Light pollution filter DSLR

[Andymac79]

Again, I had good success processing the image, it was only posted in that form to demo my light pollution to see if you guys thought it was bad enough for a filter.

Nice image however

[AndrewG]

The main advantage of the filter would be that you could increase the exposure time without washing out any of the sky due to LP; most of my images are 4 to 5 min subs to try and get as much data as possible, without the LP filter in certain parts of the sky this would have to be greatly reduced.

[Andymac79]

Thanks for that, so good news. If I can get the hardware to support 5 min subs then the filter will be of great help.

[Gina]

I use a CLS CCD clip filter with my DSLR and find it makes a huge difference. The LP here isn't bad but without it I can only manage something like 10s subs whereas with it I have used 5m subs. That's using ISO 1600 with my 1100D.

[Andymac79]

Thanks Gina, I have got a non CCD on the way, Figured I didnt need the CCD

[Gina]

Fair enough I got the CCD version because I removed both filters on my first 1100D mod.

[Andymac79]

So in the future if I do mod can I keep my non CCD?

[Gina]

Yes, I would say so

[AstroWolvy]

I would say the better LP filters are:

- Hutech IDAS P2 (best color balance)

- Astronomik CLS CCD (minor green dominance easely fixed)

i know few are using Hutech IDAS V4 in hight polluted sky, like in the center of town, but you need huge exposition.

[K3ny0n]

So am I right in saying if you only remove the colour balance filter you do not need the CLS- CCD filter? In my case I only removed the colour balance filter (the blue one) so could I buy the non CCD version?

Just to clarify .

Rob.

[studdedsole]

So am I right in saying if you only remove the colour balance filter you do not need the CLS- CCD filter? In my case I only removed the colour balance filter (the blue one) so could I buy the non CCD version?

Just to clarify .

Rob.

Rob, You removed the blue IR cut filter so would need the Astronomik EOS clip CLS-CCD filter with IR block for optimum

[K3ny0n]

Thanks again you haha. So where have I got the words colour balance filter from?

Rob.

[studdedsole]

Thanks again you haha. So where have I got the words colour balance filter from?

Rob.

The blue filter is often referred to as colour correcting and is the filter which maintains the correct colour balance for daytime use, when it is removed you get the pink hue due to the improved Ha response.

[K3ny0n]

Thanks again mate .

Rob.

[russellhq]

I've never seen an evidence based answer to this question about which filter does what (though I've not looked that hard). Some say one way, some say the other.

This site says both are UV/IR blocking:

http://www.astronomi...o.uk/eosmod.htm

[Gina]

The debate rages on!

[studdedsole]

Yes, To a large extent we are in the hands of the guys who do the mods and the experiences of the users who have had their DSLR' mod'd.

We have to accept what their experience tells us.

As we know from sites like Astronomiser and Hap Griffin the ultimate use of the DSLR is key, whether it be hung off a reflector, refractor or used with lenses, in addition the advice varies according to model.

I can advise that on a 1000D the removal of the blue rear filter prevented me focussing lenses below 12mm for wide field work, when the Baader replacement filter was installed I could focus down to 8mm. A chat with Bern at Modern Astronomy led me to choose the non CCD CLS filter and this has been fine. I was advised that choosing the CCD-CLS filter would have done exactly the same job but would have cost more and been money wasted. This filter provides the sharper cut off at IR to restore the characteristics of the original Canon filter or provide a cut off similar to the replacement Baader thereby preventing star bloat.

However, I have seen no documented.

[K3ny0n]

If you don't mind me asking, not to sound rude but on my part of not grasping the full extent, how come you used the non-CCD when you done exactly what I done, removing the blue filter on a 1000D.

Rob.

[Gina]

That is exactly the crux of the debate/argument. "Does removing the blue, colour balance filter still leasve sufficient IR cut in the remaining filter to prevent star bloat in refractors". I have not had sufficient imaging time to test this myself so can't give an opinion at present.

[studdedsole]

As Gina says this is a bit of a thorny issue which may be complicated by the changes in Canon models over the years.

I modified a 20D and at the time the advice was that a Baader replacement was required to maintain control of the IR spectrum to prevent star bloat. When I researched this at the time I used the info in this link which appeared to indicate that for the family of cameras quoted the Baader IR filter would be the optimal solution.

http://www.astrosurf...der/eval_us.htm

Certainly the spectral analyses with the 350D indicate that IR is better controlled with the replacement filter, however I couldn't find any images of nebulae or star fields at the time giving a qualitative indication of the effects of the replacement vs no filter option. To be safe I went for the replacement filter.

When I modified a 1000D things appeared to have moved on, Andy Ellis at Astronomiser indicates that the front anti-aliasing filter does an adequate job of controlling the IR/UV cut and a replacement is probably not required.

One of the SGL members did some quantitative analysis which seems to back this up, see this link http://stargazerslou...filter-element/

So I modified the 1000D and left a replacement filter off but I use my DSLR's with lenses only and couldn't achieve focus at extreme short focal lengths and had to then insert the Baader replacement filter to achieve focus.

If you read US advice you will find that it contradicts some of what is stated above, however I think that the Baader filter characteristics have now changed also, I seem to recall reading somewhere that the US Baader is different to the UK one.

So the question is which EOS clip do you use.

With a Baader replacement filter in place of the original blue filter - you do not need any further IR cut and a standard CLS filter is okay - this is why I didn't go with the CCD version.

Without a Baader replacement filter in place on the current crop of Canon DSLR's you may not need any further IR cut, but the evidence and info out there is confusing as the sources contradict each other.

Cost of standard CLS clip is £108

Cost of CCD-CLS clip is £131

I'd pay the extra £23 and be safe that you are covered in most modes of use of the camera.

Sorry to waffle, but as you can see there is just so much info out there and it is all convincing which makes nailing the best option tricky, so go for the safest option IMHO.

ps - if you need confusing any further join the "DSLR modications" Yahoo group, it is always very busy.

[K3ny0n]

Great info thanks a lot for that, I think I will take your advice because the difference in prices like you say im covered either way.

Seems very confusing all of this different termnology used, difference from UK/US, you would of thought to make things simple make and call everything so it is universal for both.

Rob.

[rfdesigner]

Someone mentioned earlier about filter curves.

Christian Buil has measured a couple of LPR filters as well as some other well used filters

http://www.astrosurf.com/~buil/filters/curves.htm

[IanL]

My Xmas 'surprise' (i.e. wife dearest, here is a link to exactly what to buy) was the IDAS P2.

LP is pretty variable where I am, no streetlights in the village so only house lights, a few bits of agricultural lighting at times and one annoying neighbour's security light. LP from nearby towns varies widely by direction; North through SE is pretty poor, with a mix of mainly Sodium and Mercury, but in other directions it is pretty good (only one tiny town with a couple of hundred low pressure Sodium between us and the North Sea). The main variable seems to be atmospheric conditions, on damp not very transparent nights the LP washes out a lot of stuff up to maybe 70 degrees in the directions of the main sources and affects the whole sky slightly. On dry transparent nights, the sky is pretty black in the good directions and not that bad in even the poor ones.

I don't think I will necessarily need to use the LP filter at all times, haven't had a chance to give it a try in anger yet. It certainly makes focussing and framing in Canon Liveview more of a challenge, only really bright stuff is showing up (maybe M1 or lower) , whereas without it I can usually see stars down to M2 or better. In the end I went for a 2" screw-in variety since it gives me more flexibility if I ever get a CCD camera for example.

Most expensive 2" circle of glass that I've ever owned, I'll say that.