Cotts
Just Wondering
Reged: 10/10/05
Posts: 912
Loc: Richmond Hill, Ontario
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I am aware of the advantage of the live focus on the 40D. What I wonder about is the actual differences between the two cameras in terms of sensitivity, sharpness, colour rendition etc. Since I have a stilletto focuser for my XTi the 40D would only have a slight advantage over the XTi in focusing capability. If I were to make the jump there would have to be a considerable improvement in the photos. In anyone's experience is there such an improvement?
BTW I will use the camera for general photography as well so I won't be getting any modification done.
Thanks, d.c.
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David Cotterell
14th Floor Observatory
Richmond Hill, Ontario
200 mm Intes f/10 Mak-Cass
80mm WO Zenithstar FD
66mm WO ED
Losmandy G-11 mount with Gemini
Ioptron minitower
Canon XSi
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rockace521
sage
Reged: 09/21/06
Posts: 298
Loc: Waco, TX
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Aside from live preview, the 40D has many other features that outstrip the XTi, not the least of which would be the bump from 12-bit to 14-bit conversion, which should directly translate into better images (experts could quantify this better than I).
Here's an interesting link, if it's okay to post it here:
http://www.komar.org/faq/camera/canon-40d-versus-rebel-xti-400d/
Best,
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Joel
8" Celestron SCT
SV80S
Atlas EQ-G
40D/Modded 20D/DSI Pro
no pictures to speak of...
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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 988
Loc: Oman
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Quote:
BTW I will use the camera for general photography as well so I won't be getting any modification done.
Thanks, d.c.
Eh? People seem to be unnecessarily worried about good daytime performance in modded cameras. There really, really is no need for worry. Modding any of the DSLRs will give much better astrophotos than any marginal improvement you can hope for between the 400D and the 40D. Make sure you end up with a modded camera and be happy, like this kid taken with a Hutech-modded 40D:
Click here for explanatory text.
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Bored? Peruse my website:
http://www.samirkharusi.net/
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Cotts
Just Wondering
Reged: 10/10/05
Posts: 912
Loc: Richmond Hill, Ontario
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Samir: Thanks for the info. What is a "rectangular passband UV/IR Blocker" ? Thanks. d.c.
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David Cotterell
14th Floor Observatory
Richmond Hill, Ontario
200 mm Intes f/10 Mak-Cass
80mm WO Zenithstar FD
66mm WO ED
Losmandy G-11 mount with Gemini
Ioptron minitower
Canon XSi
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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 988
Loc: Oman
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The stock DSLRs come with a shaped passband UV/IR Blocker that has the red tapering off to zero at around 670nm, similar to human vision. The replacement UV/IR Blocking filters used in modded cameras have a rectangular passband that stays at nearly 100% to about 700nm. H-alpha is at 656nm. So the extra sensitivity to H-alpha comes from the difference between the taper and the rectangle. More on this stuff here.
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Bored? Peruse my website:
http://www.samirkharusi.net/
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rockace521
sage
Reged: 09/21/06
Posts: 298
Loc: Waco, TX
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Samir, would you think that the upgrade from 12-bit to 14-bit processing would result in a marginal improvement of images?
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Joel
8" Celestron SCT
SV80S
Atlas EQ-G
40D/Modded 20D/DSI Pro
no pictures to speak of...
Edited by rockace521 (01/08/08 10:21 AM)
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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 988
Loc: Oman
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Quote:
Samir, would you think that the upgrade from 12-bit to 14-bit processing would result in a marginal improvement of images?
I am a bit dubious as to whether the 14 vs 12 bit internal processing actually affects STACKED results visibly. Using a high ISO already stretches the digital scale. I see stacking as increasing the resolution of analog to digital conversion in post processing. We invariably stack in 16-bits, so I suspect that we already benefit from a dithering effect, similar to "drizzle" for spatial resolution. Frankly, I suspect that we may benefit more if we stack in 18-bits rather than 16. The 14-bit processing probably does make a visible difference in unstacked, normal photography frames. I feel that you are keen to get a 40D. Get it. It's a great camera, until the 50D comes along...
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Bored? Peruse my website:
http://www.samirkharusi.net/
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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1314
Loc: Kiev, Ukraine
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Samir, don't you think that 14 bits give better dynamic range, less burned out areas?
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Fabio Papa
Pooh-Bah
Reged: 03/01/05
Posts: 1460
Loc: Piacenza, Italy
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It would, but not in the way they implemented it. They basically amplified the signal, as demonstrated by tests conducted by Buil. You get almost the same light from the 40D running at 200 ISO and a 350D running at 800.
I wanted to add, though, that for me the live focus thing alone is worth the entire camera.
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Fabio Papa
Celestron C8 F/10
Vixen ED81SWT F/7.7
Orion Atlas EQ-G
Gruppo Astrofili di Piacenza
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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1314
Loc: Kiev, Ukraine
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Sorry, seems like I missing something. So what those two additional bits contain. If data then the dynamic range is higher. If nothing (noise) then they are useless.
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ccs_hello
Post Laureate
Reged: 07/03/04
Posts: 3300
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Hmmm... strange
Base ISO usually reflects the native sensitivity where best S/N result can be obtained.
# of bits is not a direct indication on sensitivity. It's somehow supposed to be related to dynamic range but sometimes over-hyped.
Recent sensor technology (high SNR about mid 70-ish dB) is making 13-bit possible (13 * 6.5 = 84.5 theoretical, but headroom is there for reality sake), but no one want to make/use the word "13", thus 14 is used. 
Image Sensor has its rated SNR (helps Dynamic Range) and sensitivity (QE).
Programmable Gain Amplifier (PGA) amplifies signal (raises the low light sensitivity but at the same time degrades the S/N).
Some design (mainly on CMOS sensors) put the PGA inside the sensor. Some others put the PGA in the camera system board.
Overall camera system will have its system Dynamic Range and base ISO.
Clear Skies!
ccs_hello
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