Jump to content

SkySurveyBanner.jpg.21855908fce40597655603b6c9af720d.jpg

DSLR Horizontal Banding...?

AndyUK

Recommended Posts

AndyUK

AndyUK

Posted
  • Author
Posted

Mike - I recall the outside of the camera feeling quite chilly, which is why I assumed the darks would be that temp also... I'd forgotten that the sensor might heat up B)

Joselin - Thanks for the suggestion, but I think Mike's right - I don't think Canon would be that interested with such relatively long exposures...

Grant - That's a great link... Thanks! It just goes to show the temp creep starting at 22C going up to 29C over those 600s exposures with 50s pause. I see there's also reference to someone (in the US) who will undertake what looks like a cold finger cooling mod (for c. £600 :) - I think I'd rather put that halfway towards a CCD camera :grin:!)

Mike

Of course, our darks will probably be accurately recorded (in advance as the camera may already be cold) but the light frames may not have the right EXIF temperature if it's set at the start of the exposure and not the end
I agree with that logic, but I think the way around it may be to get the camera taking 3 or 4 frames whilst setting up for the last 30 mins or so (to get it to "operating" temp - They can either be junked or, if darks, sorted and added into library) and then probably accept that the last frame immediately before the first "real" frame will be dropped as it may be slightly lower temp(?)
Link to comment
Share on other sites
  • Replies 109
  • Created
  • Last Reply
MikeWilson

MikeWilson

Posted
Posted
Mike I agree with that logic, but I think the way around it may be to get the camera taking 3 or 4 frames whilst setting up for the last 30 mins or so (to get it to "operating" temp - They can either be junked or, if darks, sorted and added into library) and then probably accept that the last frame immediately before the first "real" frame will be dropped as it may be slightly lower temp(?)

^ I expect this will become (especially as summer nears) an intrinsic part of the workflow. Get the camera taking images and junk them (even if they're darks they'll suffer from the same false early-EXIF-temp). In practice, just a couple of frames at ambient temperature ought to do it. Although I'm going to pay much closer attention to recorded temperatures on my next imaging run than I have before.

I agree about the mod - if you're going to put >that< much effort in, why not just go CCD? Perhaps the DSLR has the bigger sensor so an equivalent CCD would be budget breaking. If you can do it yourself, it might be a very good value method...

You'd still have to match the dark frame temps to the light frames though...

Best,

Mike

Link to comment
Share on other sites
AndyUK

AndyUK

Posted
  • Author
Posted

Mike - I think we have a plan...?

Grant - Thanks again for that link too. Although I use the histogram to guage exposure lengths, that article seems to indicate that I may have been setting my Histogram "level" too high - I can probably reduce them to maybe 5 or 6 mins (or maybe even lower depending on subject) which will hopefully help reduce this banding and reduce noise and any guiding errors (sounds like a win-win to me!)

Link to comment
Share on other sites
MikeWilson

MikeWilson

Posted
Posted

Andy - I think we do. It's not too painful, but it's an extra step in the workflow. I may need to write a checklist!

Grant - Thanks for the article. I had seen it (but not paid attention) before. I'm not sure I quite agree that NxT == 1 x Sum(T) minute exposure. I don't expect that the camera chip is sensitive enough to pick up on tiny faint details with the lower sub lengths (or even the low ISO [200 was mentioned!]). There may simply not be enough photons hitting the camera chip to register in some cases.

I think we have our short to medium term recipe for success though:

1. Collect (over the course of many, many, nights) a series of dark images at varying temperatures. Collate these into a library.

2. Cool the camera to ambient temperature and then warm it up to operating temperature by starting the imaging run early (perhaps while setting up) and then binning those images.

3. Consider 10 minutes as the workable maximum sub length for a warm evening, but 2x5 minute subs may well be better on most targets than a single 10 minute one, assuming the formula is true: (SNR: 2(T/2) > T). (I suggest the formula IS true, but probably loses out on some faint detail).

I was hoping to try for some 20 minute exposures, but this thread has safely put me right off doing that! (I have had banding before, not quite as severe as Andy's but I'm yet to try for >8 minutes).

Mike

Link to comment
Share on other sites
AndyUK

AndyUK

Posted
  • Author
Posted

Thanks for the summary Mike...

Nadeem - Thanks.... and I'd be very interested on your prognosis on these (and of course to see what you can do with them :)). I know they're not exactly the best set of subs, but it was all I could get that night (and I have a strong suspicion there was a fair amount of haziness in the atmosphere).

Link to comment
Share on other sites
3ggman

3ggman

Posted
Posted

Andy I just picked up a Mini Fridge from argos today, the cheapest one that they had, It was 32euros here. I just finished taking it apart and it has pretty much everything you need to build a cooling box with no rewiring required. Underneath the plastic shell it has a moulded aluminium box surrounded by insulating foam and is perfect size to fit a dslr camera, the only thing its missing is a lid which could easily be cut from a sheet bought from B&Q.

It has a fan, peltier unit (small enough) power switches and it runs on both ac and dc is supplied with both an AC mains and a dc cigarrette plug adapter.

It would be a very straight forward disassembly and rebuild to suit our/your needs.

I will take some photos as I rebuild the unit and post them along with some results.

Link to comment
Share on other sites
AndyUK

AndyUK

Posted
  • Author
Posted

Hi Johnny - Okay... You certainly have my attention! I very much look forward to hearing more from you on this - If you post elsewhere, please do let me know as this is something I REALLY don't want to miss...!

Link to comment
Share on other sites
Deneb

Deneb

Posted
Posted

Well the banding is still there, but less so apparent, for now I only stacked the lights with flats & bias, when I get the chance I'll have a go at stacking with a combo of lights, flats & darks to see any difference.

Nadeem.

Link to comment
Share on other sites
joselin

joselin

Posted
Posted

You can buy die cast aluminium cases if you wish to build a Peltier cooler box which will reduce your DIY.

Also anyone looked into Peltier plates ? Would attaching one to a aluminium base and screwing that into the base of the camera body have any effect ?

Link to comment
Share on other sites
AndyUK

AndyUK

Posted
  • Author
Posted

Interesting... screws into tripod bush...? I don't suppose there's any cool-down graphs for that is there?

For anyone that's interested, I've been going through my "fridge darks" on and off today.

Based on ambient 3-4C (and aside from the 30s and 60s frames) it would seem that the chip temp finally settled between 18-20C after it had got going, but obviously took longer to get there with the shorter exposures.

I would guess that they may not have gone up quite so high / so quickly if I'd set a longer "rest" though.

(I can see I'm going to also have to take a lot more notice of ambient temp as well... or am I overkilling this issue?)

Link to comment
Share on other sites
Psychobilly

Psychobilly

Posted
Posted

I like the no nonsense "aussie" approach on Ice in Space... where the camera (in that case a 5D ) was just placed inside a camping fridge and the whole lot hung of the back... :)

Who's been Pushing the image size limits again making this a horizontal scrollable thread B)

Link to comment
Share on other sites
AndyUK

AndyUK

Posted
  • Author
Posted

Mike - He also has a version 2 on there as well... which is basically what Psychobilly's mentioned (a fridge dangling off the tube!)...

And then there's the (for me) fairly DIY intensive v3, which MIGHT just work (without looking at a "Cold finger").

Hi Joselin

Andy wont there be a lot more noise left behind in your lights if the darks are done at a different temperature?

Also how sure are you that this banding dosent appear in your lights as well ?

Yes, the bands are in the lights. What Mike and I are considering is building up a library of temperature, exposure length and ISO-based folders full of darks.

After taking a session of lights, we'll then review the exif data so that we can then select the correct temperature darks to subtract.

Assumimg that this noise/banding in the lights IS temp related(?), hopefully the same noise should also be contained in the matched temp dark and thus will be subtracted (:)).

It's worth a shot anyway...

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.