Re: Sigma 28-105/2.8-4
On Thu, 1 Dec 2005, Godfrey DiGiorgi wrote: On Dec 1, 2005, at 9:38 AM, John Francis wrote: On Thu, Dec 01, 2005 at 04:15:49PM +, Kostas Kavoussanakis wrote: On Tue, 29 Nov 2005, Godfrey DiGiorgi wrote: Be aware that the difference in field of view between 90 and 105mm is quite small. See http://homepage.mac.com/godders/2zmFoVcomp.jpg for comparison. The real advantages of the 24-90 are much more field of view at the wide and and better performance when wide open at the tele end. Thanks, Godfrey. Can you help me understand your diagram? Is the small, green rectangle the FOV at (more or less) 90? The large green rectangle is the approximate field of view at 24mm vs the larger white rectangle at 28mm. The small green rectangle is the approximate field of view at 90mm vs the smaller white rectangle at 105mm. Here is an exercise I would like to solve: "Assuming a lens at 90mm and another at 105mm, how much closer to the subject should one go so as to get a photograph with the same dimensions on the recording medium". Well, that's easy. You should move forward until you're 90/105 of the distance you started from. As John said... ;-) Two on-line calculators that are useful for FoV ... Gives you field of view at distances: http://www.dudak.baka.com/fovcalc.html Gives you angular field of view: http://www.mat.uc.pt/~rps/photos/angles.html Many thanks to you and John. That's approximately 14cm per meter; not that much, but I will try it at home to see what it means in real-life. Kostas
Re: Sigma 28-105/2.8-4
On Dec 1, 2005, at 9:38 AM, John Francis wrote: On Thu, Dec 01, 2005 at 04:15:49PM +, Kostas Kavoussanakis wrote: On Tue, 29 Nov 2005, Godfrey DiGiorgi wrote: Be aware that the difference in field of view between 90 and 105mm is quite small. See http://homepage.mac.com/godders/2zmFoVcomp.jpg for comparison. The real advantages of the 24-90 are much more field of view at the wide and and better performance when wide open at the tele end. Thanks, Godfrey. Can you help me understand your diagram? Is the small, green rectangle the FOV at (more or less) 90? The large green rectangle is the approximate field of view at 24mm vs the larger white rectangle at 28mm. The small green rectangle is the approximate field of view at 90mm vs the smaller white rectangle at 105mm. Here is an exercise I would like to solve: "Assuming a lens at 90mm and another at 105mm, how much closer to the subject should one go so as to get a photograph with the same dimensions on the recording medium". Well, that's easy. You should move forward until you're 90/105 of the distance you started from. As John said... ;-) Two on-line calculators that are useful for FoV ... Gives you field of view at distances: http://www.dudak.baka.com/ fovcalc.html Gives you angular field of view: http://www.mat.uc.pt/~rps/photos/ angles.html Godfrey
Re: Sigma 28-105/2.8-4
On Thu, Dec 01, 2005 at 04:15:49PM +, Kostas Kavoussanakis wrote: > On Tue, 29 Nov 2005, Godfrey DiGiorgi wrote: > > >Be aware that the difference in field of view between 90 and 105mm is > >quite small. See > >http://homepage.mac.com/godders/2zmFoVcomp.jpg > >for comparison. The real advantages of the 24-90 are much more field of > >view at the wide and and better performance when wide open at the tele end. > > Thanks, Godfrey. Can you help me understand your diagram? Is the > small, green rectangle the FOV at (more or less) 90? Here is an > exercise I would like to solve: "Assuming a lens at 90mm and another > at 105mm, how much closer to the subject should one go so as to get a > photograph with the same dimensions on the recording medium". Well, that's easy. You should move forward until you're 90/105 of the distance you started from.
Re: Sigma 28-105/2.8-4
On Tue, 29 Nov 2005, Godfrey DiGiorgi wrote: Be aware that the difference in field of view between 90 and 105mm is quite small. See http://homepage.mac.com/godders/2zmFoVcomp.jpg for comparison. The real advantages of the 24-90 are much more field of view at the wide and and better performance when wide open at the tele end. Thanks, Godfrey. Can you help me understand your diagram? Is the small, green rectangle the FOV at (more or less) 90? Here is an exercise I would like to solve: "Assuming a lens at 90mm and another at 105mm, how much closer to the subject should one go so as to get a photograph with the same dimensions on the recording medium". Cluelessly yours, Kostas
Re: Sigma 28-105/2.8-4
Hi! Fred, is the Tamron 28-75/2.8 too short for you? Don does not like its bokeh, though. Yes. (Do you mean the Pentax FA 28-70/2.8? - it looks like a really nice lens, but I really need something longer, to avoid changing lenses at a casual family gathering frequently.) I think that 28-105 might just do it. Thanks for the suggestion though, Kostas. Let me add my few cents worth. Sigma lenses I witnessed myself are a mixed bag. My 18/3.5 is fine lens (Thanks J.C.O). The 28-135 I bought new was rather average. A friend of mine has 70-200/3.8 (older but still AF) zoom that he seems to like, yet I think it was merely adequate... If you look for top notch quality, Sigma probably isn't the way to go. If you look for medium quality and convenience Sigma can be an option, but in this case there are few more third party lens manufacturers to consider, such as Tamron. Ultimately however if you can stick with original glass, it would be better... And then obviously you'd get to blame Pentax once more if need be ;-). I have one suspicion about /2.8-4 series of Sigma lenses - they are very cheap new and just dirt cheap used... It must be a sign of something, something not good. Boris
RE: Sigma 28-105/2.8-4
Hi Fred, I have the Sigma 2.8-4.0 and can't say I'd recommend it. I find it quite poor at the wide end and even though it's better at the long end my Tamron 28-105/4-5.6 outperforms it every time. I'd usually rather bump the ISO a notch and use the Tamron. Because the Tamron is more contrasty the autofocus is as good or better even though a stop slower. As Godfrey says the wide open contrast is what really counts in autofocusing. For the type of thing you are describing I have been using the Tamron SP90/2.8, one of my favorites. Don > -Original Message- > From: Fred [mailto:[EMAIL PROTECTED] > Sent: Tuesday, November 29, 2005 8:39 AM > To: pentax-discuss@pdml.net > Subject: Sigma 28-105/2.8-4 > > > Hi, all. > > Does anyone have any opinions on the Sigma 28-105/2.8-4 ? > > I'd like a faster autofocus 28-105 than the Pentax FA 28-105/3.2-4.5 or > either of the FA 28-105/4-5.6's (although the 28-105/3.2-4.5 is marginally > faster than the others). (This would be for use on an *ist DS.) > > However, I'm afraid of: > > 1. softness > > 2. flimsiness > > 3. bad bokeh > > I know very little about Sigma lenses (except for some generalities that > may or may not apply to this particular lens). Any opinions? Thanks. > > [Gee - I really wish that Tamron made the 28-105/2.8 in Pentax mount.] > > Fred > >
Re: Sigma 28-105/2.8-4
> I suspect he means the Tamron. It's sharp, contrasty, fast and dirt > cheap. I'm quite fond of mine (And I do like the Bokeh it produces). That sounds like a decent lens, Adam - I just wish it were somewhat longer - I am sure I'd be hitting the long end of its zoom range all too often for the informal child portraits that I do a lot of, even with the "crop factor" on the *ist DS. Fred
Re: Sigma 28-105/2.8-4
>> I think that 90mm at the long end might be a little short for the my >> usual "family photos" situation, but thanks for the suggestion. I think >> that the FA 28-105/3.2-4.5 might be a better bet. > The 28-105 is a darn good lens for the money. I'd have to say, however, > that the 24-90 outperforms it at 70mm+ focal lengths when wide open. > Stopped down 1-2 stops, the results are nearly impossible to tell apart. Hmmm... You've given some food for thought, Godfrey - maybe I'll have to look into that 24-90 some... > Be aware that the difference in field of view between 90 and 105mm is > quite small. See http://homepage.mac.com/godders/2zmFoVcomp.jpg for > comparison. The real advantages of the 24-90 are much more field of view > at the wide and and better performance when wide open at the tele end. Yes, I can see that. However, for what I'm mostly looking for (a lot of informal child portraits), it's not the wide end but the long end that is likely to be "bumped into" most of the time with a "something-to-90" or a "something-to-90" zoom, even on an APS DSLR like the DS. (The 28-200 actually does quite well - surprisingly well - I just wish it had a little more speed.) Thanks for your thoughts... Now, lemme see what Boz's site has on that 24-90... Fred
Re: Sigma 28-105/2.8-4
On Nov 29, 2005, at 10:19 AM, Fred wrote: If you want a better lens than that, the Pentax 24-90/4 is the one I'd choose. I think that 90mm at the long end might be a little short for the my usual "family photos" situation, but thanks for the suggestion. I think that the FA 28-105/3.2-4.5 might be a better bet. The 28-105 is a darn good lens for the money. I'd have to say, however, that the 24-90 outperforms it at 70mm+ focal lengths when wide open. Stopped down 1-2 stops, the results are nearly impossible to tell apart. Be aware that the difference in field of view between 90 and 105mm is quite small. See http://homepage.mac.com/godders/2zmFoVcomp.jpg for comparison. The real advantages of the 24-90 are much more field of view at the wide and and better performance when wide open at the tele end. Godfrey
Re: Sigma 28-105/2.8-4
Fred wrote: Fred, is the Tamron 28-75/2.8 too short for you? Don does not like its bokeh, though. Yes. (Do you mean the Pentax FA 28-70/2.8? - it looks like a really nice lens, but I really need something longer, to avoid changing lenses at a casual family gathering frequently.) I think that 28-105 might just do it. Thanks for the suggestion though, Kostas. Fred I suspect he means the Tamron. It's sharp, contrasty, fast and dirt cheap. I'm quite fond of mine (And I do like the Bokeh it produces). -Ada,
Re: Sigma 28-105/2.8-4
Hi, Godfrey. > I no longer even look at Sigma products, however, having been burned too > frequently in the past by them. Yes, I've heard a few disparaging comments about them. However, perhaps not all of their lenses are built the same way, and Sigma may have gone through a "cheap" period that they learned from and are now putting out better lenses - I really don't know at all. I'm much more familiar with some of the Vivitar (Series 1), Tokina (AT-X), and Tamron (SP) lenses (although almost all of my experience has been with manual focus lenses) - I don't think I've ever owned a Sigma at all. > However, I'd be very skeptical of there being any substantive > improvement between it and the Pentax 28-105/3.2-4.5. I guess the FA 28-105/3.2-4.5 sounds pretty good. It's a bit faster than the other two FA 28-105's, and I guess it's a decent lens, too. I've been using (on my DS) the FA 28-200/3.8-5.6 quite a bit (for "family photos", etc. - not really for more "serious" shooting - ), and I've been pleasantly surprised at just what it's been able to do (within its design limitations, of course) - I think it might be a better APS DSLR lens than a full-frame 35mm film lens. I'd like a faster lens, and I think that 28mm-105mm (on the DS) might be a good zoom range. > If you want a better lens than that, the Pentax 24-90/4 is the one I'd > choose. I think that 90mm at the long end might be a little short for the my usual "family photos" situation, but thanks for the suggestion. I think that the FA 28-105/3.2-4.5 might be a better bet. Fred
Re: Sigma 28-105/2.8-4
> http://www.photographyreview.com/cat/lenses/35mm-zoom/sigma/PRD_83592_3128crx.aspx > http://www.camerareview.com/templates/reviews_lens.cfm?lens_id=396 > I've been pretty impressed with most of the Sigma stuff I've bought > lately (I have the EF500 DG Super flash and the EX300/2.8 lens) but the > lens you're asking about is an older one and based on the reviews I'd > give it a miss. Thanks for the links, Mark. Yes, I've checked a number of online reviews, and the lens hasn't exactly gotten glowing rave reviews - . However, there have been some exceptions. Many of the owner reviews range from 1's to 5's (on a 1-5 scale) - while the average is middling, the average alone can't be telling the whole story, since they're such a variance in opinions. As for Sigma itself , I don't really know how it is doing now. Perhaps Sigma has learned from some of its mistakes (I've been led to believe that it has had some problems in the past), and maybe the quality has indeed improved. That would be good... Fred
Re: Sigma 28-105/2.8-4
> Fred, is the Tamron 28-75/2.8 too short for you? Don does not like its > bokeh, though. Yes. (Do you mean the Pentax FA 28-70/2.8? - it looks like a really nice lens, but I really need something longer, to avoid changing lenses at a casual family gathering frequently.) I think that 28-105 might just do it. Thanks for the suggestion though, Kostas. Fred
Re: Sigma 28-105/2.8-4
On Tue, 29 Nov 2005, Godfrey DiGiorgi wrote: On Nov 29, 2005, at 6:38 AM, Fred wrote: Does anyone have any opinions on the Sigma 28-105/2.8-4 ? I'd like a faster autofocus 28-105 than the Pentax FA 28-105/3.2-4.5 or either of the FA 28-105/4-5.6's (although the 28-105/3.2-4.5 is marginally faster than the others). (This would be for use on an *ist DS.) However, I'd be very skeptical of there being any substantive improvement between it and the Pentax 28-105/3.2-4.5. If you want a better lens than that, the Pentax 24-90/4 is the one I'd choose. Lens speed is generally not a big factor in AF speed ... wide open contrast is a much greater factor. For instance, the Pentax FA35/2 is a faster focuser than the FA50/1.4, because it achieves better contrast wide-open despite being 1 stop slower. I am not sure that's what he meant, I think he is looking for a faster (aperture-wise) lens that is AF. The 24-90 is 3.5-4.5. Fred, is the Tamron 28-75/2.8 too short for you? Don does not like its bokeh, though. Kostas
Re: Sigma 28-105/2.8-4
Fred <[EMAIL PROTECTED]> wrote: >Does anyone have any opinions on the Sigma 28-105/2.8-4 ? http://www.photographyreview.com/cat/lenses/35mm-zoom/sigma/PRD_83592_3128crx.aspx http://www.camerareview.com/templates/reviews_lens.cfm?lens_id=396 I've been pretty impressed with most of the Sigma stuff I've bought lately (I have the EF500 DG Super flash and the EX300/2.8 lens) but the lens you're asking about is an older one and based on the reviews I'd give it a miss. -- Mark Roberts Photography and writing www.robertstech.com
Re: Sigma 28-105/2.8-4
I don't know the Sigma lens in question at all. I no longer even look at Sigma products, however, having been burned too frequently in the past by them. However, I'd be very skeptical of there being any substantive improvement between it and the Pentax 28-105/3.2-4.5. If you want a better lens than that, the Pentax 24-90/4 is the one I'd choose. Lens speed is generally not a big factor in AF speed ... wide open contrast is a much greater factor. For instance, the Pentax FA35/2 is a faster focuser than the FA50/1.4, because it achieves better contrast wide-open despite being 1 stop slower. Godfrey On Nov 29, 2005, at 6:38 AM, Fred wrote: Does anyone have any opinions on the Sigma 28-105/2.8-4 ? I'd like a faster autofocus 28-105 than the Pentax FA 28-105/3.2-4.5 or either of the FA 28-105/4-5.6's (although the 28-105/3.2-4.5 is marginally faster than the others). (This would be for use on an *ist DS.) However, I'm afraid of: 1. softness 2. flimsiness 3. bad bokeh I know very little about Sigma lenses (except for some generalities that may or may not apply to this particular lens). Any opinions? Thanks. [Gee - I really wish that Tamron made the 28-105/2.8 in Pentax mount.]
