DSLR Image Buffer issue

[StarDome]

Hi all, hoping that the font of knowledge that is SGL will have hte answer to this one.

I have recently been trying to take some images using exposures of longer length, up to 25 seconds for constellations etc. The problem I am having is this.

Using both a wireless (Hahnel Giga T Pro II ) and also trying a wired digital remote, the first image of the sequence takes ok, but then the camera (EOS 7D) is buffering the resulting image so slowly that when the remote starts the next exposure, it cant handle it as the memory buffer is still reading/writing the previous image. It results in the second exposure eventually taking but only of say 15 seconds as the other time hads been taken up in processing the previous image.

I am using a fast Sandisc CF flash card, 60 mb/s so not sure what the prob is.

At the mo, if i want to do a sequence of shots I cant

any ideas? solutions? remedies greatly received.

Thanks

[jgs001]

That sounds really odd and more likely you've got in camera noise reduction turned on. ICNR takes a second exposure, leaving the shutter closed (a dark basically) and subtracts it. Turn this function off. Looks to be on page 208 of the manual, sorry I don't have time to find the page...

The manual is at http://gdlp01.c-wss.com/gds/5/0300004275/02/eos7d-im4-en.pdf

The 7d is capable of firing off 8 fps and buffering 15 x 18Mb raws whilst doing it .

[iwatkins]

I have no probs. with my 7D like this. But as JGS suggests, you may have the noise removal on.

Another possibility, only ever had this once, had similar on a 1Ds. Would shoot fine but seemed to take 20 - 30 seconds to write a RAW to the card. Simply formatting the card *from the camera* cleared the problem.

Cheers

Ian

[StarDome]

Many thanks for your help chaps, will give all those options a try and let you know how i get on

cheers

Andy

PS. Does having the noise thing turned off make a difference ot the image?

[StarDome]

Cheers Chaps!

have turned off the noise reduction things and all's working ok.

Does turning it off have a major effect on constellation images/aurora at say ISO 400 - 800? making them too noisy?

many thanks, really appreciate your help with this!

[jgs001]

It can but you can always take a set of darks at the end of the session. But the 7d ought to be much better at noise handling than my 450d anyway and I normally use ISO800.

[StarDome]

Mostly in the coming weeks I will use it for Aurora so hopefully it will be ok

[iwatkins]

Glad you got it sorted. :-)

7D is very good with noise. I'm happy to go for a 1 minute exposure at ISO1600 as an upper limit. I.e. great for a single wide angle constellation shot.

Once the 7D is on my 80ED, I tend to shoot 30 sec subs at ISO1600 or ISO800 depending on how I feel at the time.

Both cases, I don't use darks or flats.

I remember never shooting at more than ISO100 on my first DSLR, the 10D, because of the noise.

Cheers

Ian

[jgs001]

I would expect so.. I'd love to upgrade to a 7d... but glass first

[iwatkins]

Ahh, glass. Never enough can be had, especially with red rings around them.

I need a new body, my 7D hit the concrete Sunday night with an 80ED attached. Body is crushed but still works!! But cannot get battery out as that side of the body took the full force. 80ED came off a lot worse. Stupid SkyWatcher mount the cause. Oh well.

[Trull]

Both cases, I don't use darks or flats.

I remember never shooting at more than ISO100 on my first DSLR, the 10D, because of the noise.

Cheers

Ian

Tut Tut Ian - get thee a copy of Nebulosity, shoot tethered and you'll love working the bias/dark/flats in RAW so much more

[iwatkins]

Tut Tut Ian - get thee a copy of Nebulosity, shoot tethered and you'll love working the bias/dark/flats in RAW so much more

Nah, no need.

I shoot with plans tethered using APT. No darks, no flats and no bias. I used to do all that when I first started out, following the ideas in some AP books, but I can see no difference to the final image on screen or printed image so why bother? Lots of mid ISO, mid length, unguided shots seems to work. Stack them up in DSS or similar.

But as the 7D is out of action for a while, I might have to go dedicated CCD and get back into all that again.

Which is something I've been meaning to do for a while, as I would like to try narrowband which DSLRs are not really suited to.