Opinions about best surburban setup

[gregbradley]

I am interested to hear what your experience has been imaging in the suburban areas with light pollution.

As I see it if you experience poor seeing which I think is more common in a suburban environment due to the many heatsink landscape (roads, buildings) then you would be better off with a shorter focal length to overcome poor seeing (the blur is less visible in shorter focal length images).

But if you are doing narrowband there are quite a few images that show you can use long focal length scopes so perhaps they reduce the effects of seeing a bit plus the light pollution of course.

I am not sure that F ratio plays a part at all.

If using a DSLR you need shorter exposures due to their picking up skyglow.

If using a CCD cam then shorter exposures than what you would use in dark areas and stack them so a low noise camera becomes a bit more important.

As far as filters go you've got the narrowband and you'v got Hutech light pollution filter (-IDAS light pollution filter).

Opinions?

Greg.

[Paul Haese]

If I had to do things from the burbs where we live, I would go with narrow band and medium focal length. Although I don't think long focal length would be detrimental, it would just suit my needs more.

[g__day]

Discussing this today at Bintel. Their view was "if your light pollution is bad - go narrowband - like Fred Van der Haven does, but match it to a camera with Ha sensitivity and the correct pixel size for your seeing (binning if you have to). In narrow band you can image for as long as you like on a mono camera".

So basically a DSLR that isn't modified to see Ha is a limiting factor in light polluted surburbs. Even with a Hutech light pollution filter - I can barely image the Helix nebulae on the darkest of nights. Too I can't get any real red on the Tarantula - shooting on a Canon DSLR.

[gregbradley]

Yes that about sums it up. But it is surprising the number of good LRGB images taken from the burbs. So I would add to that advice to use a CCD cam, take lots of shorter subs if necessary and stack them with a camera with low noise and strong cooling and go for the brighter objects as well as narrowband.

Greg.

[Tandum]

Where I am, east is ok for RGB but there is a refinery with the eternal flame to the north while the west has huge shopping centres and the rest of greater Brisbane plus a brand new brightly lit bus shelter that I can see from the back yard:( A lot of the South is lost to me behind rooves but RGB is possible in a few spots.

I do own and have used a Hutech LP filter but the real aim of them is to lower the LP floor to allow for longer exposure times and I did think that it helped with the canon and the qhy8. But since I stopped shooting RGB to the north and west I don't use it, in fact houghy has had it on loan for the last few months.

I've been plugging away at narrowband mainly but it takes so long to get a decent result with all my current scopes that I'm thinking fast newt again. RGB is a lot quicker to achieve a result and it still works ok for me to the east with a small moon.

Here's some examples shot from home :
Helix shot east this week - 5 minute subs - 150 minutes so far. FL-1640 qhy9 (trying for star colour with 5min subs)
Helix shot east in 2008 - 10 minute subs - 9 of - vc200L @ 1250mm - canon 40D and probably an LP filter
leo trio shot north last month, not worth finishing. FL-800 qhy9 - random flaring in all 3 colour channels :(

So I'll stick with shooting east and do north and south out of town.

[gregbradley]

Interesting Robin.

I am thinking that faster optics to get the signal or longer focal length with a reducer ( the venerable AP67 reducer seems to be a one size fits all).

You probably also have to flock or make sure your scope is well baffled.

You also probably need to know a few processing tricks to help. I could probably save that Leo. Its a pain but it can done.

Greg.

[JohnH]

I have the same question.

I find myself seeing limited most often (I think), shooting targets high seems to help and shooting NB is the only way to go for me if targets are to the South (unless very bright). This combined with obstructing trees and houses means I have a limited fov and therefore limited targets I can see.

My current setup is an ED127 and opticstar 145m (sony ICX285L sensor) - image scale is 1.4"/pixel and this seems oversampled for the conditions I get. (BTW folks here discuss fl when talking about guiding/seeing but surely it image scale that is the issue?), my guiding is generally in the +/- 2" range (G11G/PHD/QHY5/Wo66SD) and a typical LRGB from last night is attached. It was windy last night and the image is therefore quite soft.

My quandry is what to upgrade, my ccd or my scope. I think I need a ccd with less noise and greater well depth - as well as a bigger sensor would be great. Bigger pixels (more sensitivity) would be welcome too. Seriously looking at the KAI 4022 based cameras but would love to know if anyone has comments about their suitability for use in suburban areas.

Or I could go for more appature and a faster F ratio - eg F5 corrected newt or similar.

[gregbradley]

Focal length does indeed come into it as you are talking about magnification.

With poor seeing you are now magnifying a blurred object. It will become more obvious with more magnification and less obvious in a wider field image simply because that blur is taking up less angle of the overall image so to speak. The blur gets hidden in the wideness of view.

As far as image scale with the CCD goes, yes I agree that also factors in but even correctly scaled pixel/seeing with long focal length will not give you sharp images under poor seeing.

I believe all scopes are limited by the seeing conditions available but some less than others.

I have found generally speaking that APOs seem less seeing affected but then they tend to be short to medium focal length - 500 to 1300mm focal length.

They also have higher contrast due to no central obstruction and relying on diffraction to work. They are less subsceptible to tube currents and mirrors not being equal in temp to the air around it. They also are not affected by collimation (rarely a problem) and less effect of dew.

Narrowband reduces the signal. So you need low noise and high QE (not always from larger pixels - KAF3200 is 87% QE and its 6.6 micron pixels).

Low noise means high cooling and excellent low noise supporting electronics.

Narrowband in the suburbs needs bigger aperture and faster F ratios for a quicker buildup of signal.

And of course its easier to image the brighter objects.

My experience is large aperture works but it will be more seeing affected more often than wider field imaging.

All a compromise.

Hopefully the above gives you a guideline about what to do with your setup.

In your example you already have a triplet refractor and a smallish sensor. Small sensors of course have the same effect as magnifying the image as now a smaller section of the light being captured becomes the full image.

I would suggest the KAF3200ME chipped cameras, the 4022 you refer is also a good chip, the 3200 is the highest QE around short of super expensive type chips. The 6303 is probably one of the best all round for your type of imaging.

Its your camera more than your scope in my opinion. Your tracking is good.

You could try a reducer to get a lower F ratio going as well to help get the signal levels up with narrowband. If the seeing is poor perhap 2x2 may help.

1.4 isn't too far off the .66 - 1 arc sec/pixel band commonly recommended based on 2-3 arc sec seeing.

Greg.

[tlgerdes]

One other thing Greg I found personally, in light polluted areas, good internal flocking can have a marked improvement. I gained an extra 50% exposure time before light pollution made itself noticeable, ie 120sec to 180sec with a DSLR. I am halfway between Sydney and Parramata.

[TrevorW]

I'm 23km from the city centre but I don't even bother imaging in a north/west direction due to LP and skyglow

all my images are taken in the West-South-East direction

[gregbradley]

That's an interesting point. I read this great thread a while ago where this guy knew all about the best black paints around. I wonder if I can find that again. I think it was on the Astrophysics Yahoo Group or perhaps the TEC. Blackboard black spray has been recommended on this site and I bought some recently to use. I'll post once I have about its performance.




Certainly some areas are worse than others. Fortunately the best imaging is at the zenith anyway.

Greg.