taking long exposures with heavy light polloution

[oldpink]

up till now I've been concentrating on the planets & moon to get used to the equipment and camera settings

but I really want to do some DSO imaging

last night after doing some planetary shots I slew round and found some stars dropped the camera in, focused through the viewfinder
then ran some exposures, at 30s / ISO 800 all I got was saturated orange images, 10s / 800 wasn't much better

only at about 5s / 800iso could I even see the stars in the shot

I wasn't using my LP filter but I will try that tonight, but is there any other tips or tricks you guys use that can help

can't wait to get away to a dark sky site to get some decent shots, but for now I'm stuck in my light polluted garden

[cowbell]

Shorter exposures and stacking?

Take a picture of the sky and use that as white balance to balance it out?  (works best with flat pollution rather than gradients).

[Leveye]

Use your L.P. Filter always in that situation.

[oldpink]

I doubt I can get anything of any use with 5s exposures even if I took hundreds and stacked them
from what I have read so far the longer the better, but I shall experiment tonight and see what I can do

[cowbell]

I doubt I can get anything of any use with 5s exposures even if I took hundreds and stacked them

from what I have read so far the longer the better, but I shall experiment tonight and see what I can do

This guy does stacking without tracking and achieves amazing results.

[Langy]

This guy does stacking without tracking and achieves amazing results.

Makes a change for me not to post this link 

If what you are shooting is lower in the sky where the LP is then it will certainly be far worse. I bet if you took some images higher in the sky then the LP impact would be far less.

However on top of that we have an almost full moon which is not the DSO Imagers friend.

It's very frustrating when we finally get some clear skies and an almost full moon when you want to look at the fainter objects. This hobby does require a lot of patience and a lot of failures as we all seek those good results that happen every now and then.

[oldpink]

yeah I've seen a few of his video's

Stacking & tracking isn't an issue more the heavy LP that I gave to deal with forcing shorter exposures than I want

[Alien 13]

I have very bad LP and no filter and my subs come out very bright orange almost white sometimes but i still find that all the data is still in there somewhere.

Alan

[DaveS]

Have to agree, LP filter all the way, either Baader UHC-S or Astronomic CLS. You could also try one of the Hutech ones.

Either that or bite the bullet and go narrow-band.

[oldpink]

may have to go to a clip filter
can't find anyway to get my 1.25 LPF mounted unless I use the barlow

I like the looks of the Astronomik Deep Sky & LP filter

or get a decent 2" LPF and mount it with the Coma corrector that I need to buy

[Russe]

I have very bad LP and am using an Astronomik clip filter in my DSLR.

[frugal]

Try dropping the ISO. If you drop from 800 to 200 you can take exposures 4 times as long. You might also find that when you stack the images there is more information in there than it first appears. But ultimately if you are only going to be able to get 20s shots at ISO200 then you might be forced to use a light pollution filter.

I have also found that the quality of the sky is a huge factor. If there is any kind of haze or thin cloud then it reflects the light pollution and saturates the image. I can do 5-10 minutes on a good night, but the past couple of weeks there has been a fine haze which has dropped my maximum exposure time down to 1-2 minutes.

[dph1nm]

from what I have read so far the longer the better, but I shall experiment tonight and see what I can do

Be aware that the reason longer exposures are better is the effect of  read noise, as you get one dose of this for every sub. Hence fewer (longer) subs means less read noise contributing to the final image. BUT this only has a significant effect whilst the read noise is similar or worse to that from the sky background on a single sub. If you have bad light pollution the sky noise is likely to overwhelm the read noise even for short exposures. In that case there is no (or very little) disadvantage to having lots of short exposures.

NigelM

[Alien 13]

I have bad LP and am limited to unguided subs of 1-2 mins max so the choice for me is based on getting the best histogram fit in the available time even if its pushed to the right.

I have found that going lower in ISO setting doesnt work for my setup (the faint stuff is swamped by the noise floor) and tend to stick to 800-1600 and 90seconds.

There are lots of posts regarding ISO (unity gain) but my own experiments on lunar images and DSS has suggested that 400-800 has the best noise performance and 1600 is not far behind.

Alan

[toxic]

i only have the skywatcher 2" LP filter but it works a treat also when using eos utility try moving your white balance bias 2 to the left and 2 up from center on the little grid it works for me and my LP is very bad i have a street light next to my garden and 3 across the street from the garden thought about getting an air rifle but then some people would complain.

[Thalestris24]

I have the same problem with lp (being in Glasgow too!). I use an Astronomik cls-ccd clip in my 1100d. It helps but only up to a point. I probably couldn't take 5 min subs even . I've just got a osc ccd so will have to get another lp filter for that. Not sure which one to get. The Hutech ones seem to be hailed as the best but are very expensive...

Louise

[oldpink]

tonight was a good example
I pointed to the darkest point I could find, and found some stars that were bright but best image was at 0.8sec at 400 ISO
I couldn't even see Orion's belt by eye tonight had to grope my way to M42 for a quick peak but hazy cloud spoiled it

can't wait to get away from here down to Galloway for a couple of decent nights of dark skies
I'll console myself with honing my planetary skills, I have a load of data to process from the last 2 nights
which has been decent until the fog came in just after midnight tonight
but gave me time to try out different settings and get some great shots of the GRS and a transit over a couple of hours
 

[lensman57]

I have the same problem with lp (being in Glasgow too!). I use an Astronomik cls-ccd clip in my 1100d. It helps but only up to a point. I probably couldn't take 5 min subs even . I've just got a osc ccd so will have to get another lp filter for that. Not sure which one to get. The Hutech ones seem to be hailed as the best but are very expensive...

Louise

Hi Louise,

I don't know if I am sticking my neck out here but I attach two images of the IC405 and the Leo Triplet that I made last night using an Ascension 80mm Apo triplet @ F4.8 with an Atik 428EXC  @-20C using an IDAS D1 filter. The IC 405 is 7 X 1200s subs with 101Bias, 51 Flats and no Darks, the Leo triplet is a stack of 14 X 900s subs with the same Bias and Flats as before and both were taken in full glow of the Moon from my backgarden in sunny Manchester. These files  have  not been processed  but with a mild gradient removal in auto mode and a straight histogram stretch applied to them so  the raw data can be converted to jpegs for posting so they are more or less in a "RAW state". I guess imaging under the Moon glow is possible with long subs but it is not optimal, your mileage varies with the set up, the subject and the phase of the Moon as well as the level of LP which from my location is horrid at about 50 degrees of elevation.

Regards,

A.G

[oldpink]

this is my problem

 

[Thalestris24]

Lensman - I don't think I'll ever be able to do such long exposures here with whatever lp filter I have! It never gets dark where I am near the city centre - obviously a white zone for lp. Maybe I'm wrong but I think I'm doomed to relatively short exposure imaging... Here's a single 120s/ iso800 sub I took last night (of M3).

If I were to try and do a 5 minute one it would be pretty much a whiteout, I think. Maybe there could still be some useable data and with stacking/darks/flats and processing maybe I'd still be able to get quite a lot out. Tbh, I don't know as I've never tried processing beyond 3min subs yet... 120s subs as above, I've been able to use ok. Guiding with the lp interference is also problematic but I'm not giving up yet!

Oldpink - sympathies! Maybe you could arrange some sort of screen to cut out the direct lp? I have a piece of cardboard on my window sill which shields the scope from the direct light caused by a street lamp about 8m away.

Louise

[frugal]

Oldpink - sympathies! Maybe you could arrange some sort of screen to cut out the direct lp? I have a piece of cardboard on my window sill which shields the scope from the direct light caused by a street lamp about 8m away.

Louise

I use the "Cone of Darkness" on my 300mm camera lens to cut out the glare of the street light that overlooks the garden:

It is just an 80p sheet of A3 black craft foam from Hobbycraft, with duct tape to hold it into shape.

[oldpink]

this is a single 1.6s exposure at 800iso taken last night

[Thalestris24]

this is a single 1.6s exposure at 800iso taken last night

Hi again

I think you'd definitely benefit from a lp filter! However, that result with such a short exposure, suggests you might be getting too much nearby/direct lp. Any shielding/screening you can arrange will help, I'm sure. The above sub of M3 I took when the nearby all-weather pitch floodlights were on and they light up the whole area with a strong white light until after 10pm during the week . I'm also limited in that I can't even see very high in the sky - maximum Alt of an object is about 32 degrees .

Good luck

Louise

[Russe]

Bless! That's horrid!! Wishing for a black out!?!?

[Thalestris24]

Bless! That's horrid!! Wishing for a black out!?!?

Ha ha that would be good providing the mains power stayed on otherwise I'd be totally bu**ered!