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 Post subject: Re: CCD vs DSLR headache
PostPosted: Mon Apr 09, 2012 4:08 pm 
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I would certainly be intrigued to see if there is an off the shelf solution. I've read Making Every Photon Count by Steve Richards and he had butchered an extension tube to make the fit. I'll see if I can dig out his book and find the details.

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 Post subject: Re: CCD vs DSLR headache
PostPosted: Mon Apr 09, 2012 4:30 pm 
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Link I got from Bob previously to PreciseParts who can make one. I just played with their calculator and EOS lens to QHY is around US$190 depending on the exact length of the adapter required.

I think it wouldn't be too hard to make one from an extension tube set. Looking on ebay basic extension tubes are around £4 delivered, so just use the end bit to mount to the lens. Somehow or other bodge that a T-thread of appropriate length and done? I guess no one has done this before since there would need to be quite a bit of flexibility to get the spacing just right.

Edit: or get this: http://www.altairastro.com/product.php?productid=16209

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 Post subject: Re: CCD vs DSLR headache
PostPosted: Mon Apr 09, 2012 4:41 pm 
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Ah yeah, I've seen the Altair ones before and forgot.

I guess there needs to be flexibility in spacing, depending on camera make.

I dug out Steve's book and he doesn't go into too much detail other than to say he had a local machine shop to alter a male T thread to attach to the extension tube.

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 Post subject: Re: CCD vs DSLR headache
PostPosted: Mon Apr 09, 2012 4:58 pm 
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From the description on altairastro, the geoptik adapter gives you 26mm of space to the sensor to play with. The QHY9 is 15mm from sensor glass, possibly up to another 2mm to the silicon surface itself. So around 9 or 10mm extension will sort that. Unfortunately that rules out using the filter wheel in this application at 19mm thickness.

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 Post subject: Re: CCD vs DSLR headache
PostPosted: Fri Apr 20, 2012 9:30 am 
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Hi popo,

In case you missed it this image of Omega Centauri posted over at the Stargazer's Lounge was taken with a modded 1000D cooled to -3°C behind a Skywatcher 8in f5 reflector. Just shows what a DSLR can achieve in the right circumstances. Such a shame this object is below our horizon here in the UK. :(

Bob.

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OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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 Post subject: Re: CCD vs DSLR headache
PostPosted: Fri Apr 20, 2012 11:20 am 
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I hate to admit I don't browse very far on SGL, so I hadn't seen that before. I also hate to admit I've never been that big a fan of clusters. I like the colourful glowing stuff more!

Back on my decisions, I think my choice of a NEQ6 based guided mount is still on the shopping list. But I keep returning to the age old question for the optics and sensor: how much will I actually use it for the cost? I'm now thinking, maybe I should just get someone in to stick a ton of concrete in the garden and be done with it. I can then have a fixed mount: align once and forget. But if I do that, the astrotrac would once again be good enough and I don't need the new mount necessarily.

In short, the more I think, the more confused I get.

On an unrelated note, I am currently wondering what the deep sky looks like in NIR? Say, 700-1000nm range. Initial research shows one Sodium spike at 818nm-ish so I've ordered cheap 850 and 950 nm filters to play with. Beyond that, what's out there? In initial searches I haven't come up with much in that area.

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 Post subject: Re: CCD vs DSLR headache
PostPosted: Fri Apr 20, 2012 1:17 pm 
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Hi popo,

There's a huge amount out there but, if memory serves, water vapour pretty much cuts most of it out unless you are very high (feet, not illicit substances :lol: ).

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject: Re: CCD vs DSLR headache
PostPosted: Fri Apr 20, 2012 4:25 pm 
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I did come across references suggesting water might be an issue, that a visibly clear sky might not be clear enough. Since most of the country is in drought status, I think that means we'll have an excess of water around. Just not the right sort of water. Trading off that, I'm told seeing can be improved for wavelength related reasons I didn't look into.

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 Post subject: Re: CCD vs DSLR headache
PostPosted: Wed May 02, 2012 9:53 am 
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Hi popo,

Even if you aren't tempted I think the "tinkerer" in you might enjoy this thread over at the Stargazer's Lounge describing, with loads of illustrations, how to add a (water-cooled) Peltier cooler to an 1100D. The difference in "Dark" noise is shown towards the end of the thread. In another thread Gina does admit that it might have been a good idea to also add a temperature probe so that the actual temperature of the sensor could be sampled. If it were me, and it definitely won't be, with a temperature sensor in place I think I'd also take the opportunity to either manually or even automatically control the Peltier cooler to achieve a constant temperature.

Anyhow that's all blue sky thinking but I thought you might enjoy the thread.

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject: Re: CCD vs DSLR headache
PostPosted: Wed May 02, 2012 12:58 pm 
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Interesting mod, but a bit too mechanical for me to bother with I think.

After an unexpected spend on the car recently I think my astro spend might be a bit short for several months now. After much consideration, I've swung back again and wonder if it's worth going for the guided mount at all if I'm not upgrading to big scopes in the short term (1 year).

Is there some cheaper way I can get the astrotrac "good enough" bearing in mind my location isn't the best anyway. This might be as simple as digging a ditch in the garden and standing a metal spike out of it. Then I can do a set and forget polar alignment.

I'm still in two minds about CCDs though. Does anyone do a cheap and small high resolution (4MP+) mono? They all seem to be one shot colour which I don't want, or so low in MP I might as well muddle on with the DSLR. I'm thinking a small cooled sensor on photo lenses would be the best cost compromise for my kit in the search for smaller targets.

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 Post subject: Re: CCD vs DSLR headache
PostPosted: Wed May 02, 2012 3:05 pm 
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Quote:
Does anyone do a cheap and small high resolution (4MP+) mono?

Short answer - possibly not. :(

Looking through OPT's listings in price order I think the closest might be the 2MP ATIK 320E which they sell for $1,105 (here). By the time you've added shipping and import duty/VAT it's hardly cheap, except by astro-CCD standards, and you've still got to fettle your lens(es) onto it and mount the assembly on your astro-trac.

On the other hand, and you know I can be a bit naughty when it's other folks cash :lol: , for not much more money than that ATIK you can buy a 6" Meade telescope on a computerised (equatorial) mount. Check out the 6" SC with LX80 Multi-Mount , the 8" SC or the Series 6000 80mm apochromatic refractor, also on the OPT site. The 80mm refractor is probably the best for astrophotography simply because it's an f/6 as opposed to f/10.

On your wider point, I could never consider not having a GoTo mount now, especially if one can set it up in a semi-permanent way. You've seen my own pier solution which allows me to set up in the evening without having to polar align. But, for me, the key is the GoTo bit as it saves fiddling about trying to find targets. I can slew to a bright (enough) star to nail the focus and then command a slew to the area of interest quickly and repeatably. That means subs are pretty well registered even when taken days or weeks apart. Sell the astro-trac! :P :lol:

OK, I'll stop being naughty now. Like you I'd want to get the best out of my current investment but it can be fun window shopping and considering alternative solutions as well. 8)

Bob.

P.S. Bad luck about the car. :(

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject: Re: CCD vs DSLR headache
PostPosted: Wed May 02, 2012 5:12 pm 
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A 2MP isn't worth bothering with. My priorities are resolution first, noise second, assuming I can get the alignment issues sorted. Bear in mind my DSLRs are effectively 3 or 4.5MP based on colour sampling.

Actually, there is one major upgrade I can do without buying more kit. Find a dark site! I am intensely jealous of people with dark sites who can achieve more with a short exposure than I can trying to fight through the LP noise floor, which effectively lowers contrast and the processing required to get around it amplifies any noise. I think this is probably the biggest reason I'm hesitant on spending megabucks on anything. Even with narrowband I think I need to invest in narrower bandwidth filters than I'm currently using, which is offset by the need to use longer exposures...

Definitely a goto would help me a lot, since I don't know where things are and it takes a little trial and error to find things. It might not be so bad now I put the 2nd gear head on, since I can use two of the axis on that to navigate RA/dec offset from another reference.

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 Post subject: Re: CCD vs DSLR headache
PostPosted: Wed May 02, 2012 5:40 pm 
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Hi popo,

I remember having huge issues with light pollution here in my village. I even packed up my kit and drove about five miles down the road to a cold and lonely spot in darkest Gloucestershire in order to capture the image in this post.

Fast forward four years and I took the image in this post from my back garden, light pollution and all. :!: High resolution versions can be seen here and here.

OK, it's not really comparing apples with apples because the first was taken with a "one shot" sensor (EOS 40D), albeit while using an IDAS LPS filter, while the second was taken with a cooled CCD and separate RGB filters, not to mention a Hα filter, and my processing skills have also improved a bit but I think an awful lot of my light pollution issues weren't light pollution at all but thermal noise. I'm lucky enough to live away from towns albeit in a large (5,000 people I think) village but there are plenty of street lights close by.

I'm wondering how you can work out if your issue is light pollution or sensor noise. The best I can come up with is to compare some longish exposures of the same duration through your Hα and LPS filters. Knowing the bandwidth of the former compared to the latter you should be able to work out what percentage of the background signal derives from the sensor as the background in the Hα exposures compared to the LPS figure should be roughly (Hα bandwidth in nm)/400 if there were no sensor noise. Hope that makes sense and I've got the numbers right - I'm sure you can fine tune them if, in my pre-prandial state :P, the brain ain't working too well. :lol:

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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 Post subject: Re: CCD vs DSLR headache
PostPosted: Wed May 02, 2012 6:22 pm 
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Your brain must be working, or at least better than mine since I had to look up the word "prandial" as it's not one I recall ever coming across before!

I can think of an easier test for sensor noise. Cool it. How, if I'm not going to open it up? Well, I have a freezer... I don't need a lens on it, just body cap and manual will do. I can reference it against a room temperature test. A domestic freezer is rated at -18C I think. I don't know how fast the sensor will heat up when I take it out though but I don't imagine it will have much thermal mass so I might not get many shots in at that temperature.

Actually, that can be a different test. I already have what I believe are light pollution limited shots. If I re-create the same settings, without any light falling on the sensor, what's left is noise. I have those already too. They're called a dark frames. The dark frames are certainly a LOT darker than my lights. Like night and day, if you'll pardon the pun. Darks are "black" apart from hot pixels. Lights are usually a strong blue cast if I'm using the CLS filter. It must be light pollution, with the orange-yellow dominant output of sodium removed it leaves the rest of the broad spectrum LP though to be detected.

I'm still kinda tempted to try the freezer test to see what the cooling effect is like...

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
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 Post subject: Re: CCD vs DSLR headache
PostPosted: Wed May 02, 2012 7:23 pm 
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A "freezer" test might be interesting. Might be difficult to increase the thermal mass unless you have one of those pouches you place in the freezer and then put in a picnic type cooler bag. But you would want to protect the camera from condensation and whatever you use should slow down the heat gain from the surroundings.

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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