Taking delivery of GSO RC12

[TrevorW]

Originally Posted by Alchemy

Looking forward to seeing some images, however as per comments made when a few got into the 8 inch version, these scopes seem only to get used on the brighter objects such as m8 eta m42 etc. I suspect it will do incredibly well on such targets but it wont see much else.

obviously a comment made without seeing some of the work of others using the 8" and 10" versions

[gregbradley]

Paul I would get the AP adapter for the face of the STL11. It bolts onto the face replacing the existing nosepiece and face plate. It opens it up a bit. You'd probably get a bit less vignetting with one of those.

Greg.

[cventer]

Geeze Greg,

Now you have me thinking I have to buy a new CCD camera or 2

I may have to keep an eye out for a 2nd hand STL.

Seems impossible to find the perfect balance between pixel, size, QE and chip size. Guess its a case of one size def does not fit all.



Good

Originally Posted by gregbradley

Choice of gear and how it is setup is heavily influenced by the type of target you intend imaging. 12 inch F8 is really a long focal length instrument ideal for galaxies with a modest chip size (STL11 would be close to ideal there). It would not be suitable for imaging the dust areas Jase recently imaged though as the FOV will be too narrow. But targets for the 12 inch RC would be the large number of galaxies that seem to all be near NGC253. There are quite a few around it for some reason.

Fast F ratio with large aperture and large chips though is the direction this pursuit is generally taking. It tends to reveal hidden dust, detail in commonly imaged targets etc. A reducer may work with this new RC, yet to be determined. It would be tough. I was not able to use one successfully with an STL on an RCOS 12.5 inch. The AP reducer was more for small chips like the ST10.

The lastest larger chips from Kodak in the really large sizes like 31megapixels and up are either one shot colour (KAF 31600, KAF40000)
with peak QE around 43% or low QE (mono versions of KAF39000 30% and KAF50100 25% which is really pretty low). STL11 is around 51% and 31% the for Ha band. The 16803 is peak 60-61% and about 58% in the Ha band. KAF3200 (peak QE around 89%) is very high in the Ha band so is the KAF6303 (65% at Ha band).

So to reveal new dust/Ha structures would require a large aperture, fast F ratio and longer total exposure to capture it with these larger chips. Or you get a back thinned very expensive chip with 93% QE or you get a compromise - the largest FOV chip, with the best QE, the largest dynamic range, lowest noise and biggest well depth (so long exposures don't overexpose stars, bright objects). It seems to be a compromise very often. Some chips seem to have a lot of these factors aligned and these are the ones that become popular - KAF8300 ( QE 56-60% full well 25,500 small pixels - good for fast systems, short focal length) 11002 chip (QE 51% full well 60,000 a good compromise that suits most scopes and does not suffer from ghosting) KAF16803 (60% QE, 100,000 full well 79db dynamic range - this is the best of the current chips).
KAF 09000 and KAF3200 suffer from RBI a lot (ghost imaging) requiring a fix in Apogee and FLI cameras that has a side effect of increased noise and really requires heavy cooling to minimise this trapped charge leakage during an exposure from the ghosting control.
Too bad. On paper the KAF 09000 would be the chip of choice.

The conclusion being that these newer really large chips (larger than 17 megapixels) are not really that suited to astrophotography.

The only factor the scope has to play here is larger aperture has a better chance of picking up smaller objects and faster f ratio or higher QE will ensure you can image it successfully without taking 2 weeks of often rare clear skies.

Even with your own home observatory there is a definite limit imposed by the weather about how much you can image a particular spot. This then tends to limit experimenting with new and untried.

I like to do better than what I did before but I also like to image new things.

A list of reasonable targets would be helpful. I am always looking for new and unusual targets. There have been a few here on this site in the last few months.

ic 2631 from the fellow in Chile (Leonardo?) I also imaged this one
Marco's Supernova remnant he imaged (I tried to image this one but its too low still)
NGC346 in the SMC I also imaged this one (yet to be released)
Jase's recent South Pole area nebulas

Many galaxies are very small and not very photogenic but there must be a decent list still of those that are not often imaged.
Can you make a list of what you think would be interesting targets? I would be interested.

Greg.

[gregbradley]

Its an interesting area. I have been studying CCD chip specs now for some time. Including the new ones about to be released in cameras.

The bottom line is the KAF8300 is the best small chip most suitable for shorter focal lengths up to medium focal lengths.

The 16803 is the best allround chip as 9 micron pixels seem to suit practically any scope. It has the best QE, deepest wells, lowest noise, least RBI (residual bulk images - ghosting) of any chip in the KAF series.

The STL11 is a venerable camera and also 9 micron pixels but slightly less QE at 51% and 31% in Ha but no RBI as it is a KAI chip and their architecture does not suffer from RBI.

In the up and coming chip departments there is a KAI29050 which is 29mp and 35mm film size (1mm smaller than an STL11 chip). QE is 45% which is "lowish" but the highest in the new range of larger sensors.
The rest are one shot colour. But someone needs to take the plunge with these new Kodak True Sense one shot colour sensors. The
Qe for these is now up around 43% peak which is a lot higher than the older one shot colour sensors which are often around 22%.

True, one sensor does not fit all requirements but if you were to pick one my advice would be to go for a 9 micron larger chip like the STL11 or 16803 (more expensive).

TheSTL11 is on sale at SBIG at the moment - a new class 2 is $4995.
There are several 2nd hand on Astromart often for around $4300.

Greg.

[cventer]

Originally Posted by gregbradley

The bottom line is the KAF8300 is the best small chip most suitable for shorter focal lengths up to medium focal lengths.

Thanks greg what do you define as medium focal length?

[gregbradley]

Based on images I have seen posted in many places I would arbitrarily consider 1000 - 1500mm medium focal length and above 1500mm long focal length.

Above a certain point and the 8300 shows up the seeing too much.
I know that for a fact with my CDK17 at 2958mm.

But with the focal reducer and reasonable seeing at 1950mm it was fine.

So that's a very arbitrary focal point. The bottom line is small pixels (5.4 - 6 microns) suit faster short focal length scopes and larger pixels suit
longer focal length.

As far as Kodak goes the trend is for more pixels and smaller pixels.
Most of their later large chips are 5.5 to 6.8 microns. The STL11 and 16803 have 9 micron pixels.

8300 images though look best in the shorter focal length images -APO refractors although Paul Haese as done quite a few really nice images with a 10 inch RC which I think is around 1500mm focal length?
Much longer than that and it will make stars look a bit fuzzy showing up poor seeing and would be limited to using it on good seeing nights or binning 2x2 on everything.

Greg.

[Leonardo70 (Leonardo Orazi)]

Interesting post ... i loose it..
Congratulation Paul ... i'll wait for some results.

All the best,
Leo

[gregbradley]

Any progress with your 12 inch RC Paul? Its been a while, did you hit a snag or just been busy?

Greg.

[Paul Haese]

Hi Greg, no snags, jsut life getting in the way at the moment. Weather has been less than co-operative too. In spare moments I am trying to cover Jupiter for this years imaging of the giant planet (that too has been less than exemplary)

I have selected the target for the imaging run and testing, it is just a matter of timing now. Sorry for the delay, but you all know how things can divert you from the course sometimes.

[gregbradley]

Yes El Nina is playing havoc with imaging opportunities. They have been few and far between where I live also.

Greg.

[allan gould]

See that Andrews Comms is advertising the imminent arrival of the 16" GSO RC
That will be interesting

[gregbradley]

Does that mean they'll do a 20 inch next?

Wow, 16 inch is serious aperture.

How much is it?

Greg.

[Paul Haese]

Wow a 16". I would have thought the metal tube would need to be replaced for that. I am going to get a machinist to do a replacement frame and carbon tubes for a truss once I get my 12" tested and start imaging. I am not certain that the rolled tube will be suitable for a 16" though.

[Paul Haese]

Ok RC12 is installed at the observatory with STL11 on the back all wiring through the mount and now waiting for clear skies. This weekend looks pretty good, fingers crossed.

[allan gould]

According to Andrews Comms the 16" is a CF tube.

[Paul Haese]

Thanks for the info Allan. That makes sense, but I am puzzled why the 12" comes with a ali tube and every other model has a carbon fibre tube??

[mithrandir (Andrew)]

Originally Posted by Paul Haese

Thanks for the info Allan. That makes sense, but I am puzzled why the 12" comes with a ali tube and every other model has a carbon fibre tube??

The 1st generation GSO RCs were Al and the CF versions came later. There might be a CF 12" sometime, but don't hold your breath.

[Paul Haese]

Well finally I have made a start (probably much to most people saying about time) with the scope.

Last night I set out doing two things, getting the scope focused and doing a pointing run.

After mounting the scope on Thursday I had thought that one 2" extension (supplied with the telescope) would be enough to gain focus. Wrong; after 4 attempts I discovered that to focus the STL11 I had to have 3x1" extensions and 1x2" extensions. The telescope only comes with enough extensions to focus the telescope with an eyepiece; so bear this in mind when buying the scope. The beauty of all this though is that this leaves plenty of room for back focus and putting an AO on the STL and a rotator.

Another observation is that the focus does move a little over the course of a night but as much as I had supposed. Especially when you consider that the scope has an ali tube. I left the focus deliberately to see how much focus shift would occur.

With getting the scope focused I set about doing the Tpoint run. After several frustrating hours and a phone call to Mark (Wysi) (thanks for being the check list mate) I discovered that the guide cable I had put on the STL was in fact not the right one. I was getting elongated stars even after 2 seconds and all travelling in RA. After finding the Do'h problem the acquistion of points began. Only to find that I could not plate solve. I went over all the issues I had sorted in previous runs and finally thought that the focal length must not be right. This was in fact the answer. Retailers are saying the telescope is a 12" f8 telescope. That should make the focal length as being 2438mm. In point of fact it is most likely around 2400mm. Using 2400mm in AAG Tpoint mapper solved everytime so long as the exposure was long enough. Retailers should state the focal length as this would help with working out image scale and help with plate solving.

Once I got the run underway all seemed to go well, especially once I set the exposure length from 5 seconds to 10 seconds. Plate solving was reasonably fast (2-4 seconds) but solving each time in all regions of the sky.

I managed to get a run of 74 points done and pointing to around 12.2" before cloud and another problem reared its head. The PME mount alarm keep stopping the mount, so I will need to address this issue (see other thread).

I did take an image, but only managed a 120 second shot near running man which was out of focus and not guided, so it is a little blurred and with tiny donuts in the stars. Suffice to say I think so far this telescope is going to be a winner (time will tell though).

Another observation was that despite suspecting that the entire assembly at the rear was flexing this did not seem to be the case. Collimation did not shift according to the position in the sky. To be definitive though I will need to complete several images in several parts of the sky. I have replaced the focusor though as I think despite it looking a little beefy, it does have flexure problems. The Feather Touch as an expensive addition but worth the month everytime.

The optics at this stage look to be sharp and what we have come to expect from this budget buy RC. I am planning to examine all the sub exposures I gather in the coming tests and give a comprehensive report on what I see. Flexure is my main concern with the OTA.

So that is where I am at present. Come the Christmas break I hope to have the review written and an image to present for all to see. So far so good.

[gregbradley]

You're off to a good start there Paul.

I also find with my CDK that sharp focus is not achieved until the mirror is within about .5C of ambient, even closer. It can give the appearance of out of focus slightly when the temp difference is too great.

Because of this I usually turn the scope's fans on a couple of hours before I use it. Which is only a partial solution as the big temp changes are after dark.

Greg.

[bert (Brett)]

Paul,

If you do a plate solve with visual pinpoint, it will calculate your exact fl.

Brett