Various focal length scopes for deep space imaging

[Alchemy (Clive)]

Originally Posted by [1ponders]

This is applied to DSO imaging rather than planetary imaging. By using many images as is done with planetary imaging improved resolution can be achieved by interating bits of repeated detail from multiple images.

just had a thought...would stacking say 20 pictures then using things like unsharp give you the extra detail similar to webcam imaging. only for deep sky.

So consider this... jases resolution chart..... the bottom end is for deep sky ie 1 photo, the top end is for planetary images 1000 photos ..........
could you then have a scale for no of images to join the two , like a log based scale. Which then you could increase your focal length and still get good results ? or

[[1ponders] (Paul)]

Fahim I think much of the secret to Erics, Pauls and Scotts images are their wonderful processing skills. Yes there equipment may be imaging at 1 arcsec resolutions, but that doesn't mean they are actually achieving 1 arcsec resolution as their results.

While I'm generally only using the ED80, either native or with the WO 0.8 FR, I have a 0.5X NextGen FR and Flattener coming for my 8" SCT which I am really looking forward to trying out. This will give me an 1.52 arcsec/pixel resolution which I think will be about as low as I can go with my atmospheric conditions on good nights.

I'm not sure how to go about binning a DSLR in PS.

Originally Posted by Alchemy

would stacking say 20 pictures then using things like unsharp give you the extra detail similar to webcam imaging. only for deep sky.

I don't believe so. If the detail/resolution isn't there in the first place no amount of unsharp masking will bring it out. You may achieve better results using a deconvolution algorithm like Lucy-Richardson or Maximum Entropy to improve resolution

[davidpretorius]

great thread

[Alchemy (Clive)]

looks like

[jase (Jason)]

Originally Posted by netwolf

And I have read somewhere b4 that binning is possible with DSLR images in photoshop, is this right?

The software binning you’re referring to follows a similar concept, but different to in camera binning. In camera binning (either 2x2, 3x3 or what ever your camera supports) electronically combines pixels. When the camera is placed into a 2x2 mode, it groups four pixels to make them act as one. This increasing camera sensitivity, but at the same time potentially reduces resolution depending on your arcsec/pixel scale.

In comparison, software binning does not increase sensitivity. It follows a similar principle of combining pixels, but does this by taking the average of each pixel to make the final pixel output. i.e. with a software 3x3 bin, results in one large pixel containing the averaged value of the nine pixels. You’re probably thinking “Why would I want to do software binning if it doesn’t improve sensitivity?”. Well… software binning from an image processing perspective is one method of smoothing data to reduce noise. As the pixels are averaged, it is makes it easy to remove outlier pixels. First upscale your data, then active the software bin mode of choice. There is of course many other noise reduction methods which I think are more efficient than software binning, but it does work well for RGB data which is later to be combined with a 1x1 luminance.

It is also important to note that with any form of binning, image size is reduce. This makes sense considering you are combining pixels. So if your camera pixel array is 1024x1024 in a 1x1 configuration, binning 2x2 results in half the array size i.e 512x512. This is the reason why I mentioned to upscale your data first so when the pixels are averaged you finish with the original sized image (before binning).

[netwolf]

jase, thanks for clearing that up. But can you explain further how you upscale data?

Paul, Is that the Optec FR your getting? How about the Optec 3.3 FR would that be any good for DSLR with the 8"?

Regards
Fahim

[Bassnut (Fred)]

Jase, one of the reasons for in cam binning rather than sofware binning is the read out noise is proportionally less after binning in cam.

[[1ponders] (Paul)]

Originally Posted by netwolf

Paul, Is that the Optec FR your getting? How about the Optec 3.3 FR would that be any good for DSLR with the 8"?

Yes it is Fahim. I'm looking forward to giving it a go. The 3.3 isn't suitable for the DSLR, the Optec site specifies a max chip diagonal of 9mm, way too small for DSLR. Even the 0.5 will be pushing it as the 300D diagonal is 27.3mm and the 0.5 is suitable for 17.5 mm. That is a lot of lost FOV but it will considerably reduce imaging time and flatten the field for what is available.

[iceman (Mike)]

So just an update on this, been thinking about it again lately..

I was hoping to get a 6" newt, thinking they'd be around 1000mm focal length, but from looking this morning, they're mostly 1200mm focal length, giving f/8 focal ratio.

It looks like Skywatcher have an 8" newt (SW600) with a focal length of 1000mm, giving f/5 focal ratio for around $600 - perfect for what I'd use it for (deep space imaging).

Anyone else got any suggestions for a ~1000mm focal length, fast focal ratio newt with a 6" or 8" mirror?

[davewaldo]

GSO have an F4 and F5 8" Newtonians. Andrews sells them with mounts but may be available OTA only. May be cheaper than the skywatchers.

[[1ponders] (Paul)]

Or you could go for a 10" MakNewt @ f4 (?). Mind you anything at these f ratios will probably neeed a coma corrector as well.

[iceman (Mike)]

Yes you're right - any of the f/4 or f/5 newts, i'd also get the baader MPCC.

I'd preferably want something 6" or 8", rather than 10".. just to keep the size/weight down.

[h0ughy (David)]

vixen R200SS

[[1ponders] (Paul)]

I've been very tempted with getting an 8" MakNewt for a while now for attaching the 300D to. I've got a NextGen 0.5 FR coming for the SCT for use with the SBIG, but there is just something about using an 8" scope (not refractor ....in my dreams ). They are a good size in aperture, not too difficult to manage weight wise on a mount and you still get a decent focal length for the f ratio.

Though a 10" is really tempting

[iceman (Mike)]

Originally Posted by h0ughy

vixen R200SS

I'm sure I mentioned my other requirement..

On a budget..

[Lee]

I've been having similar thoughts..... I love refractors, but as we know to get a good, fast refractor with a longish focal length, ie big aperture, is crippling, cost wise and mount wise!
I was thinking long the lines of a Schmidt-Newt or something too..... I figure if it is 8" f/4, you can barlow it, and only end up at f/8 - not too bad, considering the ED80 is f/7.5 anyway.....

[gbeal]

Great thread, as DP said.
I have just been down this road.
I owned a Tak refractor, a 4" f8, so about 800mm focal length. Drop dead gorgeous, and about US$2500 or so. Took great images, with both my 20D and also the ST2000XCM.
In a fit of lunacy I sold it, and bought a set of GSO 8" f4 optics (see the similarity here folks). Same focal length, so same image scale, and 4 times faster, if I am not mistaken. Biggest gain though was that it cost a fraction of the Tak price.
OK, I bought the optics, built the tube, and all, and then fitted a very expensive focuser and focus motor to it, but it is still about 250% of the price of the refractor. Images as good? I think so, and so does my wallet.
If you are not up to building one, then buy the likes of the GSO8" f4, and the Baader MPCC. AND a decent focuser.
That way Mike, you can have a lighter purpose built DSO imaging scope, plus the ED80 on the side for guiding. Later when you get to a dedicated CCD, with an in-built guide chip, you can dispense with the ED80.

[netwolf]

Interesting turn this topic has taken, this is the reason i was earlier investigating a SN8 OTA the FL is just right for what we need. But I did contact Andrewscomm about the GSO 8" f4 a while back and is well priced for the pocket. I think it was 399 for the OTA.
Maybe we can put in a bulk order Mike delivered to the NOC

Regards
Fahim

[davewaldo]

I've been thinking about a similar scope...

I just spoke to andrews... GS-600 8" F4 newt OTA. $499.

I assume this comes with rings and dovetail although I'm not sure.

As Gary has mentioned, you will want to replace the focuser, but it seems like a good buy. Much cheaper than the Meade 8" SN (but one of those would be great too )

[davewaldo]

you beat me to it Fahim

hmm.... I wonder what the best price they could do it for. I might be interested in going in on a group purchase!