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05-28-2013, 12:54 PM - 1 Like   #1
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Comparing the Bigma to the FA* 300 4.5 + TC

No big news or a find of the century here. I've been meaning to compare these two lenses for some time and finally got around to doing it today. This is not a controlled test or even worthy of comment - just a quick comparison for my own needs.

Dark rainy day - setup was on my lighter tripod with SR off and 2 second timer. I was set up on a wooden deck, so there is still some chance for vibration in the shots. My main reason for doing this test is to see if the magnification level was indeed different with the zoom against the prime. I've read a few threads here where the actual long focal distance with a zoom that has internal focus (IF) does not give you that total focal length when shooting below infinity. For example, with the DA* 60-250 at 250mm, I've been told that the actual magnification effect is in fact less than 250mm - never heard exactly how much.

So I thought I would test the Bigma (Sigma 50-500 f4.5-6.3 OS HSM) against the Pentax FA* 300 f4.5 coupled with the Vivitar 1.4x TC which should equate to 420mm. The Bigma was shot at 500mm.

This test of mine may be flawed from the start - I just looked at the Sigma site for this lens, and I don't see anywhere that it says it is an internal focus lens - huh........

Anyway, the first pic in each pair is the Bigma @500mm. I was actually pleasantly surprised that the Bigma images held up very well compared the the FA* TC combo especially in a fairly low light situation - maybe the Bigma is a keeper after all?

Weather station at a distance of ~50'

Bird house at a distance of ~100'

Second bird house at a distance of ~50'

Metal object at a distance of ~30'

05-28-2013, 01:32 PM   #2
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Interesting comparison
05-28-2013, 01:41 PM   #3
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This effect is not as pronounced as at minimum focus distance. It also depends on the lens. FWIW if you don't see any movement in the front elements when focusing it's an IF design.
05-28-2013, 02:38 PM   #4
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QuoteOriginally posted by Giklab Quote
This effect is not as pronounced as at minimum focus distance. It also depends on the lens. FWIW if you don't see any movement in the front elements when focusing it's an IF design.
Thanks for defining an IF lens.

Again I was just kind of curious about this - I guess it makes sense that the effect would be more pronounced at the MFD.

I might have to do a similar test with my DA* 60-250. This topic has come up here a couple times. One that I remember that someone was upset because they bought a zoom that goes to 250mm, but it didn't actually go to 250mm. Kind of a hard one to test or prove since there are no 250mm primes.

At any rate, the one thing that I did prove to myself with this test is that at one of my most common shooting distances, the 500mm of the Bigma does in fact give me some more reach that the 420mm setup.

05-28-2013, 02:51 PM   #5
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There is a little difference in the FL (obviously). In the first 3 sets it seems that there is just a weeeeeeee bit more contrast with the Siggy, or this could be caused by metering (first set the whites are quite a bit brighter with the FA* combo than the Siggy). The 3rd set it looks like the FA* combo is a little more sharper [going by the left side of the tree] - now, the last set you can really see a huge difference, the FA* with the TC easily wins that one.

Stan, what if you crop the 3rd set to be equivalent in FL? Maybe just crop the FA* one to match the siggy and do a side by side comparison of that.
05-28-2013, 02:59 PM   #6
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Speaking about the 3rd pair Joe - the brown bird house - when I first looked at the images at 1:1, the FA* combo was way better than the Sigma. Also on the last shot of the green metal hood. I blame that last one of the hood on a very non-contrasty subject for focusing.

I really only did this for testing the actual magnification effect between the two. I want to do a better test for image quality in the future to get the real story on that. This will tell me if I have a redundancy going on with these 2 lenses.

Did a crop anyway - the first image is the Bigma:

Last edited by stormtech; 05-28-2013 at 03:09 PM.
05-28-2013, 04:20 PM   #7
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Well, obviously the FA* is kicking butt here, even with the 1.4x teleconverter. I don't think the difference in ISO (3200 vs. 2500) is going to make the Sigma less sharp, so the FA* is doing quite well with that TC. However, just judging by the bokeh and OOF regions, it looks like the Sigma has a shallower DOF than the FA*+TC combo, or at least much better bokeh. This is confusing, as they are both shown in the EXIF as f/8, but using a TC would mean that it loses a stop of light, so even if the TC "adjusts" the reported aperture for its darkening, the FA* at f/5.6 should have shallower DOF, not greater. Or am I missing something? Was the FA* stopped down using the aperture ring?

Or (quite possible) have I had too much bourbon tonight...?
05-28-2013, 05:08 PM   #8
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QuoteOriginally posted by panoguy Quote
Well, obviously the FA* is kicking butt here, even with the 1.4x teleconverter. I don't think the difference in ISO (3200 vs. 2500) is going to make the Sigma less sharp, so the FA* is doing quite well with that TC. However, just judging by the bokeh and OOF regions, it looks like the Sigma has a shallower DOF than the FA*+TC combo, or at least much better bokeh. This is confusing, as they are both shown in the EXIF as f/8, but using a TC would mean that it loses a stop of light, so even if the TC "adjusts" the reported aperture for its darkening, the FA* at f/5.6 should have shallower DOF, not greater. Or am I missing something? Was the FA* stopped down using the aperture ring?

Or (quite possible) have I had too much bourbon tonight...?
Ha - never blame it on the bourbon!

I had the FA* w/TC set on "A" on the aperture ring, and shot in AV @ f8 for both. Now is where I get confused as my first go with a TC. Yes, I should loose ~1.5 stops, so I am thinking the actual exposure was closer to f11? I really don't know, but would like to learn about this so I know what I am doing in the future.

This will be important when I do an outright IQ comparison of these 2 lenses.

05-28-2013, 05:28 PM   #9
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QuoteOriginally posted by stormtech Quote
Ha - never blame it on the bourbon!

I had the FA* w/TC set on "A" on the aperture ring, and shot in AV @ f8 for both. Now is where I get confused as my first go with a TC. Yes, I should loose ~1.5 stops, so I am thinking the actual exposure was closer to f11? I really don't know, but would like to learn about this so I know what I am doing in the future.

This will be important when I do an outright IQ comparison of these 2 lenses.
Well, yes, you did say "not a controlled test" didn't you?

BTW, my understanding is that the loss of f-stops due to a TC only effects the metering, not the DOF (like further stopping down would do). Hence my confusion. Next, that Vivitar TC must be full of awesomesauce to not degrade the FA* very much like that!
05-28-2013, 06:06 PM   #10
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Yes, I was told from a very reliable source when I bought the TC that in fact I would see very little if any IQ loss. Of course it helps when it is behind an awesome hunk of glass.......
05-28-2013, 06:15 PM   #11
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Thanks for the comparison work Stan. I noted the bokeh from the Bigma looked nicer but seeing the DOF discussion I understand why.
05-29-2013, 05:45 AM   #12
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Nice comparison Stan. Looks like the Bigma is holding its own. You do lose a stop with the TC so F4 would be F5.6 , F5.6 would be F8, F8 would be F11 etc. I generally would adjust the Lens with the TC to match the aperture of the Bigma when attempting to compare. I would guess that DOF would be greater with the TC than without for a given aperture. Your comparison kind of makes me miss the Bigna.....

Last edited by GaryH; 05-29-2013 at 05:52 AM.
05-29-2013, 06:00 AM   #13
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You might back off the Bigma to around 420mm. That should also get you a little better IQ than 500mm. I found that my older Bigma was much sharper at less than max zoom. Another Idea would be to check the Bigma at 300mm vs the FA without the converter.
05-29-2013, 06:22 AM   #14
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QuoteOriginally posted by GaryH Quote
You might back off the Bigma to around 420mm. That should also get you a little better IQ than 500mm. I found that my older Bigma was much sharper at less than max zoom. Another Idea would be to check the Bigma at 300mm vs the FA without the converter.
When I was first setting the lens up on the big tripod, I did some testing to find the best aperture and also to see if backing off from 500mm a bit would make a difference. My test shots at f8 at 500mm and 450mm were exactly the same even when pixel peeping the test shots. I knew you and others have said the newest version of this lens was great at 500mm, but of course needed to see for myself. Really impressed with that part! If I had to shoot it at 450mm I would just as well use the FA* + TC combo. While 420mm or 450mm to 500mm isn't a huge difference, every little bit helps since I have to shoot from a stationary position.

This wasn't an outright IQ comparison test like I said - more to see the focal length differences for my own curiosity. Thanks for the tip about the aperture value with the TC. I might do another test for outright IQ so now I will know what aperture to set the FA* + TC to be equal.
05-29-2013, 07:05 AM   #15
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Thanks a pile stormtech.... when I started doing work with my 1.7 TC, and my A-400, the first thing I realized thought was, "this is not as bad as advertised." Some have said you're better to just expand your images with software, they'll be just as sharp. That definitely didn't true out to be true. It's great to see some great hard evidence thrown into the debate. One can never see too many comparative pictures.
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