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The full frame sensor in the Canon EOS 5D has been justly praised for its clean noise free images. It is my understanding that this is due to the greater full-well capacity allowed by the larger chip.

I'm not sure whether this advantage carries over to using the 5D for astrophotography where, at least for the stars, full-well capacity isn't a limitation but thermal sensor noise might be.

Does anyone have any experience using the 5D for this sort of work? If so can you comment on performance compared to cropped frame sensors? Thanks.

Bob.

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OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.

Gordon should look into this as he suprisingly often has a D5 handy
But my understanding is that the full-well capacity (FWC) is propertional to the sensor-area and thus prop. to the amount of photons captures at any given EV below FWC.
That means that for any given EV the larger FWC-sensor captures more photons and thus has a better s/n-ratio plus has a larger max capacity meaning it also can capture a higher dynamic range.
So you're better off in any case with a larger, higher FWC sensor.

But I'm not an expert, as you know

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

Yes, I was hoping Gordon might be able to "shed a little light" on the matter.

I'm no expert either and I take your point about sensor area. The noise I am thinking about is the background (thermal?) noise on pixels which haven't received any photons at all. That, together with the lack of truly dark skies in so many places, will limit how faint a star the sensor can capture. The CCD sensors typically used in dedicated astronomical cameras are mostly cooled to reduce the thermal noise which can be particularly troublesome with exposures of 15 minutes and more.

I can't think of any obvious reason why a full frame sensor should be worse than a cropped sensor in this respect. Indeed, it might even be better if a lower density of support electronics around each photodiode means that the sensor runs cooler when powered up. That said, experimental data is better than any theory, hence my hope that someone has actually looked into this.

Bob.

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OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.

Weeeell, I have several mates who are REALLY into astro photography and the 5D is a very popular choice for them, having low noise at higher ISOs. The modified bodies with the IR filters removed are also very popular...

But then the popular thing these days is stacking multiple images, so if you're willing to put the time in, I think you could probably achieve the same end-result with a cropped body as you could with full-frame in deep sky terms.

And if you're into high power planetary work, it's apparently all webcams and stacking multiple images from video grabs these days anyway!

Bob, are you getting cold feet over your possible 40D...?!

PS - I asked my expert Astro-photography mate and he says:

Suitability of 5D for astrophotography>

1. FF chip allows for wide field photography using camera lenses with fast focal ratios not available on 10-12mm efs lenses.
2. Low noise characteristics on long exposures though there is amplifier noise on one side of the image.
3. Adequate red response for H alpha regions
4. Large bright viewfinder for easier framing of faint objects.
5. mirror Lock
6. Usable at ISO 3200
7. Offering wider fields to be captured through telescopes.
8. Good preview screen offering good representation of final image.

Not exactly. In every way bar one it's my perfect camera but as you know my long term goal is FF.

In my thread Features of the Canon EOS 40D for scientific photography I reported some of the new features of the 40D which I think will significantly improve the experience of using a DSLR at the telescope. Whether it is available as early as November or as late as February I have to believe the putative 5D MkII will include the same features as they are essentially firmware driven. In other words, without wanting to get involved in "wish-list speculation", the 5D MkII may well effectively be a 40D with a full frame sensor, albeit with a slower burst rate.

Thank you to you and your astrophotography friend for taking the trouble to compile the list of factors regarding the 5D's suitability for astro work. I guess all those factors are likely to be true for the MkII as well. The H alpha response is encouraging for grabbing the occasional nebula. Is he using the camera at the prime focus for this work?

The amplifier noise referred to would be a concern to me except that the MkII will have a new sensor so, hopefully, that issue will have been corrected. With ISO 3200 being usable I have to conclude that going FF doesn't mean any inherent increase in thermal noise over a cropped sensor.

To summarise, the 5D MkII is likely to give the same or better IQ for "normal" photography as the 5D does and do as good a job as any DSLR can when photographing the stars.

If my speculations on the 5D MkII are correct that makes it my perfect camera, period. The one sure thing is that I will have to make my decision to ask if I can "convert" my 40D pre-order into one for the 5D MkII before that camera is even announced! My timetable for replacing the 400D was initially determined by my intended good home for that camera but there are ways around that if the motivation is great enough and, even though it doesn't officially exist, the 5D MkII is beginning to provide that motivation.

Going straight to full-frame without the intermediate step of the 40D is a very big decision but one thing is for sure - if I go for it I can never again make the excuse that I could take better pictures if I had a better camera.

Thanks again for your help.

Bob.

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OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.

Hi Bob, if the 5D Mark II is a slightly higher resolution 5D with the 40D's screen, live view, dust and other features, it sure will be nice - so long as it's not too pricey... I realise 6.5fps is unlikely, but I hope they squeeze 5 out of it, as 3 can feel slow for action work...

As for my mate, yep, the 5D would be for prime focus work. High power is all webcam nowadays!

Gordon

Hi Gordon,

Thanks again for your feedback regarding the 5D. Yes, I didn't talk about the likely price of the 5D replacement did I?

Regarding web-cams, it does seem extraordinary that such cheap items can produce such good results for planetary imaging but that's exactly what they do.

Veering sightly off-topic, for the first time last night I took a burst of images of the Moon by using my new 50mm f/1.8 lens to capture the light emerging from my telescope's eyepiece. As ever, focussing is difficult and I need to do better but the camera had no trouble running at 3 fps with an exposure of 1/125th of a second per frame. Holding an expensive lens that close to the eyepiece isn't something I would want to do but with the 50mm lens it's no problem.

Haven't had a chance to use this lens on the stars yet. This is the first non-USM autofocus lens I have owned and autofocussing with it is truly horrible. Manual focus works well enough though.

Bob.

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OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.

Eyepiece projection huh? Care to share your images? It's pretty hard without some kind of tubing which mounts your camera and lens at the right distance from the eyepiece though... so prime focusing or webcams for me!

I have started the thread Photographing the Image from a Telescope's Eyepiece to avoid taking this thread completely off-topic.

If any more thoughts about the advantages, or otherwise, of using full-frame DSLRs for astrophotography occur to you please continue to share. Thanks again.

Bob.

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OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.