Astrodon filters

[jaspalchadha]

Here's one for ya

So I brought a LRGB astrondon set of filters to go with my qsi 690 the scope I am using is skywatcher esprit 100ed at f5

I attempted to image seven sisters few nights about a 5 minute luminance shot led to a very over saturated image, I tried 2 minutes and seemed fine..

My LP is bad but not that bad

Any ideas

[perfrej]

Five minutes of L on that target sounds a bit high... I shoot less luminous ones at five and end up good. So, I do not think that there is a problem.

/per

[jaspalchadha]

What about LP?

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[jaspalchadha]

The screen stretch histogram is on the far right..

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[perfrej]

The right part of the histogram is the bright part of the histogram. If you're slightly over-exposed that would be where the stuff ends up. You're running at f/5, right? I have a 5m OSC of M45 with 5m exposure. The histogram shows a bulge to the right as the major stars are very, very bright.

/per

[jaspalchadha]

Interesting. . So if I was to take a 10 Ha it should be fine ( no clear skies to test yet )

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[Stephen]

Five minutes of L on that target sounds a bit high... I shoot less luminous ones at five and end up good. So, I do not think that there is a problem.

/per

I have to agree with this

Interesting. . So if I was to take a 10 Ha it should be fine ( no clear skies to test yet )

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Not sure you would get much benefit from shooting 10mins Ha on M45 ... try something like IC405

[jaspalchadha]

Great OK will try the when it's clear first I had issues with the filters not being parlfoucal ( major Un focused ) turned up the filters were loose.. seem OK now after a 2 min check but waiting to do a longer exposures.

Do you guys shoot in 2x2 bin

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[ollypenrice]

It must be down to your sky. I used 10 minutes at F5 and 15 minutes at F7 but I have a dark site. I wouldn't hestitate to go to 15 minutes at F3.9 if I could but the cores would need shorter subs to handle the dynamic range. The long subs will find all the nice brown dusty stuff.

Here's a Dropbox link to a linear stack of 15 minute lum subs from our TEC140 at F7. Have a play. https://dl.dropboxusercontent.com/u/63721631/LUM.tif

Olly

Edit; I've often wondered about Ha for M45. Theory says there won't be any but it really might be worth one long sub to confirm this.  

[Stephen]

Edit; I've often wondered about Ha for M45. Theory says there won't be any but it really might be worth one long sub to confirm this.  

There is a tiny, tiny filament of red in there. I've seen it on one of Ibbo's images Can't remember if he said it was Ha or just red though

[jaspalchadha]

Thanks olly ill check that tiff later

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[nmoushon]

I was shooting 5min subs with my ED80 at f/4.75 and I could tell I was just about the max on M45. I would think that you could take a range of subs to help control the stars but still pull out the fainter nebula around it. I know the more time you can add up the better but the processing, I think, would be similar to what I would do for M42 and just layer mask it all together. But I haven't been able to test this as its been way too cold at night for me to go outside. Like -20F cold.

Olly - Is your M45 all one sub length or do you have several sub lengths to help control the stars?

[perfrej]

Olly, the interesting thing here is the histogram. I suspect you have bulge on the right side of it in your subs (assuming dark on the left, bright on the right). You have sucked the great dark stuff out of yours but the stars should give you a bulge... (how did that sound?)...

As for parfocality. Bullocks! I have Astrodon Truebalance and Baader blabla. None of them are parfocal. If you are serious about focus you will find no piece of glass is parfocal to another. We just have to live with it and focus on filter changes (or measure offsets and just adjust).

/per

[ollypenrice]

Olly - Is your M45 all one sub length or do you have several sub lengths to help control the stars?

The image is a mixture of everything I ever took on M45 so I can't remember all the components. However, I don't think I used anything particularly short for the cores. I think that the need for short subs is much exaggerated, though they can be useful. The key thing is just to look at the linear image and see whether the cores are over-cooked. Often they are not, so you just layer mask an almost unstretched version of the same data onto a stretched version. If you want to create a 'core stretch' from data which you will also stretch to wring the neck out of it, just use a Curve like this;

The idea is to lift the faint background around the star but not lift the star more than you can help. Of course it works for galaxy cores as well.

A very simple trick is to do your core control layer in RGB only data since the addition of Luminance (which has about 3 times as much light as any one colour) tends to overcook the cores.

Per, when you combine images from totally different sessions, scopes and cameras, as in the M45 I posted, you tend to get a pretty funny histogram. I don't let this bug me. Our friend Dennis reminds us that it ain't the histogram you hang on the wall!

Olly

[Stephen]

the stars should give you a bulge... (how did that sound?)...

Wrong, very wrong

As for parfocality. Bullocks! I have Astrodon Truebalance and Baader blabla. None of them are parfocal. If you are serious about focus you will find no piece of glass is parfocal to another. We just have to live with it and focus on filter changes (or measure offsets and just adjust).

/per

Could not agree more Baader's are about the best I've used for parfocal-ity, however it was still very obvious if I did not refocus between filters

[jaspalchadha]

Astrodon ha 3 x 10 3nm from London

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[Velvet]

none of my astrodons are parfocal, but then again i never expected them to be

Velvet

[jaspalchadha]

I think only green is little out but that's expected all others are fine

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[Stephen]

From Astrodon's FAQ

When filter manufacturers state that their filters are "parfocal", they mean that the filters are made to a specified thickness tolerance. They can provide filters that will not increase the focus shift that is already in your optical system, but cannot guarantee that  you will not need to refocus among the filters.  Thus, parfocal is a system property.   It is likely that refractors will focus differently at different wavelengths (colors), moreso than pure reflectors. 

[ollypenrice]

I focus on luminance and then just run the sequences LRGB, LRGB, unless the target is low and then I go for L and B when it's high. This is with Baader filters and I do find them parfocal in both the Tak and the TEC.

I don't image at very fine pixel scales in my own rigs and I don't believe any non parfocality is going to make any difference to me. I'm sure it would be possible, with a lot of trouble and expense and some lost imaging time, slightly to enhance the focus by having it done robotically between subs but will it show in the final image?  A copy of Maxim, two Lakeside focusers, two more things to go wrong (I have thirteen cables running the dual rig as it is...)  No, at coarse pixel scales this doesn't tempt me as a way of spending a very large sum of money!

At 0.6 arcseconds per pixel I'd give it more thought... At 3.5, no.

Olly

[teleskopjo]

If you image without any filters at all ie. just the camera through the telescope does it result like the L filter ?

[jaspalchadha]

Not sure.... I u can get min subs anything over the saturated I think it's my LP

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[ollypenrice]

If you image without any filters at all ie. just the camera through the telescope does it result like the L filter ?

No, an L filter normally restricts you at both ends of the spectrum, cutting out the near UV and the near IR and beyond. You can check the cutoff points on the makers' specs. Sometimes people do want to get a wider spectrum and use a clear filter but I've never tried this.

Here's the pass window for the Baader L filter; http://www.teleskop-express.de/shop/product_info.php/language/en/info/p572_Baader-2--Infrarot-Sperrfilter-fuer-CCD---UV-IR-Sperr--und-Luminanz.html

Olly