supercoolone
member
Reged: 07/25/07
Posts: 93
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I'm torn between the Canon EF 70-200mm f/2.8L and the Canon EF 400mm f/5.6L - I've got a Canon 10d right now and plan (really pie in the sky plan) on saving for the next generation 5D when/if it comes out (for the full frame). What are your thoughts? As an aside, what are your thoughts on Tamaron and Sigma 70-200mm f/2.8 lenses also?
Thanks! 
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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What mount/tracking rig do you have?
If it was me I would go for the prime 400mm lens, but it will certainly require a good solid tracking setup so you can get exposures that will do it justice. I have a 70-300 (not L glass, just a cheap and aberration-a-plenty one) and find that I only ever use it at 300mm. For *me* at least when I want to go wider then 300 I tend to be wanting to be wider then 70 too.
If however you have not-quite-perfect tracking the faster and wider 70-200 will give you the flexibility to avoid some tracking-error induced frustration.
Keep in mind that you will likely not want to run with the aperture full-open on either lens... or at least that is my experience with my cheap kit-lens and plastic 70-300 
- Sean
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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drksky
super member
Reged: 09/01/09
Posts: 115
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I'd been asking myself the same question lately and ended up ordering a used 300mm f/4 L from KEH.com. I was torn between the 300mm f/4 and the 400mm f/5.6, but with the XSi multiplier, the 400 would turn into 640mm and that's a little longer than I wanted.
L lenses are expensive, but there's lots of good used deals floating around on eBay and KEH. Right now, KEH has a 400mm f/5.6 listed for $889. It's their "bargain" quality, but at mostly means cosmetic blemishes and not optical problems.
Their bargain quality prime L's will destroy any new zoom.
Edited by drksky (10/27/09 12:00 AM)
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Daniel Browning
super member
Reged: 08/11/08
Posts: 126
Loc: Portland, OR
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For astrophotography, the 400mm f/5.6 does far better than the 70-200. Even if you stop down the 70-200 by two stops to f/5.6, the point spread is still worse. The Tamron and Sigma equivalents fare no better.
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--Daniel
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zAmbonii
scholastic sledgehammer
Reged: 01/19/08
Posts: 848
Loc: Ypsilanti, MI
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Quote:
...I was torn between the 300mm f/4 and the 400mm f/5.6, but with the XSi multiplier, the 400 would turn into 640mm and that's a little longer than I wanted.
REMEMBER! - an APS-C crop factor has no bearing on the actual focal length of a lens. The 400mm has the same focal length on the XSi as a full frame camera....400mm.
the EFFECTIVE FIELD OF VIEW on the XSi would be 640mm (compared to a 35mm or full frame DSLR).
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Check out my Astrophotos on Flickr
C6-N 150mm f/5 Newtonian
CG-5 ASGT mount
Canon 300D self modded + IDAS LPS-P2 FF
Meade 70AZ + Meade DSI for autoguiding
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Falcon-
sage
Reged: 09/11/09
Posts: 242
Loc: Gambier Island, BC, Canada
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just by chance I had a 300mm L f/4 on loan from a friend.... and for the first time in a month I am out imaging!
I have not processed anything yet, still shooting, but VERY nice results so far! - nice sharp starts with little chromatic aberration, and they stay round right to the edge of the sensor. If the 400mm does as well as this I suspect you will be happy!
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 988
Loc: Oman
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The Canon 400mm/5.6L compares extremely well to premium astro APOs at twice the price. Here is a comparo to one of the most highly lauded small imaging APOs, a TeleVue 60is. How good does your tracking have to be? Well you need to track accurately for 4 minute subs (10 to 12 minutes if you are shooting narrowband). This can be very demanding of mount quality if you use one of the newer DSLRs with tiny pixels. On a 500D you end up with 2.5 arc-sec per pixel. For this reason, if you are unsure as regards your mount, you may be better off with the Canon 300mm/4.0. The subexposures can then be only half as long, 2 minutes each (6min narrowband) and the focal length is also more forgiving. More on the required minimal length of subs here.
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Bored? Peruse my website:
http://www.samirkharusi.net/
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drksky
super member
Reged: 09/01/09
Posts: 115
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I was hoping that folks would know that APS-C modifier wouldn't magically make the lens longer 
My 300mm f/5.6L should be here before the end of the week. I'm hoping that we might actually get some clear skies to try it out in, moon or no. Just want to shoot something while the 14-day return policy is in effect.
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Tony C
AT8RC
C6-R
CG-5 ASGT
ST80 w/StarShoot Autoguider
Canon EOS 450D (Stock)
The Drinking Bird
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hiro
sage
Reged: 07/17/07
Posts: 483
Loc: Tokyo
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Hi supercoolone,
I think that my story would help you a little bit, because I tried EF400mmF5.6L with EOS 5D before mod. once in 2006. I hoped the same as you do.
Here is a single-shot frame of Orion with EF400mmF5.6L at F5.6 and EOS 5D at ISO 640 on Takahashi EM-200 temma 2 jr. mount without autoguiding. Exposure was about nine minutes, one minute longer than the period of the equatorial mount. I reduced resolution a little down to 930 x 1395 pixels to hide some faults, and I succeeded partly, though I could not be satisfied with the result.
http://farm2.static.flickr.com/1254/1390467274_34d1cb3fba_o.jpg
Here is a 100% crop of the frame. This frame shows the real result. Stars look Z-shaped. It is due to periodic error of the mount on horizontal movement and my positioning error of the mount on vertical movement. The stars also show relatively clear chromatic aberrations near right lower corner of the original frame with the lens.
http://farm2.static.flickr.com/1228/1390497368_60cdd93b8d_o.jpg
I had no remote live-view with the first generation EOS 5D, and I am not sure now if it was focused properly, though I did my best as an amateur holiday astroimager with experience for three months. I abandoned the lens and started to prepare autoguiding system of the mount.
I do not think it easy to shoot with lenses more than 200mm in focal length without autoguiding.
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hiro
Canon EOS 5D-AP by IDAS / EOS 5Dmk2 sp2 by Seo san
Takahashi FSQ-106ED with reducer, extender, and "hiro design" off axis guider
Lenses by Canon, Nikon, Leica, and Zeiss (Cosina)
Takahashi EM-200 temma 2 jr / Kenko Skymemo-R
http://www.flickr.com/photos/hiroc/
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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 988
Loc: Oman
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One click autofocus on a planet or bright star works great on focal lengths >= 100mm. Just try it. I always use it, and even when I compared it to LiveView I could not better than the one-click. Only time it fails is when you try to focus in IR (if your modded camera has no UV/IR blocker of any kind). In that case you are better off with LiveView.
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Bored? Peruse my website:
http://www.samirkharusi.net/
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Jared68
member
Reged: 04/14/09
Posts: 46
Loc: Orange County, CA
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I love my 100-400mm... but I haven't tried the 200mm.
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Skywatcher 8inch Schmidt Cassegrain
EQ5 PRO Synscan Mount
1.25" Super Plossl 32mm and 10mm
1.25" Baader Hyperion 8-24mm Zoom
Moon Filter
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Canon SD800 IS P&S
Canon Rebel T1i 15MP
EF-S 17-55mm f2.8 IS USM
EF 100-400mm f4.5-5.6 L IS USM
OEM Hood
UV Filter
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