43.8x32.8mm sensor can deliver a crisp full length portrait against a creamy background at an aberration-free f/5.6 and a distance of 15 feet. With a standard 55mm lens”</p> <p>If creamy background refers to this dramatically shallow depth-of-field I think you can get the same Dof as his 55mm/5.6 with a 44mm/4.5 FX or even a 30mm/2.9 on the little DX. While the quality of his £1000 glass and lens design will impact the aberrations I can’t see for example a Sigma 30/1.4 Art prime stopped down being that bad. It would be interesting to see a proper comparison though...</p> <p>Even Luminous Landscapes refer to “the fact that it can shoot extremely shallow DOF” in a 645z review as an advantage and Amateur Photographer “The shallow depth of field that is afforded by the larger sensor” relative to 35mm/full frame. But with the availability of fast full frame lenses I’m not sure that statement is as unique to this digital medium format (44x33) they test as they think it is.</p> <p>This guy lost me completely:<br> gizmodo.com/why-medium-format-is-so-gorgeous-its-about-more-than-r-160193827</p> <p>“The key point as a result of that difference [MF vs FX equivalent] is that even though the field of view is wider, the geometry, or "look," of the 50mm focal length remains. You don't get the exaggerated perspective that wide angle lenses usually produce on 35mm cameras. In that regard, medium format mimics how your eyes actually see the world, at least more so than the smaller 35mm size.”</p> <p>I thought if you choose the focal lengths correctly to take into consideration the crop factors the perspectives are the same.</p> <p>Some good new though, the high megapixel count doesn’t appear to be an issue:<br> http://guyaubertin.com/review-pentax-645z-from-a-landscape-photographer.htm<br> “I don't find diffraction a problem and am happy to use F16 if needed”<br> With a pixel size of ~5.4microns at F16 the diffusion airy disc is ~22 microns. That’s 4 times the size of the pixel. I guess that’s only an issue if you print large enough to see the pixel level detail. But either way the lack of an issue would also apply to the high MP FX sensors as they wouldn’t have to stop down as far as F16 to get the same increased DOF.</p> <p>If you are interested I found one informative review of 44x33 vs 36x24 format that came with equivalent image samples and lens options comparisons (40MP 645D vs a D36MP 800). Their conclusion:<br> “Both cameras produce images of outstanding quality and the for all practical purposes the images are identical in resolution, contrast and color rendition in the ISO range 100 – 400”<br> And that was from a Pentax website so I assume it’s not biased in favour of the Nikon:<br> http://www.pentaxforums.com/reviews/nikon-d800e-vs-pentax-645d/image-quality-field-tests.html</p> <p>I don’t know what the IQ different between them really is having never tested them side by side but this aberration-free with dramatically shallow depth-of-field aspect might be exaggerated a bit but then some people will pay a lot for small improvements. Anyway, I’ve digressed form the point of the thread (sharing the maths) and I’m arriving late reading up on MF and it looks like this has all been discussed before:<br> http://www.photo.net/nikon-camera-forum/00cWTH?start=30 Is the Pentax 645Z a game changer for Nikon?</p> <p>I’m still interested in FX for the opportunity of less DoF and therefore the low light and artistic opportunities it opens up but maybe not just yet as the price of a body and a couple of lenses that would show a noticeable difference to my current DX set up add up to more than I would want to spend in one go (I'm saving). I think FX is possibly the best compromise for me as a system in the long run (size, cost, lens availability, DoF opportunities, etc.).</p> <p>As for ever getting medium format I think I’ll just take pictures at f1.8 with a Sigma 18-35 Art on my old DX (that’s only a 34-70/f3.4 on the 44x33), crop them to 3:2 or even square and save a few quid. As long as I don’t print extremely large no one will ever know :-)</p>

<p>Joe, it’s interesting you say that. I’d not paid much attention to “medium format” having never used it hence my confusing label of Pentax 645 not realising it meant 56x42 to most people. But based on this thread I Googled a bit. It was surprising what kind of information the top hits brought up.<br> Shallow depth of field appears to come up a lot with MF users. But they do come out with some confusing comparisons. This guy reviews a 44 x 33 MF sensor:<br> http://zackarias.com/for-photographers/gear-gadgets/why-i-moved-to-medium-format-phase-one-iq140-review/<br> Half way down his review he has a man sitting up at a table with back focus on the eyes, “This was shot with the 55mm 2.8 lens at f3.2. The 55mm is “about” a 35mm focal length in terms of full frame DSLRs. So it’s a bit on the wide angle side of things. Notice how I got the far eye in focus but the near eye is going soft. I’m at a decent distance from Dan with a wide lens. A DSLR with this set up at f3.2 would have held both eyes.” I think he’s mixed up his formats and talking about a larger film MF size vs 35mm – see table in image below. I'm not sure the difference is that much (say 17 v 21 cm around where he focused??).</p> <div></div>

<p>Antonio, thanks for the clarification. It looks like you used the sensor areas for the crop factor calculation and I used the diagonals.</p> <p>Also just to clarfiy I'm not saying the 645z to FF difference is "trivial", but I did say it was too exspensive for me :-)</p>

<p>Rodeo Joe, I don’t think there is an error, I think you have assumed a different sensor size than I used for the column headed “Pentax 645”. This was for the Pentax 645 digital cameras (645D and 645Z with a sensor size of 44x33). So maybe I needed a clearer heading so it’s not read as “Medium Format”. For example this Pentax 645:</p> <p>http://www.techradar.com/news/photography-video-capture/cameras/does-anyone-really-need-a-digital-medium-format-camera--1246587<br> (in a techradar article on "digital medium format")</p> <p>I don’t think you must use the diagonal but it’s a good one to use and if you believe Wikipedia the most common one:</p> <p>“In digital photography, a crop factor is related to the ratio of the dimensions of a camera's imaging area compared to a reference format; most often, this term is applied to digital cameras, relative to 35 mm film format as a reference. In the case of digital cameras, the imaging device would be a digital sensor. The most commonly used definition of crop factor is the ratio of a 35 mm frame's diagonal (43.3 mm) to the diagonal of the image sensor in question; that is, CF=diag35mm / diagsensor”</p> <p>I think we agree but we are talking at cross purposes on the assumed Pentax 645 sensor size.</p> <p>For the arbitrary ISO, well the point of it being a spreadsheet is you can put in any ISO you want to try. The screenshot happened to have the DxO low ISO figure in it as that was the last one I happened to type in.</p> <p>I was just sharing the mathematical relationships between the systems for those that might be interested. I’m not commenting on why anyone would bother switching between systems.</p> <p>Having said that I think I might agree with you about the Pentax 645 (44x33 sensor) vs full frame looking expensive for the difference you get. But then it’s not aimed at my type of photography (or my budget!).</p> <p>Antonio, How do you get 0.77? How does it make a difference or are you just suggesting I should show more decimal places?</p><div></div>

<p>Matt/Antonio,</p> <p>If you imagine two people side by side taking the same picture, one with DX, the other with FX. I think it’s widely accepted that the 1.5 crop factor makes 50mm on DX “the same” FoV as 75mm on FX. Most even agree that f2.8 in DX is “the same” as f4.2 in FX when also considering the DoF differences the sensors show in the final print.</p> <p>But what most miss when comparing the two systems is that when taking a picture of the same subject is that once you have changed the aperture you need to change the ISO to match (because the available light is the same). Otherwise you would underexpose FX when trying to get the same image (match the DX FoV and DoF). The ISO row is the ISO to go with the aperture and shutter to match the exposures for the column.</p> <p>In a way you’ve really just said a photograph taken with the same available light will show better sensor qualities when taken with settings that produce a shallower DoF.</p> <p>It was really just an excersise to understand the system differences and physical interactions and I thought others may be interested in it. Like Wouter says, it's about what each system does best, worst or not at all - that makes or breaks the choice. The spreadsheet may help some understand how and why each system behaves like it does from a purely theoretical sensor/lens point of view. No considerations for any particular camera ergonomics modelled!</p>

<p>Detail behind the table and the calculations used....</p><div></div>

<p>I thought this spreadsheet might be of interest to some. I used this to compare DX to FX as I am considering a system switch to FX and I wanted to understand what I would need to replace my DX kit with and to set my expectations. I’m considering moving from a D7100 (£750 and DxO low ISO rating of 1256) to a D750 (£1750 and DxO low ISO of 2956).<br /> <br />The notes on the side in the next image explain a bit more if you wanted to make your own version. I used a couple of simple approximations where needed to make it easier.<br /> <br />But note that by “the same” I am referring to the final photograph. So the image you would print or the image you would stick on a website. The two systems settings are considered equivalent if they would produce the same looking photographs when taken with the same available light. I guess this is only important if you are taking photos where the depth of field is critical but it might help compare the strengths and weaknesses of systems in areas where you use them most.<br /> <br />It’s also interesting to look at the pixel size vs diffusion interaction for the bigger sensors. Obviously in the real world the lens and sensor quality will be impacted by cost and manufacturability which is why some systems don't have some lenses available and there is more to an image when you include other optical characteristics beyond depth of field and diffusion.</p> <p>It seams to check out OK and it was an interesting exercise! <br /><br /></p><div></div>

<p>And a 100% crop.</p><div></div>

<p>Here's a better stabilisation example. Last Sunday I was opposite the pits at a motorsport event and specifically tried a low shutter zooming into the pits. So this is 1/100th at 600mm on a D7100 hand held.<br> <br />Here's the full image. A bit of people movement as it was a quick driver and tyre change but quite sharp enough considering the set up.</p><div></div>

<p>100% feather detail</p><div></div>

<p>I can't remember if stabalisation was on or off. I tried a few but lost track which were which. But the one below was hand held (elbows on hide window ledge), stabalisation on at 600mm and only 1/200th.</p> <p>Like I said before the weather was gloomy so ISO800 and dull light for a dull photo! It was the only thing we briefly saw while getting cold one wet Sunday down at RSPB Rye Meads and it wouldn't keep still while pecking away. Again no sharpening with a 100% crop of the feathers following.<br> <br />Yes, the new upgraded 300f4 + 1.4TC + tripod collar was my old plan but the upgraded price was too much here and I did fancy the zoom and extra reach of the Sigma.</p><div></div>

<p>Mike, I bought the Sigma recently (£1499). Although I've not had the weather (lights has been grey and dull) or time to get out with it I have a couple of snaps. This one was about the only one when the sun peaked through. Taken with a monopod. So far I'm very pleased with it although I have needed to upgrade my monopod/head. I have the USB dock but haven't tried tuing it yet. So far focus looks OK.</p> <p>Photo below was raw straight into PS Element via lightroom 4 presets. Then resized and saved a jpeg. No additional sharpening.</p><div></div>