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Old 13-09-2013, 06:08 PM
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deciding on a mono ccd

Hi,

I know this topic has been done to death here and there are several options, but after a year of experimenting with my 10inch F4 and a one shot colour, I've decided I need to go down the mono path and am looking for suggestions on what would suit a 10inch F4 in terms of illuminating the chip and providing good resolution.

My primary targets would be nebulae in narrowband and RGB or HaRGB, but I would want to image galaxies as well and be able to resolve details.

The area which I'm not clear about is the fully illuminated circle. Do I just use what newt provides and look for a sensor size that matches?
is it worth going below 4.5micron pixels? there are a few models like SXVR-H814 that have 3.69 micron pixels. would that be sampling over seeing limits?
Is there a chip than the KAF-8300 that has better dynamic range and decent well depth?
I'd like to keep it under $4k. I was hoping to use a 7 position filter wheel as well.
I love the QSI range, but they go over my budget very easily and they all use the KAF-8300 chip.
Is the qhy9 the only decent option for this budget?

Thanks
Alistair
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Old 13-09-2013, 06:26 PM
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What about sbig? I would push the budget a bit more and get something that you really want, sbig seem to be really competitive for what you are getting. Have being looking at the same future options myself today just for kicks, lol haven't got that sort of coin atm and are happy with the osc or have to be for the time being
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Old 13-09-2013, 06:43 PM
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A number of imagers here use QHY cameras. They can best answer about them.

For narrowband work the new SX 694 would be a good camera. Its only a bit smaller than the KAF8300 but its higher QE and higher QE more importantly in the Ha range.

That camera is around US$2800 though. You'd need a filter wheel. SX makes one. I think they are cheaper than other brands for filter wheels. They also sell an off axis guider and guide camera which you would need to do autoguiding with.

Or SBIG has various models using the KAF8300, some include off axis guiders.

Greg.
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Old 13-09-2013, 07:48 PM
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I use a qhy9 and they are a great camera, but if you want to add other options to them such as OAG it is a struggle. I have done it now but at the end I spent a decent sum on getting adapters made and at the end its still not an sbig. I guess what I am saying is that the more integrated systems are probably more economical if you are going to try to add the parts to a cheaper camera.
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Old 14-09-2013, 04:48 AM
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Quote:
Originally Posted by Peter.M View Post
..... and at the end its still not an sbig. I guess what I am saying is that the more integrated systems are probably more economical if you are going to try to add the parts to a cheaper camera.
SBIG have the only fully integrated system with AO and guiding ahead of the filter train....benefits of AO are very real, you might want to look at the data on their website
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Old 14-09-2013, 06:34 AM
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Check out the high end ATik cameras.....
I've been very happy with the ATik16icS, and 314L+
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Old 14-09-2013, 07:38 AM
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I don't have any practical experience with these cameras but from my research SBIG on paper does appear to provide the best integration with the chip in filter wheel in front of the filters.

Beware however that if you intend using Sequence Generator Pro which I was looking at it does not support dual chip setups like that. I know this because I asked that specific question on their Yahoo group.

Brett
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Old 14-09-2013, 10:08 AM
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hi,

thanks for the suggestions.
The 694 chip looks good but I think is a bit too small and the FOV would be rather limited with the 10inch F4.

I've been looking at various options including sbig but before I narrow down, can anyone tell me about import duty? if I buy from teleskop express or sbig direct or optcorp, what sort of duty would i have to pay? assuming they ship here.

the Atik 490ex and SX-814 with the sony 814 chip looks pretty good, the atik is significantly cheaper with the aus dealers. however the sx-814 is US$3,200 at optcorp. not sure if they ship direct and even if they do, not sure about import duty.

The SBIG STF-8300M shows as US$1995 at sbig. anyone bought direct from sbig? any advice on other charges when landed here, that is assuming they ship direct to aus.

the SX filter wheel wth a 7 position 36mm wheel seems ideal.
but anyone used the mini filter wheel which also has a 7 position 36mm wheel but comes with an OAG?

I already have the TS9OAG and will be getting a lodestar.

the Moravian G2-4000 seemed good until I noticed the Ha response, it was below 40%.

is the sony HAD2 technology as good as what they say? they've lowered the microlens layer to increase pixel aperture.

i prefer to get an external filter wheel because I will be using my mono 600D as well for LRGB. It has a decent chip size and has a decent resolution.

Cheers
Alistair
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Old 14-09-2013, 11:34 AM
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Alistair,

Ah - the eternal compromise !
Cost Vs performance, Vs weight, Vs purpose, Vs FOV, Vs image scale, Vs compatibility, Vs features . . . .

I'll toss in my thoughts here.

What is the image circle of the 10"F4 ?
How well corrected is it ? - ie how much of it will be useful ?
How much weight can your OTA/focusser support ?

Are you set on only ever using the camera on the one telescope ?
If not what would be the focal length of your possible other ? - Longer or shorter ?

If you are set on this combination of CCD/OTA then that will determine the largest CCD diagonal you would buy - so this will potentially limit your field.

The image scale of the KAF8300 chip is 1.09 arc sec/pix
The image scale of the SXVR-H814 is 0.75 arc sec/pix

I would say for a 1m fl instrument that you are over sampling for your average likely seeing conditions (say 1.5 to 3.0 arc secs/pix), but if you have great seeing and can see yourself deconvolving then maybe its worth it.
That oversampling may come at the expense of FOV, but I dont know what your image circle is so cant comment.
I am assuming that with only 1000mm you arent intending on making faint fuzzies your subject matter (so you are not aiming at 0.5 arc second resolving capability !) - so its a midfield rig

If it were me I would be considering a chip that has maybe from 7 to 9 micron pixels - yielding an image scale of around 1.5 to 1.8 as/p but maybe 6 to 10 microns

So this may help you determine what image scale you want or need
But if the FOV is quite small then maybe you are better off oversampling anyway since you may not actually be paying much for the extra real estate (that you cant use) !

The next thing I would be thinking about is the performance of the camera for that image scale.
An assumption being that you want an anti blooming camera for "pretty pictures" rather than for photometric style of use

The bigger the pixels, the deeper the wells, so you will generally get better dynamic range with the larger sized pixels - but of course the internal read noise is a real consideration and this is where seemingly the Sony HAD cameras seem to perform (at least anecdotally since their specs are hard to unravel).
Can you calculate this out ?

But choosing a camera based on dynamic range can be an exercise in frustration - they nearly all want to quote their A/D output in bits which is really meaningless in terms of what the real dynamic range output of the chip actually is when read noise is considered.

Then there is the other stuff :
Is it compatible with the software you use or intend to use, are there good drivers, that work all the time, and are they likely to be supported in the future versions of the operating systems - there are some that will not !
Do you want to guide internally, in front of the filter wheel, do you want to use AO (probably not at 1000mm), do you want an integrated internal or external guiding system, are you going to use off axis guiding or guide scope, do you want the minimum cable count for cameras, filter wheels, power supplies, is weight a consideration, what about electronic focussing and rotation, maximum cooling, download times, binning capability etc etc - all considerations that are individual to you and your gear and directions.

I have no idea on the QSI range

But if you can narrow down what your intentions and your gear will allow - the field will likely have been narrowed down sufficiently to make your final selection based on what is actually available in your budget.

Its always a compromise and you have to draw the line.
On the other hand more is better so buy two cameras !

Don't forget that second hand opens up the field considerably
Plenty of cheap STL11000's about these days !

Rally

Quote:
Originally Posted by alistairsam View Post
Hi,

I know this topic has been done to death here and there are several options, but after a year of experimenting with my 10inch F4 and a one shot colour, I've decided I need to go down the mono path and am looking for suggestions on what would suit a 10inch F4 in terms of illuminating the chip and providing good resolution.

My primary targets would be nebulae in narrowband and RGB or HaRGB, but I would want to image galaxies as well and be able to resolve details.

The area which I'm not clear about is the fully illuminated circle. Do I just use what newt provides and look for a sensor size that matches?
is it worth going below 4.5micron pixels? there are a few models like SXVR-H814 that have 3.69 micron pixels. would that be sampling over seeing limits?
Is there a chip than the KAF-8300 that has better dynamic range and decent well depth?
I'd like to keep it under $4k. I was hoping to use a 7 position filter wheel as well.
I love the QSI range, but they go over my budget very easily and they all use the KAF-8300 chip.
Is the qhy9 the only decent option for this budget?

Thanks
Alistair
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Old 14-09-2013, 11:51 AM
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Quote:
Originally Posted by rally View Post
Alistair,

What is the image circle of the 10"F4 ?
How well corrected is it ? - ie how much of it will be useful ?
How much weight can your OTA/focusser support ?


The image scale of the KAF8300 chip is 1.09 arc sec/pix
The image scale of the SXVR-H814 is 0.75 arc sec/pix


That oversampling may come at the expense of FOV, but I dont know what your image circle is so cant comment.

If it were me I would be considering a chip that has maybe from 7 to 9 micron pixels - yielding an image scale of around 1.5 to 1.8 as/p but maybe 6 to 10 microns

Don't forget that second hand opens up the field considerably
Plenty of cheap STL11000's about these days !

Rally
When it comes to newtonians the field of view is pretty much user set by the size of the secondary they choose to use, coupled with the diameter of the corrector. I too think that at this focal length you would be better off with a larger pixel camera because if you want to image deep sky oversampling reduces the amount of flux that gets to your sensor. For instance I image mainly at 1.49 arc seconds per pixel, people at 2-3 arc seconds per pixel will gather signal a lot faster.

The STL is a great choice for the 10 inch F4, however they are going to be expensive because if it is a GSO 10 inch F4 scope the secondary will not be big enough, the focuser will not hold the camera, the aluminium tube wall will flex as the scope moves, and the corrector you need to fully illuminate these chips is a 3 inch wynne or the like.
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Old 14-09-2013, 12:37 PM
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I think its worth considering how tempted you'll be to upgrade and change your OTA too, even though you obviously need to take into account what you have right now.

I'd humbly suggest a list of "dream objects" you'd like to image might help. Some people lust for galaxies, others widefield nebs. You do go through phases. Earlier on, we all want to be able to image everything of course

FWIW, I found my QHY9 mono worked really well with MPCC on a stock F5 8inch Skywatch newt. There was signficant vignetting that could usually be processed out but made mosaicing tough. I eventually lusted for a wider better corrected FOV and went FSQ and now the smaller pixels are really paying off. Its true you spend a lot of time fiddling with adaptors, stepping rings etc, but if money is an issue then QHY lets you at least get entry to CCD imaging and you can add more goodies as the budget allows. At your focal length, you probably realise good guiding through a piggy-backed scope is not a given, and OAG setups for Newts have their challenges as Peter describes.
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Old 14-09-2013, 02:04 PM
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STL is a good camera but its full frame 35mm sized and requires a largish focuser and largish corrected image circle. I wouldn't recommend it unless you had a high end scope that can cope with it. The advantage though is it includes a filter wheel and self guiding
and prices are lowish (it used to be a US$7500 camera).

The Sony 814 chip is the same size as the 694 chip so it will offer the same FOV. FOV is chip size not pixel size. Pixel size affects how much light hits on each pixel.

Both have similar QE (694 is a bit better not much) 3.69 micron pixels are getting pretty small though. A lot of images you see on this site are KAF8300 (5.4micron pixels or Kodak chips at 6-9 microns usually).

694 is the most sensitive chip around except for the older SBIG ST10XE (there's one on Astromart 2nd hand for under $2K at the moment).

Importing incurs GST if over $1000. Usually there is no import duty as GST replaced a lot of those. So add the likely shipping cost (often around US$300) then add it all together convert to Aussie dollars add about $100 and then 10% for GST to get a final cost.

There's an ST10 on the classifieds here for $1800 and it includes a filter wheel and a few filters.


Greg.
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Old 15-09-2013, 04:02 AM
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Quote:
Originally Posted by rally View Post
Alistair,

Ah - the eternal compromise !
Cost Vs performance, Vs weight, Vs purpose, Vs FOV, Vs image scale, Vs compatibility, Vs features . . . .

I'll toss in my thoughts here.

What is the image circle of the 10"F4 ?
How well corrected is it ? - ie how much of it will be useful ?
How much weight can your OTA/focusser support ?

Are you set on only ever using the camera on the one telescope ?
If not what would be the focal length of your possible other ? - Longer or shorter ?

Then there is the other stuff :
Is it compatible with the software you use or intend to use, are there good drivers, that work all the time, and are they likely to be supported in the future versions of the operating systems - there are some that will not !
Do you want to guide internally, in front of the filter wheel, do you want to use AO (probably not at 1000mm), do you want an integrated internal or external guiding system, are you going to use off axis guiding or guide scope, do you want the minimum cable count for cameras, filter wheels, power supplies, is weight a consideration, what about electronic focussing and rotation, maximum cooling, download times, binning capability etc etc - all considerations that are individual to you and your gear and directions.

Rally
Thanks for all the info Rally,

to answer a few questions,

I'm using a home built Serrurier Truss. Pic attached.
I have spent a fair bit of time on this scope to make sure it is rigid and that it holds collimation at all orientations, thankfully it does. not perfect, but acceptable.
I am using Carbon Fibre Truss nodes to minimize focus shift over the night.
The mirrors are from Orion Optics and the secondary is 70mm.

I've entered all measurements in Newt, and it says that the
100% Illumination Diameter 11.115
75% Illumination Diameter 44.414

Not sure which I should account for when thinking of a ccd diagonal.

the Focuser is a 2" moonlite and although it is not heavy duty per se, I'm told it can easily hold 3 kg's.
But obviously, the lighter, the better.
I am using an Off axis guider - the TS9OAG, and have had no issues with getting consistent 20 minute subs during testing.

Thanks for the pointers Peter, Greg and others.
I've had a look at the SBIG ST10xe specs again and dropped a PM to clive. does look very attractive with a 77k well depth, 70% plus QE and 6.8micron pixels.

As for FOV, I was told by someone here that pixel size determines FOV, apparently not.

The SBIG STF-8300M is good value at US$1995, which would equate to AUD2480 with the local supplier as according to them, purchases from SBIG direct would not carry the 2 year warranty.
I will get the SX filter wheel with the 7 position wheel and 36mm baader filters. that, along with the lodestar and my TS9OAG, would just about be within my budget.

other option is the ST10Xe which comes with filter wheels.
There are some stunning images taken with this camera, But I just worry about reliability given its age.
I've had enough with the qhy series to stay away from them, I've reached a stage where I want something that's reliable and will just work as expected.
the trius series mentions heating of the front glass and are argon filled.

last option would be the 694 chip. the 814's 3.69 micron pixel does seem to small.

As mentioned, I will be using a debayered 600D DSLR as well, not just this CCD.

Cheers
Alistair
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Old 15-09-2013, 09:58 AM
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The 3200 pixel size would be a good match for your scope in average/better seeing conditions. If you expect seeing down below 2 arcsec and want the best possible resolution, the 694 would be better (the 814 would oversample most of the time - lost sensitivity for no resolution gain).

The 694 has higher overall QE than the 3200 (without microlenses) - they are about the same at Ha and SII but the 694 is much more sensitive at OIII. The larger pixels of the 3200 will give greater sensitivity (but at lower resolution) than the 694, so either chip would be OK from a sensitivity point of view.

Don't get too hung up on well depth - the measure that you should consider is how many "noises" fit in a full well. This is the dynamic range, which is the ratio of well depth to read noise. Most of the chips out there have around 70dB dynamic range - the chips with smaller wells tend to have lower noise and you get the same result as the bigger pixel chips by taking more/shorter subs.

field of view is determined by chip size, not pixel size, as Greg points out. However, your 6MP QHY8 has a much greater field of view than a 6MP icx694, because the pixels of the 694 are smaller - and that results in a smaller chip.

If you get a chip with small pixels, you might consider getting an alternative coma corrector - the MPCC possibly adds about 2/3 of a wave spherical aberration to your optics system, which might just be noticeable at high resolution in very good seeing. There are a few alternatives, depending on the field of view you want.

Can't see reliability of an older camera being much of an issue - my brand new SX camera lasted 2 weeks before it needed repairs. Local support for SBIG seems to be pretty good.

Be careful if you are looking at AO - might be difficult to fit one into the available backfocus at f4

Last edited by Shiraz; 15-09-2013 at 10:09 AM.
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Old 15-09-2013, 10:16 AM
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I not sure what values you used for your newt analysis but I will tell you that a 70mm secondary should not produce a 11mm 100% illumination in your scope.

The factors that change the illumination are the diagonal size, the tube inside diameter, the tube wall thickness, the focuser minimum height, the spare in travel, and the additional height for camera.

The diagonal is the variable. The tube inside diameter and the wall thickness aren't that important but you must make the sum of both of them equal to double the distance from the center of the scope to the focuser baseplate. My moonlite has a minimum height of 65mm yours might be slightly shorter depending on drawtube options. The spare focuser in travel is the amount of drawtube you want to be out when the camera is focused, mine is 10mm so that it is fairly close to the scope but with room to move for different filters and temperatures. The last variable is additional height for camera and generally this will be the corrector distance because that is the distance you will have to stick too to get good correction. In this case I used 55mm as this is what most correctors need.

These are the numbers I get with estimated values.

diameter 250mm
ratio 4
diagonal 70mm
inside diameter 265mm
wall thickness 1mm
minimum height 65mm
spare in travel 10mm
additional height for camera 55mm

100% illumination 5.6mm

Generally you want to get the 100% illumination to be larger than the diagonal of your CCD, for the kaf8300 this is 22.5mm.

Just changing the secondary size until the 100% illumination covers the 23mm I get a secondary size of 83mm. Looking at the orion optics AG10 they use a 100mm secondary, obviously these scopes are built for larger sensors but you can see that 83mm does not seem silly.

Your setup looks great by the way, I have been contemplating building myself a larger faster scope and reducing it with an asa reducer to be a superfast astrograph and I love the idea of making a truss scope with carbon rods.
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Old 15-09-2013, 12:04 PM
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Originally Posted by Shiraz View Post
The 3200 pixel size would be a good match for your scope in average/better seeing conditions. If you expect seeing down below 2 arcsec and want the best possible resolution, the 694 would be better (the 814 would oversample most of the time - lost sensitivity for no resolution gain).

Be careful if you are looking at AO - might be difficult to fit one into the available backfocus at f4
Thanks Ray,

But isn't the 3200 a lot more expensive with higher noise and is NABG? I believe its equivalent is the 694 which is cheaper and low noise.

I don't think I have too many options regarding actual sensors for this price bracket. might just have to make the decision based on vendor and local support.
But in terms of dynamic range, would there be a noticeable difference between the 8300 and 694 or is the comparison not like for like?
I'm waiting for a price on the STF8300 from the local supplier and Clive's ST10Xe.
I was considering the RCC1 mainly due to backfocus requirements if I fit a filter wheel, so how does this compare to the spherical aberration with the mpcc mk3?

Can an AO unit be added to the ST10Xe?

Cheers
AListair
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Old 15-09-2013, 01:09 PM
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Hi Alastair

I was referring to Clive's 3200, not a brand new one, when comparing options. Looks like NABG can be managed - for example, John Hothersal has published some images from his 3200 with no obvious signs of blooming.

The dynamic range of the 8300 is slightly less than that of the 694. The QE is significantly lower and it is noisier. RBI can apparently be an issue if it is cooled too heavily. All this really means is that you need to spend a significantly longer time getting image data with an 8300 - you will certainly be able to produce good images with one and the pixel size is a good match to your scope.

As far as I can tell, the RCC1 does not introduce any SA, but it will add significant vignetting with anything much larger than the 694. I tested it with my QHY8 and it was just usable. Paracorr might be worth looking at for an 8300, although that will rule out AO due to limited back focus.

Not sure about AO on any chip at f4 - it's a lot to squeeze in. And there is the possibility of spherical aberration from a refractive AO (not from a reflective one though).

Agree with Peter re the secondary - I needed a 70mm in my 200f4 and would expect that you will need something above 80mm.

Last edited by Shiraz; 15-09-2013 at 04:38 PM.
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Old 15-09-2013, 01:23 PM
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Originally Posted by Peter.M View Post
I not sure what values you used for your newt analysis but I will tell you that a 70mm secondary should not produce a 11mm 100% illumination in your scope.


diameter 250mm
ratio 4
diagonal 70mm
inside diameter 265mm
wall thickness 1mm
minimum height 65mm
spare in travel 10mm
additional height for camera 55mm

100% illumination 5.6mm

Generally you want to get the 100% illumination to be larger than the diagonal of your CCD, for the kaf8300 this is 22.5mm.

Just changing the secondary size until the 100% illumination covers the 23mm I get a secondary size of 83mm. Looking at the orion optics AG10 they use a 100mm secondary, obviously these scopes are built for larger sensors but you can see that 83mm does not seem silly.
Hi Peter,

I've measured my distances, and they're attached.
I didn't realize OO used 100mm secondary for the AG10. So mine's probably undersized. will it make a difference if I used a larger secondary, say 83mm or close, if so what do you think the difference would be?

the base of my focuser is actually 172mm from the centre.
i'll enter the values again in newt and see what it comes up with.

I thought about using a larger focuser, might just do that, but then that's for later cause that'll need a larger corrector and it all adds up quickly.

I'm pretty sure the current 100% area is definitely larger than 5mm because when I view a flat with the qhy8, the vignetting is toward the edges of the frame.

Cheers
Alistair
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Old 15-09-2013, 03:06 PM
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Quote:
Originally Posted by alistairsam View Post
Hi Peter,

I've measured my distances, and they're attached.
I didn't realize OO used 100mm secondary for the AG10. So mine's probably undersized. will it make a difference if I used a larger secondary, say 83mm or close, if so what do you think the difference would be?

the base of my focuser is actually 172mm from the centre.
i'll enter the values again in newt and see what it comes up with.

I thought about using a larger focuser, might just do that, but then that's for later cause that'll need a larger corrector and it all adds up quickly.

I'm pretty sure the current 100% area is definitely larger than 5mm because when I view a flat with the qhy8, the vignetting is toward the edges of the frame.

Cheers
Alistair
Using the numbers you provide, newt spits out a 100% illuminated area of 0mm which may explain what you see. Your tube inside diameter is distance A on your diagram times 2 so 300mm. Then all you need to do is make sure all of the other values in newt sum to be the 144mm of extra distance to the focal plane and it should give you the same numbers.

What you may be seeing with the qhy8 is vignetting of the 75% rays in the corners of the chip. Though I am not familiar with that.
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Old 15-09-2013, 05:31 PM
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Nice looking scope. Newts typically need a coma corrector. Do you have one of those? MPCC is common one used.

Sounds like you've got the CCDs worked out there. Its just a matter of going through the pluses and minuses of each and which match your intended main interest in imaging. CCD calculator at New Astronomy Press (its free) gives you a simulation of the view of different deep sky objects with different cameras on the same scope. That may help with the decision process.

ST8300 is proven.

SXV694 seems to be a strong performer but a bit smaller FOV which might be good for galaxy images but not so good for wider objects. Its also very modern, has good electronics, its a Sony sensor. Mike S likes his and Rally's few images posted so far are impressive with a similar setup. It also requires a smaller corrected image circle not that KAF8300 requires a large one either. KAF8300 is about 58% QE and not sure what its QE at Ha is. 694 is 77% and 66% at Ha which is one of the highest around.

ST10 is another strong performer plus it has self guide (I presume). That is good for LRGB not so much for Ha.

Greg.
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